System and method for desulfurization and denitrification of fuel

Abstract

The present invention discloses a system and method for desulfurization and denitrification of fuel. The system includes a circulating fluidized bed boiler, a gas preheater, a gas concentration mixer, a first desulfurizer silo and a second desulfurizer silo. The circulating fluidized bed boiler includes a furnace and a cyclone separator connected to the furnace. The furnace is provided with a feed port and a first air inlet. The gas concentration mixer is provided with a primary air duct and a secondary air duct. The primary air duct is connected to the first air inlet. The secondary air duct is divided into a secondary split air nozzle and a tertiary air nozzle, which are all connected to the furnace, and a first nozzle and a second nozzle are respectively provided at the ends in the furnace. The second nozzle is tilted downward, and the height of the second nozzle is greater than that of the first nozzle. The method includes crushing coal and biomass and mixing them, and treating the mixed fuel through a fuel desulfurization and denitrification system. The system and method of the present invention can efficiently desulfurize and denitrify, reduce the emission of flue gas pollutants at the tail of the boiler, and effectively utilize the waste heat of boiler flue gas and domestic waste.

Description

Technical Field

[0001] The present invention belongs to the technical field of clean coal combustion, and relates to a system and method for desulfurizing and denitrifying fuel, and in particular to a system and method for desulfurizing and denitrifying fuel of a circulating fluidized bed coal-fired boiler. Background Art

[0002] With the rapid development of my country's industry, the requirements for fuel boilers are getting higher and higher. At present, the circulating fluidized bed boiler (CFB), which has the highest degree of industrialization, has been widely used in my country. Circulating fluidized bed boiler is a clean coal combustion technology. Compared with other types of boilers, circulating fluidized bed boiler has lower emissions of nitrogen oxides and sulfur oxides and higher combustion efficiency. It can be seen that reducing the emission of pollutants in the tail flue gas of circulating fluidized bed boilers is of great significance.

[0003] Circulating fluidized bed boiler NO x It is a fuel type, and is produced by a violent and strong oxidation reaction between oxygen atoms in the fluidizing air and nitrogen-containing organic matter in the fuel. x It is one of the main causes of acid rain, greenhouse effect and photochemical smog. Among them, N2O is a strong greenhouse gas, and its greenhouse effect is 275 times that of CO2. It will also damage the ozone layer, which is extremely harmful. SO2 is also generated by a strong oxidation reaction between oxygen atoms in the fluidizing wind and sulfur-containing organic matter in the fuel. It is one of the main causes of acid rain. At present, power stations have a variety of treatment measures to reduce the emission of the above two air pollutants. One is to add alkaline calcium bases such as limestone and calcium hydroxide as desulfurizers in the furnace. However, this type of calcium base is easy to sinter in the furnace, polluting the heating surface in the furnace, and the desulfurization activity is not strong, resulting in a large amount of addition; the other is to arrange SCR denitrification technology and desulfurization technology in the tail flue gas. Although it can effectively reduce NO x and SO2 emissions, but the cost is too high. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and to provide a system and method for desulfurizing and denitrifying fuels which can efficiently desulfurize and denitrify, reduce the emission of pollutants in the tail flue gas of a circulating fluidized bed boiler, and effectively utilize the waste heat of boiler flue gas and domestic waste.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions.

[0006] A system for desulfurizing and denitrifying fuel, characterized in that it comprises a circulating fluidized bed boiler, a gas preheater, a gas concentration mixer, a first desulfurizing agent silo and a second desulfurizing agent silo, the circulating fluidized bed boiler comprises a furnace and a cyclone separator connected to the furnace, the cyclone separator is connected to the gas preheater, the furnace is provided with a feed inlet and a first air inlet, the gas concentration mixer is provided with a primary air duct and a secondary air duct, the gas preheater is used to preheat the primary air duct and the secondary air duct, the primary air duct is connected to the first air inlet, the second The secondary air duct is divided into two branches, which are a secondary diversion air nozzle and a tertiary air nozzle respectively. The secondary diversion air nozzle is connected with the furnace, and a first nozzle is provided at the end of the secondary diversion air nozzle in the furnace. The first desulfurizer silo is arranged on the secondary diversion air nozzle. The tertiary air nozzle is connected with the furnace, and a second nozzle is provided at the end of the tertiary air nozzle in the furnace. The second nozzle is inclined downward, and the second desulfurizer silo is arranged on the tertiary air nozzle. The height of the second nozzle is greater than the height of the first nozzle.

[0007] In the above-mentioned fuel desulfurization and denitrification system, preferably, the furnace includes a dense phase zone and a dilute phase zone, the feed port is located in the dense phase zone, the first air inlet is located at the bottom of the furnace, the first nozzle and the second nozzle are located in the dilute phase zone, the first nozzle is located on one side of the furnace, the second nozzle is located on the other side of the furnace, and the angle between the working surface of the second nozzle and the vertical plane is 35° to 45°.

[0008] In the above-mentioned fuel desulfurization and denitrification system, preferably, the height of the furnace is h, the height of the first nozzle is 5 / 12h~7 / 12h, the height of the second nozzle is 9 / 12h~11 / 12h, and the furnace is also provided with a speed sensor, which is located below the first nozzle, and the height of the speed sensor is 4 / 12h~5 / 12h.

[0009] In the above-mentioned fuel desulfurization and denitrification system, preferably, the furnace is provided with a return port and a flue gas outlet, the cyclone separator is provided with a return pipe, a flue gas inlet and an air outlet connected to the flue gas inlet, the return port is connected to the return pipe, the flue gas outlet is connected to the flue gas inlet, and the air outlet is connected to the gas preheater.

[0010] In the above-mentioned fuel desulfurization and denitrification system, preferably, the primary air duct and the secondary air duct are both provided with gas flow meters, and the secondary diversion air nozzle and the tertiary air nozzle are both provided with valves.

[0011] The above-mentioned fuel desulfurization and denitrification system preferably also includes a CO2 gas supply device and an O2 gas supply device, the O2 gas supply device is connected to the gas concentration mixer through a pipeline, and the CO2 gas supply device is connected to the gas concentration mixer through a pipeline, and each pipeline is provided with a gas flow meter.

[0012] As a general technical concept, the present invention also provides a method for desulfurization and denitration of fuel, the method adopts the above-mentioned system for desulfurization and denitration of fuel, and comprises the following steps:

[0013] Coal and biomass are crushed and mixed to obtain a mixed fuel, and the mixed fuel is introduced into the furnace through the feed port, CO2 and O2 are sent to the gas concentration mixer for mixing, and the gas concentration mixer provides primary air and secondary air. The primary air is preheated by the gas preheater and sent to the furnace through the primary air duct to make the mixed fuel burn and cause a catalytic reduction reaction of nitrogen oxides to form a dense phase zone. The obtained first flue gas carries the unburned mixed fuel and rises in the furnace. After the secondary air is preheated by the gas preheater, part of the preheated secondary air is used as a secondary branch flow. The wind carries the desulfurizer dropped from the first desulfurizer silo and is sent to the furnace through the secondary diversion air nozzle, so that the unburned mixed fuel is burned and desulfurized and denitrified to form a dilute phase zone. Another part of the preheated secondary air is used as the tertiary air to carry the desulfurizer dropped from the second desulfurizer silo and is sent to the furnace through the tertiary air nozzle, so that the escaped mixed fuel and unburned coke are re-burned and desulfurized and denitrified. The obtained second flue gas is sent to the cyclone separator, and after solid-gas separation, the obtained return material is returned to the furnace. The obtained third flue gas is sent to the gas preheater for heat exchange, thereby realizing the desulfurization and denitrification of the mixed fuel.

[0014] In the above-mentioned method for desulfurization and denitrification of fuel, preferably, the injection speed of the secondary diversion air is 1.3 to 1.8 times the speed measured by the speed sensor arranged in the furnace, and the injection speed of the tertiary air is 1.4 to 2 times the injection speed of the secondary diversion air.

[0015] In the above-mentioned method for desulfurization and denitrification of fuel, preferably, the volume flow ratio of the primary air to the secondary air is 1:1, the volume flow ratio of the secondary diverter air to the tertiary air is 1:1, the oxygen volume concentration of the primary air is 50% to 70%, and the oxygen volume concentrations of the secondary air, secondary diverter air, and tertiary air are all 45% to 50%.

[0016] In the above-mentioned method for desulfurization and denitrification of fuel, preferably, the temperature of the preheated primary air is 160°C to 170°C, and the temperatures of the preheated secondary air, secondary split air, and tertiary air are all 170°C to 180°C.

[0017] In the above-mentioned method for desulfurizing and denitrifying fuel, preferably, the usage ratio of the mixed fuel to the total desulfurizing agent per unit time is 390-450:1, in kg / s.

[0018] In the above-mentioned method for desulfurization and denitrification of fuel, preferably, the excess oxygen coefficient in the furnace is 1.15-1.20, and the average temperature in the furnace is 800°C-900°C.

[0019] In the above-mentioned method for desulfurization and denitrification of fuel, preferably, the mass ratio of the coal to the biomass is 1-3:1-2, the biomass is coconut shell, the coconut shell is crushed to obtain coconut shell particles, 0<the particle size of the coconut shell particles ≤1mm, and the coal is crushed to obtain coal powder, 0<the particle size of the coal powder ≤1mm.

[0020] In the above-mentioned method for desulfurization and denitration of fuel, preferably, the desulfurizer is organic calcium, and the preparation process of the organic calcium comprises the following steps:

[0021] The waste cooking oil is mixed with dilute sulfuric acid, heated to 60°C to 70°C under stirring conditions for hydrolysis reaction to obtain a reaction product containing higher fatty acids and glycerol, and allowed to stand after the reaction until the reaction product is clearly stratified, and then extracted to obtain higher fatty acids; water is added to the higher fatty acids, and then heated until the higher fatty acids and water are miscible, the temperature of the resulting solution is maintained at 60°C to 70°C, acid is added until the pH value of the solution is 4 to 6, and crushed eggshells are added under stirring conditions, the amount of crushed eggshells added is until no bubbles appear in the solution or eggshells remain in the solution, and after sufficient reaction, a solution containing organic calcium is obtained, which is heated for evaporation and crystallization to obtain organic calcium.

[0022] The above-mentioned method for desulfurization and denitrification of fuel is preferably that during the preparation process of the organic calcium, the heating is performed using the waste heat of the flue gas after heat exchange in the gas preheater (11), the volume ratio of the waste oil to the dilute sulfuric acid is 2 to 4:1, the concentration of the dilute sulfuric acid is 3 mol / L to 4 mol / L, the time of the hydrolysis reaction is 2 h to 4 h, the volume ratio of the higher fatty acid to water is 1:2 to 3, 0 < the particle size of the crushed eggshell ≤ 1 mm, and the eggshell raw material of the crushed eggshell includes one or more of chicken eggshell, duck eggshell and quail eggshell.

[0023] In the present invention, the overall desulfurization reaction in the furnace is:

[0024] FeS2+O2→Fe2O3+SO2

[0025] FeS2+H2→H2S+FeS

[0026] H2S+O2→SO2+H2O

[0027] H2S+CaO→CaS+H2O

[0028] 2CaO+2SO2+O2→2CaSO4

[0029] CaS+2O2→CaSO4

[0030] The overall denitrification reaction in the furnace is:

[0031] Homogeneous reaction:

[0032] 2NO+2H2→N2+2H2O

[0033] 2NO+2CO→N2+2CO2

[0034] NO+C n H m +O2→N2+CO2+H2O

[0035] NO+CH4→N2+H2O+CO2

[0036] N2O+H→N2+OH

[0037] N2O+OH→N2+HO2

[0038] N2O+CO→N2+CO2

[0039] N2O→O2+N2

[0040]

[0041] Heterogeneous reactions:

[0042] NO+C→N2+CO

[0043] N2O+(-C)→N2+C(O)

[0044] The present invention uses organic calcium as a desulfurizing agent. The calcium group in the organic calcium is present in the form of sulfur in the desulfurization process:

[0045] H2S—CaS—CaSO4.

[0046] At high temperatures, the low coke content in the furnace will promote the decomposition of the desulfurization product CaSO4 to produce SO2, causing desulfurization failure. The reaction is as follows:

[0047] CaSO4+CaS→CaO+SO2

[0048] In order to prevent desulfurization failure, the present invention adds biomass to the coal powder. The volatile matter precipitated by the biomass in the dense phase zone of the furnace will burn and compete with the coal powder particles for oxygen atoms. The reducing atmosphere will be enhanced, so that the coke content will increase, and the decomposition of CaSO4 to produce SO2 will be restricted. The same is true in the dilute phase zone, which will cause the following reaction of CaSO4:

[0049] CaSO4+C→CaS+CO2

[0050] Compared with the prior art, the advantages of the present invention are:

[0051] 1. The system of the present invention realizes the effect of efficient desulfurization and denitrification of flue gas in the furnace through the design of circulating fluidized bed boiler, gas preheater, gas concentration mixer, the design of primary air duct, secondary air duct, secondary split air nozzle, tertiary air nozzle, the design of the position relationship of the first nozzle and the second nozzle, etc. The outlet flue gas is low in sulfur and nitrogen, which improves the service life of other flue gas treatment equipment in the power plant and reduces capital consumption. The device is simple, the investment is small, and the waste heat of the flue gas can also be utilized as a resource.

[0052] 2. In the system of the present invention, the secondary split air nozzle sprays desulfurizer and secondary split air into the furnace. The initial velocity of the ejected fluid is 1.3 to 1.8 times the velocity measured by the velocity sensor 25. The fluid is in a turbulent state outside, which will suck in the surrounding high-temperature flue gas and form a vortex inside the fluid, called the lower vortex, which will fully burn the high-temperature flue gas, mixed fuel and unburned coke in the dense phase area, generate local high temperature, accelerate the thermal decomposition of the desulfurizer, and improve the desulfurization efficiency. However, the suction capacity of the lower vortex is still limited by the initial injection velocity and turbulence intensity. Therefore, after a period of time, a second nozzle is installed at a certain vertical distance opposite to the secondary diverter air nozzle, and tertiary air and desulfurizer are sprayed to the upper part of the dilute phase zone. The initial velocity of the fluid sprayed from the second nozzle is 1.4 to 2 times the injection velocity of the secondary diverter air. Since the pipe close to the nozzle is arc-shaped, the fluid has a tangential velocity and a large initial fluid velocity. After the fluid is sprayed, a strong vortex will be formed in the center of the dilute phase zone with strong suction capacity, which is called the upper vortex. The upper vortex will suck and gather high-temperature flue gas and other substances escaping from the lower vortex to form a high-temperature area, so that the escaped coal powder / biomass and unburned coke will be re-burned, and the desulfurizer will be quickly pyrolyzed. This process can significantly improve the desulfurization efficiency and combustion efficiency.

[0053] 3. The method of the present invention has a wide source of raw materials, is simple to operate, and the conditions required by the method are controllable in practice. It can also make comprehensive use of waste cooking oil, eggshells and boiler tail flue gas resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a schematic structural diagram of a fuel desulfurization and denitrification system according to an embodiment of the present invention.

[0055] Figure 2 It is a three-dimensional structural schematic diagram of the installation positions of the first nozzle and the second nozzle according to an embodiment of the present invention.

[0056] Figure 3Schematic diagram of the angle between the working surface of the second nozzle and the vertical plane in an embodiment of the present invention.

[0057] Figure 4 The figure is a top view schematically showing the installation positions of the first nozzle and the second nozzle according to an embodiment of the present invention.

[0058] Figure 5 This is a flow mechanism diagram of the desulfurizer in the furnace in the method for desulfurization and denitrification of fuel according to an embodiment of the present invention.

[0059] Legend:

[0060] 1. First nozzle; 2. Primary air duct; 3. Feed inlet; 4. Furnace; 5. First desulfurizer silo; 6. Tertiary air nozzle; 7. Secondary diversion air nozzle; 8. Cyclone separator; 9. Valve; 10. Three-way joint; 11. Gas preheater; 12. Gas flow meter; 13. Gas concentration mixer; 14. First air inlet; 15. Second desulfurizer silo; 16. Second nozzle; 17. Secondary air duct; 18. Flue gas outlet; 19. Feed inlet; 20. Return port; 21. Return pipe; 22. Flue gas inlet; 23. Air outlet; 24. Slag discharge port; 25. Speed ​​sensor. DETAILED DESCRIPTION

[0061] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby. Unless otherwise specified, the materials and instruments used in the following embodiments are commercially available.

[0062] A fuel desulfurization and denitrification system of the present invention, such as Figure 1-4 As shown, it includes a circulating fluidized bed boiler, a gas preheater 11, a gas concentration mixer 13, a first desulfurizing agent silo 5 and a second desulfurizing agent silo 15. The circulating fluidized bed boiler includes a furnace 4 and a cyclone separator 8 connected to the furnace 4. The cyclone separator 8 is connected to the gas preheater 11. The furnace 4 is provided with a feed inlet 19 and a first air inlet 14. The gas concentration mixer 13 is provided with a primary air duct 2 and a secondary air duct 17. The gas preheater 11 is used to preheat the primary air duct 2 and the secondary air duct 17. The primary air duct 2 is connected to the first air inlet 14, and the secondary air duct 17 is connected to the secondary air duct 17. The air duct 17 is divided into two branches, which are a secondary diversion air nozzle 7 and a tertiary air nozzle 6. The secondary diversion air nozzle 7 is connected to the furnace 4. The end of the secondary diversion air nozzle 7 in the furnace 4 is provided with a first nozzle 1. The first desulfurizer silo 5 is arranged on the secondary diversion air nozzle 7. The tertiary air nozzle 6 is connected to the furnace 4. The end of the tertiary air nozzle 6 in the furnace 4 is provided with a second nozzle 16. The second nozzle 16 is inclined downward. The second desulfurizer silo 15 is arranged on the tertiary air nozzle 6. The height of the second nozzle 16 is greater than the height of the first nozzle 1.

[0063] As a further improvement:

[0064] The furnace 4 includes a dense phase area and a dilute phase area from bottom to top. The feed port 19 is located in the dense phase area. The first air inlet 14 is located at the bottom of the furnace 4. The first nozzle 1 and the second nozzle 16 are located in the dilute phase area. The first nozzle 1 is located on one side of the furnace 4, and the second nozzle 16 is located on the other side of the furnace 4. Figure 3 As shown, the angle between the working surface of the second nozzle 16 and the vertical surface is 35° to 45°.

[0065] Assume that the height of the furnace 4 is h, the height of the first nozzle 1 is 5 / 12h~7 / 12h, the height of the second nozzle 16 is 9 / 12h~11 / 12h, and the furnace 4 is also provided with a speed sensor 25, the speed sensor 25 is located below the first nozzle 1, and the height of the speed sensor 25 is 4 / 12h~5 / 12h.

[0066] The furnace 4 is provided with a return port 20 and a flue gas outlet 18. The return port 20 is located at the bottom of the furnace 4. The cyclone separator 8 is provided with a return pipe 21, a flue gas inlet 22 and an outlet 23 connected to the flue gas inlet 22. The return port 20 is connected to the return pipe 21 for returning part of the unburned coal powder into the furnace 4. The flue gas outlet 18 is connected to the flue gas inlet 22. The outlet 23 is connected to the gas preheater 11 for heat exchange with the flue gas separated by the cyclone separator 4.

[0067] Gas flow meters 12 are provided on the primary air duct 2 and the secondary air duct 17 for controlling the volume flow of the primary air duct 2 and the secondary air duct 17. Valves 9 are provided on the secondary branch air nozzle 7 and the tertiary air nozzle 6 for controlling the volume flow of the secondary branch air nozzle 7 and the tertiary air nozzle 6.

[0068] The system also includes a CO2 gas supply device and an O2 gas supply device. The O2 gas supply device is connected to the gas concentration mixer 13 through a pipeline. The CO2 gas supply device is connected to the gas concentration mixer 13 through a pipeline. A gas flow meter 12 is provided on each pipeline.

[0069] The secondary air duct 17 , the secondary split air nozzle 7 and the tertiary air nozzle 6 are connected via a three-way joint 10 .

[0070] A circulating fluidized bed is provided at the bottom of the furnace 4, and a slag discharge port 24 is provided on the circulating fluidized bed for discharging the slag remaining from combustion.

[0071] A method for desulfurizing and denitrifying fuel of the present invention is implemented by using the above-mentioned system for desulfurizing and denitrifying fuel, and comprises the following steps:

[0072] Coal and biomass are crushed and mixed to obtain a mixed fuel, and the mixed fuel is introduced into the furnace 4 through the feed port 19, and CO2 and O2 are sent to the gas concentration mixer 13 for mixing. The gas concentration mixer 13 provides primary air and secondary air. The primary air is preheated by the gas preheater 11 and sent to the furnace 4 through the primary air duct 2. The mixed fuel burns at the bottom of the furnace 4 to form a dense phase area and release a large amount of heat. During the combustion process, the biomass has a high volatile matter, and the combustion will produce more reducing gases such as H2, C2H2, and CH4, which promote the catalytic reduction reaction of nitrogen oxides. Under the action of air pressure, the high-temperature flue gas (first flue gas) carries part of the unburned mixed fuel to rise, and the secondary air is preheated by the gas preheater 11. The preheated part of the secondary air is used as the secondary diversion air and the first degassing air is mixed with the secondary diversion air. The desulfurizer in the sulfur agent silo 5 is mixed and sent to the furnace 4 through the secondary diversion air nozzle 7, but the oxygen concentration remains unchanged, so that the unburned mixed fuel continues to burn and desulfurizes and denitrates at the same time, forming a dilute phase zone. The other part of the secondary air after preheating is mixed with the desulfurizer in the second desulfurizer silo 15 as the tertiary air and sent to the furnace 4 through the tertiary air nozzle 6. The section of the injection pipe connected to the second nozzle 16 is arc-shaped, so the fluid formed by the tertiary air has a tangential velocity and a large initial velocity of the fluid. After the fluid is injected, a strong vortex will be formed in the center of the dilute phase zone with a strong suction ability, which is called the upper vortex. The upper vortex will suck and gather the high-temperature flue gas and other substances escaping from the lower vortex to form a high-temperature area, so that the escaped mixed fuel and unburned coke will burn again, and the desulfurizer will be quickly pyrolyzed, which will significantly improve the desulfurization and denitrification efficiency and combustion efficiency. The obtained second flue gas is sent to the cyclone separator 8, and after solid-gas separation, the obtained return material is returned to the furnace 4, and the obtained third flue gas is sent to the gas preheater 11 for heat exchange. After the heat exchange, the flue gas is treated by other flue gas cleaning processes of the power plant and discharged into the atmosphere through the chimney. When the boiler is running, the desulfurization and denitrification process of the above mixed fuel can be continuously carried out.

[0073] As a further preferred method:

[0074] The injection speed of the secondary diversion air is 1.3 to 1.8 times the speed measured by the speed sensor 25 provided in the furnace 4, and the injection speed of the tertiary air is 1.4 to 2 times the injection speed of the secondary diversion air.

[0075] The volume flow ratio of primary air to secondary air is 1:1, the volume flow ratio of secondary split air to tertiary air is 1:1, the oxygen volume concentration of primary air is 50% to 70%, and the oxygen volume concentration of secondary air, secondary split air, and tertiary air are all 45% to 50%;

[0076] The temperature of the primary air is 160°C to 170°C, and the temperatures of the secondary air, secondary split air, and tertiary air are all 170°C to 180°C;

[0077] The ratio of the mixed fuel to the total desulfurizer per unit time is 390-450:1, in kg / s;

[0078] The excess oxygen coefficient in the furnace 4 is 1.15 to 1.20;

[0079] The average temperature in the furnace 4 is 800°C to 900°C;

[0080] The mass ratio of coal to biomass is 1-3:1-2;

[0081] The biomass is preferably coconut shell, which is crushed to obtain coconut shell particles, with a particle size of 0 < coconut shell particles ≤ 1 mm, and coal is crushed to obtain coal powder, with a particle size of 0 < coal powder ≤ 1 mm.

[0082] In the present invention, the desulfurizing agent adopts organic calcium, and the preparation process of organic calcium comprises the following steps:

[0083] Mix waste oil with dilute sulfuric acid, heat to 60℃~70℃ under stirring conditions to cause hydrolysis reaction, obtain reaction products containing higher fatty acids and glycerol, let stand after reaction until obvious stratification occurs in the reaction products, then extract to obtain higher fatty acids. Add water to the higher fatty acids, then heat until the higher fatty acids and water are mutually soluble (mutually soluble at 60℃~70℃), keep the temperature of the resulting solution at 60℃~70℃, add acid until the pH of the solution is 4~6, add crushed eggshells under stirring conditions, the amount of crushed eggshells added is until no bubbles appear in the solution or eggshells remain in the solution, after sufficient reaction, obtain a solution containing organic calcium, and evaporate and crystallize by heating to obtain organic calcium.

[0084] In the preparation process of organic calcium, each heating step is implemented by using the flue gas waste heat after heat exchange in the gas preheater 11, that is, the flue gas waste heat at the tail of the boiler. The volume ratio of waste oil to dilute sulfuric acid is 2-4:1, the concentration of dilute sulfuric acid is 3mol / L-4mol / L, the hydrolysis reaction time is 2h-4h, the volume ratio of higher fatty acids to water is 1:2-3, and the particle size of the broken eggshell is 0<≤1mm.

[0085] Waste oil can be selected from waste oil, vegetable oil after multiple frying, animal fat or visceral refined oil, etc., and its main components are triglycerides and free higher fatty acids. Raw eggshells include one or more of chicken eggshells, duck eggshells, crane quail eggshells, etc., all of which belong to domestic waste. Eggshells are mainly composed of more than 96% columnar calcite crystals (mainly CaCO3) and 3.5% organic matrix.

[0086] In the present invention, the flow mechanism of the desulfurizer in the furnace 4 is as follows: Figure 5As shown, the secondary diversion air nozzle 7 sprays desulfurizer and secondary diversion air into the furnace 4. The initial velocity of the ejected fluid is 1.3 to 1.8 times the velocity measured by the velocity sensor 25. The fluid is in a turbulent state outside, which will suck in the surrounding high-temperature flue gas and form a vortex inside the fluid, called the lower vortex, which will fully burn the high-temperature flue gas, coal powder / biomass and unburned coke in the dense phase area, generate local high temperature, accelerate the thermal decomposition of the desulfurizer, and improve the desulfurization efficiency. However, the suction capacity of the lower vortex is still limited by the initial injection velocity and turbulence intensity. Therefore, after 30 to 40 seconds, a second nozzle 16 is installed at a certain vertical distance opposite to the secondary diverter air nozzle 7 to start spraying tertiary air and desulfurizer to the upper part of the dilute phase zone. The initial velocity of the fluid sprayed by the second nozzle 16 is 1.4 to 2 times the injection velocity of the secondary diverter air. Since the pipeline close to the nozzle is arc-shaped, the fluid has a tangential velocity and a large initial fluid velocity. After the fluid is sprayed, a strong vortex will be formed in the center of the dilute phase zone with a strong suction capacity, which is called the upper vortex. The upper vortex will suck and gather the high-temperature flue gas and other substances escaping from the lower vortex to form a high-temperature area, so that the escaped coal powder / biomass and unburned coke will be re-burned, and the desulfurizer will be quickly pyrolyzed to improve the desulfurization efficiency and combustion efficiency.

[0087] The desulfurization and denitrification process in the furnace 4 is as follows:

[0088] The SO2 in the furnace comes from the combustion of pyrite (FeS2) and organic sulfur (-S) in the mixed fuel. The reaction equation is as follows:

[0089] FeS2+O2→Fe2O3+SO2

[0090] FeS2+H2→H2S+FeS

[0091] H2S+O2→SO2+H2O

[0092] -S+O2→-SO2

[0093] The desulfurizer uses organic calcium, the main component of which is high-grade fatty acid calcium. High-grade fatty acid calcium is selective in the adsorption of SO2 and N2O, and will preferentially adsorb SO2. When the furnace temperature is 900°C, compared with limestone, organic calcium of the same particle size has a larger specific surface area, a larger pore volume and an average pore size than limestone. In addition, organic calcium has a strong anti-sintering ability and can maintain a high specific surface area at high temperatures. The reactions of desulfurization and denitrification in the dilute phase are as follows:

[0094] The first stage: the process of reducing gas denitration. The higher fatty acid calcium is decomposed into calcium carbonate and organic matter by heat. The organic matter is decomposed at high temperature, and the products are mainly reducing gases such as H2, CH4, CO, C2H2, C2H4, etc. The process of reducing gas denitration undergoes a homogeneous reaction:

[0095] 2NO+2H2→N2+2H2O

[0096] 2NO+2CO→N2+2CO2

[0097] NO+C n H m +O2→N2+CO2+H2O

[0098] NO+CH4→N2+H2O+CO2

[0099] N2O+H→N2+OH

[0100] N2O+OH→N2+HO2

[0101] N2O+CO→N2+CO2

[0102] The second stage: adsorption of SO2 and simultaneous desulfurization and denitrification process. When the temperature rises to 630℃, calcium carbonate begins to decompose until the decomposition is complete. The decomposition reaction of calcium carbonate is: CaCO3→CaO+CO2

[0103] Calcium oxide desulfurization mechanism process:

[0104] H2S+CaO→CaS+H2O

[0105] 2CaO+2SO2+O2→2CaSO4

[0106] CaS+2O2→CaSO4

[0107] In the denitrification process, CaO and CaS are used as catalysts to catalyze the reduction of N2O. The reaction mechanism is as follows:

[0108]

[0109] The third stage: coke denitrification process. After the SO2 on the coke surface is adsorbed by the desulfurization and denitrification agent, there is no competition between N2O and NO and coke, the contact area increases, and the catalytic reduction ability of coke to nitrogen oxides is enhanced. The denitrification reaction formula is as follows:

[0110]

[0111] Embodiment 1:

[0112] A fuel desulfurization and denitrification system of the present invention, such as Figure 1-4As shown, it includes a circulating fluidized bed boiler, a gas preheater 11, a gas concentration mixer 13, a first desulfurizer silo 5 and a second desulfurizer silo 15. The circulating fluidized bed boiler includes a furnace 4 and a cyclone separator 8 connected to the furnace 4. The cyclone separator 8 is connected to the gas preheater 11. The furnace 4 is provided with a feed inlet 19 and a first air inlet 14. The gas concentration mixer 13 is provided with a primary air duct 2 and a secondary air duct 17. The gas preheater 11 is used to preheat the primary air duct 2 and the secondary air duct 17. The primary air duct 2 is connected to the first air inlet 14. The secondary air duct 17 is divided into two branches, and the two branches are respectively a secondary split air nozzle and a secondary split air nozzle. 7 and the tertiary air nozzle 6, the secondary air duct 17, the secondary diversion air nozzle 7 and the tertiary air nozzle 6 are connected through a three-way joint 10, the secondary diversion air nozzle 7 is connected to the furnace 4, the end of the secondary diversion air nozzle 7 in the furnace 4 is provided with a first nozzle 1, the first desulfurizing agent bin 5 is arranged on the secondary diversion air nozzle 7, close to the first nozzle 1, the tertiary air nozzle 6 is connected to the furnace 4, the end of the tertiary air nozzle 6 in the furnace 4 is provided with a second nozzle 16, the second nozzle 16 is arranged downwardly inclined, the second desulfurizing agent bin 15 is arranged on the tertiary air nozzle 6, close to the second nozzle 16, and the height of the second nozzle 16 is greater than the height of the first nozzle 1. In this embodiment, the gas preheater 11 adopts a tubular air preheater, the preparation standard is NB / T47049-2016, the temperature of different pipelines can be controlled separately, the primary air duct 2 and the secondary air duct 17 pass through the gas preheater 11 respectively. The gas concentration mixer 13 adopts the LFIX-6000 series gas concentration mixer produced by Sichuan Laifeng Fluid Equipment Manufacturing Co., Ltd., which is mainly used for dilution and adjustment of the concentration ratio of oxygen and carbon dioxide. It can output oxygen and carbon dioxide in a proportion at the same time, or use them separately or select several of them to use. It can accurately control the concentration ratio and composition of oxygen and carbon dioxide, and can be a proportion range of percentage, ppm, and ppb level.

[0113] The furnace 4 includes a dense phase area and a dilute phase area from bottom to top. The feed port 19 is located in the dense phase area (the lower part of the furnace), the first air inlet 14 is located at the bottom of the furnace 4, the first nozzle 1 and the second nozzle 16 are located in the dilute phase area (the middle or upper part of the furnace), the first nozzle 1 is located on one side of the furnace 4, and the second nozzle 16 is located on the other side (opposite side) of the furnace 4, as shown in FIG. Figure 3 As shown, the angle between the working surface of the second nozzle 16 and the vertical surface is 45°.

[0114] The furnace 4 has a height of 12 m, the first nozzle 1 has a height of 6 m, the second nozzle 16 has a height of 10 m, and the furnace 4 is further provided with a speed sensor 25, which is located directly below the first nozzle 1 and has a height of 4.5 m. In this embodiment, the speed sensor 25 is an infrared speed sensor.

[0115] The furnace 4 is provided with a return port 20 and a flue gas outlet 18. The return port 20 is located in the dense phase zone, and the flue gas outlet 18 is located on the side wall of the top of the furnace 4. The cyclone separator 8 is provided with a return pipe 21, a flue gas inlet 22 and an outlet 23 connected to the flue gas inlet 22. The return port 20 is connected to the return pipe 21 for returning part of the unburned pulverized coal into the furnace 4. The flue gas outlet 18 is connected to the flue gas inlet 22, and the outlet 23 is connected to the air inlet end of the gas preheater 11 for heat exchange with the flue gas separated by the cyclone separator 4 through the gas preheater 11. The flue gas after heat exchange is treated by other flue gas cleaning processes of the power plant and then discharged into the atmosphere through the chimney.

[0116] Gas flow meters 12 are provided on the primary air duct 2 and the secondary air duct 17 for controlling the volume flow of the primary air duct 2 and the secondary air duct 17. Valves 9 are provided on the secondary branch air nozzle 7 and the tertiary air nozzle 6 for controlling the volume flow of the secondary branch air nozzle 7 and the tertiary air nozzle 6.

[0117] The system also includes a CO2 gas supply device and an O2 gas supply device, the O2 gas supply device is connected to the gas concentration mixer 13 through a pipeline, and the CO2 gas supply device is connected to the gas concentration mixer 13 through a pipeline, and each pipeline is provided with a gas flow meter 12. In this embodiment, the CO2 gas supply device is a CO2 gas supply bottle, and the O2 gas supply device is an O2 gas supply bottle.

[0118] A circulating fluidized bed is provided at the bottom of the furnace 4, and a slag discharge port 24 is provided on the circulating fluidized bed for discharging the slag remaining from combustion.

[0119] A method for desulfurizing and denitrifying fuel of the present invention is implemented by using the above-mentioned system for desulfurizing and denitrifying fuel, and comprises the following steps:

[0120] Coal and biomass are crushed and mixed to obtain a mixed fuel, which is then introduced into the furnace 4 through the feed port 19, and CO2 and O2 are sent to the gas concentration mixer 13 for mixing. The gas concentration mixer 13 provides primary air and secondary air, and the primary air is preheated by the gas preheater 11 and then sent to the furnace 4 through the primary air duct 2. The mixed fuel burns violently at the bottom of the furnace 4 to form a dense phase area, releasing a large amount of heat. During the combustion process, the biomass has a high volatile matter content, and combustion will produce more reducing gases such as H2, C2H2, and CH4, which promote the catalytic reduction reaction of nitrogen oxides. Under the action of air pressure, the high-temperature flue gas (first flue gas) carries part of the unburned mixed fuel upward, and the secondary air is preheated by the gas preheater 11. The preheated part of the secondary air is sent to the furnace 4 as the secondary diversion air through the secondary diversion air nozzle 7 to enhance the reducing gas. atmosphere, but the oxygen concentration remains unchanged. At the same time, the secondary diversion wind carries the desulfurizer dropped from the second desulfurizer silo 5 to the furnace 4, so that the unburned mixed fuel continues to burn and desulfurizes and denitrates at the same time, forming a dilute phase area. After 1 to 2 minutes, the other part of the preheated secondary air is sent to the furnace 4 through the tertiary air nozzle 6 as the tertiary air. At the same time, the tertiary air carries the desulfurizer in the second desulfurizer silo 15 to the furnace 4. The section of the injection pipeline connected to the second nozzle 16 is arc-shaped. Therefore, the fluid formed by the tertiary air has a tangential velocity and a large initial velocity of the fluid. After the fluid is injected, a strong vortex will be formed in the center of the dilute phase area with a strong suction ability, which is called the upper vortex. The upper vortex will suck and gather the high-temperature flue gas and other substances escaping from the lower vortex to form a high-temperature area, so that the escaped mixed fuel and unburned coke are re-burned, and the desulfurizer is quickly pyrolyzed, which significantly improves the desulfurization and denitrification efficiency and combustion efficiency. The obtained second flue gas is sent to the cyclone separator 8, and after solid-gas separation, the obtained return material is returned to the furnace 4, and the obtained third flue gas is sent to the gas preheater 11 for heat exchange. After the heat exchange, the flue gas is treated by other flue gas cleaning processes of the power plant and discharged into the atmosphere through the chimney. When the boiler is running, the desulfurization and denitrification process of the above mixed fuel can be continuously carried out.

[0121] In this embodiment, the speed measured by the speed sensor 25 is 3.5 m / s, the speed of the secondary diversion wind is 5 m / s, and the speed of the tertiary wind is 7.5 m / s.

[0122] In this embodiment, the volume flow ratio of primary air to secondary air is 1:1, the volume flow ratio of secondary diverter air to tertiary air is 1:1, the oxygen volume concentration of primary air is 50%, and the oxygen volume concentrations of secondary air, secondary diverter air and tertiary air are all 50%.

[0123] In this embodiment, the temperature of the primary air is 165°C, and the temperatures of the secondary air, secondary split air, and tertiary air are all 175°C.

[0124] In this embodiment, the ratio of the mixed fuel to the total desulfurizer per unit time is 430:1, expressed in kg / s, wherein the mass ratio of the desulfurizer in the nozzle chamber of the first nozzle 1 to the nozzle chamber of the second nozzle 16 is 2:1.

[0125] In this embodiment, the excess oxygen coefficient in the furnace 4 is 1.18.

[0126] In this embodiment, the circulating fluidized bed boiler adopts gas staged combustion, and the average temperature in the furnace 4 is 900°C.

[0127] In this embodiment, the mass ratio of coal to biomass is 1:1.

[0128] In this embodiment, the biomass is preferably coconut shells, which are crushed to obtain coconut shell particles, with a particle size of 0 < coconut shell particles ≤ 1 mm, and coal is crushed to obtain coal powder, with a particle size of 0 < coal powder ≤ 1 mm.

[0129] In this embodiment, the desulfurizing agent is organic calcium, and the preparation process of organic calcium includes the following steps:

[0130] The waste oil is mixed with dilute sulfuric acid, heated to 65°C under stirring conditions to undergo a hydrolysis reaction, and a reaction product containing higher fatty acids and glycerol is obtained. After the reaction, the reaction product is allowed to stand until obvious stratification occurs in the reaction product, and then extracted to obtain higher fatty acids. Water is added to the higher fatty acids, and then heated until the higher fatty acids and water are miscible, the temperature of the resulting solution is maintained at 65°C, acid is added until the pH of the solution is 5, and crushed eggshells are added under stirring conditions, the amount of crushed eggshells added is until no bubbles appear in the solution or eggshells remain in the solution, and after sufficient reaction, a solution containing organic calcium is obtained, which is heated and evaporated and crystallized to obtain organic calcium.

[0131] In the preparation process of organic calcium, each heating step is implemented by the flue gas waste heat after heat exchange in the gas preheater 11, that is, the flue gas waste heat at the tail of the boiler. The volume ratio of waste oil to dilute sulfuric acid is 3:1, the concentration of dilute sulfuric acid is 3 mol / L, the hydrolysis reaction time is 3 hours, the volume ratio of higher fatty acids to water is 1:3, and the particle size of the broken eggshell is 0 < ≤ 1 mm.

[0132] Gutter oil is made from animal fat, and eggshells are made from egg shells.

[0133] Under the condition of oxygen-enriched combustion, the present invention adopts the staged fluidized air combustion mode in the furnace, and sprays the prepared high-purity desulfurization and denitrification agent organic calcium into the furnace from the middle of the furnace, achieving the effect of high-efficiency desulfurization and denitrification, with a desulfurization rate of more than 98% and a denitrification rate of more than 80%. The present invention solves the problem of SO2 and NO in the flue gas of coal powder combustion in circulating fluidized bed boilers. xThe problem of high emission concentration has prompted the mass concentration of pollutants in the flue gas discharged from the chimney to reach the ultra-low emission concentration standard stipulated by the state. The use of waste cooking oil and eggshell waste to prepare desulfurizers has achieved the effective utilization of waste cooking oil and the recycling of eggshells. The decomposition of CaSO4 will also be limited to prevent desulfurization failure. The desulfurization product CaSO4 can be used as a cement additive.

[0134] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as above in the preferred embodiment, it is not used to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention, still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A fuel desulfurization and denitrification system, characterized in that: The invention comprises a circulating fluidized bed boiler, a gas preheater (11), a gas concentration mixer (13), a first desulfurizing agent silo (5) and a second desulfurizing agent silo (15), wherein the circulating fluidized bed boiler comprises a furnace (4) and a cyclone separator (8) connected to the furnace (4), wherein the cyclone separator (8) is connected to the gas preheater (11), wherein the furnace (4) is provided with a feed port (19) and a first air inlet (14), wherein the gas concentration mixer (13) is provided with a primary air duct (2) and a secondary air duct (17), wherein the gas preheater (11) is used to preheat the primary air duct (2) and the secondary air duct (17), wherein the primary air duct (2) is connected to the first air inlet (14), and wherein the secondary air duct (17) is connected to the first air inlet (14). ) is divided into two branches, the two branches are a secondary branch air nozzle (7) and a tertiary air nozzle (6), the secondary branch air nozzle (7) is connected to the furnace (4), a first nozzle (1) is provided at the end of the secondary branch air nozzle (7) in the furnace (4), the first desulfurizing agent silo (5) is arranged on the secondary branch air nozzle (7), the tertiary air nozzle (6) is connected to the furnace (4), a second nozzle (16) is provided at the end of the tertiary air nozzle (6) in the furnace (4), the second nozzle (16) is arranged to be inclined downward, the second desulfurizing agent silo (15) is arranged on the tertiary air nozzle (6), and the height of the second nozzle (16) is greater than the height of the first nozzle (1); The furnace (4) comprises a dense phase area and a dilute phase area, the feed port (19) is located in the dense phase area, the first air inlet (14) is located at the bottom of the furnace (4), the first nozzle (1) and the second nozzle (16) are located in the dilute phase area, the first nozzle (1) is located on one side of the furnace (4), the second nozzle (16) is located on the other side of the furnace (4), and the angle between the working surface of the second nozzle (16) and the vertical surface is 35° to 45°; Assuming that the height of the furnace (4) is h, the height of the first nozzle (1) is 5 / 12h to 7 / 12h, the height of the second nozzle (16) is 9 / 12h to 11 / 12h, and the furnace (4) is further provided with a speed sensor (25), the speed sensor (25) is located below the first nozzle (1), and the height of the speed sensor (25) is 4 / 12h to 5 / 12h.

2. The fuel desulfurization and denitrification system according to claim 1, characterized in that: The furnace (4) is provided with a return port (20) and a smoke outlet (18); the cyclone separator (8) is provided with a return pipe (21), a smoke inlet (22) and an air outlet (23) connected to the smoke inlet (22); the return port (20) is connected to the return pipe (21); the smoke outlet (18) is connected to the smoke inlet (22); and the air outlet (23) is connected to the gas preheater (11).

3. The fuel desulfurization and denitrification system according to claim 1, characterized in that: The primary air duct (2) and the secondary air duct (17) are both provided with a gas flow meter (12), and the secondary branch air nozzle (7) and the tertiary air nozzle (6) are both provided with a valve (9).

4. The fuel desulfurization and denitrification system according to claim 1, characterized in that: It also includes a CO2 gas supply device and an O2 gas supply device, wherein the O2 gas supply device is connected to the gas concentration mixer (13) through a pipeline, and the CO2 gas supply device is connected to the gas concentration mixer (13) through a pipeline, and each pipeline is provided with a gas flow meter (12).

5. A method for desulfurization and denitrification of fuel, characterized in that: The method adopts the fuel desulfurization and denitrification system according to any one of claims 1 to 4, comprising the following steps: Coal and biomass are crushed and mixed to obtain a mixed fuel, and the mixed fuel is introduced into the furnace (4) through the feed port (19), CO2 and O2 are introduced into the gas concentration mixer (13) for mixing, and the gas concentration mixer (13) provides primary air and secondary air. The primary air is preheated by the gas preheater (11) and then introduced into the furnace (4) through the primary air duct (2), so that the mixed fuel burns and a catalytic reduction reaction of nitrogen oxides occurs to form a dense phase zone. The obtained first flue gas carries the unburned mixed fuel and rises in the furnace (4). The secondary air is preheated by the gas preheater (11), and part of the preheated secondary air is used as the secondary The split air carries the desulfurizer dropped from the first desulfurizer silo (5) and is delivered to the furnace (4) through the secondary split air nozzle (7), so that the unburned mixed fuel is burned and desulfurized and denitrated, forming a dilute phase zone. Another part of the preheated secondary air is used as the tertiary air and carries the desulfurizer dropped from the second desulfurizer silo (15) and is delivered to the furnace (4) through the tertiary air nozzle (6), so that the escaped mixed fuel and unburned coke are re-burned and desulfurized and denitrated. The obtained second flue gas is delivered to the cyclone separator (8), and after solid-gas separation, the obtained return material is returned to the furnace (4). The obtained third flue gas is delivered to the gas preheater (11) for heat exchange, thereby achieving desulfurization and denitration of the mixed fuel.

6. The method for desulfurization and denitrification of fuel according to claim 5, characterized in that: The injection speed of the secondary split air is 1.3 to 1.8 times the speed measured by the speed sensor (25) provided in the furnace (4), and the injection speed of the tertiary air is 1.4 to 2 times the injection speed of the secondary split air; And / or, the volume flow ratio of the primary air to the secondary air is 1:1, the volume flow ratio of the secondary split air to the tertiary air is 1:1, the oxygen volume concentration of the primary air is 50% to 70%, and the oxygen volume concentrations of the secondary air, the secondary split air, and the tertiary air are all 45% to 50%; and / or, the temperature of the preheated primary air is 160°C to 170°C, and the temperatures of the preheated secondary air, secondary split air, and tertiary air are all 170°C to 180°C; and / or, the ratio of the mixed fuel to the total desulfurizing agent per unit time is 390-450:1, in kg / s; and / or, the excess oxygen coefficient in the furnace (4) is 1.15 to 1.20, and the average temperature in the furnace (4) is 800° C. to 900° C.; And / or, the mass ratio of the coal to the biomass is 1-3:1-2, the biomass is coconut shell, the coconut shell is crushed to obtain coconut shell particles, 0<the particle size of the coconut shell particles ≤1mm, and the coal is crushed to obtain coal powder, 0<the particle size of the coal powder ≤1mm.

7. The method for desulfurization and denitrification of fuel according to claim 5 or 6, characterized in that: The desulfurizing agent is organic calcium, and the preparation process of the organic calcium comprises the following steps: The waste cooking oil is mixed with dilute sulfuric acid, heated to 60°C to 70°C under stirring conditions for hydrolysis reaction to obtain a reaction product containing higher fatty acids and glycerol, and allowed to stand after the reaction until the reaction product is clearly stratified, and then extracted to obtain higher fatty acids; water is added to the higher fatty acids, and then heated until the higher fatty acids and water are miscible, the temperature of the resulting solution is maintained at 60°C to 70°C, acid is added until the pH value of the solution is 4 to 6, and crushed eggshells are added under stirring conditions, the amount of crushed eggshells added is until no bubbles appear in the solution or eggshells remain in the solution, and after sufficient reaction, a solution containing organic calcium is obtained, which is heated for evaporation and crystallization to obtain organic calcium.

8. The method for desulfurization and denitrification of fuel according to claim 7, characterized in that: During the preparation of the organic calcium, the heating is performed using the waste heat of the flue gas after heat exchange in the gas preheater (11), the volume ratio of the waste oil to the dilute sulfuric acid is 2-4:1, the concentration of the dilute sulfuric acid is 3 mol / L-4 mol / L, the hydrolysis reaction time is 2h-4h, the volume ratio of the higher fatty acid to water is 1:2-3, 0<the particle size of the crushed eggshell is ≤1mm, and the eggshell raw material of the crushed eggshell includes one or more of chicken eggshell, duck eggshell and quail eggshell.

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