Thermal power plant waste heat recovery and energy storage system and method

Abstract

The invention relates to a heat-engine plant waste heat recovery and energy storage system and method.The heat-engine plant waste heat recovery and energy storage system comprises an air heater, a heating medium water pump, a heat pump circulation unit and a heat storage unit connected with the heat pump circulation unit, and an air preheater, a high-temperature flue gas heat exchanger, a medium-temperature flue gas heat exchanger and a low-temperature flue gas heat exchanger are arranged in a boiler flue; the high-temperature flue gas heat exchanger absorbs heat through high-pressure water supply and discharges the heat to a coal economizer, the medium-temperature flue gas heat exchanger absorbs heat through low-pressure water supply and discharges the heat to a deaerator, and the low-temperature flue gas heat exchanger is connected with an air heater through a heating medium water pump and provides a preheating heat source for an air preheater. The medium-temperature flue gas heat exchanger and the low-temperature flue gas heat exchanger are connected with the heat pump circulating unit, flue gas heat is stored by the heat storage unit, the heat storage unit is connected with the air preheater and provides an air bin heat source for the air preheater, and the high-pressure heater can absorb heat from the heat storage unit and discharge the heat to the economizer. The operation flexibility of the generator set is improved, and meanwhile the probability of the dust deposition and scaling phenomena of the air preheater can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of waste heat recovery from thermal power generation, and particularly to a waste heat recovery and energy storage system and method for a thermal power plant. Background Art

[0002] China's energy structure is accelerating its transformation towards clean and low-carbon, and the scale of renewable energy power generation continues to expand. Coal-fired power plants are transforming from the main energy source to a regulating and standby power source, which in turn poses new urgent technical requirements for the coal-fired power generation industry, mainly reflected in: continuously improving energy utilization efficiency to reduce carbon emissions, and continuously enhancing operation flexibility to support the grid's consumption of new energy power generation.

[0003] In coal-fired generating units, due to the limitations of characteristics such as large boiler inertia, minimum stable combustion load, and energy flow coupling between the boiler and steam turbine, the operation flexibility of thermal power units in responding to the frequent and large-scale frequency modulation and peak shaving requirements of the power grid is insufficient. And the flue gas loss is the largest loss in the boiler, carrying a large amount of available heat and discharging it into the environment. If this part of the flue gas waste heat can be recovered and utilized, it can effectively improve the energy efficiency of the generating unit and reduce pollutant emissions.

[0004] As an important device for improving the thermal efficiency of heating furnaces, the air preheater is used to recover and utilize the waste heat of flue gas, reduce the heat loss carried away by the exhaust gas, and reduce the fuel consumption of the heating furnace. For coal-fired generating units, the combustion products usually contain sulfur trioxide and water vapor. When the metal wall temperature of the heat storage element filled inside the air preheater is lower than the dew point of sulfuric acid vapor, it will condense into liquid sulfuric acid, corroding the metal heat storage element. At the same time, the fly ash particles in the flue gas are easily adhered to the surface of the heat storage element, causing ash accumulation and fouling, resulting in a reduction in the heat transfer efficiency of the air preheater and an increase in the flow resistance. Summary of the Invention

[0005] To solve at least one of the above technical problems, the present invention proposes a waste heat recovery and energy storage system and method for a thermal power plant.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The present invention provides a waste heat recovery and energy storage system for a thermal power plant, which includes a boiler flue, a warm air heater, a heat medium water pump, a heat pump cycle unit, and a heat storage unit connected to the heat pump cycle unit. An air preheater, a high-temperature flue gas heat exchanger, a medium-temperature flue gas heat exchanger, and a low-temperature flue gas heat exchanger are provided in the boiler flue. The high-temperature flue gas heat exchanger absorbs heat through the connected high-pressure feedwater heater and discharges it to the economizer. The medium-temperature flue gas heat exchanger absorbs heat through the connected low-pressure feedwater heater and discharges it to the deaerator. The low-temperature flue gas heat exchanger is connected to the warm air heater through the heat medium water pump and provides a preheating heat source for the air preheater through the warm air heater. The medium-temperature flue gas heat exchanger and the low-temperature flue gas heat exchanger are connected to the heat pump cycle unit and store the flue gas heat by the heat storage unit. The heat storage unit is connected to the air preheater and provides a wind chamber heat source for the air preheater. The high-pressure feedwater heater can also absorb heat from the heat storage unit and discharge it to the economizer;

[0008] The heat storage unit includes a heat storage chamber, a heat exchange chamber, a heat storage end, and a heat release end. A heat storage material is provided in the heat storage chamber. The heat storage end is communicated with the heat storage chamber. The heat release end includes a circulating cold air inlet, a circulating hot air outlet, a working medium inlet, and a working medium outlet communicated with the heat exchange chamber. The cold side outlet of the third heat exchanger is connected to the heat storage end of the heat storage unit. The circulating cold air inlet is connected to the air outlet of the air preheater wind chamber. The circulating hot air outlet is connected to the air inlet of the wind chamber.

[0009] As a further improvement, the working medium inlet is connected to the high-pressure feedwater heater, and the working medium outlet is connected to the economizer.

[0010] As a further improvement, the air preheater includes a flue gas chamber, a primary air compartment, and a secondary air compartment. The secondary air compartment is separated by a partition to form a circulating heating compartment. The air inlet of the circulating heating compartment is connected to the circulating hot air outlet of the heat storage unit, and the air outlet of the circulating heating compartment is connected to the circulating cold air inlet of the heat storage unit.

[0011] As a further improvement, the heat pump cycle unit includes a first heat exchanger, a second heat exchanger, a compressor, a third heat exchanger, and an expander. The hot side inlet of the first heat exchanger is connected to the working medium outlet of the medium-temperature flue gas heat exchanger, and the hot side outlet is connected to the working medium inlet of the medium-temperature flue gas heat exchanger. The hot side inlet of the second heat exchanger is connected to the working medium outlet of the low-temperature flue gas heat exchanger, and the hot side outlet is connected to the working medium inlet of the low-temperature flue gas heat exchanger. The cold side outlet of the first heat exchanger is connected to the suction port of the compressor. The discharge port of the compressor is connected to the hot side inlet of the third heat exchanger. The hot side outlet of the third heat exchanger is connected to the suction port of the expander. The discharge port of the expander is connected to the cold side inlet of the second heat exchanger. The cold side outlet of the second heat exchanger is connected to the cold side inlet of the first heat exchanger.

[0012] As a further improvement, the heat pump cycle unit further includes a recuperator; the cold-side outlet of the first heat exchanger is also connected to the cold-side inlet of the recuperator, the cold-side outlet of the recuperator is connected to the suction port of the compressor, the discharge port of the compressor is connected to the hot-side inlet of the third heat exchanger, the hot-side outlet of the third heat exchanger is connected to the hot-side inlet of the recuperator, and the hot-side outlet of the recuperator is connected to the suction port of the expander.

[0013] As a further improvement, a first valve is provided on the pipeline connecting the working medium outlet of the low-temperature flue gas heat exchanger to the hot-side inlet of the second heat exchanger, a second valve is provided on the pipeline connecting the working medium outlet of the medium-temperature flue gas heat exchanger to the hot-side inlet of the first heat exchanger, a third valve is provided on the pipeline connecting the low-pressure feedwater heater feedwater to the medium-temperature flue gas heat exchanger, and a fourth valve is provided on the pipeline connecting the high-pressure feedwater heater feedwater to the working medium inlet of the heat storage unit.

[0014] As a further improvement, a fifth valve is provided on the pipeline connecting the air outlet of the air preheater air chamber to the circulating cold air inlet of the heat storage unit.

[0015] As a further improvement, the boiler flue is divided into a main flue and a bypass flue by a flue gas baffle. The air preheater is arranged in the main flue, the high-temperature flue gas heat exchanger and the medium-temperature flue gas heat exchanger are arranged in the bypass flue according to the flue gas flow direction, and the low-temperature flue gas heat exchanger is arranged at the tail of the boiler flue.

[0016] A waste heat recovery and energy storage system for a thermal power plant provided by the present invention includes a boiler flue, a warm air heater, a heat medium water pump, a heat pump cycle unit, and a heat storage unit connected to the heat pump cycle unit. An air preheater, a high-temperature flue gas heat exchanger, a medium-temperature flue gas heat exchanger, and a low-temperature flue gas heat exchanger are arranged in the boiler flue. The high-temperature flue gas heat exchanger absorbs heat through the connected high-pressure feedwater heater feedwater and discharges it to the economizer. The medium-temperature flue gas heat exchanger absorbs heat through the connected low-pressure feedwater heater feedwater and discharges it to the deaerator. The low-temperature flue gas heat exchanger is connected to the warm air heater through the heat medium water pump and provides a preheating heat source for the air preheater through the warm air heater. The medium-temperature flue gas heat exchanger and the low-temperature flue gas heat exchanger are connected to the heat pump cycle unit, and the flue gas heat is stored by the heat storage unit. The heat storage unit is connected to the air preheater and provides an air chamber heat source for the air preheater. The high-pressure feedwater heater feedwater can also absorb heat from the heat storage unit and discharge it to the economizer. The heat storage unit includes a heat storage cavity, a heat exchange cavity, a heat storage end, and a heat release end. A heat storage material is arranged in the heat storage cavity. The heat storage end is communicated with the heat storage cavity. The heat release end includes a circulating cold air inlet, a circulating hot air outlet, a working medium inlet, and a working medium outlet communicated with the heat exchange cavity. The cold-side outlet of the third heat exchanger is connected to the heat storage end of the heat storage unit. The circulating cold air inlet is connected to the air outlet of the air preheater air chamber. The circulating hot air outlet is connected to the air inlet of the air chamber. By coupling the heat storage and heat release processes, the operation flexibility of the generator set is improved, the time-varying load rate during peak shaving and frequency modulation is increased, and the unit is assisted in stable frequency modulation. At the same time, the probability of ash accumulation and scaling in the air preheater can also be reduced.

[0017] The present invention also provides a method for recovering and storing waste heat in a thermal power plant, including any further improvement of the waste heat recovery and energy storage system in a thermal power plant as described above. The response to the unit's frequency modulation and peak shaving requirements is as follows:

[0018] When the unit does not participate in frequency modulation and peak shaving, the heat pump cycle unit stops operating. The low-pressure feedwater absorbs the heat of the flue gas in the medium-temperature flue gas heat exchanger and is discharged to the deaerator. The high-pressure feedwater absorbs the heat of the flue gas in the high-temperature flue gas heat exchanger and is discharged to the economizer. The heat of the low-temperature flue gas heat exchanger provides preheating heat to the air preheater air chamber through the air heater.

[0019] When the unit reduces load during peak shaving and frequency modulation or operates at a deep low load, stop injecting low-pressure feedwater into the medium-temperature flue gas heat exchanger, and turn on the heat pump cycle unit to store heat in the heat storage unit.

[0020] When the unit increases load during peak shaving and frequency modulation, the heat pump cycle unit stops operating. The low-pressure feedwater absorbs the heat of the flue gas in the medium-temperature flue gas heat exchanger and is discharged to the deaerator. The high-pressure feedwater absorbs the heat of the flue gas in the high-temperature flue gas heat exchanger and is discharged to the economizer. At the same time, the high-pressure feedwater also absorbs the stored heat from the heat storage unit and is discharged to the economizer.

[0021] As a further improvement, when the ash deposition tendency of the air preheater increases under the unit's frequency modulation and peak shaving requirements, the air preheater absorbs the stored heat from the heat storage unit as the heat source of the air chamber to increase the temperature of the heat storage elements of the air preheater.

[0022] A method for recovering and storing waste heat in a thermal power plant provided by the present invention should have the same or corresponding technical effects due to adopting the technical content of the waste heat recovery and energy storage system in a thermal power plant as described above, and thus will not be elaborated here. Description of the Drawings

[0023] Figure 1 is a schematic structural diagram of the present invention;

[0024] Figure 2 is a schematic structural diagram of the air preheater of the present invention. Detailed Embodiments

[0025] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the drawings and specific embodiments. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0026] Combined with Figure 1As shown in the figure, an embodiment of the present invention provides a waste heat recovery and energy storage system for a thermal power plant, which includes a boiler flue 1, a warm air heater 7, a heat medium water pump 8, a heat pump cycle unit, and a heat storage unit 13 connected to the heat pump cycle unit. An air preheater 2, a high-temperature flue gas heat exchanger 4, a medium-temperature flue gas heat exchanger 5, and a low-temperature flue gas heat exchanger 6 are provided in the boiler flue 1. Specifically, as Figure 1 shown, a economizer and a denitration device are arranged in the boiler flue 1 in the direction of flue gas flow. The denitration methods of the denitration device include, but are not limited to: SCR denitration, SNCR denitration, PNCR denitration, or SNCR+PNCR combined denitration, etc. Then, the flue gas is separated by a flue gas baffle 3 to form a main flue and a bypass flue. The purpose of setting the flue gas baffle 3 is to facilitate the flue gas in the main flue to flow into the bypass flue, which is convenient for recovering and treating the heat of the flue gas. The air preheater 2 is arranged in the main flue. The high-temperature flue gas heat exchanger 4 and the medium-temperature flue gas heat exchanger 5 are arranged in the bypass flue in the direction of flue gas flow. The low-temperature flue gas heat exchanger 6 is arranged at the tail of the boiler flue 1.

[0027] The working medium inlet of the high-temperature flue gas heat exchanger 4 is connected to the feed water of the high-pressure heater, and the working medium outlet is connected to the economizer. The high-temperature flue gas heat exchanger 4 absorbs heat through the connected feed water of the high-pressure heater and discharges it to the economizer. The working medium inlet of the medium-temperature flue gas heat exchanger 5 is connected to the feed water of the low-pressure heater, and the working medium outlet is connected to the deaerator. The medium-temperature flue gas heat exchanger 5 absorbs heat through the connected feed water of the low-pressure heater and discharges it to the deaerator. The working medium outlet of the low-temperature flue gas heat exchanger 6 is connected to the working medium inlet of the warm air heater 7 through the heat medium water pump 8. The working medium outlet of the warm air heater 7 is connected to the working medium inlet of the low-temperature flue gas heat exchanger 6. The air outlet of the warm air heater 7 is connected to the air inlet of the air preheater 2. The low-temperature flue gas heat exchanger 6 provides a preheating heat source for the air preheater 2 through the warm air heater 7 via the heat medium water pump 8. The medium-temperature flue gas heat exchanger 5 and the low-temperature flue gas heat exchanger 6 are connected to the heat pump cycle unit and store the heat of the flue gas by the heat storage unit 13. The heat storage unit 13 is connected to the air preheater 2 and provides a wind chamber heat source for the air preheater 2. The feed water of the high-pressure heater can also absorb heat from the heat storage unit 13 and discharge it to the economizer.

[0028] The heat storage unit 13 includes a heat storage chamber, a heat exchange chamber, a heat storage end, and a heat release end. The heat storage chamber is provided with a high-temperature heat storage material, or both high-temperature and low-temperature heat storage materials are provided simultaneously to improve the heat storage efficiency in the heat storage chamber. The heat storage material can be selected but is not limited to molten salt or heat transfer oil. Among them, heat transfer oil, as a heat transfer medium, has strong antioxidant and anti-coking properties; the molten salt technology uses the heat cycle of molten salt to achieve the purpose of heat storage. Compared with heat transfer oil, when the working fluid temperature is above 400°C, molten salt has advantages in terms of the price and service life of the heat transfer medium. Therefore, it is selected according to production requirements. The heat storage end is connected to the heat storage chamber. The heat release end includes a circulating cold air inlet, a circulating hot air outlet, a working fluid inlet, and a working fluid outlet that communicate with the heat exchange chamber. The cold-side outlet of the third heat exchanger 12 is connected to the heat storage end of the heat storage unit 13. The circulating cold air inlet is connected to the air outlet of the air preheater 2 air chamber, and the circulating hot air outlet is connected to the air inlet of the air chamber. The air preheater 2 in the embodiment of the present invention can be selected but is not limited to a three-chamber rotary air preheater. Specifically, the air preheater 2 includes a flue gas chamber 21, a primary air chamber 22, and a secondary air chamber 23. The secondary air chamber 23 is separated by a partition 231 to form a circulating heating chamber 232. The air inlet of the circulating heating chamber 232 is connected to the circulating hot air outlet of the heat storage unit 13, and the air outlet of the circulating heating chamber 232 is connected to the circulating cold air inlet of the heat storage unit 13, so as to absorb heat from the heat storage unit 13 to increase the temperature of the cold-end heat storage element of the air preheater 2 and reduce the ash deposition tendency of the air preheater 2.

[0029] In an embodiment of the present invention, a waste heat recovery and energy storage system for a thermal power plant responds to the unit frequency modulation and peak shaving requirements as follows:

[0030] When the unit does not participate in frequency modulation and peak shaving, the heat pump cycle unit stops operating. The low-pressure feedwater heater feedwater absorbs the heat of the flue gas in the medium-temperature flue gas heat exchanger 5 and is discharged to the deaerator. The high-pressure feedwater heater feedwater absorbs the heat of the flue gas in the high-temperature flue gas heat exchanger 4 and is discharged to the economizer, reducing the flue gas discharge temperature and heat loss of the boiler and effectively improving the economic benefits of the generator set. At the same time, the heat of the low-temperature flue gas heat exchanger 6 is provided to the air preheater 2 air chamber through the air heater 7 for preheating heat. The preheated air of the air preheater 2 is sent to the boiler after heating to assist combustion and reduce the consumption of coal fuel;

[0031] When the unit reduces load during frequency modulation and peak shaving or operates at a deep low load, the injection of low-pressure feedwater heater feedwater into the medium-temperature flue gas heat exchanger 5 is stopped, and the injection of high-pressure feedwater heater feedwater into the high-temperature flue gas heat exchanger 4 works normally. The heat pump cycle unit is turned on to store heat in the heat storage unit 13;

[0032] When the unit adjusts the peak load and frequency modulation to increase the load, the heat pump cycle unit stops operating. The feed water of the low-pressure heater absorbs the heat of the flue gas in the medium-temperature flue gas heat exchanger 5 and is discharged to the deaerator. The feed water of the high-pressure heater absorbs the heat of the flue gas in the high-temperature flue gas heat exchanger 4 and is discharged to the economizer. At the same time, the feed water of the high-pressure heater also absorbs the stored heat from the heat storage unit 13 and is discharged to the economizer. The high-pressure feed water is heated by the high-temperature flue gas heat exchanger 4 and the heat storage unit 13 together, which can reduce the extraction steam volume of the high-pressure heater and achieve a rapid increase in load.

[0033] During the peak load regulation and frequency modulation of the unit, when the air preheater 2 has a tendency to accumulate ash, the air preheater 2 can absorb the stored heat from the heat storage unit 13 as the heat source of the air chamber to increase the temperature of the heat storage elements of the air preheater 2 and reduce the probability of ash fouling on the air preheater 2.

[0034] An embodiment of the present invention provides a waste heat recovery and energy storage system for a thermal power plant. By coupling the heat storage and heat release processes, the flexibility of the generator set operation is improved, the variable load rate during peak load regulation and frequency modulation is increased, and the unit is assisted in stable frequency modulation. At the same time, the probability of ash fouling on the air preheater 2 can also be reduced.

[0035] Embodiment 1 of the present invention:

[0036] The heat pump cycle unit includes a first heat exchanger 9, a second heat exchanger 10, a compressor 11, a third heat exchanger 12, and an expander 14. The hot-side inlet of the first heat exchanger 9 is connected to the working medium outlet of the medium-temperature flue gas heat exchanger 5, the hot-side outlet is connected to the working medium inlet of the medium-temperature flue gas heat exchanger 5. The hot-side inlet of the second heat exchanger 10 is connected to the working medium outlet of the low-temperature flue gas heat exchanger 6, the hot-side outlet is connected to the working medium inlet of the low-temperature flue gas heat exchanger 6. The cold-side outlet of the first heat exchanger 9 is connected to the suction port of the compressor 11, the discharge port of the compressor 11 is connected to the hot-side inlet of the third heat exchanger 12, the hot-side outlet of the third heat exchanger 12 is connected to the suction port of the expander 14, the discharge port of the expander 14 is connected to the cold-side inlet of the second heat exchanger 10, and the cold-side outlet of the second heat exchanger 10 is connected to the cold-side inlet of the first heat exchanger 9.

[0037] Embodiment 2 of the present invention:

[0038] As Figure 1As shown in the figure, the heat pump cycle unit includes a first heat exchanger 9, a second heat exchanger 10, a regenerator 15, a compressor 11, a third heat exchanger 12, and an expander 14. The hot-side inlet of the first heat exchanger 9 is connected to the working fluid outlet of the medium-temperature flue gas heat exchanger 5, and the hot-side outlet is connected to the working fluid inlet of the medium-temperature flue gas heat exchanger 5; the hot-side inlet of the second heat exchanger 10 is connected to the working fluid outlet of the low-temperature flue gas heat exchanger 6, and the hot-side outlet is connected to the working fluid inlet of the low-temperature flue gas heat exchanger 6; the cold-side outlet of the first heat exchanger 9 is connected to the cold-side inlet of the regenerator 15, the cold-side outlet of the regenerator 15 is connected to the suction port of the compressor 11, the discharge port of the compressor 11 is connected to the hot-side inlet of the third heat exchanger 12, the hot-side outlet of the third heat exchanger 12 is connected to the hot-side inlet of the regenerator 15, the hot-side outlet of the regenerator 15 is connected to the suction port of the expander 14, the discharge port of the expander 14 is connected to the cold-side inlet of the second heat exchanger 10, and the cold-side outlet of the second heat exchanger 10 is connected to the cold-side inlet of the first heat exchanger 9. The circulating working fluid in the heat pump cycle unit absorbs heat in the second heat exchanger 10, the first heat exchanger 9, and the regenerator 15 in sequence, and then enters the compressor 11 for further compression and temperature rise to improve the quality of thermal energy. The thermal energy is stored in the heat storage unit 13 through the third heat exchanger 12. Finally, the circulating working fluid enters the expander 14 to reduce the pressure; through the heat pump cycle, on the one hand, the flue gas heat originally absorbed by the low-pressure feedwater is improved in quality and stored. To make up for the low-pressure heating heat, it is necessary to increase the extraction steam of the low-pressure cylinder, resulting in a reduction in the unit power. On the other hand, the operation of the heat pump cycle also consumes the unit's electricity to achieve rapid load reduction or deep low-load operation.

[0039] When the heat pump cycle unit is provided with a regenerator 15, the heat storage efficiency can be increased, but there is a part of heat loss during the heat recovery process, which is selected according to the actual use situation.

[0040] Embodiment III of the present invention:

[0041] A first valve 161 is provided on the pipeline connecting the working fluid outlet of the low-temperature flue gas heat exchanger 6 and the hot-side inlet of the second heat exchanger 10. A second valve 162 is provided on the pipeline connecting the working fluid outlet of the medium-temperature flue gas heat exchanger 5 and the hot-side inlet of the first heat exchanger 9. A third valve 163 is provided on the pipeline connecting the low-pressure feedwater and the medium-temperature flue gas heat exchanger 5. A fourth valve 164 is provided on the pipeline connecting the high-pressure feedwater and the working fluid inlet of the heat storage unit 13, which is convenient for controlling the operation flexibility of the generator set during the frequency modulation and peak shaving of the unit. A fifth valve 165 is provided on the pipeline connecting the air outlet of the air preheater 2 air chamber and the circulating cold air inlet of the heat storage unit 13, which is convenient for controlling the temperature of the heat storage element of the air preheater 2 and reducing the occurrence of ash fouling on the air preheater 2. The specific control of the valves is as follows:

[0042] When the unit does not participate in frequency modulation and peak shaving, the third valve 163 is opened. At the same time, the first valve 161, the second valve 162, and the fourth valve 164 are closed.

[0043] When the unit is regulating peak load and frequency modulation and reducing load or operating at a deep low load, the first valve 161 and the second valve 162 are opened, and the third valve 163 and the fourth valve 164 are closed;

[0044] When the unit is regulating peak load and frequency modulation and increasing load, the third valve 163 and the fourth valve 164 are opened, and the first valve 161 and the second valve 162 are closed.

[0045] In the above several cases, the fifth valve 165 is judged according to the ash fouling phenomenon of the air preheater 2. If the ash fouling phenomenon occurs, the valve is opened, otherwise the valve is closed.

[0046] The embodiment of the present invention also provides a method for recovering and storing waste heat in a thermal power plant, including any preferred implementation manner of the waste heat recovery and energy storage system in a thermal power plant, and various combinations of the implementation manners without conflict. The response to the unit's peak load regulation and frequency modulation requirements is as follows:

[0047] When the unit does not participate in peak load regulation and frequency modulation, the heat pump cycle unit stops operating. The low-pressure feed water heater absorbs the heat of the flue gas in the medium-temperature flue gas heat exchanger 5 and discharges it to the deaerator. The high-pressure feed water heater absorbs the heat of the flue gas in the high-temperature flue gas heat exchanger 4 and discharges it to the economizer. The heat of the low-temperature flue gas heat exchanger 6 provides preheating heat to the air preheater 2 air chamber through the air preheater 7;

[0048] When the unit is regulating peak load and frequency modulation and reducing load or operating at a deep low load, stop injecting low-pressure feed water into the medium-temperature flue gas heat exchanger 5. The high-pressure feed water is injected into the high-temperature flue gas heat exchanger 4 to work normally, and the heat pump cycle unit is turned on to store heat in the heat storage unit 13;

[0049] When the unit is regulating peak load and frequency modulation and increasing load, the heat pump cycle unit stops operating. The low-pressure feed water heater absorbs the heat of the flue gas in the medium-temperature flue gas heat exchanger 5 and discharges it to the deaerator. The high-pressure feed water heater absorbs the heat of the flue gas in the high-temperature flue gas heat exchanger 4 and discharges it to the economizer. At the same time, the high-pressure feed water also absorbs the stored heat from the heat storage unit 13 and discharges it to the economizer.

[0050] Under the unit's peak load regulation and frequency modulation requirements, when the ash fouling tendency of the air preheater 2 increases, the air preheater 2 absorbs the stored heat from the heat storage unit 13 as the heat source of the air chamber to increase the temperature of the heat storage element of the air preheater 2.

[0051] A method for recovering and storing waste heat in a thermal power plant according to an embodiment of the present invention improves the operating flexibility of the generator set by coupling the heat storage and heat release processes, increases the variable load rate during peak load regulation and frequency modulation, and assists the unit in stable frequency modulation; at the same time, it can also reduce the probability of ash fouling of the air preheater 2.

[0052] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0053] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A waste heat recovery and energy storage system for a thermal power plant, characterized in that, It includes a boiler flue (1), a warm air heater (7), a heat medium water pump (8), a heat pump cycle unit, and a heat storage unit (13) connected to the heat pump cycle unit. An air preheater (2), a high-temperature flue gas heat exchanger (4), a medium-temperature flue gas heat exchanger (5), and a low-temperature flue gas heat exchanger (6) are provided in the boiler flue (1). The high-temperature flue gas heat exchanger (4) absorbs heat through the connected high-pressure feedwater heater and discharges it to the economizer. The medium-temperature flue gas heat exchanger (5) absorbs heat through the connected low-pressure feedwater heater and discharges it to the deaerator. The low-temperature flue gas heat exchanger (6) is connected to the warm air heater (7) through the heat medium water pump (8) and provides a preheating heat source for the air preheater (2) through the warm air heater (7). The medium-temperature flue gas heat exchanger (5) and the low-temperature flue gas heat exchanger (6) are connected to the heat pump cycle unit, and the flue gas heat is stored by the heat storage unit (13). The heat storage unit (13) is connected to the air preheater (2) and provides a wind chamber heat source for the air preheater (2). The high-pressure feedwater heater can also absorb heat from the heat storage unit (13) and discharge it to the economizer; The heat storage unit (13) includes a heat storage chamber, a heat exchange chamber, a heat storage end, and a heat release end. A heat storage material is provided in the heat storage chamber. The heat storage end is communicated with the heat storage chamber. The heat release end includes a circulating cold air inlet, a circulating hot air outlet, a working medium inlet, and a working medium outlet that are communicated with the heat exchange chamber. The cold side outlet of the third heat exchanger (12) is connected to the heat storage end of the heat storage unit (13). The circulating cold air inlet is connected to the air outlet of the wind chamber of the air preheater (2). The circulating hot air outlet is connected to the air inlet of the wind chamber.

2. The waste heat recovery energy storage system of a thermal power plant according to claim 1, wherein The working medium inlet is connected to the high-pressure feedwater heater, and the working medium outlet is connected to the economizer.

3. The waste heat recovery and energy storage system for a thermal power plant according to claim 2, characterized in that, The air preheater (2) includes a flue gas chamber (21), a primary air chamber (22), and a secondary air chamber (23). The secondary air chamber (23) is separated by a partition (231) to form a circulating heating chamber (232). The air inlet of the circulating heating chamber (232) is connected to the circulating hot air outlet of the heat storage unit (13), and the air outlet of the circulating heating chamber (232) is connected to the circulating cold air inlet of the heat storage unit (13).

4. A waste heat recovery and energy storage system for a thermal power plant according to any one of claims 1 to 3, characterized in that The heat pump cycle unit includes a first heat exchanger (9), a second heat exchanger (10), a compressor (11), a third heat exchanger (12), and an expander (14). The hot side inlet of the first heat exchanger (9) is connected to the working medium outlet of the medium-temperature flue gas heat exchanger (5), and the hot side outlet is connected to the working medium inlet of the medium-temperature flue gas heat exchanger (5). The hot side inlet of the second heat exchanger (10) is connected to the working medium outlet of the low-temperature flue gas heat exchanger (6), and the hot side outlet is connected to the working medium inlet of the low-temperature flue gas heat exchanger (6). The cold side outlet of the first heat exchanger (9) is connected to the suction port of the compressor (11). The discharge port of the compressor (11) is connected to the hot side inlet of the third heat exchanger (12). The hot side outlet of the third heat exchanger (12) is connected to the suction port of the expander (14). The discharge port of the expander (14) is connected to the cold side inlet of the second heat exchanger (10). The cold side outlet of the second heat exchanger (10) is connected to the cold side inlet of the first heat exchanger (9).

5. The waste heat recovery energy storage system of a thermal power plant according to claim 4, wherein The heat pump cycle unit further includes a regenerator (15); the cold-side outlet of the first heat exchanger (9) is also connected to the cold-side inlet of the regenerator (15), the cold-side outlet of the regenerator (15) is connected to the suction port of the compressor (11), the hot-side outlet of the third heat exchanger (12) is also connected to the hot-side inlet of the regenerator (15), and the hot-side outlet of the regenerator (15) is connected to the suction port of the expander (14).

6. The waste heat recovery and energy storage system for a thermal power plant according to claim 5, characterized in that, A first valve (161) is provided on the pipeline connecting the working medium outlet of the low-temperature flue gas heat exchanger (6) to the hot-side inlet of the second heat exchanger (10), a second valve (162) is provided on the pipeline connecting the working medium outlet of the medium-temperature flue gas heat exchanger (5) to the hot-side inlet of the first heat exchanger (9), a third valve (163) is provided on the pipeline connecting the low-pressure feedwater heater feedwater to the medium-temperature flue gas heat exchanger (5), and a fourth valve (164) is provided on the pipeline connecting the high-pressure feedwater heater feedwater to the working medium inlet of the heat storage unit (13).

7. A waste heat recovery energy storage system for a thermal power plant according to claim 6, characterized in that, A fifth valve (165) is provided on the pipeline connecting the air outlet of the air preheater (2) air chamber to the circulating cold air inlet of the heat storage unit (13).

8. A waste heat recovery energy storage system for a thermal power plant according to any one of claims 1 to 3, characterized in that, The boiler flue (1) is divided into a main flue and a bypass flue by a flue gas baffle (3). The air preheater (2) is arranged in the main flue, the high-temperature flue gas heat exchanger (4) and the medium-temperature flue gas heat exchanger (5) are arranged in the bypass flue according to the flue gas flow direction, and the low-temperature flue gas heat exchanger (6) is arranged at the tail of the boiler flue (1).

9. A method for recovering and storing waste heat in a thermal power plant, characterized in that, It includes a waste heat recovery and energy storage system for a thermal power plant as described in any one of claims 1 to 8, and the response to the unit's frequency modulation and peak shaving requirements is as follows: When the unit does not participate in frequency modulation and peak shaving, the heat pump cycle unit stops operating. The low-pressure feedwater heater feedwater absorbs the flue gas heat in the medium-temperature flue gas heat exchanger (5) and is discharged to the deaerator. The high-pressure feedwater heater feedwater absorbs the flue gas heat in the high-temperature flue gas heat exchanger (4) and is discharged to the economizer. The heat of the low-temperature flue gas heat exchanger (6) provides preheating heat to the air chamber of the air preheater (2) through the air heater (7). When the unit reduces load during peak shaving and frequency modulation or operates at a deep low load, the injection of low-pressure feedwater heater feedwater into the medium-temperature flue gas heat exchanger (5) is stopped, and the heat pump cycle unit is turned on to store heat in the heat storage unit (13). When the unit increases load during peak shaving and frequency modulation, the heat pump cycle unit stops operating. The low-pressure feedwater heater feedwater absorbs the flue gas heat in the medium-temperature flue gas heat exchanger (5) and is discharged to the deaerator. The high-pressure feedwater heater feedwater absorbs the flue gas heat in the high-temperature flue gas heat exchanger (4) and is discharged to the economizer. At the same time, the high-pressure feedwater heater feedwater also absorbs the stored heat from the heat storage unit (13) and is discharged to the economizer.

10. A method for recovering and storing waste heat in a thermal power plant according to claim 9, characterized in that, Under the unit's frequency modulation and peak shaving requirements, when the ash deposition tendency of the air preheater (2) increases, the air preheater (2) absorbs the stored heat from the heat storage unit (13) as the heat source of the air chamber to increase the temperature of the heat storage elements of the air preheater (2).

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