A supercritical carbon dioxide boiler system for heating recirculating flue gas

Abstract

The present invention relates to a supercritical carbon dioxide boiler system for heating recirculating flue gas, and belongs to the technical field of boiler equipment. The system comprises a supercritical carbon dioxide boiler, a turbine, a high-temperature regenerator, a low-temperature regenerator, a cooler, a compressor, a recirculating fan, a recirculating flue gas heater, a burner, an air preheater and a split economizer; the present invention uses the supercritical carbon dioxide working medium split at the high-pressure side outlet of the low-temperature regenerator and the boiler recirculating flue gas to cool the flue gas at the tail of the boiler, thereby achieving the purpose of reducing the temperature of the working medium in the boiler inlet, reducing the temperature level of the flue gas in the furnace, reducing the exhaust temperature of the boiler and improving the working conditions of the heating surface of the furnace under the premise of ensuring the efficiency of the boiler.

Description

Technical Field

[0001] The invention relates to a supercritical carbon dioxide boiler system for heating recirculating flue gas, belonging to the technical field of boiler equipment. Background Art

[0002] Compared with the water-steam Rankine cycle, the supercritical carbon dioxide Brayton cycle has the characteristics of full flow heat recovery and large heat recovery. The inlet working fluid temperature of its boiler is much higher than that of the water-steam Rankine cycle under the same parameters, which also leads to a higher working fluid temperature level of the supercritical carbon dioxide boiler furnace heating surface. According to data, in a 25MPa, 600℃ thermodynamic cycle, the inlet working fluid temperature of a water steam boiler is about 300℃, while the inlet working fluid temperature of a supercritical carbon dioxide boiler is about 450℃. In addition, due to the evaporation process of the water-cooled wall of a water steam boiler, the heat transfer coefficient in the tube is high. According to current research, the heat transfer coefficient in the tube of the furnace heating surface of a supercritical carbon dioxide boiler is usually much smaller than that of a water steam boiler. Under the same conditions, the cooling capacity of the supercritical carbon dioxide boiler furnace heating surface is poor, which leads to a further increase in the temperature of the metal tube wall of the supercritical carbon dioxide boiler furnace heating surface, greatly increasing the risk of overheating of the metal temperature of the furnace heating surface tube wall, and seriously threatening the working safety of the furnace heating surface. At the same time, due to the high inlet working fluid temperature of the supercritical carbon dioxide boiler, the heat of the flue gas in the boiler tail flue cannot be fully utilized, resulting in the boiler exhaust temperature being too high and the boiler efficiency being reduced. Therefore, the supercritical carbon dioxide boiler system configuration needs to be further optimized. Summary of the invention

[0003] The present invention provides a supercritical carbon dioxide boiler system for heating recirculating flue gas, which utilizes the supercritical carbon dioxide working medium diverted from the high-pressure side outlet of a low-temperature heat regenerator and the boiler recirculating flue gas to cool the flue gas at the tail end of the boiler, thereby achieving the purpose of reducing the boiler inlet working medium temperature, reducing the temperature level of the flue gas in the furnace, reducing the boiler exhaust temperature and improving the working conditions of the furnace heating surface while ensuring the boiler efficiency.

[0004] In order to achieve the purpose of solving the above-mentioned problems, the technical solution adopted by the present invention is to provide a supercritical carbon dioxide boiler system for heating recirculating flue gas, the boiler system comprising a supercritical carbon dioxide boiler, a turbine, a high-temperature regenerator, a low-temperature regenerator, a cooler, a compressor, a recirculation fan, a recirculating flue gas heater, a burner, an air preheater and a diversion economizer; the supercritical carbon dioxide boiler is provided with a boiler heating surface, a burner and an air preheater; the high-temperature regenerator is provided with a low-pressure side inlet, a low-pressure side outlet, a high-pressure side inlet and a high-pressure side outlet; the low-temperature regenerator is provided with a low-pressure side inlet, a low-pressure side outlet, a high-pressure side inlet and a high-pressure side outlet. The boiler heating surface of the supercritical carbon dioxide boiler is connected to the low-pressure side inlet of the high-temperature regenerator through a turbine, the low-pressure side outlet of the high-temperature regenerator is connected to the cooler through the low-pressure side inlet and the low-pressure side outlet of the low-temperature regenerator in turn, and the cooler is connected to the high-pressure side inlet of the low-temperature regenerator through a compressor; the high-pressure side outlet of the low-temperature regenerator is respectively connected to the high-pressure side inlet of the high-temperature regenerator and the diverter economizer; the diverter economizer is connected to the boiler heating surface of the supercritical carbon dioxide boiler after being connected to the high-pressure side outlet pipeline of the high-temperature regenerator; the flue gas discharged from the supercritical carbon dioxide boiler passes through the boiler heating surface, the diverter economizer, the recirculating flue gas heater and the air preheater in turn; the air preheater is respectively connected to the external environment and the recirculating fan; the recirculating fan is connected to the burner through the recirculating flue gas heater.

[0005] Preferably, the split-flow economizer and the recirculating flue gas heater are connected in parallel or in series.

[0006] Preferably, the number of the compressors is set to be greater than or equal to one.

[0007] Preferably, a flow diversion device is provided at the low-pressure side outlet of the low-temperature regenerator.

[0008] Preferably, a flue gas purification device is provided between the recirculation fan and the air preheater.

[0009] Preferably, the proportion of fluid diverted to the divert economizer through the high-pressure side outlet of the low-temperature regenerator is set to 5%-20% of the total amount.

[0010] Preferably, the proportion of the fluid passing through the air preheater to the recirculation fan is set to 5%-30% of the total amount.

[0011] Preferably, the fluid temperature at the recirculation fan inlet is less than or equal to 200°C.

[0012] Preferably, the temperature of the fluid after being heated by the recirculating flue gas heater is greater than or equal to 300°C.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. The supercritical carbon dioxide boiler system for heating the recirculated flue gas provided by the present invention reduces the overall temperature level of the flue gas in the furnace by introducing the setting of flue gas recirculation, thereby reducing the average heat load and peak heat load of radiation heat transfer in the furnace, and providing an important basic condition for reducing the temperature of the heating surface of the furnace. By setting a recirculating flue gas heater to heat the recirculating flue gas with a relatively low temperature, the exhaust temperature of the boiler is reduced, and the thermal efficiency of the boiler is ensured. Although the temperature of the recirculated flue gas entering the furnace is increased, the temperature level of the flue gas in the furnace can be further reduced by appropriately increasing the flue gas recirculation rate. The combined effect of the above-mentioned factors can effectively achieve the purpose of reducing the wall temperature of the furnace heating surface, thereby greatly avoiding the possibility of overheating of the boiler furnace heating surface, significantly extending the service life of the boiler heating surface and increasing the safety of the operation of the boiler furnace heating surface.

[0015] 2. The supercritical carbon dioxide boiler system for heating the recirculating flue gas provided by the present invention can effectively utilize the waste heat of the flue gas at the tail end of the boiler, reduce the exhaust temperature of the boiler, and ensure the thermal efficiency of the boiler by introducing the supercritical carbon dioxide working medium diverted from the high-pressure side outlet of the low-temperature regenerator into the diversion economizer. Compared with a pure diversion supercritical carbon dioxide boiler system, since a recirculating flue gas heater is provided to share part of the waste heat of the tail flue gas, the temperature of the working medium at the inlet of the supercritical carbon dioxide boiler furnace can be appropriately reduced, and the purpose of reducing the wall temperature of the furnace heating surface can be effectively achieved. By adjusting the diversion ratio of the working medium at the high-pressure side outlet of the low-temperature regenerator and the flue gas recirculation rate, the temperature of the working medium at the inlet of the supercritical carbon dioxide boiler furnace and the exhaust temperature can be effectively adjusted according to different boiler load levels, thereby increasing the flexibility of the boiler system.

[0016] 3. The present invention adopts the settings of recirculating flue gas heater and diversion economizer to carry out energy exchange. Since this energy exchange process belongs to the energy exchange inside the boiler system and does not involve energy exchange with outside the boiler system, this setting has no effect on the efficiency of the boiler system.

[0017] 4. In the present invention, the outlet temperature of the recirculating flue gas does not exceed 200°C, which maximizes the temperature increase space of the recirculating flue gas, that is, reduces the boiler exhaust temperature as much as possible, thereby maximizing the thermal efficiency of the boiler.

[0018] 5. The temperature of the recycled flue gas after heating has been significantly increased (not less than 300°C), which can minimize the impact of the introduction of recycled flue gas on the fuel ignition process, ensure the full combustion of the fuel, and create conditions for further improving the flue gas recirculation rate.

[0019] 6. The temperature difference between the cold and hot ends of the recirculating flue gas heater introduced in the present invention is large, so the heat exchanger equipment has the advantages of small size, convenient layout, low investment, etc.

[0020] 7. In the present invention, by designing a reasonable temperature of the recirculated flue gas entering the furnace and a flue gas recirculation rate, the amount of NOx generated during the combustion of fuel in the furnace can be effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of a supercritical carbon dioxide boiler system for heating recirculating flue gas according to the present invention;

[0022] Figure numerals: 1. Supercritical carbon dioxide boiler; 2. Turbine; 3. High-temperature regenerator; 4. Low-temperature regenerator; 5. Cooler; 6. Compressor; 7. Recirculation fan; 8. Recirculation flue gas heater; 9. Burner; 10. Air preheater; 11. Diverter economizer; 12. Outside cold air; 13. Flue gas. DETAILED DESCRIPTION

[0023] In order to make the present invention more clearly understood, a preferred embodiment is described in detail with reference to the accompanying drawings as follows:

[0024] like Figure 1 As shown, the present invention provides a supercritical carbon dioxide boiler system for heating recirculating flue gas, the boiler system comprises a supercritical carbon dioxide boiler 1, a turbine 2, a high-temperature regenerator 3, a low-temperature regenerator 4, a cooler 5, a compressor 6, a recirculating fan 7, a recirculating flue gas heater 8, a burner 9, an air preheater 10 and a split economizer 11; the supercritical carbon dioxide boiler 1 is provided with a boiler heating surface, a burner 9 and an air preheater 10; the high-temperature regenerator 3 is provided with a low-pressure side inlet, a low-pressure side outlet, a high-pressure side inlet and a high-pressure side outlet; the low-temperature regenerator 4 is provided with a low-pressure side inlet, a low-pressure side outlet, a high-pressure side inlet and a high-pressure side outlet; the supercritical carbon dioxide boiler 1 heating surface outlet The outlet of turbine 2 is connected to the inlet of high-temperature regenerator 3, the outlet of turbine 2 is connected to the inlet of low-pressure side of high-temperature regenerator 3, the outlet of low-pressure side of high-temperature regenerator 3 is connected to the inlet of low-pressure side of low-temperature regenerator 4, the outlet of low-pressure side of low-temperature regenerator 4 is connected to the inlet of heat release side of cooler 5, the outlet of heat release side of cooler 5 is connected to the inlet of compressor 6, the outlet of compressor 6 is connected to the inlet of high-pressure side of low-temperature regenerator 4, the outlet of high-pressure side of low-temperature regenerator 4 is split into two paths, one path is connected to the inlet of high-pressure side of high-temperature regenerator 3, and the other path is connected to the inlet of heat absorption side of split economizer 11, the outlet working fluid of heat absorption side of split economizer 11 is connected to the inlet of heating surface of supercritical carbon dioxide boiler 1 after merging with the outlet working fluid of high-pressure side of high-temperature regenerator 3.

[0025] The tail flue gas 13 of the supercritical carbon dioxide boiler 1 passes through the shunt economizer 11, the recirculating flue gas heater 8 and the air preheater 10 in turn for heat exchange and is divided into two paths. One path is connected to the heat absorption side inlet of the recirculating flue gas heater 8 through the recirculating fan 7, and the heat absorption side outlet of the recirculating flue gas heater 8 is connected to the inlet of the burner 9. The other path is discharged after flue gas treatment. The outside cold air 12 is heated by the air preheater 10 and connected to the inlet of the burner 9. The proportion of the working fluid at the high pressure side outlet of the low-temperature regenerator 4 shunt to the shunt economizer 11 is 5-20%. The flue gas recirculation rate of the recirculating flue gas is 5% to 30%. The recirculating flue gas temperature at the inlet of the recirculating fan 7 does not exceed 200°C, and the recirculating flue gas temperature after being heated by the recirculating flue gas heater 8 is not less than 300°C. In the flue gas process, the shunt economizer 11 and the recirculating flue gas heater 8 can be in parallel or in series. When the two are connected in series, their upstream and downstream order can be specifically determined according to the system parameter characteristics. The supercritical carbon dioxide cycle can adopt a circulation scheme of one compressor 6 and multiple compressors 6 (including the main compressor and other compressors). The outlet of the low-pressure side of the low-temperature regenerator 4 can take diversion measures, and the working fluid at the outlet of the low-pressure side of the low-temperature regenerator 4 can flow through the cooler 5 in whole or in part to release heat. The solid particle concentration in the recirculating flue gas at the inlet of the recirculating fan 7 must meet the anti-wear requirements of the fan blades, and a purification device can be set if necessary.

[0026] Example

[0027] The supercritical carbon dioxide working medium at the outlet of the heating surface of the supercritical carbon dioxide boiler 1 enters the turbine 2 to perform work. After performing work, the supercritical carbon dioxide working medium enters the low-pressure side of the high-temperature regenerator 3 and the low-temperature regenerator 4 in turn to release heat, and then enters the heat release side of the cooler 5 to continue cooling, and then enters the compressor 6 to increase the pressure. The low-temperature and high-pressure working medium enters the high-pressure side of the low-temperature regenerator 4 to absorb heat and then is split into two paths. One path enters the high-pressure side of the high-temperature regenerator 3 to continue absorbing heat, and the other path enters the heat absorption side of the diversion economizer 11 to increase the temperature and then merges with the working medium at the high-pressure side outlet of the high-temperature regenerator 3, and then enters the inlet of the heating surface of the supercritical carbon dioxide boiler 1 to complete the cycle; the proportion of the working medium at the high-pressure side outlet of the low-temperature regenerator 4 diverted to the diversion economizer 11 is 10%. The tail flue gas of the supercritical carbon dioxide boiler 1 passes through the diversion economizer 11, the recirculating flue gas heater 8 and the air preheater 10 in sequence for cooling and then is divided into two paths. One path is the recirculating flue gas with a flue gas circulation rate of 20%. It enters the recirculating flue gas heater 8 through the recirculating fan 7, and enters the burner 9 after the flue gas temperature is increased. The recirculating flue gas temperature at the inlet of the recirculating fan 7 is 150°C, and the recirculating flue gas temperature at the outlet of the recirculating flue gas heater 8 is 350°C; the other path is the boiler exhaust gas, which is discharged after flue gas treatment 13; the external cold air 12 is heated by the air preheater 10 and then sent to the burner 9 to participate in combustion.

[0028] The supercritical carbon dioxide boiler system for heating the recirculated flue gas described in this embodiment reduces the overall temperature level of the flue gas in the furnace by introducing the setting of flue gas recirculation, thereby reducing the average heat load and peak heat load of radiation heat transfer in the furnace, and providing an important basic condition for reducing the temperature of the heating surface of the furnace. By setting a recirculating flue gas heater to heat the recirculating flue gas with a relatively low temperature, the exhaust temperature of the boiler is reduced, and the thermal efficiency of the boiler is ensured. Although the temperature of the recirculated flue gas entering the furnace increases, the temperature level of the flue gas in the furnace can be further reduced by appropriately increasing the flue gas recirculation rate. The combined effect of the above-mentioned factors can effectively achieve the purpose of reducing the wall temperature of the furnace heating surface, thereby greatly avoiding the possibility of overheating of the boiler furnace heating surface, significantly extending the service life of the boiler heating surface and increasing the safety of the operation of the boiler furnace heating surface.

[0029] The supercritical carbon dioxide boiler system for heating the recirculated flue gas described in this embodiment can effectively utilize the waste heat of the flue gas at the tail end of the boiler, reduce the exhaust temperature of the boiler, and ensure the thermal efficiency of the boiler by introducing the supercritical carbon dioxide working medium diverted from the high-pressure side outlet of the low-temperature regenerator 4 into the diversion economizer 11. Compared with a pure diversion supercritical carbon dioxide boiler system, since the recirculating flue gas heater 8 is provided to share part of the waste heat of the tail flue gas, the temperature of the working medium at the inlet of the supercritical carbon dioxide boiler furnace can be appropriately reduced, and the purpose of reducing the wall temperature of the furnace heating surface can be effectively achieved. By adjusting the diversion ratio of the working medium at the high-pressure side outlet of the low-temperature regenerator 4 and the flue gas recirculation rate, the temperature of the working medium at the inlet of the supercritical carbon dioxide boiler furnace and the exhaust temperature can be effectively adjusted according to different boiler load levels, thereby increasing the flexibility of the boiler system.

[0030] This embodiment uses the settings of the recirculating flue gas heater 8 and the diverter economizer 11 for energy exchange. Since this energy exchange process belongs to the energy exchange within the boiler system and does not involve energy exchange with outside the boiler system, this setting has no effect on the efficiency of the boiler system.

[0031] In this embodiment, the outlet temperature of the recirculated flue gas is only 150° C., which maximizes the temperature increase space of the recirculated flue gas, that is, reduces the boiler exhaust temperature as much as possible, thereby maximizing the thermal efficiency of the boiler.

[0032] In this embodiment, the temperature of the heated recycled flue gas is significantly increased, which can minimize the impact of the introduction of recycled flue gas on the fuel ignition process, ensure the full combustion of the fuel, and create conditions for further improving the flue gas recirculation rate.

[0033] The temperature difference between the cold and hot ends of the recirculating flue gas heater 8 introduced in this embodiment is large, so the heat exchanger equipment has the advantages of small size, convenient layout, low investment, etc. In this embodiment, by designing the temperature of the recirculating flue gas entering the furnace and the flue gas recirculation rate reasonably, the NOx generation during the combustion of fuel in the furnace can be effectively reduced.

[0034] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and equivalent changes made by using the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A supercritical carbon dioxide boiler system for heating recirculating flue gas, characterized in that: The boiler system comprises a supercritical carbon dioxide boiler (1), a turbine (2), a high-temperature regenerator (3), a low-temperature regenerator (4), a cooler (5), a compressor (6), a recirculation fan (7), a recirculation flue gas heater (8), a burner (9), an air preheater (10) and a split economizer (11); the supercritical carbon dioxide boiler (1) is provided with a boiler heating surface, a burner (9) and an air preheater (10); the high-temperature regenerator (3) is provided with a low-pressure side inlet, a low-pressure side outlet, a high-pressure side inlet and a high-pressure side outlet; the low-temperature regenerator (4) is provided with a low-pressure side inlet, a low-pressure side outlet, a high-pressure side inlet and a high-pressure side outlet; the boiler heating surface of the supercritical carbon dioxide boiler (1) is connected to the low-pressure side inlet of the high-temperature regenerator (3) through the turbine (2); the low-pressure side outlet of the high-temperature regenerator (3) is connected to the cooler (5) through the low-pressure side inlet and the low-pressure side outlet of the low-temperature regenerator (4) in turn; the cooler (5) is connected to the high-pressure side inlet of the low-temperature regenerator (4) through the compressor (6); the low-temperature regenerator (4) The high-pressure side outlet is respectively connected to the high-pressure side inlet of the high-temperature regenerator (3) and the split economizer (11); the split economizer (11) is connected to the boiler heating surface of the supercritical carbon dioxide boiler (1) through the high-pressure side outlet pipeline of the high-temperature regenerator (3); the flue gas discharged from the supercritical carbon dioxide boiler (1) passes through the boiler heating surface, the split economizer (11), the recirculating flue gas heater (8) and the air preheater (10) in sequence; the air preheater (10) is respectively connected to the external environment and the recirculating fan (7) The recirculation fan (7) is connected to the burner (9) through the recirculation flue gas heater (8); the diversion economizer (11) and the recirculation flue gas heater (8) are arranged in parallel or in series; a diversion device is arranged at the low-pressure side outlet of the low-temperature regenerator (4); the proportion of fluid diverted to the diversion economizer (11) through the high-pressure side outlet of the low-temperature regenerator (4) is set to 5%-20% of the total amount; the proportion of fluid diverted to the recirculation fan (7) through the air preheater (10) is set to 5%-30% of the total amount.

2. A supercritical carbon dioxide boiler system for heating recirculating flue gas as claimed in claim 1, characterized in that: The number of the compressors (6) is set to be greater than or equal to 1.

3. A supercritical carbon dioxide boiler system for heating recirculating flue gas according to claim 1, characterized in that: A flue gas purification device is provided between the recirculation fan (7) and the air preheater (10).

4. A supercritical carbon dioxide boiler system for heating recirculating flue gas as claimed in claim 1, characterized in that: The fluid temperature at the inlet of the recirculation fan (7) is less than or equal to 200°C.

5. A supercritical carbon dioxide boiler system for heating recirculating flue gas as claimed in claim 1, characterized in that: The temperature of the fluid after being heated by the recirculating flue gas heater (8) is greater than or equal to 300°C.

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