A biomass circulating fluidized bed gasification and staged combustion process

Abstract

The present invention discloses a biomass circulating fluidized bed gasification staged combustion process, which includes: feeding biomass raw materials into a fluidized bed gasification chamber to undergo a gasification reaction with hot air, the generated combustible gas carrying part of the fine carbon particles enters a high-temperature cyclone separator, the separated solid particles are re-fed into the gasification chamber, and the combustible gas and a small amount of fine coke particles are fed into a gas combustion chamber to undergo a combustion reaction; the released heat heats the hot water from the steam drum into a steam-water mixture through a heat transfer surface and returns it to the steam drum for steam-liquid separation to separate saturated steam; the high-temperature flue gas discharged from the gas combustion chamber is sent to a waste heat recovery device for heat recovery and then enters a dust collector for dust removal and purification. A part of the purified flue gas is sent into the gasification chamber as auxiliary fluidizing air, another part is sent into a return material device as return material air, and the remaining part is discharged into the atmosphere through a chimney. The present invention can achieve efficient and low-pollution staged combustion of biomass, and at the same time can achieve rapid start-up and shut-down of the gasification furnace and large-range adjustment of the operating load.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass resource utilization, and particularly relates to a biomass circulating fluidized bed gasification and staged combustion process. Background Art

[0002] As a widely distributed, clean and zero-carbon renewable energy, biomass energy has various energy utilization methods, among which the thermochemical conversion pathway is the most widely used. Biomass gasification technology can convert low-quality biomass fuels into high-quality syngas and coke by-products. The syngas can be directly used as fuel or raw material to synthesize high-value-added chemical products, and the coke by-products can be processed into fertilizers or activated coke, etc. Therefore, compared with direct combustion technology, biomass gasification technology has good environmental and social benefits and broad application prospects.

[0003] At present, the relatively mature biomass gasification technologies in China are mainly circulating fluidized bed gasification technology and fixed bed gasification technology. For example, the Chinese patent document with the publication number CN107057771A discloses a double-circulation biomass circulating fluidized bed gasifier, which includes a gasifier, a primary cyclone separator, a secondary cyclone separator and a tertiary cyclone separator. The furnace gas outlet on the upper side of the gasifier is connected to the inlet of the primary cyclone separator through an acceleration section. The outlet at the bottom of the primary cyclone separator is connected to the furnace chamber of the gasifier through a primary return device. The outlet at the top of the primary cyclone separator is connected to the inlet of the secondary cyclone separator through an acceleration section. The outlet at the top of the secondary cyclone separator is connected to the inlet of the tertiary cyclone separator through an acceleration section. The outlet at the bottom of the secondary cyclone separator is connected to the furnace chamber of the gasifier through a secondary return device. The outlet at the bottom of the tertiary cyclone separator is connected to a fly ash collection device. The primary cyclone separator, the secondary cyclone separator and the tertiary cyclone separator all adopt annular cyclone separators.

[0004] The Chinese patent document with the publication number CN105062565A discloses a biomass fixed bed oxygen-enriched gasifier, which includes a hopper, a storage bin and a furnace body connected in sequence from top to bottom. The storage bin is connected to the hopper through an upper gate valve and to the furnace body through a lower gate valve. The furnace body is divided into an inner furnace chamber and an outer furnace chamber. The bottom of the outer furnace chamber is connected to the inner furnace chamber. The secondary air chamber is an annular air chamber located outside the outer furnace chamber. The secondary air inlet is provided along the circumference of the circular cross-section of the secondary air chamber, and a plurality of secondary air inlet nozzles are provided along the tangential direction of the inner furnace chamber towards the inner side of the circular cross-section. The bottom of the outer furnace chamber is a cone with a large upper part and a small lower part. A star ash discharge valve is connected to the cone at the bottom of the gasifier to introduce the ash layer into the ash hopper for collection and discharge.

[0005] However, the gasifiers used in these two technologies at present are all adiabatic furnaces. Although adiabatic furnaces have the advantages of good heat preservation effect and high energy utilization rate, their construction cost is high, the investment payback period is long, and the later maintenance cost is high. These unfavorable factors have hindered the market application and popularization of biomass gasification technology. Summary of the Invention

[0006] The present invention provides a biomass circulating fluidized bed gasification staged combustion process, which can realize efficient and low-pollution combustion and utilization of biomass, while realizing the rapid start and stop of the gasifier, flexible adjustment of the operating temperature, and wide-range adjustment of the operating load, and is also convenient for later maintenance.

[0007] A biomass circulating fluidized bed gasification staged combustion process, the device used includes a fluidized bed gasification chamber, a cyclone separator, a return device, a gas combustion chamber, a waste heat recovery device, and a dust collector; the fluidized bed gasification chamber is composed of a membrane water-cooled wall lined with refractory and wear-resistant castable, and the inside of the gas combustion chamber is lined with a heat exchange surface;

[0008] The specific process of the biomass fluidized bed gasification staged combustion process is as follows:

[0009] Step 1, after the crushed biomass raw material is fed into the fluidized bed gasification chamber, it is quickly mixed and heated with the high-temperature bed material, the hot air from the secondary air preheater in the waste heat recovery device, and the high-temperature bed material, and then pyrolysis gasification and combustion reactions occur. The reaction temperature is 650 - 850 °C, and high-temperature combustible gas is generated by the reaction.

[0010] Step 2, the high-temperature combustible gas containing bed material particles and ungasified biomass carbon powder particles in the fluidized bed gasification chamber flows out from the upper outlet and enters the high-temperature cyclone separator for gas-solid separation. The separated bed material particles and biomass carbon powder are re-fed into the fluidized bed gasification chamber through the return device for circulating combustion and gasification.

[0011] Step 3, the high-temperature combustible gas output from the high-temperature cyclone separator and a small amount of fine coke particles are sent into the gas combustion chamber together, and combustion reaction occurs with the staged fuel air fed into the gas combustion chamber to generate flue gas and release a large amount of heat;

[0012] The heat generated by the combustion reaction heats the hot water from the steam drum into a steam-water mixture through the heat exchange surface and returns it to the steam drum for steam-liquid separation; the saturated steam separated by the steam drum is directly supplied for external use or sent to the superheater to generate superheated steam for power generation;

[0013] Step 4, the generated high-temperature flue gas is discharged from the gas combustion chamber and enters the waste heat recovery device to exchange heat with each heat exchanger, and the low-temperature flue gas after heat exchange is discharged from the waste heat recovery device;

[0014] Step 5: The dusty low-temperature flue gas coming out of the waste heat recovery device enters the dust collector for dust removal; a part of the purified flue gas is sent into the fluidized bed gasification chamber as auxiliary fluidizing air through a fan, another part is sent into the return material device as return material air, and the remaining part is discharged into the atmosphere through a chimney.

[0015] If saturated steam is used as the final product, at this time, the heat exchangers in the waste heat recovery device are arranged in sequence of economizer, primary air preheater and secondary air preheater according to the flue gas flow direction.

[0016] If superheated steam is used as the final product, at this time, the heat exchangers in the waste heat recovery device are arranged in sequence of superheater, economizer, primary air preheater and secondary air preheater according to the flue gas flow direction.

[0017] Further, the air inlet of the primary air preheater is connected to the first fan, and the air outlet is connected to the inlet at the bottom of the fluidized bed gasification chamber; the air inlet of the secondary air preheater is connected to the second fan, and the air outlet is connected to the air inlet on the side wall of the gas combustion chamber; the outlet of the economizer is connected to the inlet of the steam drum, and the steam drum is respectively in circular communication with the membrane water wall and the heat exchange surface.

[0018] The external desalted water is heated by the economizer and then sent into the steam drum for steam-water separation. A part of the separated hot water is sent to the membrane water wall of the fluidized bed gasification chamber for furnace heat preservation, and another part is sent to the heat exchange surface of the gas combustion chamber to be further heated into saturated steam and then transported to the steam drum.

[0019] Further, the inlet of the superheater is connected to the outlet of the steam drum, and the outlet of the superheater generates superheated steam for power generation.

[0020] Further, the flue gas outlet at the top of the fluidized bed gasification chamber is connected to the flue gas inlet on the upper side of the high-temperature cyclone separator, the outlet at the lower end of the high-temperature cyclone separator is connected to the return material port on the lower side of the fluidized bed gasification chamber through a return material device, the outlet at the upper end of the high-temperature cyclone separator is connected to the flue gas inlet of the gas combustion chamber, and the flue gas outlet of the gas combustion chamber is connected to the upper side inlet of the waste heat recovery device.

[0021] Further, the flue gas inlet and the flue gas outlet of the gas combustion chamber are respectively arranged at the top and the bottom of the gas combustion chamber.

[0022] Further, in step 3, the staged fuel air sent into the gas combustion chamber is realized through multiple air inlets, and the air outlet of the secondary air preheater is connected to multiple air inlets arranged from top to bottom on the side wall of the gas combustion chamber through multiple air ducts.

[0023] Further, in step 5, according to the fuel characteristics and operating conditions, if using hot air can ensure that the operating temperature of the fluidized bed gasification chamber remains at a normal level, then hot air is used as the fluidization working medium for the fluidized bed gasification chamber. If using hot air causes the operating temperature of the fluidized bed gasification chamber to be too high, then recycled flue gas (auxiliary fluidizing air) is selected as the supplementary fluidization working medium to control the operating temperature. At the same time, when the system operates at a low load (less than 30% load), recycled flue gas (auxiliary fluidizing air) can be used as the auxiliary fluidization medium for the fluidized bed gasification chamber to ensure sufficient fluidization air volume. In addition, during the furnace shutdown stage of the fluidized bed gasification chamber, recycled flue gas (auxiliary fluidizing air) can be used as the medium to control the operating temperature of the fluidized bed gasification chamber. When shutting down the furnace, the gasification chamber converts from the gasification state to the combustion state, and sending flue gas with a low oxygen concentration into the furnace can control the furnace temperature during the process of converting from a reducing atmosphere to an oxidizing atmosphere. This method can replace the conventional furnace shutdown method using steam for temperature control to save steam.

[0024] Further, the inlet of the dust collector is connected to the outlet of the waste heat recovery device, and the outlet of the dust collector is connected to the third fan. The outlet of the third fan is connected to the bottom inlet of the fluidized bed gasification chamber, the chimney, and the return device through pipelines respectively.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention realizes the hierarchical efficient and low-pollution combustion utilization of biomass through the coupling of circulating fluidized bed gasification and high-temperature combustible gas combustion. Compared with the prior art (where ungasified biomass char needs to be separated before gas combustion), the high-temperature gas generated by the circulating fluidized bed gasifier directly enters the subsequent gas combustion chamber to continue burning and conversion with part of the unreacted biomass char carried, having the advantages of high carbon conversion rate and high system thermal efficiency.

[0027] 2. The furnace of the gasification chamber of the present invention adopts a membrane water-cooled wall structure and refractory wear-resistant castable is laid on the water-cooled wall. Compared with an adiabatic gasification furnace, the material consumption of the gasifier device is reduced, the equipment load is small, the construction cost is greatly reduced (about 20% reduction), and the later maintenance is simple and convenient.

[0028] 3. The gasification furnace hearth with a relatively thin refractory wear-resistant castable layer laid on the water-cooled wall has strong adaptability to rapid temperature changes, can realize the rapid start-stop of the gasification staged combustion device and the flexible adjustment of the operating temperature, while the adiabatic furnace is restricted by the thick refractory castable material and cannot perform rapid temperature change adjustment.

[0029] 4. Since a castable layer is laid on the membrane water wall of the fluidized bed gasification chamber and the heat absorption during operation is extremely small, the operating temperature of the circulating fluidized bed gasification circuit during low-load operation and high-load operation of the device is basically close. The high-temperature gas can maintain efficient combustion through stratified air distribution in the combustion chamber. Therefore, it can ensure stable, reliable and efficient conversion of biomass under different loads, and avoid problems such as low combustion efficiency during low-load operation of a biomass direct combustion boiler. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 FIG. is a process flow diagram of a biomass circulating fluidized bed gasification and staged combustion process with saturated steam as the product in an embodiment of the present invention;

[0031] Figure 2 FIG. is a process flow diagram of a biomass circulating fluidized bed gasification and staged combustion process with superheated steam as the product in an embodiment of the present invention.

[0032] In the figure: 1 - fluidized bed gasification chamber; 2 - membrane water wall; 3 - high-temperature cyclone separator; 4 - return device; 5 - gas combustion chamber; 6 - heat exchange surface; 7 - waste heat recovery device; 8 - economizer; 9 - primary air preheater; 10 - secondary air preheater; 11 - steam drum; 12 - dust collector; 13 - chimney; 14 - first fan, 15 - second fan, 16 - third fan; 17 - fourth fan; 18 - fifth fan; 19 - superheater. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The present invention will be further described in detail below with reference to the drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0034] According to the use of the obtained steam product, the present invention has two implementation modes.

[0035] The first implementation mode: using saturated steam as the product. As Figure 1 shown, a biomass circulating fluidized bed gasification and staged combustion process, the device used includes a fluidized bed gasification chamber 1, a high-temperature cyclone separator 3, a return device 4, a gas combustion chamber 5, a waste heat recovery device 7, a steam drum 11, a dust collector 12, a chimney 13, a first fan 14, a second fan 15, a third fan 16, a fourth fan 17, and a fifth fan 18. The fluidized bed gasification chamber 1 is composed of a membrane water wall 2 laid with refractory and wear-resistant castable. The inside of the gas combustion chamber 5 is laid with a heat exchange surface 6. The waste heat recovery device 7 is arranged with an economizer 8, a primary air preheater 9 and a secondary air preheater 10 in sequence according to the flue gas flow direction.

[0036] Process flow: The outside air is sent into the primary air preheater 9 by the first blower 14 and heated, and then sent to the fluidized bed gasification chamber 1 as the gasifying agent (also serving as the fluidizing air). Biomass materials with a certain particle size (the particle size of the crushed materials is less than 5 cm, and the particle size of the formed materials is less than 2 cm) are sent into the fluidized bed gasification chamber 1 and quickly mixed and heated with hot air and high-temperature bed materials, and then pyrolysis gasification and combustion reactions occur. The reaction temperature is 650 - 850 °C, and high-temperature combustible gas is generated. The high-temperature combustible gas carries fine bed material particles and un-gasified biomass carbon powder particles and is output from the top of the fluidized bed gasification chamber 1 and then enters the high-temperature cyclone separator 3 for gas-solid separation. The separated bed material particles and biomass carbon powder are re-sent back into the fluidized bed gasification chamber 1 through the return device 4 for circulating combustion and gasification.

[0037] The outside air is sent into the secondary air preheater 10 by the second blower 15 and heated, and then sent into the gas combustion chamber 5 as fuel air in a stratified and multi-stage manner and burns together with the combustible gas and a small amount of fine carbon particles that are not separated, generating a large amount of high-temperature flue gas and heat. The high-temperature flue gas is discharged from the gas combustion chamber 5 and enters the waste heat recovery device 7, where it exchanges heat with the economizer 8, the primary air preheater 9, and the secondary air preheater 10 in sequence. The heat-exchanged low-temperature flue gas is discharged from the waste heat recovery device 7 and then enters the dust collector 12 for dust removal. The purified flue gas is led out by the third blower 16, and a part of it is used as the fluidizing air and sent into the fluidized bed gasification chamber through the fourth blower 17. This part of the flue gas mainly has the following uses: ① If the operation temperature of the fluidized bed gasification chamber is too high when using hot air as the gasification medium, the recirculated flue gas is used as the supplementary fluidizing working medium. ② When the system operates at a low load (less than 30% of the load), the flue gas can be used as the auxiliary fluidizing medium of the fluidized bed gasification chamber to ensure sufficient fluidizing air volume. ③ During the shutdown stage of the fluidized bed gasification chamber, the recirculated flue gas can be used as the medium for controlling the operation temperature of the fluidized bed gasification chamber. When shutting down, the gasification chamber is converted from the gasification state to the combustion state, and the flue gas with a low oxygen concentration is sent into the furnace to control the furnace temperature during the process of converting from a reducing atmosphere to an oxidizing atmosphere. This method can replace the conventional steam temperature control means during shutdown to save steam.

[0038] Another part of the flue gas led out from the third blower 16 is used as the return air and sent into the return device 4 through the fifth blower 18, and the rest is discharged into the atmosphere through the chimney 13.

[0039] The outside desalted water is heated by the economizer 8 and then sent into the steam drum 11 for steam-water separation. A part of the separated hot water is sent to the membrane water wall 2 of the fluidized bed gasification chamber 1 for furnace heat preservation, and the other part is sent to the heat exchange surface 6 of the gas combustion chamber 5 to be further heated into saturated steam and then transported to the steam drum, which can be used by residents or for factory production.

[0040] The second implementation method: Using superheated steam as the product. Such as Figure 2As shown in the figure, a biomass fluidized bed gasification and staged combustion process, and the device used includes a fluidized bed gasification chamber 1, a high-temperature cyclone separator 3, a return device 4, a gas combustion chamber 5, a waste heat recovery device 7, a steam drum 11, a dust collector 12, a chimney 13, a first fan 14, a second fan 15, a third fan 16, a fourth fan 17, and a fifth fan 18. The fluidized bed gasification chamber 1 is composed of a membrane water wall 2 lined with refractory and wear-resistant castable, and a heat transfer surface 6 is lined inside the gas combustion chamber 5. The waste heat recovery device 7 is arranged in sequence with a superheater 19, a economizer 8, a primary air preheater 9, and a secondary air preheater 10 according to the flue gas flow direction.

[0041] Process flow: The outside air is sent into the primary air preheater 9 by the first fan 14 and heated to be used as a gasifying agent (also as fluidizing air) and sent to the fluidized bed gasification chamber 1. Biomass materials with a certain particle size (the particle size of crushed materials is less than 5 cm, and the particle size of formed materials is less than 2 cm) are sent into the fluidized bed gasification chamber 1 and quickly mixed and heated with hot air and high-temperature bed materials, and then pyrolysis gasification and combustion reactions occur. The reaction temperature is 650 - 850 °C, and high-temperature combustible gas is generated by the reaction. The high-temperature combustible gas carries fine bed material particles and ungasified biomass carbon powder particles and is output from the top of the fluidized bed gasification chamber 1 and then enters the high-temperature cyclone separator 3 for gas-solid separation. The separated bed material particles and biomass carbon powder are re-sent back into the fluidized bed gasification chamber 1 through the return device 4 for circulating combustion and gasification.

[0042] The outside air is sent into the secondary air preheater 10 by the second fan 15 and heated to be used as fuel air and sent into the gas combustion chamber 5 in a stratified and multi-stage manner and burns together with combustible gas and a small amount of fine carbon particles that are not separated, generating a large amount of high-temperature flue gas and heat. The high-temperature flue gas is discharged from the gas combustion chamber 5 and enters the waste heat recovery device 7 to exchange heat with the superheater 19, the economizer 8, the primary air preheater 9, and the secondary air preheater 10 in sequence. The low-temperature flue gas after heat exchange is discharged from the waste heat recovery device 7 and then enters the dust collector 12 for dust removal. The purified flue gas is led out by the third fan 16, and a part of it is used as fluidizing air and sent into the fluidized bed gasification chamber through the fourth fan 17. This part of the flue gas has the following main uses: ① If the operation temperature of the fluidized bed gasification chamber is too high when using hot air as the gasification medium, the recirculated flue gas is used as a supplementary fluidizing working medium. ② When the system operates at a low load (less than 30% load), the flue gas can be used as an auxiliary fluidizing medium for the fluidized bed gasification chamber to ensure sufficient fluidizing air volume. ③ During the shutdown stage of the fluidized bed gasification chamber, the circulating flue gas can be used as a medium to control the operation temperature of the fluidized bed gasification chamber. When shutting down, the gasification chamber is converted from the gasification state to the combustion state, and the flue gas with a low oxygen concentration is sent into the furnace to control the furnace temperature during the process of converting from a reducing atmosphere to an oxidizing atmosphere. This method can replace the conventional steam temperature control means during shutdown to save steam.

[0043] After being led out from the No. 3 fan 16, another part of the flue gas is sent as the return air through the No. 5 fan 18 into the return device, and the remaining part is discharged into the atmosphere through the chimney 13.

[0044] The external desalted water is heated by the economizer 8 and then sent into the steam drum 11 for steam-water separation. One part of the separated hot water is sent to the membrane water wall 2 of the fluidized bed gasification chamber 1 for furnace heat preservation, and the other part is sent to the heat exchange surface 6 of the gas combustion chamber 5 to be further heated into saturated steam and then sent back to the steam drum 11 for steam-water separation again. The separated saturated steam is sent to the superheater 19 to be further heated into superheated steam, which can be used for steam turbine power generation.

[0045] Example 1

[0046] The feeding amount of biomass materials is 8 t / h. The external air is preheated to 350 °C by the primary air preheater 9 and then sent to the fluidized bed gasification chamber 1 to react with the biomass. The reaction temperature is about 700 °C, and the reaction produces high-temperature combustible gas and biomass carbon powder particles. The calorific value of the combustible gas is 4.6 MJ / Nm 3 . The fine biomass carbon powder particles are separated by the high-temperature cyclone separator 3 along with the high-temperature combustible gas and then returned to the fluidized bed gasification chamber 1 through the return device 4 for further gasification. The high-temperature combustible gas and fine coke particles discharged from the high-temperature cyclone separator 3 enter the gas combustion chamber 5 to burn with the multi-stage fuel air from the secondary air preheater 10, and the combustion temperature is about 900 °C. The concentration of NOx in the flue gas generated by combustion is about 45 mg / Nm 3 , and the concentration of SO2 is about 17 mg / Nm 3 , meeting the ultra-low emission requirements. The steam flowing out from the heat exchange surface 6 of the gas combustion chamber 5 is processed by the steam drum 11 to obtain saturated steam at 240 °C and 2.4 Mpa. This steam can be used for residential heating or industrial production.

[0047] Example 2

[0048] The feeding amount of biomass materials is 12.5 t / h. The external air is preheated to 350 °C by the primary air preheater 9 and then sent to the fluidized bed gasification chamber 1 to react with the biomass. The reaction temperature is about 750 °C, and the reaction produces high-temperature combustible gas and biomass carbon powder particles. The calorific value of the combustible gas is 4.8 MJ / Nm 3 . The biomass carbon powder particles are separated by the high-temperature cyclone separator 3 along with the high-temperature combustible gas and then returned to the fluidized bed gasification chamber 1 through the return device 4 for further gasification. The high-temperature combustible gas and fine coke particles discharged from the high-temperature cyclone separator 3 enter the gas combustion chamber 5 to burn with the multi-stage fuel air from the secondary air preheater 10, and the combustion temperature is about 900 °C. The concentration of NOx in the flue gas generated by combustion is about 40 mg / Nm 3 , and the concentration of SO2 is about 18 mg / Nm 3, meeting the ultra-low emission requirements. The saturated steam separated from the steam drum 11 is heated by the superheater 19 to obtain superheated steam at 450 °C and 3.9 Mpa. This steam can be used for steam turbine power generation.

[0049] The above-described embodiments have detailed the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, and equivalent replacements made within the scope of the principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A biomass circulating fluidized bed gasification and staged combustion process, characterized in that, The device adopted includes a fluidized bed gasification chamber (1), a high-temperature cyclone separator (3), a return feeding device (4), a gas combustion chamber (5), a waste heat recovery device (7) and a dust collector (12); the fluidized bed gasification chamber (1) is composed of a membrane water wall (2) lined with refractory and wear-resistant castable, and a heat exchange surface (6) is lined inside the gas combustion chamber (5); The specific process of the biomass circulating fluidized bed gasification and staged combustion process is as follows: Step 1, after the crushed biomass raw materials are fed into the fluidized bed gasification chamber (1), they are rapidly mixed and heated with high-temperature bed materials and hot air from the secondary air preheater (10) in the waste heat recovery device (7), and then pyrolysis gasification and combustion reactions occur. The reaction temperature is 650 - 850 °C, and high-temperature combustible gas is generated by the reaction; Step 2, the high-temperature combustible gas containing bed material particles and un-gasified biomass carbon powder particles in the fluidized bed gasification chamber (1) flows out from the upper outlet and enters the high-temperature cyclone separator (3) for gas-solid separation. The separated bed material particles and biomass carbon powder are re-fed into the fluidized bed gasification chamber (1) through the return feeding device (4) for circulating combustion and gasification; Step 3, the high-temperature combustible gas output from the high-temperature cyclone separator (3) and a small amount of fine coke particles are sent into the gas combustion chamber (5) together, and combustion reactions occur with the staged fuel air fed into the gas combustion chamber (5) to generate flue gas and release a large amount of heat; The heat generated by the combustion reaction heats the hot water from the steam drum (11) into a steam-water mixture through the heat exchange surface (6) and returns it to the steam drum (11) for steam-liquid separation; the saturated steam separated by the steam drum (11) is directly supplied for external use or sent into the superheater (19) to generate superheated steam for power generation; Step 4, the generated high-temperature flue gas is discharged from the gas combustion chamber (5) and enters the waste heat recovery device (7) to exchange heat with each heat exchanger, and the low-temperature flue gas after heat exchange is discharged from the waste heat recovery device (7); Step 5, the dust-containing low-temperature flue gas coming out of the waste heat recovery device (7) enters the dust collector (12) for dust removal; a part of the purified flue gas is sent into the fluidized bed gasification chamber (1) as auxiliary fluidizing air, another part is sent into the return feeding device (4) as return feeding air, and the rest is discharged into the atmosphere through the chimney (13).

2. The biomass circulating fluidized bed gasification and staged combustion process according to claim 1, wherein Taking saturated steam as the final product, at this time, the heat exchangers in the waste heat recovery device (7) are arranged in sequence as the economizer (8), the primary air preheater (9) and the secondary air preheater (10) according to the flue gas flow direction.

3. The biomass circulating fluidized bed gasification and staged combustion process according to claim 1, characterized in that Taking superheated steam as the final product, at this time, the heat exchangers in the waste heat recovery device (7) are arranged in sequence as the superheater (19), the economizer (8), the primary air preheater (9) and the secondary air preheater (10) according to the flue gas flow direction.

4. The biomass circulating fluidized bed gasification and staged combustion process according to claim 2 or 3, characterized in that, The air inlet of the primary air preheater (9) is connected to the first fan (14), and the air outlet is connected to the inlet at the bottom of the fluidized bed gasification chamber (1); the air inlet of the secondary air preheater (10) is connected to the second fan (15), and the air outlet is connected to the air inlet on the side wall of the gas combustion chamber (5); the outlet of the economizer (8) is connected to the inlet of the steam drum (11), and the steam drum (11) is respectively connected to the membrane water wall (2) and the heat exchange surface (6) in a circulating manner; The external desalted water is heated by the economizer (8) and then sent into the steam drum (11) for steam-water separation. A part of the separated hot water is sent to the membrane water wall (2) of the fluidized bed gasification chamber (1) for furnace thermal insulation, and the other part is sent to the heat exchange surface (6) of the gas combustion chamber (5) to be further heated into saturated steam and then transported to the steam drum.

5. The biomass circulating fluidized bed gasification and staged combustion process according to claim 3, characterized in that, The inlet of the superheater (19) is connected to the outlet of the steam drum (11), and the outlet of the superheater (19) generates superheated steam for power generation.

6. The biomass circulating fluidized bed gasification staged combustion process according to claim 1, characterized in that, The flue gas outlet at the top of the fluidized bed gasification chamber (1) is connected to the flue gas inlet on the upper side of the high-temperature cyclone separator (3). The outlet at the lower end of the high-temperature cyclone separator (3) is connected to the return material port on the lower side of the fluidized bed gasification chamber (1) through the return material device (4). The outlet at the upper end of the high-temperature cyclone separator (3) is connected to the flue gas inlet of the gas combustion chamber (5). The flue gas outlet of the gas combustion chamber (5) is connected to the upper inlet of the waste heat recovery device (7).

7. The biomass circulating fluidized bed gasification staged combustion process according to claim 6, characterized in that, The flue gas inlet and the flue gas outlet of the gas combustion chamber (5) are respectively arranged at the top and the bottom of the gas combustion chamber (5).

8. The biomass circulating fluidized bed gasification and staged combustion process according to claim 1, characterized in that, In step 3, the staged fuel air sent into the gas combustion chamber (5) is realized through multiple air inlets. The air outlet of the secondary air preheater (10) is connected to multiple air inlets arranged from top to bottom on the side wall of the gas combustion chamber (5) through multiple air ducts.

9. The biomass circulating fluidized bed gasification and staged combustion process according to claim 1, characterized in that According to the fuel characteristics and operating conditions, if using hot air can ensure that the operating temperature of the fluidized bed gasification chamber (1) remains at a normal level, then use hot air as the fluidization working medium of the fluidized bed gasification chamber (1); if using hot air causes the operating temperature of the fluidized bed gasification chamber (1) to be too high, then select the auxiliary fluidization air as the supplementary fluidization working medium to facilitate the control of the operating temperature; At the same time, when the system is operating at low load, use the auxiliary fluidization air as the fluidization medium of the auxiliary fluidized bed gasification chamber (1) to ensure sufficient fluidization air volume; during the shutdown stage of the fluidized bed gasification chamber (1), use the auxiliary fluidization air as the temperature control medium of the fluidized bed gasification chamber (1) to avoid slagging and coking problems caused by over-temperature of the operating temperature when the gasification state of the reducing atmosphere is transformed into the combustion state of the oxidizing atmosphere during the shutdown stage.

10. The biomass circulating fluidized bed gasification and staged combustion process according to claim 1, characterized in that, The inlet of the dust collector (12) is connected to the outlet of the waste heat recovery device (7), and the outlet of the dust collector (12) is connected to the third fan (16); the outlet of the third fan (16) is connected to the bottom inlet of the fluidized bed gasification chamber (1), the chimney (13) and the return material device (4) through pipelines.

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