A waste heat recovery energy storage system and method for a thermal power plant

Abstract

The present invention relates to a waste heat recovery energy storage system and method for a thermal power plant, including 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 feed water of the high-pressure heater and discharges it to the economizer. The medium-temperature flue gas heat exchanger absorbs heat through the feed water of the low-pressure 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. 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 a wind box heat source for the air preheater. The feed water of the high-pressure heater can absorb heat from the heat storage unit and discharge it to the economizer. The present invention can improve the operation flexibility of the generator set and reduce the probability of ash accumulation and scaling on the air preheater at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of waste heat recovery in thermal power generation, and particularly to a waste heat recovery 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 is also continuously expanding. 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 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 a heating furnace, the air preheater is used to recover and utilize the waste heat of the flue gas, reduce the heat loss carried away by the flue 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 energy storage system and method for a thermal power plant.

[0006] The object of the present invention is achieved by 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 box 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] 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 fluid outlet of the medium-temperature flue gas heat exchanger, and the hot-side outlet is connected to the working fluid inlet of the medium-temperature flue gas heat exchanger. The hot-side inlet of the second heat exchanger is connected to the working fluid outlet of the low-temperature flue gas heat exchanger, and the hot-side outlet is connected to the working fluid 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, and the cold-side outlet of the second heat exchanger is connected to the cold-side inlet of the first heat exchanger.

[0009] As a further improvement, the heat pump cycle unit includes a first heat exchanger, a second heat exchanger, a regenerator, a compressor, a third heat exchanger, and an expander. The hot-side inlet of the first heat exchanger is connected to the working fluid outlet of the medium-temperature flue gas heat exchanger, and the hot-side outlet is connected to the working fluid inlet of the medium-temperature flue gas heat exchanger; the hot-side inlet of the second heat exchanger is connected to the working fluid outlet of the low-temperature flue gas heat exchanger, and the hot-side outlet is connected to the working fluid inlet of the low-temperature flue gas heat exchanger; the cold-side outlet of the first heat exchanger is connected to the cold-side inlet of the regenerator, the cold-side outlet of the regenerator 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 regenerator, the hot-side outlet of the regenerator 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, and the cold-side outlet of the second heat exchanger is connected to the cold-side inlet of the first heat exchanger.

[0010] As a further improvement, the heat storage unit includes a heat storage cavity, a heat exchange cavity, a heat storage end and a heat release end. The heat storage cavity is provided with heat storage materials. 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 that are 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.

[0011] 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. The air outlet of the circulating heating compartment is connected to the circulating cold air inlet of the heat storage unit.

[0012] 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. 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.

[0013] 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.

[0014] As a further improvement, the boiler flue is separated by a flue gas baffle to form a main flue and a bypass flue. 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. The low-temperature flue gas heat exchanger is arranged at the tail of the boiler flue.

[0015] 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. The boiler flue is provided with 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. 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 store the flue gas heat 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 response to the unit frequency modulation and peak shaving requirements is as follows:

[0016] When the unit does not participate in frequency regulation and peak shaving, the heat pump cycle unit stops running. 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, reducing the flue gas temperature and heat loss of the boiler and effectively improving the economic benefits of the generating unit. At the same time, the heat of the low-temperature flue gas heat exchanger provides preheating heat to the air preheater air chamber through the air heater, and the preheated air of the air preheater is heated and sent to the boiler for combustion support, reducing the consumption of coal fuel;

[0017] When the unit regulates the peak and frequency and reduces the load or operates at a deep low load, stop injecting low-pressure feedwater into the medium-temperature flue gas heat exchanger and open the heat pump cycle unit to store heat in the heat storage unit;

[0018] When the unit regulates the peak and frequency and increases the load, the heat pump cycle unit stops running. 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.

[0019] During the peak and frequency regulation of the unit, when there is a tendency of ash accumulation in the air preheater, the air preheater can absorb 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 and reduce the probability of ash fouling in the air preheater.

[0020] A waste heat recovery and energy storage system for a thermal power plant according to the present invention improves the operating flexibility of the generating unit, increases the variable load rate during peak and frequency regulation, and assists the unit in stable frequency regulation by coupling the heat storage and heat release processes; at the same time, it can also reduce the probability of ash fouling in the air preheater.

[0021] The present invention also provides a waste heat recovery and energy storage method for a thermal power plant, including any further improvement of the waste heat recovery and energy storage system for a thermal power plant described above. The response to the peak and frequency regulation requirements of the unit is as follows:

[0022] When the unit does not participate in frequency regulation and peak shaving, the heat pump cycle unit stops running. 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;

[0023] When the unit regulates the peak and frequency and reduces the load or operates at a deep low load, stop injecting low-pressure feedwater into the medium-temperature flue gas heat exchanger and open the heat pump cycle unit to store heat in the heat storage unit;

[0024] When the unit adjusts peak load and frequency modulation to increase load, the heat pump cycle unit stops operating. The feed water of the low-pressure heaters absorbs the heat of the flue gas in the medium-temperature flue gas heat exchanger and is discharged to the deaerator. The feed water of the high-pressure heaters 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 feed water of the high-pressure heaters also absorbs the stored heat from the heat storage unit and is discharged to the economizer.

[0025] As a further improvement, under the requirements of unit frequency modulation and peak load regulation, when the ash deposition tendency of the air preheater increases, 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.

[0026] A method for recovering waste heat and storing energy in a thermal power plant provided by the present invention should have the same or corresponding technical effects because it adopts the technical content of the above-mentioned waste heat recovery and energy storage system in a thermal power plant, so it will not be elaborated here. Brief Description of the Drawings

[0027] Figure 1 is a structural schematic diagram of the present invention;

[0028] Figure 2 is a structural schematic diagram of the air preheater of the present invention. Detailed Embodiments

[0029] In order to enable those skilled in the art to better understand the technical solution 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.

[0030] Combined with Figure 1 As shown, an embodiment of the present invention provides a waste heat recovery and energy storage system for a thermal power plant, including 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, an economizer and a denitration device are arranged in the boiler flue 1 in the direction of the flue gas flow first. 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, a main flue and a bypass flue are separated by a flue gas baffle 3. 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 the flue gas flow, and the low-temperature flue gas heat exchanger 6 is arranged at the tail of the boiler flue 1.

[0031] 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 air preheater 7 through the heat medium water pump 8. The working medium outlet of the air preheater 7 is connected to the working medium inlet of the low-temperature flue gas heat exchanger 6. The air outlet of the air preheater 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 air preheater 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 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 feed water of the high-pressure heater can also absorb heat from the heat storage unit 13 and discharge it to the economizer.

[0032] 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 thermal cycle of molten salt to achieve the purpose of heat storage. Compared with heat transfer oil, when the working medium 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 medium inlet, and a working medium 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 wind chamber of the air preheater 2, and the circulating hot air outlet is connected to the air inlet of the wind chamber. The air preheater 2 in the embodiment of the present invention can be selected but is not limited to a three-compartment rotary air preheater. Specifically, the air preheater 2 includes a flue gas chamber 21, a primary air compartment 22, and a secondary air compartment 23. The secondary air compartment 23 is separated by a partition 231 to form a circulating heating compartment 232. The air inlet of the circulating heating compartment 232 is connected to the circulating hot air outlet of the heat storage unit 13, and the air outlet of the circulating heating compartment 232 is connected to the circulating cold air inlet of the heat storage unit 13. By absorbing heat from the heat storage unit 13, the temperature of the heat storage element at the cold end of the air preheater 2 is increased, and the ash deposition tendency of the air preheater 2 is reduced.

[0033] In the 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:

[0034] When the unit does not participate in frequency modulation and peak load regulation, 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, reducing the flue gas temperature and heat loss of the boiler and effectively improving the economic benefits of the generating unit. At the same time, the heat of the low-temperature flue gas heat exchanger 6 is supplied to the air preheater 2 air chamber through the air heater 7 as preheating heat. The preheated air of the air preheater 2 is heated and then sent to the boiler for combustion support, reducing the consumption of coal fuel;

[0035] When the unit reduces load during peak load regulation and frequency modulation or operates at a deep low load, the injection of low-pressure heater feed water into the medium-temperature flue gas heat exchanger 5 is stopped, and the injection of high-pressure heater feed water 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;

[0036] When the unit increases load during peak load regulation and frequency modulation, 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 heater 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 rapid load increase.

[0037] 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 element of the air preheater 2 and reduce the probability of ash fouling in the air preheater 2.

[0038] An embodiment of the present invention is a waste heat recovery and energy storage system for a thermal power plant, which improves the operating flexibility of the generating unit 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 in the air preheater 2.

[0039] Embodiment 1 of the present invention:

[0040] 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, and the cold side outlet of the second heat exchanger 10 is connected to the cold side inlet of the first heat exchanger 9.

[0041] Embodiment 2 of the present invention:

[0042] As Figure 1 shown, 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 heater is improved in quality and stored. To make up for the heat of the low-pressure feedwater heater, 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.

[0043] 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.

[0044] Embodiment 3 of the present invention:

[0045] 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, and 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 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 deposition and scaling on the air preheater 2. The specific control of the valves is as follows:

[0046] 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.

[0047] When the unit is in peak shaving, frequency modulation, load reduction, or deep low-load operation, the first valve 161 and the second valve 162 are opened, and the third valve 163 and the fourth valve 164 are closed;

[0048] When the unit is in frequency modulation, peak shaving, and load increase, the third valve 163 and the fourth valve 164 are opened, and the first valve 161 and the second valve 162 are closed.

[0049] 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.

[0050] 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, as well as various combinations of the implementation manners without conflict. The response to the unit's frequency modulation and peak shaving requirements is as follows:

[0051] When the unit does not participate in frequency modulation and peak shaving, 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 heater 7;

[0052] When the unit is in peak shaving, frequency modulation, load reduction, or deep low-load operation, the injection of low-pressure feed water into the medium-temperature flue gas heat exchanger 5 is stopped, the injection of high-pressure feed water into the high-temperature flue gas heat exchanger 4 works normally, and the heat pump cycle unit is turned on to store heat in the heat storage unit 13;

[0053] When the unit is in frequency modulation, peak shaving, and load increase, 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 heater also absorbs the stored heat from the heat storage unit 13 and discharges it to the economizer.

[0054] Under the unit's frequency modulation and peak shaving 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.

[0055] The method for recovering and storing waste heat in a thermal power plant according to the 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 shaving and frequency modulation, and assists the unit in stable frequency modulation; at the same time, it can also reduce the probability of ash fouling and scaling of the air preheater 2.

[0056] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described 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.

[0057] The above-described embodiments only express several implementation manners of the present invention, and the description thereof 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 store the flue gas heat 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 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).

2. The waste heat recovery and energy storage system for a thermal power plant according to claim 1, characterized in that, the heat pump cycle unit further includes a regenerator (15); the cold side outlet of the first heat exchanger (9) is further 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 further 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).

3. The waste heat recovery and energy storage system for a thermal power plant according to any one of claims 1 to 2, characterized in that, The heat storage unit (13) includes a heat storage cavity, a heat exchange cavity, a heat storage end, and a heat release end. The heat storage cavity is provided with a heat storage material. 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 that are communicated with the heat exchange cavity. 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. The circulating hot air outlet is connected to the air inlet of the air chamber.

4. A waste heat recovery energy storage system for a thermal power plant according to claim 3, 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). The air outlet of the circulating heating chamber (232) is connected to the circulating cold air inlet of the heat storage unit (13).

5. A waste heat recovery energy storage system for a thermal power plant according to claim 1 or 2, 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 to the medium-temperature flue gas heat exchanger (5). A fourth valve (164) is provided on the pipeline connecting the high-pressure feedwater heater to the working medium inlet of the heat storage unit (13).

6. A waste heat recovery energy storage system for a thermal power plant according to claim 5, 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).

7. A waste heat recovery energy storage system for a thermal power plant according to any one of claims 1 to 2, characterized in that the boiler flue (1) is separated by a flue gas baffle (3) to form a main flue and a bypass flue. 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. The low-temperature flue gas heat exchanger (6) is arranged at the tail of the boiler flue (1).

8. A waste heat recovery energy storage method for a thermal power plant, characterized in that it includes a waste heat recovery energy storage system for a thermal power plant according to any one of claims 1 to 7, 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 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 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 preheater (2) air chamber through the air heater (7). When the unit is in peak shaving, frequency modulation, load reduction, or deep low-load operation, the injection of low-pressure feedwater heater 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 is regulating peak load and frequency modulation to increase 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.

9. A method for recovering waste heat and storing energy in a thermal power plant according to claim 8, characterized in that under the demand of unit frequency modulation and peak load regulation, 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 storage bin to increase the temperature of the heat storage element of the air preheater (2).

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