Biomass gasifier system based on decoupling partition and tar in-situ cracking and tar control method

Abstract

The invention belongs to the technical field of biomass energy, and particularly relates to a biomass gasifier system based on decoupling zoning and tar in-situ cracking and a tar control method.The biomass gasifier system comprises a furnace body, a feeding mechanism and a preheating mechanism, the furnace body is of a vertical multi-section cavity structure, and the interior of the furnace body is divided into a cracking zone, an oxidation zone and a reduction zone from top to bottom; the areas are separated by at least one group of partition plates with holes; a gas distributor is fixed at the side part of the furnace body and is communicated with the oxidation zone; a rotating blade loaded with a catalyst is arranged in the reduction area; the feeding mechanism is arranged above the furnace body and used for providing biomass raw materials for the furnace body. The system has the advantages that the tar content is reduced through decoupling partition design and catalytic cracking cooperative control, the output rate and the lower calorific value of combustible gas are improved, and the biomass gasifier system has an obvious cooperative upgrading effect on the obtained mixed gas.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass energy, and particularly relates to a biomass gasifier system and a tar control method based on decoupled zoning and in-situ tar cracking. Background Art

[0002] Biomass gasification is to carry out pyrolysis and gasification reactions on agricultural and forestry waste (such as straw, branches, wood chips, etc.) under high temperature and anoxic conditions to generate combustible gas mainly composed of carbon monoxide (CO), hydrogen (H2) and methane (CH4). The gasification process is usually divided into: ⑴ Drying and pyrolysis: The moisture in the biomass is evaporated, and macromolecular organic matter is decomposed into small molecule gases and solid residues. ⑵ Gasification and combustion: Under high temperature and anoxic conditions, the biomass is further cracked to generate combustible gas. The gasifier is the key equipment to realize biomass gasification, which has the advantages of wide raw material adaptability, high efficiency, energy saving, environmental protection, etc. However, there are also many disadvantages in the existing biomass gasifiers. Taking the fixed bed gasifier as an example:

[0003] 1. High tar content: The tar product of the traditional fixed bed gasifier is 20 - 50 g / Nm 3 , and it needs to rely on post-treatment processes such as water washing and electrostatic precipitation, with a long process and high cost;

[0004] 2. Insufficient temperature gradient between the oxidation zone and the reduction zone, large fluctuation range of the component concentrations of CO and H2, and low volume fraction of combustible gas (CO, H2), only 20% - 35%;

[0005] 3. Tar and ash coke at high temperature, shortening the equipment life, being difficult to handle and having high cost.

[0006] The tar removal methods are mainly divided into water washing method, electrostatic precipitation method and catalytic cracking method. The water washing method and the electrostatic precipitation method have a long process and high cost, and are prone to secondary pollution after failure; The catalytic cracking method converts tar into utilizable small molecules at high temperature, but there are problems such as catalyst deactivation, surface carbon deposition reducing the catalytic efficiency, and short contact time with tar quickly escaping.

[0007] In the prior art, the patent publication number: CN107418629A, discloses a biomass gasification device. Although the gas production is optimized through a multi-stage separator, the problem of in-situ tar cracking is still not solved, and the economy is poor. Summary of the Invention

[0008] To overcome the deficiencies of the prior art, the purpose of the present invention is to provide a biomass gasifier system and a tar control method based on decoupled zoning and in-situ tar cracking, reduce the tar content of the gasifier, improve the gasification efficiency, and solve the problem of easy blockage of the equipment.

[0009] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0010] A biomass gasification furnace system based on decoupling partition and in-situ tar cracking, comprising a furnace body, a feeding mechanism, and a preheating mechanism. The furnace body is a vertical multi-stage cavity structure. Inside the furnace body, it is divided into a cracking zone, an oxidation zone, and a reduction zone from top to bottom. Each zone is separated by at least one group of perforated partitions; a gas distributor is fixed on the side of the furnace body, and the gas distributor is connected to the oxidation zone; a rotating blade loaded with a catalyst is provided in the reduction zone; the feeding mechanism is arranged above the furnace body and is used to provide biomass raw materials to the furnace body.

[0011] The oxidation zone and the reduction zone are of an inner and outer double-layer structure. The inner cavity is a structure that gradually increases from the middle to both ends. The inner cavity serves as a heat exchange transfer channel to transfer the heat of the oxidation zone to the reduction zone.

[0012] The gas distributor includes a shell, a gasifying agent inlet, a spray pipe, and a gas distribution plate. A preheating pipe passes through the shell and is fixedly connected to the shell. The air inlet is arranged above the shell, and the air outlet is arranged below the shell. A gasifying agent input port is provided on the shell. A gas distribution plate is arranged inside the shell, and the gas distribution plate is fixed on the inner wall of the furnace body. Inside the shell, the gasifying agent enters the gasifying agent inlet through the gas distribution plate and then enters the inner cavity from the gasifying agent inlet; a number of through holes with a pore diameter of 0.5 - 2 mm are opened on the gas distribution plate; the spray pipe is arranged in the reduction zone, and the spray pipe is connected to the furnace body and can spray water vapor into the reduction zone.

[0013] The gas distribution plate includes the following raw materials by mass percentage: 85% - 90% of spinel, 5% - 8% of alumina powder, 3% - 5% of magnesia powder, and 2% - 3% of polyvinyl alcohol or carboxymethyl cellulose;

[0014] Under normal temperature conditions, the above raw materials are mixed and stirred evenly, pressed into shape, dried at 110 - 130 °C to remove moisture, and a dried green body is obtained; the green body is sintered at 1600 - 1650 °C for 6 - 8 h and then cooled to obtain the gas distribution plate.

[0015] A number of through holes with a pore diameter of 1 - 3 cm are provided on the partition between the cracking zone and the oxidation zone; a number of through holes are provided on the partition between the oxidation zone and the reduction zone, and the pore diameter of the upper partition is larger than that of the lower partition.

[0016] The catalyst loaded includes by mass percentage:

[0017] Ni: 20% - 25%; rare earth elements: 2% - 5%; Al2O3: 65% - 70%; MgO: 3% - 5%; SiO2: 2% - 4%;

[0018] The rare earth elements include by mass percentage: Ce: 80% - 95%, and the rest is La;

[0019] Preparation of the supported catalyst: After ball-milling and mixing Al2O3, MgO, and SiO2, a mixed solution of nickel nitrate solution and cerium nitrate solution is mixed in, and after stirring evenly, spray drying is carried out; then calcination is carried out at a temperature of 500 - 800 °C for 3 - 5 h; then rare earth elements are mixed in, and calcination is continued at a temperature of 700 - 750 °C for 1 - 3 h; then, reduction treatment is carried out in a hydrogen atmosphere, the reduction temperature is 400 - 600 °C, the reduction time is 2 - 4 h, and the supported catalyst is obtained after cooling.

[0020] The cracking zone is connected with a primer flange.

[0021] A tar control method includes:

[0022] 1) The biomass raw material is fed into the furnace body through the feed port, the temperature of the cracking zone is controlled at 400 - 600 °C, and the biomass raw material undergoes low-temperature pyrolysis to release volatiles; the temperature of the oxidation zone is controlled above 1000 °C, and the input amount of the gasifying agent is controlled by the air distributor, and thus the air-fuel ratio of the oxidation zone is controlled at 0.2 - 0.4;

[0023] 2) When the temperature of the oxidation zone is higher than 1250 °C, water vapor is sprayed through the air distributor to cool down, and the water vapor decomposes into H2 and CO in the oxidation zone;

[0024] 3) Under the action of the double-layer structure, a heat exchange and transfer channel is formed, and at the same time, the residence time of the biomass raw material in the oxidation zone is extended, and the heat of the oxidation zone is used to maintain the temperature of the reduction zone;

[0025] 4) The temperature of the reduction zone is controlled at 700 - 900 °C: the mixed gas stays in this zone for 5 - 10 s, and under the action of the supported catalyst, the gas is reduced and the tar is catalytically cracked into CO and H2.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] The present invention solves the problems of high tar content, low gas yield, and easy blockage of equipment in the gasification technology of traditional gasifier systems. Through the decoupled partition design and catalytic cracking co-control, the present invention realizes the reduction of tar content, improves the output rate and lower calorific value of combustible gas, and has an obvious synergistic upgrading effect on the obtained mixed gas through the biomass gasifier system:

[0028] 1. The gasifier adopts a decoupled partition structure. Taking the air gasifying agent as an example, the gasification efficiency is significantly improved, and the volume fraction of combustible gas is increased to more than 50%.

[0029] 2. The tar content is reduced to below 10 mg / Nm 3 Below.

[0030] 3. The gas yield of the present invention is 20% higher than that of the traditional gasifier system, and the by-product carbon powder has uniform particle size and can be directly used for further processing. Brief Description of the Drawings

[0031] Figure 1 It is a schematic structural diagram of a biomass gasifier system.

[0032] Figure 2 Tar content curve graphs of a traditional gasifier and a biomass gasifier system.

[0033] In the figure: 1 - driving motor; 2 - feed inlet; 3 - ignition flange; 4 - distributor; 5 - pyrolysis zone; 6 - oxidation zone; 7 - reduction zone; 8 - partition one; 9 - partition two; 10 - gas distributor; 11 - gasifying agent inlet; 12 - inlet of the preheating pipe; 13 - outlet of the preheating pipe; 14 - gasifying agent entrance; 15 - spray pipe; 16 - rotating blade; 18 - outer cavity. Detailed Embodiments

[0034] The present invention will be described in detail below with reference to the accompanying drawings of the specification, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0035] See Figure 1 , a biomass gasifier system based on decoupled zoning and in-situ tar cracking, comprising a furnace body, a feeding mechanism, and a preheating mechanism. The furnace body is a vertical multi-section cavity structure, and the furnace body is divided into a pyrolysis zone 5, an oxidation zone 6, and a reduction zone 7 from top to bottom. Each zone is separated by at least one group of perforated partitions; a gas distributor 10 is fixed on the side of the furnace body, and the gas distributor 10 is communicated with the oxidation zone 6; a rotating blade 16 loaded with a catalyst is arranged in the reduction zone 7; the feeding mechanism is arranged at the top of the furnace body and is used to provide biomass raw materials to the furnace body. The oxidation zone 6 and the reduction zone 7 are of an inner and outer double-layer structure. The inner cavity is a structure that gradually increases from the middle to both ends. The inner cavity serves as a heat exchange transfer channel to transfer the heat of the oxidation zone 6 to the reduction zone 7.

[0036] The gas distributor 10 includes a shell, a preheating pipe, a gasifying agent entrance 14, a spray pipe 15, and a gas distribution plate. The preheating pipe passes through the shell and is fixedly connected to the shell. The inlet 12 of the preheating pipe is arranged above the shell, and the outlet 13 of the preheating pipe is arranged below the shell. The spray pipe 15 is connected to the furnace body and can spray water vapor into the reduction zone 7; a gasifying agent inlet 11 is arranged on the shell, and a gas distribution plate is arranged inside the shell. The gas distribution plate is fixed on the outer wall of the furnace body. Inside the shell, the gasifying agent enters the gasifying agent entrance 14 through the gas distribution plate and then enters the inner cavity from the gasifying agent entrance 14. A number of through holes with a pore diameter of 0.5 - 2 mm are formed on the gas distribution plate, and the hole opening rate is 30% - 45%.

[0037] The gas distribution plate is made of refractory materials, and at the same time, the risk of increasing the tar content is avoided. The gas distribution plate comprises the following raw materials by mass percentage: 85% - 90% of aluminum-magnesium spinel, 5% - 8% of alumina powder, 3% - 5% of magnesia powder, and 2% - 3% of polyvinyl alcohol or carboxymethyl cellulose. Under normal temperature conditions, the above raw materials are mixed and stirred evenly, pressed into shape, dried at 110 - 130 °C to remove moisture, and a dried green body is obtained; the green body is sintered at 1600 - 1650 °C for 6 - 8 h and then cooled to obtain the gas distribution plate.

[0038] The feeding mechanism is a screw conveyor. The feeding port 2 of the screw conveyor is arranged at the top of the furnace body. A valve is connected to the feeding port 2, and a level gauge is installed in the furnace to control the feeding amount of the gasifier. The raw materials are fed through the feeding port 2 and are fed into the cracking zone in the furnace body under the action of the driving motor 1. The pore diameter of the through hole on the partition plate between the cracking zone 5 and the oxidation zone 6 is larger than the pore diameter of the through hole on the partition plate between the oxidation zone 6 and the reduction zone 7, that is, the through hole on the partition plate 8 is larger than the through hole on the partition plate 9. The cracking zone 5 is connected with a pilot flange 3.

[0039] The partition plate between the cracking zone 5 and the oxidation zone 6 is provided with a number of through holes; similarly, the partition plate 9 between the oxidation zone 6 and the reduction zone 7 is also provided with a number of through holes. According to needs, there is at least one or more partition plates. The cracking zone 5 is connected with a pilot flange 3.

[0040] The supported catalyst comprises by mass percentage:

[0041] Ni: 20% - 25%; rare earth elements: 2% - 5%; Al2O3: 65% - 70%; MgO: 3% - 5%; SiO2: 2% - 4%; the rare earth elements comprise by mass percentage Ce: 80% - 95%, and the rest is La.

[0042] Preparation of the supported catalyst: After ball-milling and mixing Al2O3, MgO, and SiO2, a mixed solution of nickel nitrate solution and cerium nitrate solution is mixed in, and after stirring evenly, spray drying is carried out; then calcination is carried out at a temperature of 500 - 800 °C, and the calcination time is 3 - 5 h; then rare earth elements are mixed in, and calcination is continued at a temperature of 700 - 750 °C for 1 - 3 h; then, reduction treatment is carried out in a hydrogen atmosphere, the reduction temperature is 400 - 600 °C, and the reduction time is 2 - 4 h, and the supported catalyst is obtained after cooling.

[0043] The supported catalyst has high activity, controllable cost and is suitable for high-temperature reactions (700 - 900 °C). The supported catalyst is loaded on the rotating blade 16, and the mixed gas stays here for 5 - 10 s. The supported catalyst is used to treat the gaseous tar contained in the mixed gas; tar; at least one group of supported catalyst rotating blades 16 is longitudinally arranged in the reduction zone 7 to increase the contact area and time between the tar and the catalyst, accelerate the cracking and reforming of the tar, and the problem of catalyst carbon deposition can be better solved by gravity and the centrifugal force of rotation.

[0044] A tar control method includes:

[0045] 1) Feedstock pretreatment: After the biomass feedstock is crushed, dried and screened, impurities are removed; the biomass feedstock is agricultural and forestry waste such as cotton straw and wood chips.

[0046] 2) The biomass feedstock is fed into the furnace body through the feed port 2. After entering the furnace body, the biomass feedstock successively passes through the cracking zone 5, the oxidation zone 6, and the reduction zone 7, and the generated products are discharged from the furnace body; agricultural and forestry waste such as cotton straw and wood chips can undergo a gasification reaction with a gasifying agent at high temperature in the furnace body. After high-temperature cracking, oxidation, and reduction reactions, they are converted into mixed gas such as CO, CO2, H2, CH4, etc., and at the same time, by-products such as solid carbon powder are generated; the gasifying agent can be selected from air, pure oxygen, water vapor or a composite gasifying agent.

[0047] During this process, the temperature of the cracking zone 5 is controlled at 400 - 600 °C, and the biomass feedstock undergoes low-temperature pyrolysis to release volatile components; the temperature of the oxidation zone 6 is controlled above 1000 °C. The input amount of the gasifying agent is controlled by the air distributor 10, and then the air-fuel ratio of the oxidation zone 6 is controlled at 0.2 - 0.4, as close to 0.3 as possible. The cracking heat energy is released in the oxygen zone. Due to the lack of dilution by nitrogen in this process, the calorific value of the generated mixed gas is greatly increased compared with that obtained by simply using air gasification, the gas production efficiency is increased by 20%, and the volume fraction of combustible gas rises above 50%. When the temperature of the oxidation zone 6 is higher than 1100 °C, water vapor is sprayed through the air distributor 10 to cool down, and the water vapor decomposes into H2 and CO in the reduction zone 7; the gasifying agent and different proportions of high-temperature water vapor sprayed can adjust the ratio of CO and H2 in the combustible gas, and at the same time, the addition of water vapor helps to adjust the temperature in the furnace.

[0048] 3) Under the action of the inner and outer double-layer structures, a heat exchange and transfer channel is formed, and at the same time, the residence time of the biomass feedstock in the oxidation zone 6 is extended, and the temperature of the reduction zone 7 is maintained by using the waste heat of the oxidation zone 6;

[0049] 4) The temperature in the reduction zone 7 is controlled at 700 - 900 °C: The mixed gas stays in this zone for 5 - 10 s. The mixed gas completes secondary cracking and reforming under the secondary action of the catalyst in the reduction zone 7, and the gas is reduced and the tar is catalytically cracked into CO and H2, and the total tar cracking efficiency ≥ 99%.

[0050] 5) The gasification products discharged from the furnace body recover waste heat through a heat exchanger, enter a cyclone dust collector (removing more than 80% of carbon powder) and a bag filter for purification, and obtain pure mixed gas. The carbon powder is sent to a collection box by a screw conveyor for collection and can be used for the preparation of activated carbon.

[0051] The present invention solves the problems of high tar content, low gas yield and easy blockage of equipment in the gasification technology of traditional gasification furnace systems. Through decoupled zoning design and catalytic cracking co-control, the present invention reduces the tar content, improves the output rate and lower calorific value of combustible gas, and has an obvious synergistic upgrading effect on the obtained mixed gas through the biomass gasification furnace system. See Figure 2 , the gasification furnace adopts a decoupled zoning structure. Taking air gasifying agent as an example, the gasification efficiency is significantly improved, and the volume fraction of combustible gas is increased to more than 50%. The tar content is reduced to 10mg / Nm 3 as follows.

Claims

1. A biomass gasification furnace system based on decoupled partitioning and in-situ tar cracking, characterized in that, It includes a furnace body, a feeding mechanism, and a preheating mechanism. The furnace body is a vertical multi-section cavity structure. Inside the furnace body, it is divided into a cracking zone, an oxidation zone, and a reduction zone from top to bottom. Each zone is separated by at least one group of perforated partitions; a gas distributor is fixed on the side of the furnace body, and the gas distributor is connected to the oxidation zone; a rotating blade loaded with a catalyst is provided in the reduction zone; the feeding mechanism is arranged above the furnace body and is used to supply biomass raw materials to the furnace body.

2. The biomass gasifier system based on decoupled partitioning and in-situ tar cracking according to claim 1, wherein The oxidation zone and the reduction zone are of an inner and outer double-layer structure. The inner cavity is a structure that gradually increases from the middle to both ends. The inner cavity serves as a heat exchange transfer channel to transfer the heat of the oxidation zone to the reduction zone.

3. The biomass gasification furnace system based on decoupled partitioning and in-situ tar cracking according to claim 1, wherein, The gas distributor includes a shell, a gasifying agent inlet, a spray pipe, and a gas distribution plate. The preheating pipe passes through the shell and is fixedly connected to the shell. The air inlet is arranged above the shell, and the air outlet is arranged below the shell. A gasifying agent input port is provided on the shell, and a gas distribution plate is arranged inside the shell. The gas distribution plate is fixed on the inner wall of the furnace body. Inside the shell, the gasifying agent enters the gasifying agent inlet through the gas distribution plate and then enters the inner cavity from the gasifying agent inlet; a number of through holes with a pore diameter of 0.5 - 2 mm are opened on the gas distribution plate; the spray pipe is arranged in the reduction zone, and the spray pipe is connected to the furnace body and can spray water vapor into the reduction zone.

4. A biomass gasification furnace system based on decoupling partition and in-situ tar cracking according to claim 3, characterized in that, The gas distribution plate includes the following raw materials by mass percentage: 85% - 90% of aluminum-magnesium spinel, 5% - 8% of alumina powder, 3% - 5% of magnesia powder, and 2% - 3% of polyvinyl alcohol or carboxymethyl cellulose; Under normal temperature conditions, the above raw materials are mixed and stirred evenly, pressed into shape, and dried at 110 - 130 °C to remove moisture to obtain a dry green body; the green body is sintered at 1600 - 1650 °C for 6 - 8 h and then cooled to obtain the gas distribution plate.

5. A biomass gasification furnace system based on decoupling partition and in-situ tar cracking according to claim 1, characterized in that, A number of through holes are provided on the partition; the pore diameter of the through holes on the partition between the cracking zone and the oxidation zone is larger than the pore diameter of the through holes on the partition between the oxidation zone and the reduction zone.

6. The biomass gasification furnace system based on decoupling partition and in-situ cracking of tar according to claim 1, characterized in that The catalyst-loaded includes by mass percentage: Ni: 20% - 25%; rare earth elements: 2% - 5%; Al2O3: 65% - 70%; MgO: 3% - 5%; SiO2: 2% - 4%; The rare earth elements include by mass percentage: Ce: 80% - 95%, and the rest is La; Preparation of the catalyst-loaded: After ball-milling and mixing Al2O3, MgO, and SiO2, a mixed solution of nickel nitrate solution and cerium nitrate solution is mixed in, stirred evenly and then spray-dried; then calcined at a temperature of 500 - 800 °C for 3 - 5 h; then mixed with rare earth elements and continuously calcined at a temperature of 700 - 750 °C for 1 - 3 h; then, reduction treatment is carried out in a hydrogen atmosphere, the reduction temperature is 400 - 600 °C, the reduction time is 2 - 4 h, and after cooling, the catalyst-loaded is obtained.

7. A biomass gasification furnace system based on decoupled partitioning and in-situ tar cracking according to claim 1, characterized in that, The cracking zone is connected with a fire-leading flange.

8. A method for tar control implemented by a biomass gasification furnace system based on decoupling partition and in-situ tar cracking according to any one of claims 1-7, characterized in that, It includes: 1) The biomass raw material is fed into the furnace body from the feeding port. The temperature of the cracking zone is controlled at 400 - 600 °C, and the biomass raw material undergoes low-temperature pyrolysis to release volatile components; the temperature of the oxidation zone is controlled above 1000 °C, and the input amount of the gasifying agent is controlled by the gas distributor, and then the air-fuel ratio of the oxidation zone is controlled at 0.2 - 0.4; 2) When the temperature of the oxidation zone is higher than 1250 °C, water vapor is sprayed through the air distributor to cool down, and the water vapor decomposes into H2 and CO in the oxidation zone; 3) Under the action of the double-layer structure, a heat exchange transfer channel is formed, and at the same time, the residence time of the biomass raw material in the oxidation zone is extended, and the waste heat of the oxidation zone is used to maintain the temperature of the reduction zone; 4) The temperature in the reduction zone is controlled at 700 - 900 °C: the mixed gas stays in this zone for 5 - 10 s, and under the action of the loaded catalyst, the gas reduction and tar catalytic cracking are carried out into CO and H2.

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