Coal-fired power generation system integrating flue gas waste heat recovery of multiple temperature zones and operation method of coal-fired power generation system

Abstract

The invention discloses a coal-fired power generation system integrating multi-temperature-zone flue gas waste heat recovery and an operation method of the coal-fired power generation system. By arranging the vacuum heat pipe heat exchanger, recovery of flue gas waste heat of multiple temperature zones is achieved through solid heat storage and phase change heat storage, the organic Rankine cycle system is driven to generate power through heat of medium and low temperature zones, and efficient utilization of the heat of the multiple temperature zones is achieved. The system can realize real-time and cross-time utilization of flue gas waste heat, strengthen machine-boiler decoupling and improve the operation flexibility of a coal-fired power generation system, is a novel heat energy storage technology, and can provide powerful support for stabilizing power grid and user load fluctuation, promoting new energy consumption and constructing a novel power system.

Description

Technical Field

[0001] This invention relates to the field of thermal energy storage technology, specifically to a coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery and its operation method. Background Technology

[0002] Renewable energy power generation, such as wind and solar power, exhibits significant volatility and intermittency. Its output characteristics and grid baseload demand suffer from temporal and spatial mismatch, posing a severe challenge to the safe and stable operation of the power system. Constructing a flexible and adjustable power supply structure to cope with variable load conditions has become a core issue in the construction of my country's new power system. In the field of coal-fired power generation, existing flue gas waste heat recovery technology can improve unit efficiency through waste heat utilization. However, its strong coupling characteristics with the boiler-turbine system inhibit the potential for boiler-turbine decoupling, resulting in limited peak-shaving capacity. Therefore, it is urgent to provide an adapted method to achieve inter-temporal recovery of flue gas waste heat to enhance boiler-turbine decoupling and achieve efficient energy utilization. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention aims to provide a coal-fired power generation system and its operation method that integrates multi-temperature zone flue gas waste heat recovery. This system utilizes multi-temperature zone heat storage, employing solid-state heat storage to store high-temperature heat for use in the turbine system, and phase-change heat storage to store medium- and low-temperature heat for use in the organic Rankine cycle power generation system. Furthermore, it utilizes low-temperature heat to preheat the working fluid. The heat storage and release processes can occur simultaneously and over time, achieving efficient utilization of flue gas waste heat. This is a promising new energy storage technology.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery includes a flue gas denitrification system 1, an air preheater 2, a high-temperature vacuum heat pipe heat exchanger 3, a solid heat storage device 4, a phase change heat storage packed bed 5, an expander 6, a condenser 7, a booster pump 8, a low-temperature vacuum heat pipe heat exchanger 9, and a generator 10. In the multi-temperature zone flue gas waste heat recovery system, the air preheater 2 is arranged in the main flue gas path after the flue gas denitrification system 1, and the high-temperature vacuum heat pipe heat exchanger 3 and the phase change heat storage packed bed 5 are arranged in sequence in the flue gas bypass path. Then, the main flue gas path and the bypass path merge, and the low-temperature vacuum heat pipe heat exchanger 9 is arranged at the merging point. The high-temperature vacuum heat pipe heat exchanger 3 is connected to the solid heat storage device 4. The outlet of the expander 6 is connected in sequence to the condenser 7, the booster pump 8, the low-temperature vacuum heat pipe heat exchanger 9, and the phase change heat storage packed bed 5, and finally connected to the inlet of the expander 6. The expander 6 is coaxially connected to the generator 10.

[0005] The aforementioned integrated multi-temperature zone flue gas waste heat recovery coal-fired power generation system uses a high-temperature vacuum heat pipe heat exchanger 3 in a split heat pipe form, consisting of an evaporation section and a condensation section. The evaporation section is installed in the flue gas bypass, and the condensation section is embedded with a solid heat storage device 4. The working fluid outlet of the evaporation section is connected to the working fluid inlet of the condensation section, and the working fluid outlet of the condensation section is connected to the working fluid inlet of the evaporation section. The evaporation section is arranged at a lower height than the condensation section. When the evaporation section is heated, the working fluid changes from liquid to gas. Due to the density difference, it is transported upward to the condensation section, where it exchanges heat with the solid heat storage device 4. The gaseous working fluid condenses into liquid and returns to the evaporation section under gravity, thus realizing the circulation of the working fluid within the high-temperature vacuum heat pipe heat exchanger.

[0006] The flue gas waste heat storage system using vacuum heat pipe technology has a flue gas inlet temperature range of 350-400℃ for the high-temperature vacuum heat pipe heat exchanger 3, and the working fluid of the high-temperature vacuum heat pipe heat exchanger is thermally conductive with an operating temperature range of 200-350℃.

[0007] The coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery has a flue gas temperature range of 160-200℃ at the inlet of the phase change thermal storage bed 5. The phase change material is a ternary nitrate composed of 22% sodium nitrate, 52.4% potassium nitrate and 25.6% magnesium nitrate, with a melting point of 156℃.

[0008] The coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery is described above. The expander 6 consists of at least three expanders, adopts an axial flow expander, and has an inlet-outlet expansion ratio of 7.8.

[0009] The coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery includes a low-temperature vacuum heat pipe heat exchanger 9 composed of multiple two-phase closed vacuum heat pipes. The vacuum heat pipes are arranged vertically in a staggered manner with the evaporation section at the bottom and the condensation section at the top. When the evaporation section is heated, the working fluid changes from liquid to gas. Due to the density difference, the gas is transported upward to the condensation section. The condensation section exchanges heat with the working fluid at the outlet of the booster pump 8. The gaseous working fluid condenses into liquid and returns to the evaporation section under the action of gravity, realizing the circulation of the working fluid within the heat pipe heat exchanger.

[0010] The coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery has a flue gas inlet temperature range of 100-140℃ for the low-temperature vacuum heat pipe heat exchanger 9, and uses ethanol as the working fluid in the heat exchanger with an operating temperature range of 80-120℃.

[0011] The coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery comprises an organic Rankine cycle power generation system consisting of a phase change thermal storage packed bed 5, an expander 6, a condenser 7, a booster pump 8, a low-temperature vacuum heat pipe heat exchanger 9, and a generator 10. The circulating working fluid is pentane, and the inlet temperature range of the expander 6 is 120-150℃, while the outlet temperature range is 50-60℃.

[0012] The control method for a coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery includes two processes: heat storage and heat release. In the heat storage process, the flue gas, after passing through the flue gas denitrification system 1, is split into two streams. One stream passes through the air preheater 2 in the main flue gas path, while the other stream passes sequentially through the high-temperature vacuum heat pipe heat exchanger 3 and the phase change heat storage packed bed 5 in the flue gas bypass path before merging with the main flue gas and continuing through the low-temperature vacuum heat pipe heat exchanger 9 into the subsequent desulfurization and dust removal devices. The flue gas then heats the solid heat storage device through the high-temperature vacuum heat pipe heat exchanger 3. The system is set at 4, and then the phase change thermal storage bed 5 is heated. The heat release process of the system is as follows: the working fluid from the steam turbine system is heated by the solid thermal storage device 4 and then returns to the steam turbine system, displacing the steam extracted from the steam turbine to increase the power generation of the coal-fired unit. The working fluid of the organic Rankine cycle power generation system is pressurized by the booster pump 8 and then heated by the low temperature vacuum heat pipe heater 9 and the phase change thermal storage bed 5 before entering the expander 6 to do work and drive the generator 10 to generate electricity. Finally, it enters the condenser 7 to cool. The heat storage and heat release processes can be carried out simultaneously and over time to realize the real-time and over-time recovery of flue gas waste heat.

[0013] Advantages of the present invention Compared with the prior art, the present invention has the following advantages: (1) The present invention uses a vacuum heat pipe heat exchanger to recover waste heat from flue gas, which has high heat transfer efficiency, compact structure, low maintenance cost, and is suitable for narrow bypass flues. (2) The present invention utilizes a multi-temperature zone heat storage device to recover waste heat from flue gas, thereby achieving efficient recovery of waste heat from flue gas. (3) The present invention can realize the real-time and cross-time utilization of flue gas waste heat, which can improve the operational flexibility of coal-fired units. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery according to the present invention. Detailed Implementation

[0015] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0016] like Figure 1As shown, a coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery includes a flue gas denitrification system 1, an air preheater 2, a high-temperature vacuum heat pipe heat exchanger 3, a solid heat storage device 4, a phase change heat storage packed bed 5, an expander 6, a condenser 7, a booster pump 8, a low-temperature vacuum heat pipe heat exchanger 9, and a generator 10. In the multi-temperature zone flue gas waste heat recovery system, the air preheater 2 is arranged in the main flue gas path after the flue gas denitrification system 1, and the high-temperature vacuum heat pipe heat exchanger 3 and the phase change heat storage packed bed 5 are arranged in sequence in the flue gas bypass path. After that, the main flue gas path and the bypass path merge, and the low-temperature vacuum heat pipe heat exchanger 9 is arranged at the merging point. The high-temperature vacuum heat pipe heat exchanger 3 is connected to the solid heat storage device 4. The outlet of the expander 6 is connected in sequence to the condenser 7, the booster pump 8, the low-temperature vacuum heat pipe heat exchanger 9, and the phase change heat storage packed bed 5, and finally connected to the inlet of the expander 6. The expander 6 is coaxially connected to the generator 10.

[0017] As an embodiment of the advantages of the present invention, the high-temperature vacuum heat pipe heat exchanger 3 adopts a split heat pipe form, with the evaporation section installed in the flue gas bypass and the condensation section embedded in the solid heat storage device 4. The evaporation section is arranged at a lower height than the condensation section. The working fluid in the heat pipe heat exchanger circulates by gravity, resulting in high heat transfer efficiency, compact structure, and low maintenance cost.

[0018] As an embodiment of the advantages of the present invention, the flue gas inlet temperature range of the high-temperature vacuum heat pipe heat exchanger 3 is 350-400℃, the working fluid of the high-temperature vacuum heat pipe heat exchanger is thermally conductive, the operating temperature range is 200-350℃, the heat exchange temperature difference is small, the irreversible loss is small, and the heat transfer efficiency is high.

[0019] As an embodiment of the advantages of the present invention, the flue gas temperature range at the inlet of the phase change thermal storage bed 5 is 160-200℃, the phase change material is a ternary nitrate composed of 22% sodium nitrate, 52.4% potassium nitrate and 25.6% magnesium nitrate, with a melting point of 156℃, small heat exchange temperature difference, small irreversible loss and high heat transfer efficiency.

[0020] As an embodiment of the advantages of the present invention, the expander 6 consists of at least three stages of expanders, adopts an axial flow expander, and has an inlet-outlet expansion ratio of 7.8, which has high power generation efficiency.

[0021] As an embodiment of the advantages of the present invention, the low-temperature vacuum heat pipe heat exchanger 9 adopts the form of a two-phase closed heat pipe. The heat exchanger is arranged vertically with the evaporation section at the bottom and the condensation section at the top. The working fluid in the heat pipe heat exchanger circulates by gravity, making full use of the flue structure, resulting in high heat transfer efficiency and compact structure.

[0022] As an embodiment of the advantages of the present invention, the flue gas inlet temperature range of the low-temperature vacuum heat pipe heat exchanger 3 is 100-140℃, the working fluid of the heat exchanger is ethanol, the operating temperature range is 80-120℃, the heat exchange temperature difference is small, the irreversible loss is small, and the heat transfer efficiency is high.

[0023] As an embodiment of the advantages of the present invention, the phase change thermal storage packed bed 5, expander 6, condenser 7, booster pump 8, low temperature vacuum heat pipe heat exchanger 9 and generator 10 constitute an organic Rankine cycle power generation system, the working fluid of the cycle is pentane, the inlet temperature range of expander 6 is 120-150°C, and the outlet temperature range is 50-60°C.

[0024] The control method for a coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery includes two processes: heat storage and heat release. In the heat storage process, the flue gas, after passing through the flue gas denitrification system 1, is split into two streams. One stream passes through the air preheater 2 in the main flue gas path, while the other stream passes sequentially through the high-temperature vacuum heat pipe heat exchanger 3 and the phase change heat storage packed bed 5 in the flue gas bypass path before merging with the main flue gas and continuing through the low-temperature vacuum heat pipe heat exchanger 9 into the subsequent desulfurization and dust removal devices. The flue gas then heats the solid heat storage device through the high-temperature vacuum heat pipe heat exchanger 3. The system is set at 4, and then the phase change thermal storage bed 5 is heated. The heat release process of the system is as follows: the working fluid from the steam turbine system is heated by the solid thermal storage device 4 and then returns to the steam turbine system, displacing the steam extracted from the steam turbine to increase the power generation of the coal-fired unit. The working fluid of the organic Rankine cycle power generation system is pressurized by the booster pump 8 and then heated by the low temperature vacuum heat pipe heater 9 and the phase change thermal storage bed 5 before entering the expander 6 to do work and drive the generator 10 to generate electricity. Finally, it enters the condenser 7 to cool. The heat storage and heat release processes can be carried out simultaneously and over time to realize the real-time and over-time recovery of flue gas waste heat.

Claims

1. A coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery, characterized in that, The system includes a flue gas denitrification system (1), an air preheater (2), a high-temperature vacuum heat pipe heat exchanger (3), a solid heat storage device (4), a phase change heat storage bed (5), an expander (6), a condenser (7), a booster pump (8), a low-temperature vacuum heat pipe heat exchanger (9), and a generator (10). The main flue gas path after the flue gas denitrification system (1) is equipped with an air preheater (2), and the flue gas bypass is equipped with a high-temperature vacuum heat pipe heat exchanger (3) and a phase change heat storage bed (5) in sequence from high to low. After that, the main flue gas path and the bypass merge, and a low-temperature vacuum heat pipe heat exchanger (9) is arranged at the merging point. The working fluid outlet of the expander (6) is connected in sequence to the condenser (7), the booster pump (8), the low-temperature vacuum heat pipe heat exchanger (9), and the phase change heat storage bed (5), and finally connected to the working fluid inlet of the expander (6). The expander (6) and the generator (10) are coaxially connected.

2. The coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery as described in claim 1, characterized in that: The high-temperature vacuum heat pipe heat exchanger (3) adopts a split heat pipe form, which is divided into two parts: an evaporation section and a condensation section. The evaporation section is installed in the flue gas bypass, and the condensation section is embedded in the solid heat storage device (4). The working fluid outlet of the evaporation section is connected to the working fluid inlet of the condensation section, and the working fluid outlet of the condensation section is connected to the working fluid inlet of the evaporation section. The evaporation section is arranged at a lower height than the condensation section. When the evaporation section is heated, the working fluid changes from liquid to gas. Due to the density difference, it is transferred upward to the condensation section. The condensation section exchanges heat with the solid heat storage device (4). The gaseous working fluid condenses into liquid and returns to the evaporation section under the action of gravity, thus realizing the working fluid circulation in the high-temperature vacuum heat pipe heat exchanger.

3. A coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery as described in claim 1, characterized in that: The flue gas inlet temperature range of the high-temperature vacuum heat pipe heat exchanger (3) is 350-400℃, and the working fluid of the high-temperature vacuum heat pipe heat exchanger is thermally conductive, with an operating temperature range of 200-350℃.

4. A coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery as described in claim 1, characterized in that: The flue gas temperature range at the flue gas inlet of the phase change thermal storage bed (5) is 160-200℃. The phase change material is a ternary nitrate composed of 22% sodium nitrate, 52.4% potassium nitrate and 25.6% magnesium nitrate, with a melting point of 156℃.

5. A coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery as described in claim 1, characterized in that: The expander (6) consists of at least three stages of expanders, using an axial flow expander with an inlet-outlet expansion ratio of 7.

8.

6. A coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery as described in claim 1, characterized in that: The low-temperature vacuum heat pipe heat exchanger (9) is composed of multiple two-phase closed vacuum heat pipes. The vacuum heat pipes are arranged vertically in a staggered manner with the evaporation section at the bottom and the condensation section at the top. When the evaporation section is heated, the working fluid changes from liquid to gas. Due to the density difference, it is transferred upward to the condensation section. The condensation section exchanges heat with the working fluid at the outlet of the booster pump (8). The gaseous working fluid condenses into liquid and returns to the evaporation section under the action of gravity, realizing the circulation of the working fluid in the heat pipe heat exchanger.

7. A coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery as described in claim 1, characterized in that: The flue gas inlet temperature range of the low-temperature vacuum heat pipe heat exchanger (9) is 100-140℃, the working fluid of the heat exchanger is ethanol, and the operating temperature range is 80-120℃.

8. A coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery as described in claim 1, characterized in that: The organic Rankine cycle power generation system consists of a phase change thermal storage bed (5), an expander (6), a condenser (7), a booster pump (8), a low-temperature vacuum heat pipe heat exchanger (9), and a generator (10). The working fluid is pentane. The inlet temperature range of the expander (6) is 120-150℃, and the outlet temperature range is 50-60℃.

9. The operation method of a coal-fired power generation system integrating multi-temperature zone flue gas waste heat recovery as described in any one of claims 1 to 8, characterized in that: The waste heat recovery process of the flue gas system is divided into two parts: heat storage and heat release. In the heat storage process, the flue gas is split into two streams after passing through the flue gas denitrification system (1). One stream passes through the air preheater (2) of the main flue gas path, and the other stream passes through the high-temperature vacuum heat pipe heat exchanger (3) and the phase change heat storage packed bed (5) of the flue gas bypass in sequence. After merging with the main flue gas, it continues to pass through the low-temperature vacuum heat pipe heat exchanger (9) and enters the subsequent desulfurization and dust removal device. The flue gas heats the solid heat storage device (4) through the high-temperature vacuum heat pipe heat exchanger (3), and then heats the phase change heat storage packed bed (4). 5) The heat release process of the system is as follows: the working fluid from the steam turbine system is heated by the solid heat storage device (4) and then returns to the steam turbine system to displace the steam extracted from the steam turbine and increase the power generation of the coal-fired unit. The working fluid of the organic Rankine cycle power generation system is pressurized by the booster pump (8) and then heated by the low temperature vacuum heat pipe heater (9) and the phase change heat storage bed (5) before entering the expander (6) to do work and drive the generator (10) to generate electricity. Finally, it enters the condenser (7) to cool. The heat storage and heat release processes can be carried out simultaneously and over time to realize the real-time and over-time recovery of flue gas waste heat.

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