RU2846368C2 - Ethylene production plant comprising electrically driven pyrolysis reactor and feed-to-product heat exchanger - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention relates to an ethylene production plant comprising an electrically driven pyrolysis reactor, and a method of producing a pyrolysis reactor product using an ethylene production plant. Ethylene production plant comprises an electrically driven pyrolysis reactor, wherein electrically driven pyrolysis reactor comprises inlet channel for mix of hydrocarbon stock and diluent and outlet channel for pyrolysis reactor product containing ethylene. Heat exchanger is configured to transfer heat from the pyrolysis reactor product to the pyrolysis reactor feedstock, the heat exchanger comprising a feedstock inlet channel and a raw material outlet channel located upstream of the pyrolysis reactor and additionally a pyrolysis reactor product inlet channel and a pyrolysis reactor product outlet channel, wherein between heat exchanger raw material outlet channel and pyrolysis reactor raw material inlet channel there is raw material supply channel, and additionally between reactor product outlet channel in pyrolysis reactor and heat exchanger cracking gas inlet channel there is raw material supply channel. Plant comprises a cooling section configured to further cool the reactor product obtained in the pyrolysis reactor to about ambient temperature without generating high-pressure steam, wherein the cooling section is located downstream of the cracked gas outlet channel of the heat exchanger and comprises a cooling system selected from a group of cooling water cooling systems configured to further cool the reactor product with cooling water, and air coolers made with possibility of reactor product additional cooling with air; and cooling system with quenching oil made with possibility of additional cooling of reactor product with quenching oil and located downstream of heat exchanger outlet channel for product of pyrolysis reactor and upstream of cooling water cooling system or air cooler.

EFFECT: integrating the electrically driven pyrolysis reactor into an ethylene production unit, this is achieved in the absence of high-pressure steam as a source of dilution steam and in the absence of high-pressure steam as a heating medium for hydrocarbon feedstock.

15 cl, 14 dwg, 2 tbl, 4 ex

Description

The invention relates to an ethylene production plant comprising a pyrolysis reactor with an electric drive. The invention further relates to a method for producing ethylene from hydrocarbon feedstock using an ethylene production plant in accordance with the present invention.

In conventional ethylene production plants containing a fired cracker, sufficient high pressure (HP) steam is generated to generate electrical power to drive the machinery and also to generate dilution steam to reduce the partial pressure of hydrocarbons, thereby increasing product selectivity and suppressing coke formation in the cracking reactor.

In the hot section of the plant, the dilution steam is traditionally obtained from the intermediate pressure (IP) steam, which is formed from the HP steam after generating electricity by means of one or more steam turbines. In addition, in the presence of a primary fractionation column, which is known to be used for cracking liquid feedstock, the heat recovery of the furnace outlet product (cracking product) in the quench oil loop of the primary fractionation column, which is the circulation loop of the said primary fractionation column, helps generate dilution steam, which allows a larger amount of IP steam to be depressurized for maximum electricity generation. At the same time, it is possible to recover excess heat from the product in the cooling water column and transfer this excess heat to the low-temperature sections through the circulation loop. This small amount of heat is used, for example, for preheating the feedstock in the furnace. Further evaporation of the feedstock is usually carried out using flue gas in the convection section of the said traditional cracking furnaces.

Fig. 1 shows an example of a circuit diagram for a (hot section) of a conventional plant with a fired furnace for the production of ethylene from a gaseous hydrocarbon feedstock. Fresh gaseous feedstock 1, such as ethane, propane or a mixture thereof, is first preheated in a preheater 30 using a low-temperature heat source, such as cooling water, external to the cracking furnace 1000, to heat the feedstock from ambient temperature to a temperature of approximately 50°C, suitable for introducing the feedstock into the cracking furnace 1000. Further preheating of the feedstock is carried out by means of flue gas in the convection section of the furnace using a hydrocarbon feedstock preheater 31. In order to reduce the partial pressure of hydrocarbons in the pyrolysis reactor to optimize the product yield and suppress coke formation, slightly superheated dilution steam 24 is added. The feedstock and dilution steam are preheated so that after mixing their temperature exceeds the dew point of water, which is approximately 120-130°C. Further superheating of the diluted hydrocarbon feedstock 3 with steam is achieved in a feedstock superheater in the convection section of the furnace 33 using flue gas. After proper superheating, the diluted steam feedstock enters the pyrolysis reactor 34 at a temperature of approximately 650°C - 730°C. This reactor is traditionally heated by burning fuel gas in a furnace chamber. The reactor is operated at a relatively low pressure and high temperature, since this promotes an increase in the yield of olefins. Typical process parameters at the reactor outlet are a temperature of 800°C to 870°C and a pressure of 1.6 to 2.2 bar abs; products such as ethylene, propylene, butadiene, benzene, toluene and xylene are formed. Typical by-products are hydrogen, methane, gasoline and distillate fuel. Some products, such as ethane and propane, are recycled in the reactor. The reactor product 4 contains all of these products and by-products. This reactor product 4 is cooled to a temperature of approximately 160°C to 220°C in the cracking furnace section 1000. Heat from the product, the temperature of which exceeds 350°C, is conventionally recovered using the first quencher and evaporator 35 by generating high-pressure saturated steam at a pressure of approximately 100 to 125 bar abs. At a lower heating level, heat can be recovered in the secondary quencher and evaporator 36, designed to preheat boiler feedwater or feedstock diluted with superheated steam.

From the furnace section, the product 4 is sent to the hot separation section of the plant, which mainly consists of a water cooling column 60, an acid water stripping column 70 and a dilution steam collector 80. In the water cooling column 60, the product 4 is further cooled to approximately ambient temperature. Cooling is carried out using a circulation pump that collects the aqueous product accumulated in the lower part of the plant - the so-called cooling water 14, and introduces it into the cooling water column 60 at different levels. The cooling water circuit, as a rule, consists of two stages - a lower cooling water cooling circuit 64 serving the lower section 61 of the cooling water column, and an upper cooling water cooling circuit 66 serving the upper section 62 of the cooling water column. The overhead product, the cooled gaseous phase of the reactor product, called cracked gas 9, is sent to a downstream cracked gas compression section for further separation in a cold separation unit. The coolers 65 of the lower cooling water circuit are typically used to recover as much cooling water as possible for use in other sections of the plant. Such sections include, for example, the feed preheater 30. Any excess heat must be removed by cooling with air or cooling water. The coolers 67 of the upper cooling water circuit typically remove excess heat using cooling water. The cooled injection water from the circulation pump circuit is used in the cooling water column to remove heat from the cracked gas by direct heat exchange in the appropriate internal components of the column. The main function of this column, in addition to cooling the cracked gas, is to condense and recover the dilution steam. The condensed dilution steam is the pure product from the bottom of the column along with a small amount of product in the form of heavy pyrolysis gasoline 8. Typically, these products are separated from each other using a water-gasoline separator 63. Sometimes this separator is also used to collect cooling water 14 intended for the cooling water circuit. This condensed dilution steam, called sour water 20, contains acid gases, which are stripped with stripping steam 21 in the sour water stripper 70. These acid gases 22 are returned to the cooling water column 60. The stripped water, called process water 23, is suitable for generating dilution steam. This process is carried out at a higher pressure, approximately 6 to 7 bar abs, so that the steam can be returned to the cracking furnaces. The dilution steam is generated using medium pressure steam as a heat source. The process water is collected in the dilution steam collector 80, and the dilution steam 24 is formed by means of a thermosiphon circuit from the condensing medium-pressure steam in the dilution steam generator 81. Any superheating of the medium-pressure steam is used for slightly superheating the dilution steam in the dilution steam superheater 83 to a temperature of 180°C to 210°C before returning it to the cracking furnace 1000 for diluting the hydrocarbon feedstock 1. Blowdown 26 from the dilution steam collector 80 and make-up 25 of the said collector from the dilution steam system prevent the accumulation of contaminants in the dilution steam generation circuit.

An integrated power generation scheme of a conventional ethylene production plant is shown in Fig. 2. The MP steam required for generating the dilution steam is generated in a high-pressure steam system from boiler feedwater. The boiler feedwater is obtained from demineralized water 101 in a deaerator 120, where it is stripped with stripping steam 102 to remove _CO2 and oxygen through an outlet channel 103 of the deaerator. The resulting boiler feedwater 104 is preheated in a cracking furnace 1000 by a boiler feedwater heater 121 using cracking gas and/or flue gas and collected in a high-pressure steam collector 122. A steam collector connected by natural circulation to a thermosyphon type heat exchanger called a quenching and evaporating apparatus 35 recovers heat from the product 4 of the reactor and generates high-pressure saturated steam 105; this high-pressure steam is superheated with flue gas in the convection section of the furnace 1000 using a high-pressure steam superheater 123. The high-pressure superheated steam is used to generate electric power that drives the main mechanisms in the separation section of the ethylene production plant, such as a cracking gas compressor and refrigeration compressors located in the cracking gas compressor zone and in the cold separation section of the plant, respectively (not shown for clarity). For this purpose, the pressure of the high-pressure superheated steam 107 is reduced from high to medium pressure by means of a backpressure steam turbine to generate electric power 124, and by means of a condensing turbine the pressure is reduced from medium to vacuum 125 also to generate electric power. Most of the PO steam is condensed in the surface condenser 126 of the condensing turbine 125 to provide maximum power output, but some of the steam 108 is reduced in pressure only to the medium pressure level. This medium pressure steam 108 is used to generate dilution steam and constitutes a significant percentage of the available high pressure steam stream 107. The medium pressure steam 108 is cooled in the dilution steam superheater 83 to produce superheated dilution steam and condensed in the dilution steam generator 81 to generate dilution steam 24. The resulting medium pressure condensate 109 and vacuum condensate 111 are combined and the combined condensate 112 is returned to the deaerator for reprocessing as boiler feedwater. Limited blowdown 106 of the high pressure steam header prevents the accumulation of contaminants in the high pressure steam circuit. The hot section of the block diagram of the plant for the process using liquid hydrocarbon feedstock is shown in Fig. 3. In a typical plant for producing ethylene from liquid feedstock, fresh liquid feedstock 2, such as butane, pentane or naphtha or a mixture thereof, is first preheated in a preheater 30 using a low-temperature heat source, such as cooling water external to the cracking furnace 1000, to heat the feedstock from ambient temperature to a temperature of approximately 50°C, suitable for introducing the feedstock into the cracking furnace 1000. Further preheating and partial evaporation of the feedstock is carried out by means of flue gas in a convection section of the furnace using a hydrocarbon feedstock preheater 31 and a hydrocarbon feedstock evaporator 32, respectively. In order to reduce the partial pressure of hydrocarbons in the pyrolysis reactor, which is beneficial for the product yield and the suppression of coke formation, the dilution steam 24 coming from the hot separation section is further superheated in the convection section using flue gas. This process is carried out in a dilution steam superheater 84 to ensure complete conversion into steam of the feedstock, partially evaporated after mixing. The feedstock is evaporated and the dilution steam is heated to such an extent that the temperature of the mixture significantly exceeds the dew point of water, which is approximately 130-140 °C. Further superheating of the diluted hydrocarbon feedstock 3 with steam is achieved in the feedstock superheater in the convection section 33 of the furnace using flue gas. After proper superheating, the diluted steam feedstock enters the pyrolysis reactor at a temperature of approximately 600 °C-640 °C. This reactor is traditionally heated by burning fuel gas in a furnace chamber. The reactor is operated at a relatively low pressure and high temperature, since this contributes to an increase in the yield of olefins. Typical process parameters at the reactor outlet are a temperature of 800 °C to 870 °C and a pressure of 1.6 to 2.2 bar abs; The products formed are ethylene, propylene, butadiene, benzene, toluene, and xylene. Typical byproducts are hydrogen, methane, gasoline, and distillate fuels. Some products, such as ethane and propane, are recycled in the reactor. The reactor product contains all of these products and byproducts.

This product 4 of the reactor is cooled to a temperature of approximately 350°C in the section of the cracking furnace 1000. The heat from the product, the temperature of which exceeds 350°C, is traditionally recovered using the first quenching and evaporating apparatus 35 by generating high-pressure saturated steam at a pressure of approximately 100 to 125 bar abs. At a lower heating level, from 350°C to 160°C, heat cannot be recovered using indirect heat exchange due to the fouling properties of the product, but heat recovery is carried out in the so-called quenching oil pipe 37 by injecting 27 quenching oil and injecting 28 middle oil fraction in the presence of a middle oil fraction circuit. From the furnace section, product 4 is sent to the hot separation section of the plant, which mainly consists of a primary fractionation column 50, a water cooling column 60, an acid water stripper column 70, and a dilution steam collector 80.

In the primary fractionation column 50, the product is further cooled to approximately 100°C, maintaining the temperature above the dew point of water so that water does not condense in this column. The product is then cooled using the quench oil and middle oil fraction circulation pumps and the gasoline return flow, respectively. The feedstock for the quench oil cooling circuit 54 is the heavy distillate fuel product 6, which collects at the bottom of the column. This quench oil 10 is cooled using quench oil circuit coolers 55. Part of it is directed to the quench oil port 27, and the rest is reinjected into the column below the full middle oil fraction pickup tray. The quench oil circuit coolers 55 are typically used to generate dilution steam in the dilution steam generator 82. If the temperature at the bottom of the primary fractionation column is insufficient to generate dilution steam, low pressure steam can be generated instead. The quench oil cooling circuit 54 recovers all heat from the product with a temperature typically above 170°C and down to -180°C in the presence of the middle oil fraction cooling circuit 56, otherwise it recovers heat from the product with a temperature of at least 125°C - 130°C. The quench oil cooling circuit serves the washing section 51 of the primary fractionation column - the bottom of the column.

The middle oil fraction cooling circuit 56 is optional and is intended to provide a relatively clean/foul-free intermediate cooling circuit that recovers heat from the product at a lower heating level than the quench oil circuit 54, typically at temperatures of at least 125°C 130°C. The middle oil fraction 11 is collected on a pick-up tray at the bottom of the middle oil fraction section 52 of the primary fractionation column, located above the wash section 51 in the column. The return flow 12 of the middle oil fraction is directed to the quench oil wash section 51 at the bottom of the column to provide the possibility of shifting the quench oil feed to the middle oil fraction circuit. In addition, the middle oil fraction stream 28 is directed to the quench oil branch pipe 37. The remainder is cooled by coolers 57 of the middle oil fraction circuit and returned to the column below the light distillate fuel fraction withdrawal point. The middle oil fraction cooling circuit 56 serves the middle oil fraction section 52 of the primary fractionation column.

The return flow 13 of gasoline coming from the water-gasoline separator 63 provides heat recovery in the upper part of the column, in the return flow section 53 of the gasoline of the primary fractionation column, and transfers the recovered heat to the cooling water circuit.

The column is equipped with appropriate internal components to ensure efficient heat transfer from the product to the injected quench oil, the middle oil fraction and the gasoline return flow. In addition to cooling the product, the primary fractionation column condenses the light and heavy oil fractions. The heavy distillate fuel 6 is collected in the lower section 51, while the light distillate fuel 7 is collected in the lower part of the return flow section 53 on a light oil fraction collection tray. These fractions can be stripped to control the flash point of the overall product 5 of the distillate fuel and/or to recover lighter fractions of the quench oil to control the viscosity in the quench oil circuit. In the water cooling column 60, the product 4 is further cooled to approximately ambient temperature. The overhead product, the cooled gaseous phase of the reactor product, called cracking gas 9, is sent to downstream units for further separation. Cooling is carried out using a circulation pump that collects the aqueous product accumulated in the lower part of the unit, the so-called cooling water 14, and introduces it into the cooling water column 60 at different levels. The cooling water circuit typically consists of two stages - a lower cooling water circuit 64 serving the lower section 61 of the cooling water column, and an upper cooling water circuit 66 serving the upper section 62 of the cooling water column. Coolers 65 of the lower cooling water circuit are typically used to recover as much cooling water as possible for use in other sections of the unit. Such sections include, for example, the feed heater 30 and/or the propylene stripper reboiler (not shown). Any excess heat must be removed by cooling with air or cooling water. Coolers 67 of the upper cooling water circuit typically remove excess heat using cooling water. The cooled injection water from the circulation pump circuit is used in the cooling water column to recover heat from the cracked gas by direct heat exchange in the appropriate internal components of the column. The main function of this column, in addition to cooling the cracked gas, is to condense and recover the dilution vapor. The condensed dilution vapor is the clean product from the bottom of the column along with a small amount of product in the form of heavy pyrolysis gasoline 8. As a rule, these products are separated from each other using a water-gasoline separator 63. Sometimes this separator is also used to collect cooling water intended for the cooling water circuit. This condensed dilution vapor, called sour water 20, contains acid gases that are stripped with stripping steam 21 in the sour water stripper 70. These acid gases 22 are returned to the cooling water column 60. The stripped water, called process water 23, is suitable for generating dilution steam. This process is carried out at a higher pressure, approximately 6 to 7 bar abs, so that the steam can be returned to the cracking furnace. The dilution steam is generated using medium-pressure steam. The process water is collected in a dilution steam collector 80, and the dilution steam 24 is formed by means of a thermosiphon circuit from condensing medium-pressure steam in a dilution steam generator 81 and additionally from a quenching oil cooling circuit using a dilution steam generator 82. Any superheating of the medium pressure steam is used to slightly superheat the dilution steam in the dilution steam superheater 83 to a temperature of from 180°C to 210°C before returning it to the cracking furnace 1000 for diluting the hydrocarbon feedstock 2. Blowdown 26 from the dilution steam header 80 and make-up 25 of said header prevent accumulation of contaminants in the dilution steam generation circuit. The MP steam required for generating the dilution steam is formed in the high pressure steam system from boiler feedwater in the same way as in the block diagram of a conventional plant for the production of ethylene from gaseous feedstock shown in Fig. 2 and described above. Given the need to reduce greenhouse gas emissions such as carbon dioxide and methane, there is considerable interest in optimizing ethylene plants and the operation of ethylene plants to reduce energy requirements or at least reduce the need for fossil fuels to generate the heat needed to operate the plants. A possible approach would be to replace fossil fuels with hydrogen, which can be produced by electrolysis. The required electricity could be generated using renewable energy sources or in a power plant that efficiently captures carbon dioxide, preventing its release into the air.

According to the authors of the present invention, it would also be interesting to use electricity directly to obtain part of the physical heat (heat to increase the temperature of the hydrocarbon-steam mixture) and the reaction heat for the cracking reaction. However, when using electrically driven pyrolysis reactors, preheating and evaporation of liquid feedstock cannot be carried out in the traditional way due to the lack of flue gas used as a hot energy carrier. In addition, in the absence of MP steam, it is impossible to obtain dilution steam in the traditional way.

The concept of using electrically heated pyrolysis reactors for producing olefins from hydrocarbons is known in the art. Patent EP 3 249 028 A1 relates to a process for producing olefins by steam cracking, which uses a plurality of cracking furnace tubes. At least one of the cracking furnace tubes is heated by burning a fuel (i.e. is a fired cracking furnace tube) and at least one other cracking furnace tube is heated using electricity. The reactor product (the cracked product) is rapidly cooled (quenched) to prevent unwanted side reactions. Downstream processing, such as fractionation of the cracked product, is further described. The patent discloses little information on preheating the feedstock and generating dilution steam. Since the process requires burning a fuel, hot flue gas is used for heating; its use for feeding steam directly into the tubes of a cracking furnace is mentioned, and its use for generating steam inside a tube of a cracking furnace is also mentioned. EP 3730592 A1 relates to an olefin synthesis plant comprising a pyrolysis section comprising one or more of the following: a feedstock pretreatment section, one or more pyrolysis reactors for cracking hydrocarbons in the presence of a diluent, a primary fractionation and compression section and/or a product separation section, in which, compared to a conventional plant, a greater amount of the energy and/or the net energy required to install the section thereof is provided by a non-carbon-based energy source. EP 3730592 A1 proposes essentially different embodiments of the use of electricity, heating of the feedstock and the generation of dilution steam, if used. For example, the plant may be a plant configured to carry out a steam cracking process in which, for example, part or all of the cracking reactors are electrically heated and the heat for evaporating the recirculated water to produce dilution steam is generated electrically. Furthermore, the feedstock entering the cracking reactor may be preheated electrically; it may be heated by using a large portion of the heat recovered from cooling the hot product gases; or it may be heated indirectly using a heat transfer fluid (e.g., Dowtherm or steam). Although some written examples suggest specific embodiments of the invention, the figures illustrating the relative positions of the units and the flows between the units do not provide, for example, explanations of how heat is recovered from the process streams. The examples are based on generating dilution steam directly from the product. The application of the design appears to be limited to the processing of ethane as a feedstock due to the reduced potential of the product to cause fouling compared to processes based on the use of heavier feedstocks.

The aim of the present invention is to provide a new ethylene production plant comprising an electrically driven pyrolysis reactor and, accordingly, to implement a new method for producing ethylene by steam cracking, which is reliable in terms of permissible feedstocks and at the same time provides an effective reduction in carbon dioxide emissions without the need to use fuel combustion (in particular, methane or hydrogen) to provide partial heating of the hydrocarbon feedstock entering the electrically driven pyrolysis reactor. In particular, the aim is to integrate the electrically driven pyrolysis reactor into the ethylene production plant in such a way that this is achieved in the absence of high-pressure steam as a source of dilution steam and in the absence of high-pressure steam as a heating medium for the hydrocarbon feedstock.

It has now been established that it is possible to efficiently integrate electrically driven pyrolysis devices and feedstock/product heat exchangers to recover sufficient heat from the product of said pyrolysis reactor (cracking product). In particular, this is achieved by superheating the feedstock for the pyrolysis reactor (a mixture of hydrocarbon feedstock and dilution steam) using heat from a downstream hot separation section of the plant in such a way that the excess energy consumption is minimal. The excess energy consumption is understood as the amount of energy in addition to the energy requirement for the electrically driven pyrolysis reactor, i.e. the energy required for preheating, evaporating and optionally superheating the feedstock and the energy required for generating the dilution steam or humidifying the feedstock. The additional energy required to drive the machinery in the processing sections of the plant, such as the cracking gas compressor and the refrigeration compressors, can be used in accordance with the description given in patent EP 3 748 138 A1.

Accordingly, the present invention relates to an ethylene production plant comprising an electrically driven pyrolysis reactor, wherein the electrically driven pyrolysis reactor comprises an input channel of feedstock for a mixture of hydrocarbon feedstock and diluent and an output channel for the pyrolysis reactor product containing ethylene, wherein the ethylene production plant further comprises a heat exchanger configured to transfer heat from the pyrolysis reactor product to the feedstock for the pyrolysis reactor, wherein the heat exchanger comprises an input channel for feedstock and an output channel for feedstock located upstream of the pyrolysis reactor, and further an input channel for the pyrolysis reactor product and an output channel for the pyrolysis reactor product. Between the output channel for feedstock of the heat exchanger and the input channel for feedstock of the pyrolysis reactor there is a feedstock feed channel, and further between the output channel for the reactor product in the pyrolysis reactor and the input channel for cracking gas of the heat exchanger there is a feedstock feed channel. The proposed plant further comprises a cooling section configured to additionally cool the reactor product obtained in the pyrolysis reactor to approximately ambient temperature without generating high-pressure steam, wherein the cooling section is located downstream of the outlet channel for the cracking gas of the heat exchanger and comprises a cooling system selected from a group of cooling water cooling systems configured to additionally cool the reactor product with cooling water and air coolers configured to additionally cool the reactor product with air; and a quenching oil cooling system configured to additionally cool the reactor product with quenching oil and located downstream of the outlet channel of the heat exchanger for the pyrolysis reactor product and upstream of the cooling water cooling system or air cooler. In this way, the generation of high-pressure steam by transferring heat from the reactor product can be minimized and even eliminated, which allows the plant to operate without generating high-pressure steam due to the heat transferred from the reactor product.

The advantage is that the temperature of the pyrolysis reactor product leaving the heat exchanger can be significantly below the temperature range of the generation of the very high pressure stream, typically below 500°C, preferably below 450°C.

In another or further preferred embodiment, which will be described in more detail below, the heat may be used to preheat the feedstock prior to the heat exchanger using heat from a downstream processing unit in which the reactor product is further cooled.

The invention also relates to a method for producing a pyrolysis reactor product containing ethylene from a hydrocarbon feedstock using an ethylene production plant in accordance with the present invention. The method includes feeding a mixture of hydrocarbon feedstock and steam into an electrically driven pyrolysis reactor, cracking the hydrocarbon feedstock in the presence of steam in the electrically driven pyrolysis reactor of said ethylene production plant to obtain a pyrolysis reactor product containing ethylene, feeding the pyrolysis reactor product into a heat exchanger configured to transfer heat from the pyrolysis reactor product to the mixture of hydrocarbon feedstock and steam before cracking the hydrocarbon feedstock, and transferring heat from the pyrolysis reactor product to the mixture of hydrocarbon feedstock and steam in said heat exchanger, which results in cooling the pyrolysis reactor product to a temperature at the outlet channel for the pyrolysis reactor product preferably below 500°C, more preferably to a temperature below 450°C, for example in the range of 300°C - 450°C, even more preferably to a temperature in the range of 325°C - 425°C.

BRIEF DESCRIPTION OF GRAPHIC MATERIALS

These and other distinctive features, aspects and advantages of the devices, systems and methods of the present disclosure will become more apparent from the following description, the appended claims and the accompanying drawing, in which:

Fig. 1 shows an example of a circuit diagram for (the hot section) of a conventional plant with a fired furnace for producing ethylene from gaseous hydrocarbon feedstock; Fig. 2 shows a circuit diagram of the integrated power generation of a conventional plant for producing ethylene;

Fig. 3 is a schematic representation of the hot section of the ethylene production plant according to the present invention;

Fig. 4 schematically shows aspects of an electrically driven pyrolysis reactor in combination with a feedstock/product heat exchanger;

Fig. 5 is a schematic representation of an ethylene production plant/ethylene production process according to the present invention;

Fig. 6 is a schematic representation of an ethylene production plant/ethylene production process according to the present invention;

Fig. 7 is a schematic representation of an ethylene production plant/ethylene production process according to the present invention;

Fig. 8 is a schematic representation of an ethylene production plant/ethylene production process according to the present invention;

Fig. 9 is a schematic representation of aspects relating to the hot section of the ethylene production plant/process according to the present invention;

Fig. 10 is a schematic representation of an ethylene production plant/ethylene production process according to the present invention;

Fig. 11 is a schematic representation of an ethylene production plant/ethylene production process according to the present invention;

Fig. 12 schematically illustrates aspects relating to cooling of an ethylene production plant/within the ethylene production process according to the present invention;

Fig. 13 schematically illustrates aspects related to cooling of an ethylene production plant/within the ethylene production process according to the present invention; and

Fig. 14 shows the dew point as a function of the absolute operating pressure using the example of a saturator of an ethylene production plant/ethylene production process in accordance with the present invention.

In particular, the present invention provides a number of alternative solutions for operating an ethylene production plant that does not have a high-pressure steam generation system and that does not have a fired furnace in which flue gas is generated. Thus, the plant or method according to the present invention is particularly suitable for operation in the absence of both preheating and evaporation of the feedstock by heating with available flue gas and superheating of the dilution steam. This is achieved, in particular, by using other methods of thermal integration in the ethylene production plant. Thus, the need for additional electrical energy in addition to the electrical energy used for the pyrolysis reaction can be limited. For example, in at least a number of embodiments, the plant can be operated in a normal operating mode (steady-state operation) without using electrical energy for generating dilution steam, without electrical preheating of the feedstock, etc. Thus, the use of electrical energy can remain relatively limited, without having a negative impact on greenhouse gas emissions. This is an advantage, especially when wanting to use renewable energy sources, the performance of which can vary greatly depending on, for example, weather conditions.

A person skilled in the art will be able to design and operate the corresponding working units of the ethylene production plant using the present description in combination with the general knowledge and optionally one or more of the references cited herein. In addition to the working units, channels, etc. described herein, the plant according to the present invention may comprise one or more additional units. Such units may be based on units used for such a purpose, generally known in the art or described in the references cited herein. For reasons of brevity, such units, which may be conventional, are not described in detail. In particular, upstream of the feed stream 1, 2, one or more units may be present, in particular one or more units designed to pre-treat the feed, for example by removing impurities. In particular, downstream of the hot section (downstream of line 9 in the figures) there may be one or more units for purifying the cracking product gas or for extracting a useful product from it, such as extracting hydrogen or methane from it.

According to the present invention, the electrically driven pyrolysis reactor 91 is combined with a feedstock/product heat exchanger 90 designed to transfer heat from the pyrolysis reactor product 4 to the pyrolysis reactor feedstock 3, i.e. a mixture of hydrocarbon feedstock and diluent (usually dilution steam), before feeding the feedstock to the pyrolysis reactor. This is shown schematically in Fig. 4.

Such heat exchangers are generally known in the art; they may, for example, have a shell-and-tube design. Typically, feed/product heat exchangers are operated in a counter-current configuration. In this connection, a temperature crossover is usually observed, i.e. the outlet channel temperature on the cold side exceeds the outlet channel temperature on the hot side. In principle, a cross-flow is also possible. A feed/product heat exchanger typically has a channel for the reactor product (cracking product) and a separate channel for the feed (hydrocarbon-steam mixture). Both channels are separated by a heat-conducting partition, which is designed to transfer heat from one channel to the other. In this way, the heat removed from the reactor product is used directly to heat the feed, whereby the heat from the reactor product is not used at all for generating high-pressure steam. Thus, the ethylene production plant of the present invention is typically designed to be able to operate in the absence of a high-pressure steam generator. The feed/product heat exchanger 90 is also different from a quenching device, such as a cooling water column, in which the reactor product is typically brought into direct contact with a cooling medium, such as cooling water. An advantage of the present invention is a quenching device configured to further cool the reactor product (cracking product) downstream of the feed/product heat exchanger 90, as will be described in more detail below.

The present invention provides for cracking of gaseous feedstock, liquid feedstock and mixtures thereof without the need to burn hydrocarbon fuel to generate sensible heat or reaction heat for the pyrolysis reaction, which allows for substantially completely eliminating direct CO ₂ emissions (substantially no CO ₂ is generated in the plant), ensuring readiness for the introduction of renewable energy sources. Provided that the generation of dilution steam and superheating of the gaseous feedstock and/or preheating, evaporation of the liquid feedstock are carried out with minimal additional requirements for electrical energy, CO ₂ emissions can remain at a minimum level. This allows for achieving the targets for zero carbon dioxide emissions in ethylene production as efficiently as possible.

An electrically driven pyrolysis device for producing olefins in ethylene production plants may be based on known electrically heated pyrolysis reactors. For example, the pyrolysis reactor may be a directly heated reactor in which the reactor wall (such as the wall of a cracking furnace coil) is heated by resistive heating using the wall as an electrical conductor. For example, WO 2015/197181 A1 describes a device and method for heating a fluid in a pipeline (cf. a cracking reactor tube) in the context of steam reforming. This principle may be applied to the pyrolysis reactor according to the invention. It should be noted that for the cracking according to the invention, the space in which the pyrolysis takes place is substantially free of catalytic material. In addition, the operating pressure at which the pyrolysis occurs is significantly lower than the 10 bar to 50 bar pressure applied in the reforming tubes. Indirect resistive heating of the cracking furnace coil involves electrically heating the housing in which the cracking furnace coil is located (usually a plurality of cracking furnace coils). In addition, the rotary dynamic device (RDR) is a very suitable device, in particular for transferring sensible heat and reaction heat to the pyrolysis reaction by increasing the kinetic energy through the use of static and dynamic rotors, thereby transferring the electrical energy of the drive mechanism for supplying heat to the reaction mixture (see, for example, US2021/0171836A1). A well-known supplier of RDR is Coolbrook (Helsinki, Finland; Geleen, the Netherlands).

Another example of a suitable pyrolysis reactor is based on US 7,288,690 B2 (see in particular items 8-13). Instead of a feedstock/product heat exchanger, a waste heat boiler of a cogenerator is used to preheat the diluted feedstock and the energy generated in an electric alternator is used to power the pyrolysis reactor. Suitable heating methods include direct resistance heating, also called Joule heating, inductive heating and ultrasound heating. The electrical energy required for the ethylene production plant according to the present invention may be obtained from an electrical power system that is part of the plant, or the ethylene production plant may be interconnected by an electrical power grid to an electrical power system outside the plant. At least a substantial portion of the electrical energy, preferably substantially all of the electrical energy, is obtained from a renewable source; this allows CO ₂ emissions to be minimized. Thus, the connection along the power supply chain between the energy absorbing part of the ethylene production plant, in particular the pyrolysis reactor (91), and the electric power system may be a connection to the internal power grid of the ethylene production plant for supplying at least part of the required electric power, or may be a connection to an external (remote) power plant connected to the same power grid as the ethylene production plant according to the present invention. The power supply system providing the supply of electric power from a renewable source typically comprises one or more power supply systems selected from the group consisting of wind power systems, solar power systems, hydropower systems, geothermal power systems and osmotic energy systems (also known as energy-saving energy). Alternatively or in addition to the above, one or more systems configured to generate electric power from biomass and/or one or more systems configured to generate electric power from biorenewable fuel, such as bioethanol or biodiesel, may be used. Although the use of renewable energy is preferred, in principle the electrical energy or part of it can be obtained from another source. Such a plant also has the advantage of improved thermal integration. For example, the reactor product from a steam cracking furnace typically contains some methane and some hydrogen. These can be recovered from the reactor product as a methane-rich stream and a hydrogen-rich stream. Either or both can be used to generate electrical energy in a well-known manner. In the case of hydrogen, this does not lead to increased CO ₂ emissions. If the methane is burned to form CO ₂ , the carbon dioxide can be captured to prevent emissions to the environment. However, in an advantageous embodiment, the methane and/or hydrogen can be used for higher priority purposes, such as feedstock for another chemical process.

The method according to the present invention provides that the weight ratio of the diluent gas (steam) to the hydrocarbon feedstock, also called the (weight) dilution steam ratio, can be selected within wide limits. Typically, said ratio, depending on the feedstock, is selected in the range from about 0.25 to about 1.0, preferably in the range from about 0.35 to 0.9, more preferably in the range from 0.4 to 0.8. For example, for a gaseous feedstock, the dilution steam ratio is essentially relatively low, typically from 0.3 to 0.4. For a light liquid feedstock, such as naphtha, a higher ratio may be preferred, typically in the range from 0.4 to 0.6. Heavier feedstocks, such as gas oils, are typically used at higher dilution steam ratios - from 0.6 to 1.0. In general, higher dilution steam ratios are possible, however, they are economically unattractive.

Lower values are less preferred since they can lead to product degradation and contamination. The mixture of hydrocarbon feedstock and dilution steam 3 is substantially fed to the feedstock/product heat exchanger 90 at a temperature above the dew point of water. In quantitative terms, the temperature of the mixture of hydrocarbon feedstock and diluent at the inlet channel of the feedstock/product heat exchanger 90 is substantially, depending on the feedstock, in the range of 80°C - 230°C, preferably in the range of 120°C - 180°C. For example, if the mixture is a gaseous feedstock diluted with steam coming from a humidifier, the temperature is preferably in the range of 80°C - 150°C, more preferably in the range of 90°C - 130°C. If, in addition to the humidifier, a compressor is used to compress the diluted gaseous feedstock to the furnace inlet pressure, the operating temperature can be increased by substantially 60°C to 120°C, depending on the polytropic efficiency of the compressor and the outlet pressure. For diluted liquid feedstock, the temperature is preferably in the range of 120°C to 200°C, more preferably in the range of 130°C to 180°C. Providing the diluted feedstock at the inlet channel at a temperature in the specified ranges, as opposed to overheating the feedstock to higher temperatures before entering the feedstock/product heat exchanger, provides the advantage of reducing the electrical energy requirements. In said heat exchanger, the mixture of hydrocarbon feedstock and diluent is heated, depending on the feedstock, using heat from the product of the pyrolysis reactor, typically to a temperature at the inlet to the pyrolysis reactor (91) in the range of 550°C - 750°C, preferably in the range of 570°C - 730°C. For example, if the mixture is a diluted with steam gaseous feedstock, such as ethane or propane, the temperature at the inlet to the coil is preferably in the range of 630°C - 750°C, more preferably in the range of 650°C - 730°C. For liquid feedstock, a temperature at the inlet to the coil in the range of 550°C - 670°C is preferred, more preferably in the range of 570°C - 650°C. It has been found that for ethane, preheating to 730°C is possible without fouling the upstream convection section.

The mixture of hydrocarbon feedstock and steam does not necessarily have to be heated to the temperature at which pyrolysis is carried out. Part of the sensible heat is usually supplied to the mixture using electrical energy in the pyrolysis reactor, which also provides heat of reaction. In the feedstock/product heat exchanger 90, the mixture is superheated; the relatively low temperature of the feed mixture at the inlet to the heat exchanger allows for the recovery of most of the excess heat of the reactor product, thereby reducing the amount of electrical energy required for additional heating of the feedstock inside the pyrolysis reactor.

The temperature of the reactor product (cracking product) at the inlet channel for the cracked product of the heat exchanger 90 depends on the residence time inside the reactor. For the RDR, this value is relatively low, which leads to relatively higher temperatures at the outlet of the coil compared to traditional radiant coils. In addition, the feedstock plays an important role. Gaseous feedstock has a lower degree of conversion compared to liquid feedstock, such as naphtha, and is cracked at a relatively lower temperature at the outlet of the coil. The product temperature at the inlet of the heat exchanger 90 can be in the range from 770 °C to 900 °C. The reactor product (cracking product) at the outlet channel for the cracked product of the heat exchanger 90 essentially has a temperature of at least 125 °C, preferably 150 °C to 250 °C higher than the temperature at the outlet channel on the feed side of the feed/product heat exchanger. The reactor product (cracking product) at the outlet channel for the cracked product of the heat exchanger 90 substantially has a temperature of at least 150°C, preferably 175°C to 275°C higher than the temperature of the diluted feedstock at the inlet channel for the feedstock of the feed/product heat exchanger. Substantially, the temperature of the reactor product at the outlet channel for the cracked product of the heat exchanger 90 is 500°C or less, preferably in the range of 300°C to 450°C, more preferably in the range of 325°C to 425°C. If, in addition to the humidifier, a compressor is used for compressing the diluted gaseous feedstock to the pressure at the inlet of the furnace, the operating temperature can be increased substantially by 40°C to 100°C, depending on the polytropic efficiency of the compressor and the outlet pressure.

The ethylene production plant according to the present invention typically further comprises a cooling section configured to further cool the cracked product after it leaves the feed/product heat exchanger 90. The cooling section may also be referred to as the "hot section of the plant". As such, the ethylene production plant of the present invention provides the advantage of operating without a high-pressure steam generator. Thus, in the cooling section, the pyrolysis reactor product is further cooled to ambient temperature (outside air temperature) without generating significant amounts of high-pressure steam. Suitable devices for cooling the pyrolysis reactor product are known in the art as such and may, among others, be selected from water coolers, oil quenchers and air coolers. Preferably, the plant comprises at least one device selected from the group consisting of water coolers and oil quenchers. As will be described below, such devices are not only effective in cooling; they can also be used for purification or fractionation of the product, which can also be based on principles known in the art. Furthermore, the inventors have found that in order to solve the problem of the lack of high-pressure steam generation, in particular for the production of dilution steam, it is possible to use the stream used for quenching with water and/or for quenching with oil. Instead of using the dilution steam as the (hot) stream that is mixed with the hydrocarbon feedstock, according to the present invention, during normal operation, it is possible to humidify, in particular saturate, the feedstock with water (liquid) using a humidifier (this term and the term "saturator" are used interchangeably in this document). Water coming from a water cooling device can be used as a source of water for humidifying the feedstock.

Such a method provides special advantages for humidifying at least substantially gaseous feedstock. When using a humidifier, dilution steam is essentially not required during normal operation, but can be used for plant start-up, decoking, hot standby and standby operation. Accordingly, in a plant comprising a humidifier / in a process providing (using) a humidifier for humidifying feedstock, a dilution steam generator is usually provided. Such a generator can have a relatively small capacity compared to a plant in which dilution steam is used during normal operation. In particular, a dilution steam manifold 80 with an electric boiler 85 can be provided for supplying dilution steam 24 (see, for example, Fig. 6). Further description is given below.

Fig. 5 shows a schematic of the plant/process according to the present invention and illustrates how quenching with water can be used to cool the cracked product to about ambient temperature. It also shows how sour water (condensed dilution steam containing acid gases recovered during cooling and washing of the cracked product in a water cooler) can be recycled and used to produce diluent without the need for high pressure steam.

From section 1001 of the furnace, product 4 of the pyrolysis reactor (cracking product), cooled in heat exchanger 90 of the "raw material/product" type, is sent to the hot separation section of the plant, which contains a water cooling column 60, a stripping column 70 of acidic water and a humidifier (saturator) 150. In the water cooling column 60, product 4 is further cooled to approximately ambient temperature. This is usually accomplished using a circulation pump that collects the aqueous product accumulated in the lower part of the plant - the so-called cooling water 14, and introduces it into the cooling water column 60 at different levels. The cooling water circuit, as a rule, consists of two stages - a lower cooling water cooling circuit 64 serving the lower section 61 of the cooling water column, and an upper cooling water cooling circuit 66 serving the upper section 62 of the cooling water column. Lower circuit coolers 65 are typically used to recover as much cooling water as possible for use in other sections of the plant.

The unit can be operated without a feed preheater configured to preheat the hydrocarbon feedstock before combining it with the diluent (water/steam). The heat from the cooling water is used to preheat the saturator water circuit 151, which in turn preheats and saturates the feedstock with water. Any excess heat in the cooling water circuit is typically removed by cooling with air or cooling water. The coolers 67 of the upper cooling water circuit typically remove excess heat using cooling water. The cooled injection water from the circulation pump circuit is typically used in the cooling water column to remove heat from the pyrolysis reactor product (cracking product) by direct heat exchange in the corresponding internal components of the column. The main function of this column, in addition to cooling the cracking product, is to condense and recuperate the dilution steam. The condensed dilution vapor is a pure product from the bottom of the column along with a gasoline product stream (which is essentially negligible relative to the condensed dilution vapor stream when using a gaseous feedstock). Typically, these products are separated from each other using a water-gasoline separator 63. This separator can also be used to collect cooling water 14 intended for the cooling water circuit. This condensed dilution vapor, called sour water 20, contains dissolved acid gases, which are typically stripped with stripping steam 21 in a sour water stripper column 70. These acid gases 22 are returned to the cooling water column 60. The stripped water, called process water 23, is suitable for humidifying (saturating) the feedstock. This occurs at a higher pressure than the pressure in the cooling water column and in the sour water stripper, typically at a pressure of from about 2 to about 8 bar abs, in particular from about 4 to about 6 bar abs, for feeding it to the furnace section 1001 without the need for a compressor. Humidification (saturation) of the feedstock is achieved in the saturator water heating loop 151 using cooling water as a heating medium. Process water is collected in the lower part of the saturator 150 and returned to the upper part of the saturator through the saturator water heating loop 151. The water is heated using a heater 152 of the saturator water loop with cooling water. Fresh hydrocarbon feedstock 1 enters the lower part of the saturator and is saturated using suitable internals, typically using random packing with the help of hot saturator water descending through the column. By controlling the temperature at the inlet channel for the saturator water, the level of humidification can be controlled to achieve the correct level of steam dilution for the pyrolysis reactor. The hydrocarbon feedstock diluted with steam is returned to the cracking furnace 1001, directly to the heat exchanger 90 of the "feedstock/product" type. The blowdown 26 from the saturator 150 and the make-up 25 of said saturator prevent the accumulation of contaminants in the heating circuit of the saturator water. Since the temperature level of the cooling water is limited to about 80 ° C, the temperature at the inlet channel for the hot water of the saturator is limited. The level of humidification depends on the temperature of the hot saturator and the partial pressure that the feedstock can generate in the column. The lower the boiling point of the feedstock, the easier it is to achieve a high degree of humidification. Accordingly, the principle illustrated in Fig. 5 is particularly useful for using at least a substantially gaseous feedstock for this embodiment, wherein the feedstock preferably consists essentially of at least ethane, propane or a mixture of ethane and propane. Fig. 14 shows the dependence of the dew point (°C, vertical axis) on the absolute operating pressure (kg/cm, horizontal axis) for an example saturator at a (mass) dilution steam ratio of 0.35. The rectangular block (grey) denotes the desired operating range of the system. Thus, a cooling water temperature of 80°C is too low to be used in combination with a feedstock at ambient temperature to achieve a dilution steam ratio of 0.35. Thus, at least without implementing additional measures, the scheme shown in Fig. 5 has its limitations with respect to applicable pressures and dilution steam ratios (mass ratio of dilution steam to hydrocarbon feedstock). Possible measures include: additional heating of the cooling water and/or feedstock before entering the saturator; using a relatively low ratio of diluent to feedstock; feeding the feedstock-diluent mixture into the pyrolysis reactor at a relatively low pressure.

The inventors have discovered a number of methods that are particularly well suited to addressing the limitations discussed in the description of the circuit in Fig. 5, as will be discussed below.

The ethylene production plant according to the present invention comprises a quench oil cooling system (50-57) designed for additional cooling of the pyrolysis reactor product (cracking product) and located downstream of the feed/product heat exchanger 90. When such a system is present, it is typically used in combination with a cooling water cooling system 60 (or alternatively with an air cooler), wherein the quench oil cooling system is located upstream of it. By using a quench oil cooling system equipped with a quench oil cooling circuit, the heat recovery level can be increased to a significantly higher value. This makes it possible to generate all the dilution steam in the saturator using the heat removed from the product, including at a relatively high steam dilution ratio, defined as the mass ratio of dilution steam to hydrocarbons, such as a steam dilution ratio of about 0.35 or more. This also reduces the need for cooling, such as the need for air cooling and/or water cooling. According to the present invention, the quench oil cooling system provides an advantage when using gaseous feedstock (in particular in combination with a saturator/humidifier as described above and shown in Fig. 5), liquid feedstock and combinations thereof. The quench oil cooling system 51 may be or be part of a primary fractionation system; such systems are known in the art, in particular for installations using liquid feedstock.

In particular, Fig. 6 shows a suitable ethylene production plant and, accordingly, the process of the present invention, which overcomes the disadvantages of the scheme shown in Fig. 5. This plant/process is particularly advantageous for at least substantially gaseous feedstock. In operation, it is possible to use a feedstock/product heat exchanger 90 and a pyrolysis reactor 91, as described above.

From section 1001 of the furnace, the cooled product 4 is sent to the hot separation section of the plant, which contains a quenching oil device 50 (usually containing a primary fractionation column 51 and a quenching oil cooling circuit 55), a cooling water cooling system 60 (usually a water cooling column), an acidic water stripping column 70 and a humidifier (saturator) 150.

After leaving the feed/product heat exchanger 90, the cracking product 4 (the pyrolysis reactor product) enters the hot separation section of the unit. Before entering the primary fractionation column 50, the quenching oil is usually combined with the cracking product; as a rule, the quenching oil is introduced into a so-called quenching oil nozzle before entering the primary fractionation column. Injecting the quenching oil upstream of the furnaces can provide advantages for temperature control in the lower part of the primary fractionation device (column). In the primary fractionation column 50, the pyrolysis reactor product is further cooled, for example to a temperature of about 110 °C - 125 °C. It is an advantage that the temperature is reduced to a value close to a value substantially above the dew point of water (which is typically about 75°C - 80°C), so that water does not condense in this device, for example to a temperature of from 10°C to about 50°C above the dew point, preferably in particular to a temperature in the range of from 20°C to about 45°C above the dew point, more in particular from 30°C to about 40°C above the dew point. The primary fractionation column for cracking products obtained from a substantially gaseous feedstock can be relatively simple compared to a primary fractionation column designed for cracking a liquid feedstock. In essence, for cracking products obtained from a substantially gaseous feedstock, the quenching oil washing section 51 (plus a quenching oil cooling circuit) is sufficient. In known olefin production plants, the primary fractionator typically further comprises at least a gasoline reflux section 53 and optionally a middle oil section 52 (not shown in Fig. 6). These sections are not necessary according to the present invention, at least in the case where the primary fractionator is not used to process a cracked product obtained from a substantially gaseous feedstock. The present invention (as shown in Figs. 5 and 6) provides for dilution of the (gaseous) feedstock without generating a separate dilution vapor stream that must be combined with the feedstock. Instead, by using a saturator/humidifier in which water (i.e. in the liquid state) is contacted with the feedstock to humidify the feedstock, the water injection temperature level in the upper inlet of the saturator/humidifier is so low that the operating temperature at the bottom of the primary fractionator can be reduced below the dilution vapor temperature level. The primary fractionation column can be operated at 150°C with the possibility of heating the saturator circulating water up to 140°C. This value is significantly lower than the operating temperature of the dilution steam collector, which is approximately 165°C, which provides a steam dilution ratio greater than 0.35. It should be noted that primary fractionation columns are not typically used in plants for the production of ethylene from gaseous feedstock; in particular, to the best of the knowledge of the inventors, the use of a primary fractionation column in plants for the production of ethylene from gaseous feedstock in combination with a humidifier/saturator, which is necessary solely for reducing the amount of energy consumed, is not known in the art.

The product of the pyrolysis reactor (cracking product) is cooled by means of a quenching oil. This has the advantage that the heat from the quenching oil can be recovered from the product of the pyrolysis reactor. The feedstock for the quenching oil cooling circuit 54 is the heavy distillate fuel product 6, which is collected as a liquid product at the bottom of the primary fractionation column. This quenching oil 10 is cooled by means of quenching oil circuit coolers 55. This liquid product is typically cooled to about 80°C. It can also be cooled together with the quenching oil by means of quenching oil circuit coolers 55, followed by additional cooling by means of another available cooling medium. If the flash point is too high for storage, a stripping column can be added to evaporate the light components. The details are not shown in the figure. In operation, a portion of the quench oil is typically directed to the quench oil port 27, and the remainder is typically fed to the top of the column together with a small amount of gasoline reflux 13. Compared to the reflux in a conventional fluid cracker, this flow rate is relatively small. In this case, cooling is provided primarily by the quench oil, not the reflux. The small reflux provides the ability to return fuel components. In known olefin production plants, quench oil circuit coolers 55 are typically used to generate at least a portion of the dilution steam; however, it is an advantage that, according to the present invention, the quench oil circuit is instead used (is configured to be used) to heat the saturator water circuit 151, if present. The quench oil cooling circuit is capable of serving the entire primary fractionation column 50 according to the present invention. In addition to cooling the pyrolysis reactor product, condensation of heavy oil fractions occurs in the primary fractionation column. This heavy distillate fuel 6 is the bottom product of the primary fractionation column.

As described above (see, in particular, the description of Fig. 5), in the water cooling column 60 the cracked product 4 is further cooled to approximately ambient temperature. The saturation of the feedstock is achieved in the saturator water heating circuit 151 using cooling water as a heating medium, for example as described above. The process water is collected in the lower part of the saturator 150 and returned to the upper part of the saturator through the saturator water heating circuit 151. The water is heated using the heater 152 of the saturator water circuit with cooling water. In addition to the installation/process including (using) a saturator/humidifier without a quenching oil cooling system, the quenching oil cooling system provides for the presence of an additional heating stage: heating with quenching oil. If the installation is designed with the possibility of using both cooling water and quenching oil, the cooling water cooling circuit and the quenching oil cooling circuit are essentially arranged as follows: during operation, the process water supplied to the saturator is heated using a heater 152 of the saturator water circuit with cooling water, with subsequent use of a heat exchanger for transferring heat from the quenching oil to the water, represented in the form of a heater 153 of the saturator water circuit on the quenching oil. The saturator is provided with an inlet channel for fresh (gaseous) raw material 1 (usually in the lower part of the saturator column or near it). The saturator is equipped with internal components that improve the contact between the raw material (usually moving upward) and the saturator water, which, as a rule, has a higher temperature than the raw material, and, as a rule, moves downwards along the saturator. By controlling the temperature at the saturator water inlet, the humidification level can be controlled to achieve the correct steam dilution level for the pyrolysis reactor. The steam-diluted hydrocarbon feedstock is returned to the cracking furnace 1001, directly to the feed/product heat exchanger 90.

In principle, this scheme is capable of providing most of the heat to achieve the required level of preheating and dilution of the feedstock with steam during normal operation (such as steady state operation). The product contains sufficient waste heat to saturate the feedstock to a level close to the required level, and the quench oil is hot enough to provide the required temperature level. However, dilution steam is necessary for some operations. These are the start-up operation, the decoking operation and the hot standby operation. In these cases, the feedstock is not sent to separate furnaces, such as a furnace during the decoking operation. For this reason, the block diagram preferably provides a dilution steam header 80 with an electric boiler 85 for providing dilution steam 24. In addition, the dilution steam can be used to supply the required amount of steam for stripping sour water and steam for purging the instruments. The capacity of this system can be limited compared to a known installation in which dilution steam is needed during normal operation. In addition, stripping steam can be used to meet the needs of the sour water stripper. During normal operation, to provide a slight superheat, if necessary, some dilution steam can be mixed with the diluted steam feed coming from the saturator. The advantage is that the contribution of the dilution steam collector 80 with the electric boiler 85 to the total dilution steam requirement is preferably less than 40%, more preferably less than 30% and even more preferably less than 20%. For start-up, decoking, hot standby and standby operation, the dilution steam can be sent to the furnace separately.

The purge 26 from the dilution steam manifold 80 and the make-up 25 of said saturator water heating circuit prevent the accumulation of contaminants in the saturator water circuits and the dilution steam generation. Thus, the presence of these components is preferable. In combination with the use of heat from a quench oil cooling device (as shown in the embodiment of Fig. 6), taking into account the limitations of the saturator application given in the description of Fig. 5, in particular with respect to the maximum practical ratio of dilution steam to feedstock, the inventors have found the possibility of achieving a higher level of saturation of the (essentially gaseous) feedstock with water (water vapor) by moistening the feedstock in the saturator 150 at approximately atmospheric pressure or a relatively low pressure above atmospheric pressure, i.e. at a pressure below the pressure at which the pyrolysis reactor is expected to operate, and then compressing the moistened feedstock (i.e. the mixture of feedstock and diluent) before feeding it to the cracking section. In Fig. 7 schematically shows an installation/process for producing ethylene in accordance with the present invention, including (using) a compressor for compressing the wetted feedstock.

The arrangement may be substantially the same as in Fig. 5. However, the apparatus further includes a compressor 154 downstream of the saturator/humidifier 150, the saturator/humidifier being configured to operate typically at a pressure approximately equal to atmospheric pressure. During operation, the feedstock is humidified, in particular substantially saturated, at a pressure below the pressure at which the electrically driven cracking furnace 1001 is intended to operate. Typically, a conventional radiant coil pyrolysis reactor is operated at a pressure in the range of 1.5-4.0 bar abs, in particular 1.7-3.0 bar abs. Other designs, such as the dynamic rotary device manufactured by Coolbrook, may require lower pressures. Potentially, such a pressure is approximately 2 bar abs; typically, approximately 4 bar abs. The humidified gas is compressed to the desired pressure, typically in the range of 2.0-6 bar abs., in particular 2.6-1 bar abs., using a saturated gaseous feedstock compressor 154 for feeding the humidified feedstock 3 to the furnace section 1001. This is different from the scheme in Fig. 6, which, as a rule, allows the operation to be carried out without requiring additional (electrical) energy to ensure the required level of preheating of the feedstock and its dilution with steam. In this embodiment, electric energy is required to drive the compressor, but compared to generating dilution steam using an electric boiler, this embodiment nevertheless requires 40-50% less energy, depending on the set feed pressure for the furnace. In addition, the combination of a humidifier at a relatively low pressure and a compressor for compressing the hydrocarbon feedstock and diluent mixture provides a desirable high ratio of dilution steam in the hydrocarbon feedstock and diluent mixture, in particular a ratio of about 0.35. Similar to the diagram in Fig. 6, the presence of a dilution steam collector 80 with an electric boiler 85 provides an advantage for supplying dilution steam 24. In a further embodiment, not only particularly suitable for cracking substantially gaseous feedstocks by steam cracking, but also for cracking liquid feedstocks or mixtures of gaseous and liquid feedstocks, the ethylene production plant comprises a dilution steam generator and further comprises a heat pump adapted to generate the dilution steam. Fig. 8 schematically shows an installation/process according to the present invention, providing an advantage due to the use of a heat pump and a refrigerant. The refrigerant has substantially a normal boiling point in the range from 0°C to 80°C. Although this range may be preferred for practical reasons, it should be understood that refrigerants having a boiling point outside this range may be used. The block diagram in Fig. 8 may be substantially the same as the diagram in Fig. 5, except for the presence of a dilution steam generator configured to use a condensable refrigerant 86, and the presence of a dilution steam superheater 87, which uses a refrigerant, instead of a saturator/humidifier. In operation, the availability of refrigerant heat for generating dilution steam is ensured by using a heat pump to increase the level of heat from the cooling water. A detailed diagram of a particularly suitable heat pump is shown in Fig. 9. Subcooled medium-pressure liquid refrigerant 190 from the medium-pressure refrigerant manifold 173 is passed through a liquid refrigerant pressure relief valve to a low pressure 181, which leads to the formation of a volatile low-pressure refrigerant 191. This refrigerant is separated in the low-pressure refrigerant manifold 170. The liquid fraction is recirculated by natural circulation through a thermosiphon type reboiler - a low-pressure refrigerant evaporator 171 - for evaporation using the heat of the cooling water with a lower heating level coming from the cooling water circuit. Alternatively, the low-pressure refrigerant manifold 170 and the low-pressure refrigerant evaporator 171 can also be combined into a kettle type reboiler, since the refrigerant is a clean fluid medium. The saturated low-pressure refrigerant vapor 192 is compressed to a slightly superheated medium-pressure refrigerant vapor 195a in the low-to-medium-pressure refrigerant compressor 172.

The subcooled liquid refrigerant 193 of high pressure from the economizer 175 of the refrigerant is passed through the pressure relief valve of the liquid refrigerant to the medium pressure 180, which leads to the formation of a volatile refrigerant 194 of medium pressure. This refrigerant is separated in the collector 173 of the refrigerant of medium pressure. The liquid fraction is recirculated by natural circulation through a reboiler of thermosyphon type - the evaporator 174 of the refrigerant of medium pressure - for evaporation using the heat of cooling water with a higher heating level coming from the cooling water circuit. Alternatively, the collector 173 of the refrigerant of medium pressure and the evaporator 174 of the refrigerant of medium pressure can also be combined into a reboiler of kettle type, since the refrigerant is a clean fluid medium. The saturated vapor 195b of the medium-pressure refrigerant is combined with the slightly superheated vapor 195a of the medium-pressure refrigerant and is superheated in the economizer 175 of the refrigerant to form a superheated vapor 196 of the medium-pressure refrigerant. After compression in the compressor 176 of the refrigerant from the medium to the high pressure and reaching a temperature level exceeding the temperature level for generating the dilution vapor, the refrigerant is cooled with the saturated dilution vapor in the cooler 177 of the high-pressure refrigerant. The cooled vapor 198 of the high-pressure refrigerant is condensed with the help of process water from the dilution vapor collector in the condenser 178 of the high-pressure refrigerant. The condensed liquid refrigerant 199 of the high pressure is subcooled in the economizer 175 of the refrigerant. The subcooled liquid refrigerant 193 of high pressure is recycled. By means of this scheme it is possible to increase the excess heat available in the cooling water circuit to a temperature level which is high enough to generate dilution steam. The low-pressure refrigerant serves for cooling with cooling water of a lower temperature level, while the medium-pressure refrigerant serves for cooling with cooling water of a higher temperature level. A third pressure level can be introduced to recover the heat of the cooling water at three levels instead of two. The pressure levels of the refrigerant and the refrigerant itself are selected in such a way as to recover the heat of the cooling water by evaporating the liquid refrigerant at different temperature levels corresponding to the temperatures of the coolers of the cooling water circuit, and so that the refrigerant vapor can be condensed at a temperature level suitable for generating dilution steam.

The use of an ethylene production plant comprising a heat pump system for generating dilution steam requires additional electrical energy in addition to the electrical energy for the pyrolysis reactor. However, the required amount of electrical energy, depending on the feed pressure used for the furnace, is typically 50-70% less compared to generating dilution steam using an electric boiler. This is similar to the amount of electrical energy required for a plant that uses a humidifier and a compressor to produce a humidified feedstock (see, for example, Fig. 7). An advantage of using a heat pump, as shown, for example, in Fig. 8, compared to using a saturator, as shown in Fig. 6 or 7, is that the heat pump system can also perform the function of an electric boiler outside normal operation (for example, during startup). In addition, it is believed that the embodiment using a heat pump provides particular advantages compared to a plant/process that uses a saturator to achieve a high steam to hydrocarbon feedstock mass ratio, for example a ratio greater than 0.35.

In the case of cracking at least a substantially liquid feedstock or a mixture of liquid and gaseous feedstock, it is particularly advantageous to use a system configured to preheat the feedstock and evaporate it using heat recovered from cooling water and quench oil, respectively. It is also advantageous to use heat recovered from a middle oil fraction. The advantage lies in generating the dilution steam using heat from the cooling water pumped by a heat pump, in particular as described above, preferably using the refrigerant circulation scheme given in the description of Fig. 9. The advantage of the ethylene production plant or the process of the present invention, including these measures, lies in the fact that the feedstock can be evaporated without using flue gas and that the dilution steam can be evaporated without using MP steam. When using a heat pump to generate MP steam, the power consumption can be reduced by more than 50% compared to using an electric MP boiler for this purpose. This makes it possible to significantly reduce the additional need for power. Such an advantageous process is shown further in Fig. 10. In essence, as shown in Fig. 10, in operation, the feedstock 2, preferably a liquid feedstock, in particular liquefied butane, pentane or naphtha or a mixture thereof, is first preheated in a preheater 30 with a low-temperature heat source, such as cooling water, external to the furnace 1001, to heat it from the ambient temperature to a temperature close to the highest temperature for the low-temperature heat source, such as the highest temperature in the cooling water circuit - typically to a temperature in the range of 5-10 °C from the highest temperature. In the case of the highest temperature of the cooling water, which is approximately 75-80 °C, preheating to 70-75 °C is possible. Further preheating and partial evaporation of the feedstock is achieved by means of a middle oil fraction in a hydrocarbon feedstock preheater 43 using a middle oil fraction and a partial evaporator 44 of the hydrocarbon feedstock using a middle oil fraction, external to the furnace. Partially evaporated feedstock is separated in hydrocarbon feedstock collector 45. Liquid fraction is recirculated by natural circulation through thermosyphon type reboiler - hydrocarbon feedstock evaporator using quenching oil evaporator 46 - for evaporation using quenching oil heat coming from quenching oil circuit. Completely evaporated feedstock is sent to feedstock/product heat exchanger 90 of cracking furnace 1001 with electric drive. Provided heat from quenching oil is available and temperature level is high enough, feedstock can be slightly superheated using quenching oil, as well as in hydrocarbon feedstock superheater 47 using quenching oil.

In order to suppress the partial pressure of hydrocarbons in the pyrolysis reactor, which helps to increase the yield of the product and suppress the formation of coke, the superheated dilution steam 24 (usually superheated by 30-50°C, depending on the efficiency of the refrigerant compressor), coming from the hot separation section, is also sent to the feedstock/product heat exchanger 90 before being fed to the electrically driven pyrolysis reactor 91 in the cracking furnace section 1001.

The mixture of hydrocarbon feedstock and diluted steam 3 enters the heat exchanger 90 of the "raw material/product" type at a temperature above the dew point of water and is heated by the removed heat of the product by means of the heat exchanger 90 of the "raw material/product" type to a suitable temperature at the input channel of the pyrolysis reactor 91 with an electric drive. Physical heat and reaction heat are supplied from the said pyrolysis reactor 91 to the hydrocarbon feedstock 3 diluted with steam for converting the feedstock into products. The removed heat of the product 4 of the reactor is recovered by means of the heat exchanger 90 of the "raw material/product" type.

The product is then cooled in the quenching oil pipe 37 by means of quenching oil injection 27 and middle oil fraction injection 28 in the presence of a middle oil fraction circuit. From the furnace section, the product 4 is sent to the hot separation section of the plant, mainly consisting of a primary fractionation column 50, a water cooling column 60, a sour water stripper column 70 and a dilution steam collector 80.

In the primary fractionation column 50, the product of the pyrolysis reactor (cracking product) is further cooled by maintaining a temperature above the dew point of water, preferably a temperature of 5°C above the dew point, more preferably a temperature of 5°C - 40°C above the dew point, so that water does not condense in this column. For example, for a dew point of about 90°C, the operating temperature can be controlled within the range of 95°C - 110°C, for example approximately 100°C, by controlling the injection of the reverse flow. Then the product is cooled using the circulation pumps of the quenching oil and the middle oil fraction and the reverse flow of gasoline, respectively. The feedstock for the quenching oil cooling circuit 54 is the product 6 of the heavy distillate fuel, which is collected in the lower part of the column. This quenching oil 10 is cooled by means of coolers 55 of the quenching oil circuit. Part of it is directed to the quench oil branch pipe 27, and the rest is re-injected into the column below the full middle oil fraction pick-off tray. In this case, the coolers 55 of the quench oil cooling circuit are used to evaporate the feedstock in the hydrocarbon feedstock evaporator using the quench oil evaporator 46. The temperature of the lower part of the primary fractionation column can be controlled to a temperature level at which this process becomes possible. A person skilled in the art will be able to do this on the basis of general knowledge and the information provided in the present description, for example, by controlling the amount of quench oil injected into the quench oil branch pipe. The quench oil cooling circuit serves the washing section 51 of the primary fractionation column - the lower part of the column. Preferably, the middle oil fraction cooling circuit 56 is present. Its presence provides a relatively clean/uncontaminated intermediate cooling circuit that recovers heat from the reactor product at a lower heating level than the quench oil circuit 54. The middle oil fraction 11 is collected on a pick-up tray in the lower part of the middle oil fraction section 52 of the primary fractionation column, located above the wash section 51 in the column. The return flow 12 of the middle oil fraction is directed to the quenching oil wash section 51 in the lower part of the column in order to provide the possibility of shifting the quenching oil feed to the middle oil fraction circuit. In addition, the middle oil fraction flow is directed to the quenching oil branch pipe 28. The remaining part is cooled by means of coolers 57 of the middle oil fraction circuit and returned to the column below the light distillate fuel fraction pick-up point. The middle oil fraction cooling circuit 56 serves the middle oil fraction section 52 of the primary fractionation column. In this case, the middle oil fraction can be used for preheating and partial evaporation of the hydrocarbon feedstock in the heater 43 of the hydrocarbon feedstock using the middle oil fraction and in the partial evaporator 44 of the hydrocarbon feedstock using the middle oil fraction. For this purpose, quenching oil can optionally be used.

The return stream 13 of gasoline coming from the water-gasoline separator 63 provides heat recovery in the upper part of the column, in the return stream section 53 of the primary fractionation column, and transfers the recovered heat to the cooling water circuit. The column has appropriate internal components that provide efficient heat transfer from the product to the injected quenching oil, the middle oil fraction and the return stream of gasoline. In addition to cooling the product, condensation of light and heavy oil fractions occurs in the primary fractionation column. Heavy distillate fuel 6 is collected in the lower section 51, while light distillate fuel 7 is collected in the lower part of the return stream section 53 on a partial light oil fraction collection tray. These products can be stripped to control the flash point of the total product 5 of distillate fuel and/or to recover lighter fractions of the quench oil to control the viscosity in the quench oil circuit. In addition, they can also be cooled. These details are not shown, since they are not important for this application. In the water cooling column 60, the product 4 is further cooled to approximately ambient temperature. This is done using a circulation pump, which collects the aqueous product accumulated in the lower part of the unit - the so-called cooling water 14, and introduces it into the cooling water column 60 at different levels. The cooling water circuit typically consists of two stages - a lower cooling water cooling circuit 64 serving the lower section 61 of the cooling water column, and an upper cooling water cooling circuit 66 serving the upper section 62 of the cooling water column. The coolers 65 of the lower cooling water circuit are typically used to recover as much cooling water as possible for use in other sections of the unit. Such sections include, for example, the feed heater 30 and/or the reboiler of the propylene stripping column (not shown). In this case, the heat is used to preheat the feedstock using the feed heater 30 and to evaporate the coolant using the medium-pressure coolant evaporator 174 and/or the low-pressure coolant evaporator 171 in the coolant circuit shown in Fig. 9. Any excess heat must usually be removed by cooling with air or cooling water. The coolant circuit reduces the need for these cold energy carriers and transfers heat from the cooling water at a level suitable for generating dilution steam. The cooled injection water from the circulation pump circuit is used in the cooling water column to remove heat from the cracked gas by direct heat exchange in the appropriate internal components of the column. The main function of this column, in addition to cooling the cracked gas, is to condense and recover the dilution steam. The condensed dilution steam is a clean product from the bottom of the column along with a small amount of gasoline product. Typically, these products are separated from each other using a water-gasoline separator 63. Sometimes, this separator is also used to collect cooling water intended for the cooling water circuit. This condensed dilution steam, called sour water 20, contains acid gases, which are stripped with stripping steam 21 in the sour water stripper 70. These acid gases 22 are returned to the cooling water column 60. The stripped water, called process water 23, is suitable for generating dilution steam. This occurs at a higher pressure than the pressure in the cooling water column and in the sour water stripper, typically at a pressure of about 2 to about 7 bar abs, in particular about 4 to about 6 bar abs, for feeding it to the furnace section 1001. The dilution steam is generated using a coolant. The process water is collected in the dilution steam collector 80, and by means of a thermosiphon circuit from the condensing coolant in the dilution steam generator 86 using the condensing coolant, the dilution steam 24 is formed. Any superheating of the coolant is used for slight superheating of the dilution steam in the dilution steam superheater 87 to a temperature of from 180°C to 210°C before it is returned to the cracking furnace 1001 with an electric drive for diluting the hydrocarbon feedstock 1. Blowdown 26 from the dilution steam collector 80 and make-up 25 of said collector from the dilution steam system prevent the accumulation of contaminants in the dilution steam generation circuit.

Alternative plant/process according to the present invention is based on the thermal integration scheme shown in Fig. 11. This scheme is similar to the scheme in Fig. 10, except for the thermal integration. It is also particularly effective for cracking liquid feedstocks and mixtures of liquid and gaseous feedstocks.

In the process or installation according to the present invention based on the diagram in Fig. 11, the heat from the quenching oil is used (intended) not for evaporation of the raw material, but for generation of dilution steam by means of the dilution steam generator 82 using the quenching oil. In operation in this case, evaporation of the raw material is carried out by means of a coolant in the hydrocarbon feedstock evaporator 48 using a condensable coolant and superheating by means of the hydrocarbon feedstock superheater 49 using a coolant.

The efficiency values of the process or the plant based on Fig. 10 or Fig. 11 are very close for these two schemes. In the case of the scheme in Fig. 11, it is necessary to adjust the refrigerant circuit in order to also ensure the supply of heat to the feedstock evaporator 49. Depending on the feedstock, this can be done at a higher or lower temperature level than the temperature level for generating dilution steam. A separate compressor can be installed to perform this operation, or two compressors can be connected in series.

Fig. 12 and Fig. 13 show refrigerant compressor systems that can be used in the process or installation according to the present invention. These refrigerant compressors can be mounted on a single shaft and also in a single housing, if desired. The refrigerant compressor system can be used to further reduce the amount of electrical energy required.

In Fig. 12, two separate parallel high-pressure loops are shown, a branch 1010 of the high-pressure refrigerant circuit and a branch 1011 of the ultra-high-pressure refrigerant circuit. Each of these two branches operates at different pressures and corresponding operating temperatures, for example, to optimally match the temperature levels of the dilution steam generation and the evaporation of the feedstock. This will lead to a decrease in the required amount of electrical energy. In one branch, the evaporation of the feedstock is carried out by means of the hydrocarbon feedstock evaporator 48 using a condensable refrigerant, and in the other branch, the generation of the dilution steam is carried out by means of the dilution steam generator 86 using a condensable refrigerant. If the operating temperature of the hydrocarbon feedstock evaporator is higher than the operating temperature of the dilution steam generator, the hydrocarbon feedstock evaporator will operate due to the ultra-high pressure branch 1011, and the dilution steam generator - due to the high pressure branch 1010. If the operating temperature of the hydrocarbon feedstock evaporator is lower than the operating temperature of the dilution steam generator, the hydrocarbon feedstock evaporator will operate using the high pressure branch 1010 and the dilution steam generator will operate using the high pressure branch 1011.

The subcooled liquid refrigerant 190 of medium pressure from the collector 174 of medium pressure refrigerant is passed through the pressure relief valve of liquid refrigerant to low pressure 181, which results in the formation of volatile refrigerant 191 of low pressure. This refrigerant is separated in the collector 170 of low pressure refrigerant. The liquid fraction can be recirculated by natural circulation through a thermosyphon type reboiler - the evaporator 171 of low pressure refrigerant - for evaporation using the heat of cooling water with a lower heating level coming from the cooling water circuit. Alternatively, the collector 170 of low pressure refrigerant and the evaporator 171 of low pressure refrigerant can be combined into a reboiler of kettle type, since the refrigerant is a clean fluid medium. The saturated low-pressure refrigerant vapor 192 is compressed to slightly superheated medium-pressure refrigerant vapor 195a in the low-to-medium-pressure refrigerant compressor 172.

The supercooled liquid refrigerant 206 of extreme pressure from the economizer 182 of extreme pressure and the subcooled refrigerant 193 of high pressure from the economizer 175 of high pressure refrigerant are passed through the pressure relief valves of liquid refrigerant to the medium pressure 180, which results in the formation of volatile refrigerant 194 of medium pressure. This refrigerant is separated in the collector 173 of medium pressure refrigerant. The liquid fraction can be recirculated by natural circulation through the reboiler of thermosyphon type - evaporator 174 of medium pressure refrigerant - for evaporation using the heat of cooling water with a higher heating level coming from the cooling water circuit. Alternatively, the collector 173 of the medium-pressure refrigerant and the evaporator 174 of the medium-pressure refrigerant can also be combined into a reboiler of the kettle type, since the refrigerant is a clean fluid medium. The saturated vapor 195b of the medium-pressure refrigerant is combined with the slightly superheated vapor 195a of the medium-pressure refrigerant.

At this stage, the combined flows 195a and 195b are directed into two parallel branches 1010 and 1011 of the refrigerant circuit.

The portion directed to the high-pressure branch 1010 is superheated in the high-pressure refrigerant economizer 175 to form a superheated vapor 196 of the medium-pressure refrigerant. After that, the refrigerant is compressed in the refrigerant compressor 176 from low to medium and to high pressure to a temperature level exceeding the temperature level of generating the dilution vapor or evaporation of the hydrocarbon feedstock, depending on which of the two temperature levels is lower. The refrigerant is cooled by saturated dilution vapor or hydrocarbon feedstock in the high-pressure refrigerant cooler 177 by means of the dilution vapor superheater 87 using the refrigerant or by means of the hydrocarbon feedstock superheater 49 using the refrigerant, respectively. The cooled high-pressure refrigerant vapor 198 is condensed by means of process water from the dilution vapor collector or hydrocarbon feedstock in the high-pressure refrigerant condenser 178 by means of the dilution vapor generator 86 using the condensable refrigerant or by means of the hydrocarbon feedstock evaporator 48 using the condensable refrigerant, respectively. The condensed high-pressure liquid refrigerant 199 is subcooled in the high-pressure refrigerant economizer 175. The subcooled high-pressure liquid refrigerant 193 is recirculated. The portion directed to the ultra-high-pressure branch 1011 is superheated in the ultra-high-pressure refrigerant economizer 182 with the formation of superheated medium-pressure refrigerant vapor 196. After this, the refrigerant is compressed in the refrigerant compressor 183 from medium to ultra-high pressure to a temperature level exceeding the level of the dilution vapor formation temperature or the evaporation temperature of the hydrocarbon feedstock, depending on which of the two temperature levels is higher. The refrigerant is cooled with saturated dilution vapor or hydrocarbon feedstock in the ultra-high-pressure refrigerant cooler 185 by means of a dilution vapor superheater 87 using a refrigerant or by means of a hydrocarbon feedstock superheater 49 using a refrigerant, respectively. The cooled vapor 186 of the ultra-high-pressure refrigerant is condensed by means of process water from the dilution vapor collector or hydrocarbon feedstock in the ultra-high-pressure refrigerant condenser 187 by means of a dilution vapor generator 86 using a condensable refrigerant or by means of a hydrocarbon feedstock evaporator 48 using a condensable refrigerant, respectively. The condensed ultra-high-pressure liquid refrigerant 205 is subcooled in the ultra-high-pressure refrigerant economizer 182. The subcooled ultra-high-pressure liquid refrigerant 206 is recirculated.

By means of this scheme it is possible to increase the excess heat available in the cooling water circuit to a temperature level that is high enough to generate dilution steam and evaporate the hydrocarbon feedstock in two separate branches of the refrigeration system.

The circuit in Fig. 13 is similar to the circuit in Fig. 12, except that the split between the two branches occurs downstream of the medium to high pressure compressor 176, and that the medium to ultra-high pressure compressor 183 is replaced by the high to ultra-high pressure compressor 183 such that the compressors in branches 1010 and 1011 are connected in series instead of in parallel.

As used herein, the singular forms are also intended to include the plural forms, for example, the term "cracking furnace" includes the term "cracking furnaces"; the term "burner" includes the term "a plurality of burners", etc., unless the context clearly indicates otherwise. The term "or" includes any and all combinations of one or more related listed elements, unless the context clearly indicates otherwise (e.g., when using the construction "either..., or"). It should be understood that the terms "comprises" and "comprising" indicate the presence of the listed elements, but do not exclude the presence or addition of one or more other elements. Furthermore, it should be understood that when a particular step of a process is said to be subsequent to another step, it may immediately follow said other step, or one or more intermediate steps may be performed before the particular step is performed, unless otherwise indicated. Similarly, it should be understood that when describing a connection between structures or components, this connection may be established directly or through intermediate structures or components, unless otherwise specified.

In the context of the present application, the term “about” includes, in particular, a deviation of 10% or less from the stated value, more particularly 5%, even more particularly 3% or less.

The term "(at least) substantially" or "(at least) substantially" is generally used herein to indicate the general nature or function of the element being described. In relation to a quantitative feature, the term is particularly used to indicate that it constitutes at least 75%, more particularly 90% or more, even more particularly 95% or more of the maximum value for that feature. The term "substantially free" is generally used herein to indicate that the substance is absent (at a concentration below the detection limit achievable by the analytical technology that is available as of the effective filing date of the application) or is present in such a low amount that it does not significantly affect the property of the product, which is essentially free of the said substance.

The term "high pressure steam" (HP steam) is well known in the art. Typically, the pressure of HP steam is typically at least about 40 barg, such as 80 barg, or more, such as from about 100 barg to about 130 barg, in particular 100-125 barg.

The term "medium pressure steam" (MP steam) refers to steam having an upper pressure limit of 40 barg. As used herein, the term "MP" is typically in the pressure range of about 6 to about 20 bara, more particularly in the range of 7 to 13 bara.

The term "low pressure steam" refers to steam having a pressure below the MP steam pressure.

The present invention is described more fully herein with reference to the accompanying drawings, which show embodiments of the present invention. For clarity, the absolute and relative sizes of systems, components, layers and regions in the drawings may be exaggerated. Embodiments may be described with reference to schematic illustrations and/or sectional illustrations of possibly idealized embodiments and intermediate structures of the present invention. In the description and in the drawings, like numerals refer to like elements. Relative spatial position terms, as well as their derivatives, should be understood as referring to a spatial orientation according to the corresponding description or illustration in the drawing. These relative spatial position terms are intended for convenience of description and do not imply construction or operation of the system with a particular spatial orientation, unless otherwise specified. For clarity and brevity of the description, herein features are described as part of the same or separate embodiments, however, it should be understood that the scope of the invention may include embodiments having combinations of all or some of the described features.

EXAMPLES

The present invention will be illustrated below with reference to the following non-limiting examples. In order to demonstrate the applicability of the present invention, a number of examples were prepared for a gaseous feedstock cracking unit: Comparative Example 1 with a conventional block diagram as shown in Fig. 1 to be used as a base case for comparisons; Example 2 with a block diagram comprising a primary fractionator and a humidifier/saturator as shown in Fig. 6; Example 3 with a block diagram comprising a low-pressure humidifier/saturator and a dilute feed compressor as shown in Fig. 7; and Example 4 with a block diagram as shown in Fig. 8 containing a heat pump as shown in Fig. 9. An ethane cracking unit with a capacity of 1500 kilotonnes per year (kt/y) was selected as the base case. Unconverted ethane and propane are returned to the furnace section as recycle gas and mixed with fresh feed gas. This combined feed is processed in cracking furnaces for all examples.

Example 1, the base case for comparisons, processes 359.8 t/h of gaseous feedstock, 233.5 t/h of fresh ethane feedstock and 126.3 t/h of recycle gas, mainly recycle ethane. This feedstock is fed at 20°C and heated to 55°C in hydrocarbon feedstock preheater 30. In the convection section of the furnace, the feedstock is further heated to 225°C in hydrocarbon feedstock preheater 31. Dilution steam with a temperature of 180°C is added to dilute the feedstock. The diluted feedstock is heated to 703°C in hydrocarbon feedstock dilute steam superheater 33. At a pressure of 4 bar abs. The diluted gas is fed through critical Venturi flowmeters into a large number of parallel radiant coils in the cracking furnace - the internal combustion chamber 34 of the fuel-fired furnace of the pyrolysis reactor, where the gas is heated to 855 °C. The pressure at the outlet of the reactor is 1.8 bar abs. During this process, the feedstock is converted into products. The conversion does not stop at the outlet of the reactor, but continues in the channel leading to the quenching and evaporation apparatus 35, and in the quenching and evaporation apparatus itself. In the channel leading from the coils to the quenching and evaporation apparatus, the temperature drops to 840 °C due to the endothermic reaction. In the quenching and evaporation apparatus, the product 4 of the pyrolysis reactor (also called the cracking product) is cooled to 350 °C, whereby high-pressure steam is generated. The reactor product is then further cooled to 180°C in a secondary quench and evaporator 36, which is accompanied by heating of the boiler feedwater. The reactor product is further cooled in a cooling water column 60 to 30°C to produce a gaseous cracking product 9. During this process, the dilution steam is condensed together with a small amount of gasoline 8. The gasoline/sour water mixture is separated in a water-gasoline separator at 80°C. The sour water 20 is pumped to a sour water stripper 70, where it is stripped to remove dissolved acid gases 22 at a pressure of 1.7 bar abs. The purified process water 23 is pumped to a dilution steam collector 80, where dilution steam 24 is generated from the condensed MP steam at a pressure of 6 bar abs. and a temperature of 160°C. The dilution steam is superheated to 180°C in the superheater 83 using superheated steam C D. The superheated dilution steam is sent to the feedstock dilution furnace 1. The amount of dilution steam generated is 125.9 t/h. This means that the steam dilution ratio is 0.35 (125.9 t/h / 359.8 t/h feedstock). In addition, 12.5 t/h of steam 21 for stripping sour water is generated, which is intended for stripping sour water.

Example 2 uses the same gaseous feedstock with a flow rate of 359.8 t/h. This feedstock is fed at a temperature of 20°C into the lower part of a saturator 150 operating at a pressure of 6 bar abs. In the saturator, the gas is brought into contact with the saturator circulating water with a temperature of 140°C, which is fed into the upper part of the saturator. Such a temperature can be practically achieved by heating the saturator circulating water 151 with quenching oil with a temperature of 150°C and cooling water with a temperature of 77°C. Part of the process water, 103 t/h, is mixed with the saturator circulating water. This amount of water is used as make-up to compensate for the amount of water evaporated in the saturator. The remaining part of the process water is sent to the dilution steam collector 80 with an electric boiler 80 for generating 22.8 t/h of dilution steam generated at a pressure of 6 bar abs. and a temperature of 160°C, to increase the total amount of dilution steam to 125.9 t/h, whereby the corresponding steam dilution ratio is 0.35 (125.9 t/h / 359.8 t/h of feedstock). In addition, 12.5 t/h of steam 21 for stripping sour water are generated, intended for stripping sour water.

Ethane 3 diluted with saturated steam is fed at 123°C to the feed/product heat exchanger 90 in section 1001 of the electric cracking furnace where it is heated to 703°C before entering the electric pyrolysis reactor 91. In the pyrolysis reactor the diluted feed is heated to 855°C. The pressure at the reactor outlet is 1.8 bar abs. In the channel leading from the reactor to the feed/product heat exchanger the temperature drops to 840°C due to the endothermic reaction. In the feed/product heat exchanger, the product 4 of the pyrolysis reactor (also called the cracker product) is cooled to 330°C using dilute hydrocarbon feedstock 3. The product is further cooled in the quench oil pipe 37 to 170°C and in the primary fractionation column 50 to 120°C using circulating quench oil 54. A small amount of liquid distillate fuel 6 is condensed in the primary fractionation column. The operating temperature of the lower part of the primary fractionation column is 150°C, which makes it possible to generate a quench oil stream with a temperature of 150°C. This quench oil is cooled to 110°C in order to control the temperature of the upper part of the primary fractionation column at 120°C. This quenching oil is completely used for heating the circulating water 151 of the saturator to 140°C, as already mentioned above, using the cooler 55 of the quenching oil circuit (by means of the heater 153 of the water circuit of the saturator using the heat from the quenching oil).

Finally, the product is cooled in the cooling water column 60 to 30°C using the circulating cooling water 64 and 66 to obtain the gaseous cracking product 9. The operating temperature of the column is 77°C, slightly below the dew point. The lower cooling water circuit cooler 65 (via the saturator water circuit heater 152 with cooling water) is used to heat the saturator circulating water 151 to 72°C before it enters the saturator water circuit heater 153 using the heat from the quenching oil.

In the cooling water column, the dilution steam is condensed together with a small amount of gasoline 8. The gasoline/sour water mixture is separated in a water-gasoline separator at 80°C. The sour water 20 is pumped to the sour water stripper 70, where it is stripped to remove dissolved acid gases 22 at a pressure of 1.7 bar abs. The purified process water is pumped to the saturator 150 and the dilution steam collector 80.

Example 3 uses the same gaseous feedstock with a flow rate of 359.8 t/h. This feedstock is fed at a temperature of 20°C into the lower part of saturator 150. Unlike the previous example, the working pressure of this column is not 6 bar abs, but 1.1 bar abs. In the saturator, the gas is brought into contact with the saturator circulating water with a temperature of 75°C, which enters the upper part of the saturator. Such a temperature can be practically possible by heating the saturator circulating water 151 with cooling water with a temperature of 80°C.

Part of the process water, 125.9 t/h, is mixed with the saturator circulation water. This amount of water is used as make-up to compensate for the amount of water evaporated in the saturator. This corresponds to a steam dilution ratio of 0.35 (125.9 t/h / 359.8 t/h of feedstock). The remaining part of the process water is sent to the dilution steam collector 80 with an electric boiler 80 to generate 12.5 t/h of steam for stripping the sour water.

Ethane 3 diluted with steam is compressed to a pressure of 6 bar abs. in a saturated gaseous feedstock compressor 154, increasing the temperature from 74°C to 214°C. The compressed gas is sent to a feedstock/product heat exchanger 90 in an electrically driven cracking furnace section 1001, where it is heated to 703°C, after which it enters an electrically driven pyrolysis reactor 91. In the pyrolysis reactor, the diluted feedstock is heated to 855°C. The pressure at the reactor outlet is 1.8 bar abs. In the channel leading from the reactor to the feedstock/product heat exchanger, the temperature drops to 840°C due to the endothermic reaction. In the feedstock/product heat exchanger, the product 4 of the pyrolysis reactor (also called the cracking product) is cooled to 400°C using the diluted hydrocarbon feedstock 3. The product is further cooled in the cooling water column 60 to 30°C using the circulating cooling water 64 and 66 to obtain the gaseous cracking product 9. The operating temperature of the column is 80°C. The cooler 65 of the lower cooling water circuit (via the heater 152 of the water circuit of the saturator with cooling water) is used to heat the circulating water 151 of the saturator to 75°C.

In the cooling water column, the dilution steam is condensed together with a small amount of gasoline 8. The gasoline/sour water mixture is separated in a water-gasoline separator at 80°C. The sour water 20 is pumped to the sour water stripper 70, where it is stripped to remove dissolved acid gases 22 at a pressure of 1.7 bar abs. The purified process water is pumped to the saturator 150 and the dilution steam collector 80.

In Example 4, the same gaseous feedstock with a flow rate of 359.8 t/h is used as in the other cases. This feedstock is fed at 20°C and heated to 75°C in the hydrocarbon feedstock heater 30. Dilution steam with a temperature of 200°C is added to dilute the feedstock. The diluted feedstock is fed to the feedstock/product heat exchanger 90 in the electric cracking furnace section 1001 and heated to 703°C, after which it enters the electric pyrolysis reactor 91. In the pyrolysis reactor, the diluted feedstock is heated to 855°C. The pressure at the reactor outlet is 1.8 bar abs. In the channel leading from the reactor to the feedstock/product heat exchanger, the temperature drops to 840°C due to the endothermic reaction. In the feedstock/product heat exchanger, the product 4 of the pyrolysis reactor (also called the cracking product) is cooled to 316°C using the diluted hydrocarbon feedstock 3. The product is further cooled in the cooling water column 60 to 30°C using the circulating cooling water 64 and 66 to obtain the gaseous cracking product 9. The operating temperature of the column is 80°C. The cooler 65 of the lower cooling water circuit (via the heater 152 of the water circuit of the saturator with cooling water) is used to heat the circulating water 151 of the saturator to 75°C.

In the cooling water column the dilution steam is condensed together with a small quantity of gasoline 8. The gasoline/sour water mixture is separated in a water/gasoline separator at 80°C. The sour water 20 is pumped to a sour water stripper 70 where it is stripped to remove dissolved acid gases 22 at a pressure of 1.7 bar abs. The purified process water is pumped to a dilution steam header 80 with a dilution steam generator 86 using a condensable refrigerant to generate 125.9 t/h of dilution steam generated at a pressure of 6 bar abs. and a temperature of 160°C, necessary to ensure a dilution steam ratio corresponding to the value of 0.35 (125.9 t/h / 359.8 t/h of feed). In addition, 12.5 t/h of steam 21 for stripping sour water is generated, intended for stripping sour water. The dilution steam is superheated in the dilution steam superheater 87 using superheated refrigerant.

Using the evaporators 171, 174 of the low and medium pressure refrigerant, with the help of two coolers 65 of the lower circuit of the cooling water, a refrigerant vapor is generated at a temperature of 62.5 °C and 70 °C, respectively. With the help of one of the coolers, the cooling water is cooled from 80 °C to 75 °C, and with the help of the other one - additionally to 67 °C. Using the compressors 172, 176 from low to medium pressure and from medium to high pressure, respectively, a superheated vapor of the high pressure refrigerant with a temperature of 216 °C is generated. It is used for superheating the dilution vapor in the superheater 87 of the dilution vapor (by means of the cooler 177 of the high pressure refrigerant) and for generating the dilution vapor itself in the generator 86 of the dilution vapor using the condensing refrigerant (by means of the condenser 178 of the high pressure refrigerant).

Table 1 provides an overview of the functions for the various examples, as well as the power of the corresponding compressors.

Table 2 shows the power requirements for the various examples and the potential reduction in excess power as defined above, when comparing the power requirements for feedstock dilution with the power requirements for conventional dilution steam generation as calculated for example 1, namely 90.3 MW in the absence of MP steam. The flow chart in Fig. 6 (example 2) has the highest potential for reducing power consumption, by 73%. The flow chart in Fig. 7 (example 3) has a potential for reducing power consumption of 45%. The flow charts in Figs. 8 and 9 (example 4) correspond to an intermediate value of 60%.

SYMBOLS ON FIGURES

1. Hydrocarbon feedstock (gaseous)

2. Hydrocarbon feedstock (liquid)

3. Hydrocarbon feedstock diluted with steam

4. Pyrolysis reactor product (also called cracking product)

5. Total product of distillate fuel

6. Heavy distillate fuel product

7. Light distillate fuel product

8. Heavy pyrolysis gasoline

9. Gaseous cracking product (exiting the hot section, cooled/washed)

10. Quenching oil

11. Middle oil fraction

12. Reverse flow of middle oil fraction

13. Reverse flow of gasoline

14. Cooling water

20. Sour water

21. Steam for stripping

22. Acid gases

23. Technological water

24. Dilution steam

25. Make-up of the dilution steam system

26. Blowing

27. Quenching oil flow into the quenching oil pipe

28. Flow of medium oil fraction into the quenching oil pipe

30. Hydrocarbon feedstock heater external to the furnace

31. Heater of hydrocarbon raw materials in the convection section of the furnace

32. Evaporator of hydrocarbon raw materials in the convection section of the furnace

33. Superheater of hydrocarbon feedstock diluted with steam in the convection section of the furnace

34. Internal combustion chamber of the fuel combustion furnace of the pyrolysis reactor

35. Quenching and evaporation apparatus generating high-pressure steam

36. Secondary quenching and evaporation apparatus

37. Quenching oil pipe

43. Heater of hydrocarbon feedstock using medium oil fraction

44. Partial evaporator of hydrocarbon feedstock using a medium oil fraction

45. Hydrocarbon raw material collector

46. Hydrocarbon feedstock evaporator using quenching oil

47. Hydrocarbon feedstock superheater using quenching oil

48. Hydrocarbon feedstock evaporator using condensing refrigerant

49. Superheater of hydrocarbon feedstock using a refrigerant

50. Primary fractionation column

51. Primary fractionation column washing section

52. Middle oil fraction section of the primary fractionation column

53. Section of the gasoline reverse flow of the primary fractionation column

54. Quenching oil cooling circuit

55. Quenching oil circuit coolers

56. Cooling circuit of the middle oil fraction

57. Medium oil fraction circuit coolers

60. Cooling water column

61. Lower section of the cooling water column

62. Upper section of cooling water column

63. Water-gasoline separator

64. Lower cooling circuit with cooling water

65. Lower circuit coolers for cooling water

66. Upper cooling circuit with cooling water

67. Upper circuit coolers for cooling water

70. Sour water stripping column

80. Dilution steam collector

81. Dilution steam generator using SD steam

82. Dilution steam generator using quenching oil

83. Dilution steam superheater external to the furnace

84. Dilution steam superheater in the convection section of the furnace

85. Electric boiler

86. Dilution steam generator using condensing refrigerant

87. Dilution steam superheater using refrigerant

90. Raw material/product heat exchanger

91. Electric driven pyrolysis reactor

101. Demineralized feed water

102. Steam for stripping

103. Deaerator outlet channel

104. Boiler feed water

105. High pressure saturated steam

106. Purging the steam collector

107. Superheated high pressure steam

108. Medium pressure steam

109. Medium pressure condensate

110. Vacuum condensation of steam

111. Vacuum condensate

112. Combined condensate

120. Deaerator

121. Boiler feedwater heater

122. High pressure steam collector

123. High pressure steam superheater

124. Backpressure steam turbine for reducing pressure from high to medium

125. Condensing steam turbine for reducing pressure from medium to vacuum

126. Surface condenser of a condensing steam turbine

150. Saturator

151. Saturator water heating circuit

152. Heater of water circuit of saturator with cooling water

153. Heater of the water circuit of the saturator using heat from the quenching oil

154. Compressor of saturated gaseous raw materials

170. Low pressure refrigerant manifold

171. Low pressure refrigerant evaporator

172. Low to medium pressure refrigerant compressor

173. Medium pressure refrigerant manifold

174. Medium pressure refrigerant evaporator

175. High pressure refrigerant economizer

176. Medium to high pressure refrigerant compressor

177. High pressure refrigerant cooler

178. High pressure refrigerant condenser

179. High pressure condensed refrigerant collector

180. Liquid refrigerant pressure relief valve to medium pressure

181. Liquid refrigerant pressure relief valve to low pressure

182. Ultra-high pressure refrigerant economizer

183. Medium to ultra-high pressure refrigerant compressor

184. High to ultra-high pressure refrigerant compressor

185. Ultra-high pressure refrigerant cooler

186. Ultra-high pressure refrigerant condenser

187. Ultra-high pressure condensed refrigerant collector

190. Medium pressure saturated liquid refrigerant

191. Low pressure volatile refrigerant

192. Low pressure saturated refrigerant vapor

193. Slightly superheated medium pressure refrigerant vapor

194. Saturated medium pressure refrigerant vapor

195a. Slightly superheated medium pressure refrigerant vapor

195b. Medium pressure saturated refrigerant vapor

196. Superheated medium pressure refrigerant vapor

197. Superheated high pressure refrigerant vapor

198. Cooled high pressure refrigerant vapor

199. Condensed high pressure liquid refrigerant

200. High pressure saturated liquid refrigerant

201. Superheated high pressure refrigerant vapor

202. Superheated high pressure refrigerant vapor

203. Cooled ultra-high pressure refrigerant vapor

204. Condensed ultra-high pressure liquid refrigerant

205. Saturated ultra-high pressure liquid refrigerant

1000. Fire cracking furnace

1001. Electric Driven Cracking Furnace Section

1010. High pressure refrigerant circuit branch

1011. Branch of the ultra-high pressure refrigerant circuit

Claims (23)

1. An ethylene production plant comprising: an electrically driven pyrolysis reactor (91), wherein the electrically driven pyrolysis reactor (91) comprises an input channel for a mixture of hydrocarbon feedstock and diluent and an output channel for a pyrolysis reactor product containing ethylene; a heat exchanger (90) configured to transfer heat from the product of the pyrolysis reactor to the feedstock for the pyrolysis reactor, wherein the heat exchanger (90) comprises an input channel for the feedstock and an output channel for the feedstock located upstream of the pyrolysis reactor, and additionally an input channel for the product of the pyrolysis reactor and an output channel for the product of the pyrolysis reactor, wherein between the output channel for the feedstock of the heat exchanger and the input channel for the feedstock of the pyrolysis reactor there is a feedstock feed channel, and additionally between the output channel for the reactor product in the pyrolysis reactor and the input channel for cracking gas of the heat exchanger there is a feedstock feed channel; and a cooling section configured to further cool the reactor product obtained in the pyrolysis reactor to approximately ambient temperature without generating high-pressure steam, wherein the cooling section is located downstream of the outlet channel for cracking gas of the heat exchanger (90) and comprises a cooling system (60) selected from a group of cooling water cooling systems configured to further cool the reactor product with cooling water and air coolers configured to further cool the reactor product with air; and a quench oil cooling system configured to further cool the reactor product with quench oil and located downstream of the outlet channel of the heat exchanger for the pyrolysis reactor product and upstream of the cooling water cooling system or air cooler. 2. An ethylene production plant according to claim 1, comprising a humidifier (150) upstream of the feedstock inlet channel of the heat exchanger (90), wherein the humidifier is configured to humidify the hydrocarbon feedstock, thereby ensuring the formation of a mixture of hydrocarbons and a diluent; wherein the plant optionally comprises a compressor configured to increase the pressure of the humidified hydrocarbon feedstock, wherein the compressor is located in the feed channel of the humidified hydrocarbon feedstock between the outlet channel for the humidified hydrocarbon feedstock of the humidifier (150) and the feedstock inlet channel of the heat exchanger (90), configured to transfer heat from the cracking gas from the pyrolysis reactor to the feedstock for the pyrolysis reactor. 3. An ethylene production plant according to claim 2, further comprising a cooling section configured to further cool the reactor product obtained in the pyrolysis reactor to approximately ambient temperature without generating high-pressure steam, wherein the cooling section is located downstream of the cracking gas outlet channel of the heat exchanger (90); wherein the cooling section comprises a cooling system (60) selected from a group of cooling systems with cooling water, configured to additionally cool the reactor product with cooling water, and air coolers, configured to additionally cool the reactor product with air; and wherein the cooling section comprises a quenching oil cooling system configured to additionally cool the reactor product with quenching oil, upstream from the cooling water cooling system or air cooler; wherein the apparatus further comprises a heat exchanger (153) for transferring heat from the quenching oil to water for humidifying the hydrocarbon feedstock in the humidifier (150), wherein the heat exchanger comprises a quenching oil supply channel and a water supply channel, wherein the quenching oil supply channel has an inlet channel for the quenching oil, which is connected to an outlet channel for the quenching oil of the quenching oil cooling system by means of a channel configured to transfer the quenching oil from the quenching oil cooling system to said heat exchanger (153) for transferring heat from the quenching oil to water, and an outlet channel for the quenching oil, connected to the inlet channel for the quenching oil of the quenching oil cooling system by means of a quenching oil recirculation channel, and wherein the water supply channel of the heat exchanger (153) for transferring heat from the quenching oil to the water has an input channel for water heated in the said heat exchanger (153) for transferring heat from the quenching oil to the water, and an output channel for water connected to the input channel for water of the humidifier (150). 4. An ethylene production plant according to any one of the preceding claims, comprising a dilution steam generator comprising a heat pump system configured to generate the dilution steam; optionally, the heat pump system has a plurality of heat sources, a plurality of heat sinks, or both; and optionally, further comprising a heat exchanger (30, 43) for preheating the hydrocarbon feedstock upstream of the feed inlet channel of the heat exchanger (90) upstream of the pyrolysis reactor (91), the heat exchanger being configured to receive heat from one or more of cooling water, quench oil, and middle oil fraction used to cool the product of the pyrolysis reactor. 5. An ethylene production plant according to item 4, comprising a hydrocarbon feedstock evaporator (46) configured to receive heat from a quenching oil used in a quenching oil cooling system for evaporating the hydrocarbon feedstock, wherein the quenching oil cooling system is configured to additionally cool the pyrolysis reactor product with the quenching oil or is configured to receive condensation heat from a vaporous refrigerant (48) of a heat pump for evaporating the hydrocarbon feedstock. 6. An ethylene production plant according to claim 5, comprising a hydrocarbon feedstock evaporator (44) configured to receive at least part of the heat for evaporating the hydrocarbon feedstock from the middle oil fraction used in the quench oil cooling system (52), wherein the middle oil fraction cooling system is configured to additionally cool the product of the pyrolysis reactor with the middle oil fraction. 7. An ethylene production plant according to any one of the preceding claims, comprising an electrical power supply connection configured to supply electricity to the electrically driven pyrolysis reactor, wherein the electrical power supply connection is a connection to an electrical power grid for producing electrical energy from a renewable source. 8. A method for producing a pyrolysis reactor product containing ethylene from a hydrocarbon feedstock using an ethylene production unit according to any of the preceding claims, comprising feeding a mixture of hydrocarbon feedstock and steam into an electrically driven pyrolysis reactor (91), cracking the hydrocarbon feedstock in the presence of steam in the electrically driven pyrolysis reactor (91) of said ethylene production unit to produce a pyrolysis reactor product containing ethylene, feeding the pyrolysis reactor product into a heat exchanger (90) configured to transfer heat from the pyrolysis reactor product to a mixture of hydrocarbon feedstock and steam before cracking the hydrocarbon feedstock and transferring heat from the pyrolysis reactor product to a mixture of hydrocarbon feedstock and steam in said heat exchanger (90), thereby ensuring cooling of the pyrolysis reactor product to a temperature at the outlet channel for the pyrolysis reactor product in the heat exchanger (90) below 500°C. 9. The method according to claim 8, wherein gaseous hydrocarbon feedstock is used as hydrocarbon feedstock, and wherein the gaseous hydrocarbon feedstock is humidified in a humidifier (150) upstream of the feedstock inlet channel of the heat exchanger (90), thereby ensuring the formation of a mixture of hydrocarbons and a diluent. 10. The method according to claim 8, wherein liquid hydrocarbon feedstock is used as hydrocarbon feedstock, wherein the ethylene production plant comprises a cooling section comprising a cooling water cooling system (60) equipped with a cooling water cooling circuit (65) and a primary fractionation column (50), wherein the primary fractionation column comprises the said quench oil cooling system equipped with a quench oil cooling circuit (55), and a middle oil fraction section (52) equipped with a middle oil fraction cooling circuit (57), wherein the cooling circuits are used for preheating and evaporating the liquid hydrocarbon feedstock, mixing the evaporated hydrocarbon feedstock with dilution steam and feeding the resulting mixture to the heat exchanger (90). 11. The method according to any one of paragraphs 8-10, wherein a mixture of liquid feedstock and gaseous hydrocarbon feedstock is used as the hydrocarbon feedstock. 12. The method according to any one of paragraphs. 8-11, comprising feeding a hydrocarbon-steam mixture into a heat exchanger (90) configured to transfer heat from the pyrolysis reactor product to the pyrolysis reactor feedstock at a temperature above the water dew point of the hydrocarbon-steam mixture, heating the hydrocarbon-steam mixture using heat removed from the pyrolysis reactor product in said heat exchanger (90) to a suitable temperature at the inlet of an electrically driven pyrolysis reactor (91), feeding the heated hydrocarbon-steam mixture from said heat exchanger (90) to an electrically heated pyrolysis reactor (91), wherein in the pyrolysis reactor the heated hydrocarbon-steam mixture is further heated to a pyrolysis reaction temperature, and wherein the pyrolysis reactor provides reaction heat for converting the hydrocarbon feedstock into a cracking product, thereby ensuring the formation of a cracking product; wherein the temperature at the inlet to the electric-driven pyrolysis reactor (91) is not necessarily in the range of 650-730°C for gaseous hydrocarbon feedstock or in the range of 570-650°C for liquid hydrocarbon feedstock. 13. The method according to any one of claims 8 to 12, wherein the ethylene production plant is further provided with a refrigerant circuit, the heat of which is used for at least one purpose selected from generating dilution steam, preheating the feedstock and evaporating the liquid feedstock, preferably for generating dilution steam, preheating the liquid feedstock and evaporating the liquid feedstock. 14. The method according to any one of paragraphs. 8-13, in which the cooling of the pyrolysis reactor product is ensured to a temperature at the outlet channel for the pyrolysis reactor product in the heat exchanger (90) in the range of 350-450°C. 15. The method according to claim 14, in which the cooling of the pyrolysis reactor product is ensured to a temperature at the outlet channel for the pyrolysis reactor product in the heat exchanger (90) in the range of 325-425°C.