Recycle unit, double fluidized bed reactor device using the same

Abstract

The application discloses a returning material unit, and a double-fluidized bed reaction device applying the unit. The returning material unit is arranged between a combustion chamber and a gasification chamber in the double-fluidized bed reaction device and is used in a hydrogen production process of biomass raw materials. The returning material unit comprises a returning material chamber which is communicated with the gasification chamber or the combustion chamber through a feeding pipe. A first air distribution cavity is arranged at the lower part of the returning material chamber. A loosening chamber is arranged to receive bed material particles from the combustion chamber or the gasification chamber and to block gas. The middle and upper parts of the loosening chamber are separated from the returning material chamber through a partition plate. The bottom plate of the loosening chamber is arranged to be inclined towards the partition plate. A second air distribution cavity is arranged at the lower part of the loosening chamber. The returning material unit can reduce the possibility of gas channeling between hydrogen-rich synthesis gas and flue gas and reduce the fluidized dead zone while ensuring the hydrogen production rate. The structure design of the gasification chamber of the double-fluidized bed reaction device can make the solid particles realize local core-annular flow circulation, and the heat transfer between the bed material particles and the biomass particles is enhanced.

Description

Technical Field

[0001] This invention relates to the field of biomass hydrogen production technology, and in particular to a return feed unit and a dual fluidized bed reactor using the unit. 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] Traditional fluidized bed reactors perform combustion and gasification processes within the same reactor, resulting in partial combustion of syngas and low yield. Dual fluidized bed reactors are already in use, offering the following advantages: they decouple combustion and gasification, providing indirect heating and higher hydrogen production; efficient exchange of solids and heat between the combustion and gasification chambers enables high heat flux and throughput in a smaller volume; and they have lower tar content than conventional routes, facilitating 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] The main challenge currently facing dual fluidized bed reactors lies in achieving efficient gas-solid separation between the gasification chamber and the combustion chamber, creating a stable cycle where only heat and bed material exchange occur. The circulation velocity of solid particles determines the concentration of solid particles within the fluidized bed, which plays a significant role in combustion, heat transfer, and desulfurization. Therefore, ensuring stable flow of the circulating bed material is fundamental to the normal operation of the circulating fluidized bed.

[0006] Dual fluidized bed reactors require a return feed device, which is a non-mechanical valve that drives the fluidized material to be transported as solids under pressure on both sides of the return feeder. Many issues can lead to insufficient semi-coke particles in the return feed, preventing adequate heat from combustion. Therefore, ensuring the bed material reaches the design temperature is a design challenge for circulating fluidized bed reactors. Further improvements to dual fluidized bed reactors are needed to prevent gas backflow, reduce fluidization dead zones, and increase the amount of solid particles circulating.

[0007] Therefore, there is an urgent need for a return unit and a dual fluidized bed reactor that uses this unit, so as to reduce the possibility of cross-contamination between hydrogen-rich syngas and flue gas while ensuring hydrogen production rate and reducing fluidization dead zone.

[0008] 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

[0009] The purpose of this invention is to provide a return material unit and a dual fluidized bed reactor using this unit, thereby reducing the possibility of cross-contamination between hydrogen-rich syngas and flue gas and minimizing the fluidization dead zone while ensuring hydrogen production rate.

[0010] Another objective of this invention is to provide a return material unit and a dual fluidized bed reactor using this unit, which enables the solid particles in the lower part of the gasification chamber to achieve local core-circulation flow and circulation, thereby enhancing the heat transfer between the bed material particles and the biomass particles.

[0011] To achieve the above objectives, according to a first aspect of the present invention, a return material unit is provided, applied between the combustion chamber and the gasification chamber in a dual fluidized bed reactor for a biomass feedstock hydrogen production process; comprising: a return material chamber, which is connected to the gasification chamber or the combustion chamber via a feed pipe; a first air distribution chamber is provided at the lower part of the return material chamber; a loosening chamber, which receives bed material particles from the combustion chamber or the gasification chamber and blocks gas, the middle and upper parts of the loosening chamber are separated from the return material chamber by a partition, and the bottom plate of the loosening chamber is inclined toward the partition; a second air distribution chamber is provided at the lower part of the loosening chamber.

[0012] Furthermore, in the above technical solution, the return unit is divided into an upper returner and a lower returner; wherein, the feed pipe of the upper returner is connected to the combustion chamber through a cyclone separator, and the feeding pipe is connected to the gasification chamber; the feed pipe of the lower returner is connected to the gasification chamber, and the feeding pipe is connected to the combustion chamber.

[0013] Furthermore, in the above technical solution, both the bottom plate of the loosening chamber and the bottom plate of the return material chamber are provided with air caps or air holes.

[0014] Furthermore, in the above technical solution, the wind cap or air vent is partially installed on the bottom plate of the loosening chamber, and is located on the side away from the partition.

[0015] Furthermore, in the above technical solution, the cross-sectional diameter of the loosening chamber is larger than that of the return chamber. Specifically, the cross-sectional diameter of the upper returner loosening chamber can be 1.1 to 1.5 times the cross-sectional diameter of the return chamber; the cross-sectional diameter of the lower returner loosening chamber can be 2 to 3 times the cross-sectional diameter of the return chamber.

[0016] To achieve the above objectives, according to a second aspect of the present invention, a dual fluidized bed reactor is provided, comprising the aforementioned return unit, which is divided into an upper return unit and a lower return unit. The reactor further comprises: a gasification chamber, the middle part of which is connected to the feed pipe of the upper return unit for receiving high-temperature bed material particles from the upper return unit and mixing them with room-temperature biomass feedstock. Under the combined action of fluidizing air and jetting air at the bottom of the gasification chamber, the biomass feedstock and bed material particles form a bubbling and jetting fluidized state, and hydrogen-rich gas is generated; the lower part of which is connected to the feed pipe of the lower return unit for conveying cooled bed material particles and semi-coke particles to the combustion chamber; and a combustion chamber, which receives the cooled bed material particles and semi-coke particles through the lower return unit and performs combustion, wherein a portion of the semi-coke particles heat the bed material particles through combustion heat release; and the heated bed material particles re-enter the gasification chamber through the upper return unit to form a cycle.

[0017] Furthermore, in the above technical solution, the fluidizing air can enter radially from the bottom of the gasification chamber, and the jetting air can enter axially upward from the bottom of the gasification chamber. Accordingly, a jetting fluidization mechanism is provided at the bottom of the gasification chamber, which may include: a cone whose outer wall is tangent to the fluidizing air inlet, and the surface of the cone is provided with uniformly distributed air holes; a vertical duct located above the cone with its inlet facing the jetting air inlet; the fluidizing air blows the bed material particles and biomass raw materials to the duct inlet, and then the jetting air sprays the bed material particles and biomass raw materials into the duct and then they fall off from the outside of the duct, forming a core-ring flow circulation state of the particles.

[0018] Furthermore, in the above technical solution, a particle limiter is installed at a distance above the conduit outlet to restrict the continued upward movement of bed material particles and biomass feedstock. The particle limiter can be a conical cap structure.

[0019] Furthermore, in the above technical solution, the feeding pipe of the upper return feeder and the gasification chamber can be set up in a tangential connection manner.

[0020] Furthermore, in the above technical solution, the middle section of the combustion chamber can be configured as a reduced-diameter section. An air inlet is provided at the bottom of the combustion chamber; a supplementary fuel and secondary air inlet can be provided at the top of the reduced-diameter section.

[0021] Furthermore, in the above technical solution, the bed material particles can be inert bed material or metal oxide bed material. Preferred metal oxide bed material is calcium oxide bed material, used to capture carbon dioxide in the gasification chamber to generate calcium carbonate. The calcium carbonate decomposes into carbon dioxide in the combustion chamber and is discharged with the flue gas. Both the fluidizing air and the jet air can be nitrogen or steam. When steam is used, it can reform the tar produced after the biomass feedstock gasification.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) The inclined bottom plate of the upper and lower return feeder loosening chamber in the return unit of the present invention can effectively reduce the fluidization dead zone; while reducing the fluidization dead zone, the packing sealing performance between the gasification chamber and the combustion chamber can still be guaranteed, reducing the possibility of cross-flow between hydrogen-rich syngas and flue gas, and providing a guarantee for the long-term stable operation of the dual fluidized bed device; on the basis of the inclined bottom plate, wind caps or air holes are locally set in the part away from the partition plate, and the possible agglomeration of coke particles and biomass particles is destroyed by higher gas velocity bubbling; while the particles on the side near the partition plate with a faster downward movement speed still maintain the sealed packing state of the moving bed, which can be applied to the situation where coking is easy;

[0024] 2) The combination of the cone, conduit and particle limiter at the bottom of the gasification chamber of this invention enables the solid particles to achieve local core-circulation flow, enhances the heat transfer between the bed material particles and the biomass particles, increases the residence time of the biomass particles in the gasification chamber, and can increase the depth of the gasification reaction, producing syngas with a higher hydrogen content.

[0025] 3) The reduced diameter treatment of the combustion chamber in this invention can increase the circulation of bed material particles, which can effectively improve the heating efficiency of the gasification chamber; the setting of secondary air and supplementary fuel can realize precise control of the gasification and combustion process of the reactor.

[0026] 4) The lighter ash particles formed during the hydrogen production process of this invention can be carried out of the reaction device by the airflow of the cyclone separator and then removed in the tail gas cyclone. The dual fluidized bed reactor does not need to be equipped with a separate slag discharge port.

[0027] 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

[0028] Figure 1 This is a cross-sectional schematic diagram of a return feeder in the prior art (taking the above return feeder as an example).

[0029] Figure 2 This is a cross-sectional schematic diagram of the upper return device in the return unit of the present invention (also showing the cyclone separator).

[0030] Figure 3 This is a cross-sectional schematic diagram of the first embodiment of the lower return feeder in the return unit of the present invention (also showing the lower structure of the combustion chamber).

[0031] Figure 4 This is a cross-sectional schematic diagram of the second embodiment of the lower return device in the return unit of the present invention.

[0032] Figure 5 This is a cross-sectional schematic diagram of the dual fluidized bed reactor of the present invention (showing the internal structure of the upper return feeder, gasification chamber, lower return feeder, and combustion chamber).

[0033] Figure 6 This is a schematic diagram of the simulation results of the dual fluidized bed reactor of the present invention (showing the volume percentage of solid particles in each part).

[0034] Figure 7 Is adopted Figure 4 A schematic diagram of the simulation results for the second implementation of the return feeder (showing the volume percentage of solid particles in various locations).

[0035] Figure 8 This is a schematic diagram of the simulation results when the feed pipe of the upper return feeder is tangentially connected to the gasification chamber (showing the volume percentage of solid particles in each part).

[0036] Figure 9 This is a schematic diagram of the dual fluidized bed process when calcium oxide is used as the bed material particles in this invention.

[0037] Explanation of key figure labels:

[0038] Existing technology Figure 1 In the middle, 1A-upper return feeder, 11-loosening chamber, 12-return chamber, 13-bottom plate, 130-air cap, 14-air distribution chamber, 15-feeding pipe;

[0039] This invention Figures 2 to 5 middle,

[0040] 1A-Top return feeder, 10A-Feed pipe, 11A-Loosening chamber, 12A-Return chamber, 13A-Inclined bottom plate, 130A-Air cap, 141A-First air distribution chamber, 142A-Second air distribution chamber, 15A-Feeding pipe, 16A-Baffle plate;

[0041] 1B-lower return feeder, 10B-feed pipe, 11B-loosening chamber, 12B-return chamber, 13B-inclined bottom plate, 130B-air cap, 141B-first air distribution chamber, 142B-second air distribution chamber, 15B-feeding pipe, 16B-partition plate.

[0042] 2-Gasification chamber, 20-Biomass pellet inlet, 21-Cone, 22-Vertical duct, 23-Cone cap, 3-Combustion chamber, 31-Reduced diameter section, 32-Reduced diameter inlet, 33-Expanded diameter inlet, 4-Cyclone separator. Detailed Implementation

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] This invention employs a dual fluidized bed reactor for biomass hydrogen production. Through research, the inventors discovered that the dual fluidized bed reactor offers the following advantages: Traditional routes involve combustion and gasification in the same reactor, resulting in partial combustion of the syngas and low yield. The dual fluidized bed reactor decouples combustion and gasification, using indirect heating, leading to higher hydrogen production. 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 dual fluidized bed reactor of this invention includes a gasification chamber and a combustion chamber, with an upper return feeder and a lower return feeder between them. To address the problems of poor return feed and insufficient particle circulation in dual fluidized bed reactors, which prevent timely provision of sufficient heat to the gasification chamber, this invention improves the structure of the gasification chamber, return feeder, and combustion chamber, utilizing heated bed material particles entering the gasification chamber to better provide heat for the biomass gasification reaction.

[0048] Figure 1 This is a schematic diagram of the upper return feeder 1A in an existing conventional return unit. (See diagram below.) Figure 1 As shown, the loosening chamber 11 and the return chamber 12 are typically designed to be relatively small, with the same diameter as the material leg section, facilitating rapid circulation of the bed material. The bed material is generally transported in the dilute phase within the loosening chamber of this return feeder. The inventors discovered that this existing return feeder, used for air gasification of biomass in a circulating fluidized bed reactor, can effectively transport the bed material and prevent cross-contamination due to the low hydrogen concentration in the syngas produced by air gasification. However, the hydrogen concentration produced in a dual fluidized bed reactor used for biomass hydrogen production is much higher, typically reaching 50%-78% VOL, as mentioned earlier. Conventional return feeders are not ideal in suppressing gas backflow during dilute phase transport of the bed material, and during dense phase transport, fluidization dead zones form at the bottom corners of the loosening chamber 11, causing blockage of the bed material and coke particles due to cooling, resulting in poor return flow and affecting the stable operation of the reactor.

[0049] To address the problems existing in the above-mentioned prior art, such as Figure 2 , 3 As shown, this invention provides an improved return feed unit. This return feed unit is applied between the combustion chamber and gasification chamber in a dual fluidized bed reactor for hydrogen production from biomass feedstock. The return feed unit of this invention is divided into an upper return feeder 1A (see reference). Figure 2 ) and return feeder 1B (reference) Figure 3 ), wherein the feed pipe 10A of the upper return feeder 1A is connected to the combustion chamber 3 through the cyclone separator 4, and the feed pipe 15A is connected to the gasification chamber 2 (reference). Figure 5The feed pipe 10B of the lower return feeder 1B is connected to the gasification chamber 2, and the feed pipe 15B is connected to the combustion chamber 3. The following describes the upper return feeder 1A and the lower return feeder 1B separately:

[0050] like Figure 2 As shown, the upper return feeder 1A includes a return chamber 12A and a loosening chamber 11A. The return chamber 12A is connected to the gasification chamber 2 via a feeding pipe 15A; a first air distribution chamber 141A is located at the lower part of the return chamber 12A. The loosening chamber 11A receives bed material particles from the combustion chamber 3 and blocks gas. The middle and upper parts of the loosening chamber 11A are separated from the return chamber 12A by a partition 16A. The bottom plate 13A of the loosening chamber is inclined towards the partition 16A, and a second air distribution chamber 142A is located at the lower part of the loosening chamber 11A.

[0051] like Figure 3 As shown, the lower return feeder 1B includes a return chamber 12B and a loosening chamber 11B. The return chamber 12B is connected to the combustion chamber 3 via a feed pipe 15B; a first air distribution chamber 141B is located at the lower part of the return chamber 12B. The loosening chamber 11B receives bed material particles from the gasification chamber 2 and blocks gas. The middle and upper parts of the loosening chamber 11B are separated from the return chamber 12B by a partition 16B. The bottom plate 13B of the loosening chamber is inclined towards the partition 16B, and a second air distribution chamber 142B is located at the lower part of the loosening chamber 11B.

[0052] Further as Figure 2 , 3 As shown, both the loosening chamber floor plate and the return material chamber floor plate are equipped with air caps or vents. The figure shows the air cap installation (i.e., Figure 2 The 130A windproof cap and Figure 3 (The wind cap 130B in the invention). Further, preferably but not limitingly, the cross-sectional diameter of the loosening chamber in the upper and lower return feeders of the present invention is larger than the cross-sectional diameter of the return chamber. Specifically, the cross-sectional diameter of the loosening chamber of the upper return feeder can be set to 1.1 to 1.5 times the cross-sectional diameter of the return chamber; the cross-sectional diameter of the loosening chamber of the lower return feeder can be set to 2 to 3 times the cross-sectional diameter of the return chamber.

[0053] The upper and lower return feeders of this invention can reduce the fluidization dead zone when conveying bed material in a dense phase. By increasing the size ratio of the loosening chamber and the return chamber, the volume of the loosening chamber is increased, and the bed material in the loosening chamber of the return feeder forms a dense phase accumulation to form a material seal. Figure 3The height of the loosening chamber of the middle and lower return feeders can also be increased accordingly, which improves the quality of the material seal and reduces the possibility of hydrogen-rich gas backflowing from the gasification chamber to the combustion chamber and causing deflagration under adverse operating conditions, effectively improving the safety of the device. At the same time, the inclined setting of the bottom plate of the loosening chamber can effectively reduce the friction between the particles and the bottom plate of the loosening chamber, reduce the fluidization "dead zone" at the corner of the loosening chamber, and promote the bed material particles accumulated on the inclined surface to be blown from the fluidization "dead zone" to the fluidization zone in the loosening chamber. Meanwhile, the air distribution chamber at the bottom of the inclined bottom plate (i.e., the second air distribution chamber 142A / 142B) fluidizes the bottom bed material, reduces friction with the inclined surface, and makes it easier to return the material. The return chamber volume of the upper and lower return feeders is kept relatively small, so that the bed material passing through the return chamber can still be transported to the gasification chamber or combustion chamber at a relatively fast speed by the return air (i.e., the first air distribution chamber 141A / 141B). The loosening chamber stores the incoming bed material particles, while the return chamber stores the bed material particles entering from the loosening chamber. Together, they form a material seal between the gasification chamber and the combustion chamber, preventing gas cross-contamination. The bottom plates of the loosening chamber and the return chamber are each equipped with a different number of air caps or vents to control the airflow. The air caps or vents connect to the air distribution chamber, and the lower part of the air distribution chamber connects to the return air and loosening air inlet pipes (not shown in the figure). Using the return unit provided by this invention not only avoids fluidization "dead zones" but also effectively ensures the material seal effect. See [reference needed]. Figure 6 Through simulation, the upper and lower return devices of the return unit of this invention (i.e., Figure 6 (The circled area) During fluidization, the volume ratio of solid particles in the lower part of the loosening chamber and return chamber always reaches a high level.

[0054] Further as Figure 4 As shown, preferably but not limitingly, in Figure 3 Based on the first embodiment of the return feeder, the present invention provides a second embodiment, namely, the air cap 130B or air hole is partially provided on the bottom plate 13B of the loosening chamber, specifically on the side away from the partition 16B. Figure 4The implementation method is suitable for situations where syngas is more prone to coking. Specifically, biomass pellets from different sources have different proportions of volatile matter, fixed carbon, bound water, and ash, and the composition of volatile matter is also different. When the syngas produced after gasification of the biomass pellets is more prone to coking, the bottom return feeder 1B can preferably adopt the wind cap distribution of this scheme, that is, vertically upward wind caps 130B are set on 1 / 2 or 2 / 3 of the area on one side of the inclined bottom plate 13B far from the partition plate 16B at the bottom of the loosening chamber 11B. When this setup is adopted, with the loosening air flow rate remaining constant, the increased air velocity provides a stronger purge of the bed material and coke particles on the far-partition side of the loosening chamber. This allows for bubbling fluidization of the bed material and coke particles on the far-partition side of the loosening chamber in the return feeder, breaking up any potential agglomeration between the coke particles and biomass particles. Meanwhile, the particles on the near-partition side, which move downwards at a faster speed, remain in a sealed packing state within the moving bed, thus still effectively isolating the gasification chamber and combustion chamber from cross-contamination. (Based on relevant experimental and simulation results...) Figure 7 This also proves that the solution is feasible and more suitable for situations where coking is likely.

[0055] like Figure 5 As shown, the present invention also provides a dual fluidized bed reactor. In addition to the upper return feeder 1A and lower return feeder 1B mentioned above in the return unit, the dual fluidized bed reactor also includes a gasification chamber 2 and a combustion chamber 3. The middle part of the gasification chamber 2 is connected to the feed pipe 15A of the upper return feeder 1A, and is used to receive high-temperature bed material particles from the upper return feeder 1A and mix them with room-temperature biomass feedstock (biomass feedstock particles enter the gasification chamber 2 from inlet 20). Under the combined action of fluidizing air and jetting air at the bottom of the gasification chamber 2, the biomass feedstock and bed material particles form a bubbling, jetting fluidized state, generating hydrogen-rich gas. The lower part of the gasification chamber 2 is connected to the feed pipe 10B of the lower return feeder 1B, and is used to transport cooled bed material particles and semi-coke particles generated during the gasification process to the combustion chamber. Combustion chamber 3 receives cooled bed material particles and semi-coke particles through lower return feeder 1B and performs combustion. Some of the semi-coke particles release heat through combustion to heat the bed material particles. The heated bed material particles re-enter gasification chamber 2 through upper return feeder 1A to form a cycle.

[0056] Further as Figure 5As shown, fluidizing air enters radially from the bottom of gasification chamber 2, while jetting air enters axially upward from the bottom of gasification chamber 2. Corresponding to the fluidizing and jetting air, a jetting fluidization mechanism is provided at the bottom of gasification chamber 2, specifically comprising a cone 21 and a vertical duct 22. The outer wall of cone 21 is tangential to the fluidizing air inlet, and the cone surface has uniformly distributed air holes, the direction of which is perpendicular to the cone surface (not shown in the figure). Specifically, the outer wall of cone 21, the inner wall of gasification chamber 2, and the bottom surface form a concave cavity. The tangentially entering fluidizing air flows along the outer wall of the cone within this concave cavity. Under the action of air pressure, the fluidizing air enters the air holes and blows the solid particles (including bed material particles and biomass raw material particles) on the inner wall of cone 21 to the lower inlet of vertical duct 22. Vertical duct 22 is located above cone 21, and its inlet faces the jetting air inlet. Fluidizing air first blows the bed material particles and biomass feedstock particles to the inlet of duct 22, then jet air sprays the bed material particles and biomass feedstock particles into duct 22. After being blown out of the duct, the solid particles fall from the outside of the duct. Particles that fall to the surface of the cone are further blown upward by the jet air into the duct, forming a core-ring flow circulation state of the particles (i.e., the particles rise in the center of the duct and descend in the annular space between the outer wall of the duct and the inner wall of the gasification chamber, forming a local circulation of particles). Further as... Figure 5 As shown, preferably but not limitingly, a particle limiter is provided at a distance above the outlet of the vertical conduit 22 to restrict the continued upward movement of bed material particles and biomass feed particles. The particle limiter preferably adopts a conical cap structure (see...). Figure 5 (The cone cap 23 in the middle).

[0057] This invention utilizes jetting air to induce a core-ring flow state of fluidized bed material and biomass pellets. The fluidizing air, introduced through a vertical cone surface, purges particles from the dense phase zone of the annular gap in the lower part of the gasification chamber to the duct inlet. The vertical duct design reduces radial diffusion of the jetting air, effectively decreasing the amount of air used and further enhancing core-ring flow, which is beneficial for heat transfer between the bed material, gas, and biomass pellets. Simultaneously, the jetting fluidization method allows lighter biomass pellets to be continuously ejected from the bottom, achieving internal circulation within the gasification chamber and increasing their residence time. During the jetting fluidization process, the pellets continuously mix with fresh, hot bed material from the upper return feeder, which is beneficial for the gasification reaction. Furthermore, biomass gasification mainly occurs at the boundary between the dense phase zone and the dilute phase zone (i.e., near the outlet of the vertical duct 22). The cone cap, acting as a particle limiter, restricts the injection of particles into the dilute phase zone. By altering the particle trajectory through the cone cap, it causes the particles to settle towards the dense phase zone in the lower annular gap of the gasification chamber, increasing the solid concentration in this region. The cone cap design is beneficial for the gasification reaction. In addition, the height of the gasification chamber in this invention differs from that of common biomass dual fluidized beds (such as the Gussing fluidized bed). The height of the gasification chamber is higher than that of the combustion chamber, which increases the time for the syngas to reform with steam within the gasification chamber, thereby obtaining a syngas product with a higher hydrogen concentration.

[0058] Further as Figure 5 As shown, the combustion chamber has a combustion air inlet at the bottom, and the middle section of the combustion chamber riser is a narrowing section. The narrowing of the middle section of the combustion chamber riser can accelerate the gas flow rate, so as to entrain more bed material particles and carbon particles and increase the particle circulation volume; supplementary fuel and secondary air inlets can also be set at the widening section of the combustion chamber riser, so as to more accurately control the gasification and combustion process of the reaction device.

[0059] It should be noted that the bed material particles used in this invention can be inert bed material or metal oxide bed material. Preferably, calcium oxide bed material is used, which can capture carbon dioxide in the gasification chamber to generate calcium carbonate. The calcium carbonate decomposes upon heating in the combustion chamber to release carbon dioxide, which is then discharged with the flue gas (see reference). Figure 9 The fluidizing air and jet air used in this invention can both be nitrogen or steam. When steam is used, it can reform the tar produced after the biomass feedstock is gasified.

[0060] Furthermore, when the present invention employs Figure 9In the AER process (using calcium oxide as the bed material), the calcium oxide bed material at the bottom of the gasification chamber absorbs carbon dioxide and transforms into calcium carbonate bed material. Its particle density is greater than that of the regenerated calcium oxide particles entering the gasification chamber from the top return feeder. This places higher demands on the fluidizing air; it needs to be greater than the critical fluidization velocity of the calcium carbonate bed material, otherwise the calcium carbonate bed material cannot achieve a fluidized state. However, it cannot be too high, otherwise the regenerated calcium oxide particles entering the gasification chamber from the top return feeder will be blown out. Therefore, in this case, the present invention connects the feed pipe of the top return feeder tangentially to the inner wall of the gasification chamber (not shown in the figure), instead of aligning it with the center of the gasification chamber. With this arrangement, the bed material from the top return feeder enters the gasification chamber and spirals down along the wall (see reference). Figure 8 The simulation results shown can effectively reduce the possibility of regenerated calcium oxide particles being blown out of the reactor, and at the same time play a further role in gas-solid separation of the syngas rising from the bottom of the gasification chamber, reducing the particle content of the gas in the gasification chamber and alleviating the pressure of the subsequent separation unit.

[0061] This invention improves the structure of the dual fluidized bed gasification chamber, combustion chamber, and return feeder by increasing the particle circulation rate, enhancing the sealing strength between gasification and combustion, and increasing the contact area between particles and gas to provide sufficient heat for the gasification air. This, in turn, deepens the biomass gasification reaction and increases the yield of hydrogen-rich syngas. The process of biomass hydrogen production using the dual fluidized bed reactor of this invention is described in detail below:

[0062] 1) Biomass enters the gasification chamber filled with hot bed material through a feeding screw from the hopper. Together with the bed material, it is in a sputtered-fluidized state within the gasification chamber, absorbing heat from the bed material and reacting with water vapor to produce hydrogen-rich gas and semi-coke. Solid particles ejected from the duct encounter a particle limiter, changing their direction of motion downwards, while the gas moves upwards, achieving initial gas-solid separation here; 2) The hydrogen-rich gas exits from the top outlet of the gasification chamber, while the semi-coke and cooled bed material enter the loosening chamber of the lower return feeder, forming a material seal. Syngas is blocked in the loosening chamber, while combustion air is blocked in the return chamber of the lower return feeder. The solid particles are transported to the combustion chamber by the return air from the lower return feeder; 3) Combustion air flows through the combustion chamber, igniting the carbon-containing semi-coke particles in the air, raising the temperature of the bed material particles in the combustion chamber, thus heating the bed material particles; 4) The ash particles remaining after the semi-coke is completely burned, the unburned semi-coke particles, 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. Due to the large difference in density and particle size between other particles and bed material particles, the other particles will be discharged from the top of the cyclone separator along with the flue gas. After heating, the bed material is discharged from the bottom of the cyclone separator. 5) The hot bed material particles enter the loosening chamber of the upper return feeder, forming a material seal. The syngas is blocked in the return chamber of the upper return feeder, while the flue gas is blocked in the loosening chamber of the upper return feeder by the material seal. The solid particles are transported to the gasification chamber by the upper return feeder under the action of the return air of the upper return feeder. During the falling process, the rising syngas and fluidized gas are heated and mixed, which promotes the further removal of syngas tar and improves the quality of hydrogen-rich syngas. The hot bed material particles continue to fall and mix with biomass particles to provide heat for the gasification reaction. In this way, the bed material is circulated in the dual fluidized bed system.

[0063] The present invention will be further illustrated below through two specific embodiments:

[0064] Example 1

[0065] A thermally inert bed material is used: the biomass feedstock falls into the dense phase zone of the gasification chamber under gravity, mixes with the thermally inert bed material at 1200K, and is purged by 600K fluidizing air and jet air, forming a bubbling and jetting fluidized state in the lower part of the gasification chamber. The fluidizing air and jet air are steam. The biomass pellets are heated to produce a mixture of hydrogen, carbon monoxide, carbon dioxide, and low-carbon hydrocarbons, liquids such as tar, and solid particles such as semi-coke and ash. The tar undergoes a reforming gasification reaction with the steam, 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 pellets, as well as the semi-coke and ash particles, enter the lower return feeder, gradually accumulating to form a material seal, preventing the gas in the gasification chamber from entering the combustion chamber. The solid particles at the bottom of the material seal are fluidized by the 600K loosening air (using steam) of the return feeder and transported to the combustion chamber by the return air (also using steam). Some of the semi-coke particles come into contact with the faster-flowing 600K combustion air in the combustion chamber and burn, releasing a large amount of heat. The heated and cooled bed material particles, along with the flue gas generated by combustion, carry 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 upper return feeder, gradually accumulating to form a material seal. The 1200K hot bed material particles are fluidized by the loosening air (water vapor) of the upper return feeder and are carried by the return air (also water vapor) into the gasification chamber. Under the action of gravity, they fall into the dilute phase zone of the gasification chamber, where the rising syngas and fluidizing gas mixture is heated first to promote further tar removal. Then, the biomass particles falling into the dense phase zone of the gasification chamber are heated. In this way, the bed material completes the cycle in the dual fluidized bed reactor without participating in any reaction, only serving as a heat carrier.

[0066] Example 2

[0067] This embodiment incorporates AER technology (i.e., using calcium oxide bed material), and the role of the bed material differs from that in Embodiment 1. Biomass feedstock falls into the dense phase zone of the fluidized bed under gravity, mixing with calcium oxide bed material at 1200K. It is then subjected to 600K steam fluidizing air and jetting air, resulting in a bubbling, jetting fluidized state in the lower part of the gasification chamber. The biomass particles, upon heating, 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 particles. 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 simultaneously supplying energy for the gasification reaction. Tar undergoes a reforming gasification reaction with steam, 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 material particles, along with semi-coke particles and ash particles, enter the lower return feeder, gradually accumulating to form a material seal, preventing gas from the gasification chamber from entering the combustion chamber. Solid particles at the bottom of the material seal are fluidized by the 600K loosening air (water vapor) in the lower return feeder and transported to the combustion chamber by the return air (water vapor). Some semi-coke particles come into contact with the faster-flowing 600K combustion air in the combustion chamber, burning and releasing a large amount of heat. This heats the cooled calcium carbonate bed material particles, causing them to lose carbon dioxide and regenerate calcium oxide bed material, thus completing the task of "transporting" carbon dioxide from the product gas to the flue gas. The flue gas generated 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 calcium oxide and calcium carbonate bed material particles differs significantly from other particles, the bed material particles can be separated relatively thoroughly from the flue gas and other particles. 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 upper return feeder, gradually accumulating to form a material seal. The 1200K hot bed material particles are fluidized by the loosening air (water vapor) of the upper return feeder and transported by the return air (water vapor) into the gasification chamber. Under the action of gravity, they fall into the dilute phase zone of the gasification chamber, where the rising syngas and fluidizing gas mixture is heated to promote further removal of carbon dioxide and tar. Then, they fall into the dense phase zone of the gasification chamber to heat the biomass particles falling into the gasification chamber and further capture carbon dioxide to complete carbonation. In this way, the bed material completes the circulation in the dual fluidized bed reactor, serving as a carrier of heat and carbon dioxide.

[0068] 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 return material unit, characterized in that, Used between the combustion chamber and gasification chamber in a dual fluidized bed reactor for hydrogen production from biomass feedstock; including: The return material chamber is connected to the gasification chamber or combustion chamber via a feeding pipe; the lower part of the return material chamber is provided with a first air distribution chamber. The loosening chamber receives bed material particles from the combustion chamber or gasification chamber and blocks gas. The middle and upper parts of the loosening chamber are separated from the return chamber by a partition. The bottom plate of the loosening chamber is inclined toward the partition. A second air distribution chamber is provided in the lower part of the loosening chamber. Both the loosening chamber bottom plate and the return material chamber bottom plate are provided with air caps or air holes; the air caps or air holes are partially provided on the loosening chamber bottom plate and are located on the side away from the partition; the cross-sectional diameter of the loosening chamber is larger than the cross-sectional diameter of the return material chamber.

2. The return material unit according to claim 1, characterized in that, The return unit is divided into an upper return device and a lower return device; wherein... The feed pipe of the upper return feeder is connected to the combustion chamber through a cyclone separator, and the feeding pipe is connected to the gasification chamber. The feed pipe of the lower return feeder is connected to the gasification chamber, and the feeding pipe is connected to the combustion chamber.

3. The return material unit according to claim 2, characterized in that, The cross-sectional diameter of the upper return feeder loosening chamber is 1.1 to 1.5 times the cross-sectional diameter of the return chamber; the cross-sectional diameter of the lower return feeder loosening chamber is 2 to 3 times the cross-sectional diameter of the return chamber.

4. A dual fluidized bed reactor, characterized in that, The device includes a return unit as described in any one of claims 1 to 3, the return unit being divided into an upper return device and a lower return device, and the device further includes: The gasification chamber, with its middle section connected to the feed pipe of the upper return feeder, is used to receive high-temperature bed material particles from the upper return feeder and mix them with room-temperature biomass raw materials. Under the combined action of fluidizing air and jetting air at the bottom of the gasification chamber, the biomass raw materials and bed material particles form a bubbling and jetting fluidized state, and generate hydrogen-rich gas. Its lower section is connected to the feed pipe of the lower return feeder, and is used to transport cooled bed material particles and semi-coke particles to the combustion chamber. The combustion chamber receives cooled bed material particles and semi-coke particles through a lower return feeder and burns them. Some of the semi-coke particles release heat through combustion to heat the bed material particles. The heated bed material particles are then returned to the gasification chamber through an upper return feeder to form a cycle.

5. The dual fluidized bed reactor according to claim 4, characterized in that, The fluidizing air enters radially from the bottom of the gasification chamber, and the jetting air enters axially upward from the bottom of the gasification chamber.

6. The dual fluidized bed reactor according to claim 5, characterized in that, The bottom of the gasification chamber is equipped with a jet fluidization mechanism, which includes: A cone, the outer wall of which is tangent to the fluidizing air inlet, and the surface of the cone is provided with uniformly distributed air holes; A vertical duct is located above the cone, with its inlet facing the inlet of the jetting air. The fluidizing air blows the bed material particles and biomass raw materials to the inlet of the duct, and then the jetting air sprays the bed material particles and biomass raw materials into the vertical duct, where they fall from the outside of the duct, forming a core-loop flow circulation state of the particles.

7. The dual fluidized bed reactor according to claim 6, characterized in that, A particle limiter is installed a certain distance above the outlet of the conduit to restrict the continued upward movement of bed material particles and biomass feedstock.

8. The dual fluidized bed reactor according to claim 7, characterized in that, The particle limiter has a cone-shaped structure.

9. The dual fluidized bed reactor according to claim 4, characterized in that, The feed pipe of the upper return feeder is tangentially connected to the gasification chamber.

10. The dual fluidized bed reactor according to claim 4, characterized in that, The middle section of the combustion chamber is a reduced diameter section.

11. The dual fluidized bed reactor according to claim 10, characterized in that, The combustion chamber is provided with a combustion air inlet at the bottom; and a supplementary fuel and secondary air inlet is provided at the top of the reduced diameter section.

12. The dual fluidized bed reactor according to claim 4, characterized in that, The bed material particles are inert bed material or metal oxide bed material.

13. The dual fluidized bed reactor according to claim 12, 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.

14. The dual fluidized bed reactor according to claim 4, characterized in that, Both the fluidizing air and the jetting air use nitrogen or water vapor.

15. The dual fluidized bed reactor according to claim 14, characterized in that, When the steam is used, it is used to reform the tar produced after the biomass feedstock is gasified.

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