Biomass decoupled fluidized bed oxy-combustion system and method

Abstract

This invention provides a biomass decoupled fluidized bed oxy-fuel combustion system and method. The oxy-fuel combustion system includes a biomass decoupled fluidized bed oxy-fuel combustion unit, a flue gas waste heat recovery unit, an O2 / flue gas mixing and circulation unit, an oxygen supply unit, and a flue gas treatment and compression unit. This invention achieves oxy-fuel combustion of biomass by mixing oxygen prepared by the oxygen supply unit with a portion of the circulating flue gas, thereby obtaining high-concentration CO2 flue gas for compression, capture, and storage. Simultaneously, the combustion process is decoupled into biomass pyrolysis and co-combustion of semi-coke volatiles, utilizing the volatiles to reduce NO produced during semi-coke combustion. x A small amount of secondary air is supplied to complete the combustion process. The decoupled fluidized bed oxygen-enriched combustion method for biomass proposed in this invention can effectively reduce NOx emissions from biomass combustion. x It achieves CO2 capture and negative carbon emissions from raw emissions, with low energy consumption and strong system temperature control stability.

Description

Technical Field

[0001] This invention relates to the field of biomass combustion and negative carbon emission technology, and in particular to a biomass decoupled fluidized bed oxygen-enriched combustion system and method. Background Technology

[0002] Oxygen-enriched combustion technology, as a CO2 capture and storage technology during combustion, organizes the combustion process through air separation oxygen production and partial flue gas recirculation to obtain high-concentration CO2 flue gas (>80%), which is then purified, compressed, and landfilled or utilized. Biomass oxygen-enriched combustion boilers can operate in a high-oxygen-concentration atmosphere, reducing the amount of combustion flue gas and the boiler body volume, thus lowering the initial investment. Simultaneously, this technology reduces the thermal NO content of the combustion process by removing N2. x NO is generated and used in the combustion process. x Emission reduction. However, the large-scale application of this technology still faces the following problems: 1) The addition of air separation oxygen production systems and flue gas recirculation significantly increases the operating costs of oxygen-enriched combustion systems, resulting in a decrease in power generation efficiency of about 10%, thus hindering the large-scale commercial application of this technology; 2) Traditional oxygen-enriched combustion is prone to localized peak temperature increases and heat flux fluctuations, which may lead to the risk of localized slagging in the furnace; 3) This technology targets fuel-type NO in the combustion process of high-nitrogen biomass feedstocks. x The generation was not controlled, causing the original NO to... x Emissions may be too high, so denitrification devices such as SCR are needed for nitrogen removal.

[0003] To address the aforementioned shortcomings, this invention proposes a biomass decoupled fluidized bed oxygen-enriched combustion system and method. Utilizing the coupling of biomass oxygen-enriched combustion and decoupled combustion, the peak temperature of the main combustion zone in the furnace is reduced through coordinated regulation of flue gas recirculation and decoupled zoned heat release, while simultaneously reducing fuel-type NO. x The goal is to ultimately achieve CO2 capture and storage and "negative carbon emissions". Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides a biomass decoupled fluidized bed oxygen-enriched combustion system and method, aiming to achieve CO2 capture while reducing the original NO from biomass combustion. x Emissions are reduced by absorbing fluctuating green electricity to decrease the cost of oxygen production from biomass oxygen-enriched combustion and air separation, while simultaneously producing and selling high-purity H2.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a biomass decoupled fluidized bed oxygen-enriched combustion system, the oxygen-enriched combustion system comprising a biomass decoupled fluidized bed oxygen-enriched combustion unit, a flue gas waste heat recovery unit, an O2 / flue gas mixing and circulation unit, an oxygen supply unit, and a flue gas treatment and compression unit.

[0007] The biomass decoupled fluidized bed oxygen-enriched combustion unit includes a biomass pyrolysis reactor, a circulating fluidized bed riser, and a gas-solid separation component. The solid phase outlet of the biomass pyrolysis reactor is connected to the solid phase inlet of the circulating fluidized bed riser, the gas phase outlet of the biomass pyrolysis reactor is connected to the gas phase inlet in the middle of the circulating fluidized bed riser, the material outlet of the circulating fluidized bed riser is connected to the material inlet of the gas-solid separation component, and the solid phase outlet of the gas-solid separation component is connected to the solid phase inlet of the biomass pyrolysis reactor. The biomass pyrolysis reactor is also provided with a raw material inlet.

[0008] The heat source inlet of the flue gas waste heat recovery unit is connected to the gas phase outlet of the gas-solid separation component. The heat source outlet of the flue gas waste heat recovery unit is connected to the first gas phase inlet of the O2 / flue gas mixing and circulation unit. The first gas phase outlet of the O2 / flue gas mixing and circulation unit is connected to the gas phase inlet of the flue gas treatment and compression unit. The second gas phase inlet of the O2 / flue gas mixing and circulation unit is connected to the oxygen outlet of the oxygen supply unit and the circulating flue gas outlet of the flue gas treatment and compression unit, respectively. The second gas phase outlet of the O2 / flue gas mixing and circulation unit is divided into three branches: one branch is connected to the secondary air inlet of the circulating fluidized bed riser, one branch is connected to the fluidizing air inlet of the circulating fluidized bed riser, and one branch is connected to the gas phase inlet of the biomass pyrolysis reactor.

[0009] This invention achieves oxygen-enriched combustion of biomass by mixing oxygen produced by an oxygen supply unit with a portion of the recirculated flue gas, thereby obtaining high-concentration CO2 flue gas for compression, capture, and storage. Simultaneously, the combustion process is decoupled into biomass pyrolysis and co-combustion of semi-coke volatiles, utilizing the volatiles to reduce NO produced during semi-coke combustion. x By supplying a small amount of secondary air to complete the combustion process, and through the decoupled fluidized bed oxygen-enriched combustion method for biomass, NOx emissions from biomass combustion can be effectively reduced. x It achieves CO2 capture and negative carbon emissions from raw emissions, with low energy consumption and strong system temperature control stability.

[0010] As a preferred technical solution of the present invention, the flue gas waste heat recovery unit includes a high-temperature superheater, a low-temperature superheater and an economizer arranged sequentially along the airflow direction.

[0011] As a preferred embodiment of the present invention, the oxygen supply unit includes a power supply device and a water electrolysis device.

[0012] The power supply device in the oxygen supply unit of this invention uses green energy to power the water electrolysis device, which provides oxygen for the biomass oxygen-enriched combustion process through water electrolysis and co-produces high-purity H2 products.

[0013] Preferably, the power supply device includes a wind power supply device and / or a solar power supply device.

[0014] Preferably, the flue gas treatment compression unit includes a bag filter, a desulfurization tower, a flue gas condenser, and a three-way valve arranged sequentially along the airflow direction.

[0015] This invention compresses and seals high-concentration CO2, resulting in a CO2 concentration in flue gas exceeding 90%. The CO2 multi-stage compression device typically employs a three-stage compression with intermediate cooling to form liquid CO2 at 3 MPa and -10°C for transportation and storage.

[0016] Preferably, one outlet of the three-way valve is connected to the second gas phase inlet of the O2 / flue gas mixing and circulation unit, and the other outlet is connected to the CO2 multi-stage compression device.

[0017] As a preferred embodiment of the present invention, the biomass pyrolysis reactor includes a bubble bed biomass pyrolysis reactor.

[0018] Preferably, the gas-solid separation component includes a cyclone separator.

[0019] Secondly, the present invention provides a biomass decoupled fluidized bed oxygen-enriched combustion method, wherein the biomass decoupled fluidized bed oxygen-enriched combustion method is carried out in the oxygen-enriched combustion system described in the first aspect.

[0020] As a preferred technical solution of the present invention, the oxygen-enriched combustion method includes the following steps:

[0021] Biomass feedstock enters the biomass pyrolysis reactor through the feedstock inlet, where low-oxygen pyrolysis produces pyrolysis semi-coke and pyrolysis volatiles. The pyrolysis semi-coke enters the circulating fluidized bed riser through the solid phase inlet and is combusted under the action of fluidizing air. The pyrolysis volatiles enter the circulating fluidized bed riser through the gas phase inlet in the middle of the riser and mix with the flue gas generated at the bottom of the riser for further combustion. The resulting flue gas is separated by the gas-solid separation component. The solids are returned through the solid phase inlet of the biomass pyrolysis reactor to provide heat for the low-oxygen pyrolysis process, while the gaseous gases are recovered through the flue gas waste heat recovery system. After the heat is recovered by the heat recovery unit, the gas enters the O2 / flue gas mixing and circulation unit for gas heat exchange, and then enters the flue gas treatment and compression unit for gas treatment to obtain high-pressure CO2 gas. After the treatment is completed, part of the circulating flue gas returns to the O2 / flue gas mixing and circulation unit, where it forms a circulating gas with the oxygen produced by the oxygen supply unit. After preheating, it returns to the biomass decoupled fluidized bed oxygen-enriched combustion unit and enters the middle and bottom of the circulating fluidized bed riser through the secondary air inlet and fluidizing air inlet, respectively. Another stream of circulating gas enters the biomass pyrolysis reactor through the gas phase inlet of the biomass pyrolysis reactor to achieve low-oxygen pyrolysis of biomass.

[0022] The oxygen-enriched combustion method of this invention specifically includes: biomass raw materials are fed into a bubble bed biomass pyrolysis reactor via a screw feeder to undergo a low-oxygen rapid pyrolysis reaction, generating pyrolysis semi-coke which is then transported to the bottom of the riser. Pyrolysis volatiles (CH4, CO, H2, NH3, etc.) are fed into the middle of the riser to form NO. x In the reduction zone, biomass semi-coke undergoes an oxygen-enriched (O2 / CO2) combustion reaction in a fluidized bed riser. Subsequently, along with pyrolysis volatiles, it is completely burned under the action of secondary air, forming high-concentration CO2 flue gas which is discharged through a cyclone separator. After separation, the high-temperature bed material enters the bubbling bed pyrolysis reactor. The high-concentration CO2 flue gas then undergoes multi-stage processing through the flue gas waste heat recovery unit (passing sequentially through a high-temperature superheater, a low-temperature superheater, and an economizer), the O2 / flue gas mixing and circulation unit, and the flue gas treatment and compression unit (passing sequentially through a bag filter, a desulfurization tower, a flue gas condenser, and a three-way valve). After heat exchange, dust removal, desulfurization, and condensation purification, the gas is divided into two streams. One stream is used as recirculated flue gas for dilution and temperature control, forming a circulating gas with the oxygen produced by the oxygen supply unit. Together, they return to the biomass decoupled fluidized bed oxygen-enriched combustion unit to achieve cyclic combustion. The other stream is compressed to 3MPa through multiple stages and then subjected to geological storage or chemical synthesis to achieve CO2 capture and negative carbon emissions. Green electricity generated by wind or solar energy is used to electrolyze water to produce oxygen. The generated O2 is used as an oxidant for biomass oxygen-enriched combustion, and high-purity H2 is co-produced and sold.

[0023] The present invention feeds the pyrolysis volatiles into the middle of the riser to form a local reduction zone, which is used to reduce NO produced by the combustion of semi-coke.x To achieve NO x Primary emissions are reduced by 40-60%.

[0024] As a preferred embodiment of the present invention, the particle size of the biomass raw material is <8mm.

[0025] The raw materials used in this invention are widely adaptable and are not limited to carbon-neutral raw materials such as ordinary biomass, agricultural waste, forestry waste, and organic waste (kitchen waste, sludge, and mushroom residue).

[0026] As a preferred technical solution of the present invention, the low-oxygen pyrolysis temperature of the biomass pyrolysis reactor is 400-700℃, for example, it can be 400℃, 430℃, 460℃, 490℃, 520℃, 550℃, 580℃, 610℃, 640℃, 670℃ or 700℃, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0027] The heat required for pyrolysis in this invention is provided by the low-oxygen reaction of biomass and the high-temperature circulating bed material.

[0028] Preferably, the oxygen equivalent ratio in the biomass pyrolysis reactor is 0.1-0.25, for example, it can be 0.1, 0.13, 0.16, 0.19, 0.22 or 0.25, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] As a preferred technical solution of the present invention, the combustion temperature of the fluidized bed riser is 750-900℃, for example, it can be 750℃, 780℃, 810℃, 840℃, 870℃ or 900℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the total excess oxygen coefficient of the combustion unit of the fluidized bed riser is 1.15-1.3, for example, it can be 1.15, 1.18, 1.21, 1.24, 1.27 or 1.3, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] As a preferred technical solution of the present invention, the volume fraction of oxygen in the circulating gas is 25-40%, for example, it can be 25%, 28%, 31%, 34%, 37% or 40%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 30-35%.

[0032] The proportion of recirculated flue gas in this invention is 50-80% of the total flue gas volume, for example, it can be 50%, 55%, 60%, 65%, 70%, 75% or 80%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0034] (1) Low cost of CO2 enrichment and storage: This invention uses oxygen mixed circulating flue gas prepared by green electricity electrolysis of water as an oxidation medium to achieve oxygen-enriched combustion of biomass, which significantly increases the CO2 concentration in the flue gas (>90%), which is conducive to CO2 capture and storage and negative carbon emissions, while producing high-purity H2; compared with the traditional combustion process, the flue gas CO2 capture process can be eliminated, and the carbon capture cost and energy consumption are greatly reduced;

[0035] (2) NO x Significant emission reduction: By utilizing the volatile components (CH4, CO, H2, NH3, etc.) generated by biomass pyrolysis, NO produced by semi-coke combustion can be effectively reduced. x Reduce fuel NO x At the same time, combining O2 / CO2 combustion technology to eliminate thermal NO x It can achieve NO x Primary emissions are reduced by 40-60%, resulting in a reduction of pollutant emissions;

[0036] (3) Enhanced temperature control stability: Conventional oxygen-enriched combustion provides heat capacity to control the furnace temperature through recirculated flue gas dilution. This patent releases the oxidative combustion heat zone through biomass fluidized bed decoupling, making the heat release space distribution adjustable. The coordinated flue gas circulation control of furnace temperature can reduce the fluctuation of local peak temperature and heat flux, and improve the adaptability to fuel fluctuations.

[0037] (4) Reduced risk of slagging / corrosion in the furnace: By reducing the peak temperature of the riser tube in the main reaction zone, the driving force for the rapid formation and adhesion sintering of low-melting-point salts is reduced, thereby reducing the tendency of slagging, ash accumulation and high-temperature corrosion. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the biomass decoupled fluidized bed oxygen-enriched combustion system provided in Embodiment 1 of the present invention;

[0039] Among them, 1-circulating fluidized bed riser; 2-cyclone separator; 3-bubbling bed biomass pyrolysis reactor; 4-high temperature superheater; 5-low temperature superheater; 6-economizer; 7-water electrolysis device; 8-O2 / CO2 preheater; 9-bag filter; 10-desulfurization tower; 11-flue gas condenser; 12-CO2 multi-stage compression device. Detailed Implementation

[0040] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0041] It should be clarified that any use of the process provided in the embodiments of the present invention or any substitution or change of conventional data falls within the protection and disclosure scope of the present invention.

[0042] Example 1

[0043] This embodiment provides a biomass decoupled fluidized bed oxygen-enriched combustion system, which includes a biomass decoupled fluidized bed oxygen-enriched combustion unit, a flue gas waste heat recovery unit, an O2 / flue gas mixing and circulation unit, an oxygen supply unit, and a flue gas treatment and compression unit.

[0044] The biomass decoupled fluidized bed oxygen-enriched combustion unit includes a bubbling bed biomass pyrolysis reactor 3, a circulating fluidized bed riser 1, and a cyclone separator 2. The solid phase outlet of the bubbling bed biomass pyrolysis reactor 3 is connected to the solid phase inlet of the circulating fluidized bed riser 1, the gas phase outlet of the bubbling bed biomass pyrolysis reactor 3 is connected to the gas phase inlet in the middle of the circulating fluidized bed riser 1, the material outlet of the circulating fluidized bed riser 1 is connected to the material inlet of the cyclone separator 2, and the solid phase outlet of the cyclone separator 2 is connected to the solid phase inlet of the bubbling bed biomass pyrolysis reactor 3. The bubbling bed biomass pyrolysis reactor 3 is also provided with a raw material inlet.

[0045] The heat source inlet of the flue gas waste heat recovery unit is connected to the gas phase outlet of the cyclone separator 2. The heat source outlet of the flue gas waste heat recovery unit is connected to the first gas phase inlet of the O2 / flue gas mixing and circulation unit. The first gas phase outlet of the O2 / flue gas mixing and circulation unit is connected to the gas phase inlet of the flue gas treatment and compression unit. The second gas phase inlet of the O2 / flue gas mixing and circulation unit is connected to the oxygen outlet of the oxygen supply unit and the CO2 outlet of the flue gas treatment and compression unit, respectively. The second gas phase outlet of the O2 / flue gas mixing and circulation unit is divided into three branches: one branch is connected to the secondary air inlet of the circulating fluidized bed riser 1, one branch is connected to the fluidizing air inlet of the circulating fluidized bed riser 1, and one branch is connected to the gas phase inlet of the bubbling bed biomass pyrolysis reactor 3.

[0046] The flue gas waste heat recovery unit includes a high-temperature superheater 4, a low-temperature superheater 5, and an economizer 6 arranged sequentially along the airflow direction. The oxygen supply unit includes a wind / solar power supply device and a water electrolysis device 7. The flue gas treatment and compression unit includes a bag filter 9, a desulfurization tower 10, a flue gas condenser 11, and a three-way valve arranged sequentially along the airflow direction. One outlet of the three-way valve is connected to the second gas phase inlet of the O2 / flue gas mixing and circulation unit, and the other outlet is connected to the CO2 multi-stage compression device 12. The O2 / flue gas mixing and circulation unit includes an O2 / CO2 preheater 8.

[0047] Application Example 1

[0048] This application example provides a biomass decoupled fluidized bed oxygen-enriched combustion method, which is carried out in the biomass decoupled fluidized bed oxygen-enriched combustion system provided in Example 1. The oxygen-enriched combustion method includes:

[0049] Biomass straw with a particle size of <8mm is fed into the bubble bed biomass pyrolysis reactor via a screw feeder, where it undergoes a low-oxygen rapid pyrolysis reaction, generating pyrolysis semi-coke which is transported to the bottom of the riser. Pyrolysis volatiles are fed into the middle of the riser to form NO. x In the reduction zone, the temperature of the pyrolysis reactor is controlled at 500℃, the oxygen equivalent ratio is set to 0.2, and the heat required for pyrolysis is provided by the low-oxygen reaction of biomass and the high-temperature circulating bed material.

[0050] Biomass semi-coke undergoes oxygen-enriched (O2 / CO2) combustion in a fluidized bed riser, with the combustion temperature controlled at 800℃. The pyrolysis volatiles form a reduction zone to reduce the NO generated during the semi-coke combustion. x Secondary air is arranged at the top of the riser to burn off the remaining semi-coke particles and combustible gases. The total excess oxygen coefficient is set to 1.2, of which the oxygen demand of low-oxygen pyrolysis gas and semi-coke combustion accounts for 0.8 of the theoretical oxygen demand for complete combustion.

[0051] The high-concentration CO2 flue gas is discharged through a cyclone separator, and the separated high-temperature bed material enters the bubbling bed pyrolysis reactor. The high-concentration CO2 flue gas undergoes multi-stage heat exchange, dust removal, desulfurization, and condensation purification after passing through the flue gas waste heat recovery unit (passing sequentially through a high-temperature superheater, a low-temperature superheater, and an economizer), the O2 / flue gas mixing and circulation unit, and the flue gas treatment and compression unit (passing sequentially through a bag filter, a desulfurization tower, a flue gas condenser, and a three-way valve). It is then divided into two streams, one of which is used as recirculated flue gas for dilution and temperature control, and mixes with oxygen produced by the oxygen supply unit. The gas forms a circulating gas, which returns to the biomass decoupled fluidized bed oxygen-enriched combustion unit to achieve circulating combustion. The circulating flue gas accounts for 70% of the total flue gas volume, and the oxygen ratio in the O2 / flue gas mixture is controlled at 30%. Another stream of liquid CO2, compressed to 3MPa and -10℃ through multiple stages, is transported for geological storage or chemical synthesis, achieving CO2 capture and negative carbon emissions. Green electricity generated by wind or solar energy is used to electrolyze water to produce oxygen. The generated O2 is used as an oxidant for biomass oxygen-enriched combustion, and high-purity H2 is co-produced and sold.

[0052] Application Example 2

[0053] This application example provides a biomass decoupled fluidized bed oxygen-enriched combustion method. The only difference between this biomass decoupled fluidized bed oxygen-enriched combustion method and Application Example 1 is that the volume fraction of oxygen in the circulating gas is changed to 10%, while the rest is the same as Application Example 1.

[0054] Application Example 3

[0055] This application example provides a biomass decoupled fluidized bed oxygen-enriched combustion method. The only difference between this biomass decoupled fluidized bed oxygen-enriched combustion method and Application Example 1 is that the volume fraction of oxygen in the circulating gas is changed to 50%, while the rest is the same as Application Example 1.

[0056] Performance testing

[0057] The application examples and comparative examples provide a biomass decoupled fluidized bed oxygen-enriched combustion method for NO testing. x The results of the emission and CO2 compression concentration tests are shown in Table 1.

[0058] Table 1

[0059]

[0060] As can be seen from Table 1, the design of the biomass decoupled fluidized bed oxygen-enriched combustion system and method provided by this invention, after stable operation, results in a high NO content. x Emissions are lower than the original NO emissions from conventional biomass combustion x (Conventional combustion NO) x Emissions were reduced by 60% (to 250 ppm), and the CO2 compression sequestration concentration in the flue gas was 92%, effectively reducing NOx emissions from biomass combustion. x It achieves CO2 capture and negative carbon emissions from raw emissions, with low energy consumption and strong system temperature control stability.

[0061] Comparing Application Examples 1 and 2-3, it can be seen that the volume fraction of oxygen in the circulating gas has a significant impact on the NO content of the biomass decoupled fluidized bed oxygen-enriched combustion system. x Emissions and CO2 compression concentration have a significant impact. Too low an oxygen volume fraction leads to incomplete biomass combustion, resulting in low CO2 enrichment concentration in the flue gas and a substantial increase in compression energy consumption. Too high an oxygen volume fraction leads to higher localized combustion temperatures in biomass, making it easier for fuel nitrogen in biomass to be oxidized to NO, thus reducing the original NO content after decoupled combustion. x Emissions are significantly high, NO x The emission reduction effect has been greatly reduced.

[0062] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A biomass decoupled fluidized bed oxygen-enriched combustion system, characterized in that, The oxygen-enriched combustion system includes a biomass decoupled fluidized bed oxygen-enriched combustion unit, a flue gas waste heat recovery unit, an O2 / flue gas mixing and circulation unit, an oxygen supply unit, and a flue gas treatment and compression unit. The biomass decoupled fluidized bed oxygen-enriched combustion unit includes a biomass pyrolysis reactor, a circulating fluidized bed riser, and a gas-solid separation component. The solid phase outlet of the biomass pyrolysis reactor is connected to the solid phase inlet of the circulating fluidized bed riser, the gas phase outlet of the biomass pyrolysis reactor is connected to the gas phase inlet in the middle of the circulating fluidized bed riser, the material outlet of the circulating fluidized bed riser is connected to the material inlet of the gas-solid separation component, and the solid phase outlet of the gas-solid separation component is connected to the solid phase inlet of the biomass pyrolysis reactor. The biomass pyrolysis reactor is also provided with a raw material inlet. The heat source inlet of the flue gas waste heat recovery unit is connected to the gas phase outlet of the gas-solid separation component. The heat source outlet of the flue gas waste heat recovery unit is connected to the first gas phase inlet of the O2 / flue gas mixing and circulation unit. The first gas phase outlet of the O2 / flue gas mixing and circulation unit is connected to the gas phase inlet of the flue gas treatment and compression unit. The second gas phase inlet of the O2 / flue gas mixing and circulation unit is connected to the oxygen outlet of the oxygen supply unit and part of the flue gas circulation outlet of the flue gas treatment and compression unit. The second gas phase outlet of the O2 / flue gas mixing and circulation unit is divided into three branches: one branch is connected to the secondary air inlet of the circulating fluidized bed riser, one branch is connected to the fluidizing air inlet of the circulating fluidized bed riser, and one branch is connected to the gas phase inlet of the biomass pyrolysis reactor.

2. The oxygen-enriched combustion system according to claim 1, characterized in that, The flue gas waste heat recovery unit includes a high-temperature superheater, a low-temperature superheater, and an economizer arranged sequentially along the airflow direction.

3. The oxygen-enriched combustion system according to claim 1 or 2, characterized in that, The oxygen supply unit includes a power supply device and a water electrolysis device; Preferably, the power supply device includes a wind power supply device and / or a solar power supply device; Preferably, the flue gas treatment compression unit includes a bag filter, a desulfurization tower, a flue gas condenser, and a three-way valve arranged sequentially along the airflow direction; Preferably, one outlet of the three-way valve is connected to the second gas phase inlet of the O2 / flue gas mixing and circulation unit, and the other outlet is connected to the CO2 multi-stage compression device.

4. The oxygen-enriched combustion system according to any one of claims 1 to 3, characterized in that, The biomass pyrolysis reactor includes a bubble bed biomass pyrolysis reactor; Preferably, the gas-solid separation component includes a cyclone separator.

5. A biomass decoupled fluidized bed oxygen-enriched combustion method, characterized in that, The oxygen-enriched combustion method is carried out in the oxygen-enriched combustion system according to any one of claims 1 to 4.

6. The oxygen-enriched combustion method according to claim 5, characterized in that, The oxygen-enriched combustion method includes the following steps: Biomass feedstock enters the biomass pyrolysis reactor through the feedstock inlet, where low-oxygen pyrolysis produces pyrolysis semi-coke and pyrolysis volatiles. The pyrolysis semi-coke enters the circulating fluidized bed riser through the solid phase inlet, where it is combusted under the action of fluidizing air. The pyrolysis volatiles enter the circulating fluidized bed riser through the gas phase inlet in the middle of the riser, where they mix with the flue gas generated at the bottom and are further combusted under the action of secondary air. The resulting flue gas is separated by the gas-solid separation component. The solids are returned through the solid phase inlet of the biomass pyrolysis reactor to supply heat for the low-oxygen pyrolysis process, while the gases are separated through the gas-solid separation component. After the waste heat recovery unit recovers heat, the gas enters the O2 / flue gas mixing and circulation unit for gas heat exchange, and then enters the flue gas treatment and compression unit for gas treatment to obtain high-pressure CO2 gas. After treatment, part of the circulating flue gas returns to the O2 / flue gas mixing and circulation unit, where it forms circulating gas with the oxygen produced by the oxygen supply unit. After preheating, it returns to the biomass decoupled fluidized bed oxygen-enriched combustion unit and enters the middle and bottom of the circulating fluidized bed riser through the secondary air inlet and fluidizing air inlet, respectively. Another stream of circulating gas enters the biomass pyrolysis reactor through the gas phase inlet of the biomass pyrolysis reactor to achieve low-oxygen pyrolysis of biomass.

7. The oxygen-enriched combustion method according to claim 5 or 6, characterized in that, The particle size of the biomass raw material is <8mm.

8. The oxygen-enriched combustion method according to any one of claims 5 to 7, characterized in that, The low-oxygen pyrolysis temperature of the biomass pyrolysis reactor is 400-700℃; Preferably, the oxygen equivalent ratio in the biomass pyrolysis reactor is 0.1-0.

25.

9. The oxygen-enriched combustion method according to any one of claims 5 to 8, characterized in that, The combustion temperature of the fluidized bed riser is 750-900℃; Preferably, the total excess oxygen coefficient of the combustion unit in the fluidized bed riser is 1.15-1.

3.

10. The oxygen-enriched combustion method according to any one of claims 5 to 9, characterized in that, The volume fraction of oxygen in the circulating gas is 25-40%, preferably 30-35%.

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