Coal-fired circulating fluidized bed boiler graded ammonia doping system and method capable of adjusting ammonia doping proportion

Abstract

The invention discloses a coal-fired circulating fluidized bed boiler graded ammonia doping system and method capable of adjusting the ammonia doping proportion. Comprising a first-stage ammonia gas channel, a second-stage ammonia gas channel, a third-stage ammonia gas channel, a fourth-stage ammonia gas channel, a furnace bottom primary air distribution plate, a primary fan, a primary air box, a lower secondary air cylinder, a coal spreading pipe, an upper secondary air cylinder, a cyclone separator inlet ammonia gas measuring point, a NOx measuring point and a NOx measuring point in a tail flue. The first-stage ammonia gas channel is arranged at the position of the primary air box in a penetrating mode, the second-stage ammonia gas channel is arranged between the upper secondary air cylinder and the lower secondary air cylinder, the third-stage ammonia gas channel is arranged above the upper secondary air cylinder, and the fourth-stage ammonia gas channel is arranged below the top of the hearth. The four stages of ammonia gas channels are arranged, the provided adjusting method is combined, ammonia doping adjustment of the coal-fired circulating fluidized bed boiler under different loads in different proportions is achieved, the ammonia doping flexibility is improved, and the combustion stability of the circulating fluidized bed boiler under the low load is improved.

Description

Technical Field

[0001] The invention belongs to the field of coal-fired power generation, and in particular relates to a graded ammonia doping system and method for a coal-fired circulating fluidized bed boiler with adjustable ammonia doping ratio. Background Art

[0002] Currently, CO 2 The huge impact on global climate change has received more and more widespread attention. Reducing carbon emissions from power systems dominated by coal-fired power plants is of great significance to reducing carbon peaks. Blending carbon-free fuels is a way to reduce carbon emissions from the source. Among them, ammonia and hydrogen are two carbon-free fuels that have received more attention. Compared with hydrogen, ammonia has the advantages of easy liquefaction, easy storage and transportation, and mature production and storage infrastructure. Therefore, ammonia has the potential to achieve clean combustion utilization in the short term.

[0003] Circulating fluidized bed boiler is a coal-fired boiler system that has developed rapidly in recent years. It can achieve very good combustion effect through the circulation of high-temperature particles in the furnace. Compared with traditional pulverized coal boilers, circulating fluidized bed boilers have the advantages of strong adaptability to coal types, high combustion efficiency, and simple system; especially in the medium and low load range, the advantages of circulating fluidized bed boilers are more obvious: in the medium and low load state, the heat generated by fuel combustion is stored in the circulating particles. When receiving the load increase command, it only needs to increase the air volume and fuel delivery to achieve a very fast load increase speed.

[0004] Therefore, realizing ammonia-blended combustion in a circulating fluidized bed boiler is a very promising technical direction.

[0005] In order to use ammonia as a fuel for blending in coal-fired power plants and obtain better ignition, stable combustion, burnout and emission characteristics, the structural design of the boiler is crucial. Therefore, in order to make the ammonia blending combustion cleaner, safer and more efficient, it is very necessary to design an ammonia blending combustion system suitable for coal-fired circulating fluidized bed. Summary of the invention

[0006] The present invention provides a system and method for graded ammonia doping of a coal-fired circulating fluidized bed boiler with adjustable ammonia doping ratio, which has the following characteristics:

[0007] It includes the primary ammonia channel, the secondary ammonia channel, the tertiary ammonia channel, the fourth ammonia channel, the primary air distribution plate at the bottom of the furnace, the primary fan, the primary wind box, the lower secondary air duct, the coal spreading pipe, the upper secondary air duct, the ammonia measuring point and NOx measuring point at the inlet of the cyclone separator, and the NOx measuring point in the tail flue.

[0008] The primary fan, the primary wind box and the primary wind distribution plate at the furnace bottom constitute the primary wind channel at the furnace bottom. An inspection hole is provided at the primary wind box. The first-level ammonia channel is penetrated in the primary wind box along the inspection hole. Ammonia and the primary air are mixed and enter the furnace together.

[0009] By adopting the above technical solution, the uniform mixing of the primary ammonia and the primary air can be achieved, preventing the ammonia from having too great an impact on the fluidization of the particles, and maintaining the normal circulation of the particles.

[0010] The upper and lower secondary air ducts are connected to the circulating fluidized bed body, the lower secondary air duct is arranged at the lower part of the furnace, 6 to 7 meters away from the bottom of the furnace; the secondary ammonia channel is arranged at the upper part of the lower secondary air duct, 2 to 2.5 meters away from the lower secondary air duct; the upper secondary air duct is arranged 2 to 2.5 meters above the secondary ammonia channel; the tertiary ammonia channel is arranged 2 to 2.5 meters above the upper secondary air duct.

[0011] By adopting the above technical solution, it is possible to ensure that the secondary and tertiary ammonia enter the furnace evenly and mix evenly with the fuel particles and gas, thereby improving the combustion and reduction efficiency, while also avoiding the influence of the mixed ammonia on the flow field inside the furnace.

[0012] The fourth-stage ammonia channel is connected to the circulating fluidized bed body and is located 7 to 7.5 meters below the top of the furnace.

[0013] By adopting the above technical solution, a sufficiently large space is provided for the mixing of flue gas and secondary and tertiary ammonia, thereby improving the reduction efficiency of ammonia to NOx, which is beneficial to reducing NOx emissions.

[0014] Pressure and flow measurement points are arranged in each channel.

[0015] The secondary, tertiary and quaternary ammonia channels are respectively provided with a plurality of branches, and the plurality of branches are evenly arranged on the front and rear walls of the furnace wall along the width direction of the furnace.

[0016] By adopting the above technical solution and setting up a four-stage ammonia channel, the adjustment range of the ammonia blending ratio is increased, the combustion efficiency is improved, and the NOx generation is reduced.

[0017] Preferably, it also includes an ammonia measuring point arranged before the inlet of the cyclone separator, and a NOx measuring point arranged before the inlet of the cyclone separator and before the denitration reactor device.

[0018] By adopting the above technical solution and arranging ammonia and NOx measuring points, the concentrations of ammonia and NOx can be monitored in real time to prevent the occurrence of "ammonia escape" and excessive NOx concentration problems.

[0019] Another object of the present application is to provide a method for adjusting the ammonia blending ratio of the above-mentioned coal-fired circulating fluidized bed boiler with adjustable ammonia blending ratio, characterized in that:

[0020] The following is an expression of how the ammonia blending ratio F, G, H, L of each ammonia channel within each load range of the boiler changes with boiler load Q, coal volatile matter V, coal fixed carbon FC, coal moisture M and coal ash A.

[0021] (1) For high load range (60% < load ≤ 100%)

[0022] Primary ammonia: F = 0.1Q + 0.125 (V + 0.2M)

[0023] Secondary ammonia: G = 0.5Q + 0.67 [0.3V + 0.5FC + 0.7 (M + A)]

[0024] Three times ammonia: H = 0.2Q + 0.42 [0.25V + 0.13FC + 0.21 (M + A)]

[0025] Four-stage ammonia: L = 1-FGH

[0026] (2) For medium load range (40% < load ≤ 60%)

[0027] Primary ammonia: F = 0.2Q + 0.17 (V + 0.35M)

[0028] Secondary ammonia: G = 0.4Q + 0.5 [0.3V + 0.46FC + 0.59 (M + A)]

[0029] Third-stage ammonia: H = 0.17Q + 0.38 [0.21V + 0.09FC + 0.18 (M + A)]

[0030] Four-stage ammonia: L = 1-FGH

[0031] (3) For low load range (20% < load ≤ 40%)

[0032] Primary ammonia: F = 0.67Q + 0.25 (V + 0.5M)

[0033] Secondary ammonia: G = 0.6Q + 0.5 [(0.4V + 0.37FC + 0.57 (M + A)]

[0034] Level 3 ammonia: H = 0.14Q + 0.35 [0.18V + 0.085FC + 0.16 (M + A)]

[0035] Four-stage ammonia: L = 1-FGH

[0036] In the above relationship: F, G, H, L are the proportions of ammonia in the primary, secondary, tertiary and quaternary ammonia channels to the total ammonia content of the boiler, V represents the as-received volatile matter content of coal, Q is the proportion of boiler load to rated load, FC represents the as-received fixed carbon content of coal, M represents the as-received moisture content of coal, and A represents the as-received ash content of the coal, all expressed in percentage.

[0037] (4) Control of “ammonia escape” problem

[0038] The following is the expression of the ammonia blending ratio F', G', H', L' of each ammonia channel when the boiler has an "ammonia escape" problem, that is, when the ammonia concentration measured at the ammonia measuring point is higher than 5ppm:

[0039] Primary ammonia: F'=F+1%

[0040] Secondary ammonia: G'=G+1%

[0041] Tertiary ammonia: H′=H-2%

[0042] Quaternary ammonia: L'=L

[0043] (5) Control of excessive NOx concentration

[0044] The following is the expression of the ammonia blending ratio F', G', H', L' of each ammonia channel when the boiler has a problem of too high NOx concentration, that is, when the NOx concentration measured at the NOx measuring point in front of the denitrification reactor is higher than 150ppm:

[0045] Primary ammonia: F'=F-1%

[0046] Secondary ammonia: G' = G-1%

[0047] Tertiary ammonia: H'=H-1%

[0048] Four-stage ammonia: L'=L+3%

[0049] In the above relationship, F', G', H', L' are the proportions of ammonia in the primary, secondary, tertiary and quaternary ammonia channels to the total ammonia content of the boiler.

[0050] The technical principles of the above invention are as follows:

[0051] In the high load range (60% to 100% of the rated load), the combustion inside the furnace is intense and the particle fluidization is good. At this time, ammonia should be added to the primary air in a small proportion to provide heat for the initial ignition of the fuel and ensure the normal fluidization of the particles to prevent the accumulation of particles in the cyclone separator downcomer and return valve area due to excessive particle fluidization speed, which affects the combustion and particle fluidization inside the furnace. Therefore, the ammonia mixing ratio should not exceed 10%; a large amount of ammonia should be mixed in the secondary air area to reduce the coal combustion through the combustion reaction between ammonia and oxygen. The proportion of heat occupied by particle combustion can achieve the purpose of reducing carbon dioxide emissions by burning ammonia inside the boiler. The ammonia injection ratio here should be about 70%; a lower proportion of ammonia should be burned in the upper area of ​​the secondary air. After the intense combustion in the primary and secondary air areas, the oxygen concentration in the upper area of ​​the secondary air is already very low. By burning a lower proportion of ammonia, an ammonia-rich atmosphere is formed, so that ammonia and NOx produce sufficient reduction reaction, thereby reducing the NOx concentration at the furnace outlet to meet relevant emission requirements. The ammonia injection ratio here should be about 20%.

[0052] In the medium load range (40% to 60% of the rated load), since the primary air flow rate decreases with the boiler load, the fluidization state of the particles inside the boiler becomes worse. At this time, the proportion of ammonia added to the primary air can be increased, thereby improving the fluidization state inside the furnace and enhancing the heat transfer between the gas and solid phases; the ammonia blended in the secondary air area should still maintain a large proportion, so that the ammonia burns and releases heat, thereby reducing the proportion of heat released by coal particle combustion to the heat of the fuel, so as to achieve the purpose of reducing carbon dioxide emissions by blending ammonia; as the proportion of primary ammonia increases, the NOx generated by combustion will also increase accordingly. At this time, the proportion of quaternary ammonia should be increased so that the NOx emissions meet the relevant requirements.

[0053] In the low load range (20% to 40% of the rated load), the fluidization velocity of the particles inside the furnace is further reduced, and the proportion of primary ammonia should be further increased. On the one hand, ammonia pre-cracking can produce a certain amount of hydrogen, and the highly flammable nature of hydrogen can improve the combustion stability of the circulating fluidized bed boiler under low load conditions; on the other hand, the increased ammonia flow rate can compensate for the adverse effects of the reduction in primary air flow on the fluidization state of the particles to a certain extent; the ammonia blended in the secondary air area should still maintain a large proportion, so that ammonia burns and releases heat, thereby reducing the proportion of heat released by coal particle combustion to fuel heat, so as to achieve the purpose of reducing carbon dioxide emissions by blending ammonia; as the proportion of primary ammonia increases, the NOx generated by combustion will also increase accordingly, and the proportion of quaternary ammonia should be increased at this time so that the NOx emissions meet the relevant requirements.

[0054] When the ammonia concentration at the inlet of the cyclone separator is too high, that is, when the "ammonia escape" problem occurs, an ammonia-rich atmosphere is formed in the area above the tertiary ammonia channel. At this time, ammonia reacts with NOx to reduce a large amount of NOx, so that the NOx emissions at the furnace outlet meet the relevant requirements; however, the proportion of the quaternary ammonia is slightly higher, resulting in some ammonia failing to undergo a reduction reaction, making the ammonia concentration at the inlet of the cyclone separator too high, resulting in an "ammonia escape" problem. At this time, the proportion of the quaternary ammonia should be slightly reduced to prevent ammonia escape.

[0055] When the NOx concentration at the inlet of the denitrification reactor device is too high, an ammonia-lean atmosphere is formed in the area above the tertiary ammonia channel. At this time, the ammonia is insufficient to reduce NOx to nitrogen, causing the NOx concentration at the inlet of the denitrification reactor device to be too high and not meeting the relevant emission requirements. The proportion of the quaternary ammonia should be appropriately increased to enhance the reduction effect of ammonia on NOx so that the NOx concentration meets the relevant emission requirements.

[0056] The present application has at least one of the following beneficial technical effects:

[0057] Four-stage ammonia channels are set up respectively to achieve mixed combustion of ammonia at different stages of fuel combustion, improve the adjustment range of ammonia blending ratio, and reduce the generation of nitrogen oxides. The ammonia in the first-stage ammonia channel can be initially ignited and burned with the primary air and fuel particles. The ammonia in the second-stage and third-stage ammonia channels is heated by the high-temperature flue gas reflux in the furnace, and forms stable combustion with the main flame in the furnace. The fourth-stage ammonia is mainly used to reduce NOx to prevent NOx emissions from exceeding the limit.

[0058] 1. In the high load range, a small amount of ammonia is mixed into the primary air, and a large amount of ammonia is mixed into the secondary and tertiary ammonia, so that the furnace can maintain a stable fluidized state; in the medium load range, the proportion of primary ammonia is increased to improve the fluidized state of the boiler;

[0059] 2. When the boiler load is lower than 40% of the rated load, a small amount of ammonia can be added in the late stage of combustion to ensure that the fuel is burned out; when the load is higher than 40% of the rated load, increasing the proportion of ammonia added in the late stage of combustion can improve the reduction efficiency and effectively reduce nitrogen oxide emissions;

[0060] 3. The ammonia blending ratio adjustment method adopted in this application realizes the control of the ammonia blending ratio under different loads and different emission concentrations, has little impact on the flow field organization of the original gas-solid two-phase flow, does not break the original combustion characteristics, and does not require major changes to the original circulating fluidized bed structure design and operating conditions, thereby reducing the difficulty of the technical transformation of coal-ammonia co-combustion in circulating fluidized bed boilers. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a schematic diagram of the overall structure of an embodiment of the present application;

[0062] Among them: primary ammonia channel 1, lower secondary air duct 2, coal spreading pipe 3, secondary ammonia channel 4, upper secondary air duct 5, tertiary ammonia channel 6, quaternary ammonia channel 7, ammonia measuring point before the cyclone separator inlet 8, NOx measuring point before the cyclone separator inlet 9, cyclone separator 10, NOx measuring point before the denitrification reactor device 11, primary fan 12, primary air box 13.

[0063] Figure 2 It is the distribution diagram of ammonia ratio at each level at 30%, 50% and 100% load;

[0064] Figure 3 This is the NOx concentration diagram at the cyclone separator inlet and the NOx measuring point before the denitrification reactor device simulated by Barracuda software. DETAILED DESCRIPTION

[0065] The specific implementation methods of the present application are described in detail below with reference to the accompanying drawings.

[0066] The embodiments of the present application disclose a system and method for graded ammonia doping in a coal-fired circulating fluidized bed boiler with adjustable ammonia doping ratio.

[0067] Reference Figure 1 The ammonia channel is divided into four levels. The first-level ammonia channel 1 is connected to the primary wind box 13, the second-level ammonia channel 4 is arranged above the lower secondary air duct 2, the third-level ammonia channel 6 is arranged above the upper secondary air duct 5, and the fourth-level ammonia channel 7 is arranged 7 to 7.5 meters below the top of the furnace. The four-level ammonia channels jointly realize the mixing of ammonia to form a stable coal-ammonia mixed combustion process. The second-level, third-level, and fourth-level ammonia channels respectively have multiple branches leading into the furnace, and the multiple branches are evenly arranged on the front and rear walls of the furnace wall along the width direction of the furnace.

[0068] Combination Figure 1 One end of the primary ammonia channel 1 is welded and fixed to the inspection hole of the primary wind box 13, and is used to transport a small amount of ammonia;

[0069] Ammonia measuring point 8 and NOx measuring point 9 are set at the inlet of cyclone separator to monitor the NOx and ammonia concentrations at the inlet of cyclone separator in real time, so as to timely adjust the ammonia flow in the primary ammonia channel 1, the secondary ammonia channel 4, the tertiary ammonia channel 6, and the quaternary ammonia channel 7 to ensure that the NOx and ammonia concentrations meet the relevant specifications.

[0070] The implementation principle of the above embodiment is:

[0071] First, air is introduced into the furnace from the primary fan 12. The air enters the furnace through the primary air cap, the upper and lower secondary air ducts 5 and 2. Ammonia forms a primary air and ammonia mixture with the primary air through the primary ammonia channel 1. The high-temperature bed material at the bottom of the furnace flows upward under the blowing of the primary air and ammonia mixture; the secondary and tertiary ammonia form a mixture of air, coal and ammonia through the secondary and tertiary ammonia channels 4 and 6 with the coal particles in the coal spreading pipe 3 and the secondary air in the upper and lower secondary air ducts 5 and 2, and is quickly and evenly mixed with the primary air, the primary ammonia and the high-temperature bed material, and mixed with the main flame for intense combustion. Finally, the quaternary ammonia is intensely mixed with the high-temperature flue gas generated after combustion through the quaternary ammonia channel 7, and undergoes a reduction reaction with the NOx in the flue gas, thereby realizing the mixed combustion of ammonia at different stages of coal powder combustion, with a low-nitrogen combustion effect.

[0072] Based on the coal-fired circulating fluidized bed boiler system with adjustable ammonia blending ratio proposed in the above embodiment, the present application also provides a method for adjusting the ammonia blending ratio according to the boiler load range, the type of coal burned and the emission concentration level.

[0073] Within the high load range, the combustion inside the furnace is stable and the circulation is good, so ammonia should be appropriately mixed into the primary air.

[0074] In the medium load range, the primary air flow rate decreases, so the proportion of primary ammonia should be appropriately increased to improve the fluidization state inside the furnace.

[0075] In the low load range, the temperature inside the furnace is low, the combustion intensity is low, and the particle fluidization is weakened. At this time, the blending ratio of the first-stage ammonia should be further increased, and the hydrogen produced by the pre-pyrolysis of ammonia should be used to improve the combustion stability inside the furnace.

[0076] When the ammonia concentration at the inlet of the cyclone separator is too high, that is, when the "ammonia escape" problem occurs, the ratio of primary, secondary and tertiary ammonia should be appropriately reduced to prevent corrosion to subsequent equipment and poisoning of personnel.

[0077] When the NOx concentration before the denitrification reactor is too high, the proportion of the quaternary ammonia should be appropriately increased to enhance the reduction effect of ammonia on NOx so that the NOx concentration meets the relevant emission requirements.

[0078] According to the above principle of adjusting the ammonia blending ratio, the specific adjustment method is as follows:

[0079] The following is the expression of the ammonia blending ratio F, G, H, L of each ammonia channel in each load range of the boiler as it changes with the boiler load Q, the volatile matter V of the coal type, the fixed carbon FC of the coal type, the moisture M of the coal type and the ash A of the coal type;

[0080] (1) For high load range (60% < load ≤ 100%)

[0081] 1) When the boiler load is in the high load range (60% to 100% of the rated load), the combustion inside the furnace is intense and the particle fluidization is in good condition. At this time, ammonia should be added to the primary air in a small proportion to provide heat for the initial ignition of the fuel and ensure the normal operation of the particle fluidization to prevent the accumulation of particles in the cyclone separator downcomer and return valve area due to excessive particle fluidization speed, which affects the combustion and particle fluidization inside the furnace. Therefore, the ammonia mixing ratio should not exceed 10%;

[0082] 2) A large amount of ammonia should be mixed and burned in the secondary air area. Through the combustion reaction between ammonia and oxygen, the heat ratio of coal particle combustion can be reduced, thereby achieving the purpose of reducing carbon dioxide emissions by mixing ammonia in the boiler. The ammonia injection ratio here should be about 70%;

[0083] 3) A lower proportion of ammonia should be mixed and burned in the upper area of ​​the secondary air. After the intense combustion in the primary and secondary air areas, the oxygen concentration in the upper area of ​​the secondary air is already very low. By mixing and burning a lower proportion of ammonia, ammonia and NOx can produce a sufficient reduction reaction, thereby reducing the NOx concentration to meet the relevant emission requirements. The ammonia injection ratio here should be about 20%;

[0084] Primary ammonia: F = 0.1Q + 0.125 (V + 0.2M)

[0085] Secondary ammonia: G = 0.5Q + 0.67 [0.3V + 0.5FC + 0.7 (M + A)]

[0086] Three times ammonia: H = 0.2Q + 0.42 [0.25V + 0.13FC + 0.21 (M + A)]

[0087] Four-stage ammonia: L = 1-FGH

[0088] (2) For medium load range (40% < load ≤ 60%)

[0089] 1) When the boiler load is in the medium load range (40% to 60% of the rated load), the primary air flow rate decreases with the boiler load, and the fluidization state of the particles inside the boiler becomes worse. At this time, the proportion of primary ammonia can be increased to improve the fluidization effect inside the furnace and enhance the heat transfer between the gas and solid phases;

[0090] 2) Ammonia mixed with combustion in the secondary air area should still maintain a large proportion, so that ammonia burns and releases heat, thereby reducing the proportion of heat released by coal particle combustion to fuel heat, thereby achieving the purpose of reducing carbon dioxide emissions by mixing with ammonia;

[0091] 3) As the proportion of primary ammonia increases, the NOx generated by combustion will also increase. At this time, the proportion of quaternary ammonia should be increased to make the NOx emission meet the relevant requirements;

[0092] Primary ammonia: F = 0.2Q + 0.17 (V + 0.35M)

[0093] Secondary ammonia: G = 0.4Q + 0.5 [0.3V + 0.46FC + 0.59 (M + A)]

[0094] Third-stage ammonia: H = 0.17Q + 0.38 [0.21V + 0.09FC + 0.18 (M + A)]

[0095] Four-stage ammonia: L = 1-FGH

[0096] (3) For low load range (20% < load ≤ 40%)

[0097] 1) When the boiler load is in the low load range (20% to 40% of the rated load), the proportion of primary ammonia should be further increased. On the one hand, ammonia pre-cracking can produce a certain amount of hydrogen, and the highly flammable nature of hydrogen can improve the combustion stability of the circulating fluidized bed boiler under low load conditions. On the other hand, the increased ammonia flow rate can compensate for the adverse effects of reduced primary air flow on the fluidization state to a certain extent;

[0098] 2) The proportion of ammonia mixed in the secondary air area should still be kept at a large level, so that ammonia can burn and release heat, thereby reducing the proportion of heat released by coal particle combustion to fuel heat, so as to achieve the purpose of reducing carbon dioxide emissions by mixing ammonia;

[0099] 3) As the proportion of primary ammonia increases, the NOx generated by combustion will also increase. At this time, the proportion of quaternary ammonia should be increased to make the NOx emission meet the relevant requirements;

[0100] Primary ammonia: F = 0.67Q + 0.25 (V + 0.5M)

[0101] Secondary ammonia: G = 0.6Q + 0.5 [(0.4V + 0.37FC + 0.57 (M + A)]

[0102] Level 3 ammonia: H = 0.14Q + 0.35 [0.18V + 0.085FC + 0.16 (M + A)]

[0103] Four-stage ammonia: L = 1-FGH

[0104] In the above relationship, F, G, H, L are the proportion of ammonia in the primary, secondary, tertiary and quaternary ammonia channels to the total ammonia content of the boiler, V represents the as-received volatile matter content of coal, Q is the proportion of boiler load to rated load, FC represents the as-received fixed carbon content of coal, M represents the as-received moisture content of the coal, and A represents the as-received ash content of the coal, all expressed in percentage;

[0105] (4) Control of “ammonia escape” problem

[0106] The following is the expression of the ammonia blending ratio F', G', H', L' of each ammonia channel when the boiler has an "ammonia escape" problem, that is, when the ammonia concentration measured at the ammonia measuring point is higher than 5ppm:

[0107] Primary ammonia: F'=F+1%

[0108] Secondary ammonia: G'=G+1%

[0109] Tertiary ammonia: H′=H-2%

[0110] Quaternary ammonia: L'=L

[0111] (5) Control of excessive NOx concentration

[0112] The following is the expression of the ammonia blending ratio F', G', H', L' of each ammonia channel when the boiler has a problem of too high NOx concentration, that is, when the NOx concentration measured at the NOx measuring point in front of the denitrification reactor is higher than 150ppm:

[0113] Primary ammonia: F'=F-1%

[0114] Secondary ammonia: G' = G-1%

[0115] Tertiary ammonia: H′=H-1%

[0116] Four-stage ammonia: L'=L+3%

[0117] In the above relationship: F', G', H', L' are the proportions of ammonia in the primary, secondary, tertiary and quaternary ammonia channels to the total ammonia content of the boiler.

[0118] When the above method is used to adjust the ammonia blending ratio, it is first necessary to gradually reduce the original coal particle supply rate, and after a stable combustion process is formed, adjust the ammonia amount in the four ammonia channels according to the ammonia blending ratio requirements.

[0119] Figure 2 It is the ammonia blending ratio of each level after the ammonia blending ratio adjustment method is used in the graded ammonia blending system at 30%, 50% and 100% load;

[0120] According to the above method, the present application uses the commercial software Barracuda to simulate the staged ammonia injection method proposed in the present application. The numerical simulation calculation of a boiler under 100% load is as follows: Figure 3 The results show that by adopting the graded ammonia injection method proposed in the present invention, the NOx concentration before the denitrification reactor can be as low as 100 ppm, which can achieve effective control of NOx.

[0121] The above are preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A graded ammonia doping system for a coal-fired circulating fluidized bed boiler with adjustable ammonia doping ratio, characterized in that: It includes a primary ammonia channel, a secondary ammonia channel, a tertiary ammonia channel, a quaternary ammonia channel, a primary air distribution plate at the furnace bottom, a primary fan, a primary wind box, a lower secondary air duct, a coal spreading pipe, an upper secondary air duct, ammonia measuring points and NOx measuring points at the inlet of the cyclone separator, and a NOx measuring point in the tail flue; the primary fan, the primary wind box and the primary air distribution plate at the furnace bottom constitute the primary air channel at the furnace bottom, and an inspection hole is provided at the primary wind box. The primary ammonia channel is penetrated in the primary wind box along the inspection hole, and ammonia and primary air are mixed and enter the furnace together; the lower secondary air duct is provided at the lower part of the furnace, 6 to 7 meters away from the bottom of the furnace; The upper and lower secondary air ducts are connected to the circulating fluidized bed body, the secondary ammonia channel is arranged at the upper part of the lower secondary air duct, 2 to 2.5 m away from the lower secondary air duct; the upper secondary air duct is arranged 2 to 2.5 m above the secondary ammonia channel; the tertiary ammonia channel is arranged 2 to 2.5 m above the upper secondary air duct; the quaternary ammonia channel is arranged 7 to 7.5 m below the top of the furnace; pressure and flow measuring points are arranged in each channel; the ammonia measuring point is arranged at the inlet of the cyclone separator; the NOx measuring point at the inlet of the cyclone separator is arranged behind the above-mentioned ammonia measuring point; the NOx measuring point in the tail flue is arranged in front of the denitration reactor device; A method for graded ammonia addition in a coal-fired circulating fluidized bed boiler with adjustable ammonia addition ratio, characterized in that: The following is the expression of the ammonia blending ratio F, G, H, L of the first, second, third and fourth ammonia channels in each load range of the boiler as the boiler load Q, coal volatile matter V, coal fixed carbon FC, coal moisture M and coal ash A change: (1) For high load range (60% < load ≤ 100%) Primary ammonia: F = 0.1Q + 0.125 (V + 0.2M) Secondary ammonia: G = 0.5Q + 0.67 [0.3V + 0.5FC + 0.7 (M + A)] Three times ammonia: H = 0.2Q + 0.42 [0.25V + 0.13FC + 0.21 (M + A)] Four-stage ammonia: L = 1-FGH (2) For medium load range (40% < boiler load ≤ 60%) Primary ammonia: F = 0.2Q + 0.17 (V + 0.35M) Secondary ammonia: G = 0.4Q + 0.5 [0.3V + 0.46FC + 0.59 (M + A)] Third-stage ammonia: H = 0.17Q + 0.38 [0.21V + 0.09FC + 0.18 (M + A)] Four-stage ammonia: L = 1-FGH (3) For low load range (20% < load ≤ 40%) Primary ammonia: F = 0.67Q + 0.25 (V + 0.5M) Secondary ammonia: G = 0.6Q + 0.5 [(0.4V + 0.37FC + 0.57 (M + A)] Level 3 ammonia: H = 0.14Q + 0.35 [0.18V + 0.085FC + 0.16 (M + A)] Four-stage ammonia: L = 1-FGH In the above relationship: F, G, H, L are the proportion of ammonia in the primary, secondary, tertiary and quaternary ammonia channels to the total ammonia content of the boiler, V represents the as-received volatile matter content of coal, Q is the proportion of boiler load to rated load, FC represents the as-received fixed carbon content of coal, M represents the as-received moisture content of coal, and A represents the as-received ash content of coal, all expressed in percentage; (4) Control of "ammonia escape" problem The following is the expression of the ammonia blending ratio F', G', H', L' of each ammonia channel when the boiler has an "ammonia escape" problem, that is, when the ammonia concentration measured at the ammonia measuring point before the cyclone separator inlet is higher than 5ppm: Primary ammonia: F'=F+1% Secondary ammonia: G'=G+1% Tertiary ammonia: H′=H-2% Quaternary ammonia; L'=L (5) Control of excessive NOx concentration The following is the expression of the ammonia blending ratio F', G', H', L' of each ammonia channel when the boiler has a problem of too high NOx concentration, that is, when the NOx concentration measured at the NOx measuring point before the denitration reactor device is higher than 150ppm: First-grade ammonia; F'=F-1% Secondary ammonia: G' = G-1% Tertiary ammonia; H'=H-1% Four-stage ammonia: L'=L+3% In the above relationship, F', G', H', L' are the proportions of ammonia in the primary, secondary, tertiary and quaternary ammonia channels to the total ammonia content of the boiler.

2. A system and method for graded ammonia doping of a coal-fired circulating fluidized bed boiler with adjustable ammonia doping ratio according to claim 1, characterized in that: Primary, secondary, tertiary and quaternary ammonia channels are provided, and the secondary, tertiary and quaternary ammonia channels respectively have a plurality of branches leading into the furnace, and the plurality of branches are evenly arranged on the front and rear walls of the furnace along the width direction of the furnace.

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