A method and apparatus for preparing nano-calcium carbonate by co-processing calcium-based desulfurization ash and sodium-based desulfurization ash.

Abstract

This invention provides a method and apparatus for preparing nano-calcium carbonate through the combined treatment of calcium-based desulfurization ash and sodium-based desulfurization ash. The method includes: S1, mixing calcium-based desulfurization ash and water to form a calcium-based desulfurization ash slurry; introducing carbon dioxide into the calcium-based desulfurization ash slurry to carry out a carbonization reaction, obtaining a carbonized calcium-based desulfurization ash slurry; S2, mixing the carbonized calcium-based desulfurization ash slurry and sodium-based desulfurization ash, and carrying out a metathesis reaction in the presence of an oxidant, obtaining a reacted desulfurization ash slurry; the mass ratio of calcium-based desulfurization ash to sodium-based desulfurization ash is 1:0.73~1.72; S3, subjecting the reacted desulfurization ash slurry to precipitation separation treatment to obtain a precipitate and a clear liquid; dehydrating the precipitate to obtain nano-calcium carbonate; and crystallizing the clear liquid to obtain sodium sulfate. This invention aims to use a waste-to-waste method to jointly treat two types of desulfurization ash solid waste, and absorb and fix CO2 for carbonization to obtain nano-calcium carbonate and sodium sulfate products.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology, and more specifically, to a method and apparatus for preparing nano-calcium carbonate by co-processing calcium-based desulfurization ash and sodium-based desulfurization ash. Background Technology

[0002] Semi-dry and dry desulfurization processes are widely used in the steel industry and in flue gas desulfurization facilities with small flue gas volumes and low SO2 concentrations. Unlike the gypsum produced as a byproduct of wet desulfurization, which can be directly utilized, the ash from dry / semi-dry desulfurization processes has a complex composition and lacks an effective disposal method. When using dry / semi-dry desulfurization processes, the utilization rate of desulfurizing agents is much lower than that of wet desulfurization processes. To achieve ultra-low emissions, excessive amounts of desulfurizing agents must be used, leading to a decrease in the purity of byproducts and a significant increase in the quantity of byproducts. Therefore, there is an urgent need to explore relevant utilization methods.

[0003] Calcium-based semi-dry / dry desulfurization is commonly used in sintering and pelletizing processes. The byproduct is calcium-based desulfurization ash, composed of CaSO3, CaSO4, CaCO3, Ca(OH)2, and CaO. Due to the absorption of CO2 and oxidation, calcium-based desulfurization ash expands in volume, resulting in poor volume stability and making it unsuitable for use in building materials. Therefore, it is typically disposed of through landfill or stockpiling.

[0004] Sodium-based semi-dry / dry desulfurization is commonly used in processes such as sintering, coking, hot blast stoves, and heating furnaces. The byproduct is sodium-based desulfurization ash, composed of Na₂SO₃, Na₂SO₄, Na₂CO₃, and a small amount of NaHCO₃. Sodium-based desulfurizers are readily soluble in water, causing secondary pollution, and therefore cannot be landfilled. Except for a small amount used as a de-icing agent in winter, it cannot be disposed of.

[0005] Sodium-based dry desulfurization (SDS method) involves injecting NaHCO3 into the flue gas duct for dry desulfurization at temperatures above 140°C. The byproduct is a mixture containing Na2SO3, Na2SO4, and Na2CO3. The desulfurization ash from this method requires effective utilization and disposal methods.

[0006] Sodium-based spray drying absorption (SDA sodium method) utilizes a 20%–25% Na2CO3 solution for spray drying desulfurization. The byproducts are a mixture of dry powder Na2SO3, Na2SO4, and Na2CO3, which are difficult to recover and reuse.

[0007] CN113769564A discloses a semi-dry desulfurization ash solidification method for industrial flue gas carbon dioxide and its resource utilization. This method utilizes semi-dry desulfurization ash to form a slurry, absorbs SO2 from the flue gas, then adds ammonia water to absorb CO2, and finally filters to obtain calcium carbonate. The filtrate is then evaporated and crystallized to obtain ammonium sulfate. This method absorbs sulfur dioxide content not exceeding 2000 mg / m³. 3This results in an excessively low pH value in the slurry, requiring the addition of ammonia water before CO2 can be absorbed. This is no different from directly absorbing CO2 with ammonia water, leading to additional ammonia water consumption. Moreover, the ammonia water consumption is enormous (1.6~2.2L / kg), making it a low-value byproduct of high-cost production.

[0008] CN118833843A discloses a method and application for the resource utilization of dry and semi-dry desulfurization ash. This method requires the addition of ammonium chloride, lime slurry, carbon dioxide, and ammonia, followed by filtration and drying to obtain calcium sulfate and calcium carbonate. The cost of the added reagents is significantly higher than the product cost, making it economically unfeasible. For example, the added lime slurry and ammonia can already absorb CO2, so there is no need to add them to the desulfurization ash for further CO2 absorption; adding ammonium chloride does not yield calcium sulfate filter residue.

[0009] Therefore, there is an urgent need to develop a process for the combined treatment of these two types of desulfurization ash. Summary of the Invention

[0010] To address the problems in the prior art, the present invention aims to provide a method and apparatus for preparing nano-calcium carbonate through the combined treatment of calcium-based and sodium-based desulfurization ash. The invention aims to utilize a waste-to-waste approach, combining the two types of desulfurization ash solid waste for carbonation by absorbing and fixing CO2, thereby obtaining nano-calcium carbonate and sodium sulfate products.

[0011] To achieve the above objectives, according to a first aspect of the present invention, a method for preparing nano-calcium carbonate by co-processing calcium-based desulfurization ash and sodium-based desulfurization ash is provided, comprising:

[0012] S1, calcium-based desulfurization ash and water are mixed to prepare calcium-based desulfurization ash slurry, carbon dioxide is introduced into the calcium-based desulfurization ash slurry to carry out carbonization reaction, and carbonized calcium-based desulfurization ash slurry is obtained.

[0013] S2, the carbonized calcium-based desulfurization slurry and sodium-based desulfurization ash are mixed and subjected to a metathesis reaction in the presence of an oxidant to obtain the reacted desulfurization slurry; the mass ratio of the calcium-based desulfurization ash to the sodium-based desulfurization ash is 1:0.73~1.72;

[0014] S3, the desulfurization slurry after the reaction is subjected to precipitation separation treatment to obtain precipitate and clear liquid; the precipitate is dehydrated to obtain nano calcium carbonate; the clear liquid is crystallized to obtain sodium sulfate.

[0015] In S1, the residual CaO in the calcium-based desulfurization ash reacts with water to form calcium hydroxide. The reaction formula is as follows:

[0016] CaO + H₂O = Ca(OH)₂ (1)

[0017] The original Ca(OH)2 and newly generated Ca(OH)2 in the calcium-based desulfurization ash undergo a carbonization reaction with carbon dioxide:

[0018] Ca(OH)2+CO2→CaCO3↓+H2O (2)

[0019] In S2, CaSO3 and Na2SO3 are oxidized to CaSO4 and Na2SO4 under the action of oxidant. The CaSO3 in calcium-based desulfurization ash reacts with Na2CO3 in sodium-based desulfurization ash to generate soluble salt Na2SO3, which accelerates the oxidation process. The CaSO4 in calcium-based desulfurization ash and the newly generated CaSO4 react with Na2CO3 in sodium-based desulfurization ash to generate CaCO3.

[0020] When the oxidant is oxygen, the following reaction occurs:

[0021] CaSO3+Na2CO3=CaCO3↓+Na2SO3 (3)

[0022] 2CaSO3 + O2 = 2CaSO4 (4)

[0023] 2Na₂SO₃ + O₂ = 2Na₂SO₄ (5)

[0024] CaSO4+Na2CO3=CaCO3↓+Na2SO4 (6)

[0025] It is particularly important to note that the processing method of this invention controls a specific feeding sequence. The carbonized calcium-based desulfurization slurry must be introduced into the metathesis reactor; otherwise, the Ca(OH)₂ and CaO in the calcium-based desulfurization ash will react with the Na₂CO₃ in the sodium-based desulfurization ash to produce CaCO₃ and NaOH. Calcium hydroxide and sodium carbonate will also react, with the reaction equation: Ca(OH)₂ + Na₂CO₃ → CaCO₃↓ + 2NaOH. Due to the large amount of Ca(OH)₂ and CaO, a large amount of alkaline substances will be generated, requiring further treatment. If acid neutralization is used, reagents will be consumed; adding sulfuric acid will produce more low-value sodium sulfate; adding other acids will introduce impurity ions; if CO₂ is bubbled in for neutralization, the generated Na₂CO₃ will require further treatment with the calcium-based desulfurization ash.

[0026] Furthermore, pH affects the dissolution of CaSO3: acidic environments promote the dissolution of calcium sulfite, while alkaline environments inhibit it. The pre-carbonation method of this invention can lower the pH of the slurry; otherwise, direct mixing would significantly increase the pH. This invention, through carbonation, lowers the pH and increases the slurry temperature, thereby improving the solubility and reaction rate of CaSO3, accelerating oxidation, and reducing the reaction time from 4 hours to 0.5-1 hour. Simultaneously, pre-carbonation also reduces the CaO concentration in the solution. 2+ The concentration is beneficial to the dissolution of CaSO3 and subsequent oxidation.

[0027] In some preferred embodiments of the present invention, in step S3, the dehydration process is performed by a belt dehydrator or other filter dehydrator.

[0028] In some preferred embodiments of the present invention, in step S3, the crystallization process is carried out in a concentrated crystallizer.

[0029] In some preferred embodiments of the present invention, in step S3, the crystallization process includes: evaporation and concentration, crystallization, and centrifugation. The specific equipment and processes for evaporation and concentration, crystallization, and centrifugation can employ equipment and processes commonly used in the art. The temperature and time of evaporation and concentration can be selected as needed, and the crystallization temperature can be controlled based on the crystallization temperature of Glauber's salt.

[0030] In some preferred embodiments of the present invention, in step S3, the obtained mother liquor is collected and reused.

[0031] In some preferred embodiments of the present invention, the temperature of the metathesis reaction is 55-75°C. Preferably, the temperature of the metathesis reaction is 65-75°C. Increasing the temperature will increase the solubility of calcium sulfite.

[0032] Preferably, steam condensate at 80-90°C is used as the heat source for the metathesis reaction. In existing technologies, the ash hoppers and fluidizing air ducts of desulfurization systems, as well as numerous dust collector ash hoppers, typically require steam heating, generating large amounts of steam condensate at 80-90°C, which is usually not reused and is directly discharged. This invention reuses this condensate as a heat source, further saving energy and solving the problem of steam condensate recovery and utilization.

[0033] In some preferred embodiments of the present invention, the metathesis reaction is carried out under conditions of pH 6-8. Due to the presence of CaO and Ca(OH)2 in calcium-based desulfurization ash, the pH of the calcium-based desulfurization ash slurry is strongly alkaline, and the pH can be as high as 12. The present invention can reduce the pH of the slurry to 6-8 by carrying out a carbonization reaction, and then proceed to the next metathesis process.

[0034] In some preferred embodiments of the present invention, the oxidant includes one or a combination of two or more of air, oxygen, ozone, and hydrogen peroxide. The aforementioned oxidants do not introduce impurity ions, thus improving the purity of the product.

[0035] In some preferred embodiments of the present invention, the oxidant includes air, and the ratio of air to calcium-based desulfurization ash is 1.45~3.42 L / g, which matches the sulfite content ratio in the desulfurization ash. Controlling the oxidant within the above-mentioned preferred range ensures sufficient oxidation of sulfite while reducing consumption; if it exceeds this range, too low a concentration results in insufficient oxidation, while too high a concentration increases power consumption and oxidant consumption.

[0036] In some preferred embodiments of the present invention, the mass ratio of the calcium-based desulfurization ash to the carbon dioxide is 1:0.15~0.32.

[0037] In some preferred embodiments of the present invention, the mass concentration of calcium-based desulfurization ash in the calcium-based desulfurization slurry is 15-25%.

[0038] In some preferred embodiments of the present invention, the sources of the carbon dioxide include one or more of the following: carbon dioxide captured by a carbon capture system, lime kiln flue gas, and purified waste gas.

[0039] Currently, CO2 captured by carbon capture systems (CCS) often lacks economically effective utilization pathways, and CCUS (carbon capture, utilization, and storage) lacks a utilization stage, requiring effective carbon sequestration measures. Therefore, the CO2 source of this invention can be CO2 captured by CCS. Considering the high operating costs of CCS, the CO2 source can also be lime kiln flue gas or other waste gas with a high CO2 concentration after flue gas purification.

[0040] In some preferred embodiments of the present invention, the components of the calcium-based desulfurization ash include, in molar percentage: 16%~44% CaSO3, 4%~11% CaSO4, 9%~16% CaCO3, 36%~64% Ca(OH)2, and 0%~5% CaO.

[0041] In some preferred embodiments of the present invention, the sodium-based desulfurization ash comprises, by molar percentage: 33%~62% Na2SO3, 8%~15% Na2SO4, 23%~58% Na2CO3, and 0%~5% NaHCO3.

[0042] According to another aspect of the present invention, an apparatus for carrying out the above-described processing method is provided, the apparatus comprising:

[0043] The calcium-based desulfurization slurry feeding system, carbonization reaction system, metathesis reaction system, and precipitation separation system are connected in sequence by pipelines.

[0044] The calcium-based desulfurization slurry feeding system includes a calcium-based desulfurization ash silo and a dissolving tank connected in sequence.

[0045] The carbonization reaction system includes a carbon dioxide gas source and a carbonization reactor; the outlet of the carbon dioxide gas source is connected to the inlet of the carbonization reactor.

[0046] The metathesis reaction system includes an oxidant tank, a sodium-based desulfurization ash silo, and a metathesis reactor; the outlets of the oxidant tank and the sodium-based desulfurization ash silo are respectively connected to the inlet of the metathesis reactor.

[0047] The sedimentation separation system includes a mechanical clarifier, a dewatering machine, and a concentration crystallizer connected in sequence.

[0048] In some preferred embodiments of the present invention, the bottom of the carbonization reactor is a slurry tank, and the slurry tank is equipped with a carbon dioxide gas distributor for introducing carbon dioxide.

[0049] The carbonization reactor also includes a slurry circulation system, which comprises circulation pipelines and spray equipment. One end of the circulation pipeline is connected to the outlet of the slurry tank, and the other end is connected to the inlet at the top of the carbonization reactor. The spray coverage of the spray equipment is ≥300%. The carbonization reactor is used for carbonization reaction. The slurry circulation system connects the slurry tank at the bottom of the carbonization reactor to the top space of the carbonization reactor through a slurry circulation pump, circulation pipelines, and spray equipment to achieve slurry circulation.

[0050] The aforementioned carbon dioxide gas distributor ensures that CO2 gas is evenly distributed, dissolved, and absorbed by the calcium-based desulfurization ash. Some of the incompletely absorbed CO2 escapes from the liquid surface and continues to be absorbed by the slurry sprayed from the top of the reactor in the gas phase space. The slurry in the liquid phase space is lifted by a circulation pump and then evenly sprayed into the carbonization reactor through circulation pipelines and end sprayers.

[0051] In some preferred embodiments of the present invention, the dissolving tank is used to dissolve calcium-based desulfurization ash to obtain calcium-based desulfurization ash slurry. Preferably, the dissolving tank is also equipped with a first stirrer and an industrial fresh water replenishment system. The top of the dissolving tank is provided with a calcium-based desulfurization ash inlet, and the bottom is provided with a calcium-based desulfurization ash slurry outlet.

[0052] In some preferred embodiments of the present invention, the metathesis reactor is used to carry out a metathesis reaction of carbonized calcium-based desulfurization slurry and sodium-based desulfurization ash. Preferably, the metathesis reactor is further provided with a second stirrer. The top of the metathesis reactor is provided with a feed port for carbonized calcium-based desulfurization slurry and a feed port for sodium-based desulfurization ash. The bottom of the metathesis reactor is provided with an oxidant feed port and a discharge port for desulfurization slurry after reaction.

[0053] In the treatment method of this invention, the two types of desulfurization ash act as treatment agents for each other. Therefore, the treatment method provided by this invention does not require the addition of commonly used agents in other treatment processes, such as (NH4)2CO3, NH4HCO3, NH4Cl, NH3, NH3·H2O, CaO, Na2CO3, H2SO4, HCl, and acetic acid, and thus does not introduce new impurity ions. This invention uses a small amount of agents and has high economic value.

[0054] This invention achieves the synergistic resource utilization of two types of desulfurization ash, solving the problems of calcium-based desulfurization ash not being effectively utilized and being stockpiled and landfilled for a long time, and sodium-based desulfurizing agents not being effectively treated and causing secondary pollution.

[0055] Furthermore, the carbonization reaction using carbon dioxide in this invention is a carbon reduction pathway.

[0056] This invention transforms all components in the complex desulfurization ash mixture into products; it oxidizes and stabilizes unstable CaSO3 and Na2SO3; and it converts poorly volume-stable CaO, Ca(OH)2, and CaSO3 into stable products. This invention achieves the conversion of both CaSO4 and CaSO3 into calcium carbonate, and Na2SO3 into Na2SO4. Traditional desulfurization ash treatment can only process a single component, resulting in a product that remains a mixture and unusable. Attached Figure Description

[0057] Figure 1 A schematic diagram of the combined treatment apparatus for calcium-based desulfurization ash and sodium-based desulfurization ash of the present invention is shown.

[0058] The reference numerals in the attached figures are as follows:

[0059] 1-Calcium-based desulfurization ash silo, 2-Dissolving tank, 3-Carbon dioxide gas source, 4-Carbonization reactor, 5-Oxidant tank, 6-Sodium-based desulfurization ash silo, 7-Metathesis reactor, 8-Mechanical clarification tank, 9-Dewatering machine, 10-Concentrating crystallizer, 11-First feeder, 12-First belt scale, 21-First agitator, 22-First slurry pump; 41-Slurry circulation system, 42-Second slurry pump, 61-Second feeder, 62-Second belt scale, 71-Second agitator, 72-Third slurry pump, 81-Slurry slag pump. Detailed Implementation

[0060] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0061] like Figure 1 As shown, a specific embodiment of the combined treatment device for calcium-based desulfurization ash and sodium-based desulfurization ash provided by the present invention may include:

[0062] The system consists of a calcium-based desulfurization slurry feeding system, a carbonization reaction system, a metathesis reaction system, and a sedimentation separation system, all connected sequentially by pipelines. The calcium-based desulfurization slurry feeding system includes a calcium-based desulfurization ash silo 1 and a dissolving tank 2. The carbonization reaction system includes a carbon dioxide gas source 3 and a carbonization reactor 4. The metathesis reaction system includes an oxidant tank 5, a sodium-based desulfurization ash silo 6, and a metathesis reactor 7. The sedimentation separation system includes a mechanical clarifier 8, a dewatering machine 9, and a concentrator / crystallizer 10.

[0063] The calcium-based desulfurization ash silo 1 is used to store and supply calcium-based desulfurization ash. The outlet of the calcium-based desulfurization ash silo 1 is equipped with a first feeder 11 and a first belt scale 12. The first feeder 11 is used to control the discharge volume of the calcium-based desulfurization ash silo 1 and to convey the calcium-based desulfurization ash to the first belt scale 12. The first belt scale 12 is used to weigh the calcium-based desulfurization ash and convey it into the top inlet of the dissolving tank 2. The dissolving tank 2 is equipped with a first agitator 21 for agitating the materials therein, and is also equipped with a water replenishment system for inputting the water required to dissolve the calcium-based desulfurization ash.

[0064] The bottom outlet of the dissolving tank 2 is connected to the middle inlet of the carbonization reactor 4, and a first slurry pump 22 is installed on the connecting pipe between the two.

[0065] Carbon dioxide gas source 3 is used to supply carbon dioxide gas into carbonization reactor 4, and its outlet is connected to the bottom inlet of carbonization reactor 4 and connected to CO2 gas distribution device.

[0066] Carbonization reactor 4 is used for carbonization reaction; carbonization reactor 4 is equipped with slurry circulation system 41, which connects the slurry pool at the bottom of carbonization reactor 4 to the top space of carbonization reactor 4 through slurry circulation pump, circulation pipeline and spray equipment to realize slurry circulation; the outlet of carbonization reactor 4 is connected to the upper inlet of metathesis reactor 7 to input carbonized calcium-based desulfurization slurry into metathesis reactor 7, and a second slurry pump 42 is provided on the connecting pipeline between the two.

[0067] Oxidant tank 5 is used to store and supply oxidant, and its outlet is connected to the bottom inlet of metathesis reactor 7;

[0068] The sodium-based desulfurization ash silo 6 is used to store and provide sodium-based desulfurization ash. The outlet of the sodium-based desulfurization ash silo 6 is equipped with a second feeder 61 and a second belt scale 62. The second feeder 61 is used to control the discharge amount of the sodium-based desulfurization ash silo 6 and to convey sodium-based desulfurization ash to the second belt scale 62. The second belt scale 62 is used to weigh the sodium-based desulfurization ash and convey it into the top inlet of the metathesis reactor 7.

[0069] The metathesis reactor 7 is used to carry out the metathesis reaction of carbonized calcium-based desulfurization slurry and sodium-based desulfurization ash, and is equipped with a steam condensate inlet at the top. The metathesis reactor 7 is equipped with a second agitator 71 for stirring the materials therein. The bottom outlet of the metathesis reactor 7 is connected to the inlet of the mechanical clarifier 8, and a third slurry pump 72 is installed on the connecting pipe between the two.

[0070] Mechanical clarifier 8 is used to precipitate and separate metathesis products; the bottom outlet of mechanical clarifier 8 is connected to the inlet of dewatering machine 9 for inputting the separated precipitate, and the connecting pipeline between the two is equipped with slurry pump 81; the upper outlet of mechanical clarifier 8 is connected to the inlet of thickener crystallizer 10 for inputting the separated clear liquid.

[0071] Dehydrator 9 is used to dehydrate the precipitate to obtain nano-calcium carbonate;

[0072] The concentrated crystallizer 10 is used to concentrate and crystallize the clear liquid to obtain sodium sulfate.

[0073] Comparative Example 1:

[0074] Company A currently has one set of flue gas desulfurization system for a 180-square-meter sintering machine. It employs a semi-dry desulfurization-CFB flue gas desulfurization process, using CaO as the desulfurizing agent, which is digested into Ca(OH)2 before use. This system aims to meet the local ultra-low emission standard of 5 mg / Nm³. 3 The actual Ca / S ratio is as high as 1.8~2.5, which means that 0.8~1.5 times the stoichiometric ratio of desulfurizing agent in the desulfurization byproduct—desulfurization ash—remains unreacted. Some of the unreacted desulfurizing agent absorbs CO2 from the flue gas and turns into CaCO3, while most remains as Ca(OH)2. Due to incomplete dry digestion, some CaO is still present in the desulfurizing agent. The desulfurizing agent that undergoes the desulfurization reaction produces a mixed product mainly composed of CaSO3 and some CaSO4.

[0075] To achieve an A-level performance rating, the company has constructed one hot blast stove desulfurization system, one self-owned power plant desulfurization system, and one batch of desulfurization systems for the heat treatment furnace of the steel rolling heating furnace. All of these systems use dry desulfurization-SDS desulfurization with NaHCO3 as the desulfurizing agent. Due to the dry desulfurization process, the utilization rate of the desulfurizing agent is low and is greatly affected by temperature. The Na2 / S ratio is as high as 1.6-2.4, which means that 0.6 to 1.4 times the stoichiometric ratio of the desulfurizing agent is not utilized and decomposes into Na2CO3 at high temperatures, mixing into the desulfurization byproducts Na2SO3 and Na2SO4.

[0076] Example 1:

[0077] For calcium-based and sodium-based desulfurization ash from Company A, a method for preparing nano-calcium carbonate by co-processing calcium-based and sodium-based desulfurization ash according to the present invention is adopted. The calcium-based desulfurization ash from sintering desulfurization is co-processed with sodium-based desulfurization ash from other desulfurization processes such as hot blast stoves, power plants, and heating furnaces to produce nano-calcium carbonate. The molar composition of the calcium-based desulfurization ash is: 41% CaSO3, 11% CaSO4, 9% CaCO3, 36% Ca(OH)2, and 3% CaO; the molar composition of the sodium-based desulfurization ash is: 38% Na2SO3, 13% Na2SO4, 44% Na2CO3, and 5% NaHCO3.

[0078] The device structure used is as follows: Figure 1 The specific processing procedure is as follows:

[0079] Using suction and discharge tank trucks, calcium-based desulfurization ash and sodium-based desulfurization ash are respectively pumped into the corresponding ash bins of this system. Calcium-based desulfurization ash is stored in calcium-based desulfurization ash bin 1. It is fed quantitatively by the first feeder 11 and the first belt scale 12 under the bin. 1 part by mass of calcium-based desulfurization ash is added to the dissolving tank 2, and 4 parts by mass of industrial fresh water is added. The mixture is stirred and dissolved. The stirrer runs continuously to prevent solid particles from settling. The residual CaO is digested.

[0080] The dissolved desulfurization ash is then pumped to the carbonization reactor 4 via the first slurry pump 22. Using CO2 captured by CCS as a gas source, CO2 is supplied to the carbonization reactor to carbonize the Ca(OH)2 in the desulfurization ash, generating CaCO3. The slurry circulation system 41 is then activated, continuously circulating and spraying the slurry at a coverage rate of 300% and a spray density of 57 L / Nm³. 3 By controlling the mass ratio of calcium-based desulfurization ash to added carbon dioxide to >1:0.17, residual CO2 is fully absorbed, and the pH value of the solution is reduced to 8.

[0081] The carbonized desulfurization ash slurry is then pumped to the metathesis reactor 7 by the second slurry pump 42. A sodium-based desulfurization ash silo 6 is located above this reactor. 1.25 parts by weight of sodium-based desulfurization ash are added to the metathesis reactor 7 via a second feeder 61 and a second belt scale 62 below the silo, and stirred to ensure uniform mixing. The stirrer runs continuously to prevent solid particle deposition. Air is used as the oxidant, with an oxidizing air addition rate of 2.5 L / g, which is introduced into the reactor to enhance stirring. CaSO3 and Na2SO3 in the slurry are continuously oxidized to CaSO4 and Na2SO4. The CaSO4 in the calcium-based desulfurization ash and the newly generated CaSO4 undergo a metathesis reaction with the Na2CO3 in the sodium-based desulfurization ash to produce CaCO3. To accelerate the reaction, the slurry is heated to 75°C. The heating method is either using the high-temperature condensate discharged from the desulfurization system or direct heating in the reactor. The desulfurization ash has an average residence time of 1 hour in the metathesis reactor. The sum of CaSO3 and Ca(OH)2 content in the slurry is controlled to be below 1.5% before proceeding to the next process.

[0082] Two types of desulfurization ash undergo carbonization and metathesis reactions to generate a slurry rich in insoluble CaCO3. This slurry is then pumped into a mechanical clarifier 8, where CaCO3 undergoes gravity and crowding sedimentation. The sediment at the bottom of the clarifier is then transported to a belt dewatering machine 9 for dewatering. After dewatering and drying, nano-CaCO3 product is obtained. The filtrate from the dewatering machine 9, along with the supernatant from the mechanical clarifier, enters a concentrator crystallizer 10. The concentrator crystallizer 10 employs a triple-effect evaporation system, and through evaporation, concentration, crystallization, and centrifugal separation, Glauber's salt product is obtained. The remaining mother liquor and condensate are recycled back into a dissolving tank for reuse.

[0083] Comparative Example 2:

[0084] Company B uses calcium-based ultrafine powder dry desulfurization for its blast furnace hot blast stove flue gas, employing Ca(OH)2 ultrafine powder as the desulfurizing agent, in order to meet the local ultra-low emission standard of 5 mg / Nm³. 3 Compared to wet and semi-dry desulfurization, dry desulfurization does not involve water, and the actual Ca / S ratio is as high as 3.5~5. As a result, 2.5~4 times the stoichiometric ratio of desulfurizing agent in the desulfurization by-product - desulfurization ash - has not undergone desulfurization reaction. Some of the desulfurizing agent that has not undergone desulfurization absorbs CO2 in the flue gas and turns into CaCO3, while most of it still exists as Ca(OH)2. The desulfurizing agent that has undergone desulfurization reaction generates a mixed product mainly composed of CaSO3 and some CaSO4.

[0085] The company uses sodium-based semi-dry desulfurization-SDA process for its coke oven flue gas, with Na2CO3 as the desulfurizing agent and a Na2 / S ratio of 1.3-1.6. This means that 0.3 to 0.6 times the stoichiometric ratio of the desulfurizing agent is not utilized and is still mixed in the desulfurization byproducts Na2SO3 and Na2SO4 in the form of Na2CO3.

[0086] Example 2:

[0087] For the calcium-based and sodium-based desulfurization ash in Company B, the present invention employs a method for preparing nano-calcium carbonate through joint treatment of calcium-based and sodium-based desulfurization ash. This method involves jointly treating calcium-based desulfurization ash from hot blast stove flue gas desulfurization with sodium-based desulfurization ash from coke oven flue gas desulfurization to produce nano-calcium carbonate. The molar composition of the calcium-based desulfurization ash is: 16% CaSO3, 4% CaSO4, 16% CaCO3, 64% Ca(OH)2, and 0% CaO; the molar composition of the sodium-based desulfurization ash is: 50% Na2SO3, 12.5% ​​Na2SO4, and 37.5% Na2CO3.

[0088] The device structure used is as follows: Figure 1 The specific processing procedure is as follows:

[0089] Using suction and discharge tank trucks, calcium-based desulfurization ash and sodium-based desulfurization ash are respectively pumped into the corresponding ash silos of this system. Calcium-based desulfurization ash is stored in calcium-based desulfurization ash silo 1. It is quantitatively fed by the first feeder 11 and the first belt scale 12 under the silo. One part by mass of calcium-based desulfurization ash is added to the dissolving tank 2, along with four parts by mass of industrial fresh water, for stirring and slurry preparation. The agitator runs continuously to prevent solid particle deposition. Then, the slurry-prepared desulfurization ash is pumped to the carbonization reactor 4 by the first slurry pump 22. Using lime kiln flue gas as a CO2 source and heat source, CO2 is supplied to the carbonization reactor to carbonize the Ca(OH)2 in the desulfurization ash, generating CaCO3. The slurry circulation system 41 is activated, and the slurry is continuously circulated and sprayed, with a spray coverage of 300% and a spray density of 32 L / Nm³. 3 By controlling the mass ratio of calcium-based desulfurization ash to added carbon dioxide to >1:0.32, CO2 in the flue gas is fully absorbed, the pH value of the solution is reduced to 6.5, and the decarbonized flue gas is discharged.

[0090] The carbonized desulfurization ash slurry is then pumped to the metathesis reactor 7 by the second slurry pump 42. A sodium-based desulfurization ash silo 6 is located above the reactor. 0.73 parts of sodium-based desulfurization ash are added to the metathesis reactor 7 via a second feeder 61 and a second belt scale 62 below the silo, and stirred to mix thoroughly. The stirrer runs continuously to prevent solid particle deposition. Air is used as the oxidant, with an oxidizing air addition rate of 1.45 L / g, and is introduced into the reactor. The slurry is heated to 60°C, where CaSO3 and Na2SO3 are continuously oxidized to CaSO4 and Na2SO4. The CaSO4 in the calcium-based desulfurization ash and the newly generated CaSO4 undergo a metathesis reaction with the Na2CO3 in the sodium-based desulfurization ash to produce CaCO3.

[0091] Two types of desulfurization ash undergo carbonization and metathesis reactions to produce a slurry rich in insoluble CaCO3. This slurry is then pumped to a mechanical clarifier 8, where CaCO3 undergoes gravity and crowding sedimentation. The sediment at the bottom of the clarifier is then transported to a centrifugal dewatering machine 9 for dewatering. After dewatering and drying, nano-CaCO3 product is obtained. The filtrate from the dewatering machine 9, along with the supernatant from the mechanical clarifier, enters a concentrator crystallizer 10. The concentrator crystallizer 10 employs a triple-effect evaporation system. Through evaporation, concentration, crystallization, and centrifugal separation, Glauber's salt product is obtained. The remaining mother liquor and condensate are recycled back to a dissolving tank for reuse.

[0092] Comparative Example 3:

[0093] This comparative example provides a method for the combined treatment of calcium-based desulfurization ash from sintering desulfurization with sodium-based desulfurization ash from other desulfurization processes such as hot blast stoves, power plants, and heating furnaces, without carbonization, through a metathesis reaction. The specific method is as follows:

[0094] The calcium-based desulfurization ash is mixed with water to form a slurry, which is then pumped into a metathesis reactor. Some high-temperature condensate is added and heated to 75°C. The mixture is stirred and mixed with the sodium-based desulfurization ash to carry out the metathesis reaction, and oxidizing air is introduced.

[0095] In the slurry, CaSO3 and Na2SO3 are continuously oxidized to CaSO4 and Na2SO4. The CaSO4 in the calcium-based desulfurization ash and the newly generated CaSO4 react with the Na2CO3 in the sodium-based desulfurization ash in a metathesis reaction to produce CaCO3. Ca(OH)2 and CaO in the calcium-based desulfurization ash react with the Na2CO3 in the sodium-based desulfurization ash to produce CaCO3 and NaOH, as shown in the equation: Ca(OH)2 + Na2CO3 → CaCO3↓ + 2NaOH. The sum of CaSO3 and Ca(OH)2 in the slurry is controlled to be below 1.5%, and the desulfurization ash is kept in the metathesis reactor for an average of ~2.8 hours before entering the subsequent purification reactor.

[0096] Because the desulfurization ash contains high levels of Ca(OH)2 and CaO, a large amount of alkaline substances will be produced after the metathesis reaction, requiring further treatment. Neutralization with acid requires reagents; adding sulfuric acid will produce more low-value sodium sulfate; and adding other acids will introduce impurity ions. Therefore, CO2 is bubbled in for neutralization, generating Na2CO3. Industrial-grade CaSO4 is then added to the purification reactor to further react with the neutralized Na2CO3 in a metathesis reaction, converting Na2CO3 into CaCO3. Ultimately, calcium-based desulfurization ash is converted into nano-CaCO3, and sodium-based desulfurization ash is converted into sodium sulfate.

[0097] Comparative Example 4:

[0098] This comparative example provides a method for the combined treatment of calcium-based desulfurization ash from sintering desulfurization with sodium-based desulfurization ash from other desulfurization processes such as hot blast stoves, power plants, and heating furnaces, without carbonization, and directly undergoing a metathesis reaction. Specifically, the method includes:

[0099] The calcium-based desulfurization ash is mixed with water to form a slurry, which is then pumped into a metathesis reactor. Some room-temperature water is added, and the mixture is stirred and mixed with the sodium-based desulfurization ash to carry out the metathesis reaction. Oxidizing air is then introduced.

[0100] The sum of CaSO3 and Ca(OH)2 content in the slurry is controlled to be below 1.5%, and the desulfurization ash is kept in the metathesis reactor for an average of ~4 hours before entering the subsequent purification reactor.

[0101] Because the desulfurization ash contains high levels of Ca(OH)2 and CaO, a large amount of alkaline substances will be generated after the metathesis reaction. CO2 is bubbled in to neutralize the alkaline substances, producing Na2CO3. Industrial-grade CaSO4 is then added to the purification reactor to further react with the neutralized Na2CO3, thus converting Na2CO3 into CaCO3. Ultimately, calcium-based desulfurization ash is converted into nano-CaCO3 products, and sodium-based desulfurization ash is converted into Glauber's salt products.

[0102] Comparative Example 5:

[0103] This comparative example demonstrates the combined treatment of calcium-based desulfurization ash from hot blast stove flue gas desulfurization and sodium-based desulfurization ash from coke oven flue gas desulfurization, specifically including:

[0104] The calcium-based desulfurization ash is mixed with water to form a slurry, which is then pumped into a metathesis reactor. Some high-temperature condensate is added and heated to 60°C. The mixture is stirred and mixed with the sodium-based desulfurization ash to carry out the metathesis reaction, and oxidizing air is introduced.

[0105] In the slurry, CaSO3 and Na2SO3 are continuously oxidized to CaSO4 and Na2SO4. CaSO4 in the calcium-based desulfurization ash and the newly generated CaSO4 react with Na2CO3 in the sodium-based desulfurization ash in a metathesis reaction to produce CaCO3. Ca(OH)2 and CaO in the calcium-based desulfurization ash react with Na2CO3 in the sodium-based desulfurization ash to produce CaCO3 and NaOH. The sum of CaSO3 and Ca(OH)2 content in the slurry is controlled to be below 1.5% before entering the subsequent purification reactor.

[0106] Because the desulfurization ash contains high levels of Ca(OH)2 and CaO, a large amount of alkaline substances will be produced after the metathesis reaction, requiring further treatment. Hydrochloric acid is added for neutralization, producing NaCl. Industrial-grade CaSO4 is then added to the purification reactor to further react with the neutralized Na2CO3 in a metathesis reaction, thereby converting Na2CO3 into CaCO3, ultimately realizing the conversion of calcium-based desulfurization ash into nano-CaCO3 products. The NaCl:Na2SO4 molar ratio in the solution after CaCO3 extraction is between 1:0.8 and 1:2.2, and the resulting mixed salt solution has no utilization value and is directly discarded.

[0107] The price of ordinary calcium carbonate is 500 yuan / ton, calcium sulfate dihydrate is 400 yuan / ton, desulfurized gypsum is 20 yuan / ton, sodium sulfate is 600 yuan / ton, and nano calcium carbonate is as high as 2000 yuan / ton. Meanwhile, the cost of outsourcing the treatment of sodium-based desulfurization ash is as high as 500 yuan / ton. Therefore, the process of this invention has great economic value.

Claims

1. A method for preparing nano-calcium carbonate by co-processing calcium-based desulfurization ash and sodium-based desulfurization ash, wherein, include: S1, calcium-based desulfurization ash and water are mixed to prepare calcium-based desulfurization ash slurry, carbon dioxide is introduced into the calcium-based desulfurization ash slurry to carry out carbonization reaction, and carbonized calcium-based desulfurization ash slurry is obtained. S2, the carbonized calcium-based desulfurization slurry and sodium-based desulfurization ash are mixed and subjected to a metathesis reaction in the presence of an oxidant to obtain the reacted desulfurization slurry; the mass ratio of the calcium-based desulfurization ash to the sodium-based desulfurization ash is 1:0.73~1.72; S3, the desulfurization slurry after the reaction is subjected to precipitation separation treatment to obtain precipitate and clear liquid; the precipitate is dehydrated to obtain nano calcium carbonate; the clear liquid is crystallized to obtain sodium sulfate.

2. The method for preparing nano-calcium carbonate by combined treatment of calcium-based desulfurization ash and sodium-based desulfurization ash according to claim 1, wherein, The temperature of the metathesis reaction is 55~75℃, and the pH is 6~8.

3. The method for preparing nano-calcium carbonate by combined treatment of calcium-based desulfurization ash and sodium-based desulfurization ash according to claim 1, wherein, The oxidant includes one or more of air, oxygen, ozone, and hydrogen peroxide; and / or, The oxidant includes air, and the ratio of air to calcium-based desulfurization ash is 1.45 L / g to 3.42 L / g.

4. The method for preparing nano-calcium carbonate by combined treatment of calcium-based desulfurization ash and sodium-based desulfurization ash according to claim 1, wherein, The mass ratio of the calcium-based desulfurization ash to the carbon dioxide is 1:0.15~0.

32.

5. The method for preparing nano-calcium carbonate by combined treatment of calcium-based desulfurization ash and sodium-based desulfurization ash according to claim 1, wherein, In the calcium-based desulfurization slurry, the mass concentration of the calcium-based desulfurization ash is 15-25%.

6. The method for preparing nano-calcium carbonate by combined treatment of calcium-based desulfurization ash and sodium-based desulfurization ash according to claim 1, wherein, The sources of the carbon dioxide include one or more of the following: carbon dioxide captured by the carbon capture system, lime kiln flue gas, and purified waste gas.

7. The method for preparing nano-calcium carbonate by combined treatment of calcium-based desulfurization ash and sodium-based desulfurization ash according to claim 1, wherein, The components of the calcium-based desulfurization ash, by molar percentage, include: 16%~44% CaSO3, 4%~11% CaSO4, 9%~16% CaCO3, 36%~64% Ca(OH)2, and 0%~5% CaO.

8. The method for preparing nano-calcium carbonate by combined treatment of calcium-based desulfurization ash and sodium-based desulfurization ash according to claim 1, wherein, The sodium-based desulfurization ash comprises, by molar percentage: 33%~62% Na2SO3, 8%~15% Na2SO4, 23%~58% Na2CO3, and 0%~5% NaHCO3.

9. A combined treatment apparatus for calcium-based desulfurization ash and sodium-based desulfurization ash, the apparatus being used to implement the method for preparing nano-calcium carbonate by combined treatment of calcium-based desulfurization ash and sodium-based desulfurization ash as described in any one of claims 1 to 8; the apparatus comprising: The calcium-based desulfurization slurry feeding system, carbonization reaction system, metathesis reaction system, and precipitation separation system are connected in sequence by pipelines. The calcium-based desulfurization slurry feeding system includes a calcium-based desulfurization ash silo (1) and a dissolving tank (2) connected in sequence. The carbonization reaction system includes a carbon dioxide gas source (3) and a carbonization reactor (4); the outlet of the carbon dioxide gas source (3) is connected to the inlet of the carbonization reactor (4). The metathesis reaction system includes an oxidant tank (5), a sodium-based desulfurization ash silo (6), and a metathesis reactor (7); the outlets of the oxidant tank (5) and the sodium-based desulfurization ash silo (6) are respectively connected to the inlet of the metathesis reactor (7); The sedimentation separation system includes a mechanical clarifier (8), a dewatering machine (9), and a concentration crystallizer (10) connected in sequence. The outlet of the dissolving tank (2) is connected to the inlet of the carbonization reactor (4), the outlet of the carbonization reactor (4) is connected to the inlet of the metathesis reactor (7), and the outlet of the metathesis reactor (7) is connected to the inlet of the mechanical clarification tank (8).

10. The combined treatment apparatus for calcium-based desulfurization ash and sodium-based desulfurization ash according to claim 9, wherein, The bottom of the carbonization reactor (4) is a slurry tank, which is equipped with a carbon dioxide gas distributor for introducing carbon dioxide. The carbonization reactor (4) also has a slurry circulation system (41), which has a circulation pipeline and a spraying device; one end of the circulation pipeline is connected to the outlet of the slurry tank and the other end is connected to the inlet at the top of the carbonization reactor (4); the spraying device is connected to the inlet at the top of the carbonization reactor (4); the spraying coverage of the spraying device is ≥300%.

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