Biomass gasifier

Abstract

The present application aims at providing a biomass gasification furnace, belonging to the technical field of gasification furnace, comprising a furnace body, which is sequentially provided with a drying zone, a pyrolysis zone, an oxidation zone, a reduction zone and an ash discharge zone from top to bottom, a combustion chamber is arranged in the furnace body, a feeding device is arranged at the top end of the furnace body, an ash discharge device is arranged at the bottom of the furnace body, an air inlet pipe one communicated with the pyrolysis zone and an air inlet pipe two communicated with the oxidation zone are arranged at the two sides of the furnace body respectively, and a discharging pipe is arranged at the bottom of the furnace body. By using the present application, tar can be successfully removed from the produced gas, the gasification furnace has high thermal efficiency, high operating temperature, high cold gas efficiency, high carbon conversion efficiency and high calorific value, and the overall process efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of gasification furnace technology, and specifically relates to a biomass gasification furnace. Background Technology

[0002] The overuse of fossil fuels has led to severe resource shortages and environmental pollution. The development of non-fossil energy, represented by renewable energy, has become an important component of the global energy supply system and a crucial technological measure for my country to further promote energy production and consumption. my country has a wide range of biomass sources, with nearly 1.3 billion tons of agricultural and forestry residues produced annually, making it the fourth largest energy source after coal, oil, and natural gas. However, due to the low energy value of biomass energy, its direct use is increasingly unable to meet people's demands for a high-quality modern life. Therefore, researching various new technologies to convert biomass into high-grade clean energy is an inevitable trend for the large-scale utilization of biomass energy. Biomass gasification technology is an important heat conversion technology for biomass utilization.

[0003] Chinese patent CN 115678616 A discloses a biomass gasifier with a high gas production rate. This device, through the arrangement of a feeding box, a sealed material cover, and a sealed conveying assembly, allows for continuous feeding and gasification in a relatively sealed state. The mixing section ensures sufficient contact between the biomass and the gasifying agent for a gasification reaction, accelerating the gasification process. However, this device is inconvenient for feeding larger straw and timber, easily clogging the feeding equipment. Furthermore, the feeding of crushed material into the gasifier is done manually, requiring periodic additions, resulting in high labor costs.

[0004] Because biomass is a low-grade fuel, it produces a small amount of tar after being converted into combustible gas during gasification, reducing the quality and utilization efficiency of the syngas. If the gas temperature is below the tar dew point, condensation will occur, leading to operational problems such as blockage of the intake system in gas turbines or internal combustion engines. Downdraft gasifiers are a type of biomass gasifier. Due to their thorough pyrolysis, they are particularly suitable for high-ash, low-melting-point biomass fuels. Maintaining the thickness of the ash layer inside the gasifier is fundamental to its stable operation. The main problem with high-ash biomass is that, due to the high temperature and subsequent agglomeration and deposition in relatively cooler areas of the reactor, the ash components near the combustion zone inlet may melt, blocking the feed flow and causing discontinuous gasifier operation. Ash in the area above the grate begins to accumulate after a period of time, thus hindering the reaction rate. Summary of the Invention

[0005] The purpose of this invention is to provide a biomass gasifier that can reduce tar content and improve gasifier efficiency by increasing gas recirculation in the combustion chamber, and prevent feed blockage and ash accumulation by periodically moving the grate, thus ensuring stable operation of the gasifier.

[0006] The present invention adopts the following technical solution:

[0007] A biomass gasification furnace includes a furnace body, which consists of a drying zone, a pyrolysis zone, an oxidation zone, a reduction zone, and an ash removal zone from top to bottom. The furnace body is equipped with a combustion chamber, a feeding device at the top, and an ash removal device at the bottom. The furnace body is equipped with an air inlet pipe connected to the pyrolysis zone and an air inlet pipe connected to the oxidation zone on both sides, and an outlet pipe at the bottom.

[0008] Furthermore, the feeding device includes a hopper, a support column on one side of the hopper, a feed inlet at the top of the hopper, a discharge outlet at the bottom, a sealing cover at the feed inlet, two meshing crushing wheels directly below the feed inlet, and the discharge outlet connected to the furnace body via a feed pipe, with a control valve at one end of the feed pipe.

[0009] Furthermore, the combustion chamber is fixed to the furnace body by several fins. The top of the combustion chamber is provided with a tangential inlet and the bottom with an annular outlet. The top of the combustion chamber is provided with a conical protective shell. The combustion chamber is provided with an inclined nozzle. One end of the first air inlet pipe and the second air inlet pipe extend into the furnace body and are fitted with a connector. The bottom of the connector is fitted with a branch conduit and connected to the nozzle.

[0010] Furthermore, the ash removal device includes a water tank filled with water, a vertical shaft connected to the bottom center of the water tank, a grate at the bottom of the furnace body, a rotating plate fixedly connected to the bottom of the grate, the rotating plate being connected to the vertical shaft, a motor on one side of the water tank, a reducer connected to the output end of the motor, and the output end of the reducer being connected to the rotating plate.

[0011] Furthermore, the ratio of the positions of the discharge pipe, the second air inlet pipe, and the first air inlet pipe along the height of the furnace body from the bottom is 1:3:4.

[0012] Furthermore, the discharge port of the hopper is eccentrically positioned, with one side wall forming an angle of 30° with the horizontal plane.

[0013] Furthermore, the nozzle comprises six converging and diverging nozzles arranged at equal intervals around the circumference.

[0014] Furthermore, the converging-diverging nozzle includes a converging section, a throat, and a diverging section connected in sequence.

[0015] The beneficial effects of this invention are as follows:

[0016] 1. The biomass gasifier of this invention adopts a structural design for recycling pyrolysis products. An inclined nozzle and burner are used in the oxidation zone. Six nozzles with a 60-degree inclination generate vortices that are evenly distributed in the external areas of the combustion chamber and outlet. The incoming gasification air draws in premixed pyrolysis gas, mixes it before combustion, and forms a large internal countercurrent zone in the burner, resulting in intense combustion and the destruction of tar in the production gas. Simultaneously, the inclined nozzle system provides vortices that increase the residence time of the mixed air and pyrolysis gas in the burner, ensuring a more stable and uniform combustion process. A secondary air inlet is added to the pyrolysis zone, raising the temperature of the pyrolysis zone to near that of the combustion zone, which reduces the amount of tar formed during pyrolysis. Through internal equipment modifications to the gasifier, tar is successfully removed from the production gas, resulting in high thermal efficiency, high operating temperature, high cooling gas efficiency, high carbon conversion efficiency, and high calorific value, improving overall process efficiency and avoiding the need for additional gas purification equipment.

[0017] 2. The biomass gasifier of this invention employs a structure design with a fixed-interval moving grate. When the grate is stationary, ash accumulates in the area above it after a period of time, obstructing the feed movement and causing discontinuous gasifier operation, thus hindering the reaction rate. Conversely, high-frequency grate movement leads to the loss of excess unreacted char. Therefore, this invention uses a drive motor to move the grate every 20 minutes. The clockwise and counterclockwise movement of the grate provides a torsional motion to the pellet bed, ensuring the removal of unconverted coke and ash, thereby making room for fresh pellets to enter subsequent zones and increasing reaction efficiency. Simultaneously, the increased grate movement frequency reduces the residence time of the bed material in the high-temperature combustion zone, reducing localized hot spots and improving temperature distribution.

[0018] 3. The biomass gasification furnace of this invention modifies the shape of the hopper and adds a crushing device. To prevent arching caused by the force balance between friction between materials, friction between materials and the pipe wall, the supporting force of the pipe wall on the materials, and the weight of the materials, this invention modifies the shape of the hopper, using a hopper with an eccentricity. This reduces the supporting force generated on one side, achieving the arch-breaking effect. Simultaneously, a crushing wheel is added to the hopper. Because biomass has various shapes, crushing alters the geometric dimensions of the biomass, increasing the feed density, enhancing flowability, and better utilizing biomass energy. Attached Figure Description

[0019] Figure 1 This is a three-dimensional structural diagram of the present invention;

[0020] Figure 2 This is a cross-sectional view of the furnace body of the present invention;

[0021] Figure 3 This is a cross-sectional view of the hopper of the present invention;

[0022] Figure 4 This is a three-dimensional structural diagram of the combustion chamber of the present invention;

[0023] Figure 5 This is a schematic diagram of the tilting nozzle of the present invention;

[0024] Figure 6 This is a cross-sectional view of the tilting nozzle of the present invention;

[0025] Figure 7 This is a schematic diagram of the grate structure of the present invention;

[0026] Figure 8 This is a schematic diagram of the converging and diverging nozzle of the present invention;

[0027] Wherein: 1-furnace body; 2-combustion chamber; 3-inlet pipe one; 4-inlet pipe two; 5-discharge pipe; 6-hopper; 7-support column; 8-sealing material cover; 9-crushing wheel; 10-discharge port; 11-feed pipe; 12-control valve; 13-fin; 14-conical protective shell; 15-nozzle; 16-connector; 17-branch pipe; 18-water tank; 19-vertical shaft; 20-grate; 21-rotating plate; 22-motor; 23-reducer; 24-converging section; 25-throat; 26-diverging section. Detailed Implementation

[0028] The invention will be further described with reference to the accompanying drawings.

[0029] As shown in the figure, a biomass gasification furnace includes a furnace body 1. The interior of the furnace body 1 is divided into five parts from top to bottom: a drying zone, a pyrolysis zone, an oxidation zone, a reduction zone, and an ash removal zone. A feed inlet 11 is provided at the top of the furnace body 1; an air inlet 3 is provided on the side wall of the pyrolysis zone; an air inlet 4 is provided on the side wall of the oxidation zone; and a discharge pipe 5 is provided on one side of the side wall of the reduction zone. A feeding device is connected to one side of the furnace body 1 via the feed pipe 11. The feeding device includes a hopper 6. A support column 7 is provided on one side of the hopper 6. The bottom end of the support column 7 is fixed to the ground, and the top end is fixedly connected to the hopper 6. A sealing cover 8 is movably installed at the top of the hopper 6. A leakage channel of the same size as the cover is provided inside the hopper 6. Directly below the leakage channel, two meshing crushing wheels 9 are installed on the side wall of the hopper 6. The crushing wheels 9 are driven by a drive motor inside the hopper, which facilitates the initial crushing of the raw materials, changing the biomass... The geometric dimensions of the raw material increase its bulk density and enhance its flowability. Due to gravity, the crushed raw material falls to the bottom of the hopper 6. To prevent the raw material from arching, the bottom of the hopper is designed with an eccentricity. The raw material enters the feed pipe 11 through the discharge port. A control valve 12 is installed on one side of the feed pipe 11. After the feeding is stable, the temperature-controlled feeding mode is activated. The feeding is stopped and started by measuring the gas temperature at the outlet. Feeding begins when the temperature exceeds the preset temperature and stops when the temperature is below the preset temperature.

[0030] The hopper 6 has an eccentric outlet setting with an eccentric distance. The side wall is at a 30-degree angle, which reduces the support force generated on one side, helping the material to move downwards easily while also breaking the arch.

[0031] The furnace body 1 has five insertion slots on the side wall of the oxidation zone, with five slots at the top and five at the bottom for mounting fins 13. The fins 13 fix the combustion chamber 2 inside the furnace body 1 through the insertion slots. The combustion chamber 2 is a fully annular combustion chamber with a tangential inlet at the top and an annular outlet at the bottom. Inlet pipe 1 3 and inlet pipe 2 4 are fitted with connectors 16, with branch pipes 17 fitted at the bottom of the connectors 16. A conical protective shell 14 is fitted onto the branch pipes 17. Six converging and diverging nozzles are connected to the air intake system at 60 degrees to supply air into the reactor. Nozzles 15 provide vortex airflow, preventing cold gasified air from entering the combustion chamber 2 and causing a temperature drop. This also increases the residence time of the mixed air pyrolysis gas in the burner, ensuring a more stable and uniform combustion process and a constant outlet temperature. The premixed air pyrolysis gas enters the newly developed combustion chamber 2 installed on the side wall of the furnace body's oxidation zone and forms a large annular and counter-current zone in the burner to achieve the optimal combustion temperature, resulting in the destruction of tar in the production gas.

[0032] A water tank 18 is fixedly fitted to the lower part of the furnace body 1. The water tank 18 is filled with liquid water. A vertical shaft 19 is fixedly connected to the middle of the bottom end of the water tank 18. A grate 20 is fixedly connected to the top of the vertical shaft 19 located inside the water tank. A rotating plate 21 is fixedly connected below the grate 20. A motor 22 and a reducer 23 are fixedly connected. The output end of the motor 22 is fixedly connected to the input end of the reducer 23. The output end of the reducer 23 is fixedly connected to the bottom end of the rotating plate 21. The drive device controls the rotating plate to drive the grate to move at fixed intervals. The clockwise and counterclockwise movement of the grate provides a torsional motion for the particle bed, ensuring that unconverted coke and ash fall from the grate into the water tank 18. The water in the pit prevents gas from leaking from the bottom of the gasifier, increasing the reaction efficiency.

[0033] Two air inlets are opened in the pyrolysis zone and the oxidation zone. The ratio of the positions of the discharge pipe 5, the second air inlet 4, and the first air inlet 3 along the height of the reactor from the bottom is 1:3:4. The second-stage air supply is used in the gasifier to raise the temperature of the pyrolysis zone to near the temperature of the combustion zone, which can reduce the amount of tar formed during the pyrolysis process.

[0034] The air intake channel is located at the center of the nozzle system and runs through the inclined nozzle structure. The inclined nozzle system consists of six converging and diverging nozzles connected at 60 degrees to each other, with six different tangential inlets. The inclined nozzle system is uniformly arranged around the air intake channel and adopts a coaxial swirling flow form, which allows the pyrolysis gas and the gasified air in the oxidation zone burner to recirculate, ensuring that the mixture of raw materials and air pyrolysis gas can burn intensely for a longer residence time, resulting in the destruction of tar in the production gas.

[0035] Converging and diverging nozzles are nozzles with both converging and diverging regions, such as... Figure 8 As shown, the gas enters the converging section 24 of the nozzle through the inlet, and then flows to the throat 25 of the nozzle, causing the diameter to continuously decrease from D1 to D2. After flowing through the throat 25, the gas enters the diverging section 26 of the nozzle, where the diameter increases from D3 to D4, and then flows out from the outlet nozzle orifice.

[0036] The grate of the gasifier consists of a plurality of cylindrical rods with a diameter of 1 cm and spaced 1.3 cm apart. A rotating plate is fixedly connected to the bottom of the grate. The rotating plate is fixed in the water tank by a connecting vertical shaft. The drive device drives the grate to rotate at fixed time intervals. The optimal time interval is 20 minutes. If the interval is too short, the frequent rotation will result in a thinner bed, which will increase the gas permeability and reduce the residence time. If the interval is too long, it will result in a thicker bed and ash accumulation.

[0037] Working principle: In the oxidation zone, the blown-in air mixes and burns with the material at a temperature of approximately 900~1200℃. The heat generated supports the pyrolysis reaction in the pyrolysis zone and the reduction reaction in the reduction zone. During gasification, the feed moves downward through each zone. In the drying zone, moisture in the biomass is removed. During pyrolysis, the dried biomass is decomposed into char, gas, bio-oil, and tar vapor.

[0038] During operation, the operator opens the sealing cover 8 and feeds the raw material into the hopper 6. The raw material first passes through the crushing wheel 9, which alters the geometry of the biomass raw material, increasing its bulk density and improving its flowability. After initial crushing, the raw material falls to the bottom of the hopper 6 due to gravity. By using an eccentrically positioned hopper, the possibility of the raw material arching is reduced. The raw material then enters the feed pipe 11 of the furnace body 1 through the discharge port. After achieving stable feeding, the feeding structure enters the temperature-controlled feeding mode of the control valve 12. The feeding process of the hopper is controlled by detecting the temperature of the air outlet. Feeding begins when the temperature exceeds the preset temperature and stops when the temperature falls below the preset temperature. Air is introduced into the air inlet pipe, and the incoming vaporized air acts as a driving force to draw in premixed pyrolysis gases for mixing before combustion. The nozzle 15 provides a vortex airflow, preventing cold vaporized air from entering the combustion chamber 2 and causing a temperature drop, thus increasing the residence time of the air-pyrolysis gas mixture in the combustion chamber. Premixed air pyrolysis gas enters the combustion chamber and forms a large annular and counter-current zone in the burner, achieving optimal combustion temperature and causing tar destruction in the production gas. As the reaction proceeds, the amount of ash generated continuously increases, and the ash content in the area above grate 20 begins to accumulate after a period of time. Every 20 minutes, motor 22 controls the rotating plate 21 fixedly connected below grate 20 to start moving. The clockwise and counter-clockwise movement of the grate provides a torsional motion for the particle bed, ensuring that unconverted coke and ash fall from the grate into water tank 18. The water in the pit prevents gas from leaking from the bottom of the gasifier, increasing reaction efficiency.

Claims

1. A biomass gasification furnace, characterized in that: The furnace includes a furnace body (1), which consists of a drying zone, a pyrolysis zone, an oxidation zone, a reduction zone and an ash removal zone from top to bottom. The furnace body (1) is equipped with a combustion chamber (2), a feeding device at the top of the furnace body (1), an ash removal device at the bottom, an air inlet pipe (3) communicating with the pyrolysis zone and an air inlet pipe (4) communicating with the oxidation zone on both sides of the furnace body (1), and a discharge pipe (5) at the bottom of the furnace body (1). The feeding device includes a hopper (6), a support column (7) on one side of the hopper (6), a feed inlet at the top of the hopper (6), a discharge outlet (10) at the bottom, a sealing cover (8) at the feed inlet, two intermeshing crushing wheels (9) directly below the feed inlet, and the discharge outlet (10) is connected to the furnace body (1) through a feed pipe (11). A control valve (12) is provided at one end of the feed pipe (11). The discharge port of the hopper (6) is eccentrically set, and the angle between the side wall of one side and the horizontal plane is 30°. The combustion chamber (2) is fixed inside the furnace body (1) by several fins (13). The top of the combustion chamber (2) is provided with a tangential inlet and the bottom is provided with an annular outlet. The top of the combustion chamber (2) is provided with a conical protective shell (14). The combustion chamber (2) is provided with an inclined nozzle (15). One end of the first air inlet pipe (3) and the second air inlet pipe (4) extends into the furnace body (1) and is fitted with a connector (16). The bottom of the connector (16) is fitted with a branch conduit (17) and connected to the nozzle (15). The nozzle (15) includes six converging and diverging nozzles arranged in a circumferentially spaced manner. The converging and diverging nozzle includes a converging section (24), a throat (25), and a diverging section (26) connected in sequence. The ash removal device includes a water tank (18) filled with water, a vertical shaft (19) connected to the middle of the bottom of the water tank (18), a grate (20) provided at the bottom of the furnace body (1), a rotating plate (21) fixedly connected to the bottom of the grate (20), the rotating plate (21) being connected to the vertical shaft (19), a motor (22) provided on one side of the water tank (18), a reducer (23) connected to the output end of the motor (22), and the output end of the reducer (23) being connected to the rotating plate (21).

2. A biomass gasification furnace according to claim 1, characterized in that: The ratio of the positions of the discharge pipe (5), the second air inlet pipe (4), and the first air inlet pipe (3) along the height of the furnace body (1) from the bottom is 1:3:4.

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