A supercritical carbon dioxide boiler system with a highly safe furnace heating surface

Abstract

The present invention relates to a supercritical carbon dioxide boiler system with a high-safety furnace heating surface, and belongs to the technical field of boiler equipment. It includes a supercritical carbon dioxide boiler, a turbine, a high-temperature regenerator, a low-temperature regenerator, a cooler, a compressor, a recirculation fan, a recirculation flue gas heater, a burner, an air preheater and a chimney; the present invention reduces the overall temperature level of the flue gas in the furnace by introducing a flue gas recirculation setting, thereby reducing the average heat load and the peak heat load of the radiation heat transfer in the furnace, so as to achieve the reduction of the furnace heating surface temperature. The present invention can effectively achieve the purpose of reducing the wall temperature of the furnace heating surface, thereby 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 boiler furnace heating surface.

Description

Technical Field

[0001] The invention relates to a supercritical carbon dioxide boiler system with a high-safety furnace heating surface, 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. Summary of the invention

[0003] The purpose of the invention is to solve the technical problem of overheating of the metal tube wall temperature of the heating surface of the supercritical carbon dioxide boiler furnace.

[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 with a high-safety furnace heating surface, the boiler system includes a supercritical carbon dioxide boiler, a turbine, a high-temperature regenerator, a low-temperature regenerator, a cooler, a compressor, a recirculation fan, a recirculation flue gas heater, a burner, an air preheater and a chimney; 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 supercritical carbon dioxide boiler heating surface is connected to the supercritical carbon dioxide boiler through the turbine. It is connected to the low-pressure side inlet of the high-temperature reheater, and the low-pressure side outlet of the high-temperature reheater is connected to the cooler and the compressor in sequence through the low-pressure side inlet and the low-pressure side outlet of the low-temperature reheater; the compressor is then connected to the high-pressure side inlet of the high-temperature reheater through the high-pressure side inlet and the high-pressure side outlet of the low-temperature reheater, and the high-pressure side outlet of the high-temperature reheater is connected to the heating surface of the supercritical carbon dioxide boiler through the recirculating flue gas heater; the supercritical carbon dioxide boiler is respectively connected to the chimney and the recirculating fan through the air preheater, and the recirculating fan is connected to the burner through the recirculating flue gas heater; the air preheater is respectively connected to the external environment and the burner.

[0005] Preferably, the number of the compressors is set to be greater than or equal to one.

[0006] Preferably, the low-pressure side outlet of the low-temperature regenerator is provided with a diverter device, and the low-pressure side outlet of the low-temperature regenerator is connected to the cooler through the diverter device.

[0007] Preferably, the high-pressure side outlet of the low-temperature regenerator is provided with a diverter device, and the high-pressure side outlet of the low-temperature regenerator is connected to the high-pressure side inlet of the high-temperature regenerator through the diverter device.

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

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] 1. The present invention provides a supercritical carbon dioxide boiler system with a high-safety furnace heating surface. The overall temperature level of the flue gas in the furnace is reduced by introducing a flue gas recirculation setting, thereby reducing the average heat load and peak heat load of radiation heat transfer in the furnace, providing an important basic condition for reducing the temperature of the furnace heating surface. A recirculating flue gas heater is provided to heat the recirculating flue gas with a relatively low temperature, thereby reducing the temperature level of the working fluid that is about to enter the boiler heating surface. Although the temperature of the recirculating 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.

[0011] 2. The present invention adopts the setting of the recirculating flue gas heater 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.

[0012] 3. 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, the temperature level of the working fluid about to enter the boiler heating surface is reduced as much as possible, thereby minimizing the wall temperature of the furnace heating surface.

[0013] 4. 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.

[0014] 5. The recirculating flue gas heater introduced in the present invention exchanges heat between flue gas and high-pressure working fluid. The heat exchanger equipment has small size, convenient layout and low investment.

[0015] 6. 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

[0016] Figure 1 This is a schematic diagram of the structure of a supercritical carbon dioxide boiler system with a highly safe furnace heating surface according to the present invention;

[0017] 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. Chimney. DETAILED DESCRIPTION

[0018] 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:

[0019] like Figure 1 As shown, the present invention provides a supercritical carbon dioxide boiler system with a high-safety furnace heating surface, the boiler system includes 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 chimney 11.

[0020] The outlet of the heating surface of the supercritical carbon dioxide boiler 1 is connected to the inlet of the turbine 2, the outlet of the turbine 2 is connected to the low-pressure side inlet of the high-temperature regenerator 3, the low-pressure side outlet of the high-temperature regenerator 3 is connected to the low-pressure side inlet of the low-temperature regenerator 4, the low-pressure side outlet of the low-temperature regenerator 4 is connected to the heat release side inlet of the cooler 5, the heat release side outlet of the cooler 5 is connected to the inlet of the compressor 6, the outlet of the compressor 6 is connected to the high-pressure side inlet of the low-temperature regenerator 4, the high-pressure side outlet of the low-temperature regenerator 4 is connected to the high-pressure side inlet of the high-temperature regenerator 3, the high-pressure side outlet of the high-temperature regenerator 3 is connected to the heat release side inlet of the recirculating flue gas heater 8, and the heat release side outlet of the recirculating flue gas heater 8 is connected to the inlet of the heating surface of the supercritical carbon dioxide boiler 1.

[0021] The tail flue gas of the supercritical carbon dioxide boiler 1 is cooled by the air preheater 10 and then 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 through the chimney 11 after flue gas treatment. The outside cold air is heated by the air preheater 10 and then connected to the inlet of the burner 9.

[0022] 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, then enters the heat release side of the cooler 5 to continue cooling, then enters the compressor 6 to increase the pressure, then enters the high-pressure side of the low-temperature regenerator 4 and the high-temperature regenerator 3 in turn to absorb heat, then enters the recirculating flue gas heater 8 to cool, and then enters the inlet of the heating surface of the supercritical carbon dioxide boiler 1 to complete the cycle; the tail of the supercritical carbon dioxide boiler 1 After being cooled by the air preheater 10, the flue gas is divided into two paths. One path is the recirculated flue gas with a flue gas circulation rate of 5% to 30%. 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 from the chimney 11 after flue gas treatment; the external cold air is heated by the air preheater 10 and then sent to the burner 9 to participate in combustion.

[0023] The supercritical carbon dioxide boiler system with a high-safety furnace heating surface described in this embodiment reduces the overall temperature level of the flue gas in the furnace by introducing the flue gas recirculation setting, thereby reducing the average heat load and peak heat load of radiation heat transfer in the furnace, providing an important basic condition for reducing the temperature of the furnace heating surface. By setting a recirculating flue gas heater to heat the recirculating flue gas with a relatively low temperature, the temperature level of the working fluid that is about to enter the boiler heating surface is reduced. Although the temperature of the recirculating 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 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.

[0024] The present invention adopts the setting of the recirculating flue gas heater 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.

[0025] In the present invention, the outlet temperature of the recirculating flue gas is only 150°C, which maximizes the temperature increase space of the recirculating flue gas, that is, reduces the temperature level of the working fluid about to enter the boiler heating surface as much as possible, thereby minimizing the wall temperature of the furnace heating surface.

[0026] The temperature of the recycled flue gas after heating 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.

[0027] The recirculating flue gas heater introduced in the present invention exchanges heat between flue gas and high-pressure working fluid. The heat exchanger equipment has small size, convenient layout and low investment.

[0028] In the present invention, the NOx generation amount during the combustion of fuel in the furnace can be effectively reduced by reasonably designing the temperature of the recirculated flue gas entering the furnace and the flue gas recirculation rate.

[0029] 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 with a high-safety furnace heating surface, 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 chimney (11); 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-pressure side 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 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), and the low-pressure side outlet of the high-temperature regenerator (3) is connected to the low-pressure side outlet of the high-pressure side through the low-pressure side outlet of the high-temperature regenerator (3). The low-pressure side inlet and the low-pressure side outlet of the regenerator (4) are connected to the cooler (5) and the compressor (6) in sequence; the compressor (6) is then connected to the high-pressure side inlet of the high-temperature regenerator (3) through the high-pressure side inlet and the high-pressure side outlet of the low-temperature regenerator (4); the high-pressure side outlet of the high-temperature regenerator (3) is connected to the heating surface of the supercritical carbon dioxide boiler (1) through the recirculating flue gas heater (8); the supercritical carbon dioxide boiler (1) is respectively connected to the chimney (11) and the recirculating fan (7) through the air preheater (10); the recirculating fan (7) is connected to the burner (9) through the recirculating flue gas heater (8); the air preheater (10) is respectively connected to the external environment and the burner (9).

2. A supercritical carbon dioxide boiler system with a high-safety furnace heating surface 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 with a high-safety furnace heating surface as claimed in claim 1, characterized in that: The low-pressure side outlet of the low-temperature heat regenerator (4) is provided with a flow splitter, and the low-pressure side outlet of the low-temperature heat regenerator (4) is connected to the cooler (5) via the flow splitter.

4. A supercritical carbon dioxide boiler system with a high-safety furnace heating surface as claimed in claim 1, characterized in that: The high-pressure side outlet of the low-temperature heat regenerator (4) is provided with a flow divider, and the high-pressure side outlet of the low-temperature heat regenerator (4) is connected to the high-pressure side inlet of the high-temperature heat regenerator (3) via the flow divider.

5. A supercritical carbon dioxide boiler system with a high-safety furnace heating surface as claimed in claim 1, characterized in that: A flue gas purification device is provided between the recirculation fan (7) and the air preheater (10).

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