Thermal power generating unit low-load steam supply and back pressure reduction waste heat utilization system and operation method thereof

Abstract

The thermal power generating unit low-load steam supply and back pressure reduction waste heat utilization system comprises a steam turbine intermediate-pressure cylinder, and the outlet end of the steam turbine intermediate-pressure cylinder is connected with a steam turbine low-pressure cylinder and an absorption heat pump; a steam exhaust device is connected to the bottom of the turbine low-pressure cylinder and connected with a steam exhaust pipeline, and the other end of the steam exhaust pipeline is connected with an air cooling island and a valve. The air cooling island is connected to the steam exhaust device; one path of the other end of the valve is connected with a heat exchanger, the other path is connected to an absorption heat pump, and the heat exchanger and the absorption heat pump are respectively connected to a steam exhaust device; the heat exchanger is also connected with a demineralized water replenishing tank; the heat exchanger is connected with the absorption heat pump; the absorption heat pump is connected with an electric boiler, and the electric boiler is connected with an industrial user. The invention further discloses an operation method of the thermal power generating unit low-load steam supply and back pressure reduction waste heat utilization system. According to the system, industrial steam supply of the thermal power generating unit under the 30% rated load is guaranteed, the on-grid power load of the thermal power generating unit is reduced, and deep peak regulation of a power grid is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power generation system of thermal power unit, and specifically relates to a low-load steam supply and back pressure reduction waste heat utilization system of thermal power unit. The present invention also relates to an operation method of the low-load steam supply and back pressure reduction waste heat utilization system of thermal power unit. Background Art

[0002] The access of large-scale renewable energy has brought great changes to the power system. When the power generation capacity of renewable energy accounts for a large proportion of the power grid, the uncertainty of its output will bring great challenges to the regulation ability of the power system; at the same time, a large number of uncertainties on the power generation side and the demand side also affect the safe and stable operation of the power system. In order to adapt to the new situation of the development of my country's power industry, large-scale thermal power units are in urgent need of improving their survivability through cogeneration transformation and operation flexibility transformation. At present, many large-scale cogeneration units in my country have become normalized peak-shaving units, with large fluctuations in load factors, and are often in medium and low load operation for a long time. Thermal power units are currently facing deep peak-shaving and peak-shaving amplitude, as well as how to meet the needs of industrial steam supply under low load conditions. Summary of the invention

[0003] The purpose of the present invention is to provide a low-load steam supply and back pressure reduction waste heat utilization system for thermal power units, solve the problem of ensuring industrial steam supply for thermal power units at 30% of the rated load, reduce the on-grid power load of thermal power units, and achieve the requirements of deep peak regulation of the power grid.

[0004] The technical solution adopted by the present invention is a low-load steam supply and back pressure reduction waste heat utilization system for a thermal power unit, comprising a steam turbine intermediate-pressure cylinder, the outlet end of the steam turbine intermediate-pressure cylinder is connected to a steam turbine low-pressure cylinder and an absorption heat pump through pipelines; an exhaust device is connected to the bottom of the steam turbine low-pressure cylinder, the steam outlet of the exhaust device is connected to an exhaust pipe, and the other end of the exhaust pipe is respectively connected to an air cooling island and a valve; the air cooling island is connected to the exhaust device through a pipeline; the other end of the valve is divided into two paths, one path is connected to a heat exchanger through a pipeline, and the other path is connected to the absorption heat pump through a pipeline, and the heat exchanger and the absorption heat pump are respectively connected to the exhaust device through pipelines; the heat exchanger is also connected to a demineralized water make-up tank through a pipeline; the heat exchanger is connected to the absorption heat pump; the absorption heat pump is connected to an electric boiler through a pipeline, and the electric boiler is connected to an industrial user.

[0005] The present invention is also characterized in that: A water pump is provided on the pipeline between the heat exchanger and the desalted water replenishment tank.

[0006] The absorption heat pump is connected to a deaerator via a pipeline.

[0007] The low-pressure cylinder of the steam turbine is also connected to a generator, which is connected to an electric boiler.

[0008] The pipe connecting the air-cooling island and the exhaust device is the condensate pipe.

[0009] The hot side inlet of the heat exchanger is connected to the valve, and the hot side outlet of the heat exchanger is connected to the absorption heat pump; the cold side inlet of the heat exchanger is connected to the desalted water make-up tank, and the cold side outlet of the heat exchanger is connected to the exhaust device.

[0010] The hot water side inlet of the absorption heat pump is connected to the heat exchanger, and the hot water side outlet of the absorption heat pump is connected to the electric boiler.

[0011] The heat source of the absorption heat pump is divided into two paths. One path is the exhaust air from the intermediate pressure cylinder of the steam turbine, which is absorbed by the absorption heat pump and then flows to the deaerator; the other path is the exhaust steam passing through the valve and then absorbed by the absorption heat pump and then flows to the exhaust device.

[0012] Another technical solution adopted by the present invention is an operation method of a low-load steam supply and back pressure reduction waste heat utilization system for a thermal power unit, comprising the following steps: Step 1: Part of the exhaust gas from the intermediate pressure cylinder of the steam turbine flows to the low pressure cylinder of the steam turbine to generate electricity, power the boiler and connect the electric load to the grid; the other part flows to the absorption heat pump as a driving heat source, and then flows to the deaerator after absorbing the heat; Step 2: Part of the exhaust steam passing through the low-pressure cylinder of the steam turbine flows to the air-cooling island for cooling and then flows back to the exhaust device. The other part is divided into two paths after passing through the valve. One path flows to the heat exchanger to heat the demineralized water supply tank and then flows back to the exhaust device after passing through the water pump for steam supply and water supply. The other path flows to the absorption heat pump as a low-temperature heat source and then flows back to the exhaust device after absorbing heat. Step 3: After the desalted water replenishment tank is heated in the first stage by the heat exchanger, it flows to the absorption heat pump for the second stage heating, and then flows to the electric boiler for the third stage heating. After the industrial steam supply parameters meet the requirements, it flows to industrial users.

[0013] The beneficial effects of the present invention are: The low-load steam supply and back pressure reduction waste heat utilization system of the thermal power unit of the present invention solves the problem of ensuring industrial steam supply of the thermal power unit under 30% rated load. Under the condition of meeting the parameter requirements of industrial steam supply and ensuring the steam supply of industrial steam supply, the rated load of the thermal power unit is reduced from 30% to 25%, reducing the on-grid load of the thermal power unit and achieving the requirements of deep peak regulation of the power grid. The industrial steam supply water replenishment adopts a three-stage heating system to achieve cascade utilization of heat and reduce irreversible losses. In addition, the two-stage waste heat of the exhaust steam of the low-pressure cylinder of the steam turbine is utilized to achieve effective utilization of the exhaust steam waste heat and reduce the heat load of the cold end, reduce the back pressure of the unit, improve the economy of the unit, and improve the overall effective utilization rate of the heat of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a structural schematic diagram of a low-load steam supply and back-pressure reduction waste heat utilization system for a thermal power unit of the present invention.

[0015] In the figure: 1. Steam turbine intermediate pressure cylinder; 2. Steam turbine low pressure cylinder; 3. Absorption heat pump; 4. Exhaust device; 5. Exhaust pipe; 6. Air cooling island; 7. Condensate pipe; 8. Valve; 9. Heat exchanger; 10. Demineralized water make-up tank; 11. Water pump; 12. Electric boiler; 13 Industrial user; 14. Deaerator; 15. Generator. DETAILED DESCRIPTION

[0016] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] The invention discloses a system for utilizing waste heat from a thermal power plant under low load and reducing back pressure. Figure 1 As shown, it includes a steam turbine intermediate pressure cylinder 1, and the outlet end of the steam turbine intermediate pressure cylinder 1 is connected to the steam turbine low pressure cylinder 2 and the absorption heat pump 3 through pipelines. The absorption heat pump 3 is connected to the deaerator 14 through a pipeline, and the intermediate exhaust gas in the steam turbine intermediate pressure cylinder 1 is used as the driving heat source of the absorption heat pump 3 and flows to the deaerator 14 after absorbing heat. The bottom of the steam turbine low pressure cylinder 2 is connected to the exhaust device 4, and the steam outlet of the exhaust device 4 is connected to the exhaust pipe 5, and the other end of the exhaust pipe 5 is respectively connected to the air cooling island 6 and the valve 8; the air cooling island 6 is connected to the exhaust device 4 through a pipeline to form a loop, and the pipeline connecting the air cooling island 6 and the exhaust device 4 is a condensate pipe 7.

[0018] The other end of the valve 8 is divided into two paths, one of which is connected to the heat exchanger 9 through a pipeline, and the other is connected to the absorption heat pump 3 through a pipeline. The exhaust steam is absorbed as a low-temperature heat source after passing through the valve absorption heat pump 3. The heat exchanger 9 and the absorption heat pump 3 are respectively connected to the exhaust device 4 through pipelines, that is, the exhaust steam flows back to the exhaust device after passing through the absorption heat pump 3 and the heat exchanger 9 for heat exchange / absorption. The heat exchanger 9 is also connected to the desalted water replenishment tank 10 through a pipeline, and a water pump 11 is arranged on the pipeline between the heat exchanger 9 and the desalted water replenishment tank 10. The heat exchanger 9 is connected to the absorption heat pump 3; the absorption heat pump 3 is connected to the electric boiler 12 through a pipeline, and the electric boiler 12 is connected to the industrial user 13. The hot side inlet of the heat exchanger 9 is connected to the valve 8, and the hot side outlet of the heat exchanger 9 is connected to the absorption heat pump 3; the cold side inlet of the heat exchanger 9 is connected to the desalted water replenishment tank 10, and the cold side outlet of the heat exchanger 9 is connected to the exhaust device 4. The hot water side inlet of the absorption heat pump 3 is connected to the heat exchanger 9 , and the hot water side outlet of the absorption heat pump 3 is connected to the electric boiler 12 .

[0019] The steam turbine low-pressure cylinder 2 is also connected to a generator 15, which is connected to the electric boiler 12. The exhaust gas in the turbine intermediate-pressure cylinder 1 generates electricity after working in the steam turbine low-pressure cylinder 2, part of which is used for the operation of the electric boiler 12, and the remaining part of the electric load is connected to the grid.

[0020] The operating method of the low-load steam supply and back pressure reduction waste heat utilization system of a thermal power unit of the present invention specifically comprises the following steps: Step 1: A part of the exhaust gas from the intermediate pressure cylinder 1 of the steam turbine flows to the low pressure cylinder 2 of the steam turbine to generate electricity, power the boiler 12 to operate and connect the electric load to the grid; the other part flows to the absorption heat pump 3 as a driving heat source, and then flows to the deaerator 14 after absorbing the heat; Step 2: A part of the exhaust steam passing through the low-pressure cylinder 2 of the steam turbine flows to the air-cooling island 6 to be cooled and then becomes condensed water and flows back to the exhaust device 4. The other part is divided into two paths after passing through the valve 8. One path flows to the heat exchanger 9 to heat the demineralized water supply tank 10 and then flows back to the exhaust device 4 after the steam supply water is supplied by the water pump 11. The other path flows to the absorption heat pump 3 as a low-temperature heat source to absorb heat and then flows back to the exhaust device 4. Step 3: After the desalted water replenishment tank 10 is heated in the first stage by the heat exchanger 9, it flows to the absorption heat pump 3 for the second stage heating, and then flows to the electric boiler 12 for the third stage heating. After the industrial steam supply parameters meet the requirements, it flows to the industrial user 13.

[0021] The low-load steam supply and back pressure reduction waste heat utilization system of the thermal power unit of the present invention solves the problem of ensuring industrial steam supply for the thermal power unit under 30% rated load. At the same time, a part of the low-pressure cylinder exhaust steam is diverted as the first-stage heating heat source for industrial steam supply and water replenishment, and another part of the low-pressure cylinder exhaust steam is diverted as the low-temperature heat source of the absorption heat pump. The absorption heat pump is used as the second-stage heating of industrial steam supply and water replenishment. In order to achieve the deep peak regulation demand of the thermal power unit below 30% rated load and meet the parameter requirements of industrial steam supply, an electric boiler is used as the third-stage heating of industrial steam supply and water replenishment. The power supply of the electric boiler is provided by the generator outlet of the thermal power unit, which can reduce the on-grid power load of the thermal power unit and achieve the deep peak regulation requirements of the power grid. The industrial steam supply and water replenishment adopts a three-stage heating system to realize the cascade utilization of heat and reduce irreversible losses. In addition, the low-pressure cylinder exhaust steam is diverted as the first-stage heating heat source and the second-stage heating absorption heat pump low-temperature heat source. On the one hand, it can reduce the cold end heat load, reduce the back pressure of the unit, and improve the economy of the unit; on the other hand, it realizes the effective utilization of the exhaust steam waste heat and improves the overall effective utilization rate of the unit.

[0022] Example 1 This embodiment provides a system for low-load steam supply and back pressure reduction waste heat utilization of thermal power units, such as Figure 1As shown, the outlet end of the steam turbine intermediate pressure cylinder 1 is connected to the steam turbine low pressure cylinder 2 and the absorption heat pump 3 through pipelines; the bottom of the steam turbine low pressure cylinder 2 is connected to the exhaust device 4, the steam outlet of the exhaust device 4 is connected to the exhaust pipe 5, and the other end of the exhaust pipe 5 is respectively connected to the air cooling island 6 and the valve 8; the air cooling island 6 is connected to the exhaust device 4 through a pipeline; the other end of the valve 8 is divided into two paths, one path is connected to the heat exchanger 9 through a pipeline, and the other path is connected to the absorption heat pump 3 through a pipeline, and the heat exchanger 9 and the absorption heat pump 3 are respectively connected to the exhaust device 4 through pipelines; the heat exchanger 9 is also connected to the desalted water make-up tank 10 through a pipeline; the heat exchanger 9 is connected to the absorption heat pump 3; the absorption heat pump 3 is connected to the electric boiler 12 through a pipeline, and the electric boiler 12 is connected to the industrial user 13.

[0023] Example 2 This embodiment provides a system for low-load steam supply and back pressure reduction waste heat utilization of thermal power units, such as Figure 1 As shown, the steam turbine intermediate pressure cylinder 1, the outlet end of the steam turbine intermediate pressure cylinder 1 is respectively connected to the steam turbine low pressure cylinder 2 and the absorption heat pump 3 through pipelines, and the absorption heat pump 3 is connected to the deaerator 14 through pipelines. The bottom of the steam turbine low pressure cylinder 2 is connected to the exhaust device 4, the steam outlet of the exhaust device 4 is connected to the exhaust pipe 5, and the other end of the exhaust pipe 5 is respectively connected to the air cooling island 6 and the valve 8; the air cooling island 6 is connected to the exhaust device 4 through a pipeline; the other end of the valve 8 is divided into two ways, one is connected to the heat exchanger 9 through a pipeline, and the other is connected to the absorption heat pump 3 through a pipeline, and the heat exchanger 9 and the absorption heat pump 3 are respectively connected to the exhaust device 4 through pipelines; the heat exchanger 9 is also connected to the desalted water replenishment tank 10 through a pipeline, and a water pump 11 is arranged on the pipeline between the heat exchanger 9 and the desalted water replenishment tank 10. The heat exchanger 9 is connected to the absorption heat pump 3; the absorption heat pump 3 is connected to the electric boiler 12 through a pipeline, and the electric boiler 12 is connected to the industrial user 13.

[0024] Example 3 This embodiment provides a system for low-load steam supply and back pressure reduction waste heat utilization of thermal power units, such as Figure 1As shown, the steam turbine intermediate pressure cylinder 1, the outlet end of the steam turbine intermediate pressure cylinder 1 is respectively connected to the steam turbine low pressure cylinder 2 and the absorption heat pump 3 through pipelines, and the absorption heat pump 3 is connected to the deaerator 14 through pipelines. The bottom of the steam turbine low pressure cylinder 2 is connected to the exhaust device 4, the steam outlet of the exhaust device 4 is connected to the exhaust pipe 5, and the other end of the exhaust pipe 5 is respectively connected to the air cooling island 6 and the valve 8; the air cooling island 6 is connected to the exhaust device 4 through a pipeline; the other end of the valve 8 is divided into two ways, one is connected to the heat exchanger 9 through a pipeline, and the other is connected to the absorption heat pump 3 through a pipeline, and the heat exchanger 9 and the absorption heat pump 3 are respectively connected to the exhaust device 4 through pipelines; the heat exchanger 9 is also connected to the desalted water replenishment tank 10 through a pipeline, and a water pump 11 is arranged on the pipeline between the heat exchanger 9 and the desalted water replenishment tank 10. The heat exchanger 9 is connected to the absorption heat pump 3; the absorption heat pump 3 is connected to the electric boiler 12 through a pipeline, and the electric boiler 12 is connected to the industrial user 13.

[0025] The steam turbine low-pressure cylinder 2 is also connected to a generator 15 , and the generator 15 is connected to the electric boiler 12 .

[0026] Example 4 This embodiment provides a system for low-load steam supply and back pressure reduction waste heat utilization of thermal power units, such as Figure 1 As shown, the steam turbine intermediate pressure cylinder 1, the outlet end of the steam turbine intermediate pressure cylinder 1 is respectively connected to the steam turbine low pressure cylinder 2 and the absorption heat pump 3 through pipelines, and the absorption heat pump 3 is connected to the deaerator 14 through pipelines. The bottom of the steam turbine low pressure cylinder 2 is connected to the exhaust device 4, the steam outlet of the exhaust device 4 is connected to the exhaust pipe 5, and the other end of the exhaust pipe 5 is respectively connected to the air cooling island 6 and the valve 8; the air cooling island 6 is connected to the exhaust device 4 through a pipeline, and the pipeline connecting the air cooling island 6 and the exhaust device 4 is a condensate pipe 7. The other end of the valve 8 is divided into two paths, one of which is connected to the heat exchanger 9 through a pipeline, and the other is connected to the absorption heat pump 3 through a pipeline, and the heat exchanger 9 and the absorption heat pump 3 are respectively connected to the exhaust device 4 through pipelines; the heat exchanger 9 is also connected to the desalted water supply tank 10 through a pipeline, and a water pump 11 is arranged on the pipeline between the heat exchanger 9 and the desalted water supply tank 10. The heat exchanger 9 is connected to the absorption heat pump 3 ; the absorption heat pump 3 is connected to the electric boiler 12 through a pipeline, and the electric boiler 12 is connected to the industrial user 13 .

[0027] The steam turbine low-pressure cylinder 2 is also connected to a generator 15 , and the generator 15 is connected to the electric boiler 12 .

[0028] Example 5 This embodiment provides a system for low-load steam supply and back pressure reduction waste heat utilization of thermal power units, such as Figure 1As shown, the steam turbine intermediate pressure cylinder 1, the outlet end of the steam turbine intermediate pressure cylinder 1 is respectively connected to the steam turbine low pressure cylinder 2 and the absorption heat pump 3 through pipelines, and the absorption heat pump 3 is connected to the deaerator 14 through pipelines. The bottom of the steam turbine low pressure cylinder 2 is connected to the exhaust device 4, the steam outlet of the exhaust device 4 is connected to the exhaust pipe 5, and the other end of the exhaust pipe 5 is respectively connected to the air cooling island 6 and the valve 8; the air cooling island 6 is connected to the exhaust device 4 through a pipeline, and the pipeline connecting the air cooling island 6 and the exhaust device 4 is a condensate pipe 7. The other end of the valve 8 is divided into two paths, one of which is connected to the heat exchanger 9 through a pipeline, and the other is connected to the absorption heat pump 3 through a pipeline, and the heat exchanger 9 and the absorption heat pump 3 are respectively connected to the exhaust device 4 through pipelines; the heat exchanger 9 is also connected to the desalted water supply tank 10 through a pipeline, and a water pump 11 is arranged on the pipeline between the heat exchanger 9 and the desalted water supply tank 10. The heat exchanger 9 is connected to the absorption heat pump 3 ; the absorption heat pump 3 is connected to the electric boiler 12 through a pipeline, and the electric boiler 12 is connected to the industrial user 13 .

[0029] The steam turbine low-pressure cylinder 2 is also connected to a generator 15 , and the generator 15 is connected to the electric boiler 12 .

[0030] The hot side inlet of the heat exchanger 9 is connected to the valve 8, and the hot side outlet of the heat exchanger 9 is connected to the absorption heat pump 3; the cold side inlet of the heat exchanger 9 is connected to the desalted water replenishment tank 10, and the cold side outlet of the heat exchanger 9 is connected to the exhaust device 4.

[0031] The hot water side inlet of the absorption heat pump 3 is connected to the heat exchanger 9 , and the hot water side outlet of the absorption heat pump 3 is connected to the electric boiler 12 .

[0032] The heat source of the absorption heat pump 3 is divided into two paths. One path is the middle exhaust air of the intermediate pressure cylinder 1 of the steam turbine, which is absorbed by the absorption heat pump 3 and then flows to the deaerator 14; the other path is the exhaust steam passing through the valve 8, which is absorbed by the absorption heat pump 3 and then flows to the exhaust device 4.

[0033] Example 6 This embodiment provides an operation method of a low-load steam supply and back pressure reduction waste heat utilization system for a thermal power unit, specifically comprising the following steps: Step 1: A part of the exhaust gas from the intermediate pressure cylinder 1 of the steam turbine flows to the low pressure cylinder 2 of the steam turbine to generate electricity, power the boiler 12 to operate and connect the electric load to the grid; the other part flows to the absorption heat pump 3 as a driving heat source, and then flows to the deaerator 14 after absorbing the heat; Step 2: A part of the exhaust steam passing through the low-pressure cylinder 2 of the steam turbine flows to the air-cooling island 6 for cooling and then flows back to the exhaust device 4, and the other part is divided into two paths after passing through the valve 8. One path flows to the heat exchanger 9 to heat the demineralized water supply tank 10 and then flows back to the exhaust device 4 after the steam supply water is supplied by the water pump 11, and the other path flows to the absorption heat pump 3 as a low-temperature heat source to absorb heat and then flows back to the exhaust device 4; Step 3: After the desalted water replenishment tank 10 is heated in the first stage by the heat exchanger 9, it flows to the absorption heat pump 3 for the second stage heating, and then flows to the electric boiler 12 for the third stage heating. After the industrial steam supply parameters meet the requirements, it flows to the industrial user 13.

[0034] After the implementation of this system, the problem of ensuring industrial steam supply for thermal power units at 30% rated load can be solved. Under the condition of meeting the parameter requirements of industrial steam supply and ensuring the steam supply volume of industrial steam supply, the rated load of thermal power units can be reduced from 30% to 25%, reducing the on-grid load of thermal power units and achieving the requirements of deep peak regulation of the power grid. The industrial steam supply water supply adopts a three-stage heating system to achieve cascade utilization of heat and reduce irreversible losses. In addition, the two-stage waste heat of the low-pressure cylinder exhaust steam is utilized to achieve effective utilization of the waste heat of the exhaust steam and reduce the heat load of the cold end, reduce the back pressure of the unit, improve the economy of the unit, and improve the overall effective utilization rate of the unit's heat.

Claims

1. A low-load steam supply and back-pressure reduction waste heat utilization system for thermal power units, characterized in that: The invention comprises a steam turbine intermediate pressure cylinder (1), wherein the outlet end of the steam turbine intermediate pressure cylinder (1) is respectively connected to a steam turbine low pressure cylinder (2) and an absorption heat pump (3) via pipelines; the bottom of the steam turbine low pressure cylinder (2) is connected to an exhaust device (4), the steam outlet of the exhaust device (4) is connected to an exhaust pipe (5), and the other end of the exhaust pipe (5) is respectively connected to an air cooling island (6) and a valve (8); the air cooling island (6) is connected to the exhaust device (4) via pipelines; the other end of the valve (8) The end is divided into two paths, one of which is connected to a heat exchanger (9) through a pipeline, and the other is connected to an absorption heat pump (3) through a pipeline. The heat exchanger (9) and the absorption heat pump (3) are respectively connected to a steam exhaust device (4) through pipelines; the heat exchanger (9) is also connected to a desalted water replenishment tank (10) through a pipeline; the heat exchanger (9) is connected to the absorption heat pump (3); the absorption heat pump (3) is connected to an electric boiler (12) through a pipeline, and the electric boiler (12) is connected to an industrial user (13).

2. The low-load steam supply and back pressure reduction waste heat utilization system for thermal power units according to claim 1 is characterized in that: A water pump (11) is provided on the pipeline between the heat exchanger (9) and the desalted water replenishment tank (10).

3. The low-load steam supply and back pressure reduction waste heat utilization system for thermal power units according to claim 1 is characterized in that: The absorption heat pump (3) is connected to a deaerator (14) via a pipeline.

4. The low-load steam supply and back pressure reduction waste heat utilization system for thermal power units according to claim 1 is characterized in that: The steam turbine low-pressure cylinder (2) is also connected to a generator (15), and the generator (15) is connected to the electric boiler (12).

5. The low-load steam supply and back-pressure reduction waste heat utilization system for thermal power units according to claim 1 is characterized in that: The pipe connecting the air cooling island (6) and the steam exhaust device (4) is a condensate pipe (7).

6. The low-load steam supply and back pressure reduction waste heat utilization system for thermal power units according to claim 1 is characterized in that: The hot side inlet of the heat exchanger (9) is connected to the valve (8), and the hot side outlet of the heat exchanger (9) is connected to the absorption heat pump (3); the cold side inlet of the heat exchanger (9) is connected to the demineralized water replenishment tank (10), and the cold side outlet of the heat exchanger (9) is connected to the steam exhaust device (4).

7. The low-load steam supply and back-pressure reduction waste heat utilization system for thermal power units according to claim 1 is characterized in that: The hot water side inlet of the absorption heat pump (3) is connected to the heat exchanger (9), and the hot water side outlet of the absorption heat pump (3) is connected to the electric boiler (12).

8. The low-load steam supply and back pressure reduction waste heat utilization system for thermal power units according to claim 3 is characterized in that: The heat source of the absorption heat pump (3) is divided into two paths. One path is the exhaust air from the intermediate pressure cylinder (1) of the steam turbine, which is absorbed by the absorption heat pump (3) and then flows to the deaerator (14); the other path is the exhaust steam passing through the valve (8), which is absorbed by the absorption heat pump (3) and then flows to the exhaust device (4).

9. The method for operating the low-load steam supply and back pressure reduction waste heat utilization system for thermal power units according to any one of claims 1 to 8, characterized in that: The steps include: Step 1: A portion of the exhaust gas from the steam turbine intermediate pressure cylinder (1) flows to the steam turbine low pressure cylinder (2) to generate electricity for power boiler (12) operation and to connect the electric load to the grid; the other portion flows to the absorption heat pump (3) as a driving heat source, where the heat is absorbed and then flows to the deaerator (14); Step 2: A portion of the exhaust steam passing through the low-pressure cylinder (2) of the steam turbine flows to the air cooling island (6) to be cooled and then flows back to the exhaust device (4); the other portion flows through a valve (8) and is divided into two paths. One path flows to the heat exchanger (9) to heat the desalted water makeup tank (10) and then flows back to the exhaust device (4) after being supplied with steam and water by a water pump (11); the other path flows to the absorption heat pump (3) as a low-temperature heat source to absorb heat and then flows back to the exhaust device (4); Step 3: After the desalted water replenishment tank (10) is heated in the first stage by the heat exchanger (9), it flows to the absorption heat pump (3) for second stage heating, and then flows to the electric boiler (12) for third stage heating. After the industrial steam supply parameters meet the requirements, it flows to the industrial user (13).

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