Hydrogen production system and method using biomass double moving bed gasification

Abstract

The application discloses a biomass double-moving-bed gasification hydrogen production system and method, and relates to the field of biomass hydrogen production technology. The system comprises a feeding unit for providing and continuously feeding pretreated large-size high-density biomass raw materials mixed with biochar containing alkali metal oxides and salts thereof; a microwave pyrolysis unit comprising a microwave heating cavity and a conveying screw, which is used for receiving the biomass raw materials from the feeding unit, and performing microwave pyrolysis on the biomass raw materials while the biomass raw materials are pushed and moved in the microwave heating cavity; the microwave heating cavity is provided with a washing gas channel for radial circumferential injection; a combustion gasification unit arranged at the lower part of the microwave pyrolysis unit and receiving gaseous volatile components and solid biochar from the microwave pyrolysis unit; the combustion gasification unit is provided with a throat combustion zone and a gasification zone. The application can effectively improve the biomass pyrolysis efficiency, enhance the lightness of pyrolysis products, reduce hydrogen loss caused by combustion, significantly improve the hydrogen production yield, improve the tar removal intensity of combustion gasification, and create better conditions for obtaining a final hydrogen product with higher quality.

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 hydrogen from biomass using a dual moving bed. Background Technology

[0002] Biomass is the only green "zero-carbon" fuel among renewable energy sources, possessing significant resource potential and "carbon sink" advantages for hydrogen production. Biomass gasification hydrogen production technology can directly convert biomass into hydrogen-rich small molecule compounds, representing an important biomass hydrogen production pathway. Currently, conventional biomass gasification hydrogen production suffers from common problems such as low hydrogen conversion rate and concentration, difficulty in removing tar and ash from hydrogen, and poor gasifier stability. It is necessary to innovate biomass hydrogen production routes, develop competitive biomass green hydrogen technologies, and promote the large-scale development of the biomass hydrogen energy sector.

[0003] The biomass dual moving bed hydrogen production route spatially decouples and integrates multiple processes such as biomass pyrolysis, gasification, and tar cracking into a single reaction system. This differs from the interference issues inherent in conventional single-bed routes where multiple processes are coupled, and also from the physical barriers between conventional multi-reactor systems. It offers significant advantages in hydrogen yield and quality control. Currently, biomass dual moving bed hydrogen production mainly includes Viking and WoodRoll technologies.

[0004] Viking technology first pyrolyzes biomass in a primary reactor. The pyrolysis products then undergo incomplete combustion in the throat region, with the residue (mainly non-condensable gaseous products and solid biochar) falling into a secondary reactor for further steam vaporization. This residue also serves as a high-temperature carbon layer to deeply remove trace amounts of tar from the gasification products. This technology significantly reduces tar content to 15 mg / m³. 3 However, due to the use of air as an auxiliary combustion fuel, the hydrogen concentration is only about 34%. The WoodRoll technology differs from the Viking technology in two ways: first, it changes the direct combustion of pyrolysis products for heating to indirect combustion heat exchange; second, it only combusts the gaseous pyrolysis products, with hydrogen mainly obtained through a shift reaction between biochar and steam. This not only avoids dilution of the hydrogen products by the auxiliary combustion fuel but also significantly reduces the tar content carried by the gaseous products. As a result, the hydrogen concentration rises to 55-58%, while the tar content does not exceed 30 mg / m³. 3 .

[0005] However, the two technologies mentioned above share the following common problems: First, the use of non-contact heat transfer for biomass pyrolysis places high demands on the raw materials and results in low heating efficiency, typically requiring the raw materials to be crushed and loosened. Second, the pyrolysis products under non-contact heat transfer are heavier, requiring more combustion-supporting fuel. In direct combustion, this leads to hydrogen dilution and reduced yield; while in indirect combustion, the system's self-heating may not meet the reaction's heat requirements, also affecting hydrogen production efficiency. Third, using small-sized and low-density raw materials limits the height of the secondary gasification carbon layer, resulting in reduced tar removal efficiency and large fluctuations in gasification operating pressure.

[0006] Therefore, there is an urgent need for a biomass hydrogen production system and method that can both improve hydrogen production efficiency and significantly enhance hydrogen quality.

[0007] 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

[0008] The purpose of this invention is to provide a system and method for producing hydrogen from biomass using a dual moving bed. By combining the microwave pyrolysis of biomass feedstock with the combustion and gasification of pyrolysis products, the system can effectively improve the pyrolysis efficiency of biomass, enhance the lightness of pyrolysis products, reduce hydrogen loss caused by combustion, and significantly improve the hydrogen production yield. It can also improve the tar removal intensity of combustion and gasification, creating better conditions for obtaining higher quality hydrogen products.

[0009] To achieve the above objectives, according to a first aspect of the present invention, a biomass dual moving bed gasification hydrogen production system is provided, comprising: a feeding unit for continuously feeding pretreated large-size, high-density biomass feedstock, wherein the biomass feedstock is mixed with biochar containing alkali metal oxides and their salts; a microwave pyrolysis unit comprising a microwave heating cavity and a conveying screw for receiving the biomass feedstock from the feeding unit, wherein microwave pyrolysis is performed while the biomass feedstock is tumbled and moved in the microwave heating cavity, wherein the microwave heating cavity is provided with a scrubbing gas channel for radial circumferential injection; and a combustion gasification unit disposed below the microwave pyrolysis unit and receiving gaseous volatiles and solid biochar from the microwave pyrolysis unit; the combustion gasification unit is provided with a throat combustion zone and a gasification zone.

[0010] Furthermore, in the above technical solution, the biomass raw material can be the raw material formed by dispersing and extruding dried and crushed biomass; the length of the large-size high-density biomass raw material in the maximum dimension direction is 10 to 100 mm, and the bulk density is 500 to 1000 g / L.

[0011] Furthermore, in the above technical solution, the washing gas channel is rotatably arranged, located in the center of the microwave heating cavity and extending along the axial direction of the cavity; the washing gas channel is provided with washing holes facing the wall of the microwave heating cavity, which are used to spray water vapor and / or oxygen onto the wall while the microwave pyrolysis is taking place.

[0012] Furthermore, in the above technical solution, the washing hole radially injects washing gas during rotation. The upward radial injection is used to remove tar and coke adhering to the wall, and the downward radial injection is used to crack, reform, and gasify the primary pyrolysis products to obtain lighter pyrolysis products.

[0013] Furthermore, in the above technical solution, the washing holes can be arranged with increasing density along the running direction of the biomass raw materials.

[0014] Furthermore, in the above technical solution, the radially injected scrubbing gas moves axially toward the inlet of the combustion gasification unit under the micro-negative pressure environment of the microwave heating cavity.

[0015] Furthermore, in the above technical solution, the microwave heating cavity is provided with a metal shell, and microwave generators are arranged at uniform intervals along the circumference of the metal shell, with a microwave quartz window set at the corresponding position of each microwave generator.

[0016] Furthermore, in the above technical solution, the feeding unit may include upper and lower silos, and the feeding and conveying process is continuous by opening and closing a ball valve between the two silos.

[0017] Furthermore, in the above technical solution, a feeding vibrator is connected to the lower part of the lower hopper, and the outlet end of the feeding vibrator is connected to the microwave heating cavity.

[0018] Furthermore, in the above technical solution, the throat combustion zone is located at the inlet of the combustion gasification unit, and oxygen and water vapor are injected through nozzles to crack and reform the pyrolysis products from the microwave pyrolysis unit.

[0019] Furthermore, in the above technical solution, the nozzle may be provided with a dual-air-path annular channel and a swirling mixing channel, wherein the dual-air-path annular channel includes: an inner annular channel, which is located on the inner side and is used to introduce oxygen; and an outer annular channel, which is located on the outer side and is used to introduce water vapor.

[0020] Furthermore, in the above technical solution, the swirling mixing channel can be a conical structure and connected to the outlets of the inner and outer ring channels, and the angle between the inclined surface of the cone and the bottom surface can be 20 to 70°.

[0021] Furthermore, in the above technical solution, the gasification zone receives the pyrolysis products from the throat combustion zone from which most of the tar has been removed, and carries out a secondary reaction under the combined action of alkali metal oxides and their salts and water vapor to remove residual tar.

[0022] Furthermore, in the above technical solution, a slag discharge grate may be provided at the lower part of the gasification zone. The slag discharge grate is adjacent to the slag discharge port and connected to a solid slag collector through a pipeline. It is used to collect biochar rich in alkali metals and reuse it for the pretreatment of biomass raw materials.

[0023] According to a second aspect of the present invention, the present invention provides a method for producing hydrogen from biomass via dual moving bed gasification, comprising the following steps: A) continuously feeding pretreated large-size, high-density biomass feedstock; B) simultaneously heating the biomass feedstock with microwaves, removing wall-adhering tar and coke through radially injected scrubbing gas, and pyrolyzing, reforming, and gasifying the resulting primary pyrolysis products in situ; C) burning and gasifying the pyrolysis products generated by microwave pyrolysis, and generating hydrogen-rich gaseous products under the combined action of oxidizing gas and water vapor.

[0024] Furthermore, in the above technical solution, the pretreatment in step A may include drying, crushing, dispersing and forming processes; the dispersion process specifically involves: uniformly dispersing biochar containing alkali metal oxides and their salts into the biomass raw material, wherein the mass ratio of the biomass raw material to the biochar containing alkali metal oxides and their salts may be 1:0.02 to 1; and the mass percentage content of alkali metal oxides and their salts in the biochar may be 5% to 50%.

[0025] Furthermore, in the above technical solution, the microwave heating reaction time in step B is 2–10 minutes, and the microwave power density is 0.1 × 10⁻⁶. 5 ~1×10 5 W / m 3 The temperature in the microwave pyrolysis zone reaches 400–700℃.

[0026] Furthermore, in the above technical solution, the water vapor flow rate in the scrubbing gas is 0.01–0.1 m³ / s. 3 / h, oxygen flow rate is 0.005~0.05m³ / h. 3 / h.

[0027] Furthermore, in the above technical solution, the combustion in step C is a single reaction occurring in the throat combustion zone, with a temperature of 900–1100°C and a reaction time of 1–5 seconds; the reaction conditions for this single reaction are: oxygen flow rate of 0.1–0.5 m³ / s. 3 / h, water vapor flow rate 0.02~0.2m³ / h 3 / h.

[0028] Furthermore, in the above technical solution, the vaporization in step C is a secondary reaction carried out in the vaporization zone, the temperature of the vaporization zone is 750–850℃, and the reaction time in the vaporization zone is 5–10 minutes; the secondary reaction conditions are: water vapor flow rate 0.2–0.6 m³ / s. 3 / h.

[0029] Furthermore, in the above technical solution, the hydrogen concentration in the hydrogen-rich gaseous product of step C can reach over 60%, the carbon monoxide content is between 25% and 35%, the carbon dioxide content is less than 5%, and the tar content is less than 1 mg / Nm³. 3 The hydrogen production process shall yield no less than 60 g / kg dry biomass.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1) This invention uses a combination of microwave pyrolysis and conventional gasification. Microwave heating overcomes the problems of low efficiency and heavy products in conventional heat transfer. In particular, the addition of biochar containing alkali metal oxides and their salts to biomass feedstock can significantly enhance the wave absorption characteristics of biomass, significantly improve the pyrolysis efficiency of biomass and promote the lightening of products. At the same time, it significantly reduces the amount of combustion-supporting gas used in the gasification stage, reduces the dilution of gasification products, and achieves a double improvement in hydrogen product concentration and yield.

[0032] 2) Existing dual moving bed gasification technology requires the biomass feedstock to be crushed and loosened. This crushing and loosening process not only consumes a lot of energy, but also results in a large fluctuation in the pressure drop during gasification due to the small size of the feedstock. This invention directly uses large-size, high-density biomass feedstock for pyrolysis, ensuring a higher carbon layer height in the gasification zone. This solves the problems of raw material crushing and loosening and large pressure drop fluctuations during gasification in conventional dual moving bed gasification technology, and also provides a new approach for large-scale applications such as biomass densification, collection, and transportation.

[0033] 3) The microwave pyrolysis of the present invention adopts a treatment method of rotating radial jet scrubbing gas, which can remove tar and coke adhering to the wall in real time, unblock the microwave heating channel, further enhance the microwave pyrolysis effect and ensure the long-term stable operation of the microwave generation system; at the same time, it can react with biomass raw materials to crack, reform and gasify the primary pyrolysis products in situ, obtain higher quality gaseous volatiles, that is, lighter tar, which is easier to burn when it reaches the throat area, creating conditions for the subsequent generation of higher quality hydrogen products;

[0034] 4) After the washing gas is radially ejected, it can also flow axially in the microwave heating cavity under the micro negative pressure environment, which helps to accelerate the rapid heat transfer between the high temperature zone with material and the low temperature zone without material, and can change the temperature field distribution of the microwave heating cavity, promoting uniform microwave heating and precise temperature control.

[0035] 5) The combustion gasification unit of this invention utilizes the throat combustion zone to simultaneously and rapidly combust both homogeneous and heterogeneous pyrolysis products at high temperatures. Since the biochar containing alkali metal oxides and their salts is mixed into the biomass feedstock, the alkali metals are in liquid or gaseous state at high temperatures, which catalyzes the gasification of carbon, promotes the reaction between water vapor and carbon, and reduces the amount of water vapor input. That is, by utilizing the moving catalysis of alkali metals in the biochar gasification zone, the efficient conversion of biochar can be achieved at a lower temperature, thereby obtaining high-quality hydrogen. The biochar rich in alkali metals remaining after gasification can be recycled for biomass feedstock pretreatment, reducing the amount of alkali metal oxides and their salts used, and further improving the economics of the biomass hydrogen production process.

[0036] 6) The nozzle in the throat combustion zone of this invention has a dual-gas-path annular channel and a swirling mixing channel structure, which makes the mixing of oxygen and water vapor more complete and the cracking and reforming effect of pyrolysis products better.

[0037] 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

[0038] Figure 1 This is a schematic diagram of the biomass dual moving bed hydrogen production system of the present invention.

[0039] Figure 2 This is a schematic diagram of the nozzle structure in the throat combustion zone of the biomass dual moving bed hydrogen production system of the present invention.

[0040] Explanation of key figure labels:

[0041] 1-Feeding unit, 11-First hopper, 12-Second hopper, 13-Vibrating feeder;

[0042] 2-Microwave pyrolysis unit, 21-Conveying spiral, 22-Microwave generator, 23-Washing hole, 24-Washing gas inlet, 25-Rotary joint;

[0043] 3-Pyrolysis product combustion and gasification unit, 31-Throat combustion zone, 32-Nozzle, 32A-Dual gas path annular channel, 32a-Inner annular channel, 32b-Outer annular channel, 32B-Swirl mixing channel, 33-Gasification zone, 34-Steam inlet, 35-Slag discharge grate, 36-Product gas outlet, 37-Slag discharge pipe, 38-Slag collector. Detailed Implementation

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The inventors discovered through research that conventional biomass dual moving bed gasification for hydrogen production typically employs non-contact heat transfer for the first stage of biomass pyrolysis. This requires crushing and loosening of the feedstock to accelerate heat and mass transfer, increasing energy consumption in biomass crushing. Furthermore, using small-sized, low-density feedstock limits the height of the second-stage gasification carbon bed, leading to reduced tar removal efficiency and large fluctuations in gasification operating pressure. Additionally, the pyrolysis products under non-contact heat transfer are heavier, requiring more combustion-supporting fuel. In direct combustion, this dilutes the hydrogen and reduces its yield; while in indirect combustion, the system's self-heating may not meet the reaction's heat requirements, also impacting hydrogen production efficiency.

[0049] Example 1

[0050] Based on the above research, such as Figure 1As shown, this embodiment provides a biomass dual moving bed hydrogen production system. The system includes a feeding unit 1, a microwave pyrolysis unit 2, and a combustion gasification unit 3. The feeding unit 1 continuously feeds pre-treated, large-size, high-density biomass feedstock, which is mixed with biochar containing alkali metal oxides and their salts. The microwave pyrolysis unit 2 includes a microwave heating chamber and a conveying screw 21, used to receive the biomass feedstock from the feeding unit 1. Microwave pyrolysis is performed while the biomass feedstock is tumbled and moved within the microwave heating chamber. The microwave heating chamber is equipped with a scrubbing gas channel 22 for radial circumferential injection. The combustion gasification unit 3 is located below the microwave pyrolysis unit 2 and receives gaseous volatiles and solid biochar from the microwave pyrolysis unit 2. The combustion gasification unit 3 includes a throat combustion zone 31 and a gasification zone 33.

[0051] This embodiment achieves continuous and efficient pyrolysis of large-size, high-density biomass feedstock. The scrubbing gas channel can remove tar and coke adhering to the wall in real time, and the microwave heating channel can be unblocked. High-quality hydrogen is obtained through throat combustion and bed gasification in the combustion gasification unit.

[0052] Further as Figure 1As shown, the feeding unit 1 is used to continuously feed large-sized, high-density biomass raw materials. Specifically, the feeding unit 1 includes upper and lower hoppers (i.e., the first hopper 11 and the second hopper 12) and a vibrating feeder 13. The two hoppers are connected by valves (preferably ball valves in this embodiment, not shown in the figure) to achieve continuous feeding and loading. 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 1, the biomass raw materials can be pre-treated. For low-density biomass raw materials such as straw that need to be shaped, the pre-treatment process includes drying, crushing, dispersing, and shaping. The specific treatment conditions are as follows: the dried biomass is crushed to less than 5mm, and then biochar containing alkali metal oxides and their salts is evenly dispersed into the biomass raw materials. The biomass is then physically extruded and shaped under conditions of 10-20MPa to obtain the biomass raw materials. Preferably, but not limitingly, the length of the large-size, high-density biomass feedstock in the direction of maximum size can be 10–100 mm, and the bulk density can be 500–1000 g / L. For high-density biomass feedstocks such as wood blocks that do not require shaping, biomass feedstocks close to the shaped size can be obtained directly by cutting or other methods. The inlet end of the feed vibrator 13 is connected to the second hopper 12 through a pipeline, and the outlet end is connected to the microwave heating cavity of the microwave pyrolysis unit 2. In this embodiment, the biomass feedstock is mixed with biochar containing alkali metal oxides and their salts, which can significantly enhance the microwave absorption characteristics of biomass during the microwave pyrolysis stage, significantly improve the biomass pyrolysis efficiency, and promote the lightening of the product, creating more favorable conditions for the subsequent combustion and gasification stages. This can significantly reduce the amount of combustion-supporting fuel used in the combustion and gasification stages, reduce the dilution of the gasification product, and ultimately improve the hydrogen product concentration and yield.

[0053] Further as Figure 1 As shown, the microwave pyrolysis unit 2 includes a microwave heating cavity and a conveying spiral 21. The conveying spiral 21 has a rotatable hollow shaft, and the hollow part serves as a scrubbing gas channel in this embodiment. The channel is arranged in the center of the microwave heating cavity and extends along the axial direction of the cavity. The scrubbing gas channel has scrubbing holes 23 facing the wall of the microwave heating cavity, used to spray water vapor and / or oxygen onto the wall during microwave pyrolysis. Specifically, the scrubbing holes 23 can be distributed in multiple rows along the axial direction, with 4 to 10 rows. Each row of scrubbing holes is evenly arranged along the circumference of the cylinder wall, with 3 to 9 holes per row. The overall length of the scrubbing holes 23 distribution can be 20% to 60% of the overall length of the conveying spiral 21 axial surface, and the diameter of the scrubbing holes 23 is 1 to 10 mm. Preferably, but not limitingly, the scrubbing holes are along the running direction of the biomass raw material (i.e.,...). Figure 1The washing gas is arranged in a gradually denser pattern from right to left. The washing gas enters through the washing gas inlet 24 connected to the conveying screw 21 and flows through the washing gas channel into the washing hole 23. The flow direction is radial (from the screw axis to the circumference of the microwave heating cavity). The washing gas inlet 24 is connected to the conveying screw 21 via a rotary joint 25. The washing gas first flows axially within the washing gas channel and then flows radially out of the washing hole 23. The axial flow of washing gas within the washing gas channel increases with the rising temperature of the microwave heating cavity, ensuring the reactivity of the washing gas and accelerating rapid heat transfer within the screw shaft, preventing screw shaft deformation and extending its service life. Under the rotation of the channel, the radially flowing washing gas is evenly sprayed onto the inner wall of the microwave heating cavity. Radial upward spraying (which can be sprayed onto the upper part of the cavity's unused wall surface) removes adhering tar and coke, clearing the microwave heating channel. Radial downward spraying (which can be sprayed onto the biomass raw material in the lower part of the cavity) cracks, reforms, and gasifies the primary pyrolysis products, obtaining lighter pyrolysis products. Specifically, the biomass moves horizontally along the axial direction under the action of the conveying screw 21, making full contact and interacting with the radially flowing scrubbing gas. While the biomass feedstock is being microwave-heated, the primary pyrolysis products generated are pyrolyzed, reformed, and gasified in situ, which can reduce the amount of tar carried in the gas. In addition, since the entire system is in a slightly negative pressure environment, the radially injected scrubbing gas can move axially towards the inlet of the combustion gasification unit under the slightly negative pressure environment of the microwave heating cavity. The radial and axial flow of scrubbing gas helps to accelerate the rapid heat transfer between the high-temperature zone with feed and the low-temperature zone without feed, which can change the temperature field distribution of the microwave heating cavity and promote uniform microwave heating and precise temperature control.

[0054] Further as Figure 1 As shown, the microwave generators 22 used in the microwave pyrolysis unit 2 are mounted on the metal outer shell surrounding the microwave heating cavity, and the microwave generators 22 are evenly arranged along the circumferential direction of the metal outer shell. Specifically, the cavity of the microwave pyrolysis unit 2 is provided with a certain number of microwave quartz windows, each window corresponding to one microwave generator 22. 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 0.1×10⁻⁶. 5 ~1×10 5 W / m 3 .

[0055] Further as Figure 1As shown, the combustion gasification unit 3 is located below the microwave pyrolysis unit 2 and receives gaseous volatiles and solid biochar from the microwave heating cavity through airflow and gravity. The combustion gasification unit 3 has a throat combustion zone 31 for introducing oxidizing gas and a gasification zone 33 for introducing water vapor. The oxidizing gas is mainly oxygen and can be one of the following: oxygen, air, oxygen and water vapor, or air and water vapor. A mixture of oxygen and water vapor is preferred, with an oxygen flow rate of 0.1–0.5 m³ / s. 3 / h, water vapor flow rate 0.02~0.2m³ / h 3 / h; water vapor (see Figure 1 The steam inlet 34) has a flow rate of 0.2–0.6 m³ / h. 3 / h. The temperature in the combustion zone is 900~1100℃, and the temperature in the vaporization zone is 750~850℃; the reaction time in the combustion zone is 1~5 seconds, and the reaction time in the vaporization zone is 5~10 minutes.

[0056] Further as Figure 1 As shown, the throat combustion zone 31 is located at the upper part of the combustion gasification unit 3, and the throat combustion zone 31 is provided with several nozzles 32 (see reference). Figure 2 Nozzles 32 are evenly arranged around the circumference of the throat combustion zone 31, with a number ranging from 3 to 20. The nozzles face the center of the throat region. Each nozzle 32 contains a dual-gas-path annular channel 32A and a swirling mixing channel 32B, used to introduce oxygen and water vapor and to crack and reform the pyrolysis products. Specifically, the dual-gas-path annular channel includes an inner annular channel 32a and an outer annular channel 32b. The inner annular channel 32a is located at the innermost edge and introduces oxygen; the outer annular channel 32b is located outside the inner annular channel 32a and introduces water vapor. The outlet of the dual channels connects to the swirling mixing channel 32B, which has a conical structure with an angle of 20° to 70° between the inclined surface and the bottom surface. This nozzle structure ensures more thorough mixing of the two gases, resulting in better cracking and reforming of the pyrolysis products.

[0057] Further as Figure 1 As shown, the gasification zone 323 receives the pyrolysis products from the throat combustion zone 31, from which most of the tar has been removed. Under the combined action of alkali metal oxides and their salts, and water vapor, a secondary reaction occurs to remove residual tar. A slag discharge grate 35 is installed at the bottom of the gasification zone, adjacent to the slag discharge pipe 37 and connected to a solid slag collector 38. The slag discharge grate 35 can be any type, such as a fixed grate, a reciprocating grate, a vibrating grate, or a rotating grate. By controlling the grate's operating frequency, lumpy, granular, and powdery solid slag can be discharged. The products after the pyrolysis passes through the combustion zone and the gasification zone include product gas and solid slag. The product gas is produced through the product gas outlet 36, while the solid slag is sent to the solid slag collector 38 through the slag discharge pipe 37.

[0058] In this embodiment, the primary pyrolysis products generated in the microwave pyrolysis unit 2 are cracked, reformed, and gasified in situ through the combined action of microwave heating and scrubbing gas to generate lighter pyrolysis products. The pyrolysis products enter the combustion gasification unit 3, where the lighter pyrolysis products undergo a primary reaction in the throat region and are then combusted through a dual-gas-path swirl mixing nozzle to remove most of the tar from the pyrolysis products. A secondary reaction then occurs in the gasification zone, causing most of the biochar to undergo gasification and low-carbon hydrocarbon reforming, removing residual tar and obtaining higher quality hydrogen products.

[0059] Example 2

[0060] This invention also provides a method for producing hydrogen from biomass via dual moving bed gasification, comprising the following steps:

[0061] In step S101, the pretreated large-size, high-density biomass raw material is continuously fed through upper and lower two-stage feeding. The biomass raw material can be a substance containing lignocellulose. Further, the pretreatment specifically includes processes such as drying, crushing, dispersing, and shaping. Dispersing involves uniformly dispersing biochar containing alkali metal oxides and their salts into the biomass raw material, with a mass ratio of biomass raw material to biochar containing alkali metal oxides and their salts of 1:0.02–1. The mass percentage of alkali metal oxides and their salts in the biochar is 5%–50%. Blending biochar containing alkali metal oxides and their salts into the biomass raw material can significantly enhance the microwave absorption characteristics of the biomass, and can significantly improve the biomass pyrolysis efficiency and promote the lightweighting of the product during the microwave pyrolysis process in step S102. This invention uses large-size, high-density biomass raw materials for pyrolysis, ensuring a higher gasification carbon layer height. This solves the problems of raw material crushing and loosening, and large pressure drop fluctuations during gasification operation that exist in conventional dual moving bed gasification technology. It also provides a new approach for large-scale application scenarios such as biomass densification treatment and collection and transportation methods.

[0062] Step S102 involves simultaneously microwave heating of the biomass feedstock and radially injected scrubbing gas to remove adhering tar and coke from the walls, while the resulting primary pyrolysis products are pyrolyzed, reformed, and gasified in situ. Specifically, the radially flowing scrubbing gas, under the rotation of the conveying screw shaft (i.e., the hollow scrubbing gas channel), is uniformly injected into the upper inner wall of the microwave heating cavity, removing adhering tar and coke and unblocking the microwave heating channel. The radially flowing scrubbing gas also accelerates rapid heat transfer between the high-temperature zone with feed and the low-temperature zone without feed, altering the temperature field distribution within the microwave heating cavity and promoting uniform microwave heating and precise temperature control. Furthermore, the radially flowing scrubbing gas, under the rotation of the conveying screw shaft, is uniformly injected into the lower part of the microwave heating cavity, fully interacting with the axially moving biomass feedstock in the lower part of the microwave heating cavity, resulting in the in-situ pyrolysis, reforming, and gasification of the generated primary pyrolysis products. The microwave heating reaction time can be 2–10 minutes, with a microwave power density of 0.1 × 10⁻⁶. 5 ~1×10 5 W / m 3 The temperature in the pyrolysis zone can reach 400–700℃; the water vapor flow rate in the scrubbing gas is 0.01–0.1 m³ / s. 3 / h, oxygen flow rate 0.005~0.05m³ / h 3 / h.

[0063] This step addresses the common problems encountered when heating biomass materials in a spiral moving bed using microwaves, such as tar and coke contamination of the heating chamber wall, resulting in decreased microwave heating efficiency, large temperature field gradient, and low pyrolysis efficiency. It utilizes a spiral shaft with a scrubbing gas channel to uniformly release radially flowing water vapor and oxygen as scrubbing gases. The radial jetting of these scrubbing gases cleans the inner wall of the microwave heating chamber, removing adhering tar and coke and clearing the microwave heating channel. The radially flowing scrubbing gas alters the temperature field distribution within the microwave heating chamber, simultaneously causing the generated primary pyrolysis products to be cracked, reformed, and gasified in situ, yielding lighter pyrolysis products. This facilitates the subsequent production of high-quality hydrogen under milder gasification conditions.

[0064] Step S103 involves burning and gasifying the pyrolysis products generated by microwave pyrolysis, producing hydrogen-rich gaseous products under the combined action of oxidizing gas and water vapor. Specifically, the combustion and gasification processes occur in the throat combustion zone and the gasification zone, respectively. The temperature in the throat combustion zone is 900–1100℃, and the temperature in the gasification zone is 750–850℃. The reaction time in the combustion zone is 1–5 seconds, and the reaction time in the gasification zone is 5–10 minutes. The pyrolysis products first undergo a primary reaction in the throat combustion zone under the combined action of oxygen and water vapor in a two-channel swirling mixture, removing most of the tar. Then, in the gasification zone, a secondary reaction occurs under the combined action of alkali metals and water vapor, causing most of the biochar to gasify and undergo low-carbon hydrocarbon reforming, while simultaneously removing residual tar. The primary reaction conditions are: oxygen flow rate 0.1–0.5 m³ / h. 3 / h, water vapor flow rate 0.02~0.2m³ / h 3 / h; Secondary reaction conditions: steam flow rate 0.2–0.6 m³ / h. 3 / h.

[0065] After the aforementioned steps S101 to S103, the resulting hydrogen product has a concentration of over 60%, carbon monoxide content between 25% and 35%, carbon dioxide content below 5%, and tar content below 1 mg / Nm³. 3 The hydrogen yield throughout the process is no less than 60 g / kg dry biomass. The solid residue remaining after gasification is biochar rich in alkali metals, which can be reused for biomass feedstock pretreatment, reducing the amount of alkali metal oxides and their salts used.

[0066] The following is a detailed explanation using a specific example:

[0067] First, the dried biomass is crushed to 2mm. The biochar containing 20% ​​alkali metal oxides and their salts is evenly dispersed into the biomass raw material according to the mass ratio of biomass raw material to biochar of 1:0.1. The biochar is then physically extruded and molded under 10MPa conditions to obtain biomass raw material with a maximum dimension of 40mm and a bulk density of 800g / L.

[0068] Secondly, the pretreated large-size, high-density biomass raw materials are fed into the microwave pyrolysis unit through upper and lower silos. The microwave heating reaction time is 8 minutes, and the microwave power density is 0.5 × 10⁻⁶. 5 The pyrolysis zone temperature reaches 600℃, yielding lighter pyrolysis products. Simultaneously, microwave pyrolysis is assisted by the uniform rotation of a spiral shaft equipped with a scrubbing gas channel, releasing radially flowing water vapor and oxygen. The water vapor flow rate is 0.05 m³ / h. 3 / h, oxygen flow rate 0.01m 3 / h;

[0069] Then, the lightweight pyrolysis products fall into the combustion gasification unit under the influence of gravity and airflow. First, under the dual-path swirling injection of oxygen and water vapor, a single reaction occurs in the throat combustion zone under the following conditions: throat combustion zone temperature 1000℃, reaction time 2 seconds, and oxygen flow rate 0.2 m³ / s. 3 / h, water vapor flow rate 0.05m 3 / h; then, in the gasification zone, a secondary reaction occurs under the combined action of alkali metals and water vapor, with the following conditions: gasification zone temperature 800℃, reaction time 8 minutes, and water vapor flow rate 0.5m³ / h. 3 / h;

[0070] Finally, the combustion gasification unit releases a high-quality product rich in hydrogen, with a hydrogen concentration of 70%, carbon monoxide content of 26%, carbon dioxide content of 4%, and tar content of less than 1 mg / Nm³. 3 The entire process yields a hydrogen production rate of 75 g / kg dry biomass. The solid residue remaining after gasification is biochar rich in alkali metals, which can be reused for biomass feedstock pretreatment, reducing the amount of alkali metal oxides and their salts used.

[0071] 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 method for producing hydrogen from biomass via dual moving bed gasification, characterized in that, A biomass dual moving bed gasification hydrogen production system is adopted, which includes: The feeding unit is used to continuously feed pre-treated large-size, high-density biomass feedstock, which is blended with biochar containing alkali metal oxides and their salts. A microwave pyrolysis unit includes a microwave heating cavity and a conveying screw for receiving biomass feedstock from the feeding unit. The biomass feedstock is tumbled and moved within the microwave heating cavity while undergoing microwave pyrolysis. The microwave heating cavity is equipped with a radially circumferential scrubbing gas channel. This scrubbing gas channel is rotatable, located at the center of the microwave heating cavity, and extends axially along the cavity. The scrubbing gas channel has scrubbing holes facing the wall of the microwave heating cavity, used to spray water vapor and oxygen onto the wall during microwave pyrolysis. During rotation, the scrubbing holes radially spray scrubbing gas, using upward radial spraying to remove tar and coke adhering to the wall, and downward radial spraying to crack, reform, and gasify the primary pyrolysis products, obtaining lighter pyrolysis products. The radially sprayed scrubbing gas moves axially towards the inlet of the combustion gasification unit under the slight negative pressure environment of the microwave heating cavity. A combustion gasification unit is disposed below the microwave pyrolysis unit and receives gaseous volatiles and solid biochar from the microwave pyrolysis unit; the combustion gasification unit is provided with a throat combustion zone and a gasification zone; The method includes the following steps: A. Continuously feed the pre-treated large-size, high-density biomass raw materials; B. While the biomass raw material is microwave heated, the tar and coke adhering to the wall are removed by radially injected scrubbing gas, and the resulting primary pyrolysis products are cracked, reformed and gasified in situ. C. The pyrolysis products generated by microwave pyrolysis are burned and gasified, and under the combined action of oxidizing gas and water vapor, hydrogen-rich gaseous products are generated.

2. The biomass dual moving bed gasification hydrogen production method according to claim 1, characterized in that, The biomass raw material is formed by dispersing and extruding dried and pulverized biomass; the length of the large-size high-density biomass raw material in the maximum dimension direction is 10~100mm, and the bulk density is 500~1000g / L.

3. The biomass dual moving bed gasification hydrogen production method according to claim 1, characterized in that, The washing holes are arranged with increasing density along the direction of biomass feedstock movement.

4. The biomass dual moving bed gasification hydrogen production method according to claim 1, characterized in that, The microwave heating cavity is provided with a metal shell, and microwave generators are arranged at uniform intervals along the circumference of the metal shell. A microwave quartz window is provided at the corresponding position of each microwave generator.

5. The biomass dual moving bed gasification hydrogen production method according to claim 1, characterized in that, The feeding unit includes upper and lower hoppers, and the feeding and feeding process is continuous by opening and closing a ball valve between the two hoppers.

6. The biomass dual moving bed gasification hydrogen production method according to claim 5, characterized in that, A feeding vibrator is connected to the lower part of the lower hopper, and the outlet end of the feeding vibrator is connected to the microwave heating cavity.

7. The biomass dual moving bed gasification hydrogen production method according to claim 5, characterized in that, The throat combustion zone is located at the inlet of the combustion gasification unit, and oxygen and water vapor are injected through nozzles to crack and reform the pyrolysis products from the microwave pyrolysis unit.

8. The biomass dual moving bed gasification hydrogen production method according to claim 7, characterized in that, The nozzle is provided with a dual-air-path annular channel and a swirling mixing channel, wherein the dual-air-path annular channel includes: The inner ring channel is located on the inside and is supplied with oxygen. The outer ring channel is located on the outside and allows water vapor to pass through.

9. The biomass dual moving bed gasification hydrogen production method according to claim 8, characterized in that, The swirling mixing channel has a conical structure and is connected to the outlets of the inner and outer ring channels. The angle between the inclined surface of the cone and the bottom surface is 20~70°.

10. The biomass dual moving bed gasification hydrogen production method according to claim 1, characterized in that, The gasification zone receives pyrolysis products from the throat combustion zone, from which most of the tar has been removed. Under the combined action of the alkali metal oxides and their salts, and water vapor, a secondary reaction is carried out to remove residual tar.

11. The biomass dual moving bed gasification hydrogen production method according to claim 10, characterized in that, The lower part of the gasification zone is equipped with a slag discharge grate, which is adjacent to the slag discharge port and connected to a solid slag collector through a pipeline. This grate is used to collect biochar rich in alkali metals and reuse it for the pretreatment of biomass raw materials.

12. The biomass dual moving bed gasification hydrogen production method according to claim 1, characterized in that, The pretreatment in step A includes drying, crushing, dispersing and forming processes; the dispersion process specifically involves uniformly dispersing biochar containing alkali metal oxides and their salts into the biomass raw material, wherein the mass ratio of the biomass raw material to the biochar containing alkali metal oxides and their salts is 1:0.02~1; and the mass percentage of the alkali metal oxides and their salts in the biochar is 5%~50%.

13. The biomass dual moving bed gasification hydrogen production method according to claim 1, characterized in that, The microwave heating reaction time in step B is 2-10 minutes, and the microwave power density is 0.1×10⁻⁶. 5 ~1×10 5 W / m 3 The temperature in the microwave pyrolysis zone reaches 400~700℃.

14. The biomass dual moving bed gasification hydrogen production method according to claim 1, characterized in that, The water vapor flow rate in the scrubbing gas is 0.01~0.1 m³ / s. 3 / h, oxygen flow rate is 0.005~0.05 m³ / h. 3 / h.

15. The biomass dual moving bed gasification hydrogen production method according to claim 1, characterized in that, The combustion in step C is a single reaction occurring in the throat combustion zone, with a temperature of 900-1100℃ and a reaction time of 1-5 seconds. The reaction conditions for this single reaction are: oxygen flow rate of 0.1-0.5 m³ / s. 3 / h, water vapor flow rate 0.02~0.2m³ / h 3 / h.

16. The biomass dual moving bed gasification hydrogen production method according to claim 1, characterized in that, The vaporization in step C is a secondary reaction that takes place in a vaporization zone at a temperature of 750-850°C for 5-10 minutes. The secondary reaction conditions are: a water vapor flow rate of 0.2-0.6 m³ / s. 3 / h.

17. The biomass dual moving bed gasification hydrogen production method according to claim 1, characterized in that, In step C, the hydrogen-rich gaseous product has a hydrogen concentration of over 60%, a carbon monoxide content between 25% and 35%, a carbon dioxide content of less than 5%, and a tar content of less than 1 mg / Nm³. 3 The hydrogen production process shall yield no less than 60 g / kg dry biomass.

Images