Deep waste heat cascade utilization system of heat and power unit based on two-stage compression heat pump

Abstract

The application discloses a kind of based on two-stage compression heat pump's heat engine unit deep waste heat cascade utilization system, comprising, negative pressure flash gas flue waste heat recovery system, two-stage voltage compression heat pump unit, coal-fired cogeneration unit and heat network heater;Through two-stage compression heat pump, the deep utilization of circulating water waste heat and flue gas waste heat is carried out in turn, based on the principle of negative pressure flash, make slurry flash cooling, achieve the purpose of indirect recovery of flue gas waste heat, improve the flue gas waste heat utilization depth of unit, improve overall thermal efficiency and heating capacity, reduce coal consumption, realize energy saving and carbon reduction;The system improves the heating capacity while increasing peak shaving depth, meet the technical requirements of flexible adjustment and energy saving and carbon reduction in three improvement linkage requirements, can actively respond to the depth of power grid peak shaving ball, while meeting the heating load demand, reduce the coal consumption of unit.

Description

Technical Field

[0001] This invention belongs to the field of thermal power unit heating retrofit technology, and particularly relates to a deep waste heat cascade utilization system for thermal power units based on a two-stage compression heat pump. Background Technology

[0002] A coal-fired power unit is a power generation facility that uses coal as its primary fuel. These units convert the heat energy generated from burning coal into electrical energy, supplying power to various sectors including industry, commerce, and homes. Coal-fired power units generate high-temperature, high-pressure heat energy by burning coal, typically within a boiler. This heat energy is used to heat water, producing high-temperature, high-pressure steam. The steam is then introduced into a steam turbine, whose high-speed rotation drives a connected generator rotor, generating electricity. Through the principle of electromagnetic induction, the rotor in the generator rotates in a magnetic field, generating an electric current, ultimately converting mechanical energy into electrical energy.

[0003] Coal-fired combined heat and power (CHP) units typically operate at base load, offering stable and reliable power output. Coal, as a relatively inexpensive and widely available fuel, contributes to the relatively low cost of power generation for coal-fired units. In many regions, the infrastructure for coal-fired power units is already in place, eliminating the need for large-scale new infrastructure construction. However, traditional coal-fired technologies have relatively low energy conversion efficiency, leading to energy waste. In some regions, coal-fired power units still primarily handle electricity while also fulfilling significant heat load demands, necessitating technological improvements and environmental protection measures to mitigate their negative impacts.

[0004] Two-stage compression heat pump technology has made some progress in the energy sector. This technology can achieve more efficient heat energy conversion and transfer through multi-stage compression and expansion, thereby improving energy utilization efficiency. However, integrating two-stage compression heat pump technology with thermal power units and waste heat cascade utilization systems requires consideration of how to coordinate and optimize different devices to achieve optimal overall heating performance, improve heating capacity, and reduce coal consumption for power generation. This is a problem that urgently needs to be solved. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a deep waste heat cascade utilization system for thermal power units based on two-stage compression heat pump technology. Through coordination and optimization between different devices, it effectively improves the heating capacity and increases the peak shaving depth, meeting the technical requirements of flexible adjustment and energy saving and carbon reduction in the three-level linkage requirements. It can actively respond to the grid's deep peak shaving requirements, meet the heating load demand, and reduce the unit's coal consumption.

[0006] This invention is achieved through the following technical solution:

[0007] A deep waste heat cascade utilization system for a thermal power unit based on a two-stage compression heat pump includes,

[0008] Negative pressure flash flue gas waste heat recovery system, two-stage electric compression heat pump unit, coal-fired cogeneration unit and heating network heater;

[0009] The drain side of the heating network heater is connected to the deaerator of the coal-fired cogeneration unit, and the steam side of the heating network heater is connected to the heating extraction steam pipeline of the coal-fired cogeneration unit; the circulating water side of the heating network heater is connected to the primary network circulating water system.

[0010] The dual-stage electric compression heat pump unit includes a low-temperature loop recovery unit and a medium-temperature loop recovery unit; the low-temperature loop recovery unit is connected to the condenser of the coal-fired cogeneration unit; and the medium-temperature loop recovery unit is connected to the negative pressure flash flue gas waste heat recovery system.

[0011] Preferably, the cryogenic loop recovery unit includes a condenser, a high-pressure stage compressor, a low-pressure stage compressor, an evaporator, a second expansion valve, and a working fluid heat exchanger connected in sequence.

[0012] Preferably, the medium-temperature loop recovery unit includes a condenser, a high-pressure stage compressor, an intermediate heat exchanger, a working fluid heat exchanger, and a first expansion valve connected in sequence.

[0013] Preferably, the negative pressure flash flue gas waste heat recovery system includes a desulfurization slurry spray pump, a negative pressure flash tank, a negative pressure vacuum pump, a desulfurization slurry return pump, a flash steam condensate pump, and a flash steam condensate tank.

[0014] The negative pressure vacuum pump is installed on the negative pressure flash tank; the desulfurization slurry spray pump is installed on the desulfurization tower slurry inlet pipe of the negative pressure flash tank; and the desulfurization slurry return pump is installed on the desulfurization tower slurry outlet pipe of the negative pressure flash tank. The top outlet of the negative pressure flash tank is connected to the inlet of the intermediate heat exchanger. The outlet of the intermediate heat exchanger is connected to the bottom circulating water inlet of the negative pressure flash tank and the flash steam condensate tank, respectively. The flash steam condensate pump is installed on the confluence pipe between the bottom circulating water inlet of the negative pressure flash tank and the flash steam condensate tank.

[0015] Preferably, a first electric regulating valve is installed on the bottom circulating water pipeline of the negative pressure flash tank; a second electric regulating valve is installed on the inlet pipeline of the flash condensate tank; and a check valve is installed on the pipeline between the top of the negative pressure flash tank and the intermediate heat exchanger.

[0016] Preferably, the coal-fired power generation unit further includes a boiler, a steam turbine unit, a low-pressure heater unit, and a high-pressure heater unit;

[0017] The boiler, turbine unit, condenser, low-pressure heater group, deaerator and high-pressure heater group are connected in sequence.

[0018] The deaerator's drain side is connected to the drain side of the heating network heater; the heating network heater's circulating water inlet is connected to the return water pipe of the primary network circulating water system, and the heating network heater's circulating water outlet is connected to the primary network circulating water system's water supply pipe.

[0019] The waste heat side of the condenser is connected to the water side of the evaporator; a condensate pump is installed on the connecting pipeline between the condensate outlet of the condenser and the low-pressure heater group; a feed water pump is installed between the high-pressure heater group and the deaerator.

[0020] Preferably, the turbine unit includes a high-pressure cylinder, an intermediate-pressure cylinder, and a low-pressure cylinder.

[0021] One steam-side outlet of the boiler is connected to the high-pressure cylinder of the steam turbine, and the other steam-side outlet of the boiler is connected in sequence to the intermediate-pressure cylinder and the low-pressure cylinder of the steam turbine. The heating extraction steam pipes of the intermediate-pressure cylinder and the low-pressure cylinder of the steam turbine are connected to the steam-side inlet of the heating network heater. The exhaust outlet of the low-pressure cylinder of the steam turbine is connected in sequence to the condenser, the low-pressure heater group, the deaerator, the high-pressure heater group and the water-side inlet of the boiler.

[0022] Preferably, a steam butterfly valve is installed on the connecting pipeline between the intermediate-pressure cylinder and the low-pressure cylinder of the steam turbine; a steam check valve is installed on the heating extraction steam pipeline; and the high-pressure cylinder, intermediate-pressure cylinder and low-pressure cylinder of the steam turbine drive a generator to generate electricity through a transmission shaft.

[0023] Preferably, the circulating water inlet of the heating network heater is connected to the return water pipe of the primary circulating water system through a condenser; the circulating water outlet of the heating network heater is connected to the water supply pipe of the primary circulating water system.

[0024] Preferably, a heating network circulating water pump is installed on the return water pipe of the primary network circulating water system.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] This invention aims to provide a deep waste heat cascade utilization system for thermal power units based on a two-stage compression heat pump. It establishes a flue gas waste heat recovery system using a two-stage electric compression heat pump coupled with a negative pressure flash tank. The two-stage electric compression heat pump divides the heat pump compression process into high and low pressure stages for staged compression of the working fluid, splitting the internal circulating working fluid into two paths. A working fluid heat exchange process is set in the middle to distinguish the waste heat recovery temperatures of the two paths. The low-temperature loop recovers low-temperature waste heat from the unit, and the medium-temperature loop recovers medium-temperature waste heat from the unit. Based on the principle of temperature matching and cascade utilization, various waste heat sources are utilized in a cascade manner, improving energy utilization and unit thermal efficiency. The negative pressure flash tank creates a negative pressure vacuum environment inside the tank, causing the desulfurization slurry to flash and cool down, generating some water vapor carrying a large amount of latent heat. This portion of water vapor does not contain desulfurization solvents and is equivalent to water vapor with low-grade waste heat formed after filtering the slurry. This portion of water vapor serves as the medium-temperature heat source for the heat pump, while the low-temperature heat source for the heat pump is the waste heat from the circulating water. The waste heat recovery system utilizes a two-stage compression heat pump to utilize the waste heat from the circulating water and flue gas at different temperatures in a cascaded manner. First, the waste heat from the cold end of the turbine is indirectly recovered in the low-temperature loop, and then the waste heat from the flue gas is indirectly recovered. At the same time, the power consumption of the heat pump compressor during the deep peak shaving period is provided by the power generation of the unit, which increases the heating capacity and the peak shaving depth, meets the technical requirements of flexible adjustment and energy saving and carbon reduction in the three-reform linkage requirements, can actively respond to the grid's deep peak shaving requirements, and at the same time meet the heating load demand while reducing the unit's coal consumption. This system utilizes the principle of negative pressure flash evaporation to cool the slurry, indirectly recovering waste heat from flue gas, thus increasing the depth of waste heat utilization, improving overall thermal efficiency and heating capacity, reducing coal consumption, and achieving energy conservation and carbon reduction. The two-stage compression heat pump sequentially utilizes the waste heat from circulating water and flue gas, adhering to the principles of temperature matching and tiered utilization to improve energy efficiency. Simultaneously, the two-stage compression process reduces compressor power consumption, increases the heat pump's COP, and enhances energy savings. This system allows for free allocation of heat and power loads, offering higher depth peak shaving, faster ramp-up, and heating capacity compared to conventional cogeneration units. It contributes to the stable operation of new power systems, offers good flexibility, and allows for significant space for renewable energy grid connection.

[0027] Furthermore, the coal-fired cogeneration unit consists of a boiler, high, medium and low pressure cylinders, a generator and auxiliary regeneration equipment. Its principle is the same as that of a conventional supercritical unit. The waste heat of the turbine exhaust cold end is recovered on the closed circulating water side of the condenser as low-temperature waste heat in the waste heat recovery unit. The bypass extraction steam pipe at the medium and low pressure connection pipe provides heating extraction steam for the heating network heater, which is used to perform peak heating of the heating network circulating water to ensure that it can meet the primary network water supply requirements.

[0028] Furthermore, the waste heat recovery unit consists of an electrically driven two-stage compression heat pump coupled with a negative pressure flash flue gas waste heat recovery unit. The principle of negative pressure flash flue gas waste heat recovery is based on the characteristic that the saturation temperature of water in the desulfurization slurry decreases with decreasing pressure. The desulfurization slurry is sprayed into a negative pressure vacuum flash tank for cooling and flash evaporation. The vacuum pump maintains the negative pressure inside the tank. Some of the water in the desulfurization slurry evaporates into water vapor carrying a large amount of low-grade heat energy. This water vapor enters the intermediate heat exchanger as the medium-temperature waste heat of the heat pump. The two-stage compression heat pump performs staged recovery of waste heat, among which the circulating water carrying the waste heat of the exhaust steam is the low-temperature waste heat. The two-stage compression heat pump divides the working fluid into two loops through staged compression. The medium-temperature loop first absorbs some heat from the low-temperature loop, and then indirectly recovers the waste heat contained in the flue gas through an intermediate heat exchanger. The low-temperature loop first transfers some heat to the medium-temperature loop, and then recovers the low-temperature waste heat of the circulating water in the evaporator. After being compressed by the low-pressure stage compressor, it is mixed with the working fluid of the medium-temperature loop and then compressed by the high-pressure stage compressor. Finally, it enters the condenser to condense and release heat to heat the circulating water of the heating network. The power supply of the heat pump compressor is the unit's power generation, which increases the heating capacity while reducing the unit's power generation, improving the system's operational flexibility and deep peak-shaving capability.

[0029] Furthermore, the circulating water of the heating network is heated sequentially by a heat pump and a heating network heater. The heat pump recovers waste heat from the cold end and flue gas as the basic heat source for the circulating water of the heating network, while the heating network heater uses heating steam extraction as the peak heat source for the circulating water of the heating network. The two complement each other and can freely allocate the proportion of heating amount of the heating network water. If the output of the heat pump is low, the amount of heating steam extraction is increased; if the amount of heating steam extraction is low, the power consumption of the heat pump is increased. The unit's heat and power load distribution has a high degree of freedom.

[0030] Furthermore, during the recovery of waste heat from flue gas, some water vapor in the flue gas condenses and is released. This water vapor is then purified by flash evaporation and enters the condensate tank. The water quality is relatively good and can be used as makeup water for the heating network circulation, reducing the amount of water needed for system makeup and lowering water consumption costs. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a high back-pressure unit thermoelectric synergistic optimization system based on deep flue gas waste heat utilization.

[0032] In the diagram: 1-Boiler; 2-High-pressure cylinder of steam turbine; 3-Intermediate-pressure cylinder of steam turbine; 4-Steam butterfly valve; 5-Low-pressure cylinder of steam turbine; 6-Condenser; 7-Condensate pump; 8-Low-pressure heater group; 9-Deaerator; 10-Feed water pump; 11-High-pressure heater group; 12-Generator; 13-Steam check valve; 14-Heating network circulating water pump; 15-Condenser; 16-Heating network heater; 17-First expansion valve; 18-Working fluid heat exchanger ; 19-Intermediate heat exchanger; 20-High-pressure stage compressor; 21-Second expansion valve; 22-Evaporator; 23-Low-pressure stage compressor; 24-Flash steam condensate pump; 25-First electric regulating valve; 26-Second electric regulating valve; 27-Flash steam condensate tank; 28-Negative pressure flash tank; 29-Check valve; 30-Negative pressure vacuum pump; 31-Desulfurization slurry spray pump; 32-Desulfurization slurry return pump; 33-Circulating water pump. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0034] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0035] This invention aims to provide a deep waste heat cascade utilization system for thermal power units based on a two-stage compression heat pump. It establishes a flue gas waste heat recovery system using a two-stage electric compression heat pump coupled with a negative pressure flash tank. The two-stage electric compression heat pump divides the heat pump compression process into high and low pressure stages for staged compression of the working fluid, splitting the internal circulating working fluid into two paths. A working fluid heat exchange process is set in the middle to distinguish the waste heat recovery temperatures of the two paths. The low-temperature loop recovers low-temperature waste heat from the unit, and the medium-temperature loop recovers medium-temperature waste heat from the unit. Based on the principle of temperature matching and cascade utilization, various waste heat sources are utilized in a cascade manner, improving energy utilization and unit thermal efficiency. The negative pressure flash tank creates a negative pressure vacuum environment inside the tank, causing the desulfurization slurry to flash and cool down, generating some water vapor carrying a large amount of latent heat. This portion of water vapor does not contain desulfurization solvents and is equivalent to water vapor with low-grade waste heat formed after filtering the slurry. This portion of water vapor serves as the medium-temperature heat source for the heat pump, while the low-temperature heat source for the heat pump is the waste heat from the circulating water. The waste heat recovery system utilizes a two-stage compression heat pump to utilize the waste heat from the circulating water and flue gas at different temperatures in a cascaded manner. First, the waste heat from the cold end of the turbine is indirectly recovered in the low-temperature loop, and then the waste heat from the flue gas is indirectly recovered. At the same time, the power consumption of the heat pump compressor during the deep peak shaving period is provided by the power generation of the unit, which increases the heating capacity and the peak shaving depth, meets the technical requirements of flexible adjustment and energy saving and carbon reduction in the three-reform linkage requirements, can actively respond to the grid's deep peak shaving requirements, and at the same time meet the heating load demand while reducing the unit's coal consumption.

[0036] Specifically, including, such as Figure 1 As shown,

[0037] Negative pressure flash flue gas waste heat recovery system, two-stage electric compression heat pump unit, coal-fired cogeneration unit and heat network heater 16;

[0038] The drain side of the heat network heater 16 is connected to the deaerator 9 of the coal-fired cogeneration unit, the steam side of the heat network heater 16 is connected to the heating steam extraction pipeline of the coal-fired cogeneration unit, and the circulating water side of the heat network heater 16 is connected to the primary network circulating water system.

[0039] The two-stage electric compression heat pump unit includes a low-temperature loop recovery unit and a medium-temperature loop recovery unit; the low-temperature loop recovery unit is connected to the condenser 6 of the coal-fired cogeneration unit; and the medium-temperature loop recovery unit is connected to the negative pressure flash flue gas waste heat recovery system.

[0040] The cryogenic loop recovery unit includes a condenser 15, a high-pressure stage compressor 20, a low-pressure stage compressor 23, an evaporator 22, a second expansion valve 21, and a working fluid heat exchanger 18 connected in sequence.

[0041] The medium-temperature loop recovery unit includes a condenser 15, a high-pressure stage compressor 20, an intermediate heat exchanger 19, a working fluid heat exchanger 18, and a first expansion valve 17 connected in sequence.

[0042] The negative pressure flash flue gas waste heat recovery system includes a desulfurization slurry spray pump 31, a negative pressure flash tank 28, a negative pressure vacuum pump 30, a desulfurization slurry return pump 32, a flash steam condensate pump 24, and a flash steam condensate tank 27.

[0043] The negative pressure vacuum pump 30 is installed on the negative pressure flash tank 28, the desulfurization slurry spray pump 31 is installed on the desulfurization tower slurry inlet pipe of the negative pressure flash tank 28, and the desulfurization slurry return pump 32 is installed on the desulfurization tower slurry outlet pipe of the negative pressure flash tank 26; the top outlet of the negative pressure flash tank 28 is connected to the inlet of the intermediate heat exchanger 19; the outlet of the intermediate heat exchanger 19 is connected to the bottom circulating water inlet of the negative pressure flash tank 28 and the flash steam condensate tank 27 respectively; the flash steam condensate pump 24 is installed on the confluence pipe of the bottom circulating water inlet of the negative pressure flash tank 28 and the flash steam condensate tank 27.

[0044] A first electric regulating valve 25 is installed on the bottom circulating water pipeline of the negative pressure flash tank 26; a second electric regulating valve 26 is installed on the inlet pipeline of the flash condensate tank 27; and a check valve 29 is installed on the pipeline between the top of the negative pressure flash tank 26 and the intermediate heat exchanger 19.

[0045] The coal-fired power generation unit also includes a boiler 1, a steam turbine unit, a low-pressure heater unit 8, and a high-pressure heater unit 11;

[0046] The boiler 1, turbine unit, condenser 6, low-pressure heater group 8, deaerator 9 and high-pressure heater group 11 are connected in sequence.

[0047] The deaerator 9 has its drain side connected to the drain side of the heating network heater 39; the circulating water inlet of the heating network heater 39 is connected to the return water pipe of the primary circulating water system, and the circulating water outlet of the heating network heater 39 is connected to the water supply pipe of the primary circulating water system.

[0048] The waste heat side of the condenser 6 is connected to the water side of the evaporator 22; a condensate pump 7 is installed on the connecting pipeline between the condensate outlet of the condenser 6 and the low-pressure heater group 8; a feed water pump 10 is installed between the high-pressure heater group 11 and the deaerator 9.

[0049] The turbine unit includes a high-pressure cylinder 2, an intermediate-pressure cylinder 3, and a low-pressure cylinder 5.

[0050] One steam-side outlet of the boiler 1 is connected to the high-pressure cylinder 2 of the steam turbine, and the other steam-side outlet of the boiler 1 is connected in sequence to the intermediate-pressure cylinder 3 and the low-pressure cylinder 5 of the steam turbine. The heating extraction steam pipes of the intermediate-pressure cylinder 3 and the low-pressure cylinder 5 of the steam turbine are connected to the steam-side inlet of the heating network heater 16. The exhaust outlet of the low-pressure cylinder 5 of the steam turbine is connected in sequence to the condenser 6, the low-pressure heater group 8, the deaerator 9, the high-pressure heater group 11 and the water-side inlet of the boiler 1.

[0051] A steam butterfly valve 4 is installed on the connecting pipeline between the intermediate pressure cylinder 3 and the low pressure cylinder 5 of the steam turbine; a steam check valve 13 is installed on the heating steam extraction pipeline; the high pressure cylinder 2, the intermediate pressure cylinder 3 and the low pressure cylinder 5 of the steam turbine drive the generator 12 to generate electricity through a transmission shaft.

[0052] The circulating water inlet of the heat network heater 16 is connected to the return water pipe of the primary circulating water system through the condenser 15; the circulating water outlet of the heat network heater 16 is connected to the water supply pipe of the primary circulating water system.

[0053] A heating network circulating water pump 14 is installed on the return water pipe of the primary network circulating water system.

[0054] This system utilizes the principle of negative pressure flash evaporation to cool the slurry, indirectly recovering waste heat from flue gas. This improves the depth of waste heat utilization in the unit, enhances overall thermal efficiency and heating capacity, reduces coal consumption, and achieves energy conservation and carbon reduction. During the waste heat recovery process, some water vapor in the flue gas condenses and is purified through flash evaporation before entering the condensate tank. The resulting water is of good quality and can be used as makeup water for the heating network, reducing system makeup water volume and lowering water consumption costs. The two-stage compression heat pump sequentially utilizes the waste heat from the circulating water and flue gas, adhering to the principles of temperature matching and tiered utilization to improve energy efficiency. Simultaneously, the two-stage compression process reduces compressor power consumption, increases the heat pump COP, and improves energy savings. The system allows for free allocation of heat and power loads, offering higher depth peak shaving, rapid ramp-up, and heating capacity compared to conventional cogeneration units. This contributes to the stable operation of new power systems, provides good flexibility, and allows for significant space for renewable energy to be fed into the grid.

[0055] The specific operation method is as follows:

[0056] When the deep waste heat cascade utilization system of the thermal power unit based on the two-stage compression heat pump is put into operation, the boiler feedwater is heated and evaporated in boiler 1, becoming superheated steam, which enters the high-pressure cylinder 2 of the turbine to do work. The exhaust steam returns to boiler 1 for reheating and then enters the intermediate-pressure cylinder 3 of the turbine to do work. The exhaust steam is split into two paths in the intermediate-low pressure connecting pipe. One path enters the low-pressure cylinder 5 of the turbine through the steam butterfly valve 4 to do work, and the other path enters the heating network heater 16 through the check valve 13 to heat the heating network circulating water. The exhaust steam from the low-pressure cylinder 5 of the turbine enters the condenser 6 to transfer the waste heat of the exhaust steam to the circulating water. The condensate at the outlet of the condenser 6 is pressurized by the condensate pump 7 and sent to the low-pressure heater group 8 for heating, and then enters the deaerator 9 for deoxygenation. After being pressurized by the feedwater pump 10, it is then... The feedwater is fed into the high-pressure heater group 11 for heating, and then returns to the boiler 1 to complete the circulation. The high, medium and low pressure cylinders drive the generator 12 to generate electricity through the intermediate shaft. The return water of the heating network is pressurized by the heating network circulating water pump 14 and first passes through the heat pump condenser 15 for primary heating. Then it enters the heating network heater 16 and is heated to the supply water temperature by the heating extraction steam. Finally, it is supplied to the outside. The steam source of the heating network heater is the heating extraction steam extracted from the medium and low pressure connecting pipe bypass. The steam butterfly valve 4 is used to regulate the amount of heating extraction steam entering the heating network heater 16. The waste heat recovery unit is composed of an electrically driven two-stage compression heat pump and a negative pressure flash evaporation loop coupled together. The two-stage compression heat pump consists of a condenser 15, a first expansion valve 17, a working fluid heat exchanger 18, and an intermediate heat exchanger. The system consists of a compressor 19, a high-pressure stage compressor 20, a second expansion valve 21, an evaporator 22, and a low-pressure stage compressor 23. The internal working fluid is condensed and releases heat in the condenser 15 to heat the circulating water in the heating network. The outlet working fluid is split into two streams. One stream passes through the first expansion valve 17 to reduce pressure and temperature before entering the working fluid heat exchanger 18 to absorb heat from the other stream. It then enters the intermediate heat exchanger 19 to absorb waste heat from the flash steam in the negative pressure flash loop and mixes with the other stream of working fluid. The other stream of working fluid first transfers heat to the medium-temperature loop working fluid through the working fluid heat exchanger 18, then reduces pressure and temperature through the second expansion valve 21 before entering the evaporator 22 to evaporate and absorb waste heat from the circulating water. It is then compressed by the low-pressure stage compressor 23 and mixed with the medium-temperature loop working fluid before being sent together to the high-pressure stage compressor. After compression, the slurry is sent to the condenser 15 to complete the cycle. In the negative pressure flash evaporation loop, the desulfurization slurry is first sprayed into the negative pressure flash evaporation tank 28 by the desulfurization slurry spray pump 31 for flash evaporation and cooling. The cooled slurry is sent back to the desulfurization tower by the desulfurization slurry return pump 32 to spray and cool the flue gas. The negative pressure vacuum pump 30 is used to maintain the negative pressure vacuum in the tank. The flash steam enters the intermediate heat exchanger 19 through the check valve 29 to extract residual heat and condense. The flash condensate is drawn out by the flash condensate pump 24 and sent back to the negative pressure flash evaporation tank 28 through the first electric regulating valve 25. When the liquid level in the tank is too high, the opening of the first electric regulating valve 25 and the second electric regulating valve 26 is adjusted to increase the amount of condensate entering the flash steam condensate tank 27, thereby achieving dynamic water balance.

[0057] A coal-fired cogeneration unit consists of a boiler, high, medium, and low pressure cylinders, a generator, and auxiliary regenerative equipment. Its operating principle is the same as that of a conventional supercritical unit. Waste heat from the turbine exhaust steam is recovered on the closed-loop circulating water side of the condenser as low-temperature waste heat in the waste heat recovery unit. Heating extraction steam is provided to the heating network heaters via a bypass extraction pipe at the medium and low pressure interconnection pipe, used for peak heating of the heating network circulating water to ensure it meets the primary network water supply requirements. The waste heat recovery unit consists of an electrically driven two-stage compression heat pump coupled with negative pressure flash flue gas. The waste heat recovery unit consists of a negative pressure flash evaporation flue gas system. The principle of waste heat recovery utilizes the characteristic that the saturation temperature of water in the desulfurization slurry decreases with decreasing pressure. The desulfurization slurry is sprayed into a negative pressure vacuum flash tank for cooling and flash evaporation. A vacuum pump maintains the negative pressure inside the tank. Part of the water in the desulfurization slurry evaporates into water vapor carrying a large amount of low-grade heat energy. This water vapor enters the intermediate heat exchanger as the medium-temperature waste heat for the heat pump. The two-stage compression heat pump performs staged recovery of the waste heat, with the circulating water carrying the waste steam heat being low-grade waste heat. The two-stage compression heat pump utilizes staged compression to divide the working fluid into two loops. The intermediate-temperature loop first absorbs some heat from the low-temperature loop, then indirectly recovers the waste heat contained in the flue gas via an intermediate heat exchanger. The low-temperature loop first transfers some heat to the intermediate-temperature loop, then recovers the low-temperature waste heat from the circulating water in the evaporator. After being compressed by the low-pressure stage compressor, it mixes with the working fluid from the intermediate-temperature loop, is compressed by the high-pressure stage compressor, and then enters the condenser where it condenses and releases heat to heat the circulating water in the heating network. The power supply for the heat pump compressor is the unit's electricity generation. This increases heating capacity while reducing unit power generation, improving system operational flexibility and deep peak-shaving capability. The circulating water in the heating network is heated sequentially by a heat pump and a heating network heater. The heat pump recovers waste heat from the cold end and flue gas as the basic heat source for the circulating water, while the heating network heater uses heating steam extraction as the peak heat source for the circulating water. The two complement each other, allowing for free allocation of the proportion of heating water to be heated. If the heat pump output is low, the heating steam extraction rate is increased; if the heating steam extraction rate is low, the heat pump power consumption is increased. This results in a high degree of freedom in the allocation of the unit's thermal and electrical loads.

[0058] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0059] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or it can be in a centered component. When a component is said to be "connected to" another component, it can be directly connected to the other component or it may also be in a centered component. When a component is said to be "set to" another component, it can be directly set on the other component or it may also be in a centered component.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A deep waste heat cascade utilization system for a thermal power unit based on a two-stage compression heat pump, characterized in that, include, Negative pressure flash flue gas waste heat recovery system, two-stage electric compression heat pump unit, coal-fired cogeneration unit and heat network heater (16). The drain side of the heat network heater (16) is connected to the deaerator (9) of the coal-fired cogeneration unit, and the steam side of the heat network heater (16) is connected to the heating extraction steam pipeline of the coal-fired cogeneration unit; the circulating water side of the heat network heater (16) is connected to the primary network circulating water system. The dual-stage electric compression heat pump unit includes a low-temperature loop recovery unit and a medium-temperature loop recovery unit; the low-temperature loop recovery unit is connected to the condenser (6) of the coal-fired cogeneration unit; the medium-temperature loop recovery unit is connected to the negative pressure flash flue gas waste heat recovery system; The low-temperature loop recovery unit includes a condenser (15), a high-pressure stage compressor (20), a low-pressure stage compressor (23), an evaporator (22), a second expansion valve (21), and a working fluid heat exchanger (18) connected in sequence. The medium-temperature loop recovery unit includes a condenser (15), a high-pressure stage compressor (20), an intermediate heat exchanger (19), a working fluid heat exchanger (18), and a first expansion valve (17) connected in sequence.

2. The deep waste heat cascade utilization system of a thermal power unit based on a two-stage compression heat pump according to claim 1, characterized in that, The negative pressure flash flue gas waste heat recovery system includes a desulfurization slurry spray pump (31), a negative pressure flash tank (28), a negative pressure vacuum pump (30), a desulfurization slurry return pump (32), a flash steam condensate pump (24), and a flash steam condensate tank (27). The negative pressure vacuum pump (30) is installed on the negative pressure flash tank (28), the desulfurization slurry spray pump (31) is installed on the desulfurization tower slurry inlet pipe of the negative pressure flash tank (28), and the desulfurization slurry return pump (32) is installed on the desulfurization tower slurry outlet pipe of the negative pressure flash tank (26); the top outlet of the negative pressure flash tank (28) is connected to the inlet of the intermediate heat exchanger (19); the outlet of the intermediate heat exchanger (19) is connected to the bottom circulating water inlet of the negative pressure flash tank (28) and the flash steam condensate tank (27) respectively; the flash steam condensate pump (24) is installed on the confluence pipe of the bottom circulating water inlet of the negative pressure flash tank (28) and the flash steam condensate tank (27).

3. A deep waste heat cascade utilization system for a thermal power unit based on a two-stage compression heat pump according to claim 2, characterized in that, A first electric regulating valve (25) is installed on the bottom circulating water pipeline of the negative pressure flash tank (28); a second electric regulating valve (26) is installed on the inlet pipeline of the flash steam condensate tank (27); and a check valve (29) is installed on the pipeline between the top of the negative pressure flash tank (28) and the intermediate heat exchanger (19).

4. A deep waste heat cascade utilization system for a thermal power unit based on a two-stage compression heat pump according to claim 3, characterized in that, The coal-fired power generation unit also includes a boiler (1), a steam turbine unit, a low-pressure heater unit (8), and a high-pressure heater unit (11). The boiler (1), turbine unit, condenser (6), low-pressure heater group (8), deaerator (9) and high-pressure heater group (11) are connected in sequence; the drain side of the deaerator (9) is connected to the drain side of the heat network heater (39); the circulating water inlet of the heat network heater (39) is connected to the return water pipe of the primary network circulating water system, and the circulating water outlet of the heat network heater (39) is connected to the water supply pipe of the primary network circulating water system; the waste heat side of the condenser (6) is connected to the water side of the evaporator (22); a condensate pump (7) is installed on the connecting pipe between the condensate outlet of the condenser (6) and the low-pressure heater group (8); a feed water pump (10) is installed between the high-pressure heater group (11) and the deaerator (9).

5. A deep waste heat cascade utilization system for a thermal power unit based on a two-stage compression heat pump according to claim 4, characterized in that, The turbine unit includes a high-pressure cylinder (2), an intermediate-pressure cylinder (3), and a low-pressure cylinder (5). One steam-side outlet of the boiler (1) is connected to the high-pressure cylinder (2) of the turbine. The other steam-side outlet of the boiler (1) is connected in sequence to the intermediate-pressure cylinder (3) and the low-pressure cylinder (5) of the turbine. The heating extraction pipe of the intermediate-pressure cylinder (3) and the low-pressure cylinder (5) of the turbine is connected to the steam-side inlet of the heating network heater (16). The exhaust outlet of the low-pressure cylinder (5) of the turbine is connected in sequence to the condenser (6), the low-pressure heater group (8), the deaerator (9), the high-pressure heater group (11), and the water-side inlet of the boiler (1).

6. A deep waste heat cascade utilization system for a thermal power unit based on a two-stage compression heat pump according to claim 5, characterized in that, A steam butterfly valve (4) is installed on the connecting pipeline between the intermediate pressure cylinder (3) and the low pressure cylinder (5) of the steam turbine; a steam check valve (13) is installed on the heating extraction steam pipeline.

7. A deep waste heat cascade utilization system for a thermal power unit based on a two-stage compression heat pump according to claim 6, characterized in that, The high-pressure cylinder (2), intermediate-pressure cylinder (3), and low-pressure cylinder (5) of the steam turbine drive the generator (12) to generate electricity through a transmission shaft.

8. A deep waste heat cascade utilization system for a thermal power unit based on a two-stage compression heat pump according to claim 5, characterized in that, The circulating water inlet of the heat network heater (16) is connected to the return water pipe of the primary circulating water system through the condenser (15); the circulating water outlet of the heat network heater (16) is connected to the water supply pipe of the primary circulating water system.

9. A deep waste heat cascade utilization system for a thermal power unit based on a two-stage compression heat pump according to claim 8, characterized in that, A heating network circulating water pump (14) is installed on the return water pipe of the primary network circulating water system.

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