System and method for the production of syngas from biomass thermal conversion

Abstract

The application discloses a system and method for preparing synthesis gas by biomass thermal conversion, and the system comprises: a feeding unit which provides two kinds of biomass raw materials with different sizes and feeds alternately; a microwave pyrolysis unit, the cavity of which is a sleeve structure, and the two kinds of biomass raw materials form a moving bed layer which is distributed along the axis direction alternately in the inner sleeve; oxygen enters from the upper space between the inner sleeve and the outer sleeve and flows along the radial direction in the lower part of the inner sleeve, and the oxygenated pyrolysis is carried out while the biomass raw materials are heated by the microwave, and the generated gas phase product flows out from the gas phase channel which extends along the axis of the inner sleeve. The application can significantly improve the quality of the gas phase product by the feeding unit and the microwave pyrolysis unit, and create conditions for obtaining the final synthesis product gas with higher quality, and solve the problem of microwave energy consumption. The product gas quality can be further improved by the joint action of the solid-state biochar gasification unit and the gaseous volatile splitting and reforming unit.

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 syngas from biomass thermal conversion. 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] Existing microwave pyrolysis gasification systems suffer from the following technical problems: Without the action of exogenous reactive gases, it is difficult to obtain high-yield syngas solely through the decomposition of biomass; uneven heating occurs inside and outside the microwave reactor, resulting in limited pyrolysis efficiency; during syngas production, microwave pyrolysis, biogas cracking and reforming, and bio-coke gasification processes are superimposed, making it difficult to completely remove tar from the gas; dust removal is poor; microwave energy consumption is high, and insufficient installed microwave power can lead to low heating efficiency.

[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 producing syngas from biomass through thermal conversion that can significantly 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 syngas from biomass thermal conversion. By using a feeding unit and a microwave pyrolysis unit, the quality of the gaseous products can be significantly improved, creating better conditions for obtaining higher quality syngas products, while also solving the problem of microwave energy consumption.

[0008] Another objective of this invention is to further improve the quality of the product gas through the combined action of the solid biochar gasification unit and the gaseous volatilization and reforming unit.

[0009] To achieve the above objectives, according to a first aspect of the present invention, the present invention provides a system for producing syngas from biomass through thermal conversion, comprising: a feeding unit that provides two biomass feedstocks of different particle sizes and feeds them alternately; a microwave pyrolysis unit having an inner and outer sleeve structure, wherein the two biomass feedstocks form a moving bed layer that is alternately distributed along the axial direction in the inner sleeve; oxygen enters from the upper part of the space between the inner and outer sleeves and flows radially in the lower part of the inner sleeve, and aerobic pyrolysis is performed while the biomass feedstocks are heated by microwaves, and the generated gaseous products flow out from a gaseous channel extending along the axis of the inner sleeve.

[0010] Furthermore, in the above technical solution, the feeding unit may include: a parallel dual silo, which contains biomass raw materials of two different sizes of particles respectively; a conveying screw, whose inlet end is connected to the dual silo through a Y-shaped pipe, and whose outlet end is connected to the inner sleeve of the microwave pyrolysis unit.

[0011] Furthermore, in the above technical solution, the microwave pyrolysis unit also includes a microwave generator, which can be set on the outer side of the outer sleeve wall and evenly arranged along the circumferential direction of the outer sleeve wall.

[0012] Furthermore, in the above technical solution, the lower part of the inner sleeve can be provided with oxygen vents for radial flow of oxygen; the lower part of the gas phase channel and the bottom can be provided with gas phase product vents.

[0013] Furthermore, in the above technical solution, the wall height of the oxygen vent can be 30% to 60% of the overall height of the inner sleeve, and the vent diameter of the oxygen vent is 0.5 to 5 mm; the wall height of the gas phase product vent can be 1 / 3 to 2 / 3 of the overall height of the gas phase channel, the vent diameter of the gas phase product vent is 0.2 to 2 mm, and the opening rate is 10% to 30%.

[0014] Furthermore, in the above technical solution, the gaseous product generated by the microwave pyrolysis unit is a gaseous volatile component. The system of the present invention also includes: a gaseous volatile component splitting and reforming unit, which is arranged above the airflow bed and has a throat structure. The throat region is provided with nozzles arranged circumferentially along the airflow bed and extending radially. The nozzles are provided with a multi-air-path annular channel and a swirling mixing channel for introducing oxygen and water vapor and splitting and reforming the gaseous volatile component.

[0015] Furthermore, in the above technical solution, the multi-gas-path annular channel may include: an inner ring channel, which is located on the innermost side and is vented with oxygen; a middle ring channel, which is located on the outer side of the inner ring channel and is vented with gaseous volatiles; and an outer ring channel, which is located on the outer side of the middle ring channel and is vented with water vapor.

[0016] Furthermore, in the above technical solution, the swirling mixing channel can be configured as a conical structure, with the angle between the inclined surface of the cone and the bottom surface being 20 to 70°.

[0017] The system of the present invention may further include: a solid biochar gasification unit, which is disposed in the lower part of the fluidized bed and receives solid biochar from the microwave pyrolysis unit cavity through a biochar conveying spiral; the solid biochar gasification unit is provided with a combustion zone for introducing oxygen and a reduction zone for introducing water vapor; the gasified product rises into the throat region for secondary reaction to obtain product gas.

[0018] Furthermore, in the above technical solution, a grate can be installed between the combustion zone and the reduction zone; an inclined gas distributor is provided below the grate at the corresponding position of the steam inlet.

[0019] According to a second aspect of the present invention, the present invention provides a method for producing syngas from biomass through thermal conversion, comprising the following steps: A. feeding pretreated biomass raw materials of two different sizes alternately; B. performing aerobic pyrolysis by radially flowing oxygen while heating the biomass raw materials with microwaves; C. exporting the generated gaseous volatiles from the inner sleeve of the microwave pyrolysis unit along a gas phase channel provided along the axis.

[0020] Furthermore, in the above technical solution, step B may further include: B1, radially flowing oxygen and axially downward moving solid biomass raw materials form a crossflow for dust removal of gaseous products; aerobic pyrolysis provides heat for the microwave reaction, and the generated heat is transferred to the axis through radial airflow; B2, a large particle low-temperature zone and a small particle high-temperature zone are formed in the microwave field, the small particle high-temperature zone first pyrolyzes to produce oil and gas, and the oil and gas flow to the large particle low-temperature zone with lower gas resistance. During the flow, the heavy component tar in the oil and gas condenses and adheres to the large particle low-temperature zone.

[0021] Furthermore, in the above technical solution, the biomass raw material in step A can be a substance containing lignocellulose; the pretreatment may include drying, crushing and molding.

[0022] Furthermore, in the above technical solution, the microwave heating reaction time can be 5–20 minutes, and the microwave power density is 0.1 × 10⁻⁶. 5 ~1×10 5 W / m 3 With the participation of aerobic pyrolysis, the temperature in the axial region of the inner sleeve can reach 400-600℃, and the temperature in the circumferential region of the cylinder wall can reach 600-800℃; the temperature in the high-temperature region of small particles is 50-100℃ higher than that in the low-temperature region of large particles.

[0023] The method of the present invention may further include: D. introducing the solid biochar generated by microwave aerobic pyrolysis into a gasification unit, where a gaseous product rich in syngas is generated under the combined action of oxygen and water vapor; E. introducing the gaseous volatiles generated in step C into a cracking and reforming unit, where a multi-channel swirling mixture of gaseous volatiles, oxygen, and water vapor is formed in the throat region for a primary reaction; the gaseous product rich in syngas generated in step D enters the throat region and undergoes a secondary reaction at high temperature to obtain the syngas product.

[0024] Furthermore, in the above technical solution, the solid biochar gasification unit has a combustion zone and a reduction zone, with the combustion zone temperature being 900–1200℃ and the reduction zone temperature being 800–1000℃; the reaction time of the solid biochar gasification unit is 5–20 minutes.

[0025] Furthermore, in the above technical solution, the primary reaction conditions in step E can be: oxygen flow rate 0.5–5 m³ / h. 3 / h, water vapor flow rate 0.5~5m 3 / h; the secondary reaction temperature can be 1000~1200℃.

[0026] Furthermore, in the above technical solution, the syngas product in step E is rich in hydrogen and carbon monoxide, with a hydrogen to carbon monoxide ratio between 1.5 and 3.0; the carbon dioxide content is less than 25%, and the tar content is less than 1 mg / Nm³. 3 Ash content not exceeding 10 mg / Nm 3 The gas yield throughout the process is no less than 2.5 Nm³. 3 / kg dry basis biomass.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) This invention achieves a combined aerobic pyrolysis and microwave heating by introducing oxygen into the microwave pyrolysis unit. When oxygen is introduced into the microwave field, the oxidation reaction, being exothermic, provides additional heat to the reaction. Simultaneously, the generated heat is transferred radially towards the axis by the gas flow, enhancing radial heat transfer, particularly reinforcing the temperature of the axial region of the inner sleeve, and raising the overall bed temperature, thus promoting complete biomass pyrolysis. This significantly reduces microwave energy consumption, enhances the quality of the radial gas flow process, 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 the gas products.

[0029] 2) This invention employs an alternating feeding method for particles of different sizes, forming a double-particle layer distribution in the microwave pyrolysis unit. It utilizes the differential heating characteristics of microwaves on particles of different sizes, creating a low-temperature zone for large particles and a high-temperature zone for small particles within the microwave field. The high-temperature zone of small particles pyrolyzes first, producing oil and gas, which then flows more easily to the low-temperature zone of large particles with lower gas resistance. Simultaneously, gas channels are formed in the large particle bed region, minimizing the flow resistance of the pyrolysis gas phase products, preventing damage to light components, and achieving selective pyrolysis of heavy components. During the flow process, the heavy tar components in the oil and gas condense and adhere to the low-temperature zone of large particles. The radial flow of the airflow and the axial flow of the solid material create a cross-flow effect, effectively removing dust from the gas and gas, thus significantly improving oil and gas quality and yield.

[0030] 3) The microwave pyrolysis of this invention can obtain higher quality gaseous volatiles, creating conditions for the subsequent generation of higher quality synthetic product gas. By coupling and integrating processes such as microwave pyrolysis, solid biochar gasification, and gaseous volatile decomposition and reforming, tar carried by the gas can be removed more effectively. The gaseous volatile decomposition and reforming unit uses nozzles with multi-channel annular channels and swirling mixing channels in the throat region, which can ensure uniform gas mixing and effectively avoid nozzle clogging. The through-flow arrangement of the solid biochar gasification unit and the gaseous volatile decomposition and reforming unit in the fluidized bed can realize primary and secondary reactions in the throat region, ensuring the calorific value of the raw materials, thereby achieving the acquisition of high-quality synthetic product gas.

[0031] 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

[0032] Figure 1 This is a schematic diagram of the system structure for producing syngas from biomass thermal conversion according to the present invention.

[0033] Figure 2 This is a schematic diagram of the structure of the nozzle in the throat region of the gaseous volatilization splitting and reforming unit in the system of the present invention.

[0034] Explanation of key figure labels:

[0035] 1-Feeding unit, 11-First hopper, 12-Second hopper, 13-Y-type conveying pipe, 14-First conveying screw;

[0036] 2-Microwave pyrolysis unit, 20-Microwave generator, 21-Outer sleeve, 22-Inner sleeve, 23-Oxygen inlet, 24-Gas phase channel, 25-Gaseous volatile matter outlet, 26-Second conveying screw;

[0037] 3-Solid bio-coke gasification unit, 31-Oxygen inlet, 32-Grate, 33-Gas distributor, 34-Steam inlet;

[0038] 4-Gaseous volatilization splitting and reforming unit, 41-Throat region, 42-Nozzle, 42A-Multi-channel annular channel, 42a-Inner annular channel, 42b-Middle annular channel, 42c-Outer annular channel, 42B-Swirl mixing channel, 43-Synthetic product gas outlet. Detailed Implementation

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 efficiency, and poor gas quality control. Furthermore, the unidirectional heat and mass transfer of microwaves easily generates 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.

[0044] Based on the above research, such as Figure 1 As shown, this invention provides a system for producing syngas from biomass through thermal conversion. The system includes a feeding unit 1 and a microwave pyrolysis unit 2. The feeding unit and microwave pyrolysis unit significantly improve the quality of the gaseous products, creating better conditions for obtaining higher-quality syngas, while also solving the problem of microwave energy consumption. The system may also include a solid biochar gasification unit 3 and a gaseous volatilization and reforming unit 4. The combined effect of these two units further improves the quality of the syngas.

[0045] Further as Figure 1As shown, the feeding unit 1 is used to provide biomass raw materials of two different particle sizes and feed them alternately. Specifically, the feeding unit further includes a parallel double hopper and a first conveying screw 14. The parallel double hopper includes a first hopper 11 and a second hopper 12, each containing biomass raw materials of two different particle sizes. 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. Before entering the feeding unit, the biomass raw materials can be pre-treated. For low-density biomass raw materials such as straw that require molding, the pre-treatment process includes drying, crushing, and molding. The specific treatment conditions are as follows: the dried biomass is directly crushed to below 2mm and then physically extruded under 10-20MPa conditions to obtain biomass raw materials; for high-density biomass raw materials such as wood blocks that do not require molding, biomass raw materials close to the molding size are obtained directly through cutting or other methods. The inlet end of the first conveying screw 14 is connected to two silos via a Y-shaped pipeline. A star valve is installed on the pipeline. The outlet end of the first conveying screw 14 is connected to the inner sleeve of the microwave pyrolysis unit 2, which is used to alternately convey two biomass raw materials of different sizes to the microwave pyrolysis unit 2.

[0046] Further as Figure 1 As shown, the cavity of the microwave pyrolysis unit 2 has an inner and outer sleeve structure (including an outer sleeve 21 and an inner sleeve 22). Due to alternating feeding, two biomass raw materials form a moving bed layer that is alternately distributed along the axial direction in the inner sleeve. The height ratio of the small-sized raw material bed to the large-sized raw material bed can be selected as 1:0.1 to 0.5, with the small-sized raw material particle size being 6 to 20 mm and the large-sized raw material particle size being 40 to 100 mm. The alternating arrangement of the two sizes of raw material layers is beneficial for changing the original reaction path of microwave pyrolysis, promoting process efficiency and improving the quality of pyrolysis products. Preferably, but not limitingly, the lower part of the inner sleeve 22 has oxygen vents for radial oxygen outflow. The oxygen vents can be distributed in multiple layers along the axial direction, with 4 to 10 layers. Each layer is evenly arranged along the circumference of the sleeve wall, with 6 to 60 vents per layer. The height of the oxygen vent distribution layer can be 30% to 60% of the height of the inner sleeve, and the vent diameter is 0.5 to 5 mm. Oxygen enters from the upper part of the space between the inner and outer sleeves (i.e.) Figure 1The oxygen inlet 23 flows radially in the lower part of the inner sleeve, from the circumference of the sleeve wall to the axis. Simultaneously, the biomass feedstock moves axially downwards under gravity, forming a cross-flow with the radially flowing oxygen. Aerobic pyrolysis occurs simultaneously with microwave heating of the biomass feedstock, and the generated gaseous products flow upwards from the gas phase channel 24, which extends along the axis of the inner sleeve 22, and exit from the gas volatiles outlet 25. This cross-flow facilitates dust removal from the gaseous products. Since the oxidation reaction is exothermic, the heat generated during the radial flow of oxygen is transferred to the axis through the radial airflow, helping to compensate for the temperature loss during microwave heating in the axis region. In other words, with the participation of radially flowing oxygen, a combination of aerobic pyrolysis and microwave heating is achieved. Furthermore, due to alternating feeding, the moving bed consists of alternating large and small particles distributed axially. In the microwave field, this creates a low-temperature zone for large particles and a high-temperature zone for small particles. The high-temperature zone of small particles pyrolyzes first to produce oil and gas, which then flows towards the low-temperature zone of large particles with lower gas resistance. During this flow, the heavy tar components in the oil and gas condense and adhere to the low-temperature zone of large particles, resulting in cleaner gaseous products. Further... Figure 1 As shown, the lower wall and bottom of the gas phase channel 24 are provided with gas phase product pores. The pore diameter can be 0.2-2 mm, the opening ratio can be 10-30%, and the height of the opening area is 1 / 2 to 4 / 5 of the height of the inner sleeve 22. The microwave generator 20 used in the microwave pyrolysis unit 2 is set on the outer wall of the outer sleeve 21 and is evenly arranged along the circumferential direction of the outer wall of the outer sleeve 21. Specifically, the cavity of the microwave pyrolysis unit 2 is provided with a certain number of microwave quartz windows, each window corresponding to a microwave generator 20. The power of a single microwave generator can be 500-2000W. The specific number of windows is set according to the volume of the reactor, etc., generally 2-10, to ensure that the power density in the reaction cavity is 0.1×10 5 ~2×10 5 W / m 3 .

[0047] Further as Figure 1 As shown, the solid biochar gasification unit 3 is located at the lower part of the fluidized bed 30 and is connected to the biochar conveying spiral (i.e., Figure 1 The second feeding screw 26 in the microwave pyrolysis unit 2 receives solid biochar from the bottom of the cavity. This solid biochar gasification unit 3 is equipped with a combustion zone for the introduction of working gas 1 and a reduction zone for the introduction of working gas 2. Working gas 1 is primarily oxygen (see...). Figure 1 The oxygen inlet 31 can be one of oxygen, air, or a mixture of oxygen and nitrogen, preferably a mixture of oxygen and nitrogen, wherein the mixing ratio of oxygen and nitrogen is 1:0.05 to 0.5, and the flow rate is controlled at 0.1 to 1 m³ / s. 3 / h; Working gas 2 is mainly water vapor (see...) Figure 1The steam inlet 34 contains one of water vapor, carbon dioxide, or a mixture thereof, preferably water vapor, with a flow rate controlled between 0.05 and 0.5 m³ / s. 3 / h. Combustion zone temperature 900–1200℃, reduction zone temperature 800–1000℃; reaction time in the solid biochar gasification unit 5–20 minutes. Further details... Figure 1 As shown, a grate 32 is arranged between the combustion zone and the reduction zone, and an inclined gas distributor 33 is provided below the grate 32 at the corresponding position of the steam inlet 34. The gas distributor 33 can be any type such as a sieve type, a pipeline type, or a grid type; the grate 32 can be any type such as a fixed grate, a reciprocating grate, a vibrating grate, or a rotating grate, and the powdery ash can be discharged by controlling the working frequency of the grate. The products of solid biochar after gasification in the combustion zone and the reduction zone rise into the gaseous volatilization and decomposition reforming unit 4 of this invention.

[0048] Further as Figure 1 As shown, the solid biochar gasification unit 3 and the gaseous volatile matter decomposition and reforming unit 4 are directly connected. The gaseous volatile matter decomposition and reforming unit 4 has a throat region 41 at its upper part, and several nozzles 42 are arranged in the throat region 41. The nozzles 42 are evenly arranged along the circumference of the fluidized bed 30, with the number ranging from 3 to 20, and the nozzles 42 face towards the center of the fluidized bed 30. A synthesis product gas outlet 43 is located at the top of the gaseous volatile matter decomposition and reforming unit 4. Further details are provided below. Figure 2 As shown, the nozzle 42 is equipped with a multi-channel annular channel 42A and a swirling mixing channel 42B for introducing oxygen and water vapor and for cracking and reforming gaseous volatiles. Specifically, the multi-channel annular channel 42A includes an inner annular channel 42a, a middle annular channel 42b, and an outer annular channel 42c. The inner annular channel 42a is located at the innermost edge and introduces oxygen. The middle annular channel 42b is located outside the inner annular channel and introduces gaseous volatiles from the microwave pyrolysis unit 2. The outer annular channel 42c is located outside the middle annular channel and introduces water vapor. The outlet of each channel is connected to the swirling mixing channel 42B, which has a conical structure with an angle of 20° to 70° between the inclined surface and the bottom surface. Through this nozzle structure, the three gases are mixed more thoroughly, resulting in better cracking and reforming of gaseous volatiles.

[0049] In the solid biochar gasification unit 3 of the present invention, a gaseous product rich in syngas can be generated under the combined action of oxygen and water vapor. When the gaseous volatiles generated in the microwave pyrolysis unit 2 are introduced into the cracking and reforming unit 4, a multi-channel swirling mixture of gaseous volatiles, oxygen and water vapor is formed in the throat region for a primary reaction. The gaseous product rich in syngas generated in the solid biochar gasification unit 3 enters the throat region and undergoes a secondary reaction at high temperature, thereby obtaining a higher quality syngas product.

[0050] The present invention also provides a method for producing syngas from biomass thermal conversion, comprising the following steps:

[0051] Step S101 involves alternating the feeding of two pretreated biomass feedstocks of different particle sizes. The biomass feedstock can be a substance containing lignocellulose; the pretreatment specifically includes drying, crushing, and molding.

[0052] In step S102, while the biomass feedstock is being microwave-heated, aerobic pyrolysis is carried out via radially flowing oxygen. Further, the radially flowing oxygen and the axially downward-moving solid biomass feedstock form a cross-flow for dust removal of the gaseous products; aerobic pyrolysis provides heat for the microwave reaction, and the generated heat is transferred to the axis through the radial airflow; additionally, a large-particle low-temperature zone and a small-particle high-temperature zone are formed in the microwave field. The small-particle high-temperature zone pyrolyzes first to produce oil and gas, which then flows towards the large-particle low-temperature zone with lower gas resistance. During this flow, the heavy tar component in the oil and gas condenses and adheres to the large-particle low-temperature zone. The microwave heating reaction time is 5–20 minutes, and the microwave power density is 0.1 × 10⁻⁶. 5 ~1×10 5 W / m 3 Under these conditions, with the participation of aerobic pyrolysis, the temperature in the axial region of the inner sleeve can reach 400-600℃, and the temperature in the circumferential region of the cylinder wall can reach 600-800℃; the temperature in the high-temperature region of small particles is 50-100℃ higher than that in the low-temperature region of large particles.

[0053] This step addresses common problems encountered when microwave heating large-capacity biomass, such as uneven heating of the material, limited pyrolysis efficiency, and poor product quality control due to the gradual decrease in microwave penetration depth caused by temperature rise. It utilizes the limitation of microwave penetration depth in the raw material layer to induce the decomposition of organic matter and the generation of primary products in the external raw material (i.e., biomass raw material near the circumference of the cylinder wall), forming highly active biomass rich in free radicals. Then, it fully utilizes the heterogeneous oxidation reaction between oxidizing gases and the highly active biomass rich in free radicals to supplement the heat supply within the cavity. The high-temperature gaseous products generated in situ act as a heat carrier, driving the gas flow from the conventional axial vertical flow to a radial horizontal flow, i.e., the airflow moves from the external high-temperature zone to the internal low-temperature zone. This allows for rapid heat and mass transfer in the low-temperature zone, rapidly decomposing the heavy components trapped there into lighter components and small-molecule gases. This weakens the release path of pyrolysis gaseous products through the high-temperature zone, which helps reduce secondary pyrolysis reactions and achieves in-situ filtration and dust removal of the pyrolysis oil and gas, thus improving the quality of the pyrolysis oil and gas.

[0054] Step S103: The generated gaseous volatiles are exported from the inner sleeve of the microwave pyrolysis unit along the gas phase channel set along the axis.

[0055] In step S104, the solid biochar produced by microwave aerobic pyrolysis is introduced into the gasification unit, where, under the combined action of oxygen and water vapor, a gaseous product rich in syngas is generated. Specifically, the solid biochar gasification unit has a combustion zone and a reduction zone. The temperature of the combustion zone is controlled at 900–1200°C, and the temperature of the reduction zone is controlled at 800–1000°C. The reaction time of the solid biochar gasification section is 5–20 minutes.

[0056] In step S105, the gaseous volatiles generated in step S103 are introduced into the cracking and reforming unit, where a multi-channel swirling mixture of gaseous volatiles, oxygen, and water vapor is formed in the throat region for a primary reaction. The gaseous product rich in syngas generated in step S104 enters the throat region and undergoes a secondary reaction at high temperature to obtain syngas product. The primary reaction conditions are: oxygen flow rate 0.5–5 m³ / h. 3 / h, water vapor flow rate 0.5~5m 3 / h; the secondary reaction temperature is 1000~1200℃.

[0057] Following steps S101 to S105, the resulting syngas product is rich in hydrogen and carbon monoxide, with a hydrogen to carbon monoxide ratio between 1.5 and 3.0; the carbon dioxide content is less than 25%, and the tar content is less than 1 mg / Nm³. 3 Ash content not exceeding 10 mg / Nm 3 The gas yield throughout the process is no less than 2.5 Nm³. 3 / kg dry basis biomass.

[0058] Example 1

[0059] Combination Figure 1 As shown:

[0060] First, the feeding unit continuously feeds biomass feedstocks of two sizes into the microwave pyrolysis unit, maintaining a height ratio of 1:0.2 between the smaller and larger feedstock beds, while simultaneously operating at a microwave power density of 0.2 × 10⁻⁶. 5 W / m 3 And oxygen flow rate 0.5m 3 Under the combined effect of / h, the temperature of the axial region of the microwave pyrolysis unit cavity is 450℃, the temperature of the circumferential region of the microwave pyrolysis unit cylinder wall is 650℃, and the average temperature of the small-sized raw material layer is 60℃ higher than that of the large-sized raw material layer. Under the above conditions, the pyrolysis reaction is carried out for 15 minutes to obtain high-quality gaseous volatiles and by-product solid biochar.

[0061] Secondly, the solid biochar is discharged from the bottom of the microwave pyrolysis unit and sent to the solid biochar gasification unit, where working gas 1 (a mixture of oxygen and nitrogen with a volume ratio of 1:0.5 and a flow rate controlled at 1 m³ / s) is used.3 / h) and working gas 2 (water vapor, flow rate controlled at 0.5m 3 Under the combined action of / h), the temperature in the combustion zone reaches 1000℃ and the temperature in the reduction zone reaches 850℃. Under the above conditions, the reaction takes 15 minutes to generate gaseous products rich in syngas.

[0062] Then, the gaseous volatiles released from the top of the microwave pyrolysis unit are introduced into the gaseous volatile decomposition and reforming unit at an oxygen flow rate of 1.5 m³ / s. 3 / h and water vapor flow rate 3m 3 A primary reaction is carried out under the combined action of [amount] and [amount]; a secondary reaction is then carried out with the syngas-rich gaseous products from the solid biochar gasification unit at a temperature of 1100℃, yielding a high-quality syngas product: a hydrogen / carbon monoxide ratio of 2.2, a carbon dioxide content of 21.9%, a nitrogen content of 9.2%, no tar in the gas, and an ash content of 10 mg / Nm³. 3 The gas yield for the entire process was 3.8 Nm³. 3 / kg dry basis biomass.

[0063] 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 syngas from biomass through thermal conversion, characterized in that, include: The feeding unit provides biomass feedstock in two different sizes of pellets and feeds them alternately. The microwave pyrolysis unit has an inner and outer sleeve structure. The two biomass raw materials form a moving bed layer that is alternately distributed along the axial direction in the inner sleeve. Oxygen enters from the upper part of the space between the inner and outer sleeves and flows radially in the lower part of the inner sleeve. While the biomass raw materials are heated by microwave, aerobic pyrolysis is carried out. The generated gaseous products flow out from the gaseous channel that extends along the axis of the inner sleeve. Radial flow of oxygen and axially downward-moving solid biomass feedstock form a crossflow for dust removal of gaseous products; aerobic pyrolysis provides heat for the microwave reaction, and the generated heat is transferred to the axis through radial airflow; the axially alternating moving bed forms a large-particle low-temperature zone and a small-particle high-temperature zone in the microwave field. The small-particle high-temperature zone pyrolyzes first to produce oil and gas, which then flows to the large-particle low-temperature zone with lower gas resistance. During the flow, the heavy component tar in the oil and gas condenses and adheres to the large-particle low-temperature zone.

2. The system for producing syngas from biomass through thermal conversion according to claim 1, characterized in that, The feeding unit includes: The parallel dual-feed bins contain biomass raw materials of the two different sizes of particles respectively; The feeding screw has its inlet end connected to the dual material bins via a Y-shaped pipe, and its outlet end connected to the inner sleeve of the microwave pyrolysis unit.

3. The system for producing syngas from biomass through thermal conversion according to claim 1, characterized in that, The microwave pyrolysis unit further includes: A microwave generator is disposed on the outer side of the outer sleeve wall and is evenly arranged along the circumferential direction of the outer sleeve wall.

4. The system for producing syngas from biomass through thermal conversion according to claim 3, characterized in that, The lower part of the inner sleeve is provided with oxygen vents for radial flow of oxygen; the lower part of the gas phase channel and the bottom are provided with gas phase product vents.

5. The system for producing syngas from biomass through thermal conversion according to claim 4, characterized in that, The wall height of the oxygen vent is 30% to 60% of the overall height of the inner sleeve, and the diameter of the oxygen vent is 0.5 to 5 mm; the wall height of the gas phase product vent is 1 / 3 to 2 / 3 of the overall height of the gas phase channel, the diameter of the gas phase product vent is 0.2 to 2 mm, and the opening rate is 10% to 30%.

6. The system for producing syngas from biomass through thermal conversion according to claim 1, characterized in that, The gaseous products generated by the microwave pyrolysis unit are gaseous volatiles, and the system further includes: The gaseous volatile matter splitting and reforming unit is located above the flow bed and has a throat structure. The throat region is provided with nozzles arranged circumferentially along the flow bed and extending radially. The nozzles are provided with multi-channel annular channels and swirling mixing channels for introducing oxygen and water vapor and splitting and reforming the gaseous volatile matter.

7. The system for producing syngas from biomass through thermal conversion according to claim 6, characterized in that, The multi-air-path annular channel includes: The inner ring channel is located on the innermost side and is supplied with oxygen. A middle ring channel is located outside the inner ring channel and is introduced into the gaseous volatiles; The outer ring channel is located outside the middle ring channel and is vented with water vapor.

8. The system for producing syngas from biomass through thermal conversion according to claim 7, characterized in that, The swirling mixing channel has a conical structure with an angle of 20° to 70° between the inclined surface and the bottom surface.

9. The system for producing syngas from biomass through thermal conversion according to claim 6, characterized in that, The system also includes: A solid biochar gasification unit is located at the bottom of the gas flow bed and receives solid biochar from the microwave pyrolysis unit cavity through a biochar conveying spiral. The solid biochar gasification unit is provided with a combustion zone for introducing oxygen and a reduction zone for introducing water vapor. The gasified product rises into the throat region for secondary reaction to obtain product gas.

10. The system for producing syngas from biomass through thermal conversion according to claim 9, characterized in that, A grate is provided between the combustion zone and the reduction zone; an inclined gas distributor is provided below the grate at the corresponding position of the steam inlet.

11. A method for producing syngas from biomass through thermal conversion, characterized in that, Includes the following steps: A. Alternate feeding of two types of pretreated biomass raw materials with different particle sizes; B. While the biomass raw material is heated by microwave, aerobic pyrolysis is carried out by radially flowing oxygen; step B further includes: B1. The radially flowing oxygen and the axially downward moving solid biomass raw material form a crossflow for dust removal of gaseous products; aerobic pyrolysis provides heat for the microwave reaction, and the generated heat is transferred to the axis through radial airflow; B2. A large particle low-temperature zone and a small particle high-temperature zone are formed in the microwave field. The small particle high-temperature zone pyrolyzes first to produce oil and gas, and the oil and gas flows to the large particle low-temperature zone with lower gas resistance. During the flow, the heavy component tar in the oil and gas condenses and adheres to the large particle low-temperature zone. C. The generated gaseous volatiles are exported from the inner sleeve of the microwave pyrolysis unit along the gas phase channel set along the axis.

12. The method for producing syngas from biomass thermal conversion according to claim 11, characterized in that, The biomass raw material in step A is a substance containing lignocellulose; the pretreatment includes drying, crushing and molding.

13. The method for producing syngas from biomass thermal conversion according to claim 11, characterized in that, The microwave heating reaction time is 5-20 minutes, and the microwave power density is 0.1×10⁻⁶. 5 ~1×10 5 W / m 3 With the participation of aerobic pyrolysis, the temperature of the axial region of the inner sleeve reaches 400~600℃, and the temperature of the circumferential region of the cylinder wall reaches 600~800℃; the temperature of the high-temperature region of the small particles is 50~100℃ higher than that of the low-temperature region of the large particles.

14. The method for producing syngas from biomass thermal conversion according to claim 11, characterized in that, The method further includes: D. The solid biochar produced by microwave aerobic pyrolysis is introduced into the gasification unit, where it generates gaseous products rich in syngas under the combined action of oxygen and water vapor. E. The gaseous volatiles generated in step C are introduced into the cracking and reforming unit, where the gaseous volatiles, oxygen, and water vapor are mixed in a multi-channel swirling flow in the throat region for a primary reaction; the gaseous products rich in syngas generated in step D enter the throat region and undergo a secondary reaction at high temperature to obtain syngas products.

15. The method for producing syngas from biomass thermal conversion according to claim 14, characterized in that, The solid biochar gasification unit has a combustion zone and a reduction zone. The temperature of the combustion zone is 900~1200℃, and the temperature of the reduction zone is 800~1000℃. The reaction time of the solid biochar gasification unit is 5~20 minutes.

16. The method for producing syngas from biomass thermal conversion according to claim 14, characterized in that, The primary reaction conditions in step E are: oxygen flow rate 0.5~5m³ / h. 3 / h, water vapor flow rate 0.5~5m 3 / h; the secondary reaction temperature is 1000~1200℃.

17. The method for producing syngas from biomass thermal conversion according to claim 14, characterized in that, The syngas product in step E is rich in hydrogen and carbon monoxide, with a hydrogen to carbon monoxide ratio between 1.5 and 3.0; the carbon dioxide content is less than 25%, and the tar content is less than 1 mg / Nm³. 3 Ash content not exceeding 10 mg / Nm 3 The gas yield throughout the process is no less than 2.5 Nm³. 3 / kg dry basis biomass.

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