Biomass gasification coupling combustion system and method

Abstract

The invention discloses a biomass gasification coupling combustion system and method.The system comprises a hearth and a fire grate arranged on the lower portion of the hearth, a plurality of air chambers are arranged at the bottom of the fire grate, and the fire grate comprises a drying pyrolysis area on the front section and a coke combustion area on the middle-rear section; the hearth comprises a vaporizing chamber and a hearth main combustion chamber, a front arch is arranged between the vaporizing chamber and the hearth main combustion chamber, reducing gas generated in the fire grate drying pyrolysis area enters the vaporizing chamber, and the reducing gas in the vaporizing chamber is jetted into the hearth main combustion chamber through a gap of the front arch. By means of the gasification-combustion double-hearth coupling design, gas production of fuel on the fire grate at all stages is effectively regulated and controlled, and the gasification chamber enriches reducing gas generated in the fire grate drying pyrolysis area and is used for in-situ reduction of smoke of a main combustion chamber of the hearth; the reducing gas can strengthen the mixing effect in the main combustion chamber, and the combustion efficiency is improved; the method is an efficient and economical method for solving the problems of low efficiency and high pollution emission of a biomass direct-fired boiler.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass direct combustion power generation / heat supply, and specifically relates to a biomass gasification coupled combustion system and method. Background Art

[0002] At present, biomass direct-fired boilers are mainly grate furnaces. Biomass raw materials do not need to be pre-treated, or they are directly fed into the boiler grate after a small amount of treatment. In the furnace, the fuel goes through the processes of drying, ignition, combustion and emberization in sequence, and finally turns into slag. The flue gas generated on the grate surface contains a large amount of combustible components, which enter the furnace space and further burn under the action of secondary air, and are finally discharged from the furnace in the form of flue gas. The structural form of the grate and furnace, the air distribution and other factors all affect the combustion efficiency and pollutant emission intensity of the direct-fired boiler.

[0003] In traditional grate-type biomass direct-fired boilers, the grate is water-cooled and vibrates. The fuel moves forward under the vibration of the grate with a certain inclination. The high, medium and low wind chambers at the bottom of the grate blow primary air into the fuel above the grate. Under the action of primary air and radiation heating from the upper furnace, the fuel is dried, pyrolyzed, ignited, burned and burned out in sequence, converting the biomass raw materials into flue gas (including a part of combustible gas) and sent to the upper furnace for gas phase combustion to further release heat. The fuel on the grate is fully burned, and the remaining slag is discharged into the slag removal port. Although traditional biomass vibrating grate boilers can process agricultural and forestry biomass on a large scale, due to the single furnace design, the reducing gas and combustion flue gas generated at each stage on the grate cannot be controlled separately, which limits the efficient combustion and control of nitrogen oxides in the furnace. Summary of the invention

[0004] Technical problems to be solved: In response to the above technical problems, the present invention provides a biomass gasification coupled combustion system and method, which can effectively solve the shortcomings of the above direct-fired boilers such as low combustion efficiency and high pollutant emission intensity.

[0005] Technical solution: In the first aspect, the present invention provides a biomass gasification coupled combustion system, comprising a furnace and a grate arranged at the lower part of the furnace, a plurality of wind chambers are arranged at the bottom of the grate, the grate comprises a front drying and pyrolysis zone and a middle and rear coke combustion zone; the furnace comprises a gasification chamber and a furnace main combustion chamber, a front arch is arranged between the gasification chamber and the furnace main combustion chamber, the reducing gas generated in the grate drying and pyrolysis zone enters the gasification chamber, and the reducing gas in the gasification chamber is sprayed into the furnace main combustion chamber through the gap of the front arch.

[0006] Preferably, the grate is a chain grate or a reciprocating grate.

[0007] Preferably, the reducing gas includes carbon monoxide, hydrogen and methane.

[0008] Preferably, a plurality of secondary air nozzles are provided on the side walls of the main combustion chamber of the furnace.

[0009] In a second aspect, the present invention provides a method for biomass gasification coupled combustion based on the system described in the first aspect, characterized in that: the biomass is fed into the grate, undergoes an oxygen-deficient reaction in the drying pyrolysis zone to generate reducing gas and coke, the reducing gas enters the gasification chamber for a reforming reaction, and is then sprayed into the main combustion chamber of the furnace through the gap of the front arch, where it is mixed and burned with the flue gas in the main combustion chamber of the furnace, while producing an in-situ gas phase reduction effect on NOx; the coke enters the coke combustion zone to further burn and is discharged out of the furnace in the form of ash, and the flue gas generated in the coke combustion zone enters the throat of the incinerator along the front arch and the rear arch and enters the main combustion chamber of the furnace.

[0010] Beneficial effects: 1) The present invention realizes effective regulation of gas production at each stage of fuel on the grate through the gasification-combustion dual-furnace coupling design. The gasification chamber enriches the reducing gas generated in the grate drying and pyrolysis zone, which is used for in-situ reduction of the flue gas in the main combustion chamber of the furnace; the main combustion chamber of the furnace receives the flue gas generated in the grate combustion zone and reducing gases such as CO, and fully utilizes the heat through the secondary air distribution; 2) Since the reducing gas generated in the gasification chamber of the present invention can enhance the mixing effect in the main combustion chamber, the combustion efficiency is improved; 3) The method and system proposed in the present invention have simple structure, low cost and simple installation, and are an efficient and economical method to solve the low efficiency and high pollution emission of biomass direct-fired boilers. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a structural schematic diagram of a biomass gasification coupled combustion system of the present invention; Figure 2 It is a schematic flow diagram of a biomass gasification coupled combustion method of the present invention; Figure 3 is a schematic diagram of the combustion characteristics of wheat straw on the grate in the system of the present invention; Figure 4 It is a schematic diagram of the furnace combustion temperature distribution characteristics in the system of the present invention; Figure 5 It is a schematic diagram of the distribution characteristics of the main smoke components of the furnace combustion in the system of the present invention; Figure 6 It is a schematic diagram of the NOx distribution characteristics of the furnace combustion in the system of the present invention; Serial numbers in the figure: 1. grate, 2. gasification chamber, 3. front arch, 4. rear arch, 5. main combustion chamber of the furnace. DETAILED DESCRIPTION

[0012] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments: Example 1

[0013] like Figure 1 As shown, a biomass gasification coupled combustion system comprises a furnace and a grate 1 arranged at the lower part of the furnace, a plurality of wind chambers are arranged at the bottom of the grate 1, and the grate 1 comprises a front drying and pyrolysis zone and a middle and rear coke combustion zone; the furnace comprises a gasification chamber 2 and a furnace main combustion chamber 5, a front arch 3 is arranged between the gasification chamber 2 and the furnace main combustion chamber 5, the reducing gas generated in the drying and pyrolysis zone of the grate 1 enters the gasification chamber 2, and the reducing gas in the gasification chamber 2 is sprayed into the furnace main combustion chamber 5 through the gap of the front arch 3.

[0014] The grate 1 is a chain grate or a reciprocating grate.

[0015] The above-mentioned reducing gas mainly includes carbon monoxide, hydrogen and methane.

[0016] The side wall of the main combustion chamber of the furnace is provided with a plurality of secondary air nozzles for burning and extinguishing the combustible components in the flue gas.

[0017] like Figure 2 As shown, a method for coupled combustion of biomass gasification based on the above combustion system is specifically as follows: the straw biomass is fed into the grate 1, and undergoes an oxygen-deficient reaction in the drying pyrolysis zone to generate reducing gas and coke. The reducing gas enters the gasification chamber 2 for a reforming reaction and is then injected into the main combustion chamber 5 of the furnace through the gap of the front arch 3, where it is mixed and burned with the flue gas in the main combustion chamber 5 of the furnace, and at the same time, an in-situ gas phase reduction effect is produced on NOx; the coke enters the coke combustion zone for further combustion and is discharged out of the furnace in the form of ash, and the flue gas generated in the coke combustion zone enters the throat of the incinerator along the front arch 3 and the rear arch 4 and enters the main combustion chamber 5 of the furnace.

[0018] On the one hand, the present invention divides the grate into a drying pyrolysis zone, a main combustion zone and a coke combustion zone, and can effectively dry, pyrolyze, gasify and burn the biomass raw materials entering the grate through segmented air distribution; on the other hand, the furnace is divided into a gasification chamber and a main combustion chamber, and the reducing gas generated by the pyrolysis and gasification section undergoes a certain degree of gasification reforming in the gasification chamber, and the reducing gas in the gasification chamber enters the main combustion chamber through a connecting channel, and the NOx in the main combustion chamber is reduced in the furnace to reduce the generation of NOx; in addition, the reducing gas generated in the gasification chamber can enhance the mixing effect in the main combustion chamber and improve the combustion efficiency. In addition, the method and system have a simple structure, low cost, and simple installation, and are an efficient and economical method to solve the low efficiency and high pollution emissions of biomass layer-fired boilers. Example 2

[0019] The combustion system and combustion method of Example 1 were used to burn wheat straw. The numerical simulation results of the gasification coupled combustion of wheat straw are shown in FIG. Figure 3 As shown: Wheat straw is burning on the grate. By optimizing the primary air distribution, the primary air volumes of the five sections of the grate are 80:80:150:200:50 Nm 3 / min, the total primary air excess air coefficient is 0.86. Under this air distribution condition, the wheat straw can be fully burned on the grate, the carbon conversion rate reaches 98.8%, and the carbon content of the ash at the grate outlet is as low as 3.79 wt.%, with a good burning effect. Example 3

[0020] The combustion system and combustion method of Example 1 were used to burn wheat straw. The CFD simulation results of the furnace combustion are shown as follows: Figure 4-Figure 6 As shown in the figure: the reducing gas in the gasification chamber in the gasification coupled combustion system produces strong turbulence on the main combustion chamber of the furnace, which intensifies the combustion. The carbon monoxide concentration in the flue gas at the furnace outlet is as low as 72 ppm, and the gas phase combustion effect is good. From the furnace combustion temperature distribution results, it can be seen that under the dual effects of secondary air and reducing gas in the gasification chamber, the furnace flue gas temperature is evenly distributed with a small temperature deviation. The nitrogen oxide emission results show that the reducing gas in the gasification chamber has a significant effect on the emission of NOx. The final original emission concentration of NOx in the flue gas at the furnace outlet is 156 ppm, which is lower than that of conventional biomass boilers.

[0021] Therefore, the boiler including the biomass gasification coupled combustion system of the present invention is a clean, efficient direct combustion system suitable for large-scale processing of straw biomass.

[0022] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A biomass gasification coupled combustion system, characterized in that: The invention comprises a furnace and a grate (1) arranged at the lower part of the furnace, wherein a plurality of air chambers are arranged at the bottom of the grate (1), and the grate (1) comprises a front drying and pyrolysis zone and a middle and rear coke combustion zone; the furnace comprises a gasification chamber (2) and a furnace main combustion chamber (5), and a front arch (3) is arranged between the gasification chamber (2) and the furnace main combustion chamber (5); reducing gas generated in the drying and pyrolysis zone of the grate (1) enters the gasification chamber (2), and reducing gas in the gasification chamber (2) is sprayed into the furnace main combustion chamber (5) through the gap of the front arch (3).

2. The biomass gasification coupled combustion system according to claim 1, characterized in that: The grate (1) is a chain grate or a reciprocating grate.

3. The biomass gasification coupled combustion system according to claim 1, characterized in that: The reducing gas includes carbon monoxide, hydrogen and methane.

4. The biomass gasification coupled combustion system according to claim 1, characterized in that: A plurality of secondary air nozzles are arranged on the side wall of the main combustion chamber of the furnace.

5. A method for biomass gasification coupled combustion based on the system according to any one of claims 1 to 4, characterized in that: The biomass is fed into the grate (1) and undergoes an oxygen-deficient reaction in the drying pyrolysis zone to generate reducing gas and coke. The reducing gas enters the gasification chamber (2) and undergoes a reforming reaction. The reducing gas is then injected into the main combustion chamber (5) of the furnace through the gap of the front arch (3) to mix and burn with the flue gas in the main combustion chamber (5) of the furnace, and at the same time, an in-situ gas-phase reduction effect is generated on NOx. The coke enters the coke combustion zone and further burns and is discharged from the furnace in the form of ash. The flue gas generated in the coke combustion zone enters the throat of the incinerator along the front arch (3) and the rear arch (4) and enters the main combustion chamber (5) of the furnace.

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