Two-stage built-in dual fluidized bed reactor

Abstract

This invention discloses a two-stage built-in dual fluidized bed reactor for a biomass feedstock chemical chain hydrogen production process. Each built-in dual fluidized bed includes: a gasification chamber, which is a cylindrical structure with a conical surface at the bottom, and an opening on the conical surface for introducing bubbling fluidizing air; a combustion chamber, which is a tubular structure and fitted inside the gasification chamber, with an open bottom located within the conical surface area for introducing vertically upward combustion air; and a return unit, which is located in the upper middle part of the reactor, is a hollow disc structure fitted outside the combustion chamber, and is used to transport high-temperature bed material particles from the combustion chamber to an annular gasification zone outside the combustion chamber for mixing with the biomass feedstock in the gasification zone to produce hydrogen. The return unit includes a loosening chamber and a return chamber. The two built-in dual fluidized beds are connected in series for introducing the hydrogen-containing syngas produced by the first dual fluidized bed into the combustion chamber of the second dual fluidized bed.

Description

Technical Field

[0001] This invention relates to the field of biomass hydrogen production technology, and in particular to a two-stage built-in dual fluidized bed reactor for producing high-purity hydrogen. Background Technology

[0002] As a highly efficient and clean energy source, hydrogen energy development is timely. Among the various technical routes for producing hydrogen from biomass, the use of fluidized bed reactors for efficient thermal conversion to produce hydrogen-rich gas shows promising prospects.

[0003] Dual fluidized bed reactors are already in use in existing technologies. They have the following advantages: they decouple combustion and gasification, provide indirect heating, and have a high hydrogen production rate; there is only efficient exchange of solids and heat between the combustion chamber and the gasification chamber, which can achieve high heat flux and high throughput with a small volume; and the tar content is lower than that of conventional routes, which facilitates subsequent tar removal.

[0004] Chinese patent application CN109704278A discloses an apparatus and method for producing hydrogen through dual fluidized bed biomass pyrolysis and gasification. The dual fluidized bed includes a fluidized bed pyrolysis furnace and a fluidized bed combustion furnace. The fluidized bed pyrolysis furnace includes a pyrolysis furnace riser, with a pyrolysis furnace cyclone separator connected to its rear end. The upper part of the pyrolysis furnace cyclone separator is connected to a shift reactor, and the lower part is connected to a pyrolysis furnace return valve. Another outlet of the pyrolysis furnace return valve is connected to the fluidized bed combustion furnace, which includes a combustion furnace riser. Another outlet of the pyrolysis furnace return valve is connected to the bottom of the combustion furnace riser. An oxygen-carrying cyclone separator is installed in the middle of the combustion furnace riser, and a CO2 absorbent cyclone separator is installed at the top. This method eliminates the need for pure oxygen as a gasifying agent during the preparation process; the system only requires supplemental air for gasification to meet production needs, resulting in low production costs. Furthermore, since the pyrolysis furnace does not use air for fluidization, the biomass fuel gas has a high content of effective components.

[0005] Existing dual fluidized bed reactors separate the gasification chamber from the combustion chamber, using feed pipes and a return feeder for heat exchange with the bed material. However, heat loss occurs during transport between the two fluidized beds, preventing the already low-calorific-value biomass feedstock from self-heating through the combustion of residual carbon to power the gasification reaction. This necessitates the addition of fuel in the combustion chamber, reducing economic efficiency. Furthermore, during transport to the combustion chamber, the tar adhering to the surface of the low-temperature bed material particles becomes more viscous as the temperature decreases, leading to particle agglomeration and bridging. This can clog the reactor feed pipes, affecting reactor circulation and limiting the plant's operating cycle.

[0006] In addition, since the regeneration of AER bed material (AER technology adds three effects of absorption, enhancement and reform compared to ordinary dual fluidized bed technology) requires a certain amount of time, and the combustion chamber of existing dual fluidized bed devices is mostly a fast fluidized bed, although a high solids conveying rate can be maintained, the bed material regeneration time is relatively short.

[0007] Furthermore, existing dual fluidized beds generally adopt a "single-stage" structure. This one-step process for biomass hydrogen production usually suffers from unstable operation of the equipment and a decrease in hydrogen concentration, which also greatly affects the economics of chemical looping hydrogen production.

[0008] Therefore, there is an urgent need for a two-stage dual fluidized bed reactor, with each stage employing a built-in heat-exchange dual fluidized bed. This built-in heat-exchange design avoids the use of external feed pipes and prevents the feed pipes and return feeder from being exposed to room temperature, reducing reactor heat loss and improving the economics of the route and the operating cycle of the unit. It also allows sufficient regeneration time for the bed material while maintaining a high solids delivery rate. The two-stage structure effectively improves the stability of the unit's operation and ensures that the produced hydrogen has high purity.

[0009] 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

[0010] The purpose of this invention is to provide a two-stage built-in dual fluidized bed reactor, in which the external dual fluidized bed in each stage is replaced with an internal one, avoiding the exposure of the feed pipe and return feeder to room temperature and reducing reactor heat loss. Simultaneously, this device provides sufficient regeneration time for the bed material while maintaining a high solids delivery rate. The two-stage structure effectively improves the stability of the device operation and ensures that the produced hydrogen has high purity.

[0011] To achieve the above objectives, the present invention provides a two-stage built-in dual fluidized bed reactor for a biomass feedstock chemical chain hydrogen production process. Each built-in dual fluidized bed includes: a gasification chamber, which is a cylindrical structure with a conical surface at the bottom, and an opening on the conical surface for introducing bubbling fluidizing air; a combustion chamber, which is a tubular structure and sleeved within the gasification chamber, with an open bottom located within the conical surface area for introducing vertically upward combustion air; and a return unit, which is located in the upper middle part of the reactor, is a hollow disc structure and sleeved outside the combustion chamber, for transporting high-temperature bed material particles from the combustion chamber to an annular gasification zone outside the combustion chamber and mixing them with the biomass feedstock in the gasification zone to produce hydrogen. The return unit includes a loosening chamber and a return chamber. The two built-in dual fluidized beds are connected in series for introducing the hydrogen-containing syngas produced by the first dual fluidized bed into the combustion chamber of the second dual fluidized bed.

[0012] Furthermore, in the above technical solution, the loosening chamber can be annular and located on the inner side, with the outer wall of the loosening chamber being coplanar with the wall of the combustion chamber; the inner wall of the loosening chamber extends upward, making the loosening chamber a narrow annular space, forming a material seal with densely packed bed material particles inside the loosening chamber, and the top of the loosening chamber can be open.

[0013] Furthermore, in the above technical solution, the return chamber can be annular and located on the outside, and the return chamber is connected to the annular space of the gasification chamber through an annular feeding trough.

[0014] Furthermore, in the above technical solution, the loosening chamber receives bed material particles from the combustion chamber and blocks gas; the middle and upper parts of the loosening chamber are separated from the return chamber by a partition; the lower part of the loosening chamber is provided with a first air distribution chamber; the return chamber is connected to the gasification chamber; and the lower part of the return chamber is provided with a second air distribution chamber.

[0015] Furthermore, in the above technical solution, both the loosening chamber bottom plate and the return material chamber bottom plate can be provided with air caps or air holes; the first air distribution chamber and the second air distribution chamber can be supplied with air through air pipes extending to the outside of the reaction device. The air pipes can be arranged in a cross shape.

[0016] Furthermore, in the above technical solution, a cyclone separator may be provided at the top of the gasification chamber. The top of the cyclone separator is provided with an air inlet and a flue gas outlet that are connected to the dual fluidized bed combustion chamber of this section, and the bottom is connected to the loosening chamber through a feed pipe.

[0017] Furthermore, in the above technical solution, the feed inlet of biomass raw materials can be located at the bottom of the material layer in the gasification chamber, above the material layer, and / or at the top of the reaction device, and the feeding method can be screw feeding.

[0018] Furthermore, in the above technical solution, the conical surface of the gasification chamber may be provided with an inclined chute structure for extending the residence time of the bed material particles at the bottom and for gas sealing.

[0019] Furthermore, in the above technical solution, the inclined chute structure may specifically include: a first conical surface that extends downward at an angle from the outer wall of the combustion chamber; a second conical surface that extends upward at an angle from the outer wall of the combustion chamber and encloses the first conical surface and the outer wall of the combustion chamber to form a relatively closed structure; and an inclined chute is formed between the second conical surface and the conical surface at the bottom of the gasification chamber.

[0020] Furthermore, in the above technical solution, the sealed structure can be a ventilation cavity for introducing secondary air from outside the reaction device.

[0021] Furthermore, in the above technical solution, inclined upward secondary air holes can be opened on the upper part of the air cavity and the combustion chamber wall. The secondary air works in conjunction with the combustion-supporting air at the bottom of the combustion chamber to extend the residence time of the bed material particles at the bottom.

[0022] Furthermore, in the above technical solution, the pores on the conical surface at the bottom of the gasification chamber can be configured to have a gradually decreasing diameter from bottom to top.

[0023] Furthermore, in the above technical solution, the bed material particles of the first stage built-in dual fluidized bed can be inert bed material or metal oxide bed material; the bed material particles of the second stage built-in dual fluidized bed can be iron-based oxygen carrier.

[0024] Furthermore, in the above technical solution, the metal oxide bed material can be calcium oxide bed material, which is used to capture carbon dioxide in the gasification chamber to generate calcium carbonate. The calcium carbonate is heated and decomposed into carbon dioxide in the combustion chamber and discharged with the flue gas.

[0025] Furthermore, in the above technical solution, the first-stage dual fluidized bed and the second-stage dual fluidized bed can be connected by a pipeline. One end of the pipeline is connected to the hydrogen-containing synthesis gas outlet of the first-stage dual fluidized bed, and the other end is connected to the combustion air inlet of the combustion chamber of the second-stage dual fluidized bed.

[0026] Furthermore, in the above technical solution, a turbocharger can be installed on the pipeline to provide sufficient fluidization velocity for the combustion chamber of the second-stage dual fluidized bed.

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

[0028] 1) This invention solves the problem of chemical chain hydrogen production from complex biomass feedstocks by adopting a two-stage built-in dual fluidized bed, and solves the problems of unstable operation and decreased hydrogen concentration in conventional one-step methods, thereby improving the economic efficiency of chemical chain hydrogen production. The two-stage structure is designed with pipelines connected in series. One end of the pipeline is connected to the hydrogen-containing syngas outlet of the first-stage dual fluidized bed, and the other end is connected to the combustion air inlet of the combustion chamber of the second-stage dual fluidized bed. The hydrogen-rich gas generated in the first stage is turbocharged and then enters the second-stage dual fluidized bed reactor through the combustion air inlet and the secondary air inlet of the second stage, which can effectively ensure the fluidization rate of solid particles in the second-stage combustion chamber.

[0029] 2) The present invention uses a “built-in” design for each section of the dual fluidized bed, that is, the combustion chamber is set inside the gasification chamber to form a jacket structure, which can avoid the feed pipe and return device being exposed to room temperature in the prior art (“external” design), effectively reducing the heat loss of the reaction device, improving the economy of the route and the operating cycle of the device;

[0030] 3) Through the “built-in” design of each section of the dual fluidized bed, the present invention can also effectively improve the heat transfer efficiency. The combustion chamber can not only transfer heat through the circulation of hot bed material, but also transfer heat to the gasification zone between the outer wall of the combustion chamber and the gasification chamber cylinder through the heat conduction of the vessel wall.

[0031] 4) The return material unit of the present invention can not only reduce heat loss, but also form a material seal by the dense phase accumulation of the bed material in the loosening chamber. The height of the material seal is increased accordingly by the setting of the narrow annular space of the loosening chamber, which can effectively improve the quality of the material seal and reduce the possibility of hydrogen-rich gas backflow from the gasification chamber to the combustion chamber under adverse working conditions, thus improving the safety of the device. The volume of the return material chamber of the return material unit is kept relatively small, so that the bed material passing through the return material chamber can still be transported to the gasification chamber by the return air at a relatively fast speed.

[0032] 5) With the return material unit of the present invention, the upper part of the loosening chamber maintains an open structure, which makes it easier for manual maintenance and slag removal to be carried out in a timely manner;

[0033] 6) The cyclone separator of the present invention is also a built-in design, which avoids the cyclone separator being exposed to room temperature and can effectively improve heat exchange efficiency; lighter ash particles are carried out of the reaction device by the airflow and then removed in the tail gas cyclone, so that the two reactors of the present invention do not need to be set with separate slag discharge ports.

[0034] 7) The inclined chute structure at the bottom of the gasification chamber (i.e., gas production chamber) of this invention broadens the operating range of the dual fluidized bed, enabling the reactor to adapt to more complex raw material and process conditions; at the same time, the inclined chute structure can better achieve the material sealing effect by reducing the size of the original particle channel.

[0035] 8) The secondary air distribution configuration of the combustion chamber in this invention allows for a reduction in the bottom combustion air, causing the particles to bubble at the bottom of the combustion chamber. As the bubbling particles fluidize to the vicinity of the secondary air, they are accelerated by the upward-sloping secondary air and rapidly transported to the return unit. Above the secondary air is a rapid fluidized bed. This design increases the residence time of the particles in the high-temperature zone at the bottom, allowing for more effective combustion of the tar on their surface. This provides more heat for gasification, reduces the tar content in the flue gas, facilitates flue gas post-treatment, and improves the economics of the process. When applying the AER process, it also improves the particle regeneration rate, which is more conducive to the capture of carbon dioxide in the gasification chamber, thereby increasing the hydrogen production concentration.

[0036] 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

[0037] Figure 1 This is a schematic diagram of the dual fluidized bed process when calcium oxide is used as the bed material particles in this invention.

[0038] Figure 2 This is a perspective schematic diagram of the two-stage built-in dual fluidized bed reactor of the present invention.

[0039] Figure 3 This is an internal cross-sectional schematic diagram of the two-stage built-in dual fluidized bed reactor of the present invention (the first embodiment in which both stages adopt dual fluidized beds).

[0040] Figure 4 This is a perspective view of each section of the built-in heat exchange dual fluidized bed of the present invention.

[0041] Figure 5 This is an internal cross-sectional schematic diagram of the first embodiment of the built-in heat exchange dual fluidized bed of the present invention (without secondary air cavity and inclined chute structure).

[0042] Figure 6 This is a schematic internal cross-sectional view of the return unit in each section of the built-in dual fluidized bed of the present invention.

[0043] Figure 7 This is a schematic diagram of the external structure of the return unit in each section of the built-in dual fluidized bed of the present invention.

[0044] Figure 8 This is an internal cross-sectional schematic diagram of the second embodiment of the built-in heat exchange dual fluidized bed of the present invention (with a secondary air cavity and an inclined chute structure).

[0045] Figure 9 This is a simulation diagram of the first section of the built-in dual fluidized bed reactor of the present invention (showing the density of solid particles in each region of the reactor).

[0046] Explanation of key figure labels:

[0047] 100 - First stage built-in heat exchange dual fluidized bed; 101 - First product gas outlet; 102 - Connecting pipeline; 200 - Second stage built-in heat exchange dual fluidized bed; 201 - Second product gas outlet;

[0048] 1-Gasification chamber, 11-Conical surface, 110-Air hole, 2-Combustion chamber, 21-Combustion air inlet, 3-Return material unit, 30-Air pipe, 31-Loosening chamber, 310-First air distribution chamber, 311-Loosening chamber inner wall, 32-Return material chamber, 320-Second air distribution chamber, 33-Feeding trough, 4-Cyclone separator, 40-Air inlet, 41-Discharge pipe, 42-Flue gas outlet, 5-Air chamber, 50-Secondary air hole, 51-First conical surface, 52-Second conical surface, 53-Inclined chute. Detailed Implementation

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] This invention employs a dual fluidized bed process for biomass hydrogen production (see process flow diagram). Figure 1Combining AER technology with conventional dual-fluidized bed technology, this method offers advantages over conventional dual-fluidized bed technology by adding three effects: absorption, enhancement, and reforming. Water vapor, acting as the gasification air, also reforms the tar produced during gasification, reducing the tar content in the product gas. The bed material not only serves as a heat carrier but also performs absorption and enhancement functions. AER bed materials are primarily metal oxides. In the gasification chamber, they absorb carbon dioxide, completing carbon dioxide carbonation and releasing heat. This not only reduces the carbon dioxide content in the product gas, improving its quality, but also provides heat for the gasification reaction, enhancing the biomass gasification process. The carbonized bed material decomposes under heat in the combustion chamber, releasing carbon dioxide. This carbon dioxide is then transported into the flue gas, and the bed material returns to its oxide form, re-capturing carbon dioxide in the gasification chamber.

[0054] The inventors discovered through research that dual fluidized bed reactors for biomass hydrogen production offer the following advantages: The dual fluidized bed reactor decouples combustion and gasification, providing indirect heating and resulting in a high hydrogen production rate. The hydrogen content in the dry gas exiting the dual fluidized bed reactor can reach over 50%, and combined with in-situ carbon dioxide capture, the hydrogen content can reach 78%. Using a dual fluidized bed reactor, where there is only efficient exchange of solids and heat between the combustion and gasification chambers, high heat flux and high throughput can be achieved with a smaller volume. The tar content in the gas from the dual fluidized bed reactor is 2-10 g / m³. 3 The tar content is lower than that of conventional routes, facilitating subsequent tar removal. The built-in dual fluidized bed reactor of this invention adopts a two-stage structure (see reference). Figure 2 , 3 As shown, the two sections are connected in series via connecting pipes. Each section has a combustion chamber designed as a tube and built into a cylindrical gasification chamber, forming an annular space outside the tubular structure as the gasification zone. This avoids the exposed feed pipes and return feeders caused by the "complete separation of the gasification chamber and combustion chamber" (i.e., external design) in existing technologies, which can greatly reduce heat loss. It can also effectively prevent the tar adhering to the surface of the bed material particles from becoming more viscous as the temperature decreases during the transportation to the combustion chamber, making it easy for particles to clump and bridge. At the same time, the modification of the bottom of the gasification chamber can maintain a high solids conveying rate and provide bed material regeneration time.

[0055] like Figure 2 , 3As shown, this invention provides a two-stage built-in dual fluidized bed reactor, comprising a first-stage built-in heat-exchange dual fluidized bed 100 (with a product gas outlet 101 at the top) and a second-stage built-in heat-exchange dual fluidized bed 200 (with a product gas outlet 201 at the top) connected in series. It is used for chemical chain hydrogen production processes from complex raw materials such as biomass. The biomass feed inlet (not shown in the figure) can be located at the bottom of the material layer, above the material layer, and / or at the top of the dual fluidized bed 100 in the gasification chamber 1 of the reactor (depending on the type of raw material). (Feeding can be done at different locations depending on the type and particle density), and the feeding method can be a spiral feed. The first stage of the built-in heat exchange dual fluidized bed 100 of the present invention includes at least a gasification chamber 1, a combustion chamber 2, and a return unit 3. The gasification chamber 1 has a cylindrical structure and a conical surface 11 at the bottom, with openings on the conical surface 11 for introducing bubbling fluidizing air. The combustion chamber 2 has a tubular structure and is fitted inside the gasification chamber 1. The bottom of the combustion chamber 2 is open and located in the conical area at the bottom of the gasification chamber for introducing vertically upward combustion air (see reference). Figure 3 The combustion air inlet 21 is located in the upper middle part of the reaction device. The return unit 3 is a hollow disc structure and is fitted outside the combustion chamber 2. It is used to transport the high-temperature bed material particles from the combustion chamber 2 to the annular gasification zone outside the combustion chamber (i.e., the annular space outside the wall of the combustion chamber 2 and inside the wall of the cylindrical gasification chamber 1) and mix them with the biomass feedstock in the gasification zone to produce hydrogen. The return unit 3 is equipped with a loosening chamber 31 and a return chamber 32 (see reference). Figure 6 This invention features two internally connected dual fluidized beds connected in series, used to feed the hydrogen-containing syngas produced by the first dual fluidized bed into the combustion chamber of the second dual fluidized bed. By embedding the combustion chamber 2 within the gasification chamber 1, this invention effectively solves the problems of high heat loss and easy clogging of the external feed pipe of the dual fluidized bed, effectively reducing heat loss and preventing particles from clogging the feed pipe due to cooling. The two-stage reactor solves the problem of chemical looping hydrogen production from complex biomass feedstocks, addresses the issues of stable operation and hydrogen concentration decline in conventional one-step processes, and improves the economics of chemical looping hydrogen production. The bed material of the first dual fluidized bed reactor can be inert materials such as olivine and quartz sand, or materials such as calcium oxide particles that can be used for in-situ carbon dioxide capture using AER technology, and other materials. The bed material of the second stage can be an iron-based oxygen carrier. The internal structures of the two reactors are identical; the following detailed description uses the first stage reactor as an example.

[0056] Specifically, further reference Figure 4 , Figure 5The "built-in" structural design of this invention features a jacketed structure for the gasification chamber 1 and combustion chamber 2. The combustion chamber 2 has a vertically upward-facing combustion air intake, while the gasification chamber 1 has a fluidizing air intake via a vertical conical surface 11. The combustion air is air, and the fluidizing air is water vapor, both introduced via air caps. The pore size of the fluidizing air caps gradually decreases from bottom to top (i.e., the fluidization state of the solid particles gradually decreases from bottom to top, acting as a material seal). The ratio of fluidizing air to combustion air is optimized to ensure that air does not diffuse into the gasification chamber. The combustion chamber 2 contains a rapid fluidized bed, while the area outside the combustion chamber 2 (i.e., the bottom of the gasification chamber 1) is a bubbling fluidized bed. The combustion chamber 2 wall and the heated bed material provide as much heat as possible to the gasification chamber. Further details are provided below. Figure 4 , 5 As shown, a cyclone separator 4 can be connected to the upper part of the combustion chamber 2 to separate flue gas, fly ash, and hot bed material. Flue gas and fly ash enter the inlet 40 and are discharged through the flue gas outlet 42 at the top of the cyclone separator. Bed material particles return to the combustion chamber 2 through the feed pipe 41 at the bottom. The height of the gasification chamber in this invention differs from that of existing biomass dual fluidized beds (such as Gussing fluidized beds). The combustion chamber 2 can not only transfer heat through the circulation of hot bed material, but also transfer heat to the gasification zone through heat conduction through the reactor wall, avoiding heat loss caused by the external dual fluidized bed reactor combustion chamber and feed pipe being exposed to room temperature.

[0057] Further as Figure 6 , 7 As shown, the specific structure of the return material unit 3 of the present invention is as follows: The loosening chamber 31 is annular and disposed inside the return material unit. The outer wall of the loosening chamber 31 is coplanar with the wall of the combustion chamber 2 (serving as a partition between the loosening chamber 31 and the return material chamber 32). The inner wall 311 of the loosening chamber 31 extends upward, making the loosening chamber 31 a narrow annular space, forming a material seal with densely packed bed material particles inside the loosening chamber 31. The top of the loosening chamber is open. The return material chamber 32 is annular and disposed outside the return material unit. The return material chamber 32 is connected to the annular space of the gasification chamber 1 through an annular feeding trough 33 (see reference). Figure 5The loosening chamber 31 receives bed material particles from the combustion chamber 2 and blocks gas. The middle and upper parts of the loosening chamber 31 are separated from the return chamber 32 by a partition (i.e., part of the combustion chamber wall). The lower part of the loosening chamber 31 is provided with a first air distribution chamber 310. The return chamber 32 is connected to the gasification chamber 1, and the lower part of the return chamber 32 is provided with a second air distribution chamber 320. Both the bottom plate of the loosening chamber 31 and the bottom plate of the return chamber 32 are provided with air caps or air holes (not shown in the figure). The first air distribution chamber 310 and the second air distribution chamber 320 are supplied with gas through air pipes 30 extending to the outside of the reaction device. By introducing external gas sources into the first air distribution chamber 310 and the second air distribution chamber 320, bubbles are formed in the lower part of the loosening chamber and the return chamber, so that the bed material particles are transported to the feeding trough 33 and then flow into the gasification chamber 1. Preferably, but not limitingly, the air pipes 30 are arranged in a cross shape (see reference). Figure 7 This makes the circumferential air distribution more uniform.

[0058] The inventors discovered through research that existing return feed devices typically have relatively small loosening and return chambers, with diameters matching those of the feed leg section, facilitating rapid bed material circulation. The bed material is generally transported in a dilute phase within the loosening chamber of such return feed devices. This type of return feed device is used for air gasification of biomass in circulating fluidized bed reactors. Because the hydrogen concentration in the syngas produced by air gasification is low, it can effectively transport the bed material and prevent cross-contamination. However, dual fluidized bed reactors used for biomass hydrogen production produce higher hydrogen concentrations (50% VOL-78% VOL). Existing return feed devices are not ideal in suppressing gas backflow during dilute phase transport of the bed material, affecting the stable operation of the reactor. Furthermore, their relatively sealed internal structure makes equipment maintenance more difficult. To address the problems in the prior art, the inventors developed the return material unit 3 of this invention. The bed material in the loosening chamber 31 of the return material unit 3 forms a dense-phase accumulation to create a material seal. The height of the loosening chamber is also increased accordingly (i.e., a narrow, elongated annular space), which improves the quality of the material seal and reduces the possibility of hydrogen-rich gas backflowing from the gasification chamber 1 to the combustion chamber 2 under adverse operating conditions, leading to deflagration and improving the safety of the device. The return material chamber 32 of the return material unit 3 has a relatively small volume, allowing the bed material passing through the return material chamber to be transported to the gasification chamber by the return air at a relatively fast speed. Simultaneously, the upper part of the loosening chamber 31 maintains an open structure, facilitating timely manual maintenance and slag removal. This invention utilizes an integrally annular return unit 3, where a loosening chamber 31 stores incoming bed material particles, and a return chamber 32 stores bed material particles entering from the loosening chamber. Airflow can be controlled by installing different numbers of air caps or perforated plates on the bottom plates of both chambers. The air caps or perforated plates connect to the air distribution chambers (i.e., the first air distribution chamber 310 and the second air distribution chamber 320), and the lower part of the air chambers connects to the return air and loosening air inlet pipes (i.e., air pipes 30). The feeding trough 33 directly connects to the gasification chamber 1, avoiding the heat loss and blockage problems caused by the feeding pipe being exposed to room temperature in existing return devices (see [reference needed] for the specific bed material particle orientation). Figure 6 (The dashed arrow in the middle indicates the direction).

[0059] Further as Figure 4 , 5 As shown above, the cyclone separator 4 at the top of the combustion chamber 2 is used to separate flue gas, fly ash, and hot bed material. Specifically, the cyclone separator 4 is located in the annular space of the gasification chamber 1 and communicates with the combustion chamber 2. The top of the cyclone separator 4 has an air inlet 40 and a flue gas outlet 42 communicating with the combustion chamber 2, and the bottom is connected to the combustion chamber 2 via a feed pipe 41, specifically to the loosening chamber 31 in the open state within the combustion chamber 2. This arrangement and connection ensures that the bed material particles further separated by the cyclone separator 4 can fall into the return material unit 3. Multiple cyclone separators 4 can be configured and arranged circumferentially, which can more effectively separate fly ash, flue gas, and bed material particles, and prevent the temperature of the bed material particles from decreasing, thereby improving heat exchange efficiency.

[0060] Further as Figure 8 As shown, in the first embodiment at the bottom of the aforementioned vaporization chamber (i.e. Figure 5 Based on the above, an inclined chute structure (i.e., the second embodiment at the bottom of the gasification chamber) can be provided at the conical surface 11 of the gasification chamber 1 to prolong the residence time of the bed material particles at the bottom and for gas sealing. The inclined chute structure specifically includes a first conical surface 51 and a second conical surface 52. The first conical surface 51 extends downwards at an angle from the outer wall of the combustion chamber 2; the second conical surface 52 extends upwards at an angle from the outer wall of the combustion chamber 2 and forms a relatively sealed structure with the first conical surface 51 and the outer wall of the combustion chamber 2. Thus, an inclined chute 53 is formed between the second conical surface 52 and the conical surface 11 at the bottom of the gasification chamber 1. This sealed structure is a wind chamber 5 for introducing secondary air from outside the reaction device (see [reference]). Figure 8 Preferably, but not limitingly, the upper part of the air cavity 5 and the wall of the combustion chamber 2 are provided with inclined upward secondary air holes 50. The secondary air cooperates with the combustion-supporting air at the bottom of the combustion chamber 2 to prolong the residence time of the bed material particles at the bottom.

[0061] The inclined chute 53 effectively reduces the diameter of the particle running channel, allowing the bed material to maintain a gas seal even under high-speed circulation. This design broadens the operating range of the reactor, enabling it to adapt to more complex raw material and process conditions. Simultaneously, the first conical surface 51 and the second conical surface 52 can be used for secondary air distribution in the combustion chamber 2. With secondary air present, the bottom combustion air can be appropriately reduced, causing the particles to bubble at the bottom of the combustion chamber 2. As the bubbling fluidizes to the vicinity of the secondary air, the particles are accelerated by the upward-sloping secondary air and rapidly transported to the return unit 3. Above the secondary air is a rapid fluidized bed. This design increases the residence time of the particles in the high-temperature zone at the bottom, allowing for more effective combustion of the tar on their surface, providing more heat for gasification, reducing the tar content in the flue gas, facilitating flue gas post-treatment, and improving the process's economics. When applying the AER process, it also improves the particle regeneration rate, further facilitating carbon dioxide capture in the gasification chamber, thereby increasing the hydrogen production concentration.

[0062] The structure of the second-stage built-in heat exchange dual fluidized bed 200 of this invention is the same as that of the first-stage built-in heat exchange dual fluidized bed 100, and will not be described in detail here. The only difference is the bed material particles; the second stage uses an iron-based oxygen carrier. The first-stage dual fluidized bed 100 and the second-stage dual fluidized bed 200 are connected by a pipeline 102. One end of the pipeline is connected to the hydrogen-containing synthesis gas outlet (i.e., the first product gas outlet 101) of the first-stage dual fluidized bed, and the other end is connected to the combustion air inlet of the combustion chamber of the second-stage dual fluidized bed 200. Preferably, but not limitingly, a turbocharger (not shown in the figure) is provided on the connecting pipeline 102 to provide sufficient fluidizing air velocity to the combustion chamber of the second-stage dual fluidized bed 200.

[0063] The following describes the application of this invention. Figure 3 The biomass-to-hydrogen process of the two-stage reaction unit shown is described in detail below (in conjunction with references). Figure 5 ):

[0064] 1) Biomass enters the gasification chamber 1 (i.e., gasification chamber) of the first stage double fluidized bed filled with hot bed material through the feeding screw from the hopper. Together with the bed material, it is in a bubbling fluidized state in the gasification chamber 1, absorbs the heat of the bed material, and undergoes a gasification reaction with water vapor to produce hydrogen-rich gas and semi-coke. The semi-coke particles and cooled bed material particles move downward, while the gas moves upward, achieving preliminary gas-solid separation here.

[0065] 2) Hydrogen-rich gas is discharged from outlet 101 of the first-stage dual-fluidized bed gasification chamber 1, and the semi-coke and cooling bed material are subjected to cone-shaped water vapor (i.e., Figure 5 The loosened fluidizing air enters the bottom of the combustion chamber and is rapidly fluidized under the action of the combustion air (air). Here, the water vapor at the bottom of the vaporization chamber acts as a barrier to hydrogen-rich gas and air and as a fluidizing agent for particles.

[0066] 3) In the combustion chamber 2 of the first-stage dual fluidized bed, carbon-containing semi-coke particles are ignited in the air, raising the temperature of the bed material particles in the combustion chamber; the ash particles remaining after the semi-coke is burned out, the unburned semi-coke particles, a portion of the bed material, and the fine powder generated by the wear of the bed material are carried by the flue gas to the cyclone separator 4. Since the density and particle size of other particles and bed material particles are significantly different, they are discharged from the flue gas outlet 42 at the top of the cyclone separator along with the flue gas, while the bed material is discharged from the feed pipe 41 of the cyclone separator 4 to the loosening chamber 31 of the return unit 3.

[0067] 4) Another portion of the bed material particles with lower particle velocity directly "overflow" into the open loosening chamber 31. The converging hot bed material particles form a material seal in the loosening chamber 31 of the return unit. The syngas generated in the gasification chamber 1 is blocked in the return chamber 32 of the return unit 3, while the flue gas is blocked in the loosening chamber 31 by the material seal. The particles are transported to the gasification chamber 1 by the return air of the return unit. During the falling process, the rising syngas and fluidized gas are heated and mixed, promoting further removal of syngas tar and improving the quality of hydrogen-rich syngas. The hot bed material particles continue to fall and mix with the biomass particles, providing heat for the gasification reaction. This forms a circulation of the bed material in the dual fluidized bed system. Through simulation using finite element software, the results show that the present invention... Figure 5 In the case of the first stage with a built-in dual fluidized bed, the "solid phase particle volume ratio" in each region is as follows: Figure 9 As shown;

[0068] 5) The hydrogen-rich gas generated by the first-stage built-in dual fluidized bed is pressurized by the compressor and then enters the second-stage dual fluidized bed reactor through the combustion air inlet and secondary air inlet. It reacts with the iron-based oxygen carrier (Fe3O4) entering the second-stage combustion chamber, reducing it to elemental Fe or FeO. The syngas is oxidized into flue gas, releasing a large amount of heat in the process. The particles are in a bubbling fluidized state at the bottom of the second-stage combustion chamber, and then undergo rapid fluidization under the action of secondary air. The generated low-valent iron-based oxygen carrier or elemental iron enters the cyclone separator, while the flue gas is discharged from the top. The low-valent iron-based oxygen carrier or elemental iron falls into the return unit below the cyclone and is then transported by the return air (water vapor) to the second-stage dual fluidized bed gasification chamber (i.e., the gasification chamber). The high-temperature low-valent iron-based oxygen carrier or elemental iron particles react with the water vapor introduced from the bottom conical surface of the gasification chamber to produce high-purity hydrogen and iron-based oxygen carrier (Fe3O4). The high-purity hydrogen is discharged from the top of the gasification chamber for further purification. The cooled iron-based oxygen carrier (Fe3O4) is loosened by the water vapor on the conical surface and enters the bottom of the second-stage combustion chamber to continue to be reduced, thus completing the cycle regeneration of the oxygen carrier.

[0069] Example 1

[0070] The ambient temperature biomass feedstock in the hopper is fed into the gasification chamber of the first-stage dual fluidized bed reactor via a screw feeder. The feedstock falls into the dense phase zone of the fluidized bed under gravity, mixing with the thermally inert bed material at 1200K. It is then bubbling and fluidized at the bottom of the fluidized bed under the influence of 600K fluidizing air. The fluidizing gas is water vapor. The biomass pellets, when heated, produce a mixture of hydrogen-rich gases including hydrogen, carbon monoxide, carbon dioxide, and low-carbon hydrocarbons, as well as liquids such as tar, and solid particles such as semi-coke and ash. If the gasification gas is water vapor, the tar will undergo a reforming gasification reaction with the water vapor, decomposing into low-carbon hydrocarbon gases, which are discharged as product gas along with the hydrogen-rich gas. The hydrogen yield in the dry product gas can reach 55%. The cooled bed material particles, as well as semi-coke particles and ash particles, are loosened by the water vapor on the cone surface and enter the bottom of the combustion chamber. Under the action of the combustion air, they are rapidly fluidized. Some of the semi-coke particles come into contact with the fast-flowing 600K combustion air in the combustion chamber, and combustion releases a large amount of heat, which heats the cooled bed material particles. The flue gas produced by combustion carries the bed material particles, incompletely burned semi-coke particles, and ash particles into the cyclone separator. Because the actual density of the bed material particles differs significantly from that of other particles, the bed material particles can be separated from the flue gas and other particles relatively thoroughly. The flue gas and other particles are discharged from the top of the cyclone separator, while the bed material particles are discharged from the bottom of the cyclone separator and fall into the return unit. The particles gradually accumulate to form a material seal. The 1200K hot bed material particles are fluidized by the loosening air (water vapor) of the return unit and are carried by the return air (water vapor) into the gasification chamber. Under the action of gravity, they fall into the dilute phase zone of the fluidized bed. First, the rising syngas and the fluidized gas mixture are heated to promote further removal of tar from the syngas. Then, the biomass particles falling into the dense phase zone of the gasification chamber are heated. In this way, the bed material completes the circulation in the first stage of the dual fluidized bed reactor without participating in any reaction, only serving as a heat carrier.

[0071] The hydrogen-rich gas generated in the first-stage dual fluidized bed reactor is pressurized by a compressor and then enters the second-stage dual fluidized bed reactor through the second-stage combustion air inlet and secondary air inlet. There, it reacts with the iron-based oxygen carrier (Fe3O4) entering the second-stage combustion chamber, reducing it to elemental Fe or FeO. The syngas is oxidized into flue gas, releasing a large amount of heat in the process. The particles are in a bubbling fluidized state at the bottom of the second-stage combustion chamber at a bed temperature of 1123 K. Subsequently, under the action of secondary air, they undergo rapid fluidization. The generated low-valent iron-based oxygen carrier or elemental iron enters the cyclone separator, while the high-temperature flue gas is discharged from the top. The low-valent iron-based oxygen carrier or elemental iron falls into the return unit below the cyclone and is then transported by the return air (water vapor) to the second-stage dual fluidized bed gasification chamber. The high-temperature low-valent iron-based oxygen carrier or elemental iron particles react with the water vapor introduced from the bottom conical surface of the gasification chamber to produce 91%-99% high-purity hydrogen and iron-based oxygen carrier (Fe3O4). The cooled iron-based oxygen carrier (Fe3O4) is loosened by the water vapor on the conical surface and enters the bottom of the second-stage combustion chamber to continue to be reduced. In this way, the oxygen carrier is regenerated. The high-purity hydrogen is discharged from the top of the gasification chamber for further purification.

[0072] Example 2

[0073] When incorporating AER technology, the role of the first-stage bed material differs from that in Example 1. The ambient-temperature biomass feedstock in the hopper is fed into the gasification chamber of the first-stage dual fluidized bed reactor via a screw feeder. The feedstock falls into the dense phase zone of the fluidized bed under gravity, mixing with hot calcium oxide bed material at 1200K. It is then bubbly fluidized at the bottom of the fluidized bed by 600K fluidizing air. The fluidizing gas is water vapor. The biomass pellets, upon heating, produce a mixture of hydrogen, carbon monoxide, carbon dioxide, and low-carbon hydrocarbons (hydrogen-rich gas), liquids such as tar, and solid particles such as semi-coke and ash. Carbon dioxide combines with the calcium oxide bed material to form calcium carbonate bed material, releasing a certain amount of heat. This heat captures carbon dioxide from the gas while supplying some energy for the gasification reaction. Tar undergoes a reforming gasification reaction with water vapor, decomposing into low-carbon hydrocarbon gases, which are discharged as product gas along with the hydrogen-rich gas. Thus, the hydrogen content in the dry product gas can reach 78%. Cooled calcium carbonate bed particles, along with semi-coke and ash particles, are loosened by water vapor from the conical surface and enter the bottom of the combustion chamber. Under the action of combustion air, they rapidly fluidize. Some semi-coke particles come into contact with the fast-flowing 600K combustion air in the combustion chamber, burning and releasing a large amount of heat. This heats the cooled calcium carbonate bed particles, causing them to lose carbon dioxide and regenerate calcium oxide bed particles, thus completing the task of "transporting" carbon dioxide from the product gas to the flue gas. The flue gas produced by combustion carries the bed particles, incompletely burned semi-coke particles, and ash particles into the cyclone separator. Because the actual density of the bed material particles differs significantly from that of other particles, the bed material particles can be separated from the flue gas and other particles relatively thoroughly. The flue gas and other particles are discharged from the top of the cyclone separator, while the bed material particles are discharged from the bottom of the cyclone separator and fall into the return unit. The particles gradually accumulate to form a material seal. The 1200K hot bed material particles are fluidized by the loosening air (water vapor) of the return unit and are carried by the return air (water vapor) into the gasification chamber. Under the action of gravity, they fall into the dilute phase zone of the fluidized bed. First, the rising syngas and the fluidized gas mixture are heated to promote further removal of tar from the syngas. Then, the biomass particles falling into the dense phase zone of the gasification chamber are heated to further capture carbon dioxide and complete carbonation. In this way, the bed material completes the circulation in the first stage of the dual fluidized bed reactor, serving as a carrier of heat and carbon dioxide.

[0074] The hydrogen-rich gas, which is purer and has less tar than that produced in Example 1, generated by the first-stage dual fluidized bed is pressurized by a compressor and then enters the second-stage dual fluidized bed reactor through the combustion air inlet and secondary air inlet. There, it reacts with the iron-based oxygen carrier (Fe3O4) entering the second-stage combustion chamber, reducing it to elemental Fe or FeO. The syngas is oxidized into flue gas, releasing a large amount of heat in the process. The particles are in a bubbling fluidized state at the bottom of the second-stage combustion chamber at a bed temperature of 1123 K, and then undergo rapid fluidization under the action of secondary air. The resulting low-valent iron-based oxygen carrier or elemental iron enters the cyclone separator. High-temperature flue gas is discharged from the top, while low-valent iron-based oxygen carriers or elemental iron fall into the return unit below the cyclone. They are then transported by the return air (water vapor) to the second-stage dual fluidized bed gasification chamber. The high-temperature low-valent iron-based oxygen carriers or elemental iron particles react with the water vapor introduced from the bottom conical surface of the gasification chamber to produce 91%-99% high-purity hydrogen and iron-based oxygen carrier (Fe3O4). The cooled iron-based oxygen carrier (Fe3O4) is loosened by the water vapor on the conical surface and enters the bottom of the second-stage combustion chamber to continue to be reduced. This completes the cycle and regeneration of the oxygen carrier. The high-purity hydrogen is discharged from the top of the gasification chamber for further purification.

[0075] 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 two-stage built-in dual fluidized bed reactor, characterized in that, For biomass feedstock chemical chain hydrogen production processes, each segment includes a built-in dual fluidized bed: The vaporization chamber is a cylindrical structure with a conical surface at the bottom, and the conical surface has holes for introducing bubbling fluidizing air. The combustion chamber is a tubular structure and is fitted inside the gasification chamber. The bottom of the combustion chamber is open and located in the conical area for introducing vertically upward combustion air. The return unit is located in the upper middle part of the reaction device. It is a hollow disc structure and is sleeved outside the combustion chamber. It is used to transport the high-temperature bed material particles from the combustion chamber to the annular gasification zone outside the combustion chamber and mix them with the biomass feedstock in the gasification zone to produce hydrogen. The return unit is equipped with a loosening chamber and a return chamber. The two built-in dual fluidized beds are connected in series to allow the hydrogen-containing syngas produced by the first dual fluidized bed to be introduced into the combustion chamber of the second dual fluidized bed.

2. The two-stage built-in dual fluidized bed reactor according to claim 1, characterized in that, The loosening chamber is annular and located on the inner side, with the outer wall of the loosening chamber coplanar with the wall of the combustion chamber; the inner wall of the loosening chamber extends upward, making the loosening chamber a narrow annular space, forming a material seal with densely packed bed material particles inside the loosening chamber, and the top of the loosening chamber is open.

3. The two-stage built-in dual fluidized bed reactor according to claim 2, characterized in that, The return chamber is annular and located on the outside. The return chamber is connected to the annular space of the gasification chamber through an annular feeding trough.

4. The two-stage built-in dual fluidized bed reactor according to claim 3, characterized in that, The loosening chamber receives bed material particles from the combustion chamber and blocks gas. The middle and upper parts of the loosening chamber are separated from the return chamber by a partition. The lower part of the loosening chamber is provided with a first air distribution chamber. The return chamber is connected to the gasification chamber. The lower part of the return chamber is provided with a second air distribution chamber.

5. The two-stage built-in dual fluidized bed reactor according to claim 4, characterized in that, Both the loosening chamber bottom plate and the return material chamber bottom plate are equipped with air caps or air holes; the first air distribution chamber and the second air distribution chamber are supplied with air through air pipes extending to the outside of the reaction device.

6. The two-stage built-in dual fluidized bed reactor according to claim 5, characterized in that, The trachea are arranged in a cross shape.

7. The two-stage built-in dual fluidized bed reactor according to claim 1, characterized in that, The upper part of the gasification chamber is equipped with a cyclone separator. The top of the cyclone separator is equipped with an air inlet and a flue gas outlet that are connected to the dual fluidized bed combustion chamber of this section, and the bottom is connected to the loosening chamber through a feed pipe.

8. The two-stage built-in dual fluidized bed reactor according to claim 1, characterized in that, The biomass feed inlet is located at the bottom of the material layer in the gasification chamber, above the material layer, and / or at the top of the reaction device, and the feeding method is screw feeding.

9. The two-stage built-in dual fluidized bed reactor according to claim 1, characterized in that, The conical surface of the gasification chamber is provided with a chute structure for extending the residence time of bed material particles at the bottom and for gas sealing.

10. The two-stage built-in dual fluidized bed reactor according to claim 9, characterized in that, The inclined chute structure specifically includes: The first conical surface extends downward at an angle from the outer wall of the combustion chamber; The second conical surface extends obliquely upward from the outer wall of the combustion chamber and encloses the first conical surface and the outer wall of the combustion chamber to form a relatively sealed structure; an inclined chute is formed between the second conical surface and the conical surface at the bottom of the gasification chamber.

11. The two-stage built-in dual fluidized bed reactor according to claim 10, characterized in that, The sealed structure is a ventilation chamber used to introduce secondary air from outside the reaction device.

12. The two-stage built-in dual fluidized bed reactor according to claim 11, characterized in that, The upper part of the air cavity and the wall of the combustion chamber are provided with inclined upward secondary air holes. The secondary air works in conjunction with the combustion-supporting air at the bottom of the combustion chamber to prolong the residence time of the bed material particles at the bottom.

13. The two-stage built-in dual fluidized bed reactor according to claim 1, characterized in that, The diameter of the pores on the conical surface at the bottom of the vaporization chamber gradually decreases from bottom to top.

14. The two-stage built-in dual fluidized bed reactor according to claim 1, characterized in that, The bed material particles of the built-in dual fluidized bed described in the first paragraph are inert bed material or metal oxide bed material; the bed material particles of the built-in dual fluidized bed described in the second paragraph are iron-based oxygen carriers.

15. The two-stage built-in dual fluidized bed reactor according to claim 14, characterized in that, The metal oxide bed material is calcium oxide bed material, which is used to capture carbon dioxide in the gasification chamber to generate calcium carbonate. The calcium carbonate is heated in the combustion chamber to decompose into carbon dioxide and is discharged with the flue gas.

16. The two-stage built-in dual fluidized bed reactor according to claim 1, characterized in that, The first and second fluidized beds are connected by a pipeline. One end of the pipeline is connected to the hydrogen-containing synthesis gas outlet of the first fluidized bed, and the other end is connected to the combustion air inlet of the combustion chamber of the second fluidized bed.

17. The two-stage built-in dual fluidized bed reactor according to claim 16, characterized in that, The pipeline is equipped with a turbocharger to provide sufficient fluidization velocity for the combustion chamber of the second-stage dual fluidized bed.

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