CN102911691A - Method for preparing bio-oil through supercritical pyrolysis of civil sludge - Google Patents

Abstract

The invention discloses a method for preparing bio-oil by supercritical pyrolysis of municipal sludge: directly put the sludge from the factory into a high-pressure sealed reaction kettle, and use nitrogen to repeatedly purge to achieve an inert atmosphere; The water in the sludge reaches a supercritical state in the reactor, and then the pyrolysis reaction of the sludge in the supercritical water is realized; the reaction product is vacuum filtered, liquid extraction, and rotary evaporation to obtain pyrolysis bio-oil. The treatment system applying this method mainly includes a sequencing batch type high-pressure resistant sealed reaction kettle, a booster pump, a condenser, a rotary evaporator and a vacuum pump. The invention avoids the sludge drying and dehydration link in the existing sludge low-temperature pyrolysis oil production process, breaks through the problem of using a large amount of catalysts in the sludge direct liquefaction oilification process, and also avoids the secondary pollution problem of heavy metals, and can obtain Bio-oil with higher added value.

Description

Method for preparing bio-oil by supercritical pyrolysis of municipal sludge

technical field

The invention relates to solid waste treatment, in particular to a method for preparing bio-oil by supercritical pyrolysis of municipal sludge.

Background technique

At present, the sludge treatment methods mainly include agricultural use, landfill and incineration. With the gradual emergence of the disadvantages of the traditional treatment methods, more and more attention has been paid to the utilization of sludge resources, among which the sludge pyrolysis liquefaction technology has been well developed. The pyrolysis liquefaction of organic waste is a resource recovery method, the main purpose is to obtain liquid fuel with maximum yield and highest calorific value. Sewage sludge, like most organic wastes, contains a large amount of volatile organic compounds. Through pyrolysis, the energy stored in the sludge can be released in the form of fuel. It can be known from the above discussion that the sludge pyrolysis liquefaction technology is a new technology developed by making full use of the high content of organic matter in sludge. It can not only treat a large amount of sludge, but also achieve the purpose of harmlessness and reduction. Moreover, a large amount of liquid fuel and solid semi-coke with adsorption can be produced to realize the synchronous growth of economic and social benefits.

The existing sludge oilification technology can be divided into two methods: low temperature pyrolysis method and direct thermochemical liquefaction method.

(a) Low-temperature pyrolysis of sludge to oil

Low-temperature pyrolysis oil is heated and dried to a certain temperature (<500°C) under anaerobic conditions, and the sludge is converted into oil, reaction water, non-condensable gas (NCG) and charcoal due to dry distillation and thermal decomposition Four flammable products.

The earliest report on sludge low-temperature pyrolysis technology can be traced back to a French patent in 1939, in which Shibata clarified the sludge pyrolysis treatment process for the first time. By the 1970s, German scientists Bayer and Kutubuddin conducted in-depth research on the process and developed a sludge low-temperature pyrolysis process.

The pyrolysis process is carried out under the conditions of slight positive pressure, pyrolysis temperature of 250-500°C, and lack of oxygen. After staying for a certain period of time, the organic matter in the sludge is converted into gas through thermal cracking, and pyrolysis oil is obtained after condensation. Sludge pyrolysis oil is mainly composed of aliphatic, olefinic and a small amount of other compounds. By comparing the hydrocarbon maps of sludge and its derived oil with petroleum, Bayer believes that the process of sludge conversion into oil is a series of biomass deammonization, water and carbon dioxide reactions. It is similar to the formation process of petroleum, and the source of oil is mainly It is fat and protein in sludge. The feasibility of the technology for sludge treatment is proved.

In 1986, the second-generation pilot plant was established in Perth and Sydney, Australia. The experimental results provided a lot of data and experience for the development of large-scale sludge low-temperature pyrolysis oil technology. In the late 1990s, the first commercial sludge refinery was built in Subiaco sewage treatment plant in Perth, Australia, with a treatment scale of 25 tons of dry sludge per day, and each ton of dry sludge can produce 200-300 liters of diesel oil. Similar fuel and half a ton of sintered carbon, the patented process is the Enersludge process. Frost research shows that the produced oil has a high calorific value and has a good market application prospect.

(b) Sludge direct liquefaction oil technology

This method is to put mechanically dehydrated sludge (with a water content of about 70%-80%) in pressurized hot water at a temperature of 250-340°C under _N2 environment, using sodium carbonate as a catalyst, and there are nearly 50% of the organic matter can be converted into low-molecular oil through a series of reactions such as hydrolysis, condensation, dehydrogenation, and cyclization, and the obtained heavy oil product is separated and collected with an extractant. The composition and properties of the heavy oil product depend on the catalyst loading and reaction temperature. During the reaction process, a liquid fuel with a calorific value of about 33MJ/kg can be obtained, and the yield can reach about 50% (based on dry organic matter), while producing a large amount of non-condensable gas and solid residue.

The source of sludge direct thermochemical liquefaction technology can be traced back to the experiment of obtaining liquid fuel from coal or coal tar by hydrogenation at high temperature and high pressure (400-450°C, 20MPa) carried out by German F. Bergius in 1913. After 1980, the United States first applied the technological framework of this technology to sludge treatment, and published a research report in the mid-1980s. Later, other countries also began to conduct research in this area, making the technological process gradually finalized.

Ching-Yuan Chang et al. performed pyrolysis treatment on activated sludge, digested sludge and paint sludge, and the oil production rates were 31.4%, 11.0% and 14.0%, respectively. It can be seen that different types of sludge have different oil production rates. Gasco's research shows that the oil yield mainly depends on the crude fat content in the sludge. Shen's research shows that undigested raw sludge is suitable for sludge liquefaction, especially raw raw sludge and raw mixed sludge, and its oil production rate is 8% higher than other sludges.

The operating conditions of sludge liquefaction have a great influence on the direct thermochemical liquefaction process, such as reaction temperature, residence time, heating rate, etc. Isabel Fonts reported that the reaction temperature greatly affects the oil yield. Under the conditions of no catalyst addition and a residence time of 2 h, the oil yield does not change from 300 °C. If the catalyst is added, the oil production will increase somewhat above 300°C. This shows that oil production mainly occurs at 300°C. Oil yield increases with residence time, the higher the temperature, the less the effect of residence time. Shen reported that the effect of heating rate was only important at lower pyrolysis temperatures (such as at 450 °C); while at higher pyrolysis temperatures, the effect of heating rate was negligible (such as at 650 ℃). At 450°C, the higher heating rate makes the pyrolysis more efficient, producing more liquid and gaseous components while reducing the amount of solid residues.

The existing sludge low-temperature pyrolysis oil production and direct liquefaction oil-to-oil technologies all inevitably require sludge pretreatment. Among them, the low-temperature pyrolysis oil production technology requires drying and dehydration to meet the oil production requirements; direct liquefaction The oilification technology can only be completed under high pressure and catalyst conditions; and the water content of municipal sludge is extremely high, so it needs to consume a lot of energy or chemicals.

How to realize efficient recycling of municipal sludge is an urgent problem to be solved in turning municipal sludge into treasure.

Contents of the invention

The purpose of the present invention is to provide a method for supercritical pyrolysis and liquefaction of municipal sludge to solve the problems of high disposal cost and complicated pretreatment in the existing sludge pyrolysis oil production technology, so as to obtain high value-added bio-oil and recover Solid semi-coke and flammable pyrolysis gas.

The present invention is realized through the following technical solutions.

A method for preparing bio-oil by supercritical pyrolysis of municipal sludge has the following steps:

(1) Place the ex-factory sludge from the sewage treatment plant directly in a closed high-pressure reaction kettle, and purge it with inert gas. When the pressure in the kettle reaches 0.1MPa, open the exhaust valve to release the pressure to an atmospheric pressure state, and close the valve again , pressurize to 0.1MPa with inert gas, and repeat this operation 3 to 5 times, so that the pyrolysis environment reaches an inert atmosphere;

(2) Heat the kettle body, set the final pyrolysis temperature at 350-500°C, and the pressure relief pressure at 22-25MPa, so that the water in the raw sludge reaches a supercritical state in the reactor, and the reaction pressure is determined by the raw sludge The steam pressure generated by heating with moisture is realized, and the catalytic effect is realized by supercritical water, and then the pyrolysis reaction of sludge in supercritical water is realized; after reaching the final temperature of pyrolysis, stay for 0-1h;

(3) After the reaction is over, the kettle body is cooled to release the pressure, the solid-liquid mixture is collected, the reaction product is vacuum filtered, and the oil and water are separated to obtain bio-oil.

The inert gas in the step (1) is nitrogen.

The raw material sludge in the step (1) is factory wet sludge with a water content above 80%.

Apply the treatment system of the method for preparing bio-oil by supercritical pyrolysis of municipal sludge of claim 1, comprise reactor, cooling pipe, condenser, filter, vacuum pump and separator, it is characterized in that, described reactor is The high-pressure reactor (4), the front end of the high-pressure reactor (4) is provided with a nitrogen storage tank (1), a booster pump (2) and a high-pressure gas storage tank (3), which are connected to the high-pressure reactor (4) through pipelines. connection, the connecting pipe is provided with a valve and a pressure gauge; the top of the high-pressure reactor (4) is provided with a sampling port (14), and the rear end of the sampling port (14) is connected to the cooling pipe (6) and the condenser (7) in sequence, The two ends of the condenser (7) are respectively provided with a liquid collection tank (8) and an air collection bag (9); (15) is connected with the filter (10), liquid separator (12) and rotary evaporator (13) in sequence, and at the same time, the filter (10) is connected with the vacuum pump (11), and the liquid separator (12) is connected with the collector Liquid tank (8) is connected.

The high-pressure reaction kettle (4) is a sequence batch type high-pressure resistant sealed reaction kettle with a specification of 2L in volume, a design temperature of 550°C, and a design pressure of 30MPa.

Compared with the traditional sludge disposal and sludge bio-oil production methods, the sludge supercritical pyrolysis oil production method has the following advantages:

1. The preparation of bio-oil from municipal sludge breaks through the traditional process of preparing biofuel from biomass, and also realizes the resource disposal of solid waste.

2. Use the sludge from the sewage treatment plant directly as raw material, and pyrolyze it under the supercritical condition of water, which avoids the sludge drying and dehydration link in the existing sludge low-temperature pyrolysis oil production process, and at the same time, utilizes the characteristics of supercritical water , breaking through the problem of using a large amount of catalysts in the sludge direct liquefaction and oilization process, so as to obtain bio-oil with higher added value.

3. Using municipal sludge to prepare bio-oil, on the one hand, realizes turning waste into treasure, and has good environmental and economic benefits; on the other hand, under high-temperature pyrolysis conditions, 90% of the heavy metals in the sludge are solidified to pyrolysis In the carbon residue, the secondary pollution problem of heavy metals is avoided.

Description of drawings

Accompanying drawing 1, is the processing system structural diagram of the method for preparing bio-oil by supercritical pyrolysis of municipal sludge of the present invention.

The reference numerals of the present invention are:

1——Nitrogen storage tank 2——Boost pump

3——High pressure gas storage tank 4——High pressure reactor

5——control panel 6——cooling pipe,

7——Condenser 8——Liquid collection tank

9——air bag 10——filter

11——vacuum pump 12——liquid dispenser

13——rotary evaporator 14——sampling port

15——rotary outlet of kettle body

Nitrogen is a, wet sludge is b, pyrolysis solid-liquid mixture product is c, pyrolysis gas is d, sampling gas is e, cooling water is f, oil-water mixture is g, non-condensable gas is h, pyrolysis residue Carbon is i, extractant is j, separated water is k, and bio-oil is l.

Detailed ways

Fig. 1 is a schematic structural diagram of the treatment system of the method for preparing bio-oil by supercritical pyrolysis of municipal sludge according to the present invention. The reaction kettle of this treatment system is a high-pressure reactor 4, which is a sequence batch type high-pressure resistant sealed reactor; the front end of the high-pressure reactor 4 is successively provided with a nitrogen storage tank 1, a booster pump 2 and a high-pressure gas storage tank 3, through which the pipeline and The high-pressure reactor 4 is connected, and the connecting pipe is provided with a valve and a pressure gauge; the top of the high-pressure reactor 4 is provided with a sampling port 14, and the rear end of the sampling port 14 is connected to the cooling pipe 6 and the condenser 7 in turn, and the two ends of the condenser 7 The liquid collecting tank 8 and the air collecting bag 9 are arranged at the end respectively; The evaporator 13 is connected, and at the same time, the filter 10 is connected with the vacuum pump 11 , and the liquid separator 12 is connected with the liquid collection tank 8 .

The present invention adopts the above-mentioned treatment system to prepare bio-oil by supercritical pyrolysis of municipal sludge, and the specific process flow is as follows:

Take the wet sludge b from the sewage treatment plant that has been dehydrated by mechanical pressure filtration and has a moisture content of more than 80%, weigh 500g, directly add it to the high-pressure reactor 4, seal the lid of the kettle, and close the exhaust valves connected to the reactor , open the nitrogen storage tank 1, and purge the system with nitrogen a; when the pressure in the reactor reaches 0.1MPa, open the exhaust valve to release the pressure to an atmospheric pressure state, close the valve again, and pressurize to 0.1MPa with nitrogen, and so on This operation is performed three times to achieve an inert atmosphere in the high-pressure reactor 4; adjust the control panel 5, set the final temperature of pyrolysis to 375°C, and program the temperature rise. The reaction pressure is realized by the vapor pressure generated by heating the water contained in the raw sludge, and the catalytic effect Realized by supercritical water, after reaching the final temperature of pyrolysis, stay for 30 minutes; in order to ensure the safe operation of the equipment, the pressure relief pressure of the back pressure valve is set at 25MPa; during the heating and pyrolysis process, when the pressure inside the reactor 4 is higher than 25MPa, The back pressure valve connected to the reactor body automatically releases the pressure, and the overflow pyrolysis gas d enters the cooling pipe 6 through the sampling port 14 for cooling, and then enters the condenser 7 for secondary water cooling; while the pyrolysis gas is cooling, the pressure drops, and oil and water can be condensed The mixture g is condensed in the liquid collection tank 8, and the non-condensable gas h is discharged through the pipeline, which can be collected by the gas collection bag 9; Sampling port 14 of the kettle body, the pyrolysis gas d is also cooled by secondary water, and the oil-water mixture g and the non-condensable gas h are separated; The feed port 15 pours out the reaction product, and then vacuum filters to separate the solid-liquid product. The solid substance obtained is the pyrolysis residue i, and the liquid substance is the oil-water mixture g; the liquid mixture in the kettle body and the liquid collection tank all enters the liquid separator 12 At the same time, dichloromethane is added as extractant j, oil and water are separated, and the separated water is directly removed, the extract enters the rotary evaporator 13, the evaporation temperature is set at 40°C, and rotary evaporation is performed, thereby separating bio-oil l, and recovering extractant j , return to the dispenser for recycling.

Claims (5)

1. the overcritical pyrolysis of municipal sludge prepares the method for bio oil, has following steps:

(1) mud that dispatches from the factory with sewage work directly places the enclosed high pressure reactor, pass into inert gas purge, when the still internal pressure reaches 0.1MPa, opening vent valve bleeds off pressure to an atmospheric pressure state, valve-off again, be pressurized to 0.1MPa with rare gas element, this operation is 3～5 times so repeatedly, makes pyrolysis environment reach inert atmosphere;

(2) heating kettle, setting the pyrolysis final temperature is 350～500 ℃, pressure release pressure is 22～25MPa, make the water in the raw sludge in reactor, reach supercritical state, reaction pressure adds thermogenetic vapour pressure by the raw sludge contained humidity and realizes, catalytic effect is realized by supercritical water, and then is realized the pyrolytic reaction of mud in supercritical water; After reaching the pyrolysis final temperature, stop 0～1h;

(3) after reaction finished, solidliquid mixture was collected in kettle cooling pressure release, and reaction product is carried out vacuum filtration, carries out oily water separation again, makes bio oil.

2. according to claim 1 the overcritical pyrolysis of municipal sludge prepares the method for bio oil, it is characterized in that the rare gas element of described step (1) is nitrogen.

3. according to claim 1 the overcritical pyrolysis of municipal sludge prepares the method for bio oil, it is characterized in that the raw sludge of described step (1) is that water ratio is at the wet mud that dispatches from the factory more than 80%.

4. the overcritical pyrolysis of municipal sludge of application rights requirement 1 prepares the treatment system of the method for bio oil, comprise reactor, cooling tube, condenser, strainer, vacuum pump and skimmer, it is characterized in that, described reactor is autoclave (4), the front end of autoclave (4) is disposed with nitrogen storage tank (1), boosting pump (2) and high pressure gas storage tank (3), be connected with autoclave (4) by pipeline, be provided with valve and tensimeter on the connecting tube; The top of autoclave (4) is provided with thief hole (14), and the rear end of thief hole (14) connects cooling tube (6) and condenser (7) successively, and the two ends of condenser (7) are respectively arranged with liquid collecting tank (8) and gas collection bag (9); Autoclave (4) also is provided with kettle rotating discharge port (15), kettle rotating discharge port (15) is connected with strainer (10), skimmer (12) and Rotary Evaporators (13) successively, simultaneously, strainer (10) is connected with vacuum pump (11), and skimmer (12) is connected with liquid collecting tank (8).

5. according to claim 4 the overcritical pyrolysis of application municipal sludge prepares the treatment system of the method for bio oil, it is characterized in that described autoclave (4) is sequence batch (high-pressure-resistant sealed reactor, specification is volume 2L, 550 ℃ of design temperatures, design pressure 30MPa.