CN113932213B - Steam-water system of power generation turbine unit and coal-fired power generation unit - Google Patents

Abstract

The invention relates to the technical field of turbines, and discloses a steam-water system of a generating turbine unit and a coal-fired generator unit, wherein the system comprises: the system comprises a boiler, a steam turbine, a condenser, a plurality of low-pressure condensing water heaters, a deaerator, a plurality of high-pressure feed water heaters, a plurality of low-pressure steam extraction pipelines, a deaerating steam extraction pipeline and a plurality of high-pressure steam extraction pipelines, wherein the boiler, the steam turbine, the condenser, the plurality of low-pressure condensing water heaters, the deaerating steam extraction pipelines, the plurality of high-pressure feed water heaters, the plurality of low-pressure steam extraction pipelines, the deaerating steam extraction pipelines and the plurality of high-pressure steam extraction pipelines are sequentially communicated; and the heat exchanger is also communicated with a high-pressure water supply outlet of the deaerator and the boiler and is used for heating part of high-pressure water supply flowing out of the deaerator by utilizing extraction steam from the steam turbine so as to supply the boiler. According to the invention, the heat of the steam overheated part in the corresponding pipeline can be recycled by arranging the heat exchanger, so that the heat efficiency and the power generation output power of the steam-water circulation system are improved.

Description

Steam-water system of power generation steam turbine units and coal-fired generator units

Technical Field

The invention relates to the technical field of steam turbines, and in particular to a steam-water system of a power generation steam turbine unit and a coal-fired generator unit.

Background technique

The steam-water system of the steam turbine generator set based on the Rankine cycle is composed of equipment such as a boiler, a steam turbine, a condenser, a deaerator, a feedwater heater, and connecting pipes. As shown in FIG1 , the high-temperature and high-pressure steam generated by the boiler 1 enters the high, medium, and low-pressure steam turbines (2, 3, 4) along the steam pipeline, and the steam after work is discharged into the condenser 6 to cool into condensed water. The condensed water is pressurized and transported by the condensate pump 7 to the low-pressure condensate heater series (8-11) to be heated step by step using part of the extraction steam from the low-pressure steam turbine 4, and then enters the deaerator 12 to be heated using part of the extraction steam from the medium-pressure steam turbine 3, and then pressurized by the feedwater booster pump 13 to enter the high-pressure feedwater heater series (14-16) to be heated step by step using part of the extraction steam from the high and medium-pressure steam turbines (2, 3) to the feedwater temperature required by the boiler, and then returns to the boiler 1 to generate steam again to drive the steam turbine to drive the generator 5 to generate electricity output, and so on. However, the comprehensive thermal efficiency of the steam-water cycle system is low.

CN102720550A discloses a dual-machine heat recovery steam extraction steam thermal system, in which the middle stage of the high-pressure cylinder of the main steam turbine is provided with a high-pressure steam extraction port, which is respectively connected to the steam inlet of the small steam turbine and a high-pressure heater with the highest steam inlet parameter among several high-pressure heaters through a high-pressure steam extraction pipeline, and the middle stage of the small steam turbine is provided with several heat recovery steam extraction ports, which are respectively connected to the remaining high-pressure heaters except the high-pressure heater with the highest steam inlet parameter through the heat recovery steam extraction pipeline, and the exhaust port of the small steam turbine is connected to the deaerator through the small steam turbine exhaust pipeline. The system can save the high-temperature pre-steam cooler and reduce the boiler feed water temperature, which is conducive to improving the boiler efficiency and reducing the heat consumption of the unit, but the system is complex and the investment and operation and maintenance costs are high.

US3291105A discloses a technology for using low-pressure condensed water to cool the deaerator steam extraction, which is mainly used for regulation under emergency conditions and does not have the purpose and effect of improving the thermal efficiency of the steam-water circulation system.

Therefore, it is necessary to provide a new steam-water system for a power generation steam turbine unit.

Summary of the invention

The purpose of the present invention is to solve the problem of low thermal efficiency of the existing steam-water circulation system, and to provide a steam-water system for a power generation steam turbine unit and a coal-fired generator unit, which can significantly improve the thermal efficiency and power generation output power of the steam-water circulation system.

In order to achieve the above-mentioned objectives, the first aspect of the present invention provides a steam-water system for a power generation steam turbine unit, comprising: a boiler, a steam turbine, a condenser, a plurality of low-pressure condensate heaters, a deaerator, a plurality of high-pressure feedwater heaters connected in sequence, and a plurality of low-pressure steam extraction pipes connecting the steam turbine and the plurality of low-pressure condensate heaters, a deaerator steam extraction pipe connecting the steam turbine and the deaerator, and a plurality of high-pressure steam extraction pipes connecting the steam turbine and the plurality of high-pressure feedwater heaters; heat exchangers are respectively arranged on the deaerator steam extraction pipe and/or the plurality of low-pressure steam extraction pipes, and the heat exchanger is also connected to the high-pressure feedwater outlet of the deaerator and the boiler, and is used to heat part of the high-pressure feedwater flowing out of the deaerator using the extraction steam from the steam turbine to supply the boiler.

A second aspect of the present invention provides a coal-fired power generation unit, comprising the steam-water system of the power generation steam turbine unit described in the first aspect of the present invention.

Through the above technical scheme, the present invention arranges heat exchangers on the deaeration steam extraction pipe and/or multiple low-pressure extraction pipes respectively, so that part of the high-pressure feed water absorbs the heat of the superheated part of the steam in the deaeration steam extraction pipe and/or the low-pressure steam extraction pipe through the heat exchanger, thereby heating this part of the high-pressure feed water to supply the boiler. Such an arrangement can reduce the water flow entering the high-pressure feed water heater, and correspondingly reduce the steam extraction amount of the high-pressure feed water heater to the high-pressure section of the turbine, thereby increasing the power generation output of the turbine. At the same time, since the heat of the superheated part of the steam in the low-pressure steam extraction pipe and the deaeration steam extraction pipe is converted to high-pressure feed water heating, the energy can be upgraded and used, thereby improving the comprehensive thermal efficiency of the steam-water circulation system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a steam-water system of a typical existing steam turbine generator set;

FIG2 is a schematic diagram of a steam-water system of a power generation steam turbine unit according to a preferred embodiment of the present invention;

FIG3 is a schematic diagram of a steam-water system of a power generation steam turbine unit according to another preferred embodiment of the present invention.

Description of Reference Numerals

1 Boiler 2 High-pressure steam turbine 3 Medium-pressure steam turbine

4 Low-pressure turbine 5 Generator 6 Condenser

7 Condensate pump 8 Primary low-pressure condensate heater 9 Secondary low-pressure condensate heater

10Third-stage low-pressure condensate heating 11Final stage low-pressure condensate heating 12Deaerator

13 Feedwater booster pump 14 Primary high pressure feedwater heater 15 Secondary high pressure feedwater heater

16 Final stage high pressure feed water heater 17 First heat exchanger 18 Second heat exchanger

Detailed ways

The endpoints and any values of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

At present, the heat source for low-pressure condensate heaters, deaerators and high-pressure feedwater heaters at all levels generally comes from some steam (called extraction steam) that has done work in some intermediate stages of the steam turbine. In principle, the latent heat released by the extraction steam condensation is mainly used to heat the feedwater, so that the steam temperature of the heated water is close to the saturation temperature at the corresponding pressure. However, the extraction steam used for each level of water heater has a certain degree of superheat relative to the outlet water temperature of the heater. In this way, the heat of the superheated section where the temperature of the steam turbine extraction steam is higher than the saturation temperature is used for water heating, which is of high quality and low use. In order to solve the above problems, the inventors of the present invention have found through research that by arranging a heat exchanger on the extraction pipe, the heat of the superheated part of the steam can be recovered and utilized, thereby improving the thermal efficiency of the system. Furthermore, taking a typical 320MW subcritical condensing power generation unit as an example, the extraction steam used for heating the deaerator is superheated steam at 325°C at about 7.6 bar, which is much higher than the saturation temperature of 168°C required for heating the deaerator; the steam used for heating the final low-pressure condensate heater is superheated steam at 222°C at about 3 bar, which is much higher than the outlet water temperature of 131°C of the final low-pressure condensate heater. It can be seen that the extraction steam used for the deaerator and the final low-pressure condensate heater has a relatively large superheat temperature. The method provided by the present invention can be used to further improve the thermal efficiency of the system by arranging a heat exchanger on the extraction pipes of the deaerator and the final low-pressure condensate heater to recover the heat of these superheated parts and upgrade their use.

As described above, the first aspect of the present invention provides a steam-water system for a power generation steam turbine unit, comprising: a boiler, a steam turbine, a condenser, a plurality of low-pressure condensate heaters, a deaerator, a plurality of high-pressure feed water heaters connected in sequence, and a plurality of low-pressure steam extraction pipes connecting the steam turbine and the plurality of low-pressure condensate heaters, a deaerator steam extraction pipe connecting the steam turbine and the deaerator, and a plurality of high-pressure steam extraction pipes connecting the steam turbine and the plurality of high-pressure feed water heaters; heat exchangers are respectively arranged on the deaerator steam extraction pipe and/or the plurality of low-pressure steam extraction pipes, and the heat exchanger is also connected to the high-pressure feed water outlet of the deaerator and the boiler, and is used to heat part of the high-pressure feed water flowing out of the deaerator using the extraction steam from the steam turbine to supply the boiler.

In some embodiments of the present invention, preferably, the system further comprises a condensate pump and a feedwater pressure pump, wherein the condensate pump is arranged between the condenser and the first-stage low-pressure condensate heater, and is used to pump the condensate into the low-pressure condensate heater for heating; the feedwater pressure pump is arranged between the deaerator and the first-stage high-pressure feedwater heater, and is used to pressurize the condensate deoxygenated by the deaerator so that it enters the high-pressure feedwater heater for further high-pressure heating. The high-pressure feedwater of the present invention is essentially obtained by pressurizing the condensate deoxygenated by the deaerator through the feedwater pressure pump, that is, the feedwater at the outlet of the feedwater pressure pump.

In some embodiments of the present invention, there is no particular limitation on the type of the steam turbine, as long as it can output high-pressure extraction steam, medium-pressure extraction steam and low-pressure extraction steam. For example, the steam turbine can be an integrated steam turbine including a high-pressure cylinder, a medium-pressure cylinder and a low-pressure cylinder, or it can be a separate high-pressure steam turbine, a medium-pressure steam turbine and a low-pressure steam turbine. The high-pressure cylinder or high-pressure steam turbine is connected to a plurality of high-pressure feedwater heaters through a plurality of high-pressure extraction steam pipes; the medium-pressure cylinder or medium-pressure steam turbine is connected to a deaerator and a portion of high-pressure feedwater heaters through a deaeration extraction steam pipe and a portion of high-pressure extraction steam pipes; the low-pressure cylinder or low-pressure steam turbine is connected to a plurality of low-pressure condensate heaters through a plurality of low-pressure extraction steam pipes.

In some embodiments of the present invention, there is no particular limitation on the heat exchanger, and any existing vapor-liquid (such as steam-water) indirect heat exchanger in the art may be used, for example, including but not limited to shell-tube type heat exchangers.

The purpose of the deaerator described in the present invention is to use turbine extraction steam to heat boiler feed water to the saturation temperature corresponding to the operating pressure of the deaerator, and remove oxygen and other non-condensable gases dissolved in the water, thereby improving the quality of boiler feed water and preventing or reducing oxygen corrosion of boilers, turbines and their ancillary equipment, pipelines, etc.

The low-pressure condensate heater of the present invention utilizes part of the steam extraction from the low-pressure steam turbine to heat the condensate flowing out of the condenser to the temperature required for entering the deaerator. The high-pressure feedwater heater utilizes part of the steam extraction from the high-pressure steam turbine or the medium-pressure steam turbine to heat the high-pressure feedwater to the feedwater temperature required by the boiler.

In some embodiments of the present invention, preferably, the pressure of the high-pressure feed water is higher than the pressure of the steam extraction from the steam turbine of the deaerator and/or the low-pressure condensate heater, and the temperature of the high-pressure feed water is lower than the temperature of the steam extraction from the steam turbine of the deaerator and/or the low-pressure condensate heater, so that the superheated heat in the relatively low-pressure and high-temperature extraction steam (i.e., the heat of the saturated steam temperature section with a temperature higher than the extraction pressure) is no longer used to heat the water in the deaerator and/or the low-pressure condensate heater, but is used to heat the boiler feed water with a higher pressure, so that the superheated heat of the low-pressure extraction steam is upgraded. At the same time, since part of the feed water at the outlet of the feed water booster pump is diverted into the heat exchanger for heating, the water flow entering the high-pressure feed water heater is correspondingly reduced, and the high-pressure feed water heater's demand for high-pressure extraction steam from the steam turbine is reduced, thereby increasing the power output of the steam turbine and improving the comprehensive thermal efficiency of the steam-water circulation system.

In some embodiments of the present invention, the heat exchanger can be arranged on the deoxygenation steam extraction pipe and/or multiple low-pressure exhaust pipes to recover and utilize the heat of the superheated steam in the deoxygenation steam extraction pipe and/or multiple low-pressure exhaust pipes, that is, the heat exchanger can be arranged only on the deoxygenation steam extraction pipe, or only on multiple low-pressure exhaust pipes, or on the deoxygenation steam extraction pipe and multiple low-pressure exhaust pipes at the same time. Preferably, the heat exchanger is respectively arranged on the deoxygenation steam extraction pipe and/or on the last-stage low-pressure exhaust pipe among the multiple low-pressure exhaust pipes.

In some embodiments of the present invention, there is no particular limitation on the amount of high-pressure feed water flowing into the heat exchanger. The amount of water flowing in is based on maintaining the return water temperature at the outlet of the heat exchanger not lower than the feed water temperature required at the boiler inlet under the corresponding working conditions, that is, as long as the return water temperature of the high-pressure feed water flowing into the heat exchanger after passing through the heat exchanger meets the water temperature of the boiler water, preferably, the temperature of the return water at the outlet of the heat exchanger is the same as the feed water temperature at the inlet of the boiler economizer under the corresponding load. The present invention can adjust the flow rate of the high-pressure feed water flowing into the heat exchanger by arranging a flow control valve on the connecting pipe between the outlet of the feed water booster pump and the inlet of the heat exchanger, thereby controlling the return water temperature at the outlet of the heat exchanger to be the same as the feed water temperature at the inlet of the boiler economizer under the corresponding load.

In some embodiments of the present invention, the high-pressure feed water flowing out of the heat exchanger outlet can, in principle, be returned to any position in the feed water heating system connection pipeline downstream of the feed water booster pump outlet. Preferably, the return point of the outlet return water of the heat exchanger is set on the connecting pipeline between the high-pressure feed water outlet of the deaerator and the inlet of the boiler economizer. Further preferably, the return point of the outlet return water of the heat exchanger is set at the outlet of the final-stage high-pressure feed water heater, the inlet of the boiler economizer, or the connecting pipeline between the outlet of the final-stage high-pressure feed water heater and the inlet of the boiler economizer, so that it is easier to return the heated high-pressure feed water to the boiler for reuse.

A second aspect of the present invention provides a coal-fired power generation unit, comprising the steam-water system of the power generation steam turbine unit described in the first aspect of the present invention.

The present invention will be described in detail below through two preferred embodiments.

A preferred specific implementation manner, as shown in FIG2 , is a schematic diagram of a typical steam-water system of a power generation steam turbine unit, the steam-water system of the power generation steam turbine unit comprises: a boiler 1, a high-pressure steam turbine 2, a medium-pressure steam turbine 3, a low-pressure steam turbine 4, a condenser 6, a condensate pump 7, a first-stage low-pressure condensate heater 8, a second-stage low-pressure condensate heater 9, a third-stage low-pressure condensate heater 10, a final-stage low-pressure condensate heater 11, a deaerator 12, a feedwater booster pump 13, a first-stage high-pressure feedwater heater 14, a second-stage high-pressure feedwater heater 15, a final-stage high-pressure feedwater heater 16 and a first heat exchanger 17, and a generator 5 connected to the high-pressure steam turbine 2, the medium-pressure steam turbine 3 and the low-pressure steam turbine 4 in sequence, the low-pressure steam turbine 4 are respectively connected to the first-stage to the last-stage low-pressure condensate heaters (8-11) through the first-stage to the last-stage low-pressure steam extraction pipeline, the medium-pressure steam turbine 3 is respectively connected to the deaerator 12 and the first-stage high-pressure feedwater heater 14 through the deaeration steam extraction pipeline and the first-stage high-pressure steam extraction pipeline, the high-pressure steam turbine 2 is respectively connected to the second-stage high-pressure feedwater heater 15 and the last-stage high-pressure feedwater heater 16 through the second-stage high-pressure steam extraction pipeline and the last-stage high-pressure steam extraction pipeline, and the first heat exchanger 17 is arranged on the deaeration steam extraction pipeline; the high-temperature and high-pressure steam generated by the boiler 1 enters the high, medium and low-pressure steam turbines (2, 3, 4) along the steam pipeline, and the steam generated after the work is cooled into condensate by the condenser 6, and the condensate is pressurized by the condensate pump 7 and transported to the first-stage to the last-stage In the low-pressure condensate heater (8-11), the first to last stage low-pressure condensate heater (8-11) uses part of the steam extracted from the low-pressure steam turbine 4 to heat the condensate step by step, and the heated condensate enters the deaerator 12, and the deaerator 12 uses part of the steam extracted from the medium-pressure steam turbine 3 to further heat the condensate and remove oxygen therein, and then the condensate obtained above is pressurized by the feed water pressure pump 13, and a part of the high-pressure feed water flowing out of the outlet of the feed water pressure pump 13 enters the first to last stage high-pressure feed water heater (14-16), and the first to last stage high-pressure feed water heater (14-16) uses part of the steam extracted from the medium and high-pressure steam turbines (3, 2) to heat the high-pressure feed water step by step to meet the boiler water demand. The water temperature is adjusted, and then it flows out from the outlet of the final stage high-pressure feed water heater 16; another part of the high-pressure feed water flowing out from the outlet of the feed water booster pump 13 flows into the first heat exchanger 17 through the flow control valve and the inlet of the first heat exchanger 17, and the first heat exchanger 17 uses part of the extraction steam from the medium-pressure steam turbine 3 to heat the inflowing part of the high-pressure feed water so that the temperature of the return water at the outlet of the first heat exchanger 17 is the same as the feed water temperature at the inlet of the boiler economizer under the corresponding load, and the heated part of the high-pressure feed water flows out from the outlet of the first heat exchanger 17 and returns to the outlet of the final stage high-pressure feed water heater 16, mixes with the part of the high-pressure feed water flowing out from the outlet of the final stage high-pressure feed water heater 16, and then returns to the boiler 1 together, and the cycle is repeated.

Compared with the steam-water system of the power generation steam turbine unit without the first heat exchanger 17, on the basis of maintaining the same full-load main steam parameters, the power generation output power of the steam-water system of the power generation steam turbine unit of the present invention is increased by about 0.3MWe, and the net heat rate of the system is reduced by about 10kJ/kWh, which is equivalent to reducing the coal consumption for power generation by about 0.3g/kWh.

Another preferred specific embodiment is shown in FIG3 which is a schematic diagram of a steam-water system of a typical power generation steam turbine unit, wherein the steam-water system of the power generation steam turbine unit comprises: a boiler 1, a high-pressure steam turbine 2, a medium-pressure steam turbine 3, a low-pressure steam turbine 4, a condenser 6, a condensate pump 7, a first-stage low-pressure condensate heater 8, a second-stage low-pressure condensate heater 9, a third-stage low-pressure condensate heater 10, a final-stage low-pressure condensate heater 11, a deaerator 12, a feed water booster pump 13, a first-stage high-pressure feed water heater 14, a second-stage high-pressure feed water heater 15, a final-stage high-pressure feed water heater 16, a first heat exchanger 17 and a second heat exchanger 18, and a generator 5 connected to the high-pressure steam turbine 2, the medium-pressure steam turbine 3 and the low-pressure steam turbine 4, wherein the low-pressure steam turbine 4 is connected to the first-stage to the final-stage low-pressure condensate through a first-stage to the final-stage low-pressure steam extraction pipeline. The medium-pressure steam turbine 3 is connected to the deaerator 12 and the first-stage high-pressure feedwater heater 14 through the deaeration steam extraction pipeline and the first-stage high-pressure steam extraction pipeline, respectively. The high-pressure steam turbine 2 is connected to the second-stage high-pressure feedwater heater 15 and the last-stage high-pressure feedwater heater 16 through the second-stage high-pressure steam extraction pipeline and the last-stage high-pressure steam extraction pipeline, respectively. The first heat exchanger 17 is arranged on the deaeration steam extraction pipeline, and the second heat exchanger 18 is arranged on the last-stage low-pressure steam extraction pipeline. The high-temperature and high-pressure steam generated by the boiler 1 enters the high, medium and low-pressure steam turbines (2, 3, 4) along the steam pipeline, and the steam generated after the work is performed is cooled into condensate by the condenser 6. The condensate is pressurized by the condensate pump 7 and sequentially transported to the first-stage to the last-stage low-pressure condensate heaters (8-11). The first-stage to the last-stage low-pressure condensate heaters (8-11) are used to The condensate is heated step by step by using part of the extracted steam from the low-pressure steam turbine 4. The heated condensate enters the deaerator 12. The deaerator 12 further heats the condensate and removes oxygen therein by using part of the extracted steam from the medium-pressure steam turbine 3. The condensate obtained above is then pressurized by the feed water pressure pump 13. A part of the high-pressure feed water flowing out of the outlet of the feed water pressure pump 13 enters the first to last stage high-pressure feed water heater (14-16). The first to last stage high-pressure feed water heater (14-16) heats the high-pressure feed water step by step by using part of the extracted steam from the medium and high-pressure steam turbines (3, 2) to meet the water temperature of the boiler water. Then, the feed water flows out from the outlet of the last stage high-pressure feed water heater 16. Another part of the high-pressure feed water flowing out of the outlet of the feed water pressure pump 13 passes through the flow control valve, the inlet of the first heat exchanger 17 and the inlet of the second heat exchanger 18. The inlet flows into the first heat exchanger 17 and the second heat exchanger 18 respectively. The first heat exchanger 17 uses part of the extraction steam from the medium-pressure steam turbine 3 to heat part of the high-pressure feed water flowing in so that the temperature of the return water at the outlet of the first heat exchanger 17 is the same as the feed water temperature at the inlet of the boiler economizer under the corresponding load. The second heat exchanger 18 uses part of the extraction steam from the low-pressure steam turbine 4 to heat part of the high-pressure feed water flowing in so that the temperature of the return water at the outlet of the second heat exchanger 18 is the same as the feed water temperature at the inlet of the boiler economizer under the corresponding load. The heated part of the high-pressure feed water flows out from the outlets of the first heat exchanger 17 and the second heat exchanger 18 respectively and returns to the outlet of the final-stage high-pressure feed water heater 16, mixes with the high-pressure feed water flowing out from the outlet of the final-stage high-pressure feed water heater 16, and then returns to the boiler 1 together, and the cycle is repeated.

Compared with the steam-water system of the power generation steam turbine unit without the first heat exchanger 17 and the second heat exchanger 18, on the basis of maintaining the same full-load main steam parameters, the power generation output power of the steam-water system of the power generation steam turbine unit of the present invention is increased by about 0.45MWe, and the net heat rate of the system is reduced by about 16kJ/kWh, which is equivalent to reducing the coal consumption for power generation by about 0.5g/kWh.

In addition, the first heat exchanger 17 and the second heat exchanger 18 of the present invention are not limited to the above two configurations, but can also be used in combination with the feedwater bypass of the existing high-pressure feedwater heater or the existing superheater desuperheating water bypass to reduce the investment cost of additional pipelines. The present invention can be used not only in the design of new generator sets, but also in the technical transformation of existing generator sets.

The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims (13)

1. A steam-water system for a power generation steam turbine unit, comprising: a boiler, a steam turbine, a condenser, a plurality of low-pressure condensate heaters, a deaerator, a plurality of high-pressure feedwater heaters connected in sequence, and a plurality of low-pressure steam extraction pipes connecting the steam turbine and the plurality of low-pressure condensate heaters, a deaerator steam extraction pipe connecting the steam turbine and the deaerator, and a plurality of high-pressure steam extraction pipes connecting the steam turbine and the plurality of high-pressure feedwater heaters; characterized in that heat exchangers are respectively arranged on the deaerator steam extraction pipe and/or the plurality of low-pressure steam extraction pipes, and the heat exchanger is also connected to the high-pressure feedwater outlet of the deaerator and the boiler, and is used to heat part of the high-pressure feedwater flowing out of the deaerator with the extraction steam from the steam turbine to supply the boiler; wherein the pressure of the high-pressure feedwater is higher than the pressure of the steam extraction from the deaerator and/or the low-pressure condensate heater from the steam turbine, and the temperature of the high-pressure feedwater is lower than the temperature of the steam extraction from the deaerator and/or the low-pressure condensate heater from the steam turbine. 2 . The system according to claim 1 , wherein a heat exchanger is respectively arranged on the deaeration steam extraction pipeline and/or on the last-stage low-pressure steam extraction pipeline among the plurality of low-pressure steam extraction pipelines. 3. The system according to claim 2, wherein a heat exchanger is provided on the deaeration steam extraction pipeline. 4. The system according to claim 3, wherein the return water temperature reached by the high-pressure feed water flowing into the heat exchanger after passing through the heat exchanger meets the water temperature of boiler water. 5. The system according to claim 4, wherein the temperature of the return water at the outlet of the heat exchanger is the same as the feed water temperature at the inlet of the boiler economizer under the corresponding load. 6. The system according to claim 5, wherein the return point of the outlet return water of the heat exchanger is arranged on the connecting pipeline between the high-pressure feed water outlet of the deaerator and the inlet of the boiler economizer. 7. The system according to claim 6, wherein the return point of the outlet return water of the heat exchanger is arranged on the outlet of the last stage high pressure feed water heater, the inlet of the boiler economizer or the connecting pipeline between the outlet of the last stage high pressure feed water heater and the inlet of the boiler economizer. 8. The system according to claim 2, wherein a first heat exchanger is provided on the deaeration steam extraction pipeline, and a second heat exchanger is provided on the final low-pressure steam extraction pipeline. 9. The system according to claim 8, wherein the return water temperature reached by the high-pressure feed water flowing into the first heat exchanger or the second heat exchanger respectively after passing through the first heat exchanger or the second heat exchanger meets the water temperature of boiler water. 10. The system according to claim 9, wherein the temperature of the return water at the outlet of the first heat exchanger or the second heat exchanger is the same as the feed water temperature at the inlet of the boiler economizer under the corresponding load. 11. The system according to claim 10, wherein a return point of the outlet return water of the first heat exchanger or the second heat exchanger is arranged on a connecting pipeline between the high-pressure feed water outlet of the deaerator and the inlet of the boiler economizer. 12. The system according to claim 11, wherein the return point of the outlet return water of the first heat exchanger or the second heat exchanger is set on the outlet of the last stage high-pressure feed water heater, the inlet of the boiler economizer, or the connecting pipeline between the outlet of the last stage high-pressure feed water heater and the inlet of the boiler economizer. 13. A coal-fired power generation unit, comprising the steam-water system of the power generation steam turbine unit according to any one of claims 1 to 12.