Method for preparing BC dry powder extinguishing agent from fly ash washing byproduct potassium sodium salt

Abstract

The invention provides a method for preparing a BC dry powder extinguishing agent from fly ash washing byproduct potassium sodium salt. The method comprises the following steps: a fly ash pretreatment module: mixing pyrolytic fly ash with water to obtain a fly ash suspension; adding a chelating agent, a flocculating agent and a sodium carbonate solution, carrying out heating reaction, and carrying out solid-liquid separation to obtain a first solution; the NaHCO3 dry powder purification module is used for mixing the first solution with ammonia water, introducing carbon dioxide and stirring for reaction, filtering and adjusting the pH value of filtrate, carrying out pressurized carbonization reaction and then carrying out solid-liquid separation to obtain a second solution and sodium bicarbonate crude salt; the KHCO3 dry powder purification module is used for mixing the second solution, ammonia water and an organic alcohol solution, and performing solid-liquid separation after reaction to obtain a third solution and potassium bicarbonate crude salt; and the ultrafine powder graded grinding module is used for carrying out graded ultrafine grinding on the sodium bicarbonate crude salt and / or the potassium bicarbonate crude salt. According to the method, the BC dry powder extinguishing agent is prepared from the fly ash salt water washing byproduct composite sodium potassium bicarbonate, and a new thought is provided for fly ash water washing salt resource utilization.

Description

Technical Field

[0001] The invention relates to the field of fire extinguishing agents, and in particular to a method for preparing BC dry powder fire extinguishing agent by washing fly ash with by-product potassium and sodium salts. Background Art

[0002] Commonly used fire extinguishing agents are divided into four categories: gas, dry powder, water and foam. Dry powder fire extinguishing agents are the most commonly used fire extinguishing agents in people's daily lives because of their low price, ease of use, and suitability for three types of fires: A (ordinary solid fire), B (flammable liquid fire), and C (gas fire). Dry powder fire extinguishing agents are fine particles made by mixing fire extinguishing groups (ammonium phosphate, carbonate) and appropriate lubricants (magnesium stearate, mica powder, talcum powder, etc.), and a small amount of moisture-proof agents (silicone, silicone oil, etc.), and then deeply grinding them. Carbon dioxide is used as the spraying power. The sprayed powder has a dense concentration and fine particles. It can form an isolation layer that hinders combustion when covered on solid or liquid combustion materials. At the same time, it precipitates non-combustible gases, reduces the surrounding oxygen concentration, and suppresses flames. There are currently two main types of dry powder fire extinguishing agents on the market. One is sodium bicarbonate and potassium bicarbonate ultrafine dry powder (also known as BC dry powder), which is suitable for extinguishing BC fires. The other is ammonium carbonate / ammonium sulfate dry powder (also known as ABC dry powder), which is suitable for extinguishing ABC fires. The two types of fire extinguishing agents mainly rely on chemical inhibition to extinguish fires. Among them, ammonium bicarbonate / sodium carbonate dry powder is not suitable for extinguishing common solid fires. Ammonium phosphate / ammonium sulfate dry powder can extinguish solid fires, but the national standard stipulates that the water content is less than 0.3%. Therefore, the cooling effect during fire extinguishing is poor, which is easy to cause resurgence. Due to their own physical and chemical properties, these two types of dry powder fire extinguishing agents are prone to agglomeration if they contain more water, and cannot be sprayed out smoothly under gas drive. Therefore, in order to prevent agglomeration, a considerable amount (mass ratio 5-10%) of talcum powder, silicone oil and other additives must be added, which will prevent agglomeration and have a certain impact on the fire extinguishing performance.

[0003] Fly ash from the incineration of domestic waste contains a large amount of soluble salts, mainly chloride salts of sodium, potassium and calcium. When the fly ash is washed with water, the chloride salts are leached out, producing a large amount of high-salt wastewater, and the heavy metals in the fly ash are leached out at the same time. The treatment of fly ash washing liquid is mainly to remove heavy metals and then recover the inorganic salts therein. The purity of industrial salts of sodium chloride, potassium chloride and calcium chloride extracted from fly ash is difficult to meet the standards due to the complex composition of the aqueous solution, resulting in low market prices and unstable market demand. At present, there is an urgent need to provide a new method for preparing BC dry powder fire extinguishing agent from potassium-sodium complex salts produced as a by-product of fly ash washing. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for preparing BC dry powder fire extinguishing agent by using potassium and sodium salts produced as byproducts of fly ash washing. The present invention obtains composite sodium potassium bicarbonate by using fly ash salt washing conversion, and the composite sodium potassium bicarbonate can be used to effectively prepare ultrafine BC dry powder fire extinguishing agent, providing a new idea for the resource utilization of fly ash washing salt.

[0005] In a first aspect, the present invention provides a method for preparing potassium and sodium salts produced as by-products of fly ash washing, comprising: 1) Fly ash pretreatment module: Dioxin degradation: The fly ash is subjected to vacuum pyrolysis to obtain pyrolysis fly ash.

[0006] Water washing: mixing the pyrolysis fly ash with water to obtain a fly ash suspension.

[0007] Heavy metal impurity removal and precipitation of calcium and magnesium: adding a chelating agent, a flocculant and a sodium carbonate solution to the fly ash suspension, heating the suspension for reaction, and then performing solid-liquid separation to obtain a first solution.

[0008] 2) NaHCO 3 Dry powder purification module: The first solution is mixed with ammonia water, carbon dioxide is introduced and stirred for reaction, filtered and the pH value of the filtrate is adjusted, and solid-liquid separation is performed after pressurized carbonization reaction to obtain a second solution and crude sodium bicarbonate salt.

[0009] 3) KHCO 3 Dry powder purification module: The second solution, aqueous ammonia and organic alcohol solution are mixed, and solid-liquid separation is performed after the reaction to obtain a third solution and crude potassium bicarbonate salt.

[0010] 4) Ultrafine powder classification and grinding module: Sodium bicarbonate coarse salt and / or potassium bicarbonate coarse salt are graded to be ultrafinely ground.

[0011] The present invention processes fly ash through specific process steps to obtain high-purity sodium bicarbonate and potassium bicarbonate. The fly ash is subjected to vacuum pyrolysis to effectively degrade dioxins therein. The pyrolyzed fly ash is washed with water and solid-liquid separated to extract soluble salts. Then, a chelating agent and a flocculant are added to remove heavy metal impurities in the washing liquid. By adding a sodium carbonate solution and heating the reaction, calcium and magnesium ions are precipitated to obtain a purified solution. The solution is mixed with ammonia water and carbon dioxide is introduced to react to generate high-purity sodium bicarbonate crude salt. The potassium bicarbonate crude salt is separated by selective dissolution and precipitation with an organic alcohol solution, and dried to obtain sodium bicarbonate and potassium bicarbonate crude salts with high stability and purity.

[0012] Preferably, in step 1), the dioxin degradation comprises vacuum pyrolysis of the fly ash at 400-600°C for 30-60 minutes, maintaining an oxygen concentration of ≤1%. Preferably, in the water washing, the liquid-to-solid ratio of the pyrolysis fly ash to water is 1.2-1.8 mL:1 g, and the shaking mixing is performed for 15±2 minutes.

[0013] Further preferably, in step 1), the flocculant is anionic polyacrylamide, preferably with a molecular weight of 6 million to 8 million; the chelating agent is dithiocarbamate and tetramethylthiuram disulfide, and the mass ratio of the dithiocarbamate and tetramethylthiuram disulfide is (2-3):(1-2), preferably 2:1; the ratio of the chelating agent, the flocculant and the fly ash suspension is (0.8-1.4) g:(1.4-2.0) g:100 mL, preferably 1.2 g:1.7 g:100 mL.

[0014] Further preferably, in step 1), the volume ratio of the fly ash suspension treated with the chelating agent and flocculant to the sodium carbonate solution is (8.5-10):1, and the mass concentration of the sodium carbonate solution is 10-15%; and / or, centrifugal filtration or filter press filtration is adopted; the speed of centrifugal filtration is 2500-3000r / min, and the time is 10-15min; the filter press filtration pressure is 6-8kg / cm 2 , the filtration time is 20-30min.

[0015] Further preferably, in step 2), the volume ratio of the first solution to aqueous ammonia is (10-20):1, and the mass concentration of aqueous ammonia is preferably 30±2%; the flow rate of the carbon dioxide is 70-90 L / min, the reaction temperature is 18-20°C, and the stirring reaction is 50-70 min; the pH of the filtrate is adjusted to 10-10.5, the temperature of the pressurized carbonization reaction is 52-56°C, and the pressure is 0.4-0.42 MPa; the sodium bicarbonate crude salt n(NaHCO 3 ) / n(KHCO 3 )≥7.6, mass fraction of sodium bicarbonate≥88%.

[0016] Further preferably, in step 3), the organic alcohol solution is a 45-55% sec-butyl alcohol solution, and the reaction temperature is 40-45°C; and / or, the third solution is circulated back to step 2); and / or, the volume ratio of the second solution, aqueous ammonia and the organic alcohol solution is (10-20):1:(0.25-0.4); and / or, n(KHCO 3 ) / n(NaHCO 3 )≥8.2, mass fraction of potassium bicarbonate≥92%.

[0017] More preferably, the method further comprises the following step of drying the crude sodium bicarbonate and potassium bicarbonate salts: drying the crude sodium bicarbonate and potassium bicarbonate salts at a drying temperature of 60-65°C.

[0018] Further preferably, in step 4), the crude sodium bicarbonate salt and the crude potassium bicarbonate salt are mixed and then ground to obtain ultrafine potassium and sodium powder as by-products of fly ash washing, and a surface modifier is preferably added during the grinding process.

[0019] Preferably, in step 4), the particle size d90 of the dry powder after grinding is 10-15 μm, and the specific surface area is 1.6-2.2 m 2 / g; the mass ratio of the crude sodium bicarbonate salt to the crude potassium bicarbonate salt is (4.0-5.6):1; the surface modifier is potassium aluminum sulfate; the mass ratio of the surface modifier to the potassium and sodium salt produced as a by-product of fly ash washing is (0.025-0.03):1.

[0020] The present invention can significantly improve the processing effect of each step and the quality of the final product by optimizing the above parameters, and has better environmental and economic benefits.

[0021] In a second aspect, the present invention provides potassium and sodium salts as by-products of fly ash washing obtained by the above-mentioned preparation method.

[0022] In a third aspect, the present invention provides a BC dry powder fire extinguishing agent, using the fly ash water washing byproduct potassium sodium salt or the fly ash water washing byproduct potassium sodium salt obtained by the above-mentioned preparation method. The BC dry powder fire extinguishing agent prepared using the fly ash water washing byproduct potassium sodium salt exhibits excellent fire extinguishing performance, reflecting the innovative idea of ​​resource utilization.

[0023] In a fourth aspect, the present invention provides a method for preparing BC dry powder fire extinguishing agent by using potassium and sodium salts as by-products of fly ash washing, and the BC dry powder fire extinguishing agent is prepared by using potassium and sodium salts as by-products of fly ash washing obtained by the above-mentioned preparation method.

[0024] Preferably, the steps of preparing BC dry powder fire extinguishing agent include: mixing the potassium and sodium salts produced as by-products of fly ash washing with mineral dry powder to obtain a mixed dry powder, mixing modified silicone oil and additives with the mixed dry powder and then ball milling to obtain an ultrafine dry powder; filling the ultrafine dry powder into a fire extinguisher and filling it with argon gas.

[0025] Preferably, the mass ratio of the fly ash washing by-product potassium and sodium salt to the mineral dry powder is (5-7):(2-4); the mineral dry powder is silicon dioxide and aluminum oxide in a volume ratio of (1-2):(1-2); the mass ratio of the additive to the mixed dry powder is (0.025-0.03):1; the additive is talc, mica and activated clay in a mass ratio of 2.5:2.5:(1.25-2.5); the mass ratio of the modified silicone oil to the mixed dry powder is (1.2-1.5):36; and the ball milling time is 30-50min.

[0026] Preferably, the argon gas is high-purity argon gas, and the filling argon gas pressure is 1.1-1.3 MPa.

[0027] In the present invention, specific sodium bicarbonate crude salt and potassium bicarbonate crude salt are mixed and then ground, and the process is optimized to prepare fly ash washing by-product potassium sodium salt (sodium potassium composite bicarbonate), which provides a basis for the subsequent preparation of high-performance and high-efficiency fire extinguishing agent, and the sodium potassium composite bicarbonate is mixed with mineral dry powder, and modified silicone oil, additives, etc. are mixed with the mixed dry powder and ball-milled, thereby improving the uniformity, stability, fluidity and other properties of the fire extinguishing agent, thereby ensuring its excellent fire extinguishing performance.

[0028] In a fifth aspect, the present invention provides a BC dry powder fire extinguishing agent obtained by the above preparation method.

[0029] The present invention provides a method for preparing BC dry powder fire extinguishing agent from potassium-sodium complex salt produced as a by-product of fly ash washing. The method provides a new idea for resource utilization of fly ash washing salt. The obtained BC dry powder fire extinguishing agent has high efficiency fire extinguishing ability, good stability, low cost, and is suitable for a variety of fire extinguishing application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 A schematic diagram of a module flow for preparing BC dry powder fire extinguishing agent from potassium-sodium double salt produced by washing fly ash provided in an embodiment of the present invention.

[0032] Figure 2 A schematic diagram of the process flow for preparing BC dry powder fire extinguishing agent from potassium-sodium double salt produced by washing fly ash provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0035] Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods. If no specific techniques or conditions are specified in the examples, they are all conventional methods or the techniques or conditions described in the literature in this field, or according to the product instructions. If the manufacturers of the reagents and instruments are not specified, they are all conventional products that can be purchased through regular channels.

[0036] In the present invention, the specific source of fly ash is not limited. In the embodiment of the present invention, the mainstream flue gas treatment process of the waste incineration plant is SNCR + semi-dry method + dry method + activated carbon + bag filter. The fly ash comes from the bottom ash of the semi-dry spray tower and the powder collected by the bag filter. The main components include CaSO 3 , Ca(OH) 2 、CaCO 3 , CaClOH, NaCl, KCl, CaSO 4 and SiO 2 .

[0037] The present invention will be further described below with reference to the embodiments.

[0038] Example 1 (compound preparation of dry powder fire extinguishing agent from sodium bicarbonate and potassium bicarbonate) This embodiment provides a composite sodium potassium bicarbonate obtained by washing and converting fly ash with salt water, and an ultra-fine BC dry powder fire extinguishing agent prepared therefrom, the process is as follows: Figure 1 and Figure 2 As shown, the specific preparation steps are as follows: 1) Degradation of dioxins The fly ash is sent into the dioxin vacuum pyrolysis furnace, the temperature is 500±25℃, the pyrolysis residence time is 45±5min, the oxygen volume concentration in the furnace is not higher than 1%, and the dioxin degradation rate is not lower than 99%. When the dioxin residue content is lower than 50ng-TEQ / kg, proceed to the next step.

[0039] 2) Washing Step (1) The fly ash after pyrolysis and tap water are placed in a screw-cap container at a liquid-to-solid ratio of 1.5 mL / g and mixed. After sufficient shaking and mixing for 15 minutes, the water washing liquid is vacuum filtered to obtain a fly ash water washing liquid after solid-liquid separation. The main components of the fly ash water washing liquid are shown in the following table.

[0040] Table 1 Main components and contents of fly ash washing liquid

[0041] 3) Heavy metal removal The fly ash washing liquid obtained in step (2) was added with flocculants (anionic polyacrylamide, molecular weight 6 million to 8 million) and chelating agents (dithiocarbamate and tetramethylthiuram disulfide, mass ratio 2:1) to remove heavy metals. The ratio of chelating agent, flocculant and fly ash washing liquid was 1.2 g:1.7 g:100 mL. The heavy metal concentration was measured. The removal rates of five heavy metals, Cd, Cu, Mn, Pb and Zn, reached 99%, 92%, 92%, 99% and 95% or more, respectively. Solution 3 was obtained by centrifugal filtration.

[0042] 4) Precipitation of calcium and magnesium Sodium carbonate solution (mass concentration 12.5%, sodium carbonate grade ≥ 99.5%) was added to the solution 3 obtained in step (3) to precipitate calcium and magnesium. The volume ratio of solution 3 to sodium carbonate solution was 9:1. The reaction was carried out at a constant temperature (temperature 68±1°C). The reaction was fully stirred for 35 minutes and centrifuged to obtain a sodium-potassium mixed solution 4. The Ca removal rate was ≥ 99.98%, and n(Na) / n(K) = 1.35±0.05.

[0043] 5) Separate and obtain crude sodium bicarbonate salt Ammonia water (volume concentration 30%, volume ratio of ammonia water to solution 4 1:15) was added to the sodium-potassium mixed solution 4 obtained in step (4), and carbon dioxide gas was introduced (flow rate 80 L / min, continuously introduced), and stirred for reaction (stirring time 60 min, reaction temperature controlled at 19±1° C.). When the crystal product is no longer produced, stirring was stopped, and the solid-liquid mixture was filtered to obtain filter cake S5. The filtrate (pH adjusted to 10.2) was pumped into a carbonization reactor, and carbon dioxide was continuously introduced. The reaction temperature was maintained at 54±1° C. The reactor was pressurized to 0.41 MPa. When the pH value of the solution in the reactor dropped to 8.1-8.3, the pressurized carbonization reaction was terminated to obtain solution L5-1. Solution L5-1 was first heat-insulated and precipitated, and then centrifuged to obtain a mixed solid of sodium bicarbonate and potassium bicarbonate (n(NaHCO 3 ) / n(KHCO 3 )≥7.6, mass fraction of sodium bicarbonate≥88%), and the filtrate L5-2 was obtained by centrifugation.

[0044] 6) Separate and obtain crude potassium bicarbonate salt Ammonia water and an organic alcohol solution (sec-butyl alcohol, 50% concentration) were added to the filtrate L5-2 obtained in step (5), and the volume ratio of the filtrate L5-2, ammonia water and organic alcohol solution was 15:1:0.35. The reaction was carried out at a constant temperature (temperature controlled at 42±1°C). The generated crystals were separated by centrifugation to obtain a solid phase product 6-1 (n(KHCO 3 ) / n(NaHCO 3 )≥8.2, mass fraction of potassium bicarbonate≥92%), and the filtrate is recycled to step 5.

[0045] 7) Drying of sodium bicarbonate and potassium bicarbonate crude salt Sodium bicarbonate crude salt and potassium bicarbonate crude salt were dried at 62±0.5°C to constant weight to obtain S7-1 and S7-2 dry powders, respectively.

[0046] 8) The BC dry powder fire extinguishing agent provided in this embodiment has sodium potassium complex bicarbonate, silica mineral material and alumina mixture as the main fire extinguishing ingredients, and is supplemented with surface modifier potassium aluminum sulfate grinding modification and driving gas argon. The volume ratio of sodium potassium complex bicarbonate, silica and alumina is 6:1:1, and the mass ratio of the additive to the above three mixed materials is 0.025:1. In order to improve the fluidity of the powder, the mass ratio of the additives talcum powder, mica and activated clay is 2.5:2.5:1.25. The details are as follows: Preparation of BC dry powder fire extinguishing agent: dry S7-1 and S7-2 solid phase dry powders were mixed in a mass ratio of 5:1 and then subjected to graded mechanical ultrafine grinding. After high-speed grinding and the action of induced draft fan, mixed dry powder 8-1 was obtained. The dry powder particle size d90 was reduced to 14μm and the specific surface area was 1.9m 2 / g, and the surface modifier potassium aluminum sulfate needs to be added during the grinding process (the mass ratio of the surface modifier to the mixed dry powder 8-1 is 0.028:1).

[0047] Silica mineral material (purity ≥85%) and alumina powder were mixed in a volume ratio of 1:1, and then graded mechanical ultrafine grinding was used to obtain ultrafine mineral dry powder 8-2. The particle size d50 of the dry powder was reduced to less than 8μm, and the specific surface area was 225m 2 / g.

[0048] Mixed dry powder 8-1 and ultrafine mineral dry powder 8-2 are mixed in a mass ratio of 6:2 to obtain mixed dry powder 8-3, and modified silicone oil and additives are added. The mass ratio of modified silicone oil to mixed dry powder 8-3 is 1.2:36, and the mass ratio of additives to mixed dry powder 8-3 is 0.025:1. The additives are talcum powder, mica, and activated clay in a mass ratio of 2.5:2.5:1.25. After mixing, add to a ball mill and ball mill for 40 minutes to further homogenize and improve fluidity.

[0049] The refined dry powder is filled into the portable fire extinguisher cylinder, and the filling argon is high-purity argon with a filling pressure of 1.2MPa and a purity of 99.99%.

[0050] Example 2 (Preparation of dry powder fire extinguishing agent using sodium bicarbonate alone) This embodiment provides a composite sodium potassium bicarbonate obtained by washing and converting fly ash with salt water, and an ultrafine BC dry powder fire extinguishing agent prepared therefrom. The specific preparation steps are the same as those in Example 1, except that: in step 8), when preparing the BC dry powder fire extinguishing agent, the dried S7-1 and S7-2 solid phase dry powders are mixed in a mass ratio of 1:0.

[0051] Comparative Example 1 The BC dry powder fire extinguishing agent provided in this comparative example is a commercially available BC dry powder fire extinguishing agent.

[0052] Table 2 Main performance indicators of BC dry powder fire extinguishing agent

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing potassium and sodium salts produced as by-products from fly ash washing, characterized in that: include: 1) Fly ash pretreatment module: Degradation of dioxins: The fly ash is subjected to vacuum pyrolysis to obtain pyrolysis fly ash; Water washing: mixing the pyrolysis fly ash with water to obtain a fly ash suspension; Heavy metal impurity removal and precipitation of calcium and magnesium: adding a chelating agent, a flocculant and a sodium carbonate solution to the fly ash suspension, heating the suspension for reaction, and then separating the solid and the liquid to obtain a first solution; 2) NaHCO3 dry powder purification module: The first solution is mixed with aqueous ammonia, carbon dioxide is introduced and stirred for reaction, the filtrate is filtered and the pH value of the filtrate is adjusted, and solid-liquid separation is performed after pressurized carbonization reaction to obtain a second solution and crude sodium bicarbonate salt; 3) KHCO3 dry powder purification module: The second solution, aqueous ammonia and an organic alcohol solution are mixed, and solid-liquid separation is performed after the reaction to obtain a third solution and crude potassium bicarbonate salt; 4) Ultrafine powder classification and grinding module: Sodium bicarbonate coarse salt and / or potassium bicarbonate coarse salt are graded to be ultrafinely ground.

2. The preparation method according to claim 1, characterized in that: In step 1), the dioxin degradation comprises subjecting the fly ash to vacuum pyrolysis at 400-600° C. for 30-60 min, maintaining an oxygen concentration of ≤1%; And / or, in the water washing, the liquid-to-solid ratio of the pyrolysis fly ash to water is 1.2-1.8 mL:1 g, and the shaking mixing is performed for 15±2 min.

3. The preparation method according to claim 1 or 2, characterized in that: In step 1), the flocculant is anionic polyacrylamide, preferably with a molecular weight of 6 million to 8 million; the chelating agent is dithiocarbamate and tetramethylthiuram disulfide, and the mass ratio of the dithiocarbamate and tetramethylthiuram disulfide is (2-3):(1-2); the ratio of the chelating agent, the flocculant and the fly ash suspension is (0.8-1.4 g):(1.4-2.0 g):100 mL.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step 1), the volume ratio of the fly ash suspension treated with the chelating agent and flocculant to the sodium carbonate solution is (8.5-10):1, and the mass concentration of the sodium carbonate solution is 10-15%; and / or, centrifugal filtration or filter press filtration is adopted; the speed of centrifugal filtration is 2500-3000r / min, and the time is 10-15min; the pressure of filter press filtration is 6-8kg / cm 2 , the filtration time is 20-30min.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In step 2), the volume ratio of the first solution to aqueous ammonia is (10-20):1, and the mass concentration of aqueous ammonia is preferably 30±2%; the flow rate of the carbon dioxide is 70-90 L / min, the reaction temperature is 18-20°C, and the stirring reaction is 50-70 min; the pH of the filtrate is adjusted to 10-10.5, the temperature of the pressurized carbonization reaction is 52-56°C, and the pressure is 0.4-0.42 MPa; n(NaHCO3) / n(KHCO3) in the crude sodium bicarbonate salt is ≥7.6, and the mass fraction of sodium bicarbonate is ≥88%; and / or, in step 3), the organic alcohol solution is a 45-55% sec-butyl alcohol solution, and the reaction temperature is 40-45°C; and / or, the third solution is circulated back to step 2); and / or, the volume ratio of the second solution, aqueous ammonia and the organic alcohol solution is (10-20):1:(0.25-0.4); and / or, in the crude potassium bicarbonate salt, n(KHCO3) / n(NaHCO3)≥8.2, and the mass fraction of potassium bicarbonate is ≥92%; preferably, the following steps are also included, drying the sodium bicarbonate and the crude potassium bicarbonate salt: drying the crude sodium bicarbonate salt and the crude potassium bicarbonate salt at a drying temperature of 60-65°C.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In step 4), the crude sodium bicarbonate salt and the crude potassium bicarbonate salt are mixed and ground to obtain ultrafine potassium and sodium salt powder produced as a byproduct of fly ash washing, and a surface modifier is preferably added during the grinding process; Preferably, in step 4), the particle size d90 of the dry powder after grinding is 10-15 μm, and the specific surface area is 1.6-2.2 m 2 / g; the mass ratio of the crude sodium bicarbonate salt to the crude potassium bicarbonate salt is (4.0-5.6):1; the surface modifier is potassium aluminum sulfate; the mass ratio of the surface modifier to the potassium and sodium salt produced as a by-product of fly ash washing is (0.025-0.03):

1.

7. The fly ash washing method obtained by the preparation method according to any one of claims 1 to 6 produces potassium and sodium salts as by-products.

8. A BC dry powder fire extinguishing agent, characterized in that: The fly ash washing by-product potassium sodium salt obtained by the preparation method according to any one of claims 1 to 6 or the fly ash washing by-product potassium sodium salt according to claim 7.

9. A method for preparing BC dry powder fire extinguishing agent by washing fly ash with potassium and sodium salt as byproducts, characterized in that: The BC dry powder fire extinguishing agent is prepared by using the fly ash water washing by-product potassium and sodium salt obtained by the preparation method according to any one of claims 1 to 6; preferably, the method comprises: mixing the fly ash water washing by-product potassium and sodium salt with mineral dry powder to obtain a mixed dry powder, mixing modified silicone oil and additives with the mixed dry powder and then ball milling to obtain an ultrafine dry powder; filling the ultrafine dry powder into a fire extinguisher and filling it with argon gas.

10. The method according to claim 9, characterized in that The mass ratio of the fly ash washing byproduct potassium and sodium salt to the mineral dry powder is (5-7):(2-4); the mineral dry powder is silicon dioxide and aluminum oxide in a volume ratio of (1-2):(1-2); the mass ratio of the additive to the mixed dry powder is (0.025-0.03):1; the additive is talc, mica and activated clay in a mass ratio of 2.5:2.5:(1.25-2.5); the mass ratio of the modified silicone oil to the mixed dry powder is (1.2-1.5):36; the ball milling time is 30-50min; And / or, the argon gas is high-purity argon gas, and the filling argon gas pressure is 1.1-1.3 MPa.

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