Thermal power plant energy-saving system, method for deep utilization of its waste heat, and operation method

Abstract

The present invention discloses an energy-saving system for a thermal power plant, a method for deep utilization of waste heat thereof, and an operation method. The system includes: a boiler that provides thermal energy for the thermal power plant; a high-temperature steam discharge pipe and a flue gas discharge pipe are provided on the boiler, and a steam turbine generator set is connected to the high-temperature steam discharge pipe; a steam outlet end of the steam turbine generator set is connected to the boiler through a circulation loop; a flue gas waste heat deep recovery and energy storage system that is used to receive part of the flue gas discharged from the boiler, recover the heat of the flue gas, and store it; a regenerative system that uses the heat stored in the flue gas waste heat deep recovery and energy storage system to heat the medium in the circulation loop; a photovoltaic heat pump condensate waste heat recovery system that recovers the waste heat in the circulation loop and stores the recovered heat in the flue gas waste heat deep recovery and energy storage system. Starting from the perspective of deep utilization of waste heat, the present invention combines energy storage technology, renewable energy technology, and heat pump technology, greatly improving the waste heat utilization level of the thermal power plant.

Description

Technical Field

[0001] The present invention relates to the technical field of power generation in thermal power plants, and particularly relates to an energy-saving system for a thermal power plant, a method for deeply utilizing waste heat thereof, and an operation method thereof. Background Art

[0002] Coal-fired thermal power generating units are the focus of energy conservation and emission reduction work. Among the various losses of thermal power units, the cold source loss and the flue gas loss are the two largest losses. The cold source heat loss is caused by the heat dissipation of the cold source of the unit, and the flue gas loss is caused by factors such as the incomplete utilization of the heat in the flue gas in the boiler and the heat exchange loss of the air preheater, resulting in the flue gas temperature at the outlet of the air preheater still being above 150°C, and at the same time, there is a great waste of the heat of the flue gas in the air preheater. Therefore, the waste heat recovery and utilization in these two aspects will greatly improve the heat utilization level and development level of coal-fired thermal power generating units.

[0003] On the other hand, if a thermal power plant can combine renewable energy technologies while saving energy, it can not only promote the deep energy conservation of the thermal power plant, but also promote the development and progress of renewable energy technologies, providing a solution for exploring new energy supply models in the future.

[0004] In recent years, the technology for deeply utilizing flue gas waste heat has received wide attention, but there are still certain problems: First, the existing technology only utilizes the waste heat of the flue gas after the air preheater and cannot reduce the loss of the air preheater; Second, there is a large amount of energy waste in the existing technology when the unit load changes or the load is too low; Third, the existing technology uses too much electricity for waste heat recovery and utilization, which runs counter to the original intention of energy conservation and environmental protection; Fourth, most of the existing technologies are simple combinations of various energy-saving technologies and cannot deeply couple each device with the thermal power unit to improve the degree of cascade utilization of heat; Fifth, after the thermal power plant generates electricity using a steam turbine generator set, the steam discharged from the steam turbine generator set still has a certain amount of heat. If it is not utilized, it will cause waste of heat, resulting in a low degree of cascade utilization of heat in the existing technology. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of low degree of cascade utilization of heat and a large amount of energy waste in the existing technology, and provide an energy-saving system for a thermal power plant, a method for deeply utilizing waste heat thereof, and an operation method thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] An energy-saving system for a thermal power plant, comprising:

[0008] A boiler, which is used to provide heat energy for a thermal power plant; a high-temperature steam discharge pipe and a flue gas discharge pipe are arranged on the boiler, and a steam turbine generator set for generating electricity by using the high-temperature steam discharged from the boiler is connected to the high-temperature steam discharge pipe; the steam outlet end of the steam turbine generator set is connected to the boiler through a circulation loop;

[0009] A flue gas waste heat deep recovery and energy storage system, which is branched through an auxiliary flue gas pipeline and arranged on the main flue gas pipeline between the flue gas discharge pipe of the boiler and the air preheater, and is used to receive part of the flue gas discharged from the boiler, recover the heat of the flue gas and store it;

[0010] A regenerative system, which is arranged on the circulation loop and is used to heat the medium in the circulation loop by using the heat stored in the flue gas waste heat deep recovery and energy storage system;

[0011] A photovoltaic heat pump condensate waste heat recovery system, which exchanges heat with the circulation loop located between the steam turbine generator set and the regenerative system, and is used to recover the waste heat in the circulation loop and store the recovered heat in the flue gas waste heat deep recovery and energy storage system.

[0012] Further optimizing the technical solution, the circulation loop exchanges heat with the photovoltaic heat pump condensate waste heat recovery system through a first condenser, and the first condenser is arranged on the circulation loop; a condensate pump is arranged on the circulation loop.

[0013] Further optimizing the technical solution, a second condenser is also arranged on the circulation loop behind the first condenser, and the second condenser is used to condense the medium in the circulation loop.

[0014] Further optimizing the technical solution, the photovoltaic heat pump condensate waste heat recovery system includes:

[0015] A working medium annular circulation pipeline;

[0016] A first heat pump heat exchanger, which is arranged on the working medium annular circulation pipeline and exchanges heat with the first condenser;

[0017] A heat pump compressor, which is arranged on the working medium annular circulation pipeline and drives the movement of the medium inside the working medium annular circulation pipeline;

[0018] A photovoltaic power generation system, which is used to generate electric energy by using solar energy and drive the heat pump compressor to act;

[0019] A second heat pump heat exchanger, which is arranged on the working medium annular circulation pipeline and exchanges heat with the flue gas waste heat deep recovery and energy storage system.

[0020] Further optimizing the technical solution, a throttle valve is also arranged on the working medium annular circulation pipeline.

[0021] Further optimize the technical solution. The flue gas waste heat deep recovery and energy storage system includes:

[0022] At least one stage of waste heat recovery heat exchanger, which are sequentially arranged on the auxiliary flue gas pipeline respectively, and are used for heat exchange with the flue gas in the auxiliary flue gas pipeline;

[0023] At least one waste heat storage tank, which exchanges heat with each waste heat recovery heat exchanger respectively and recovers and stores the heat in the flue gas.

[0024] Further optimize the technical solution. The waste heat recovery heat exchanger is provided with three stages, namely the first waste heat recovery heat exchanger, the second waste heat recovery heat exchanger, and the third waste heat recovery heat exchanger; the waste heat storage tank is provided with three, namely the first waste heat storage tank, the second waste heat storage tank, and the third waste heat storage tank; heat exchange is carried out between the first waste heat storage tank and the first waste heat recovery heat exchanger, heat exchange is carried out between the second waste heat storage tank and the second waste heat recovery heat exchanger, and heat exchange is carried out between the third waste heat storage tank and the third waste heat recovery heat exchanger; the third waste heat storage tank is used for recovering and storing the heat transmitted by the photovoltaic heat pump condensate water waste heat recovery system.

[0025] Further optimize the technical solution. The regenerative system includes:

[0026] A low-pressure regenerative heater group, including several low-pressure regenerative heaters, and each low-pressure regenerative heater is sequentially arranged on the circulation loop; the low-pressure regenerative heater group is supplied with heat through the second waste heat storage tank and the third waste heat storage tank, and then heats the medium on the circulation loop;

[0027] A high-pressure regenerative heater group, including several high-pressure regenerative heaters, and each high-pressure regenerative heater is sequentially arranged on the circulation loop; the high-pressure regenerative heater is supplied with heat through the third waste heat storage tank, and then heats the medium on the circulation loop;

[0028] An deaerator, which is arranged on the circulation loop between the low-pressure regenerative heater group and the high-pressure regenerative heater group, and is used for removing oxygen in the medium in the circulation loop;

[0029] A feed water pump, which is arranged on the circulation loop between the low-pressure regenerative heater group and the high-pressure regenerative heater group, and is used for increasing the feed water pressure entering the high-pressure regenerative heater group and the boiler.

[0030] Further optimize the technical solution. The steam turbine generator set includes:

[0031] A high-pressure cylinder of the steam turbine, the inner cavity of which is connected to the high-temperature steam discharge pipe, and is used for rotating by using the high-temperature steam generated by the boiler;

[0032] The intermediate-pressure cylinder of the steam turbine is internally connected with a secondary steam discharge pipe. The high-pressure cylinder of the steam turbine is connected to the secondary steam discharge pipe through a steam return pipe. Part of the junction of the steam return pipe and the secondary steam discharge pipe is arranged inside the boiler, and the boiler reheats the steam in the steam return pipe.

[0033] The low-pressure cylinder of the steam turbine is connected to the inner cavity of the intermediate-pressure cylinder of the steam turbine through a steam connection pipe; the rotating shafts of the high-pressure cylinder, intermediate-pressure cylinder, and low-pressure cylinder of the steam turbine are connected in sequence.

[0034] The generator is connected to the rotating shaft of the low-pressure cylinder of the steam turbine and is used to convert the mechanical energy generated by the rotation of the high-pressure cylinder, intermediate-pressure cylinder, and low-pressure cylinder of the steam turbine into electrical energy.

[0035] To further optimize the technical solution, it further includes:

[0036] The flue gas pollutant removal system is connected and arranged at the tail of the auxiliary flue gas pipeline and is used to remove pollutants in the flue gas.

[0037] The method for deep utilization of waste heat in the energy-saving system of a thermal power plant includes the following steps:

[0038] S1. Part of the flue gas discharged from the boiler enters the flue gas waste heat deep recovery and energy storage system for waste heat recovery:

[0039] The flue gas exchanges heat with the multi-stage waste heat recovery heat exchanger, and each stage of the waste heat recovery heat exchanger respectively recovers and stores the heat in each waste heat storage tank;

[0040] S2. The flue gas after waste heat recovery in step S1 enters the flue gas pollutant removal system for flue gas treatment;

[0041] S3. The high-temperature steam generated by the boiler enters the steam turbine generator set for power generation and then enters the first condenser, and the waste heat in the medium discharged from the steam turbine generator set is recovered through the photovoltaic heat pump condensate waste heat recovery system. The photovoltaic heat pump condensate waste heat recovery system stores the recovered heat through the flue gas waste heat deep recovery and energy storage system;

[0042] S4. The medium on the circulation loop after heat exchange in step S3 enters the regenerative system for heating. The heating heat of the regenerative system comes from the heat stored in the flue gas waste heat deep recovery and energy storage system, and the medium after being heated by the regenerative system returns to the boiler.

[0043] The operation method of the energy-saving system of a thermal power plant includes the following steps:

[0044] S101. Obtain the operating status and load demand of the unit;

[0045] S102. Control the flue gas waste heat deep recovery and energy storage system to provide heat for the feed water of the unit according to the operating state of the unit and the load demand, so as to ensure a constant feed water temperature or the highest unit efficiency.

[0046] The technical solution of the present invention has the following advantages:

[0047] 1. The energy-saving system for thermal power plants provided by the present invention starts from the perspective of deep utilization of waste heat, combines energy storage technology, renewable energy technology and heat pump technology, and greatly improves the waste heat utilization level of thermal power plants. The photovoltaic heat pump condensate waste heat recovery system can recover the heat in the steam discharged from the steam turbine generator set and store the recovered heat in the flue gas waste heat deep recovery and energy storage system, and part of the heat in the flue gas discharged from the boiler can be stored in the flue gas waste heat deep recovery and energy storage system, thereby achieving the purpose of deep utilization of waste heat.

[0048] 2. The energy-saving system for thermal power plants provided by the present invention reasonably distributes the flue gas waste heat, extracts part of the flue gas before the air preheater to reduce the loss of the air preheater, and recovers and stores the waste heat in the flue gas through the flue gas waste heat deep recovery and energy storage system.

[0049] 3. The energy-saving system for thermal power plants provided by the present invention combines waste heat utilization with energy storage technology, realizes energy storage during low load of the unit and energy supply during high load, improves the off-design efficiency of the unit and reduces the energy loss of the boiler during low load.

[0050] 4. The energy-saving system for thermal power plants provided by the present invention is driven by photovoltaic power generation for the photovoltaic heat pump condensate waste heat recovery system, recovers the waste heat of the steam turbine exhaust, increases its temperature, and the increased heat enters the third waste heat storage tank for storage, which can be used for regenerative heating or flue gas reheating. The present invention combines photovoltaic power generation technology to reduce the energy consumption brought by waste heat utilization equipment.

[0051] 5. The energy-saving system for thermal power plants provided by the present invention combines heat pump technology to improve the degree of waste heat utilization and achieve the purpose of deep utilization of waste heat.

[0052] 6. The energy-saving system for thermal power plants provided by the present invention recovers and utilizes waste heat in multiple stages step by step, improves the coupling degree of the unit, and reduces loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0054] Figure 1 It is a schematic structural diagram of the energy-saving system for a thermal power plant according to the present invention;

[0055] Figure 2 It is a schematic structural diagram of the photovoltaic heat pump condensate waste heat recovery system in the energy-saving system for a thermal power plant according to the present invention;

[0056] Figure 3 It is a schematic structural diagram of the flue gas waste heat deep recovery and energy storage system in the energy-saving system for a thermal power plant according to the present invention;

[0057] Figure 4 It is a schematic structural diagram of the flue gas pollutant removal system in the energy-saving system for a thermal power plant according to the present invention;

[0058] Figure 5 It is a schematic structural diagram of the waste heat deep utilization system according to the present invention;

[0059] Figure 6 It is a flowchart of the waste heat deep utilization method for the energy-saving system of a thermal power plant according to the present invention.

[0060] Reference numerals:

[0061] 10. Waste heat deep utilization system; 110. Thermal power unit; 120. Multi-stage flue gas and condensate waste heat recovery system; 130. Flue gas and condensate waste heat energy storage and peak shaving system; 140. Controller;

[0062] 201. Boiler; 202. High-pressure cylinder of steam turbine; 203. Intermediate-pressure cylinder of steam turbine; 204. Low-pressure cylinder of steam turbine; 205. Generator; 206. First condenser; 207. Second condenser; 208. Condensate pump; 209. Fourth low-pressure regenerative heater; 210. Third low-pressure regenerative heater; 211. Second low-pressure regenerative heater; 212. First low-pressure regenerative heater; 213. Deaerator; 214. Feed water pump; 215. Third high-pressure regenerative heater; 216. Second high-pressure regenerative heater; 217. First high-pressure regenerative heater; 218. High-temperature steam discharge pipe; 219. Flue gas discharge pipe; 220. Circulation loop; 221. Steam return pipe; 222. Secondary steam discharge pipe; 223. Steam connection pipe;

[0063] 30. Photovoltaic heat pump condensate waste heat recovery system; 301. Photovoltaic power generation system; 302. First heat pump heat exchanger; 303. Heat pump compressor; 304. Second heat pump heat exchanger; 305. Throttle valve; 306. Working fluid annular circulation pipeline;

[0064] 40. Flue gas waste heat deep recovery and energy storage system; 401. First waste heat recovery heat exchanger; 402. Second waste heat recovery heat exchanger; 403. Third waste heat recovery heat exchanger; 404. First waste heat storage tank; 405. Second waste heat storage tank; 406. Third waste heat storage tank;

[0065] 50. Flue gas pollutant removal system; 501. Low-temperature electrostatic precipitator; 502. Induced draft fan; 503. Wet flue gas desulfurization device; 504. Flue gas reheater; 505. Chimney. Detailed implementation manners

[0066] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0067] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0068] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0069] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0070] Embodiment 1

[0071] Based on the existing coal-fired power generation units, the present invention introduces multiple devices to work together to achieve the purpose of improving the waste heat utilization level and energy-saving level of the units. The accompanying drawings and introduction in the specification of the present invention take a typical 300MW coal-fired power generation unit as an example, and can be extended to various different types of units.

[0072] As Figures 1 to 5 shown, a specific implementation of the energy-saving system for a thermal power plant includes a boiler 201, a flue gas waste heat deep recovery and energy storage system 40, a regenerative system, and a photovoltaic heat pump condensate waste heat recovery system 30.

[0073] The boiler 201 is used to provide heat energy for the thermal power plant, and the boiler used is a coal-fired boiler. The boiler 201 can generate high-temperature flue gas and exchange heat with steam to generate high-temperature steam, which enters the steam turbine unit for power generation. The flue gas (about 350 °C) after combustion heat exchange enters the air preheater to heat the air and then is discharged (about 150 °C).

[0074] A high-temperature steam discharge pipe 218 and a flue gas discharge pipe 219 are provided on the boiler 201. The high-temperature steam discharge pipe is connected to a steam turbine generator set, and the steam turbine generator set uses the high-temperature steam discharged from the boiler 201 for power generation. The steam outlet end of the steam turbine generator set is connected to the boiler 201 through a circulation loop 220.

[0075] The flue gas waste heat deep recovery and energy storage system 40 is branched through an auxiliary flue gas pipeline and arranged on the main flue gas pipeline between the flue gas discharge pipe of the boiler 201 and the air preheater. Before the flue gas enters the air preheater, part of the flue gas is extracted and enters the flue gas waste heat deep recovery and energy storage system. After the heat of the flue gas is recovered, it is sent to the heat storage tank for storage and used to heat the boiler feed water in the regenerative system.

[0076] The regenerative system is arranged on the circulation loop 220 and is used to heat the medium in the circulation loop 220 by using the heat stored in the flue gas waste heat deep recovery and energy storage system 40.

[0077] The photovoltaic heat pump condensate waste heat recovery system 30 exchanges heat with the circulation loop 220 located between the steam turbine generator set and the regenerative system, and is used to recover the waste heat in the circulation loop 220 and store the recovered heat in the flue gas waste heat deep recovery and energy storage system 40. The photovoltaic heat pump condensate waste heat recovery system 30 is driven by photovoltaic power generation, recovers the waste heat of the steam turbine exhaust, and raises its temperature. The increased heat enters the third waste heat storage tank for storage and can be used for regenerative heating or flue gas reheating.

[0078] In the above-mentioned energy-saving system for a thermal power plant, the photovoltaic heat pump condensate waste heat recovery system 30 can recover the heat in the steam discharged from the steam turbine generator set and store the recovered heat in the flue gas waste heat deep recovery and energy storage system 40. Moreover, the heat of part of the flue gas discharged from the boiler 201 can be stored in the flue gas waste heat deep recovery and energy storage system 40, thereby achieving the purpose of deep utilization of waste heat.

[0079] The steam turbine generator set includes a steam turbine high-pressure cylinder 202, a steam turbine intermediate-pressure cylinder 203, and a steam turbine low-pressure cylinder 204.

[0080] The inner cavity of the high-pressure cylinder 202 of the steam turbine is connected to the high-temperature steam discharge pipe 218. The high-temperature steam generated by the boiler enters the high-pressure cylinder of the steam turbine, and the steam expands and does work inside the high-pressure cylinder 202 of the steam turbine, driving its rotation to generate mechanical energy. A steam return pipe 221 is connected to the outlet end of the high-pressure cylinder 202 of the steam turbine, and the steam return pipe 221 returns the discharged steam to the boiler for reheating.

[0081] The inner cavity of the intermediate-pressure cylinder 203 of the steam turbine is connected with a secondary steam discharge pipe 222. The high-pressure cylinder 202 of the steam turbine is connected and communicated with the secondary steam discharge pipe 222 through the steam return pipe 221. Part of the junction of the steam return pipe 221 and the secondary steam discharge pipe 222 is arranged inside the boiler, and the boiler reheats the steam in the steam return pipe 221 again. The steam reheated by the boiler enters the intermediate-pressure cylinder of the steam turbine, and the steam expands and does work, driving its rotation to generate mechanical energy. The discharged steam enters the low-pressure cylinder of the steam turbine.

[0082] The low-pressure cylinder 204 of the steam turbine is connected and communicated with the inner cavity of the intermediate-pressure cylinder 203 of the steam turbine through a steam connection pipe 223. The steam discharged from the intermediate-pressure cylinder 203 of the steam turbine enters the low-pressure cylinder 204 of the steam turbine, further expands and does work, driving its rotation to generate mechanical energy. The exhaust steam (about 35 °C) enters the condenser.

[0083] The rotating shafts of the high-pressure cylinder 202 of the steam turbine, the intermediate-pressure cylinder 203 of the steam turbine, and the low-pressure cylinder 204 of the steam turbine are connected in sequence.

[0084] The generator 205 is connected to the rotating shaft of the low-pressure cylinder 204 of the steam turbine, and is used to convert the mechanical energy generated by the rotation of the high-pressure cylinder 202 of the steam turbine, the intermediate-pressure cylinder 203 of the steam turbine, and the low-pressure cylinder 204 of the steam turbine into electrical energy.

[0085] A heat exchange is carried out between the circulation loop 220 and the photovoltaic heat pump condensate waste heat recovery system 30 through the first condenser 206, and the first condenser 206 is arranged on the circulation loop 220. Furthermore, the circulation loop 220 can transfer heat to the first condenser 206 to realize the recovery of the heat in the circulation loop 220. The first condenser is used to recover part of the steam turbine exhaust heat (cold source loss), and the amount of recovery depends on the photovoltaic power generation.

[0086] A second condenser 207 is also arranged on the circulation loop 220 behind the first condenser 206. The second condenser 207 is used to condense the medium in the circulation loop 220. The exhaust steam that cannot be recovered by heat enters the second condenser for further condensation to meet the standards for the steam to enter the condensate pump and the low-pressure regenerative heating system. That is, when the photovoltaic power generation is insufficient, the second condenser 207 condenses the steam turbine exhaust steam. The recovered condensate enters the condensate pump.

[0087] A condensate pump 208 is provided on the circulation loop 220 to increase the pressure of the condensate water entering the low-pressure regenerative system.

[0088] Further, the photovoltaic heat pump condensate waste heat recovery system 30 in this embodiment includes a working fluid annular circulation pipeline 306, a first heat pump heat exchanger 302, a heat pump compressor 303, a photovoltaic power generation system 301, and a second heat pump heat exchanger 304.

[0089] The first heat pump heat exchanger 302 is provided on the working fluid annular circulation pipeline 306 and exchanges heat with the first condenser 206. The first heat pump heat exchanger 302 uses the exhaust steam of the steam turbine as a cold source to recover the heat therein.

[0090] The heat pump compressor 303 is provided on the working fluid annular circulation pipeline 306 and drives the movement of the medium inside the working fluid annular circulation pipeline 306. The heat pump compressor 303 consumes the electric energy provided by the photovoltaic power generation system, compresses the working fluid to increase the temperature of the working fluid, so as to utilize renewable energy to improve the energy grade of the exhaust steam waste heat of the steam turbine.

[0091] The photovoltaic power generation system 301 is used to generate electric energy by using solar energy and drive the heat pump compressor 303 to act, and then drive the entire heat pump system to recover the exhaust steam heat (cold source loss) of the steam turbine. The heat pump compressor 303 in the present invention is driven by the electric energy generated by the photovoltaic power generation system 301, without consuming additional resources such as coal.

[0092] The second heat pump heat exchanger 304 is provided on the working fluid annular circulation pipeline 306 and exchanges heat with the flue gas waste heat deep recovery and energy storage system 40. The second heat pump heat exchanger 304 is used to discharge high-temperature heat, and the temperature can reach 120 °C, and the heat enters the third waste heat storage tank for storage.

[0093] A throttle valve 305 is also provided on the working fluid annular circulation pipeline 306 to reduce the pressure of the working fluid through the throttle valve 305, so that the medium enters the first heat pump heat exchanger 302 again to absorb heat.

[0094] The flue gas waste heat deep recovery and energy storage system 40 includes at least one stage of waste heat recovery heat exchanger and at least one waste heat storage tank. Each waste heat recovery heat exchanger is sequentially provided on the auxiliary flue gas pipeline and is used to exchange heat with the flue gas in the auxiliary flue gas pipeline. Each waste heat storage tank exchanges heat with each waste heat recovery heat exchanger and recovers and stores the heat in the flue gas.

[0095] More specifically, there are three stages of waste heat recovery heat exchangers, namely a first waste heat recovery heat exchanger 401, a second waste heat recovery heat exchanger 402, and a third waste heat recovery heat exchanger 403.

[0096] The first waste heat recovery heat exchanger 401 is used to recover the high-temperature waste heat of the flue gas, and the temperature of the recovered flue gas is 350°C to 200°C.

[0097] The second waste heat recovery heat exchanger 402 is used to recover the medium-temperature waste heat of the flue gas, and the temperature of the recovered flue gas is 200°C to 120°C.

[0098] The third waste heat recovery heat exchanger 403 is used to recover the low-temperature waste heat of the flue gas, and the temperature of the recovered flue gas is 120°C to 50°C.

[0099] There are three waste heat storage tanks, namely the first waste heat storage tank 404, the second waste heat storage tank 405, and the third waste heat storage tank 406.

[0100] The first waste heat storage tank 404 is a cascade heat storage tank, which is used to store heat from 350°C to 200°C. Heat exchange occurs between the first waste heat storage tank 404 and the first waste heat recovery heat exchanger 401.

[0101] The second waste heat storage tank 405 is a cascade heat storage tank, which is used to store heat from 200°C to 120°C. Heat exchange occurs between the second waste heat storage tank 405 and the second waste heat recovery heat exchanger 402.

[0102] The third waste heat storage tank 406 is a cascade heat storage tank, which is used to store heat from 120°C to 50°C. Heat exchange occurs between the third waste heat storage tank 406 and the third waste heat recovery heat exchanger 403. The third waste heat storage tank 406 is used to recover and store the heat transferred by the photovoltaic heat pump condensate waste heat recovery system 30.

[0103] The regenerative system includes a low-pressure regenerative heater group, a high-pressure regenerative heater group, a deaerator 213, and a feed water pump 214.

[0104] The low-pressure regenerative heater group includes a number of low-pressure regenerative heaters, which are arranged in sequence on the circulation loop 220; the low-pressure regenerative heater group is supplied with heat through the second waste heat storage tank 405 and the third waste heat storage tank 406, and then heats the medium on the circulation loop 220.

[0105] The low-pressure regenerative heater group includes a first low-pressure regenerative heater 212, a second low-pressure regenerative heater 211, a third low-pressure regenerative heater 210, and a fourth low-pressure regenerative heater 209 connected in sequence.

[0106] The fourth low-pressure regenerative heater 209 is used to increase the temperature of the condensate and heats the condensate using the steam extraction from the steam turbine. The inlet water is about 30°C.

[0107] The third low-pressure regenerative heater 210 is used to increase the temperature of the condensate and heats the condensate using the steam extraction from the steam turbine. The outlet water is about 85°C.

[0108] The second low-pressure regenerative heater 211 is used to increase the temperature of the condensate and heats the condensate by using the steam extraction of the steam turbine. The inlet water is about 85°C.

[0109] The first low-pressure regenerative heater 212 is used to increase the temperature of the condensate and heats the condensate by using the steam extraction of the steam turbine. The outlet water is about 150°C.

[0110] The high-pressure regenerative heater group includes several high-pressure regenerative heaters, and each high-pressure regenerative heater is sequentially arranged on the circulation loop 220. The high-pressure regenerative heaters are supplied with heat through the third waste heat storage tank 406, and then heat the medium on the circulation loop 220.

[0111] The high-pressure regenerative heater group includes a third high-pressure regenerative heater 215, a second high-pressure regenerative heater 216, and a first high-pressure regenerative heater 217 that are sequentially connected.

[0112] The third high-pressure regenerative heater 215 is used to increase the feed water temperature and heats the feed water by using the steam extraction of the steam turbine. The inlet water is about 190°C.

[0113] The second high-pressure regenerative heater 216 is used to increase the feed water temperature and heats the feed water by using the steam extraction of the steam turbine.

[0114] The first high-pressure regenerative heater 217 is used to increase the feed water temperature and heats the feed water by using the steam extraction of the steam turbine. The outlet water is about 320°C

[0115] The deaerator 213 is arranged on the circulation loop 220 between the low-pressure regenerative heater group and the high-pressure regenerative heater group, and is used to heat the water coming from the low-pressure heater by using the steam extraction of the steam turbine and remove the oxygen therein.

[0116] The feed water pump 214 is arranged on the circulation loop 220 between the low-pressure regenerative heater group and the high-pressure regenerative heater group, and is used to increase the feed water pressure entering the high-pressure regenerative heater group and the boiler.

[0117] The above-mentioned energy-saving system of the thermal power plant further includes a flue gas pollutant removal system 50, which is connected and arranged at the tail of the auxiliary flue gas pipeline. The flue gas after the waste heat recovery of the flue gas waste heat deep recovery and energy storage system 40 is processed through the flue gas pollutant removal system 50 to remove the pollutants in the flue gas and ensure that the treated flue gas will not pollute the environment.

[0118] Specifically, the flue gas pollutant removal system 50 includes a low-temperature electrostatic precipitator 501, an induced draft fan 502, a wet flue gas desulfurization device 503, a flue gas reheater 504, and a chimney 505 that are sequentially connected.

[0119] The low-temperature electrostatic precipitator 501 is used to remove the particulate matter in the flue gas to meet the environmental protection emission standards. The low temperature (about 50°C) can greatly improve the efficiency of the low-temperature electrostatic precipitator.

[0120] The induced draft fan 502 is used to provide wind pressure and drive the flue gas to flow.

[0121] The wet flue gas desulfurization device 503 is used to absorb sulfur-containing pollutants in the flue gas by using calcium oxide.

[0122] The flue gas reheater 504 is used to raise the temperature of the flue gas to above 85 °C, so as to reduce the low-temperature corrosion phenomenon in the chimney, reduce the visible effect of water vapor, and meet the environmental protection requirements.

[0123] As a further improved embodiment, a heat exchange is also carried out between the flue gas reheater 504 in this embodiment and the third waste heat storage tank 406. That is, the heat in the flue gas reheater 504 in this embodiment is the heat released by the third waste heat storage tank 406, thereby avoiding the purpose of energy loss caused by heating the flue gas reheater 504 with coal energy.

[0124] The chimney 505 is vertically arranged and is used to discharge the remaining flue gas.

[0125] As a further improved embodiment, this embodiment further improves the energy-saving system of the thermal power plant, that is, the energy-saving system of the thermal power plant is controlled by the waste heat deep utilization system 10. The waste heat deep utilization system 10 includes a thermal power unit 110, a multi-stage flue gas and condensate waste heat recovery system 120, a flue gas and condensate waste heat energy storage and peak shaving system 130, and a controller 140.

[0126] Among them, the thermal power unit 110 and the multi-stage flue gas and condensate waste heat recovery system 120 are respectively connected to the controller 140 for interaction. The flue gas and condensate waste heat energy storage and peak shaving system 130 is used to adjust the multi-stage flue gas and condensate waste heat recovery system 120 according to the unit operation status and load demand, store energy during low load of the unit, supply energy during high load, improve the variable working condition efficiency of the unit and reduce the energy loss of the boiler during low load, so as to achieve the purpose of energy storage and peak shaving.

[0127] Embodiment 2

[0128] This embodiment discloses a waste heat deep utilization method, which is carried out based on the energy-saving system of the thermal power plant and includes the following steps:

[0129] S1. Part of the flue gas discharged from the boiler 201 enters the flue gas waste heat deep recovery and energy storage system 40 for waste heat recovery. The flue gas exchanges heat with the multi-stage waste heat recovery heat exchanger, and each stage of the waste heat recovery heat exchanger respectively recovers and stores the heat in each waste heat storage tank.

[0130] More specifically, the specific steps of step S1 are as follows:

[0131] After the flue gas of the boiler 201 passes through the economizer and before entering the air preheater (about 350 °C), the flue gas is divided into two parts. Since the heat transfer efficiency of the air preheater is relatively low at this stage and the loss is large, the heat transfer amount in the air preheater is reduced, and this part of the heat transfer amount is input into the second waste heat storage tank 405 or the third waste heat storage tank 406 for heat exchange, which will not be elaborated in the attached drawings of the specification.

[0132] The flue gas separated from the boiler 201 enters the flue gas waste heat deep recovery and energy storage system 40:

[0133] First, it enters the first waste heat recovery heat exchanger 401 to recover the high-temperature waste heat of the flue gas, with the temperature approximately ranging from 350 °C to 200 °C. The recovered heat enters the first waste heat storage tank 404 for storage.

[0134] Subsequently, the flue gas enters the second waste heat recovery heat exchanger 402 to recover the medium-temperature waste heat of the flue gas, with the temperature approximately ranging from 200 °C to 120 °C. The recovered heat enters the second waste heat storage tank 405 for storage.

[0135] Finally, the flue gas enters the third waste heat recovery heat exchanger 403 to recover the low-temperature waste heat of the flue gas, with the temperature approximately ranging from 120 °C to 50 °C. The recovered heat enters the third waste heat storage tank 406 for storage. Using a three-stage waste heat recovery system to recover the flue gas waste heat in a graded and gradient manner can greatly reduce the irreversible loss in the flue gas waste heat recovery.

[0136] S2. The flue gas after waste heat recovery in step S1 enters the flue gas pollutant removal system 50 for flue gas treatment.

[0137] More specifically, the specific steps of step S2 are as follows:

[0138] The temperature of the flue gas after waste heat recovery has dropped below 50 °C and enters the flue gas pollutant removal system 50, where the low-low temperature electrostatic precipitator 501 has better removal efficiency and lower energy consumption levels at a lower flue gas temperature.

[0139] Subsequently, it enters the wet flue gas desulfurization device 503 to remove sulfur-containing pollutants in the flue gas.

[0140] Finally, it enters the flue gas reheater 504, and the flue gas temperature is raised to 85 °C again and then discharged to the chimney 505. The energy source of the flue gas reheater is the third waste heat storage tank. Raising the flue gas temperature can greatly reduce the low-temperature corrosion problem in the tail flue and the visible effect of water vapor (commonly known as "dewhiting").

[0141] S3. The high-temperature steam generated by the boiler 201 enters the steam turbine generator set for power generation and then enters the first condenser 206, and the waste heat in the medium discharged from the steam turbine generator set is recovered through the photovoltaic heat pump condensate waste heat recovery system 30. The photovoltaic heat pump condensate waste heat recovery system 30 stores the recovered heat through the flue gas waste heat deep recovery and energy storage system 40.

[0142] More specifically, the specific steps of step S3 are as follows:

[0143] The high-temperature steam generated by the boiler 201 enters the high-pressure cylinder 202, intermediate-pressure cylinder 203, and low-pressure cylinder 204 of the steam turbine, and after generating electricity through the steam turbine generator set, it enters the first condenser 206 to recover most of the exhaust heat.

[0144] Among them, the waste heat is recovered by the photovoltaic heat pump condensate waste heat recovery system 30, which is driven by the electric power generated by the photovoltaic power generation system 301, improves the energy grade of the exhaust heat, raises it from about 35°C to 120°C, and the recovered heat enters the third waste heat storage tank 406 for storage. When the photovoltaic power generation system 301 is not sufficient to drive the heat pump system, the second condenser 207 condenses the exhaust steam.

[0145] S4. The medium on the circulation loop 220 after heat exchange in step S3 enters the regenerative system for heating. The heating heat of the regenerative system comes from the heat stored in the flue gas waste heat deep recovery and energy storage system 40, and the medium after being heated by the regenerative system returns to the boiler 201.

[0146] Among them, the waste heat storage tanks in the flue gas waste heat deep recovery and energy storage system 40 are three-stage waste heat storage tanks, and all three-stage waste heat storage tanks are cascade heat storage tanks, which can store the temperature in stages. The three-stage storage temperatures are 350°C to 200°C, 200°C to 120°C, and 120°C to 50°C respectively.

[0147] The heat of the first waste heat storage tank 404 is used to heat part of the feed water. The working medium is separated after the feed water pump 214 (about 190°C) and enters after the first high-pressure regenerative heater 217 (about 350°C).

[0148] The heat of the second waste heat storage tank 405 is used to heat part of the condensate. The working medium is separated before the second low-pressure regenerative heater 211 (about 110°C) and enters after the first low-pressure regenerative heater 212 (about 180°C).

[0149] The third waste heat storage tank 406 is used to heat part of the condensate and provide heat for the flue gas reheater 504. The condensate is separated after the condensate pump 208 (about 35°C) and enters after the third low-pressure regenerative heater 210 (about 110°C).

[0150] The three-stage heat storage can store the corresponding temperatures separately and utilize them in a cascade manner, which can improve the degree of energy cascade utilization, the waste heat utilization level, and the energy-saving level of the entire unit.

[0151] Example 3

[0152] This embodiment discloses an operation method of an energy-saving system for a thermal power plant. The entire energy-saving system of the thermal power plant is designed based on the rated capacity of the coal-fired thermal power generating unit.

[0153] As Figure 6 shown, the operation method of the energy-saving system for the thermal power plant includes the following steps:

[0154] S101. Obtain the unit operation status and load demand.

[0155] S102. Control the flue gas waste heat deep recovery and energy storage system 40 to provide heat for the feed water of the unit according to the unit operation status and load demand, so as to ensure a constant feed water temperature or the highest unit efficiency.

[0156] When the system operates at a load lower than the design load, especially at a relatively low load, the heat generated by the boiler will be greater than the energy that can be utilized by the steam turbine. A large amount of waste heat generated can be completely recovered by the three-stage waste heat storage tank and the heat is stored for the following two purposes:

[0157] One, the stored heat is used to heat part of the working medium in the regenerative system of the steam turbine unit, and the flue gas heat is fully recovered into the regenerative system and returned to the cycle of the steam turbine generator set to improve the power generation efficiency;

[0158] Two, when the entire generator set rapidly increases the load, since the heat release rate of the heat storage tank is greater than the load increase rate of the boiler, a large amount of heat in the heat storage tank can be released to quickly increase the temperature of the working medium, so as to accelerate the system load change speed. On the contrary, when the unit rapidly decreases the load, the waste heat generated by the boiler that cannot be decreased in time can be quickly stored to reduce energy waste.

[0159] And this embodiment combines waste heat utilization and energy storage technologies to realize energy storage during low load of the unit and energy supply during high load, improve the unit's off-design efficiency, reduce the energy loss of the boiler during low load, and achieve the purpose of energy storage peak shaving.

[0160] Obviously, the above embodiments are only examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or alterations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or alterations derived therefrom are still within the protection scope of the present invention.

Claims

1. The energy-saving system of a thermal power plant is characterized in that, Comprising: A boiler (201) for providing heat energy for a thermal power plant; a high-temperature steam discharge pipe (218) and a flue gas discharge pipe (219) are arranged on the boiler (201), and a steam turbine generator set for generating electricity by using the high-temperature steam discharged from the boiler (201) is connected to the high-temperature steam discharge pipe; the steam outlet end of the steam turbine generator set is connected to the boiler (201) through a circulation loop (220); A flue gas waste heat deep recovery and energy storage system (40), which is branched through an auxiliary flue gas pipeline on the main flue gas pipeline between the flue gas discharge pipe of the boiler (201) and the air preheater, and is used for receiving a part of the flue gas discharged from the boiler (201) and storing the recovered flue gas heat; A regenerative system, which is arranged on the circulation loop (220) and is used for heating the medium in the circulation loop (220) by using the heat stored in the flue gas waste heat deep recovery and energy storage system (40); A photovoltaic heat pump condensate waste heat recovery system (30), which exchanges heat with the circulation loop (220) located between the steam turbine generator set and the regenerative system, and is used for recovering the waste heat in the circulation loop (220) and storing the recovered heat in the flue gas waste heat deep recovery and energy storage system (40); Heat exchange is carried out between the circulation loop (220) and the photovoltaic heat pump condensate waste heat recovery system (30) through a first condenser (206), and the first condenser (206) is arranged on the circulation loop (220); a condensate pump (208) is arranged on the circulation loop (220); The flue gas waste heat deep recovery and energy storage system (40) includes a waste heat recovery heat exchanger and a waste heat storage tank; the waste heat recovery heat exchanger has three stages, namely a first waste heat recovery heat exchanger (401), a second waste heat recovery heat exchanger (402), and a third waste heat recovery heat exchanger (403), which are sequentially arranged on the auxiliary flue gas pipeline and are used for exchanging heat with the flue gas in the auxiliary flue gas pipeline; there are three waste heat storage tanks, namely a first waste heat storage tank (404), a second waste heat storage tank (405), and a third waste heat storage tank (406); heat exchange is carried out between the first waste heat storage tank (404) and the first waste heat recovery heat exchanger (401), heat exchange is carried out between the second waste heat storage tank (405) and the second waste heat recovery heat exchanger (402), and heat exchange is carried out between the third waste heat storage tank (406) and the third waste heat recovery heat exchanger (403); the third waste heat storage tank (406) is used for recovering and storing the heat transmitted by the photovoltaic heat pump condensate waste heat recovery system (30); The regenerative system includes: A low-pressure regenerative heater group, which includes a plurality of low-pressure regenerative heaters and each low-pressure regenerative heater is sequentially arranged on the circulation loop (220); the low-pressure regenerative heater group is supplied with heat through the second waste heat storage tank (405) and the third waste heat storage tank (406), so as to heat the medium on the circulation loop (220); The high-pressure regenerative heater group includes several high-pressure regenerative heaters, and each high-pressure regenerative heater is sequentially arranged on the circulation loop (220); the high-pressure regenerative heater is supplied with heat through the third waste heat storage tank (406), and then heats the medium on the circulation loop (220). The deaerator (213) is arranged on the circulation loop (220) between the low-pressure regenerative heater group and the high-pressure regenerative heater group, and is used to remove oxygen in the medium in the circulation loop (220). The feed water pump (214) is arranged on the circulation loop (220) between the low-pressure regenerative heater group and the high-pressure regenerative heater group, and is used to increase the feed water pressure entering the high-pressure regenerative heater group and the boiler.

2. The energy-saving system of a thermal power plant according to claim 1, is characterized in that, A second condenser (207) is also arranged on the circulation loop (220) behind the first condenser (206), and the second condenser (207) is used to condense the medium in the circulation loop (220).

3. The energy-saving system of a thermal power plant according to claim 1, is characterized in that, The photovoltaic heat pump condensate waste heat recovery system (30) includes: The working medium annular circulation pipeline (306); The first heat pump heat exchanger (302) is arranged on the working medium annular circulation pipeline (306) and exchanges heat with the first condenser (206). The heat pump compressor (303) is arranged on the working medium annular circulation pipeline (306) and drives the movement of the medium inside the working medium annular circulation pipeline (306). The photovoltaic power generation system (301) is used to generate electric energy by using solar energy and drive the heat pump compressor (303) to operate. The second heat pump heat exchanger (304) is arranged on the working medium annular circulation pipeline (306) and exchanges heat with the flue gas waste heat deep recovery and energy storage system (40).

4. The energy-saving system of a thermal power plant according to claim 3, is characterized in that, A throttle valve (305) is also arranged on the working medium annular circulation pipeline (306).

5. The energy-saving system of a thermal power plant according to any one of claims 1 to 4, is characterized in that, The steam turbine generator set includes: The high-pressure cylinder of the steam turbine (202), the inner cavity of which is connected to the high-temperature steam discharge pipe (218), and is used to rotate by using the high-temperature steam generated by the boiler. The intermediate-pressure cylinder of the steam turbine (203), the inner cavity of which is connected with a secondary steam discharge pipe (222). The high-pressure cylinder of the steam turbine (202) is connected to the secondary steam discharge pipe (222) through a steam return pipe (221). Part of the junction of the steam return pipe (221) and the secondary steam discharge pipe (222) is arranged inside the boiler, and the boiler reheats the steam in the steam return pipe (221). The low-pressure cylinder of the steam turbine (204) is connected to the inner cavity of the intermediate-pressure cylinder of the steam turbine (203) through a steam connection pipe (223); the rotating shafts of the high-pressure cylinder of the steam turbine (202), the intermediate-pressure cylinder of the steam turbine (203), and the low-pressure cylinder of the steam turbine (204) are sequentially connected. The generator (205) is connected to the rotating shaft of the low-pressure cylinder of the steam turbine (204), and is used to convert the mechanical energy generated by the rotation of the high-pressure cylinder of the steam turbine (202), the intermediate-pressure cylinder of the steam turbine (203), and the low-pressure cylinder of the steam turbine (204) into electric energy.

6. The energy-saving system of a thermal power plant according to any one of claims 1 to 4, is characterized in that, It also includes: The flue gas pollutant removal system (50) is connected to the tail of the auxiliary flue gas pipeline and is used to remove pollutants in the flue gas.

7. The method for deep utilization of waste heat of the energy-saving system of a thermal power plant according to any one of claims 1 to 6, is characterized in that, It includes the following steps: S1. Part of the flue gas discharged from the boiler (201) enters the flue gas waste heat deep recovery and energy storage system (40) for waste heat recovery: The flue gas exchanges heat with the multi-stage waste heat recovery heat exchanger, and each stage of the waste heat recovery heat exchanger respectively recovers and stores the heat in each waste heat storage tank; S2. The flue gas after waste heat recovery in step S1 enters the flue gas pollutant removal system (50) for flue gas treatment; S3. The high-temperature steam generated by the boiler (201) enters the steam turbine generator set for power generation and then enters the first condenser (206), and the waste heat in the medium discharged from the steam turbine generator set is recovered through the photovoltaic heat pump condensate waste heat recovery system (30). The photovoltaic heat pump condensate waste heat recovery system (30) stores the recovered heat through the flue gas waste heat deep recovery and energy storage system (40); S4. The medium on the circulating loop (220) after heat exchange in step S3 enters the regenerative system for heating. The heating heat of the regenerative system comes from the heat stored in the flue gas waste heat deep recovery and energy storage system (40), and the medium heated by the regenerative system returns to the boiler (201).

8. The operation method of the energy-saving system for a thermal power plant according to any one of claims 1 to 6, characterized in that, It includes the following steps: S101. Obtain the unit operation status and load demand; S102. Control the flue gas waste heat deep recovery and energy storage system (40) to provide heat for the feed water of the unit according to the unit operation status and load demand, so as to ensure a constant feed water temperature or the highest unit efficiency.

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