Apparatus and method for reducing combustible gas concentration in a chemical looping combustion system

Abstract

This invention relates to the field of chemical looping combustion technology, aiming to solve the problems of incomplete reaction, high combustible gas concentration, significant particulate abrasion, increased escape, and high risk of equipment wear in existing technologies. It provides a device and method for reducing the combustible gas concentration in a chemical looping combustion system, comprising a fuel reactor, an air reactor, a first cyclone separator, a first return feeder, a second return feeder, a second cyclone separator, and a third return feeder. The fuel reactor has a lower bubbling bed section, a middle lifting section, and an upper expansion and deceleration section. The upper expansion and deceleration section is sequentially connected to the first cyclone separator, the first return feeder, and the lower bubbling bed section. After the reaction, the oxygen carrier is transported to the air reactor via the second return feeder, which is sequentially connected to the second cyclone separator, the third return feeder, and the middle lifting section. The beneficial effects of this invention are improved reaction efficiency, reduced combustible gas concentration, increased fuel conversion rate, improved carbon dioxide capture purity, and prevention of subsequent equipment erosion and wear.

Description

Technical Field

[0001] This invention relates to the field of chemical chaining combustion technology, and more specifically, to a device and method for reducing the concentration of combustible gases in a chemical chaining combustion system. Background Technology

[0002] Chemical looping combustion technology is widely considered one of the key technological pathways for achieving efficient carbon capture and carbon neutrality in the future thermal power and industrial heating sectors. This technology achieves oxygen transfer and indirect fuel combustion through the circulation of an oxygen carrier between the fuel reactor and the air reactor. Its core advantage lies in its ability to directly separate high concentrations of carbon at low cost. It is considered a key technology for achieving carbon neutrality in fields such as thermal power and industrial heating.

[0003] Currently, fuel reactors in CLC systems typically employ a bubbling fluidized bed structure to provide sufficient contact time for the coal gasification reaction. This study, through in-depth analysis and experiments, reveals for the first time that under low gas velocity conditions, high-density fresh oxygen-carrying particles, dominated by gravity, rapidly settle to the bottom bed, making them difficult to effectively transport to the upper part of the reactor. This results in excessively high concentrations of unreacted combustible gases in the tail flue of the fuel reactor, causing fuel chemical energy loss and outlet... The decrease in purity results in insufficient concentration and residence time of fresh oxygen-carrying particles in the upper and middle regions where the combustible gas concentration is highest, preventing sufficient mixing and reaction between the gas and solid phases. Simply increasing the overall fluidizing gas velocity of the fuel reactor to enhance particle entrainment and solve the problem of insufficient particle concentration and residence time in the upper part of the fuel reactor would lead to an excessively high particle velocity, resulting in a larger mass flow rate entering the cyclone separator. This would exacerbate particle wear and escape, and the high concentration and high velocity of particles would also significantly increase the risk of erosion and wear on equipment such as the fuel reactor and cyclone separator, threatening the long-term reliability and economy of the equipment. Therefore, the existing technology is caught in a dilemma: maintaining a low gas velocity in the bubbling bed results in incomplete reaction and high combustible gas concentration; increasing the velocity exacerbates oxygen-carrying particle wear and escape, and significantly increases the risk of equipment wear.

[0004] To address this critical technical challenge, which has been clearly revealed for the first time and urgently needs to be solved, this invention proposes an innovative fuel reactor design. The lower part of the fuel reactor is a bubbling bed structure, following the traditional fuel reactor design. The middle section is transformed into a high-velocity lifting section by reducing its cross-sectional area. The upper part is a gradually expanding deceleration section, allowing oxygen-carrying particles to slow down in this area and fall slowly along the wall. This design, while maintaining the existing advantages of low wear and high gas-solid contact efficiency of the fuel reactor, directionally enhances the particle concentration and residence time of oxygen-carrying particles in the upper part of the fuel reactor, thereby fundamentally overcoming the aforementioned bottleneck. Summary of the Invention

[0005] The present invention aims to provide a device and method for reducing the concentration of combustible gases in a chemical looping combustion system, in order to solve the problems in the prior art that result in incomplete reaction, high concentration of combustible gases, large particle wear, increased escape, and high risk of equipment wear when maintaining a low gas velocity in the bubbling bed.

[0006] The embodiments of the present invention are implemented as follows: This invention provides a device for reducing the concentration of combustible gases in a chemical looping combustion system, comprising a fuel reactor, an air reactor, a first cyclone separator, a first return feeder, a second return feeder, a second cyclone separator, and a third return feeder; The aforementioned fuel reactor is provided with a lower bubbling bed section, a middle lifting section, and an upper diameter expansion and deceleration section in sequential order from bottom to top, all in fluid communication. The cross-sectional area of ​​the middle lifting section is smaller than that of the lower bubbling bed section, and the cross-sectional area of ​​the upper diameter expansion and deceleration section gradually expands upward from its inlet. The top gas outlet of the aforementioned upper diameter expansion and deceleration section is connected to the inlet of the aforementioned first cyclone separator, and the solid outlet of the aforementioned first cyclone separator is connected to the aforementioned lower bubbling bed section through the aforementioned first return feeder. The oxygen carrier after reaction in the fuel reactor is conveyed to the bottom of the air reactor through the second return feeder. The top outlet of the air reactor is connected to the inlet of the second cyclone separator. The solid outlet of the second cyclone separator is connected to the middle lifting section through the third return feeder. The bottom of the aforementioned lower bubbling bed section is equipped with a fluidizing medium inlet and a fuel feed port.

[0007] This embodiment discloses a device for reducing the concentration of combustible gases in a chemical chaining combustion system. It employs a three-section variable-diameter fluidized bed structure, with the lower bubbling bed section, the middle lifting section, and the upper expansion and deceleration section sequentially connected in fluid. Furthermore, the highly reactive oxygen carrier regenerated from the air reactor is directionally transported to the middle lifting section via the third return feeder, providing sufficient residence time for fuel gasification and initial reaction. This strongly entrains the highly reactive oxygen carrier to the high-concentration combustible gas zone in the upper part of the reactor, promoting internal reflux of the oxygen carrier to extend residence time and reduce equipment wear risk. Consequently, this device for reducing the concentration of combustible gases in a chemical chaining combustion system offers the beneficial effects of improved reaction efficiency, reduced combustible gas concentration, increased fuel conversion rate, improved carbon dioxide capture purity, and prevention of subsequent equipment erosion and wear.

[0008] Optionally, the height-to-diameter ratio of the lower bubbling bed section is 2:1 to 5:1, and the fluidizing gas velocity is 1 m / s to 4 m / s.

[0009] This configuration provides ample space and residence time for fuel gasification and initial reduction reactions, ensuring sufficient initial fuel reaction. At the same time, the low fluidizing gas velocity avoids excessive wear and escape of oxygen carrier particles due to high gas velocity. While ensuring the initial conversion efficiency of fuel, it reduces particle loss and equipment erosion risk, creating favorable initial conditions for the subsequent coordinated optimization of gas-solid reaction in the aforementioned middle lifting section and the aforementioned upper diameter expansion and deceleration section, thus helping to achieve a balance between high system efficiency and low wear.

[0010] Optionally, the aforementioned middle lifting section adopts a constant diameter or reduced diameter structure, and the height-to-diameter ratio of the aforementioned middle lifting section is 3:1 to 10:1.

[0011] This design, on the one hand, combines a narrow or constant diameter design with a specific height-to-diameter ratio, which can naturally increase the gas velocity in this section to a rapid fluidization state of 3 / s to 14 m / s without increasing the total fluidizing air volume. This can strongly entrain the highly active fresh oxygen carrier transported by the third return feeder and directionally transport it to the upper part of the fuel reactor where the combustible gas concentration is high. On the other hand, the reasonable height-to-diameter ratio ensures that the oxygen carrier particles have sufficient transmission path and mixing space in the middle lifting section, which enhances the gas-solid two-phase mixing intensity and lays the foundation for the full reaction of the highly active oxygen carrier and combustible gas. At the same time, it avoids particle accumulation or poor transmission caused by improper structural design.

[0012] Optionally, the above-mentioned upper diameter expansion and deceleration section is a tapered gradually expanding structure with an angle of 10° to 30° between the sidewall and the vertical direction, or a stepped diameter expansion structure.

[0013] This configuration effectively reduces the high-speed gas-solid flow from the aforementioned middle lifting section to below 1 m / s to 4 m / s, causing the oxygen-carrying particles to separate under gravity and form an internal backflow along the sidewall of the aforementioned upper diameter-expanding deceleration section. This significantly extends their residence time in the upper critical reaction zone of the fuel reactor, facilitating a full reaction with the high-concentration combustible gas. In addition, it can significantly reduce the particle velocity and concentration entering the subsequent first cyclone separator, fundamentally mitigating the erosion and wear of the equipment caused by high-velocity particles, reducing particle wear rate and escape rate. At the same time, the two diameter-expanding structure designs can adapt to different operating conditions, ensuring the long-term reliability of the system while overcoming the predicament of increased wear due to high gas velocity in traditional technologies.

[0014] Optionally, the number of sidewalls of the above-mentioned upper diameter expansion and deceleration section is one side or both sides, and the oxygen carrier particles flow downward along the sidewalls to form internal particle reflux.

[0015] This configuration allows for flexible adaptation to different reactor spaces and operating conditions by arranging the sidewalls on one or both sides, avoiding problems such as insufficient backflow intensity or airflow disturbance caused by a single sidewall design. In addition, the internal particle backflow formed along the sidewall can transport the oxygen carrier particles back to the middle and even lower reaction zones, significantly increasing the concentration and residence time of the oxygen carrier in the upper key reaction zone of the fuel reactor. This helps it to fully react with high-concentration combustible gas to reduce combustible gas residue. At the same time, the backflow process does not require additional power, taking into account both improved reaction efficiency and system energy consumption control. Furthermore, combined with the diameter expansion and deceleration function, it enhances the ability to overcome the dual challenges of high-velocity wear and incomplete reaction.

[0016] Optionally, the top of the lower bubbling bed section is connected to the middle lifting section at any position, the middle lifting section is connected to the upper diameter expansion and deceleration section, and the cross-sectional shape of the top of the lower bubbling bed section, the middle lifting section, and the upper diameter expansion and deceleration section is rectangular, circular, or elliptical.

[0017] This design ensures a smooth transition between gas and solid phases, reducing airflow resistance and local eddies, and guaranteeing stable transport and reaction of oxygen-carrying particles. Furthermore, the variety of cross-sectional shapes allows for adaptation to different industrial scenarios' equipment sizes, installation space requirements, and material handling capacity needs, enhancing the device's versatility and compatibility. This facilitates flexible design of new systems and upgrades existing chemical looping combustion system fuel reactors, ensuring system reaction stability while reducing engineering application difficulty and cost.

[0018] Optionally, the reversing port of the third return feeder is located on the side wall of the middle lifting section, and the reversing port of the third return feeder is connected to the middle lifting section.

[0019] This configuration allows the highly reactive oxygen carrier, which has been oxidized and regenerated in the air reactor, to be directly injected into the high-speed airflow region of the aforementioned middle riser section. With the help of the high gas velocity in the middle riser section, it is rapidly entrained and directionally transported to the high-concentration combustible gas region in the upper part of the reactor, achieving a precise match between the highly reactive oxygen carrier and the high-concentration combustible gas, thereby enhancing reaction efficiency.

[0020] In one embodiment of this invention, a method for reducing the concentration of combustible gases in a chemical looping combustion system is also provided, comprising the following steps: Step 1: Control the fluidizing gas velocity of the lower bubbling bed section to 1 m / s to 4 m / s to provide residence time for fuel gasification and preliminary reduction reaction. At the same time, control the fluidizing gas velocity of the middle lifting section to 3 m / s to 14 m / s to use high gas velocity to entrain and lift oxygen carrier particles. Step 2: Through the gradual expansion structure of the upper expansion and deceleration section, the gas velocity entering this section is reduced to below 1m / s to 4m / s, which causes the oxygen carrier particles to decelerate, separate, and form internal backflow along the sidewall, thus prolonging the residence time of the oxygen carrier in the upper region of the fuel reactor. Step 3: The highly reactive oxygen carrier that has been oxidized and regenerated by the air reactor is transported to the middle lifting section through the third return feeder. The high gas velocity in the middle lifting section will preferentially distribute the highly reactive oxygen carrier in the upper reaction area of ​​the fuel reactor. Step four: Combining the internal circulation formed by the first cyclone separator and the first return feeder with the external circulation formed by the second return feeder, the second cyclone separator, and the third return feeder, the particle distribution and reaction efficiency within the system are optimized, and the concentration of combustible gas is reduced.

[0021] Optionally: In step one, by adjusting the cross-sectional area ratio between the lower bubbling bed section and the middle lifting section, the middle lifting section can naturally form an operating air velocity of 3m / s to 14m / s without changing the total fluidizing air volume.

[0022] This configuration eliminates the need for additional power equipment such as fans to increase the gas velocity, thus avoiding increased system energy consumption and structural complexity. Furthermore, while maintaining a low gas velocity of 1m / s to 4m / s in the lower bubbling bed section to meet the requirements of fuel gasification and initial reaction and reduce particle wear, the middle lifting section utilizes high gas velocity to powerfully entrain and transport highly reactive oxygen carriers to the upper part of the reactor. This achieves a synergistic effect of "low-consumption and stable reaction in the lower section, and efficient particle transport in the middle section." It not only solves the problem of "incomplete reaction at low gas velocity" in traditional technologies but also avoids the risk of increased wear caused by overall gas velocity increases, ensuring a balance between high efficiency and low consumption in the system.

[0023] Optionally, in step two, the residence time of the oxygen carrier particles in the upper region of the fuel reactor is extended to 7 to 10 seconds, and the carbon dioxide volume concentration at the outlet of the fuel reactor is increased to over 95%.

[0024] This configuration extends the residence time of oxygen carrier particles in the upper region of the fuel reactor to 7-10 seconds, ensuring sufficient contact and reaction time between the oxygen carrier and the high-concentration combustible gas in the upper and middle parts. This significantly improves the conversion efficiency of combustible gas and reduces unreacted combustible gas residue. Simultaneously, it increases the carbon dioxide volume concentration at the fuel reactor outlet to over 95%, directly meeting the requirements for high-purity carbon dioxide capture. This aligns with the core objective of chemical looping combustion technology to achieve efficient carbon capture. It not only solves the problems of incomplete reaction and low carbon dioxide purity caused by insufficient residence time of the oxygen carrier in traditional technologies but also reduces the processing difficulty and cost of subsequent carbon capture stages, further solidifying the technical foundation for carbon neutrality applications of chemical looping combustion systems in thermal power and industrial heating sectors.

[0025] Optionally: In step three, the particle size of the aforementioned highly active oxygen carrier is 200. ~300 Furthermore, the volume fraction of the highly active oxygen carrier in the aforementioned middle elevation section remains stable at 1% to 5%.

[0026] This configuration serves two purposes. First, oxygen carriers within this particle size range are easily and stably entrained by the high gas velocity of 3m / s to 14m / s in the central lift section, avoiding excessive escape due to excessively small particle size or difficulty in transport due to excessively large particle size. Second, a stable volume fraction of 1% to 5% ensures sufficient contact between the gas and solid phases in the central lift section, providing ample active material for the subsequent transport of oxygen carriers to the upper part of the reactor to react with high-concentration combustible gases. This not only ensures the rate and depth of the reduction reaction and reduces combustible gas residue, but also avoids airflow blockage caused by excessively high oxygen carrier concentration or insufficient reaction caused by excessively low concentration. This further helps the system achieve a balance between high-efficiency reaction and low wear, improving the purity of carbon dioxide capture.

[0027] In summary, the device and method for reducing the concentration of combustible gases in a chemical looping combustion system disclosed in this invention have the beneficial effects of improving reaction efficiency, reducing the concentration of combustible gases, increasing fuel conversion rate, improving the purity of carbon dioxide capture, and avoiding erosion and wear of subsequent equipment. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of a device for reducing the concentration of combustible gases in a chemical chaining combustion system according to an embodiment of the present invention.

[0030] Icons: 1-Fuel reactor, 2-Air reactor, 3-First cyclone separator, 4-First return feeder, 5-Second return feeder, 6-Second cyclone separator, 7-Third return feeder, 8-Lower bubbling bed section, 9-Middle lifting section, 10-Upper diameter expansion and deceleration section. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0032] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0033] Example 1 See Figure 1 This embodiment proposes a device for reducing the concentration of combustible gases in a chemical looping combustion system, including a fuel reactor 1, an air reactor 2, a first cyclone separator 3, a first return feeder 4, a second return feeder 5, a second cyclone separator 6, and a third return feeder 7. The fuel reactor 1 is provided with a lower bubbling bed section 8, a middle lifting section 9 and an upper expansion and deceleration section 10 in series from bottom to top, which together constitute a three-section variable diameter fluidized bed reactor; the cross-sectional area of ​​the middle lifting section 9 is smaller than that of the lower bubbling bed section 8, and the cross-sectional area of ​​the upper expansion and deceleration section 10 gradually expands from its inlet upwards. The top gas outlet of the upper diameter expansion and deceleration section 10 is connected to the inlet of the first cyclone separator 3, and the solid outlet of the first cyclone separator 3 is connected to the lower bubbling bed section 8 through the first return feeder 4. The oxygen carrier after reaction in fuel reactor 1 is conveyed to the bottom of air reactor 2 through the second return feeder 5. The top outlet of air reactor 2 is connected to the inlet of second cyclone separator 6. The solid outlet of second cyclone separator 6 is connected to the middle lifting section 9 through the third return feeder 7. The bottom of the lower bubbling bed section 8 is equipped with a fluidizing medium inlet (not shown in the figure) and a fuel feed inlet (not shown in the figure).

[0034] See Figure 1The device for reducing the concentration of combustible gases in a chemical chaining combustion system disclosed in this embodiment adopts a three-section variable-diameter fluidized bed structure in which the lower bubbling bed section 8, the middle lifting section 9, and the upper diameter expansion and deceleration section 10 are sequentially fluidly connected. Furthermore, the highly reactive oxygen carrier regenerated from the air reactor 2 is directionally transported to the middle lifting section 9 via the third return feeder 7, providing sufficient residence time for fuel gasification and initial reaction. This strongly entrains the highly reactive oxygen carrier to the high-concentration combustible gas zone in the upper part of the reactor, promoting internal reflux of the oxygen carrier to extend the residence time and reduce the risk of equipment wear. Consequently, this device for reducing the concentration of combustible gases in a chemical chaining combustion system has the beneficial effects of improved reaction efficiency, reduced combustible gas concentration, increased fuel conversion rate, improved carbon dioxide capture purity, and prevention of subsequent equipment erosion and wear.

[0035] See Figure 1 The lower bubbling bed section 8 has a height-to-diameter ratio of 2:1 to 5:1 and a fluidizing gas velocity of 1 m / s to 4 m / s. This provides sufficient space and residence time for fuel gasification and initial reduction reactions, ensuring sufficient initial fuel reaction. At the same time, the low fluidizing gas velocity can avoid excessive wear and escape of oxygen carrier particles due to high gas velocity. While ensuring the initial conversion efficiency of fuel, it reduces particle loss and equipment erosion risk, creating good initial conditions for the subsequent synergistic optimization of gas-solid reaction in the middle lifting section 9 and the upper diameter expansion and deceleration section 10, and helping to achieve a balance between efficient system reaction and low wear.

[0036] The middle lifting section 9 adopts a constant-diameter or reduced-diameter structure, and the height-to-diameter ratio of the middle lifting section 9 is 3:1 to 10:1. On the one hand, the reduced-diameter or constant-diameter design combined with a specific height-to-diameter ratio can naturally increase the gas velocity of this section to a rapid fluidization state of 3 / s to 14m / s without increasing the total fluidizing air volume. This can strongly entrain the highly active fresh oxygen carrier conveyed by the third return feeder 7 and directionally transport it to the upper part of the fuel reactor 1 where the concentration of combustible gas is high. On the other hand, the reasonable height-to-diameter ratio ensures that the oxygen carrier particles have sufficient transmission path and mixing space in the middle lifting section 9, which enhances the gas-solid two-phase mixing intensity and lays the foundation for the full reaction of the highly active oxygen carrier and combustible gas. At the same time, it avoids particle accumulation or poor transmission caused by improper structural design.

[0037] See Figure 1The upper expansion and deceleration section 10 is a tapered, gradually expanding structure with a sidewall angle of 10° to 30° with the vertical direction, or a stepped expansion structure. This effectively decelerates the high-speed gas-solid flow from the middle lifting section 9 to below 1 m / s to 4 m / s, causing the oxygen-carrying particles to separate under gravity and form an internal backflow along the sidewall of the upper expansion and deceleration section 10. This significantly extends their residence time in the upper key reaction zone of the fuel reactor 1, helping them to fully react with high-concentration combustible gases. In addition, it can significantly reduce the particle velocity and concentration entering the subsequent first cyclone separator 3, fundamentally reducing the erosion and wear of the equipment caused by high-velocity particles, and reducing the particle wear rate and escape rate. At the same time, the two expansion structure designs can adapt to different operating conditions, ensuring the long-term reliability of the system while overcoming the dilemma of increased wear due to high gas velocity in traditional technologies.

[0038] The upper expansion and deceleration section 10 has one or two sidewalls, and the oxygen carrier particles flow downward along the sidewalls to form internal particle reflux. This single or double sidewall arrangement can flexibly adapt to different reactor spaces and operating conditions, avoiding insufficient reflux intensity or airflow disturbance problems caused by a single sidewall design. In addition, the internal particle reflux formed along the sidewalls can transport the oxygen carrier particles back to the middle and even lower reaction zones, significantly increasing the concentration and residence time of the oxygen carrier in the upper key reaction zone of the fuel reactor 1, helping it to fully react with high-concentration combustible gas to reduce combustible gas residue. At the same time, the reflux process does not require additional power drive, taking into account both reaction efficiency improvement and system energy consumption control. This, combined with the expansion and deceleration function, strengthens the solution to the dual dilemmas of high gas velocity abrasion and incomplete reaction.

[0039] The top of the lower bubbling bed section 8 is connected to the middle lifting section 9 at any position. The middle lifting section 9 is connected to the upper expansion and deceleration section 10. The cross-sectional shape of the top of the lower bubbling bed section 8, the middle lifting section 9, and the upper expansion and deceleration section 10 is rectangular, circular, or elliptical. On the one hand, this ensures a smooth transition between the gas and solid flows, reduces airflow resistance and local eddies, and ensures stable transport and reaction of oxygen-carrying particles. On the other hand, various cross-sectional shapes can be adapted to the equipment size, installation space, and material handling capacity requirements of different industrial scenarios, improving the versatility and compatibility of the device. This facilitates the flexible design of new systems and the upgrading and transformation of existing chemical looping combustion system fuel reactors 1, reducing the difficulty and cost of engineering applications while ensuring the stability of the system reaction.

[0040] See Figure 1The return port of the third return feeder 7 is located on the side wall of the middle lifting section 9, with the lower edge of the return port of the third return feeder 7 located more than 0.8m above the bottom of the middle lifting section 9. This allows the highly reactive oxygen carrier, which has been oxidized and regenerated by the air reactor 2, to be directly injected into the high-speed airflow area of ​​the middle lifting section 9. With the help of the high gas velocity of the middle lifting section 9, it is quickly entrained and directionally transported to the high-concentration combustible gas area in the upper part of the reactor, achieving precise matching between the highly reactive oxygen carrier and the high-concentration combustible gas, thus enhancing reaction efficiency. In addition, the specific height of the return port avoids the accumulation problem caused by the oxygen carrier falling directly into the low gas velocity area at the bottom of the middle lifting section 9, and also prevents the oxygen carrier from having an excessively high return port, resulting in a short transport path and insufficient mixing. This ensures that the oxygen carrier participates stably in the reaction, further helping to overcome the technical dilemma of incomplete reaction at low gas velocity and increased wear at high gas velocity, and improving the stability of system operation.

[0041] See Figure 1 In one embodiment of this invention, a method for reducing the concentration of combustible gases in a chemical looping combustion system is also provided, comprising the following steps: Step 1: Control the fluidizing gas velocity of the lower bubbling bed section 8 to 1 m / s to 4 m / s to provide residence time for fuel gasification and preliminary reduction reaction. At the same time, control the fluidizing gas velocity of the middle lifting section 9 to 3 m / s to 14 m / s to use high gas velocity to entrain and lift oxygen carrier particles. Step 2: Through the gradual expansion structure of the upper diameter expansion and deceleration section 10, the gas velocity entering this section is reduced to below 1m / s to 4m / s, which causes the oxygen carrier particles to decelerate, separate, and form internal reflux along the sidewall, thus prolonging the residence time of the oxygen carrier in the upper region of the fuel reactor 1. Step 3: The highly active oxygen carrier regenerated by oxidation in the air reactor 2 is transported to the middle lifting section 9 through the third return feeder 7. With the help of the high air velocity in the middle lifting section 9, the highly active oxygen carrier is preferentially distributed in the upper reaction area of ​​the fuel reactor 1. Step four: The internal circulation formed by the first cyclone separator 3 and the first return feeder 4 works synergistically with the external circulation formed by the second return feeder 5, the second cyclone separator 6 and the third return feeder 7 to optimize the particle distribution and reaction efficiency within the system and reduce the concentration of combustible gas.

[0042] See Figure 1In step one, by adjusting the cross-sectional area ratio of the lower bubbling bed section 8 and the middle lifting section 9, the middle lifting section 9 naturally forms an operating gas velocity of 3m / s to 14m / s without changing the total fluidizing air volume. This eliminates the need for additional power equipment such as fans to increase the gas velocity, avoiding increased system energy consumption and structural complexity. In addition, while ensuring that the lower bubbling bed section 8 maintains a low gas velocity of 1m / s to 4m / s to meet the requirements of fuel gasification and preliminary reaction and reduce particle wear, the middle lifting section 9 uses a high gas velocity to strongly entrain and transport highly active oxygen carriers to the upper part of the reactor, achieving a synergistic effect of "low-consumption and stable reaction in the lower part, and efficient particle transport in the middle part". This not only solves the problem of "incomplete reaction at low gas velocity" in traditional technology, but also avoids the risk of increased wear caused by increasing the overall gas velocity, ensuring a balance between high efficiency and low consumption in the system.

[0043] See Figure 1 In step two, the residence time of the oxygen carrier particles in the upper region of fuel reactor 1 is extended to 7 to 10 seconds, and the carbon dioxide volume concentration at the outlet of fuel reactor 1 is increased to over 95%. Extending the residence time of the oxygen carrier particles in the upper region of fuel reactor 1 to 7 to 10 seconds can fully guarantee the contact reaction time between the oxygen carrier and the high concentration of combustible gas in the upper part, significantly improving the conversion efficiency of combustible gas and reducing the residue of unreacted combustible gas. At the same time, the carbon dioxide volume concentration at the outlet of fuel reactor 1 is increased to over 95%, directly meeting the requirements for high-purity carbon dioxide capture. This aligns with the core objective of chemical looping combustion technology to achieve efficient carbon capture. It not only solves the problems of incomplete reaction and low carbon dioxide purity caused by insufficient residence time of oxygen carrier in traditional technologies, but also reduces the processing difficulty and cost of subsequent carbon capture stages of the system, further consolidating the technical foundation for the application of chemical looping combustion systems in the fields of thermal power and industrial heating for carbon neutrality.

[0044] See Figure 1 In step three, the particle size of the highly active oxygen carrier is 200. ~300 Furthermore, the volume fraction of the highly active oxygen carrier within the middle riser section 9 is consistently maintained at 1%–5%. On one hand, oxygen carriers within this particle size range are easily and stably entrained by the high gas velocity of 13 m / s–14 m / s in the middle riser section 9, avoiding excessive escape due to excessively small particle size or difficulty in transport due to excessively large particle size. On the other hand, the stable volume fraction of 1%–5% ensures sufficient contact between the gas and solid phases within the middle riser section 9, providing sufficient active material for the subsequent transport of the oxygen carrier to the upper part of the reactor to react with the high concentration of combustible gas. This not only ensures the rate and depth of the reduction reaction and reduces combustible gas residue, but also avoids airflow blockage caused by excessively high oxygen carrier concentration or insufficient reaction caused by excessively low concentration. This further helps the system achieve a balance between high-efficiency reaction and low wear, and improves the purity of carbon dioxide capture.

[0045] See Figure 1 In this embodiment, the fuel reactor 1 includes a lower bubbling bed section 8, a middle lifting section 9 and an upper diameter expansion and deceleration section 10 that are fluidly connected from bottom to top, which together form a three-section variable diameter structure. The gas velocity in the lower bubbling bed section 8 is maintained at 1 m / s to 4 m / s in a bubbling fluidized state, and its height-to-diameter ratio is 2:1 to 5:1, providing sufficient residence time for fuel gasification and preliminary reduction reaction; the bottom of the lower bubbling bed section 8 is provided with a fluidized medium inlet and a fuel feed port. The cross-sectional area of ​​the middle lifting section 9 is smaller than that of the lower bubbling bed section 8, and its gas velocity increases accordingly to 3m / s to 14m / s, forming a rapid fluidization state. The height-to-diameter ratio is 3:1 to 10:1. This design is used to maintain low-speed fluidization in the lower bed while forming a high-speed airflow in the middle region, strongly entraining and lifting most of the highly active fresh oxygen carrier particles from the third return feeder 7, aiming to directionally enhance the gas-solid mixing intensity in the upper space of the fuel reactor 1. The cross-sectional area of ​​the upper expansion and deceleration section 10 is a tapered or stepped expansion structure from the highest point of the middle lifting section 9 upwards. It adopts a tapered expansion structure with a sidewall angle of 10° to 30° with the vertical direction, or a stepped expansion structure. The gas velocity in this area gradually decreases from the inlet to the outlet to below 1 m / s to 4 m / s. The core function of this structure is to effectively decelerate the high-speed gas-solid flow from the middle lifting section 9, so that the entrained oxygen-carrying particles can be initially separated under the action of gravity, and most of the particles are caused to fall slowly along the expanding sidewall surface, forming a strong internal particle backflow, returning to the middle and even lower reaction zones, thereby significantly extending the residence time of the oxygen-carrying material in the key reaction zone. At the same time, it effectively reduces the particle velocity and concentration entering the subsequent first cyclone separator 3, reducing the risk of equipment erosion and particle wear from the root. The top gas outlet of the upper expansion and deceleration section 10 is connected to the inlet of the first cyclone separator 3; the solid outlet of the first cyclone separator 3 is connected to the lower bubbling bed section 8 of the fuel reactor 1 through the first return feeder 4; the gas outlet of the first cyclone separator 3 is used to discharge the high carbon dioxide concentration flue gas from the fuel reactor 1. The oxygen carrier after reaction in fuel reactor 1 is transported to the bottom of air reactor 2 through the second return feeder 5; the top outlet of air reactor 2 is connected to the inlet of the second cyclone separator 6; the solid outlet of the second cyclone separator 6 is connected to the middle lifting section 9 of fuel reactor 1 through the third return feeder 7 to complete the external circulation of oxygen carrier; the gas outlet of the second cyclone separator 6 is used to discharge oxygen-deficient air. The oxygen carrier, fully oxidized and regenerated by the air reactor 2, has a high lattice oxygen content and strong oxidizing activity, and is called fresh oxygen carrier. The third return feeder 7 directly transports this highly active fresh oxygen carrier to the middle lift section 9 of the fuel reactor 1. Through the high gas velocity operation of the middle lift section 9, most of these highly active particles are directionally and rapidly lifted to the upper part of the fuel reactor 1, which happens to be the area with the highest concentration of combustible gas. This achieves precise matching and enhanced reaction between the highly active oxidized oxygen carrier and the high concentration of combustible gas in the most critical reaction space, greatly promoting the rate and depth of the reduction reaction, and fundamentally ensuring low combustible gas concentration and high carbon dioxide capture purity.

[0046] See Figure 1 In this embodiment, the lower part of the fuel reactor 1 is a bubbling bed structure, following the traditional reactor design; the middle part is transformed into a high-velocity lifting section by reducing the cross-sectional area; and the upper part is a gradually expanding deceleration section, allowing the oxygen-carrying particles to slow down in this area and fall slowly along the wall. This approach can directionally enhance the particle concentration and residence time of the oxygen-carrying particles in the upper part of the fuel reactor 1 while maintaining the existing advantages of low wear and high gas-solid contact efficiency, thereby fundamentally overcoming the aforementioned bottlenecks.

[0047] See Figure 1 In this embodiment, the innovative and synergistic structure of the bubbling bed, riser, and expansion section effectively solves the core contradiction of uneven gas-solid distribution and the difficulty in simultaneously addressing system wear in traditional fuel reactor 1. This design directionally enhances the concentration and residence time of oxygen-carrying particles in the upper region of the reactor, significantly improving the conversion efficiency of combustible gases and increasing the carbon dioxide purity at the outlet of fuel reactor 1 to over 95%. Simultaneously, it fundamentally avoids the risk of severe particle wear and equipment erosion caused by high gas velocities, ensuring the long-term reliability and economy of the system. By enhancing the local particle transport capacity, the dilemma of "incomplete reaction at low gas velocities" and "exacerbated wear at high gas velocities" is resolved. Furthermore, this solution has a simple structure, requiring no additional complex subsystems. It can be applied to new systems and is easy to upgrade existing fuel reactor 1, with low implementation costs and good compatibility. It provides a high-efficiency, stable, and low-consumption key equipment foundation for the large-scale industrial application of chemical looping combustion technology.

[0048] Specific beneficial effects: 1. Significantly improved reaction efficiency: By forcibly entraining particles through the high-velocity boosting section in the middle, the problem of insufficient oxygen carrier concentration in the upper part of fuel reactor 1 is effectively solved, allowing the combustible gas to fully contact and react with the oxygen carrier, greatly reducing the concentration of combustible gas in the tail flue gas, and improving fuel conversion rate and carbon dioxide capture purity.

[0049] 2. Effective control of system wear: The design of the upper diameter expansion section enables high-speed particles to be effectively decelerated and separated before entering the tail flue and cyclone separator, which fundamentally avoids the erosion and wear of the high-concentration, high-velocity particle flow on the subsequent equipment, reduces the mechanical wear rate and escape rate of the particles, and ensures the reliability of the system in long-term operation.

[0050] 3. Good economic efficiency: Without sacrificing the advantages of good gas-solid contact and long residence time of the bubbling bed, this design locally enhances the transmission capacity, solves the dilemma of "incomplete reaction at low gas velocity" and "intensified wear at high gas velocity", achieves a balance between high efficiency and low wear, and improves the overall economic efficiency of the system.

[0051] 4. Optimized Reaction Path and Synergistic Effect: By directly feeding the highly reactive fresh oxygen carrier to fuel reactor 1 via a return feeder, the lifting effect of this section precisely delivers it to the upper-middle space where the reaction is most needed. This synergistic design of the material circulation path and reactor structure achieves active and efficient mixing of reactants (combustible gas and high-oxygen carrier) in the optimal reaction zone, rather than relying on traditional passive diffusion—a feature not disclosed in existing technologies. It further amplifies the benefits of the three-stage structure, maximizing the improvement in reaction efficiency and the optimization of techno-economic performance.

[0052] Example 2 See Figure 1 Based on Example 1, this example is as follows: 1. System Construction and Startup: A chemical looping combustion system based on an industrial pilot-scale was constructed. Its core fuel reactor 1 adopts the segmented structure of this scheme, which is coaxially connected from top to bottom by an upper diameter expansion and deceleration section 10, a middle lifting section 9, and a lower bubbling bed section 8.

[0053] Lower bubbling bed section 8: Designed with a rectangular cross-section, measuring 4m × 2m, and a height of 8m (height-to-diameter ratio ~2:1). In this area, the apparent gas velocity is maintained at 3m / s (bubbling fluidization state), providing ample space for the gasification and initial reaction of lignite fuel.

[0054] Middle Lifting Section 9: Designed with a rectangular cross-section, measuring 1.5m × 2m, and a height of 8m (height-to-diameter ratio ~8:1). This design naturally increases the gas velocity flowing through this section to 8m / s, enabling powerful entrainment and lifting of oxygen-carrying particles.

[0055] Upper expansion and deceleration section 10: adopts a conical design (the angle between the sidewall and the vertical direction is 15°), and the top outlet size is restored to 4m×2m, which aims to decelerate the high-speed airflow and achieve gas-solid separation.

[0056] Air reactor 2 and the second return feeder 5 connecting fuel reactor 1 and air reactor 2, the first cyclone separator 3 and its first return feeder 4, the second cyclone separator 6 and its third return feeder 7 are all designed according to... Figure 1 The connection is shown. The return feed port from the third return feeder 7 to the fuel reactor 1 is located on the side wall of the middle lifting section 9, with its lower edge approximately 1 meter above the bottom of the middle lifting section 9.

[0057] The system uses a particle size D50 of 250. The performance of the ilmenite particles used as oxygen carriers and lignite as fuel was verified.

[0058] 2. Performance Comparison Test: 2.1 Conventional fuel reactor 1: A conventional constant-section bubbling bed fuel reactor 1, with a cross-section of 4m × 2m and a height of 16m, operates at a lower gas velocity of 3m / s. In the upper-middle region of the fuel reactor (above 18m), the average volume fraction of oxygen-carrying particles is less than 0.5%, and the residence time of these particles is short, with most rapidly circulating to the bottom. After stable operation, the concentration of combustible gas in the outlet flue gas of fuel reactor 1 is approximately 14.7% (of which carbon dioxide is approximately 9.0%). Approximately 5.0%, The concentration of carbon dioxide is approximately 84.5% (approximately 0.7%). Insufficient reaction intensity in the upper and middle parts leads to incomplete conversion of combustible gases, resulting in carbon loss and a decrease in carbon dioxide purity.

[0059] 2.2 Fuel reactor 1 in this scheme: In this design, the lower bubbling bed of fuel reactor 1 maintains a constant gas velocity of 3 m / s, while the gas velocity in this zone reaches 8 m / s through the central narrowing structure. The fully regenerated, highly reactive oxygen carrier output from air reactor 2 is directly injected into the high-speed airflow center region of the central lifting section 9 via the third return feeder 7 and its return port located 1 meter above the bottom of the central lifting section 9. These highly reactive particles are strongly entrained and lifted by the high-speed airflow in this section.

[0060] The volume fraction of oxygen-carrying particles in the middle riser section 9 stabilized at 1%–5%. The upper expansion section created a stable and strong internal particle recirculation, increasing the overall particle volume fraction in the upper region of fuel reactor 1 to 1%–5%, more than double that of the comparative example. The establishment of internal circulation extended the residence time of oxygen-carrying particles in the critical reaction zone to 7–10 seconds. At the same lignite feed rate, the system reached a steady state. Analysis of the flue gas at the outlet of fuel reactor 1 showed significant improvement, with a combustible gas volume concentration of approximately 3.2% (of which carbon dioxide was approximately 2.0%). Approximately 1.0%, The combustible gas concentration was approximately 0.2%, a decrease of 78.2% compared to conventional fuel reactor 1, while the carbon dioxide volume concentration was approximately 95%, an increase of 10.6% compared to conventional fuel reactor 1.

[0061] This solution successfully addresses the core challenge of uneven gas-solid distribution on an industrial scale. Increased gas velocity and optimized structure ensure efficient delivery of the active oxygen carrier to the upper part of the reactor, where it is thoroughly mixed and reacted with all combustible gases. This reduces the concentration of unburned gases to extremely low levels, achieving a significant leap in combustion efficiency and carbon dioxide capture purity.

[0062] 3. Simplified solution comparison test: 3.1 Lower bubbling bed section 8 + upper diameter expansion and deceleration section 10: Structure: The middle lifting section 9 is removed, and the upper expansion and deceleration section 10 is directly connected to the lower bubbling bed section 8. The outlet of the upper expansion and deceleration section 10 is still connected to the inlet of the first cyclone separator 3. The overall height of the device remains unchanged, forming a simple "bubbling bed ~ expansion bed" structure. The air velocity in the lower bubbling bed section 8 is maintained at 3 m / s.

[0063] Results: Due to the lack of high-velocity entrainment in the middle booster section 9, the oxygen-carrying particles were difficult to effectively lift to the upper part of the reactor. The booster section alone could only increase the particle concentration in the lower part of the upper expansion section, thus reducing the combustible gas concentration to some extent. The combustible gas volume concentration in the outlet flue gas was as high as 12.1%, while the carbon dioxide concentration was only 86.5%. These results indicate that without a forced booster, the expansion section alone cannot solve the problem of insufficient particle concentration in the upper and middle parts.

[0064] 3.2, Lower bubbling bed section 8 + Middle lifting section 9: Structure: The upper expansion and deceleration section 10 is removed, and the height of the middle lifting section 9 is increased so that its outlet is directly connected to the inlet of the first cyclone separator 3. The overall height of the device remains unchanged, forming a "bubbling bed ~ lifting pipe" structure. The air velocity in the lower bubbling bed is 3 m / s, and the air velocity in the middle lifting section 9 is 8 m / s.

[0065] Results: The central lift section 9 effectively entrained particles, enhancing mixing in the middle of the reactor. The volume concentration of combustible gas in the outlet flue gas was approximately 5.5%, and the volume concentration of carbon dioxide was approximately 89%. However, the direct impact of the high-speed gas-solid flow on the cyclone separator significantly increased the risk of particle wear and equipment erosion, making long-term stable operation impossible. The results indicate that the lack of a diameter-expanding deceleration section makes it impossible to solve the wear problem caused by high gas velocities.

[0066] In summary, this embodiment, through a system comparison of the traditional scheme, two simplified schemes, and the three-stage structure of this scheme, fully demonstrates the necessity and synergy of the design: the traditional bubbling bed fuel reactor 1 suffers from incomplete reaction due to insufficient particle volume fraction (<0.5%) in the upper and middle parts, resulting in a combustible gas concentration as high as 14.7%; the bubbling bed + expansion section scheme lacks forced lifting capability, resulting in an upper particle volume fraction still below 1%, and the combustible gas concentration only decreasing to 12.1%; the bubbling bed + lifting section scheme, while improving the reaction efficiency in the middle part (combustible gas concentration 5.5%), leads to a surge in system wear rate of 180%, rendering it impractical. Only the complete three-stage structure of this scheme, through the enhanced particle entrainment in the middle lifting section 9 (gas velocity 8m / s), raises the concentration in the upper and middle parts to 15-20%, and combined with the upper expansion section, controls the cyclone separator wear rate to a reasonable range of only 15% increase. Simultaneously, through a direct supply strategy of highly active oxygen carrier, it ultimately achieves excellent results, with the combustible gas concentration reduced to a minimum of 3.2% and the carbon dioxide concentration reaching a maximum of 95.1%. These three structural sections are interdependent and complementary in function. The lifting section solves the problem of reaction efficiency, while the diameter expansion section solves the wear problem caused by the lifting section. Together, they overcome the technical contradiction between "incomplete reaction at low gas speed" and "intensified wear at high gas speed". The overall effect is far superior to any local improvement scheme, which fully demonstrates the non-obvious innovation and engineering application value of this scheme.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A device for reducing the concentration of combustible gases in a chemical looping combustion system, characterized in that: It includes a fuel reactor (1), an air reactor (2), a first cyclone separator (3), a first return feeder (4), a second return feeder (5), a second cyclone separator (6), and a third return feeder (7); The fuel reactor (1) is provided with a lower bubbling bed section (8), a middle lifting section (9) and an upper diameter expansion and deceleration section (10) in sequential order from bottom to top; the cross-sectional area of ​​the middle lifting section (9) is smaller than that of the lower bubbling bed section (8), and the cross-sectional area of ​​the upper diameter expansion and deceleration section (10) gradually expands upward from its inlet. The top gas outlet of the upper diameter expansion and deceleration section (10) is connected to the inlet of the first cyclone separator (3), and the solid outlet of the first cyclone separator (3) is connected to the lower bubbling bed section (8) through the first return feeder (4). The oxygen carrier after reaction in the fuel reactor (1) is transported to the bottom of the air reactor (2) through the second return feeder (5). The top outlet of the air reactor (2) is connected to the inlet of the second cyclone separator (6). The solid outlet of the second cyclone separator (6) is connected to the middle lifting section (9) through the third return feeder (7). The bottom of the lower bubbling bed section (8) is provided with a fluidized medium inlet and a fuel feed port.

2. The device for reducing the concentration of combustible gases in a chemical looping combustion system according to claim 1, characterized in that: The height-to-diameter ratio of the lower bubbling bed section (8) is 2:1 to 5:1, and the fluidizing gas velocity is 1 m / s to 4 m / s.

3. The device for reducing the concentration of combustible gases in a chemical looping combustion system according to claim 1, characterized in that: The middle lifting section (9) adopts a structure with the same diameter or a reduced diameter, and the height-to-diameter ratio of the middle lifting section (9) is 3:1 to 10:

1.

4. The device for reducing the concentration of combustible gases in a chemical looping combustion system according to claim 1, characterized in that: The upper diameter expansion and deceleration section (10) is a tapered gradually expanding structure with an angle of 10° to 30° between the sidewall and the vertical direction, or a stepped diameter expansion structure.

5. The device for reducing the concentration of combustible gases in a chemical looping combustion system according to claim 1, characterized in that: The upper diameter expansion and deceleration section (10) has one or two sidewall arrangements, and the oxygen carrier particles flow downward along the sidewall to form internal particle reflux.

6. The device for reducing the concentration of combustible gases in a chemical looping combustion system according to claim 1, characterized in that: The top of the lower bubbling bed section (8) is connected to the middle lifting section (9) at any position. The middle lifting section (9) is connected to the upper diameter expansion and deceleration section (10). The cross-sectional shape of the top of the lower bubbling bed section (8), the middle lifting section (9) and the upper diameter expansion and deceleration section (10) is rectangular, circular or elliptical.

7. The device for reducing the concentration of combustible gases in a chemical looping combustion system according to claim 1, characterized in that: The return port of the third return feeder (7) is located on the side wall of the middle lifting section (9), and the third return feeder (7) is connected to the middle lifting section (9).

8. A method for reducing the concentration of combustible gases in a chemical looping combustion system using the device according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Control the fluidizing gas velocity of the lower bubbling bed section (8) to 1 m / s to 4 m / s to provide residence time for fuel gasification and preliminary reduction reaction. At the same time, control the fluidizing gas velocity of the middle lifting section (9) to 3 m / s to 14 m / s to use high gas velocity to entrain and lift oxygen carrier particles. Step 2: Through the gradual expansion structure of the upper expansion deceleration section (10), the gas velocity entering the section is reduced to below 1m / s to 4m / s, which causes the oxygen carrier particles to decelerate, separate and form internal backflow along the side wall, thus prolonging the residence time of the oxygen carrier in the upper region of the fuel reactor (1). Step 3: The highly active oxygen carrier that has been oxidized and regenerated by the air reactor (2) is transported to the middle lifting section (9) through the third return feeder (7). With the help of the high gas velocity of the middle lifting section (9), the highly active oxygen carrier is preferentially distributed in the upper reaction area of ​​the fuel reactor (1). Step four: The internal circulation formed by the first cyclone separator (3) and the first return feeder (4) works synergistically with the external circulation formed by the second return feeder (5), the second cyclone separator (6) and the third return feeder (7) to optimize the particle distribution and reaction efficiency in the system and reduce the concentration of combustible gas.

9. The method for reducing the concentration of combustible gases in a chemical looping combustion system according to claim 8, characterized in that: In step one, by adjusting the cross-sectional area ratio of the lower bubbling bed section (8) to the middle lifting section (9), the middle lifting section (9) is made to naturally form an operating air velocity of 3m / s to 14m / s without changing the total fluidizing air volume.

10. The method for reducing the concentration of combustible gases in a chemical looping combustion system according to claim 8, characterized in that: In step two, the residence time of the oxygen carrier particles in the upper region of the fuel reactor (1) is extended to 7 to 10 seconds, and the carbon dioxide volume concentration at the outlet of the fuel reactor (1) is increased to over 95%.

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