External pulverized coal combustion device, circulating fluidized bed boiler and operation method

Abstract

The invention discloses an external pulverized coal combustion device, a circulating fluidized bed boiler and an operation method. The external pulverized coal combustion device comprises a pulverized coal combustion chamber, a pulverized coal combustor air pipe, a pulverized coal spray pipe, a high-temperature steam spray pipe and a high-temperature gas-solid fuel branch pipe; the pulverized coal burner air pipe is arranged at the front end of the pulverized coal combustion chamber and provides and controls the pulverized coal combustion air volume, so that pulverized coal is combusted in an oxygen-deficient state; the pulverized coal spray pipe is arranged in the pulverized coal burner air pipe and used for conveying pulverized coal into a pulverized coal combustion chamber. The high-temperature steam spray pipe is arranged in the middle of the pulverized coal combustion chamber, and high-temperature and high-pressure steam is introduced into the pulverized coal combustion chamber through the high-temperature steam spray pipe; the high-temperature gas-solid fuel branch pipe is arranged at the tail end of the pulverized coal combustion chamber and used for being connected with a circulating fluidized bed boiler. And the high-temperature gas-solid fuel mixture is quickly mixed with oxygen provided by secondary air in the hearth and is combusted, so that the combustion stability and the denitration reaction efficiency of the circulating fluidized bed boiler under low load are improved.

Description

Technical Field

[0001] This invention belongs to the field of circulating fluidized bed technology. Specifically, it relates to an external pulverized coal combustion device, a circulating fluidized bed boiler, and an operating method, which are used for low-load stable combustion scenarios of circulating fluidized bed generator sets to improve the combustion stability of circulating fluidized bed units at low loads. Background Technology

[0002] With the rapid growth of installed capacity of new energy sources such as wind power and photovoltaics, their strong randomness and volatility have led to a surge in grid peak-shaving pressure. Against this backdrop, circulating fluidized bed (CFB) units, with their unique fluidized combustion technology, have become a key peak-shaving power source supporting a high proportion of new energy consumption. Further reduction of operating load and extremely deep peak-shaving of CFB units are needed, but their deep peak-shaving capabilities face multiple technical challenges and optimization requirements: (1) The combustion stability of circulating fluidized bed units usually deteriorates when the load drops to 30%. This is mainly reflected in the decrease in bed temperature, difficulty in combustion and burnout of CFB granular coal, increase in carbon content of bottom ash, and increase in mechanical incomplete combustion losses.

[0003] (2) The environmental performance of circulating fluidized bed units usually deteriorates when the load drops to 30%. At low load, the bed temperature and the temperature of the upper part of the furnace of the circulating fluidized bed unit both decrease, falling below 800℃, which is significantly lower than the temperature of the non-catalytic reduction (SNCR) denitrification reaction zone of the fluidized bed boiler, resulting in extremely low denitrification efficiency.

[0004] To improve the bed temperature and combustion stability of circulating fluidized bed (CFB) units under low loads, and to increase the boiler furnace outlet temperature and SNCR reaction efficiency, adjusting the particle size of the CFB coal and reducing the primary air volume can raise the bed temperature, but the effect is very limited, only increasing it by 5-10°C. Furthermore, current CFB units primarily burn low-quality coal gangue, which is hard and difficult to crush. Existing equipment struggles to further control its combustion to an ideal state, and crushing energy consumption increases rapidly. Reducing the primary air volume can also easily lead to poor fluidization in the CFB boiler, and in severe cases, cause boiler coking.

[0005] These problems are caused by the fuel characteristics of circulating fluidized bed boilers (large fuel particle size and poor coal quality) and the circulating combustion method, and are difficult to solve fundamentally. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an external pulverized coal combustion device, a circulating fluidized bed boiler and an operation method, so as to improve the combustion temperature and combustion stability of the circulating fluidized bed unit under low load, and to improve the boiler furnace outlet temperature and SNCR reaction efficiency.

[0007] To solve the above technical problems, according to one aspect of the present invention, an external pulverized coal combustion device is provided, comprising a pulverized coal combustion chamber, a pulverized coal burner duct, a pulverized coal injection pipe, a high-temperature steam injection pipe, and a high-temperature gas-solid fuel branch pipe; The pulverized coal burner duct is located at the front end of the pulverized coal combustion chamber. The pulverized coal burner duct provides and controls the pulverized coal combustion air volume, so that the pulverized coal can burn under oxygen-deficient conditions. The coal powder burner duct is equipped with the coal powder injection pipe, which is used to deliver coal powder into the coal powder combustion chamber. The high-temperature steam nozzle is located in the middle of the pulverized coal combustion chamber, through which high-temperature and high-pressure steam is introduced into the pulverized coal combustion chamber. The high-temperature gas-solid fuel branch pipe is located at the end of the pulverized coal combustion chamber and is used to connect to the circulating fluidized bed boiler.

[0008] Furthermore, the cross-section of the pulverized coal combustion chamber is L-shaped.

[0009] Furthermore, the pulverized coal burner duct is also equipped with an oil gun and ignition system, which is used to ignite the pulverized coal conveyed by the pulverized coal nozzle when it is put into operation.

[0010] Furthermore, a makeup air pipe is installed downstream of the pulverized coal combustion chamber, through which air is supplied according to the internal temperature of the pulverized coal combustion chamber.

[0011] Furthermore, the inner wall of the pulverized coal combustion chamber is lined with high-temperature resistant and wear-resistant castable.

[0012] According to another aspect of the present invention, a circulating fluidized bed boiler is provided, comprising the external pulverized coal combustion device described above, a high-temperature gas-solid fuel branch pipe connected to the secondary air duct of the circulating fluidized bed boiler, and a high-temperature gas-solid fuel mixture obtained by combustion of the external pulverized coal combustion device being transported through the high-temperature gas-solid fuel branch pipe to the interior of the secondary air duct of the circulating fluidized bed boiler and entering the boiler furnace together with the secondary air.

[0013] According to another aspect of the present invention, an operating method for improving the low-load performance of a circulating fluidized bed boiler is provided, implemented based on the circulating fluidized bed boiler described above, comprising the following steps: S1: Start the external pulverized coal combustion device. The pulverized coal burner duct provides and controls the pulverized coal combustion air volume, so that the pulverized coal is partially burned in a hypoxic state and the internal temperature of the combustion chamber is maintained at 900℃-1100℃. S2: High-temperature and high-pressure steam is introduced into the pulverized coal combustion chamber through a high-temperature steam nozzle. The high-temperature and high-pressure steam reacts with the partially burned pulverized coal to produce a combustible gas rich in hydrogen, carbon monoxide and methane, and forms a high-temperature gas-solid fuel mixture with the incompletely burned pulverized coal. S3: The high-temperature gas-solid fuel mixture obtained in step S2 is transported to the secondary air duct of the circulating fluidized bed boiler through the high-temperature gas-solid fuel branch pipe and enters the boiler furnace along with the secondary air. S4: The high-temperature gas-solid fuel mixture is rapidly mixed with oxygen supplied by secondary air and combusted in the furnace.

[0014] Furthermore, the air volume provided by the pulverized coal burner duct is 18-22% of the air volume required for complete combustion of pulverized coal.

[0015] Furthermore, high-temperature and high-pressure steam at 0.55-0.65 MPa and 190-210℃ is input through the high-temperature steam nozzle.

[0016] Furthermore, the temperature of the high-temperature gas-solid fuel mixture entering the furnace is 800℃-900℃.

[0017] This invention adds an external pulverized coal combustion device to the existing circulating fluidized bed boiler. Within this device, the pulverized coal partially combusts and releases heat to maintain a high temperature inside the combustion chamber. Then, a high-temperature, high-pressure steam flow is introduced. The high-temperature gas-solid fuel mixture formed after pulverized coal combustion and coal gasification enters the boiler furnace for combustion through a secondary air duct. The high-temperature gas-solid fuel mixture enters the furnace at a temperature of 800-900℃ and contains flammable and easily ignited components such as H2, CH4, CO, and preheated pulverized coal. The secondary air duct provides the oxygen required for the combustion of the high-temperature gas-solid fuel mixture, enabling it to ignite rapidly and release heat, heating the bed material and increasing the bed and furnace temperatures. This improves the combustion stability and denitrification efficiency of the circulating fluidized bed boiler at low loads. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the external pulverized coal combustion device of the present invention; Figure 2 This is a schematic diagram of the overall structure of the circulating fluidized bed boiler of the present invention.

[0019] In the diagram, 1-Pulverized coal combustion chamber, 2-Pulverized coal burner duct, 3-Pulverized coal nozzle, 4-High-temperature steam nozzle, 5-High-temperature gas-solid fuel branch pipe, 6-Make-up air pipe, 7-Oil gun and ignition system, 8-Secondary air duct, 9-Dense phase zone of furnace, 10-Dilute phase zone of furnace, 11-CFB coal pipe, 12-Return feeder, 13-Separator, 14-High-temperature wear-resistant castable. Detailed Implementation

[0020] The basic concept of this application is to add an external pulverized coal combustion device to the existing circulating fluidized bed boiler. The external pulverized coal combustion device realizes the partial combustion and gasification of pulverized coal, generating a high-temperature gas-solid fuel mixture containing combustible components such as H2, CH4, and CO, as well as preheated pulverized coal. This mixture is sent into the furnace through the secondary air duct 8 for rapid combustion, effectively increasing the bed temperature and furnace temperature, and enhancing the combustion stability and denitrification efficiency under low load.

[0021] Based on the above ideas, and referring to Figure 1 An external pulverized coal combustion device provided in a typical embodiment of the present invention includes a pulverized coal combustion chamber 1, a pulverized coal burner duct 2, a pulverized coal spray pipe 3, a high-temperature steam spray pipe 4, and a high-temperature gas-solid fuel branch pipe 5.

[0022] The external pulverized coal combustion device adopts a fully insulated structure, which can reduce external heat dissipation, minimize heat loss, maintain a high temperature inside the combustion chamber, and make combustion more stable and the combustion chamber temperature easier to control.

[0023] The main body of the external pulverized coal combustion device is the pulverized coal combustion chamber, and the walls of the pulverized coal combustion chamber are lined with high-temperature resistant and wear-resistant castable 14. Preferably, the cross-section of the pulverized coal combustion chamber is L-shaped.

[0024] Among them, the pulverized coal burner duct 2 is located at the front end of the pulverized coal combustion chamber 1. The pulverized coal burner duct 2 provides and controls the pulverized coal combustion air volume, so that the pulverized coal burns in a low oxygen state and the internal temperature of the combustion chamber is maintained between 900℃ and 1100℃.

[0025] The coal pulverized burner duct 2 is equipped with the coal pulverized spray pipe 3, which is made of high-temperature resistant stainless steel. High-concentration coal pulverized material is introduced into the coal pulverized spray pipe 3 by compressed air pneumatic conveying.

[0026] The high-temperature steam nozzle 4 is located in the middle of the pulverized coal combustion chamber 1. High-temperature and high-pressure steam is introduced into the pulverized coal combustion chamber 1 through the high-temperature steam nozzle 4. On the one hand, it provides the H2O required for the pulverized coal to carry out the water-gas reaction. On the other hand, the high-pressure and high-speed steam flow enters the combustion chamber and forms a suction force, which drives the pulverized coal combustion products to flow and mix, thereby reducing the air supply pressure and energy consumption of the blower.

[0027] Among them, the high-temperature gas-solid fuel branch pipe 5 is located at the end of the pulverized coal combustion chamber 1 and is used to connect to the circulating fluidized bed boiler. The number of high-temperature gas-solid fuel branch pipes 5 is at least two. By using multiple high-temperature gas-solid fuel branch pipes to enter the furnace for combustion, on the one hand, the pulverized coal combustion in the furnace can be more uniform, and the bed temperature and furnace temperature distribution can be more uniform; on the other hand, it also reduces the control difficulty and manufacturing cost of the pulverized coal combustion device, making the system simpler and easier to use.

[0028] In this embodiment, the pulverized coal undergoes combustion and heat release in the oxygen-deficient portion of the pulverized coal combustion chamber 1, maintaining a high internal temperature of 900-1100°C. Then, a high-temperature, high-pressure steam flow is introduced. On the one hand, the steam flow provides the H2O required for the pulverized coal to undergo the water-gas reaction. On the other hand, the high-pressure, high-speed steam flow enters the combustion chamber and forms a suction force, driving the flow and mixing of the pulverized coal combustion products, thereby reducing the air supply pressure and energy consumption of the blower.

[0029] The high-temperature gas-solid fuel mixture (mainly composed of preheated pulverized coal, H2, CH4, and CO) formed after pulverized coal combustion and gasification enters the boiler furnace through the secondary air duct 8 via the high-temperature gas-solid fuel branch pipe 5. The high-temperature gas-solid fuel mixture enters the furnace at a very high temperature, between 800-900℃, and contains easily flammable and ignitable components such as H2, CH4, CO, and preheated pulverized coal. Furthermore, the secondary air duct 8 can rapidly provide the oxygen required for the combustion of the high-temperature gas-solid fuel mixture. Therefore, the high-temperature gas-solid fuel mixture can ignite and release heat quickly, heating the bed material and increasing the bed and furnace temperatures. This improves the combustion stability and denitrification efficiency of the circulating fluidized bed boiler at low loads.

[0030] In a preferred embodiment, the pulverized coal burner duct 2 is also equipped with an oil gun and an ignition system 7, which is mainly used for ignition when the external pulverized coal combustion starts to operate, and for igniting the pulverized coal.

[0031] In another preferred embodiment, an air supply pipe 6 is provided downstream of the pulverized coal combustion chamber to supply air according to the internal temperature of the pulverized coal combustion chamber 1. By providing oxygen, combustion is increased, and the flue gas temperature is controlled to be maintained between 900-1100°C, thereby promoting further gasification of the high-temperature gas-solid fuel.

[0032] Another typical embodiment of the present invention provides a circulating fluidized bed boiler, which includes conventional components such as a secondary air duct 8, a dense phase zone 9 of the furnace, a dilute phase zone 10 of the furnace, a CFB coal pipe 11, a return feeder 12, and a separator 13, as well as the external pulverized coal combustion device described in the above embodiments. A high-temperature gas-solid fuel branch pipe 5 is connected to the secondary air duct 8. The high-temperature gas-solid fuel mixture obtained from combustion by the external pulverized coal combustion device is transported through the high-temperature gas-solid fuel branch pipe 5 to the interior of the secondary air duct 8 of the circulating fluidized bed boiler, and enters the boiler furnace along with the secondary air. It burns rapidly and releases heat in the furnace, with the oxygen for combustion provided by the secondary air duct 8.

[0033] Another typical embodiment of the present invention provides an operating method for improving the low-load performance of a circulating fluidized bed boiler, which is implemented based on the circulating fluidized bed boiler described in the above embodiments.

[0034] The external pulverized coal combustion device is started, and the pulverized coal conveyed by the pulverized coal nozzle is ignited through the oil gun and ignition system 7.

[0035] The pulverized coal in the nozzle of the pulverized coal burner is transported by dense-phase pneumatic conveying. On the one hand, this reduces the amount of high-pressure air used and energy consumption. On the other hand, it reduces the amount of air supplied, enabling the pulverized coal to burn under oxygen-deficient conditions, thereby reducing the amount of NOx generated.

[0036] The duct of the pulverized coal burner provides and controls the air volume for pulverized coal combustion, enabling partial combustion of pulverized coal under oxygen-deficient conditions; the provided air volume is approximately 18-22% of the air volume required for complete combustion of pulverized coal, preferably 20%; and the temperature of the combustion products is controlled between 900-1100℃.

[0037] The purpose of partial combustion of pulverized coal in an external pulverized coal combustion device is to use the exothermic heat from the partial combustion of pulverized coal to heat the interior of the pulverized coal combustion chamber and maintain it between 900-1100℃, so that the coal, flue gas and H2O can undergo pyrolysis and gasification without the need for an external heating source, thereby reducing the amount of NOx generated.

[0038] High-temperature and high-pressure steam is introduced into the pulverized coal combustion chamber through a high-temperature steam nozzle. The pressure of the introduced high-temperature and high-pressure steam is 0.55-0.65MPa and the temperature is 190-210℃. It is preferred to introduce high-temperature and high-pressure steam at 0.6MPa and 200℃. Directly introducing high-temperature and high-pressure steam reduces the heat absorption of water vaporization and makes it easier to maintain the temperature of the combustion gasification chamber.

[0039] During this process, air is supplied through the make-up air pipe 6 when the temperature of the combustion gasification products decreases, so that the combustible components can burn and release heat, thereby increasing the temperature of the gas-solid mixture and achieving staged air supply.

[0040] High-temperature, high-pressure steam reacts with partially burned coal powder to produce a water-gas mixture rich in hydrogen, carbon monoxide, and methane, which then forms a high-temperature gas-solid fuel mixture with the incompletely burned coal powder.

[0041] The obtained high-temperature gas-solid fuel mixture is transported through the high-temperature gas-solid fuel branch pipe to the secondary air duct 8 of the circulating fluidized bed boiler, and enters the boiler furnace along with the secondary air.

[0042] The high-temperature gas-solid fuel mixture is rapidly mixed with oxygen supplied by secondary air and combusted inside the furnace.

[0043] When the high-temperature gas-solid fuel mixture enters the furnace, its temperature is between 800-900℃. The mixture contains flammable and easily ignited components such as H2, CH4, CO, and preheated pulverized coal. Furthermore, the secondary air duct 8 can rapidly supply the oxygen required for combustion of the high-temperature gas-solid fuel mixture. Therefore, the high-temperature gas-solid fuel mixture can ignite and release heat quickly, heating the bed material and increasing the bed and furnace temperatures. This improves the combustion stability and denitrification efficiency of the circulating fluidized bed boiler at low loads. The abundant air supply provides combustion oxygen and reduces the average temperature of the combustion zone, thus decreasing NOx formation. The presence of H2, CH4, and CO also reduces NOx formation.

Claims

1. An external pulverized coal combustion device, characterized in that: This includes a pulverized coal combustion chamber, pulverized coal burner duct, pulverized coal injection pipe, high-temperature steam injection pipe, and high-temperature gas-solid fuel branch pipe; The pulverized coal burner duct is located at the front end of the pulverized coal combustion chamber. The pulverized coal burner duct provides and controls the pulverized coal combustion air volume, so that the pulverized coal can burn under oxygen-deficient conditions. The coal powder burner duct is equipped with the coal powder injection pipe, which is used to deliver coal powder into the coal powder combustion chamber. The high-temperature steam nozzle is located in the middle of the pulverized coal combustion chamber, through which high-temperature and high-pressure steam is introduced into the pulverized coal combustion chamber. The high-temperature gas-solid fuel branch pipe is located at the end of the pulverized coal combustion chamber and is used to connect to the circulating fluidized bed boiler.

2. The external pulverized coal combustion device according to claim 1, characterized in that: The cross-section of the pulverized coal combustion chamber is L-shaped.

3. The external pulverized coal combustion device according to claim 1 or 2, characterized in that: The pulverized coal burner duct is also equipped with an oil gun and ignition system, which is used to ignite the pulverized coal conveyed by the pulverized coal nozzle when it is put into operation.

4. The external pulverized coal combustion device according to claim 3, characterized in that: A makeup air pipe is installed downstream of the pulverized coal combustion chamber, through which air is supplied according to the internal temperature of the pulverized coal combustion chamber.

5. The external pulverized coal combustion device according to claim 1 or 4, characterized in that: The inner wall of the pulverized coal combustion chamber is lined with high-temperature and wear-resistant castable.

6. A circulating fluidized bed boiler, characterized in that: The device includes an external pulverized coal combustion device as described in any one of claims 1-5, wherein a high-temperature gas-solid fuel branch pipe is connected to the secondary air duct of a circulating fluidized bed boiler, and the high-temperature gas-solid fuel mixture obtained by combustion of the external pulverized coal combustion device is transported to the interior of the secondary air duct of the circulating fluidized bed boiler through the high-temperature gas-solid fuel branch pipe and enters the boiler furnace together with the secondary air.

7. An operating method for improving the low-load performance of a circulating fluidized bed boiler, characterized in that, Based on the circulating fluidized bed boiler as described in claim 6, the implementation includes the following steps: S1: Start the external pulverized coal combustion device. The pulverized coal burner duct provides and controls the pulverized coal combustion air volume, so that the pulverized coal is partially burned in a hypoxic state and the internal temperature of the combustion chamber is maintained at 900℃-1100℃. S2: High-temperature and high-pressure steam is introduced into the pulverized coal combustion chamber through a high-temperature steam nozzle. The high-temperature and high-pressure steam reacts with the partially burned pulverized coal to produce a combustible gas rich in hydrogen, carbon monoxide and methane, and forms a high-temperature gas-solid fuel mixture with the incompletely burned pulverized coal. S3: The high-temperature gas-solid fuel mixture obtained in step S2 is transported to the secondary air duct of the circulating fluidized bed boiler through the high-temperature gas-solid fuel branch pipe and enters the boiler furnace along with the secondary air. S4: The high-temperature gas-solid fuel mixture is rapidly mixed with oxygen supplied by secondary air and combusted in the furnace.

8. The method according to claim 8, characterized in that: The air volume provided by the pulverized coal burner duct is 18-22% of the air volume required for complete combustion of pulverized coal.

9. The method according to claim 8, characterized in that: High-temperature steam nozzles input high-temperature and high-pressure steam at 0.55-0.65MPa and 190-210℃.

10. The method according to claim 8 or 9, characterized in that: The temperature of the high-temperature gas-solid fuel mixture when it enters the furnace is 800℃-900℃.

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