A circulating fluidized bed boiler system and method for pure ammonia combustion

Abstract

The application discloses a circulating fluidized bed boiler system and method for realizing pure ammonia combustion, and the boiler system comprises a furnace, a wind distribution device, a cyclone separator and a return valve, a large amount of solid bed material particles in a good fluidized state are filled in the furnace, and the furnace has excellent heat transfer performance and large thermal inertia, so that stable combustion of pure ammonia fuel is realized under fluidization conditions, the combustion of pure ammonia meets the burnout requirement, the proportion of ammonia in the fuel is 100%, the pure ammonia is not mixed with other kinds of carbon-containing fossil fuels such as natural gas and coal, and zero carbon emission is truly realized. Meanwhile, the fluidization of the bed material particles strengthens the heat exchange between the inside of the fluidized bed and the wall surface of the fluidized bed, avoids the overheating phenomenon caused by heat accumulation, and improves the heat exchange performance. The combustion method provided by the application has high combustion efficiency and low nitrogen oxide emission, thereby effectively promoting the large-scale utilization of ammonia fuel, promoting the transformation and upgrading of an energy system, and reducing environmental pollution.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of clean energy, and in particular relates to a circulating fluidized bed boiler system and method for realizing efficient combustion of pure ammonia. BACKGROUND

[0002] Compared with hydrogen, ammonia has higher volumetric energy density, milder liquefaction conditions, and more mature and economical storage and transportation systems, and has broad application prospects. As a carbon-free energy, ammonia can store hydrogen produced by new energy in a more cost-advantageous way, and can be directly used in various combustion equipment. The widespread application of hydrogen-derived fuels including ammonia will effectively promote energy transformation and upgrading and the realization of the double carbon target.

[0003] Currently, the direct combustion of ammonia is mostly used in internal combustion engines, gas turbines and gas boilers. In addition, the low-carbon modification of many existing gas or coal-fired equipment is also a hot direction for ammonia combustion utilization, that is, ammonia is mixed with natural gas or coal for combustion, which promotes the orderly progress of low-carbon transformation of fossil energy. However, ammonia fuel has low flame propagation speed, difficult ignition, poor combustion stability, and contains ammonia elements itself, so two potential problems of low combustion efficiency and high nitrogen oxide emissions need to be solved for large-scale application of ammonia fuel as fuel. Although mixing ammonia fuel with organic gas components such as methane and solid fuels such as coal can significantly improve the combustion performance, but burning / mixing ammonia fuel in fossil fuels will still produce a considerable amount of carbon emissions, so in the long run, pure ammonia combustion technology needs to be developed. The scheme for improving the ignition and combustion performance of ammonia fuel in related technologies mostly needs to add additional equipment such as pre-cracking furnaces, noble metal catalysts, plasma ignition devices, etc., which increases the system investment and operation and maintenance costs. In addition, many ammonia combustion methods need to rely on tail SCR and other denitration devices to reduce NO x emissions, further reducing the economy. SUMMARY

[0004] The present application aims to at least partially solve one of the technical problems in the related art. To this end, embodiments of the present application propose a circulating fluidized bed boiler system for realizing pure ammonia combustion. Embodiments of the present application also propose a method for realizing pure ammonia combustion.

[0005] The circulating fluidized bed boiler system for realizing pure ammonia combustion provided by the embodiment of the present application comprises: a hearth, which has an ammonia gas inlet, a primary air inlet and a flue gas outlet, the ammonia gas inlet and the primary air inlet are arranged at the bottom of the hearth, pure ammonia is introduced into the ammonia gas inlet, the primary air inlet is used for introducing primary air to mix with the pure ammonia for combustion, the flue gas outlet is arranged at the top of the hearth, the hearth is filled with a fluidized bed formed by solid bed material particles, the ammonia gas inlet is located below the bed material surface, and the bed material particles are in a fluidized state under the action of airflow; an air distribution device, which has a plurality of air distribution units distributed on a horizontal plane, is arranged in the hearth and communicates with the ammonia gas inlet for air distribution; a cyclone separator and a return valve, the cyclone separator communicates with the flue gas outlet for solid-gas separation, and the return valve is arranged between the solid outlet of the cyclone separator and the hearth for returning the bed material particles separated by the cyclone to the hearth.

[0006] The core of the circulating fluidized bed boiler system and method for realizing pure ammonia combustion provided by the embodiment of the present application is that the hearth is filled with a large number of solid bed material particles in a good fluidized state, which has excellent heat transfer performance and large thermal inertia, so that the pure ammonia fuel can be stably combusted under the condition of fluidization, the combustion requirement of pure ammonia is met, the proportion of ammonia in the fuel is 100%, the fuel is not mixed with other types of carbon-containing fossil fuels such as natural gas and coal, and zero carbon emission is truly achieved. At the same time, the fluidization of the bed material particles strengthens the heat exchange between the inside of the fluidized bed and the wall surface of the hearth, avoids the overheating phenomenon caused by heat accumulation, and improves the heat exchange performance.

[0007] In addition, since complete combustion of pure ammonia is realized, hydrogen gas is not needed for mixing and combustion assistance, the storage and transportation problems of hydrogen are avoided, and high-cost auxiliary combustion means such as plasma ignition and noble metal catalyst are not relied on, thereby reducing the equipment cost and raw material cost.

[0008] In some embodiments, the bed material particles are metal oxide particles or fine coal ash particles with catalytic activity; and / or, the average particle size of the bed material particles is less than or equal to 150 μm.

[0009] In some embodiments, the hearth further has at least one secondary air inlet, the secondary air inlet is located above the bed material surface, the orientation of the secondary air inlet is front-to-back wall face-to-face collision, and the secondary air inlet is perpendicular to the main flow direction in the hearth;

[0010] When the secondary air inlets are multiple, the multiple secondary air inlets are arranged at intervals in the vertical direction, the distance between the lowermost secondary air inlet and the air distribution device in the vertical direction is 5%-10% of the height of the inner cavity of the hearth, and / or the distance between the uppermost secondary air inlet and the air distribution device in the vertical direction is 15%-20% of the height of the inner cavity of the hearth.

[0011] In some embodiments, the furnace is further provided with at least one auxiliary ammonia gas inlet located above the bed material surface, when the auxiliary ammonia gas inlet is multiple, the multiple auxiliary ammonia gas inlets are vertically spaced, the auxiliary ammonia gas inlet corresponds to the secondary air inlet one by one, the auxiliary ammonia gas inlet is located 1m-3m below the corresponding secondary air inlet in the vertical direction, and is higher than the secondary air inlet of the next level.

[0012] In some embodiments, further comprising: a pressure drop testing device for measuring the pressure drop of the fluidized bed in the furnace; a feeding device, a material inlet is provided on the side wall of the furnace, the material inlet is located above the bed material surface, the feeding device communicates with the material inlet, and the feeding device is used to supplement the bed material particles in the middle of the fluidized bed through the material inlet when the pressure drop of the fluidized bed is less than the lower limit of the set range.

[0013] In some embodiments, an ammonia supplement inlet is provided at the inlet of the cyclone separator, and a certain amount of ammonia gas is injected through the ammonia supplement inlet to reduce the residual nitrogen oxides in the flue gas.

[0014] Another aspect of the present application provides a method for realizing pure ammonia combustion, comprising the following steps:

[0015] The pure ammonia is sent into the furnace bottom of the furnace through the air distribution device, mixed with the primary air for reaction and combustion, and the flue gas stream generated by the combustion makes the bed material particles of the fluidized bed fluidized;

[0016] The flue gas carrying part of the bed material particles moves upward and enters the cyclone separator for gas-solid separation, the gas enters the tail convection flue from the gas outlet of the cyclone separator, and the bed material particles return to the furnace.

[0017] In some embodiments, at least one of the following conditions is met:

[0018] The combustion temperature in the furnace is between 800℃ and 900℃;

[0019] The temperature difference between the upper and lower parts of the fluidized bed is less than or equal to 30℃;

[0020] The oxygen content of the flue gas at the flue gas outlet is 3.0%-4.5%;

[0021] The fluidized wind speed in the furnace is greater than or equal to 2.5m / s and less than or equal to 3.5m / s;

[0022] The average pressure drop of the bed layer in the upper dilute phase section of the fluidized bed is at least 30Pa / m;

[0023] The average particle size of the bed material particles is less than or equal to 150μm.

[0024] In some embodiments, the method for achieving pure ammonia combustion satisfies the following conditions: the proportion of the ammonia injection amount of each of the plurality of auxiliary ammonia gas inlets to the total fuel amount decreases from bottom to top; and / or, the ammonia injection amount of the auxiliary ammonia gas inlet located at the bottom accounts for 10-15% of the total fuel amount.

[0025] In some embodiments, the method for achieving pure ammonia combustion further comprises: monitoring the concentration of nitrogen oxides at the inlet of the cyclone separator, and when the concentration of nitrogen oxides exceeds the upper limit of the set range, a certain amount of ammonia gas is injected through the ammonia supplement inlet to reduce the residual nitrogen oxides in the flue gas. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a structural schematic diagram of a circulating fluidized bed boiler system provided by an embodiment of the present application.

[0027] Figure 2 is a structural schematic diagram of a circulating fluidized bed boiler system provided by an embodiment of the present application.

[0028] Figure 3 is a structural schematic diagram of a circulating fluidized bed boiler system provided by an embodiment of the present application.

[0029] Figure 4 is a structural schematic diagram of a circulating fluidized bed boiler system provided by an embodiment of the present application.

[0030] Figure 5 is a structural schematic diagram of a circulating fluidized bed boiler system provided by an embodiment of the present application.

[0031] REFERENCE SIGNS:

[0032] 1 - liquid ammonia tank; 2 - gasification buffer tank; 3 - furnace; 31 - ammonia gas inlet; 32 - primary air inlet; 33 - flue gas outlet; 34 - fluidized bed; 35 - return material inlet; 361 - upper secondary air inlet; 362 - lower secondary air inlet; 371 - upper auxiliary ammonia gas inlet; 372 - lower auxiliary ammonia gas inlet; 4 - cyclone separator; 5 - return material valve; 6 - primary air fan; 7 - return material fan; 8 - air distribution device; 81 - air distribution unit; 9 - secondary air fan; 10 - material bin; 11 - first pressure sensor; 12 - second pressure sensor; 13 - ammonia supplement inlet. DETAILED DESCRIPTION

[0033] Embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings. The embodiments described below by reference to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0034] The following is based on Figures 1-5The basic structure of the circulating fluidized bed boiler system for realizing pure ammonia combustion is provided by the embodiment of the present application.

[0035] The circulating fluidized bed boiler system comprises a furnace 3, a cyclone separator 4, a return valve 5 and an air distribution device 8.

[0036] The furnace 3 has an ammonia inlet 31, a primary air inlet 32 and a flue gas outlet 33, the ammonia inlet 31 and the primary air inlet 32 are arranged at the bottom of the furnace 3, and the flue gas outlet 33 is arranged at the top of the furnace 3. The furnace 3 is filled with a fluidized bed 34 formed by solid bed material particles, the ammonia inlet 31 is located below the bed material surface of the fluidized bed 34, and the bed material surface of the fluidized bed 34 is the upper surface of the bed material. The air distribution device 8 has a plurality of air distribution units 81 distributed in the horizontal plane, and the air distribution device 8 is arranged in the furnace 3 and communicates with the ammonia inlet 31 for air distribution. Pure ammonia (ammonia ratio is 100%) is introduced into the ammonia inlet 31, primary air is introduced into the primary air inlet 32, and the primary air and the pure ammonia are mixed and combusted to generate flue gas. The flue gas flows upward, and the bed material particles are in a fluidized state under the action of the gas flow. The flue gas flows out from the flue gas outlet 33. Part of the fine particles in the fluidized bed 34 are carried upward by the flue gas flow and flow out from the flue gas outlet 33. The inlet of the cyclone separator 4 communicates with the flue gas outlet 33 for solid-gas separation, and the return valve 5 is arranged between the solid outlet of the cyclone separator 4 and the furnace 3 for returning the cyclone-separated bed material particles to the furnace 3.

[0037] The embodiment of the present application also provides a method for realizing pure ammonia combustion based on the circulating fluidized bed boiler system provided by any one of the embodiments of the present application, which comprises the following steps:

[0038] Pure ammonia (ammonia ratio is 100%) is sent into the furnace bottom of the furnace 3 through the air distribution device 8, mixed with the primary air for reaction and combustion, and the flue gas flow generated by the combustion makes the bed material particles of the fluidized bed 34 fluidize;

[0039] The flue gas carrying part of the bed material particles moves upward, enters the cyclone separator 4 for gas-solid separation, and the separated gas enters the tail convection flue from the gas outlet of the cyclone separator 4. The separated bed material particles return to the furnace 3 through the return valve 5.

[0040] The core of the circulating fluidized bed boiler system and the method for realizing pure ammonia combustion provided by the embodiment of the present application is that the furnace is filled with a large number of solid bed material particles in a good fluidized state, which has excellent heat transfer performance and large thermal inertia, so that the pure ammonia fuel can be stably combusted under the condition of fluidization, the combustion requirement of pure ammonia is met, the proportion of ammonia in the fuel is 100%, and the fuel is not mixed with other kinds of carbon-containing fossil fuels such as natural gas and coal, so that zero carbon emission is truly achieved. At the same time, the fluidization of the bed material particles strengthens the heat exchange between the inside of the fluidized bed and the wall surface of the furnace, avoids the over-temperature phenomenon caused by heat accumulation, and improves the heat exchange performance.

[0041] Furthermore, since the complete combustion of pure ammonia is achieved, there is no need for hydrogen to be mixed in for combustion, thus avoiding the problems of hydrogen storage and transportation. It also does not rely on high-cost auxiliary combustion methods such as plasma ignition and precious metal catalysts, thereby reducing equipment and raw material costs.

[0042] In the method for achieving pure ammonia combustion provided in the embodiments of the present invention, in order to form a bed with a relatively high particle concentration in the furnace and at the same time form strong solid axial back mixing to increase the gas-solid residence time, it is further preferred that the bed material particles in the furnace are in a rapid fluidized state during operation.

[0043] The following is based on Figures 1-5 This invention describes a circulating fluidized bed boiler system and method for achieving pure ammonia combustion in several specific embodiments provided by the present invention.

[0044] Example 1:

[0045] like Figure 1 As shown, the circulating fluidized bed boiler system provided in this embodiment includes a liquid ammonia tank 1, a gasification buffer tank 2, a furnace 3, a cyclone separator 4, a return valve 5, a primary air fan 6, a return air fan 7, an air distribution device 8, and an ammonia injection device for the air distribution zone.

[0046] Liquid ammonia tank 1 is used to store liquid ammonia. The inlet of vaporization buffer tank 2 is connected to the outlet of liquid ammonia tank 1, and it is used to convert liquid ammonia into gaseous pure ammonia and buffer it. Vaporization buffer tank 2 is connected to the ammonia inlet 31 of furnace 3, and an ammonia injection device (not shown in the figure) is provided at the ammonia inlet 31. The pure ammonia in vaporization buffer tank 2 is injected into furnace 3 through the ammonia injection device. The primary air inlet 31 of furnace 3 is located at the bottom of furnace 3. The circulating fluidized bed boiler system also includes a primary air duct connected to the primary air inlet 31, and a primary air fan 6 is installed in the primary air duct to blow primary air into the primary air inlet 31.

[0047] Ammonia gas entering furnace 3 mixes and reacts with primary air, then flows upwards through air distribution device 8 into the fluidized bed 34 of furnace 3. The flue gas flow generated by ammonia combustion fluidizes the bed material particles. Due to the excellent heat transfer performance and high thermal inertia of the bed material particles, pure ammonia fuel achieves stable combustion under fluidized bed conditions, while simultaneously meeting the burnout requirements of pure ammonia. Furthermore, the proportion of ammonia in pure ammonia fuel is 100%, and it is not co-fired with other types of fuels such as natural gas or coal, truly achieving low cost and zero carbon emissions.

[0048] The flue gas entrains part of the bed material fine particles to move upward, and flows out from the flue gas outlet 33 at the top of the furnace 3 into the cyclone separator 4 for gas-solid separation. The separated flue gas flows into the tail-end convection flue from the gas outlet of the cyclone separator 4 for subsequent treatment, and the separated solid bed material particles flow out from the bottom of the cyclone separator 4 and return to the furnace 3 through the return valve 5 on the return pipe.

[0049] As shown in Figure 1 , the return valve 5 is provided with a return fan 7, which is used to blow gas into the return pipe to push the bed material particles into the furnace 3.

[0050] Further, the interface between the return pipe and the furnace 3 (i.e. the return inlet 35 of the furnace 3 as shown in Figure 1 ) is located below the bed material surface of the fluidized bed 34.

[0051] In this embodiment, in order to promote the oxidation of ammonia and the reduction of ammonia oxides, metal oxide particles or fine coal ash particles with relevant catalytic activity are selected as bed material particles. The surface of such bed material particles has significant catalytic activity for the oxidation of ammonia, which promotes the combustion and burnout of ammonia, and has the advantages of good stable combustion performance and low ammonia escape rate. In addition, the fluidization of the bed material particles greatly increases the gas-solid phase interface area, which is beneficial to the heterogeneous reactions such as catalytic oxidation of ammonia on the surface of active bed material particles and catalytic reduction of nitrogen oxides (NO x ), and helps to improve the ammonia conversion rate.

[0052] Further, in order to obtain a larger specific surface area of particles and reduce the wind resistance, and to ensure that the particles in the furnace 3 can be in fast fluidization, preferably, the bed material particles are selected from active metal oxide powders or fine coal ash particles belonging to Geldart A or B particles.

[0053] Further preferably, the average particle size of the bed material particles is less than or equal to 150 μm.

[0054] In the combustion method based on the circulating fluidized bed boiler system provided in this embodiment, the temperature of the furnace 3 is set by comprehensively considering the ignition characteristics of ammonia and the emission characteristics of nitrogen oxides, and preferably, the combustion temperature in the furnace 3 is between 800℃ and 900℃, and the temperature difference between the upper and lower parts of the fluidized bed is less than or equal to 30℃.

[0055] If the combustion temperature in the furnace 3 is less than 800℃, the temperature is too low, which is not conducive to the ignition and burnout of ammonia, and the ammonia escape rate is high; if the combustion temperature in the furnace 3 is higher than 900℃, the temperature is too high, which will cause a large amount of nitrogen oxide emissions. Therefore, the combustion temperature in the furnace 3 is between 800℃ and 900℃, that is, the ammonia can be burned out, and the nitrogen oxide emissions can be reduced. In addition, the combustion temperature in the fluidized bed is moderate and the bed temperature distribution is uniform, which can prevent local heat accumulation and overheating, avoid accidents such as damage to the furnace heating surface and pipe explosion.

[0056] Further, the oxygen content of the flue gas at the flue gas outlet 33 is set by comprehensively considering the ammonia combustion and nitrogen oxide emission characteristics, and preferably, the oxygen content of the flue gas at the flue gas outlet 33 is 3.0%-4.5%. If the oxygen content of the flue gas at the flue gas outlet 33 is less than 3.0%, the oxygen content is too low, which is not conducive to the burnout of ammonia; if the oxygen content of the flue gas at the flue gas outlet 33 is higher than 4.5%, the oxygen content is too high, which will lead to a large amount of nitrogen oxide emissions. Therefore, the oxygen content of the flue gas at the flue gas outlet 33 is 3.0%-4.5%, which is helpful for the burnout of ammonia and the reduction of nitrogen oxide emissions.

[0057] Further, in the method for realizing pure ammonia combustion provided by the embodiment, the bed material particles are in a good fluidized state, and a certain particle suspension concentration needs to be ensured, so as to meet the stable combustion and burnout requirements of the fuel ammonia by means of the high heat transfer performance and large thermal inertia of the bed material particles. In order to achieve the ideal gas-solid fluidization state and improve the ammonia conversion rate and heat transfer performance, the fluidization wind speed, the upper bed layer pressure drop and the average bed material particle size need to be controlled within a certain range.

[0058] Preferably, the fluidization wind speed in the furnace 3 is greater than or equal to 2.5m / s, and the fluidization wind speed refers to the flow speed of the flue gas flow in the furnace 3. Further, in order to ensure sufficient gas residence time for the burnout of the fuel ammonia, the fluidization wind speed cannot be too high, and the fluidization wind speed in the furnace 3 is more preferably greater than or equal to 2.5m / s and less than or equal to 3.5m / s, which is helpful for the burnout of the fuel ammonia.

[0059] Preferably, the average pressure drop of the upper dilute phase section bed layer of the fluidized bed is at least 30Pa / m, and the average particle size of the bed material particles is less than or equal to 150μm.

[0060] Embodiment two:

[0061] As shown in Figure 2 The circulating fluidized bed boiler system provided by the embodiment includes a liquid ammonia tank 1, a gasification buffer tank 2, a furnace 3, a cyclone separator 4, a return material valve 5, a primary air fan 6, a return material fan 7, a wind distribution device 8 and a wind distribution area ammonia injection device. The connection relationship and arrangement mode of the above-mentioned devices can refer to embodiment one, and details are not described here. Only the different parts are described.

[0062] The circulating fluidized bed boiler system provided by the embodiment further comprises a secondary air fan 9 and a secondary air duct, the furnace 3 is further provided with at least one secondary air port, the secondary air duct is in communication with each secondary air port, and the secondary air fan 9 is arranged in the secondary air duct and used for blowing secondary air into the secondary air port through the secondary air duct. The secondary air port is located above the bed material surface of the fluidized bed 24, and the secondary air port 36 is oriented to face the front and back walls and is perpendicular to the main flow direction in the furnace 2, thereby strengthening the mixing of the secondary air and the main flow gas.

[0063] The embodiment adopts air staging, and the blowing of the secondary air is used to reduce the combustion proportion of the bottom of the furnace, avoid over-temperature of the bottom, and protect the hypoxic atmosphere of the lower part of the furnace 3, thereby helping to inhibit the original generation of nitrogen oxides and further reduce the emission of nitrogen oxides.

[0064] Specifically, as shown in the figure, Figure 2 the circulating fluidized bed boiler system provided by the embodiment adopts double air staging, the side wall of the furnace 3 is provided with two secondary air ports, namely an upper secondary air port 361 and a lower secondary air port 362, the upper secondary air port 361 is located above the lower secondary air port 362 in the vertical direction, both of the two secondary air ports are oriented to face the front and back walls, and both of the two secondary air ports are located above the bed material surface.

[0065] In order to achieve the ideal air staging effect, in the embodiment, the distance between the lower secondary air port 362 and the air distribution device 8 in the vertical direction is preferably 5%-10% of the height of the inner cavity of the furnace 3, and the distance between the upper secondary air port 361 and the air distribution device 8 in the vertical direction is preferably 15%-20% of the height of the inner cavity of the furnace 3.

[0066] Further, the primary air proportion is set to 40%-60%, and the secondary air proportion of the upper secondary air port 361 is 15%-25% when double air staging is adopted.

[0067] In other alternative embodiments, the circulating fluidized bed boiler system adopts single air staging, and the secondary air port is one, that is, single air staging is adopted, and the distance between the secondary air port and the air distribution device 8 in the vertical direction is preferably 5%-10% of the height of the inner cavity of the furnace 3.

[0068] Alternatively, in other alternative embodiments, the secondary air port can be more than two, and the plurality of secondary air ports are arranged at intervals in the vertical direction, the distance between the lowermost secondary air port and the air distribution device 8 in the vertical direction is preferably 5%-10% of the height of the inner cavity of the furnace 3, and / or the distance between the uppermost secondary air port and the air distribution device 8 in the vertical direction is preferably 15%-20% of the height of the inner cavity of the furnace 3.

[0069] Embodiment three:

[0070] As shown in the figure, Figure 3As shown, the circulating fluidized bed boiler system provided by the embodiment includes a liquid ammonia tank 1, a gasification buffer tank 2, a furnace 3, a cyclone separator 4, a return valve 5, a primary air fan 6, a return air fan 7, a wind distribution device 8, an ammonia injection device in the wind distribution area, and a secondary air fan 9. The connection relationship and arrangement mode of the above devices can refer to Embodiment Two, which will not be described herein again, and only the different parts will be described.

[0071] The circulating fluidized bed boiler system provided by the embodiment adopts fuel staging, and the furnace 3 is further provided with at least one auxiliary ammonia gas inlet. The auxiliary ammonia gas inlet is located above the bed material surface of the fluidized bed 34, and is used to introduce pure ammonia into the furnace 3, so as to effectively reduce the part of nitrogen oxides generated by ammonia combustion in the lower part of the furnace 3, thereby reducing the emission concentration of the final nitrogen oxides.

[0072] Specifically, as shown in the figure, Figure 3 The furnace 3 is provided with an upper auxiliary ammonia gas inlet 371 and a lower auxiliary ammonia gas inlet 372. The upper auxiliary ammonia gas inlet 371 and the lower auxiliary ammonia gas inlet 372 are arranged in a vertically opposite direction and are located above the bed material surface of the fluidized bed. The upper auxiliary ammonia gas inlet 371 and the lower auxiliary ammonia gas inlet 372 are both connected to the gas outlet of the gasification buffer tank through a pipeline.

[0073] In order to simplify the system arrangement, as shown in the figure, Figure 3 The upper auxiliary ammonia gas inlet 371 and the lower auxiliary ammonia gas inlet 372 are arranged on the front wall of the furnace 3 and are introduced from one side. By spraying a small amount of ammonia fuel into the furnace 3 through the upper auxiliary ammonia gas inlet 371 and the lower auxiliary ammonia gas inlet 372 at different heights, the auxiliary sprayed ammonia fuel can effectively reduce the part of nitrogen oxides generated by ammonia combustion in the lower part of the furnace 3, thereby reducing the emission concentration of the final nitrogen oxides.

[0074] In other alternative embodiments, single fuel staging can be adopted, that is, only the lower auxiliary ammonia gas inlet 372 can be provided, and optionally, the proportion of ammonia sprayed from the lower auxiliary ammonia gas inlet 372 to the total fuel amount is 10%-15%. Alternatively, in other alternative embodiments, the auxiliary ammonia gas inlet can be more than two, and the multiple auxiliary ammonia gas inlets are arranged in a vertically opposite direction and are located above the fluidized bed 34.

[0075] Further, in order to achieve the ideal fuel staging effect and ensure that the staged ammonia fuel can be burned out, the auxiliary ammonia gas inlet corresponds to the secondary air port one by one, and the auxiliary ammonia gas inlet is located below the corresponding secondary air port in the vertical direction and is higher than the secondary air port of the next level.

[0076] Specifically, as shown in the figure, Figure 3As shown, the lower auxiliary ammonia gas inlet 372 is located 1-3 m below the lower secondary air inlet 362 and above the bed material surface of the fluidized bed 34, and the upper auxiliary ammonia gas inlet 371 is located 1-3 m below the upper secondary air inlet 361 and above the lower secondary air inlet 362.

[0077] Further, in the embodiment provided with multiple auxiliary ammonia gas inlets, the method for realizing pure ammonia combustion satisfies at least one of the following conditions:

[0078] The proportion of the ammonia injection amount of the multiple auxiliary ammonia gas inlets to the total fuel amount decreases from bottom to top;

[0079] The ammonia injection amount of the lowermost auxiliary ammonia gas inlet accounts for 10%-15% of the total fuel amount.

[0080] As an example, in the combustion method based on the circulating fluidized bed boiler system provided by the embodiment, the proportion of the ammonia injected from the lower auxiliary ammonia gas inlet 372 to the total fuel amount is set to 10%-15%, and the proportion of the ammonia injected from the upper auxiliary ammonia gas inlet 371 to the total fuel amount is set to 5%-10%.

[0081] Embodiment Four:

[0082] As shown, Figure 4 the circulating fluidized bed boiler system provided by the embodiment includes a liquid ammonia tank 1, a gasification buffer tank 2, a hearth 3, a cyclone separator 4, a return material valve 5, a primary air fan 6, a return material fan 7, a wind distribution device 8, a wind distribution zone ammonia injection device, and a secondary air fan 9. The connection relationship and arrangement mode of the above-mentioned devices can refer to Embodiment Three, which will not be described here again, and only the different parts will be described.

[0083] The circulating fluidized bed boiler system provided by the embodiment further includes a pressure drop testing device and a feeding device. The pressure drop testing device is used to measure the pressure drop of the fluidized bed 34 in the hearth 3. A material inlet is arranged on the side wall of the hearth 3, which is located above the bed material surface of the fluidized bed 34. The feeding device is in communication with the material inlet and is used to supplement bed material particles to the middle part of the fluidized bed 34 through the material inlet when the pressure drop of the fluidized bed 34 is less than the lower limit of the set range.

[0084] This is because, after a long period of operation, part of the bed material particles in the hearth 3 are worn and generate fine particles, which may leave from the gas outlet of the cyclone separator 4 in the form of fly ash, resulting in a decrease in the bed inventory and then deviating from the set fluidization state. New bed material particles need to be supplemented from time to time to meet the ammonia combustion demand.

[0085] Specifically, as shown, Figure 4As shown, the pressure drop testing device comprises a first pressure sensor 11 and a second pressure sensor 12, the first pressure measuring point is arranged at the upper position of the furnace 3, and the second pressure measuring point is arranged at the lower position of the furnace 3, the first pressure measuring point is above the bed material surface of the fluidized bed 34, the second pressure measuring point is below the bed material surface of the fluidized bed 34, and in order to avoid measurement error, the second pressure measuring point is above the air distribution device 8. The first pressure sensor 11 is arranged at the first pressure measuring point, and the second pressure sensor 12 is arranged at the second pressure measuring point, and the first pressure sensor 11 and the second pressure sensor 12 are used to measure the pressure drop of the fluidized bed 34 in the furnace 3. The feeding device is a material bin 10, which is in communication with the material inlet.

[0086] The combustion method of the circulating fluidized bed boiler system provided in the embodiment further comprises the following feeding and material inventory adjusting operations:

[0087] a) Before the system is started, a sufficient amount of bed material particles are sent into the furnace 3, and a certain amount of bed material particles are stored in the material bin 10;

[0088] b) During operation, the bed pressure drop in the furnace 3 is obtained through the first pressure sensor 11 and the second pressure sensor 12, when the bed pressure drop is within the set range, it indicates that the inventory of bed material particles in the furnace 3 is normal, and no feeding is required; when the bed pressure drop is less than the lower limit of the set range, it indicates that the inventory of bed material particles in the furnace 3 is insufficient, the material bin 10 needs to be opened to supplement the bed material particles to the furnace 3, so that the bed pressure drop in the furnace 3 returns to the set range.

[0089] Optionally, the average particle size of the bed material particles supplemented through the material bin 10 is less than or equal to 100 μm.

[0090] Embodiment 5:

[0091] As shown in the figure, Figure 5 The circulating fluidized bed boiler system provided in the embodiment comprises a liquid ammonia tank 1, a gasification buffer tank 2, a furnace 3, a cyclone separator 4, a return valve 5, a primary air fan 6, a return air fan 7, an air distribution device 8, an air distribution zone ammonia injection device, and a secondary air fan 9. The connection relationship and arrangement mode of the above-mentioned devices can refer to Embodiment Four, which will not be described here again, and only the different parts will be described.

[0092] The inlet of the cyclone separator 4 of the circulating fluidized bed boiler system provided in the embodiment is provided with a supplementary ammonia inlet 13, a certain amount of ammonia gas is injected through the supplementary ammonia inlet 13 to reduce the residual nitrogen oxides in the flue gas, so as to further ensure that the content of nitrogen oxides in the discharged flue gas meets the standard.

[0093] Specifically, as shown in the figure, Figure 5As shown, the flue gas outlet 33 of the furnace 3 is communicated with the inlet of the cyclone separator 4 through a horizontal flue, and the ammonia supplement inlet 13 is arranged in the horizontal flue. The outlet of the gasification buffer tank 2 is communicated with the ammonia supplement inlet 13, so as to spray a certain amount of ammonia into the ammonia supplement inlet 13, to reduce the residual nitrogen oxides in the flue gas, so as to ensure that the nitrogen oxides meet the emission standard.

[0094] The combustion method based on the circulating fluidized bed boiler system provided in the embodiment further includes the following steps:

[0095] The concentration of nitrogen oxides at the inlet of the cyclone separator 4 (i.e. at the flue gas outlet 33 of the furnace 3) is monitored, and when the concentration of nitrogen oxides exceeds the upper limit of the set range, a certain amount of ammonia gas is sprayed into the ammonia supplement inlet 13 to reduce the residual nitrogen oxides in the flue gas.

[0096] In some preferred embodiments, the ammonia nitrogen ratio at the inlet of the cyclone separator 4 is maintained within the range of 1.5-2.0.

[0097] In the method for realizing pure ammonia combustion provided in the embodiment, liquid ammonia is gasified and then sent into the furnace of the circulating fluidized bed boiler, reacts with air and burns, the flue gas makes the bed material particles in the furnace in a fluidized state, and the solid particles form a circulation in the furnace under the action of the separator and the material returning device, and the high-temperature flue gas enters the tail part of the convection flue. In the fluidized combustion state, the bed material particles have very high heat transfer performance, which is beneficial to the ignition of ammonia. A large number of circulating active solid particles provide a heterogeneous catalytic surface for ammonia oxidation, which promotes the burnout of ammonia. The temperature distribution in the fluidized bed is uniform, which can prevent heat accumulation, and in combination with the heterogeneous reduction of nitrogen oxides, the emission of nitrogen oxides can be effectively reduced. The combustion method provided in the embodiment has high combustion efficiency and low nitrogen oxide emission, thereby effectively promoting the large-scale utilization of ammonia fuel, promoting the transformation and upgrading of the energy system, and reducing environmental pollution.

[0098] In summary, the circulating fluidized bed boiler system and method for realizing pure ammonia combustion provided in the embodiment have the following advantages and outstanding technical effects:

[0099] ① 100% pure ammonia fuel combustion is realized, without mixing with other carbon-containing fossil fuels, achieving zero carbon emission;

[0100] ② Hydrogen mixing for combustion is not required, avoiding the storage and transportation difficulties of hydrogen, and avoiding the use of high-cost auxiliary combustion means such as plasma ignition and noble metal catalysts, thereby reducing the fuel cost;

[0101] ③ A large number of solid bed material particles in a fluidized state exist in the circulating fluidized bed, these bed material particles have excellent heat transfer performance, large thermal inertia, and some active particle surfaces have significant catalytic activity for ammonia oxidation, thereby effectively promoting the ignition and burnout of ammonia, and having good stable combustion performance and low ammonia escape rate;

[0102] ④The combustion temperature in the fluidized bed is moderate, and the bed temperature distribution is uniform, which can prevent local heat accumulation from overheating, and avoid accidents such as damage of the furnace heating surface and pipe explosion;

[0103] ⑤Due to the medium-temperature combustion, combined with the air staging and fuel staging measures, the generation of nitrogen oxides is reduced, and some active particle surfaces can also selectively catalyze the reduction of nitrogen oxides by ammonia, thereby reducing the nitrogen oxide emission concentration of the boiler, and having the advantage of low-nitrogen combustion;

[0104] ⑤The bed material inventory in the furnace is monitored by using the bed pressure drop dynamics, and the feeding device can be used to realize long-term stable operation of the system.

[0105] In the description of the present application, it should be understood that the orientations or positional relationships indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0106] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise explicitly specified and limited.

[0107] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection", "fixing" and the like should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected or in communication with each other; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0108] In the present application, unless specifically stated and limited otherwise, a first feature "on" or "under" a second feature can be directly in contact with the second feature, or indirectly in contact with the second feature through an intermediate medium. Also, a first feature "over", "above" and "on top of" a second feature can be directly above or obliquely above the second feature, or simply means that the first feature is horizontally higher than the second feature. A first feature "under", "below" and "underneath" a second feature can be directly below or obliquely below the second feature, or simply means that the first feature is horizontally lower than the second feature.

[0109] In the present application, the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" mean that a particular feature, structure, material or characteristic is included in at least one embodiment or example of the present application. Exemplary representations of the above terms in the specification are not necessarily directed to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics can be combined in any suitable manner in one or more embodiments or examples. In addition, different embodiments or examples described in the specification and features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0110] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A circulating fluidized bed boiler system enabling pure ammonia combustion, characterized in that, The furnace comprises: a furnace chamber, the furnace chamber having an ammonia gas inlet, a primary air inlet, and a flue gas outlet, the ammonia gas inlet and the primary air inlet being arranged at the bottom of the furnace chamber, the ammonia gas inlet being connected to pure ammonia, the primary air inlet being connected to primary air for mixing combustion with pure ammonia, the flue gas outlet being arranged at the top of the furnace chamber, the furnace chamber being filled with a fluidized bed formed by solid bed material particles, the ammonia gas inlet being located below the bed material surface, the bed material particles being in a fluidized state under the action of the gas flow; an air distribution device arranged in the furnace chamber and communicating with the ammonia gas inlet for air distribution; a cyclone separator communicating with the flue gas outlet for solid-gas separation, and a return valve arranged between the solid outlet of the cyclone separator and the furnace chamber for returning the cyclone-separated bed material particles to the furnace chamber; a pressure drop testing device for measuring the pressure drop of the fluidized bed in the furnace chamber; a feeding device, a material inlet being arranged on the side wall of the furnace chamber and located above the bed material surface, the feeding device communicating with the material inlet, the feeding device being used to supplement bed material particles to the middle of the fluidized bed through the material inlet when the pressure drop of the fluidized bed is less than the lower limit of the set range; the bed material particles are metal oxide particles or fine coal ash particles with catalytic activity; and / or, the average particle size of the bed material particles is less than or equal to 150 μm.

2. The circulating fluidized bed boiler system for achieving pure ammonia combustion according to claim 1, characterized by, The furnace chamber further comprises at least one secondary air inlet, the secondary air inlet being located above the bed material surface, the secondary air inlet being oriented to face the front wall and the back wall, and being perpendicular to the main flow direction in the furnace chamber; when the secondary air inlets are multiple, the multiple secondary air inlets are arranged in the vertical direction, the distance between the lowermost secondary air inlet and the air distribution device in the vertical direction is 5%-10% of the height of the inner cavity of the furnace chamber, and / or, the distance between the uppermost secondary air inlet and the air distribution device in the vertical direction is 15%-20% of the height of the inner cavity of the furnace chamber.

3. The circulating fluidized bed boiler system for achieving pure ammonia combustion according to claim 2, characterized by, The furnace chamber further comprises at least one auxiliary ammonia gas inlet, the auxiliary ammonia gas inlet being located above the bed material surface, when the auxiliary ammonia gas inlets are multiple, the multiple auxiliary ammonia gas inlets are arranged in the vertical direction, the multiple auxiliary ammonia gas inlets correspond to the multiple secondary air inlets one by one, the auxiliary ammonia gas inlet is located 1m-3m below the corresponding secondary air inlet in the vertical direction, and is higher than the secondary air inlet at the next level.

4. The circulating fluidized bed boiler system for achieving pure ammonia combustion according to claim 1, wherein, An ammonia supplement inlet is arranged at the inlet of the cyclone separator, a certain amount of ammonia gas is injected through the ammonia supplement inlet to reduce the residual nitrogen oxides in the flue gas.

5. A method for pure ammonia combustion based on the circulating fluidized bed boiler system according to any one of claims 1 - 4, characterized by The method comprises the following steps: pure ammonia is sent into the furnace bottom of the furnace chamber through the air distribution device, mixed with primary air for reaction and combustion, and the flue gas flow generated by combustion fluidizes the bed material particles of the fluidized bed; the flue gas carrying part of the bed material particles moves upward, enters the cyclone separator for gas-solid separation, the gas enters the tail section of the convection flue from the gas outlet of the cyclone separator, and the bed material particles return to the furnace chamber.

6. The method of achieving pure ammonia combustion as claimed in claim 5 wherein, at least one of the following conditions is met: the combustion temperature in the furnace chamber is between 800℃ and 900℃; The temperature difference between the upper and lower parts of the fluidized bed is less than or equal to 30℃; The oxygen content of the flue gas at the flue gas outlet is 3.0%-4.5%; The fluidization air speed in the furnace is greater than or equal to 2.5m / s and less than or equal to 3.5m / s; The average pressure drop of the upper dilute phase section of the fluidized bed is at least 30Pa / m; The average particle size of the bed material is less than or equal to 150μm.

7. The method of achieving pure ammonia combustion as claimed in claim 5 wherein, The method for achieving pure ammonia combustion is based on the circulating fluidized bed boiler system of claim 3, and the auxiliary ammonia gas inlets are multiple, and the method for achieving pure ammonia combustion satisfies the following conditions: The proportion of the ammonia injection amount of the multiple auxiliary ammonia gas inlets to the total fuel amount decreases from bottom to top; And / or, the ammonia injection amount of the auxiliary ammonia gas inlet at the bottom accounts for 10%-15% of the total fuel amount.

8. The method of achieving pure ammonia combustion as claimed in claim 5 wherein, The method for achieving pure ammonia combustion is based on the circulating fluidized bed boiler system of claim 4, and the method for achieving pure ammonia combustion further comprises: Monitoring the concentration of nitrogen oxides at the inlet of the cyclone separator, and when the concentration of nitrogen oxides exceeds the upper limit of the set range, a certain amount of ammonia gas is injected through the ammonia supplement inlet to reduce the residual nitrogen oxides in the flue gas.

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