Fluidized bed combustion system and method

Abstract

The invention provides a fluidized bed combustion system and a combustion method. The fluidized bed combustion system comprises a fluidized bed combustion reaction device and a mild gasification reaction device, the fluidized bed combustion reaction device comprises a dilute-phase region arranged in the middle and a dense-phase region arranged at the lower part; a gas phase outlet of the mild gasification reaction device is connected with a gas phase inlet of the dilute phase zone, and a solid phase outlet of the mild gasification reaction device is connected with a solid phase inlet of the dense phase zone. The system is stable in combustion, high in denitration efficiency, compact in structure, easy and convenient to operate, low in operation cost and suitable for low-nitrogen transformation and new projects of coal and biomass combustion devices, and has good industrial application prospects and popularization value.

Description

Technical Field

[0001] This invention relates to the field of solid fuel combustion and pollution control technology, and in particular to a fluidized bed combustion system and method. Background Technology

[0002] Nitrogen oxides can cause environmental problems such as acid rain, photochemical smog, and the greenhouse effect, posing serious threats to both the atmospheric environment and human health. The government has already implemented strict control measures, requiring key regions and industries to achieve ultra-low nitrogen oxide levels (50 mg / Nm³). 3 Solid fuels (such as coal and biomass) produce fuel-type and thermal-type nitrogen oxides during combustion. Fluidized bed combustion technology, due to its relatively low combustion temperature, primarily produces fuel-type nitrogen oxides; therefore, controlling fuel nitrogen formation is crucial.

[0003] In existing technologies, research and patents have proposed various approaches to the staged conversion, zoned combustion, and synergistic control of pollutants in solid fuels. For example, patent CN1203117A discloses a decoupled circulating fluidized bed (CFB) combustion system and its desulfurization and denitrification methods. This system couples the dry distillation (or pyrolysis) of coal with the combustion process using high-temperature circulating ash and other solids as heat carriers, and utilizes pyrolysis gas to reduce nitrogen oxides in flue gas. This device is developed based on traditional coal fuel and mainly uses high-temperature circulating ash as a heat carrier for pyrolysis. When operating conditions are adjusted or fuel properties change, the system's heat matching and material residence characteristics are prone to deviation, making it difficult to maintain operational stability and hindering large-scale industrial application. Patents CN109539245B and CN101158468B respectively disclose a coal powder pyrolysis decoupled combustion device and a coal powder high-temperature preheating method. The core point is that coal powder can achieve stable and low-NOx combustion by being modified through high-temperature preheating and then reburned. However, the above-mentioned devices are mainly designed for pulverized coal boilers, and there are also problems such as complex preheater structure and reduced combustion efficiency.

[0004] Furthermore, during combustion, fuel nitrogen is mainly released in the form of ammonia and hydrogen cyanide, which are key intermediates for the formation and reduction of nitrogen oxides, directly determining the formation of nitrogen oxides during combustion. In the paper "BAI Z, JIANG XZ, LUOK H. A reactive molecular dynamics study of NO removal by nitrogen-containing species in coal pyrolysis gas[J]. Proceedings of the Combustion Institute,2023, 39(4): 4573-4581", ammonia reacts with NO under oxygen-deficient conditions to mainly produce nitrogen and water, with very little N2O as a byproduct; while HCN easily generates NO and N2O in the low-temperature region (873-1200 K), and NO generation increases significantly in the high-temperature region (>1200 K). In the paper “WARGADALAM VJ, LöFFLER G, WINTER F, et al. Homogeneous formation of NO and N2O from the oxidation of HCN and NH3 at 600-1000℃[J]. Combustion and Flame, 2000, 120(4): 465-478”, it was found that when NH3 and HCN coexist, NH3 preferentially participates in the reduction reaction of NO, while HCN reacts later and is more likely to generate N2O, significantly reducing the denitrification effect. Therefore, reducing the amount of HCN generated and increasing the NH3 / HCN ratio (ammonia-cyanide ratio) have become key technical approaches to enhance the gas-phase reduction of nitrogen oxides from crude coal gas or pyrolysis gas.

[0005] In conclusion, it is necessary to develop an efficient, low-NOx combustion system and supporting technical solutions that are easy to implement in engineering, and there is an urgent need for clean and efficient low-NOx combustion technology. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a fluidized bed combustion system and method that achieves efficient and synergistic control of low nitrogen oxide emissions while taking into account both engineering feasibility and combustion stability, and is applicable to CFB and BFB furnace types as well as retrofitting of old boilers.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a fluidized bed combustion system, the fluidized bed combustion system comprising a fluidized bed combustion reactor and a mild gasification reactor;

[0009] The fluidized bed combustion reactor includes a dilute phase zone in the middle and a dense phase zone in the lower part;

[0010] The gas phase outlet of the mild gasification reaction device is connected to the gas phase inlet of the dilute phase region, and the solid phase outlet of the mild gasification reaction device is connected to the solid phase inlet of the dense phase region.

[0011] As a preferred embodiment of the present invention, the fluidized bed combustion system includes an air supply system.

[0012] Preferably, the air supply system includes a conveying air system, a burnout air system, and a fluidizing air system. The gas outlet of the conveying air system is connected to the material inlet of the mild gasification reaction device, the gas outlet of the burnout air system is connected to the burnout air inlet of the dilute phase zone, and the gas outlet of the fluidizing air system is connected to the fluidizing air inlet of the dense phase zone.

[0013] As a preferred technical solution of the present invention, the fluidized bed combustion reactor includes a circulating fluidized bed and / or a bubbling fluidized bed.

[0014] As a preferred embodiment of the present invention, a gas-solid separation component is connected to the top of the dilute phase region.

[0015] Preferably, the gas-solid separation assembly has an exhaust port at the top.

[0016] Preferably, the bottom of the gas-solid separation component is connected to a return leg, which is connected to the dense phase region.

[0017] Preferably, the bottom of the return leg is provided with a loosening air inlet.

[0018] As a preferred technical solution of the present invention, the mild gasification reaction device includes a cyclone mild gasification reaction device and / or a spiral mild gasification reaction device.

[0019] The cyclone-type mild gasification reactor of the present invention can be used for high nitrogen-containing solid fuels with small particle size (e.g., less than 1 mm), such as pulverized coal, biomass pellets and their mixed fuels; the spiral-type mild gasification reactor can be used for medium or large particle size fuels, such as 1-5 mm pulverized coal, briquetted biomass, pellet biomass and coal-biomass mixed fuels.

[0020] Preferably, 1 to 4 mild gasification reaction devices can be arranged circumferentially along the fluidized bed combustion reaction device, for example, 1, 2, 3 or 4.

[0021] The mild gasification reaction device of the present invention can be arranged in several places along the circumference of the combustion reaction device, which can realize multi-point crude gas injection and multi-point semi-coke feeding to adapt to different processing volume requirements and enhance spatial uniformity and operational flexibility.

[0022] In a second aspect, the present invention provides a fluidized bed combustion method, wherein the fluidized bed combustion method is carried out in the fluidized bed combustion system described in the first aspect.

[0023] As a preferred technical solution of the present invention, the fluidized bed combustion method includes the following steps: fuel and additives are mixed in proportion and then enter the mild gasification reaction device to generate semi-coke and crude coal gas; the semi-coke and residual fuel enter the dense phase zone through the solid phase inlet, and the crude coal gas enters the dilute phase zone through the gas phase inlet, and mixes with the flue gas generated by fluidized combustion in the dense phase zone for further combustion.

[0024] The fluidized bed combustion method of this invention specifically includes: fuel and additives are mixed in proportion and then enter the mild gasification reaction device under the action of conveying air, where they are combusted to generate semi-coke and crude coal gas; the semi-coke and residual fuel enter the dense phase zone through the solid phase inlet, where they are combusted under the action of fluidizing air to generate flue gas; the crude coal gas enters the dilute phase zone through the gas phase inlet and mixes with the flue gas generated by fluidized combustion in the dense phase zone for further combustion; the fluidized bed combustion device is provided with a burnout air inlet at the top for burning the remaining combustibles in the flue gas to improve burnout efficiency and reduce pollutant emissions; finally, the flue gas is separated and discharged through the gas-solid separation component; if the fluidized bed combustion reaction device is provided with a return leg and a loosening air inlet, the particles separated by the gas-solid separation component can be returned to the dense phase zone; by adjusting the ratio of conveying air, fluidizing air and burnout air, the atmosphere and temperature inside the combustion reaction device are made to reach the optimal reduction state of nitrogen oxides, while ensuring high combustion efficiency.

[0025] The deep denitrification mechanism and process of this invention include: under oxygen-deficient conditions in a mild gasification reactor, fuel is converted into NH3 and HCN by additives, where the NH3 content increases and HCN formation is inhibited; the generated semi-coke enters the semi-coke combustion zone and is burned to produce NO and N2O under fluidized air oxygen supply; the crude gas enters the dilute phase zone, mixes with the semi-coke flue gas, and undergoes a selective reduction reaction; in this process, NH3 reacts with NO to produce N2 and H2O, resulting in a large amount of NO being consumed; while HCN is used as N2O. The main precursor of the gas reacts with NO via an NCO intermediate to generate N2O. However, since NO has been preferentially reduced by NH3, the amount of N2O generated is significantly reduced. At the same time, reducing gases such as CH4, CO, and H2 in the crude gas generate H, OH, and O free radicals, which can further decompose N2O to generate N2, thus achieving the dual removal of NO and N2O. The burnout air is supplied to the upper oxygen-enriched zone to fully oxidize the unburned CO and soot, generating N2, CO2, and H2O. The exhaust gas contains only a small amount of NO, N2O, and CO.

[0026] In the above-mentioned fluidized bed combustion method, the dense phase zone is the main combustion and heat release zone, and the dilute phase zone is the gas-phase reduction reaction zone, so that the present invention can be used for retrofitting existing CFB and BFB boilers, as well as for new boiler types.

[0027] The total amount of delivery air and fluidizing air in the above combustion process is 0.9-1.0 of the theoretical combustion air volume.

[0028] As a preferred embodiment of the present invention, the fuel includes coal and / or biomass.

[0029] Preferably, the additive includes an oxide or salt containing at least one element selected from iron, calcium, or aluminum.

[0030] The additives added during the combustion process of this invention act during the mild gasification stage, promoting the conversion of fuel nitrogen to reducing components such as NH3 and inhibiting HCN formation, thereby improving the crude gas's resistance to NO. x It enhances the selective reduction capability of crude coal gas and reduces the risk of N2O generation, thereby strengthening the selective reduction of nitrogen oxides in combustion flue gas.

[0031] As a preferred embodiment of the present invention, the mass ratio of the fuel to the additive is ≥10.

[0032] As a preferred technical solution of the present invention, the gas phase inlet of the dilute phase zone is set in the temperature range of 700-950°C along the height direction of the fluidized bed combustion reactor. For example, it can be 700°C, 750°C, 800°C, 850°C, 900°C or 950°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] In the fluidized bed combustion method of this invention, crude coal gas enters the dilute phase zone through a crude coal gas inlet and mixes with the flue gas within a temperature range of 700-950 °C. The reducing components in the crude coal gas, such as NH3, C4, CO, and H2, are used to reduce NO. x And some N2O is reduced.

[0034] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0035] (1) High operational stability: This invention utilizes part of the combustion heat of the solid fuel itself as a gasification heat source, does not rely on a high-temperature circulating ash system, has low thermal inertia and fast response speed, and is easy to flexibly adjust the distribution ratio of conveying air and fuel according to load changes, thus significantly improving operational stability;

[0036] (2) Wide fuel adaptability and good furnace type compatibility: The mild gasification reaction device adopts two general structures, cyclone type and spiral type. The main furnace body can be CFB or BFB furnace type. It is suitable for biomass fuels such as fine pulverized coal and straw pellets, as well as block coal or briquetted biomass and coal-biomass mixed fuels. It can be easily installed or modified on existing fluidized bed boilers, and has strong engineering applicability.

[0037] (3) Significant denitrification effect: Experimental verification shows that by adding an additive during the mild gasification stage, the ratio of NH3 to HCN in the crude coal gas can be significantly changed, the NH3 / HCN ratio can be increased, and the oxidation of HCN to NO and N2O can be inhibited. Laboratory experiments have verified that when municipal sludge particles are used as raw materials for combustion, compared with traditional combustion methods, in the combustion temperature range of 750 to 950℃, the conversion rate of fuel nitrogen to nitrogen oxides in the gas phase reduction system involved in this invention can be reduced from 18.57% to 10.68% to about 11.29% to 5.41%, a reduction of about 45% to 50%; when calcium oxide is used as an additive (50% of the raw material), the conversion rate can be further reduced to about 7.84% to 4.87%, and the denitrification efficiency is increased by about 10% to 31% compared with the system without additives. Under the condition of 850℃, the comprehensive emission reduction can reach about 64%, and the denitrification effect is significant.

[0038] (4) High combustion efficiency and good carbon utilization: The main furnace body of this invention maintains a good fluidization state in the dense phase zone, which can fully burn semi-coke and direct-feed fuel; the dilute phase zone is equipped with burnout air to further burn off residual CO and soot and other combustibles. Through staged air supply and multi-point feeding, the carbon conversion rate and burnout efficiency can be improved and the carbon content of fly ash can be reduced while ensuring uniform furnace temperature;

[0039] (5) Simplified structure, flexible layout, and significant environmental benefits: This invention abandons the traditional method of using high-temperature circulating ash as a pyrolysis / gasification heat source, and achieves self-heating gasification by burning part of the fuel; by utilizing the adjustable-height crude gas inlet and the multi-point mild gasification reaction device to construct a flexible decoupled combustion structure, the overall system is simpler, more feasible, and suitable for new construction and renovation projects. By increasing the NH3 / HCN ratio, enhancing gas-phase reduction, and improving NO... x Synergistic control with N2O can significantly reduce nitrogen oxide emissions from coal and biomass boilers, resulting in outstanding environmental benefits. Attached Figure Description

[0040] Figure 1 This is a simplified diagram of the overall structure and function of the fluidized bed combustion system and combustion method provided by the present invention;

[0041] Figure 2 This is a schematic diagram of the deep denitrification mechanism and process provided by the present invention;

[0042] Figure 3 This is the fluidized bed combustion system provided in Embodiment 1 of the present invention;

[0043] Figure 4 This is the fluidized bed combustion system provided in Embodiment 2 of the present invention;

[0044] In the diagram: 1-Cyclone-type mild gasification reactor, 2-Dense phase zone, 3-Dilute phase zone, 4-Gas-solid separation component, 5-Return leg, 6-Loose gas inlet, 7-Raw gas inlet, 8-Feed inlet, 9-Spiral-type mild gasification reactor. Detailed Implementation

[0045] 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.

[0046] 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.

[0047] Example 1

[0048] This embodiment provides a fluidized bed combustion system, which includes a fluidized bed combustion reactor, a cyclone-type mild gasification reactor 1, and an air supply system;

[0049] The fluidized bed combustion reactor includes a dilute phase zone 3 located in the middle and a dense phase zone 2 located in the lower part;

[0050] The gas phase outlet of the cyclone-type mild gasification reaction device 1 is connected to the gas phase inlet 7 of the dilute phase region 3, and the solid phase outlet of the cyclone-type mild gasification reaction device 1 is connected to the solid phase inlet 8 of the dense phase region 2.

[0051] The air supply system includes a conveying air system, a burnout air system, and a fluidizing air system. The gas outlet of the conveying air system is connected to the material inlet of the cyclone-type mild gasification reaction device 1. The gas outlet of the burnout air system is connected to the burnout air inlet of the dilute phase zone 3. The gas outlet of the fluidizing air system is connected to the fluidizing air inlet of the dense phase zone 2.

[0052] The top of the dilute phase zone is connected to a gas-solid separation component 4, which has an exhaust port at the top and a return leg 5 at the bottom. The return leg 5 is connected to the dense phase zone 2, and the bottom of the return leg 5 has a loosening air inlet 6.

[0053] Example 2

[0054] This embodiment provides a fluidized bed combustion system, which includes a fluidized bed combustion reactor, a spiral mild gasification reactor 9, and an air supply system;

[0055] The fluidized bed combustion reactor includes a dilute phase zone 3 located in the middle and a dense phase zone 2 located in the lower part;

[0056] The gas phase outlet of the spiral mild gasification reactor 9 is connected to the gas phase inlet 7 of the dilute phase region 3, and the solid phase outlet of the spiral mild gasification reactor 9 is connected to the solid phase inlet 8 of the dense phase region 2.

[0057] The air supply system includes a conveying air system, a burnout air system, and a fluidizing air system. The gas outlet of the conveying air system is connected to the material inlet of the spiral mild gasification reaction device 9. The gas outlet of the burnout air system is connected to the burnout air inlet of the dilute phase zone 3. The gas outlet of the fluidizing air system is connected to the fluidizing air inlet of the dense phase zone 2.

[0058] The top of the dilute phase region is connected to a gas-solid separation component 4, and the top of the gas-solid separation component is provided with an exhaust port.

[0059] Example 3

[0060] This embodiment provides a fluidized bed combustion system. The only difference between the fluidized bed combustion system and Embodiment 1 is that another cyclone-type mild gasification reaction device 1 is set at the relative position of the cyclone-type mild gasification reaction device 1 relative to the fluidized bed combustion reaction device. All other aspects are the same as Embodiment 1.

[0061] Application Example 1

[0062] This application example provides a fluidized bed combustion method, which employs the fluidized bed combustion system provided in Example 1. The fluidized bed combustion method includes:

[0063] After coal fuel is mixed with additive CaO (10% of the raw material feed), it is sent into a cyclone-type mild gasification reactor through conveying air. Part of the fuel is burned under the action of conveying air to provide mild gasification heat, while part of the fuel is mildly gasified under high temperature and oxygen-deficient conditions of 700℃ to generate crude coal gas and semi-coke. The remaining fuel directly enters the dense phase zone of the fluidized bed, where the combustion temperature is 880℃.

[0064] The generated crude gas is fed into the fluidized bed dilute phase zone through the crude gas inlet. There are three crude gas inlets in the furnace height direction, and the installation position is slightly higher than the middle of the dilute phase zone. The generated semi-coke falls into the dense phase zone through the feed inlet and enters the fluidized bed dense phase zone directly with the remaining fuel, where it is burned under the action of fluidizing air.

[0065] The total amount of fluidizing air and conveying air is configured at 0.9 of the total excess air coefficient, so that the dense phase zone is in an oxygen-deficient state, and the flue gas generated by combustion carries some solid particles into the dilute phase zone, where it is fully mixed with the crude gas injected from the crude gas inlet.

[0066] The gas-solid mixture carried out from the upper part of the dilute phase zone enters the gas-solid separation component. The separated solid particles return to the dense phase zone through the downward flow bed under the action of loosening gas to participate in combustion again. The purified flue gas is discharged outside the furnace. A burnout tuyer is set at the upper part of the dilute phase zone to supplement oxygen to oxidize residual CO and soot, ensuring complete combustion.

[0067] Application Example 2

[0068] This application example provides a fluidized bed combustion method, which employs the fluidized bed combustion system provided in Example 2. The fluidized bed combustion method includes:

[0069] The municipal sludge fuel is divided into two streams by the feeding device. The first part of the fuel is mixed with the additive CaO (10% of the raw material feed) and then sent to the spiral mild gasification reactor. The reactor is a horizontally arranged spiral conveying structure with a conveying air channel on the outside. The fuel is mildly gasified during the spiral propulsion process. The mild gasification temperature is 650℃, producing crude coal gas and semi-coke.

[0070] The generated crude gas is piped to the outside of the main furnace body and sent into the dilute phase zone through the crude gas inlet. The generated semi-coke and another part of the ungasified fuel fall into the dense phase zone for combustion through the feed inlet. The fluidized bed combustion temperature is 800℃. The dense phase zone adopts a bubbling fluidized bed structure. Fluidizing air is evenly sent in from the bottom air distribution plate to form a bubbling fluidized state.

[0071] The flue gas from the dense phase zone rises into the dilute phase zone, where it mixes and reacts with the raw coal gas. A burnout vent is installed at the top of the dilute phase zone to complete the final burnout. The flue gas is then discharged after being dusted by a cyclone separator.

[0072] Application Example 3

[0073] This application example provides a fluidized bed combustion method, which employs the fluidized bed combustion system provided in Example 3. The fluidized bed combustion method includes:

[0074] After coal fuel is mixed with additive CaO (10% of the raw material feed), it is sent into a cyclone-type mild gasification reactor through conveying air. Part of the fuel is burned under the action of conveying air to provide mild gasification heat, while part of the fuel is mildly gasified under high temperature and oxygen-deficient conditions of 700℃ to generate crude coal gas and semi-coke. The remaining fuel directly enters the dense phase zone of the fluidized bed, where the combustion temperature is 880℃.

[0075] The generated crude gas is fed into the fluidized bed dilute phase zone through the crude gas inlet. There are three crude gas inlets in the furnace height direction, and the installation position is slightly higher than the middle of the dilute phase zone. The generated semi-coke falls into the dense phase zone through the feed inlet and enters the fluidized bed dense phase zone directly with the remaining fuel, where it is burned under the action of fluidizing air.

[0076] The total amount of fluidizing air and conveying air is configured at 0.9 of the total excess air coefficient, so that the dense phase zone is in an oxygen-deficient state, and the flue gas generated by combustion carries some solid particles into the dilute phase zone, where it is fully mixed with the crude gas injected from the crude gas inlet.

[0077] The gas-solid mixture carried out from the upper part of the dilute phase zone enters the gas-solid separation component. The separated solid particles return to the dense phase zone through the downward flow bed under the action of loosening gas to participate in combustion again. The purified flue gas is discharged outside the furnace. A burnout tuyer is set at the upper part of the dilute phase zone to supplement oxygen to oxidize residual CO and soot, ensuring complete combustion.

[0078] Application Example 4

[0079] This application example provides a fluidized bed combustion method, which differs from Application Example 1 only in that the additive CaO is not added; otherwise, they are the same as Application Example 1.

[0080] Application Example 5

[0081] This application example provides a fluidized bed combustion method, which differs from Application Example 2 only in that the additive CaO is not added; otherwise, they are the same as Application Example 2.

[0082] Performance testing

[0083] The nitrogen oxide emissions were tested using the fluidized bed combustion method provided in the application example, and the results are shown in Table 1.

[0084] Table 1

[0085]

[0086] A comprehensive comparison of Application Examples 1 and 4 shows that, through the design of the combustion method described above, preliminary coal test results under the conditions of a mild gasification temperature of 700℃ and a fluidized bed combustion temperature of 880℃ demonstrate that, compared to conventional fluidized bed combustion, NO emissions can be reduced from approximately 250 ppm (based on an O2 content of 11%) to 100 ppm, a reduction of approximately 60%, and N2O emissions can be reduced from approximately 140 ppm to 60 ppm, a reduction of approximately 57%. Furthermore, when CaO (10% of the feed amount) is introduced as an additive during the mild gasification process, the NO emission concentration is reduced to approximately 85 ppm, a reduction of approximately 66%, and N2O is further reduced to 50 ppm, a reduction of approximately 65%. These data indicate that, through the regulation of reducing components such as NH3 / HCN during the mild gasification stage, this invention holds promise for enhancing the reduction process of nitrogen oxides.

[0087] A comprehensive comparison of Application Examples 2 and 5 shows that, through the design of the combustion method described above, preliminary experimental results of municipal sludge combustion under mild gasification temperature of 650℃ and fluidized bed combustion temperature of 800℃ indicate that, compared to conventional fluidized bed combustion, NO emissions can be reduced from approximately 420 ppm (based on an O2 content of 11%) to 160 ppm, a reduction of approximately 62%, and N2O emissions can be reduced from approximately 370 ppm to 120 ppm, a reduction of approximately 67%. Furthermore, when CaO (10% of the feed amount) is introduced as an additive during the mild gasification process, the NO emission concentration is reduced to approximately 130 ppm, a reduction of approximately 68%, and N2O is further reduced to 95 ppm, a reduction of approximately 74%. These data indicate that, through the regulation of reducing components such as NH3 / HCN during the mild gasification stage, this invention has the potential to enhance the reduction process of nitrogen oxides.

[0088] 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 fluidized bed combustion system, characterized in that, The fluidized bed combustion system includes a fluidized bed combustion reactor and a mild gasification reactor; The fluidized bed combustion reactor includes a dilute phase zone in the middle and a dense phase zone in the lower part; The gas phase outlet of the mild gasification reaction device is connected to the gas phase inlet of the dilute phase region, and the solid phase outlet of the mild gasification reaction device is connected to the solid phase inlet of the dense phase region.

2. The fluidized bed combustion system according to claim 1, characterized in that, The fluidized bed combustion system includes an air supply system; Preferably, the air supply system includes a conveying air system, a burnout air system, and a fluidizing air system. The gas outlet of the conveying air system is connected to the material inlet of the mild gasification reaction device, the gas outlet of the burnout air system is connected to the burnout air inlet of the dilute phase zone, and the gas outlet of the fluidizing air system is connected to the fluidizing air inlet of the dense phase zone.

3. The fluidized bed combustion system according to claim 1 or 2, characterized in that, The fluidized bed combustion reactor includes a circulating fluidized bed and / or a bubbling fluidized bed.

4. The fluidized bed combustion system according to any one of claims 1 to 3, characterized in that, A gas-solid separation component is connected to the top of the dilute phase region; Preferably, the gas-solid separation assembly has an exhaust port at the top; Preferably, the bottom of the gas-solid separation component is connected to a return leg, which is connected to the dense phase region; Preferably, the bottom of the return leg is provided with a loosening air inlet.

5. The fluidized bed combustion system according to any one of claims 1 to 4, characterized in that, The mild gasification reaction device includes a cyclone mild gasification reaction device and / or a spiral mild gasification reaction device; Preferably, 1-4 mild gasification reaction devices can be arranged circumferentially along the fluidized bed combustion reaction device.

6. A fluidized bed combustion method, characterized in that, The fluidized bed combustion method is carried out in the fluidized bed combustion system according to any one of claims 1 to 5.

7. The fluidized bed combustion method according to claim 6, characterized in that, The fluidized bed combustion method includes the following steps: After the fuel and additives are mixed in proportion, they enter the mild gasification reaction device and are burned to produce semi-coke and crude coal gas. The semi-coke and the remaining fuel enter the dense phase zone through the solid phase inlet, and the crude coal gas enters the dilute phase zone through the gas phase inlet, and mixes with the flue gas generated by the fluidized combustion in the dense phase zone for further combustion.

8. The fluidized bed combustion method according to claim 7, characterized in that, The fuel includes coal and / or biomass; Preferably, the additive includes an oxide or salt containing at least one element selected from iron, calcium, or aluminum.

9. The fluidized bed combustion method according to claim 7, characterized in that, The mass ratio of fuel to additives is ≥10.

10. The fluidized bed combustion method according to claim 7, characterized in that, The gas phase inlet of the dilute phase zone is set in the temperature range of 700-950℃ along the height direction of the fluidized bed combustion reactor.

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