System and method for producing a gaseous fuel from biomass

Abstract

The application discloses a system and method for preparing gas fuel from biomass, and the system comprises a microwave reaction unit, which further comprises: a cavity in a sleeve structure, an inner sleeve of which receives pretreated biomass raw materials; a pyrolysis zone is arranged at the upper part of the inner sleeve, and the biomass raw materials are subjected to aerobic pyrolysis while being heated by microwaves; a gasification zone is arranged at the lower part of the inner sleeve, and working gas for gasification flows from the axis of the inner sleeve to the direction of the cylinder wall; the prepared fuel product gas flows out of the cavity from the space between the inner sleeve and the outer sleeve of the gasification zone; and a microwave generator is arranged outside the cylinder wall of the outer sleeve corresponding to the pyrolysis zone and is uniformly arranged along the circumferential direction of the outer sleeve. The system and method can effectively improve the product gas quality and solve the problem of microwave energy consumption.

Description

Technical Field

[0001] This invention relates to the field of biomass energy utilization technology, and in particular to a system and method for producing gaseous fuel from biomass. Background Technology

[0002] Biomass mainly refers to lignocellulose (or lignin) from straw and trees, excluding grains and fruits, produced during agricultural and forestry production. Utilizing biomass to produce combustible gases such as fuel gas, syngas, hydrogen, and methane is an important pathway for realizing the value-added utilization of biomass. Currently, biomass gaseous fuel production methods include fixed-bed, fluidized-bed, entrained-flow, plasma, and microwave gasification. Among these, microwave gasification of biomass allows energy to be rapidly applied to the biomass interior, fundamentally overcoming energy transfer losses inherent in conventional heating. It offers advantages such as rapid heating rate, high energy utilization efficiency, and low thermal inertia. Furthermore, the gaseous products have higher concentrations of combustible components such as hydrogen, carbon monoxide, and methane, which can be directly or further processed for use as chemical raw materials such as syngas and hydrogen, as well as new energy sources, demonstrating excellent application prospects.

[0003] Currently, various pilot-scale biomass microwave pyrolysis gasification systems of varying sizes have been built both domestically and internationally. Existing microwave pyrolysis gasification systems suffer from the following technical problems: due to the complex composition of the gas and the presence of tar, the obtained product gas differs significantly from expectations; microwave energy consumption is high, with issues including insufficient microwave power resulting in low heating efficiency, as well as electromagnetic conversion efficiency problems when using high-power (synthetic) microwave sources; and problems such as imprecise microwave output control and inaccurate temperature measurement and control in microwave reactor systems.

[0004] Chinese patent application CN105524662A discloses a method for producing syngas from biomass via microwave pyrolysis and gasification. The method includes the following steps: biomass feedstock and catalyst are fed into a microwave pyrolysis reactor, sequentially passing through a preheating zone, a pyrolysis zone, a gasification zone, and a reforming zone, undergoing dehydration, pyrolysis, gasification, and reforming reactions. The reformed products undergo gas-solid separation, where the gas, along with a small amount of tar and coke carried therein, undergoes further pyrolysis in a gas riser. Syngas is released from the outlet, while the coke and ash obtained from the gas-solid separation are discharged from the reactor. Although this method achieves a high biomass gasification rate and effectively improves the quality of the syngas product, it does not solve the problem of microwave energy consumption, and the temperature in the middle of the reactor cannot be guaranteed.

[0005] Therefore, there is an urgent need for a system and method for biomass-to-gas fuel production that can effectively improve the quality of the product gas and solve the problem of microwave energy consumption.

[0006] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a system and method for producing gaseous fuel from biomass that can effectively improve the quality of the product gas and solve the problem of microwave energy consumption.

[0008] To achieve the above objectives, according to a first aspect of the present invention, the present invention provides a system for producing gaseous fuel from biomass, comprising a microwave reaction unit, the microwave reaction unit further comprising: a cavity having an inner and outer sleeve structure, the inner sleeve receiving pretreated biomass raw materials; a pyrolysis zone provided in the upper part of the inner sleeve, wherein the biomass raw materials are subjected to aerobic pyrolysis while being heated by microwaves; a gasification zone provided in the lower part of the inner sleeve, wherein the gasification working gas flows radially from the axis of the inner sleeve towards the cylinder wall; the produced fuel product gas flows upward from the space between the inner and outer sleeves of the gasification zone and flows out of the cavity; and a microwave generator disposed on the outer side of the cylinder wall of the outer sleeve corresponding to the pyrolysis zone and uniformly arranged along the circumferential direction of the outer wall of the outer sleeve.

[0009] Furthermore, in the above technical solution, there can be multiple oxygen inlets in the pyrolysis zone, which can be respectively located on the top of the inner sleeve and on the cylinder wall in the pyrolysis zone. Oxygen can enter along the axial and radial directions of the cavity to form cross-flow.

[0010] Furthermore, in the above technical solution, an L-shaped pipe can be inserted through the bottom of the inner sleeve along the axis, and the L-shaped pipe has air holes at the corresponding positions in the gasification zone, so that the gasification working gas flows in the radial direction.

[0011] Furthermore, in the above technical solution, the gasification working gas can be a mixture of water vapor and oxygen, with a mixing ratio of 1 to 10:1.

[0012] Furthermore, in the above technical solution, the cavity wall can be provided with multiple microwave quartz windows, each window corresponding to a microwave generator. The power of each microwave generator can be 500–2000W, and the microwave power density inside the cavity can be 0.1 × 10⁻⁶. 5 ~2×10 5 W / m 3 .

[0013] Furthermore, in the above technical solution, the biomass raw material can be a substance containing lignocellulose, and the system can also include a feeding unit, which specifically includes: a pre-processor, which dries, crushes, shapes and preheats the biomass raw material; and a feeder, whose inlet end is connected to the pre-processor through a star valve and whose outlet end is connected to the microwave reaction unit.

[0014] Furthermore, in the above technical solution, the system may also include a slag discharge unit connected to the solid slag outlet of the microwave reaction unit, the slag discharge unit being equipped with a grate and a slag discharge spiral.

[0015] Furthermore, in the above technical solution, the system may also include a combustion unit, which is connected to the slag discharge spiral. The high-temperature flue gas generated after the solid slag is burned is used to preheat the biomass raw materials.

[0016] According to a second aspect of the present invention, the present invention provides a method for producing gaseous fuel from biomass, comprising the following steps: A. Preheating biomass raw materials to obtain pyrolysis precursor materials with certain reactivity; B. The pyrolysis precursor materials enter the pyrolysis zone in the upper part of the inner sleeve, and the biomass raw materials undergo aerobic pyrolysis by oxygen flowing in through a cross-flow while being heated by microwaves, generating gaseous volatiles and biochar; C. After the gaseous volatiles and biochar fall into the gasification zone in the lower part of the inner sleeve, fuel product gas is generated under the action of gasification working gas flowing radially from the inside to the outside; D. The fuel product gas flows out upward through the space between the inner and outer sleeves.

[0017] Furthermore, in the above technical solution, the method may also include: burning the solid residue of the bio-coke remaining at the bottom of the gasification zone, and preheating the biomass raw material by recovering the high-temperature flue gas generated after combustion.

[0018] Furthermore, in the above technical solution, the exothermic effect of aerobic pyrolysis in the pyrolysis zone compensates for the temperature loss near the axis of the pyrolysis zone during microwave heating.

[0019] Furthermore, in the above technical solution, the temperature near the axis of the pyrolysis zone can be 300–500℃; the temperature near the cylinder wall of the pyrolysis zone can be 600–800℃; the reaction time in the pyrolysis zone can be 5–30 minutes; and the oxygen flow rate in the pyrolysis zone can be 0.2–2 m³ / min. 3 / h.

[0020] Furthermore, in the above technical solution, the radial flow of the working gas in the gasification zone from the inside out compensates for the temperature loss near the axis of the gasification zone caused by microwave heating. At the same time, the radially flowing gas can simultaneously crack and remove the biochar, solid particles and dust carried by the gas as the temperature rises.

[0021] Furthermore, in the above technical solution, the temperature near the axis of the gasification zone can be 500-800℃; the temperature near the cylinder wall of the gasification zone can be 900-1200℃; and the reaction time of the gasification zone can be 5-30 minutes.

[0022] Furthermore, in the above technical solution, the fuel product gas can be hydrogen and carbon monoxide, and the ratio of hydrogen to carbon monoxide can be between 2.0 and 3.0.

[0023] Furthermore, in the above technical solution, the preheating conditions in step A are: temperature 150–250℃, time 10–30 minutes, and high-temperature flue gas flow rate 1–2 m³ / h. 3 / h.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) This invention, through the inner and outer double-sleeve structure of the microwave reactor cavity and the design of the L-shaped pipe in the gasification zone, ensures the movement of biomass materials under gravity while achieving axial and radial mixing flow of gaseous products and working gas in the reactor pyrolysis zone and radial flow from the inside to the outside in the gasification zone. The gasification zone creates a cross-flow effect between the gas and solid phases, allowing for full contact and reaction between the two phases. In particular, the gravity-driven solid phase can simultaneously crack and remove tar, particles, and dust carried by the horizontal airflow.

[0026] 2) The gas in the gasification zone of this invention is changed from the conventional axial vertical flow to radial horizontal flow, that is, the gas flow diffuses from the internal low temperature zone to the external high temperature zone, so that the tar and light components carried by the gas in the low temperature zone are fully cracked and reformed in the high temperature zone, achieving the goal of obtaining high-quality gas products in one reactor. This not only solves the technical problems of the difficulty in removing tar carried by the gas and the difficulty in removing the complex gas composition from the gas, but also overcomes the engineering problem that microwave pyrolysis of biomass is limited by the penetration depth and is not easy to scale up.

[0027] 3) This invention effectively compensates for the temperature loss near the axis of the pyrolysis zone by utilizing the exothermic effect of aerobic pyrolysis in the pyrolysis zone. Addressing the high energy consumption issue of full microwave heating of biomass, this invention combines aerobic pyrolysis with microwave heating, significantly reducing microwave energy consumption, mitigating gradient differences in the microwave temperature field, enhancing the quality improvement of the radial gas flow process, and increasing the gasification efficiency of biochar. Simultaneously, compared to conventional biomass gasification technology, it significantly reduces oxygen consumption and improves the hydrogen-to-carbon ratio and composition control of the gaseous products.

[0028] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it according to the contents of the specification, and to make the above and other objects, technical features and advantages of the present invention easier to understand, one or more preferred embodiments are listed below and described in detail with reference to the accompanying drawings. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the system structure for producing gaseous fuel from biomass according to the present invention.

[0030] Explanation of key figure labels:

[0031] 1-Preprocessor, 11-Star valve, 2-Feeder, 3-Microwave reactor, 31-Outer sleeve, 32-Inner sleeve, 33-Working gas inlet 1, 34-Inner sleeve gas channel, 4-Microwave generator, 5-L-shaped pipe, 6-Grate, 7-Slag discharge container, 8-Slag discharge spiral, 9-Combustion unit. Detailed Implementation

[0032] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0033] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0034] In this document, for ease of description, spatial relative terms such as “below,” “under,” “down,” “above,” “above,” “upper,” etc., are used to describe the relationship of one element or feature to another element or feature in the accompanying drawings. It should be understood that spatial relative terms are intended to encompass different orientations of an object in use or operation, in addition to those depicted in the figures. For example, if an object in the figure is flipped, an element described as “below” or “under” another element or feature would be oriented “above” that element or feature. Thus, the exemplary term “below” can encompass both the downward and upward orientations. An object may also have other orientations (rotated 90 degrees or other orientations), and the spatial relative terms used herein should be interpreted accordingly.

[0035] In this document, the terms "first," "second," etc., are used to distinguish two different elements or parts, and are not used to define specific positions or relative relationships. In other words, in some embodiments, the terms "first," "second," etc., can also be used interchangeably.

[0036] The inventors discovered through research that, based on the unique characteristic that microwave penetration depth decreases with increasing medium absorption, the microwave penetration depth gradually decreases due to temperature rise when heating large-volume biomass. This easily leads to common problems such as uneven heating inside and outside the material, limited pyrolysis and gasification efficiency, and poor gas quality control. Furthermore, the unidirectional heat and mass transfer properties of microwaves easily generate intermediate components, including tar and light hydrocarbons; the dielectric heating characteristics of microwaves result in heating difficulties and high microwave energy reflection losses for biomass with poor absorption, while for biochar with strong absorption, they result in excessively rapid heating and easy overheating, leading to significant differences in process control before and after the reaction; biomass itself lacks effective decarbonization and heating factors, making it impractical to rely solely on microwave energy for the pyrolysis process.

[0037] Based on the above research, such as Figure 1 As shown, this invention provides a system for producing gaseous fuel from biomass. The system includes a microwave reaction unit, which further includes a microwave reactor 3 and a microwave generator 4. The microwave reactor 3 has an inner and outer sleeve structure. The inner sleeve 32 receives pre-treated biomass raw materials. A pyrolysis zone is provided in the upper part of the inner sleeve 32, where the biomass raw materials can undergo aerobic pyrolysis (oxygen from...) while being heated by microwaves within the pyrolysis zone. Figure 1 The working gas 1); the lower part of the inner sleeve 32 is provided with a vaporization zone, in which the working gas (i.e., Figure 1 The working gas 2) flows radially from the inner sleeve axis towards the cylinder wall (i.e., from the inside to the outside). The produced fuel product gas flows upward from the space between the inner sleeve 32 and the outer sleeve 31 in the gasification zone and exits the cavity of the microwave reactor 3. The microwave generator 4 is located on the outer side of the cylinder wall of the outer sleeve 31 corresponding to the pyrolysis zone and is evenly arranged along the circumferential direction of the outer wall of the outer sleeve 31.

[0038] Further as Figure 1 As shown, the biomass-to-gas fuel system of the present invention may further include a feeding unit, which specifically includes a pre-processor 1 and a feeder 2. The pre-processor 1 performs drying, crushing, molding, and preheating treatment on the biomass raw materials. Specifically, the biomass raw materials can be derived from any material containing lignocellulose, such as corn stalks, rice husks, wheat straw, wood blocks, leaves, or branches. For low-density biomass raw materials such as straw that require molding, the specific processing conditions are as follows: the dried biomass is directly crushed to below 2mm, and then physically extruded and molded under 10-20MPa conditions to obtain the biomass raw material; for high-density biomass raw materials such as wood blocks that do not require molding, biomass raw materials close to the molding size can be obtained directly through cutting or other methods. The size of the biomass raw materials is between 10-100mm, preferably 20-40mm. Preheating treatment refers to processing under the presence of high-temperature gas, with the following conditions: temperature 150-250℃, time 10-30 minutes, and high-temperature gas flow rate 1-2m³ / h. 3 / h; the high-temperature gas may include one of the following: flue gas, a mixture of flue gas and air, or a mixture of flue gas and nitrogen. The high-temperature flue gas may be the flue gas generated during the combustion of the solid slag containing biochar remaining after the production of gaseous fuel according to this invention. Figure 1 The high-temperature flue gas produced by the combustion unit 9. Further, as... Figure 1 As shown, the feeder 2 is used to transport the pretreated biomass raw materials to the microwave reactor 3. The inlet end of the feeder 2 is connected to the pre-processor 1 through a star valve 11, and the outlet end is connected to the microwave reactor 3. This invention obtains pyrolysis precursor materials with certain reactivity by preheating the biomass raw materials.

[0039] Further as Figure 1As shown, the microwave reactor 3 has multiple oxygen inlets in its pyrolysis zone, located at the top of the inner sleeve 32 and on the cylinder wall within the pyrolysis zone. Oxygen enters along the axial and radial directions of the cavity, forming a cross-flow. Specifically, the oxygen comes from working gas 1, which can be one or more of oxygen, air, or a mixture of oxygen and air. The placement of the working gas 1 inlets ensures a more uniform oxygen distribution in the pyrolysis zone, with flow directions including radial flow from the cylinder wall to the axis and axial flow from top to bottom. The radially flowing working gas 1 inlets are evenly arranged along the circumference of the cylinder wall and layered, with 2 to 3 layers and 4 inlets per layer, with the inlet direction being horizontal and inward. The axially flowing working gas 1 inlets can be distributed in multiple rings, with 1 to 3 rings and 4 inlets per ring, with the inlet direction being vertical and downward. Due to the uniform distribution of oxygen in the pyrolysis zone, aerobic pyrolysis is achieved. The exothermic effect of aerobic pyrolysis in the pyrolysis zone (the oxidation reaction of biomass feedstock is exothermic) effectively compensates for the temperature loss near the axis of the pyrolysis zone caused by microwave heating. Therefore, aerobic pyrolysis in the pyrolysis zone can effectively reduce the power consumption of microwave generator 4, while maintaining the same power consumption and ensuring the temperature at the axial center of the pyrolysis zone. The radial temperature field of the pyrolysis zone in the microwave reactor exhibits a gradient distribution, with the temperature increasing from the axial center towards the circumference of the cylinder wall. Using the combined aerobic pyrolysis and microwave heating method of this invention, each microwave quartz window corresponds to one microwave generator 4. When the power of a single microwave generator is 500–2000 W, the power density within the reactor is 0.1 × 10⁻⁶ W. 5 ~2×10 5 W / m 3 Under these conditions, the flow rate of working gas 1 is controlled between 0.2 and 2 m³ / s. 3 The temperature near the axis of the pyrolysis zone can reach 300-500℃ per hour; the temperature near the circumference of the cylinder wall in the pyrolysis zone can reach 600-800℃; the reaction time in the pyrolysis zone is 5-30 minutes. The pyrolysis precursor material from the pretreatment unit enters the pyrolysis zone in the upper part of the inner sleeve 32. While being heated by microwaves, the material undergoes aerobic pyrolysis through cross-flowing oxygen, generating gaseous volatiles and biochar.

[0040] Further as Figure 1 As shown, gaseous volatiles and biochar fall into the gasification zone inside the microwave reactor 3 under the influence of gravity. Working gas 2 is introduced into the gasification zone and flows radially from the axis of the inner sleeve 32 towards the cylinder wall, i.e., flowing radially from low to high temperature, resulting in high-quality fuel product gas. Specifically, an L-shaped pipe 5 is inserted along the axis at the bottom of the inner sleeve 32. The L-shaped pipe 5 is positioned at a corresponding location in the gasification zone (i.e.,... Figure 1The L-shaped pipe 5 extends into the vertical portion of the inner sleeve and has vent holes, allowing the working gas 2 (i.e., the vaporization working gas) to flow radially from the inside to the outside. The vent diameter in the vertical portion is preferably 0.5 mm, with an opening rate of 20%, and these vents face horizontally. The top of the vertical portion of the L-shaped pipe 5 is sealed, and the height of the vertical portion is preferably 1 / 3 of the height of the inner sleeve. The working gas 2 can be one or a mixture of two or more of water vapor, oxygen, carbon dioxide, air, and flue gas, preferably a combination of water vapor and oxygen, with a mixing ratio of 1 to 10:1. Using the above-described arrangement of the present invention, the solid material moves axially downwards into the vaporization zone under the action of gravity, while the working gas 2 carries gaseous volatiles and flows radially from the axis of the inner sleeve to the circumference of the cylinder wall, i.e., flowing radially from low to high temperature, forming a cross-flow interaction between the airflow and the solid material within the vaporization zone. Through the radial flow of working gas 2 from the inside out in the gasification zone, the temperature loss near the axis of the gasification zone due to microwave heating is compensated (working gas 2 mainly consists of high-temperature water vapor). The radially flowing gas moves from the low-temperature zone at the axis to the high-temperature zone around the cylinder wall. As the temperature rises, the carried biochar, solid particles, and dust can be simultaneously cracked and removed, resulting in higher-quality fuel product gas. This achieves the coupling and integration of multiple processes such as gas production, separation, and purification, greatly simplifying subsequent gas product processing and reducing costs. The radial flow of gas also helps reduce gas flow resistance, further reducing reactor operating pressure and achieving controllable and adjustable reactions. When the power of a single microwave generator is 500–2000W, the power density within the reactor is 0.1 × 10⁻⁶. 5 ~1×10 5 W / m 3 Under these conditions, the flow rate of working gas 2 is controlled between 0.1 and 2 m³ / s. 3 / h, the temperature near the axis of the gasification zone can reach 500-800℃; the temperature near the circumference of the cylinder wall in the gasification zone can reach 900-1200℃; the reaction time in the gasification zone is 5-30 minutes.

[0041] Further as Figure 1 As shown, the fuel product gas obtained after the gasification reaction enters the space between the inner sleeve 32 and the outer sleeve 31 through the wall surface of the opening at the lower part of the inner sleeve 32 (i.e., the gas channel 34 of the inner sleeve) and flows out upwards. The fuel product gas produced by the system and method of the present invention is rich in hydrogen and carbon monoxide, with a hydrogen / carbon monoxide ratio between 2.0 and 3.0, a carbon dioxide content of less than 20%, other impurity gases not exceeding 0.2%, and a tar content of less than 10 mg / Nm³. 3 Ash content not exceeding 10 mg / Nm 3 The gas yield throughout the process is no less than 2.0 Nm³. 3 / kg dry basis biomass.

[0042] Further as Figure 1 As shown, the biomass-to-gas fuel system of the present invention may further include a slag discharge unit connected to the solid slag outlet of the microwave reactor 3. Preferably, but not limitingly, the slag discharge unit may be equipped with a grate 6 and a slag discharge screw 8. The solid slag enters the slag discharge container 7 through the grate 6 and is further transported to the combustion unit 9 through the slag discharge screw 8. The combustion unit is connected to the slag discharge screw 8, and the high-temperature flue gas generated after the solid slag is burned can be used to preheat the biomass raw materials in the pre-processor 1.

[0043] The system and method for producing gaseous fuel from biomass of the present invention, through the inner and outer double-sleeve structure of the microwave reactor cavity and the design of the L-shaped pipe in the gasification zone, ensures the movement of biomass materials under the action of gravity, while realizing the axial and radial mixing flow of gaseous products and working gas in the reactor pyrolysis zone and the radial flow from the inside to the outside in the gasification zone. This creates a cross-flow effect between the gas and solid phase materials, allowing for full contact and reaction between the gas and solid phases. In particular, the solid phase material moving downwards under gravity can simultaneously crack and remove tar, particles, and dust carried by the horizontal airflow.

[0044] Furthermore, the gas flow in the gasification zone is adjusted from the conventional axial vertical flow to radial horizontal flow, that is, the gas flow diffuses from the internal low temperature zone to the external high temperature zone. This allows the tar and light components carried by the gas in the low temperature zone to be fully cracked and reformed in the high temperature zone, achieving the goal of obtaining high-quality gas products in one reactor. This not only solves the "bottleneck" technical problems such as the difficulty in removing tar carried by the gas and the difficulty in removing gas with complex composition, but also overcomes the engineering problem that microwave pyrolysis of biomass is limited by the penetration depth and cannot be scaled up.

[0045] Furthermore, this invention addresses the high energy consumption issue associated with microwave-heated biomass by combining aerobic pyrolysis with microwave heating. This significantly reduces microwave energy consumption, alleviates gradient differences in the microwave temperature field, enhances the quality improvement of the radial flow process of gas, and improves the gasification efficiency of biochar. Compared to conventional biomass gasification technology, it also significantly reduces oxygen consumption and improves the hydrogen-to-carbon ratio and composition control of gas products.

[0046] Example 1

[0047] First, in this embodiment, biomass is fed into the feeding unit using high-temperature flue gas (i.e., using...). Figure 1 The high-temperature flue gas generated after the combustion of medium-solid slag is preheated under the following conditions: temperature 200℃, time 15 minutes, and high-temperature flue gas flow rate 1m³ / h. 3 / h, to obtain pyrolysis precursor materials with high reactivity;

[0048] Secondly, the pyrolysis precursor material is fed into the pyrolysis zone of the microwave reactor, and then... Figure 1The system shown has an oxygen flow rate of 1 m³ / s in the working gas 1. 3 / h and microwave power 0.5×10 5 W / m 3 Under the combined effect of these factors, the temperature near the circumference of the cylinder wall in the pyrolysis zone of the microwave reactor reaches 800℃, while the temperature near the axis of the pyrolysis zone reaches 500℃. Under these conditions, the pyrolysis reaction lasts for 30 minutes, generating gaseous volatiles and biochar.

[0049] Then, the gaseous volatiles and biochar fall into the gasification zone of the microwave reactor under the influence of gravity, employing... Figure 1 The system shown has a working gas 2 mixed gas flow rate (water vapor / oxygen volume ratio 5:1) of 0.5 m³ / s. 3 / h and microwave power density 0.5×10 5 W / m 3 Under the influence of the microwave reactor, the temperature near the circumference of the gasification zone in the microwave reaction section reaches 1000℃, and the temperature near the axis of the gasification zone reaches 600℃. Under these conditions, the gasification reaction lasts for 10 minutes, yielding a high-quality gaseous fuel product rich in hydrogen and carbon monoxide, with a hydrogen / carbon monoxide ratio of 2.6, a carbon dioxide content of 15%, other impurities of 0.15%, and a tar content of 6 mg / Nm³. 3 The ash content is 8 mg / Nm³. 3 The gas yield for the entire process was 2.4 Nm³. 3 / kg dry basis biomass.

[0050] The foregoing description of specific exemplary embodiments of the present invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. Any simple modifications, equivalent changes, and alterations made to the foregoing exemplary embodiments should fall within the scope of protection of the present invention.

Claims

1. A system for producing gaseous fuel from biomass, characterized in that, Includes a microwave reaction unit, which further includes: The cavity comprises an inner and outer sleeve structure. The inner sleeve receives pretreated biomass raw materials, which involves preheating the biomass raw materials to obtain pyrolysis precursor materials with certain reactivity. The high-temperature flue gas generated after the solid slag combustion is used to preheat the biomass raw materials. A pyrolysis zone is located in the upper part of the inner sleeve, where the biomass raw materials undergo aerobic pyrolysis while being microwave-heated. The pyrolysis zone has multiple oxygen inlets, located at the top of the inner sleeve and on the cylinder wall within the pyrolysis zone, respectively. Oxygen enters the cavity axially and radially, forming a cross-flow. A gasification zone is located in the lower part of the inner sleeve, where the gasification working gas flows radially from the axis of the inner sleeve towards the cylinder wall. The produced fuel product gas flows upward through the space between the inner and outer sleeves of the gasification zone and exits the cavity. A microwave generator is disposed on the outer side of the outer sleeve wall corresponding to the pyrolysis zone and is uniformly arranged along the circumferential direction of the outer sleeve wall.

2. The system for producing gaseous fuel from biomass according to claim 1, characterized in that, An L-shaped pipe is inserted through the bottom of the inner sleeve along the axis, and the L-shaped pipe has air holes at the corresponding positions in the gasification zone, so that the gasification working gas flows in the radial direction.

3. The system for producing gaseous fuel from biomass according to claim 1, characterized in that, The working gas for gasification is a mixture of water vapor and oxygen, with a mixing ratio of 1 to 10:

1.

4. The system for producing gaseous fuel from biomass according to claim 1, characterized in that, The cavity wall is provided with multiple microwave quartz windows, each window corresponding to one of the microwave generators. Each microwave generator has a power of 500~2000W, and the microwave power density inside the cavity is 0.1×10⁻⁶. 5 ~2×10 5 W / m 3 .

5. The system for producing gaseous fuel from biomass according to claim 1, characterized in that, The biomass raw material is a substance containing lignocellulose, and the system further includes a feeding unit, which specifically includes: A preprocessor that dries, crushes, shapes, and preheats the biomass raw materials; The feeder has its inlet end connected to the preprocessor via a star valve, and its outlet end connected to the microwave reaction unit.

6. The system for producing gaseous fuel from biomass according to claim 1, characterized in that, The system also includes a slag discharge unit connected to the solid slag outlet of the microwave reaction unit, the slag discharge unit being equipped with a grate and a slag discharge spiral.

7. The system for producing gaseous fuel from biomass according to claim 6, characterized in that, The system also includes a combustion unit that is connected to the slag discharge spiral.

8. A method for producing gaseous fuel from biomass, characterized in that, The system described in any one of claims 1 to 7 comprises the following steps: A. Preheat biomass raw materials to obtain pyrolysis precursor materials with certain reactivity; B. The pyrolysis precursor material enters the pyrolysis zone in the upper part of the inner sleeve. While being heated by microwaves, the biomass raw material undergoes aerobic pyrolysis through the cross-flowing oxygen to generate gaseous volatiles and biochar. C. After the gaseous volatiles and biochar fall into the gasification zone at the bottom of the inner sleeve, they generate fuel product gas under the action of the gasification working gas flowing radially from the inside to the outside. D. The fuel product gas flows out upward through the space between the inner and outer sleeves.

9. The method for producing gaseous fuel from biomass according to claim 8, characterized in that, The method further includes: burning the solid residue of the biochar remaining at the bottom of the gasification zone, and using the high-temperature flue gas generated after combustion to preheat the biomass raw materials.

10. The method for producing gaseous fuel from biomass according to claim 8, characterized in that, The exothermic effect of aerobic pyrolysis in the pyrolysis zone compensates for the temperature loss near the axis of the pyrolysis zone caused by microwave heating.

11. The method for producing gaseous fuel from biomass according to claim 10, characterized in that, The temperature near the axis of the pyrolysis zone is 300~500℃; the temperature near the cylinder wall of the pyrolysis zone is 600~800℃; the reaction time in the pyrolysis zone is 5~30 minutes; and the oxygen flow rate in the pyrolysis zone is 0.2~2 m³ / min. 3 / h.

12. The method for producing gaseous fuel from biomass according to claim 8, characterized in that, The radial flow of the working gas in the gasification zone from the inside out compensates for the temperature loss caused by microwave heating near the axis of the gasification zone. As the temperature rises, the radially flowing gas simultaneously breaks down and removes the biochar, solid particles, and dust it carries.

13. The method for producing gaseous fuel from biomass according to claim 12, characterized in that, The temperature near the axis of the gasification zone is 500~800℃; the temperature near the cylinder wall of the gasification zone is 900~1200℃; and the reaction time of the gasification zone is 5~30 minutes.

14. The method for producing gaseous fuel from biomass according to claim 8, characterized in that, The fuel product gas is hydrogen and carbon monoxide, with the ratio of hydrogen to carbon monoxide between 2.0 and 3.

0.

15. The method for producing gaseous fuel from biomass according to claim 9, characterized in that, The preheating conditions in step A are: temperature 150–250°C, time 10–30 minutes, and high-temperature flue gas flow rate 1–2 m³ / h. 3 / h.

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