Method for preparing anhydrous calcium chloride by chlorination roasting of calcium carbonate concentrates

Abstract

The application discloses a method for preparing anhydrous calcium chloride by chlorination roasting of calcium carbonate briquetting. The method comprises the following steps: mixing calcium carbonate with auxiliary materials to obtain a briquetting, drying the briquetting, and then placing the briquetting in a vertical reactor to mix and roast with ammonium chloride pyrolysis gas, so as to obtain the anhydrous calcium chloride; or mixing calcium carbonate, ammonium chloride and auxiliary materials to obtain a briquetting, drying the briquetting, and then placing the briquetting in a vertical reactor to roast, so as to obtain the anhydrous calcium chloride. The auxiliary materials comprise water and a binder. In the method, ammonium chloride is used as a chlorinating agent for chlorination roasting of calcium carbonate, the calcium carbonate is mixed with auxiliary materials to form a briquetting, and then the briquetting is roasted in a vertical reactor, so that the calcium carbonate can absorb HCl generated by decomposition of the ammonium chloride in stages, the ammonium chloride is fully utilized, and the problem of pipeline blockage caused by excessive ammonium chloride is avoided.

Description

Technical Field

[0001] This invention relates to a method for preparing anhydrous calcium chloride, specifically a method for preparing anhydrous calcium chloride by chlorination roasting of calcium carbonate ore, belonging to the field of chemical metallurgical technology. Background Technology

[0002] Ammonium chloride is a commonly used calcination additive in the production of anhydrous calcium chloride from calcium carbonate. Ammonium chloride is a chemical product; over 90% of my country's ammonium chloride comes from the soda ash production process using the combined alkali process, and it is a byproduct of the decomposition of sodium chloride and ammonium carbonate to precipitate sodium bicarbonate. It is mainly used in fertilizers, batteries, hydrometallurgy, food, and pharmaceuticals. The main market for ammonium chloride is concentrated in agriculture, with over 95% used as nitrogen fertilizer. However, for crops, chloride ions are only an essential micronutrient; excessive amounts are harmful, causing leaf burn, soil compaction, and salinization, leading to market difficulties and a large backlog of unsold ammonium chloride. This significantly reduces the economic benefits of soda ash enterprises and restricts the development of the soda ash industry. Therefore, in recent years, the calcination of ammonium chloride and calcium carbonate to regenerate ammonia and produce anhydrous calcium chloride as a byproduct has attracted considerable attention.

[0003] Ammonium chloride begins to volatilize significantly when heated to 100℃, and completely decomposes into ammonia and hydrogen chloride at 338℃. Upon cooling, the ammonia and hydrogen chloride recombine to form extremely fine ammonium chloride particles. Because of this characteristic, when calcium carbonate powder is roasted with ammonium chloride, an excess of ammonium chloride must be added, typically at least 150% of the stoichiometric ratio of the two compounds, to ensure a calcium carbonate conversion rate of over 90%. Excess ammonium chloride sublimates upon heating and recondenses in the flue gas duct, clogging the pipes and causing production equipment to malfunction.

[0004] Calcining calcium carbonate powder and ammonium chloride crystals with water significantly reduces the leakage of HCl gas generated by the pyrolysis of ammonium chloride during the calcination process, greatly reducing the excess coefficient of ammonium chloride. However, the resulting calcination product is foamed calcium chloride, and its production can only be achieved through static calcination. Furthermore, the low thermal conductivity of foamed calcium chloride severely limits the capacity of the calcination equipment.

[0005] Preventing calcium chloride from absorbing moisture and deliquescing during the roasting process has long been a difficult problem in existing roasting technologies. It is well known that the roasting reaction of calcium carbonate powder with ammonium chloride produces water, and the roasted material may also contain moisture. Anhydrous calcium chloride is highly hygroscopic; once the calcium chloride produced by the reaction deliquesces and sticks to the walls of the furnace, the equipment cannot operate normally. While the principle of producing anhydrous calcium chloride by roasting calcium carbonate powder with ammonium chloride seems simple, there are still many technical problems that urgently need to be solved in the industrial production process. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention aims to provide a method for preparing anhydrous calcium chloride by chlorination roasting of calcium carbonate ore. This method uses ammonium chloride as the chlorinating agent in the chlorination roasting of calcium carbonate. Calcium carbonate is mixed with auxiliary materials to form ore, which is then roasted in a vertical reactor. This achieves the stepwise absorption of HCl produced by the decomposition of ammonium chloride by calcium carbonate, allowing ammonium chloride to be fully utilized and avoiding the problem of pipeline blockage caused by excessive ammonium chloride.

[0007] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing anhydrous calcium chloride by chlorination roasting of calcium carbonate ore, characterized in that: calcium carbonate and auxiliary materials are blended into ore to obtain ore pellets, which are then dried and placed in a vertical reactor to be mixed with ammonium chloride pyrolysis gas for roasting, thereby obtaining the final product; or, calcium carbonate, ammonium chloride and auxiliary materials are blended into ore pellets to obtain ore pellets, which are then dried and placed in a vertical reactor for roasting, thereby obtaining the final product; the auxiliary materials include water and a binder.

[0008] As a preferred embodiment, the calcium carbonate is at least one of the following: natural minerals containing calcium carbonate, heavy calcium carbonate, light calcium carbonate, calcium carbonate reagents, and synthetic calcium carbonate.

[0009] As a preferred embodiment, the calcium carbonate has a particle size of -250 mesh.

[0010] As a preferred embodiment, the auxiliary material further includes coke powder; the particle size of the ore agglomerate is 0.3–30 cm.

[0011] As a preferred embodiment, during the calcination process, the molar ratio of Ca to Cl is 1:1.9 to 2.1.

[0012] As a preferred embodiment, the roasting process is carried out at a temperature of 330–680℃ for a time of 0.5–2.5 h. The parameters of the roasting process must be strictly followed as described above. Temperature control ensures that ammonium chloride is completely decomposed into NH3 and HCl gases upon heating, and that calcium carbonate is successfully converted into calcium chloride. If the reaction temperature is too low, unreacted ammonium chloride will remain in the resulting roasted mortar, affecting the conversion rate of calcium carbonate; if the reaction temperature is too high, approaching the melting point of calcium chloride, it will cause the material to soften and collapse, affecting the permeability between material layers.

[0013] As a preferred embodiment, the binder in the auxiliary material is at least one of quicklime, bentonite, clay, perlido, and modified starch.

[0014] As a preferred embodiment, the amount of binder added to the auxiliary material is 0.3% to 3% of the total mass of the ore pellet.

[0015] As a preferred embodiment, the flue gas generated during the roasting process also needs to be treated by multi-stage countercurrent liquid phase absorption. The flue gas generated during the preparation of calcium chloride contains a large amount of CO2 and NH3. Direct emission not only harms the environment but also causes a significant waste of resources. This invention, through a multi-stage countercurrent liquid phase absorption method, achieves the harmless treatment of the flue gas on the one hand, and converts the C and N elements in the flue gas into economical products on the other hand, thereby achieving the technical objective of recycling or resource recovery.

[0016] As a preferred embodiment, the multi-stage countercurrent liquid phase is water or calcium chloride solution.

[0017] This invention first grinds calcium carbonate into powder, then forms agglomerates, which increases the contact area for the gas-solid reaction and improves the permeability of the material during roasting. The dried agglomerates are added from the top of a vertical reactor and discharged from the bottom after roasting. The flue gas generated during roasting automatically exits from the top of the reactor, while the roasted material gradually moves downwards under gravity. This causes the gas and solid phases to move towards each other within the reactor, creating an excellent environment for the calcium carbonate agglomerates to absorb HCl gas in stages. This process is similar to an infinitely multi-stage countercurrent extraction process. More precisely, it is more like a column process of ion exchange, where HCl and CO2 gases continuously exchange within the calcium carbonate agglomerate bed, ensuring that the HCl gas produced by the pyrolysis of ammonium chloride is completely absorbed by the bed. The basic principle of producing anhydrous calcium chloride by chlorination roasting of calcium carbonate agglomerates is as follows:

[0018] 2NH4Cl + CaCO3 =Δ= CaCl2+ 2NH3↑+ CO2↑+ H2O↑ (1)

[0019] 2NH3+ CO2+ H2O = (NH4)2CO3 (2)

[0020] NH3 + CO2 + H2O = NH4HCO3 (3)

[0021] Ammonium chloride decomposes into NH3 and HCl gases upon heating. The hot HCl gas is continuously absorbed by calcium carbonate aggregates during its ascent, converting into calcium chloride and releasing CO2 gas. This process continues until all the HCl gas in the roasting flue gas is absorbed, resulting in a mixture of carbon dioxide and ammonia gas without HCl. Meanwhile, the calcium carbonate aggregates, during their downward movement, continuously absorb HCl gas and are eventually completely converted into anhydrous calcium chloride, which is discharged from the bottom of the reactor. Furthermore, the HCl-free roasting flue gas can be cooled and absorbed using different liquid phases to obtain different economical byproducts. For example, water absorption produces ammonium carbonate or ammonium bicarbonate, while calcium chloride solution absorption produces calcium carbonate and ammonium chloride.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0023] 1) In the method for preparing anhydrous calcium chloride provided by the present invention, after the calcium carbonate powder is agglomerated, it can not only ensure that the HCl gas generated by the pyrolysis of ammonium chloride can be effectively absorbed by calcium carbonate and avoid the overflow of HCl gas generated by the pyrolysis of ammonium chloride, but also enhance the permeability of the material layer so that the gas containing CO2 and NH3 generated by the reaction can be discharged smoothly. In addition, after agglomeration, the contact area between the material and the reactor wall is significantly reduced, and the possibility of roasted sand sticking to the wall and forming in the kiln during the roasting process is greatly reduced.

[0024] 2) In the technical solution provided by this invention, the calcium carbonate ore is roasted in a vertical reactor. The ore is added from the top of the reactor, the roasted sand is discharged from the bottom of the reactor, and the flue gas generated during roasting is automatically discharged from the top of the reactor. The roasted material gradually moves downward under the action of gravity, thereby creating a gas-solid two-phase reaction trajectory in the reactor moving towards each other. This creates favorable conditions for the HCl gas generated by the pyrolysis of ammonium chloride to be completely absorbed by calcium carbonate, thereby maximizing the effective utilization rate of ammonium chloride. Therefore, by choosing a vertical reactor for the chlorination roasting of calcium carbonate ore, ammonium chloride only needs to be added according to the stoichiometric amount and does not need to be added in excess. Detailed Implementation

[0025] The present invention will be further described below with reference to embodiments. These embodiments are intended to illustrate the present invention and not to further limit the present invention.

[0026] Example 1

[0027] First, limestone ore with a CaCO3 content of 97.6% is crushed and ground to 900 mesh. Then, hydrated lime is added to the limestone powder at a ratio of 1% as a binder. Water is added to form ore pellets with a particle size of 1.5–3.5 cm. After drying, the pellets are added to a hot blast furnace with a diameter of 1.5 m and a height of 6 m. Hot air containing ammonium chloride pyrolysis gas at a temperature >330℃ is introduced from about 70 cm below the furnace bottom. The contact time between the pellets and the ammonium chloride pyrolysis gas is controlled to be about 1 hour. Chlorination is introduced into the furnace at a rate of 100 mg / kg per unit time. The pyrolysis rate of ammonium chloride is adjusted by setting the molar ratio of Cl in the ammonium pyrolysis gas to Ca in the ore entering the furnace at 2:1. The roasted ore after chlorination is discharged from the bottom of the furnace. The flue gas discharged from the top of the hot blast stove is absorbed by calcium chloride solution, filtered, and dried to obtain light calcium carbonate. The filtrate is cooled and crystallized to precipitate ammonium chloride. The obtained ammonium chloride crystals are returned to the pyrolysis process for recycling. Samples are taken for analysis after the hot blast stove has been running for 1.5 hours. The obtained roasted ore is anhydrous calcium chloride with a CaCl2 content of 97.8% and a CaCO3 content of <0.2%.

[0028] Example 2

[0029] First, limestone ore with a CaCO3 content of 98.3% is crushed and ground to 1250 mesh. Then, limestone and ammonium chloride crystals are mixed at a molar ratio of ammonium chloride to calcium carbonate of 2:1. Modified starch is added to the mixture as a binder at a ratio of 0.3%. Water is added to form ore agglomerates with a particle size of 2.5-4.5 cm. After the ore agglomerates are naturally dried, they are mixed with coke blocks and loaded into a vertical shaft furnace modified from a blast furnace. The ratio of ore agglomerates to coke blocks is based on the highest temperature in the kiln reaching ~650℃. During the roasting process, the residence time of the ore agglomerates in the furnace is controlled to be ~45 min. The roasted calcined sand is discharged from the bottom of the furnace. The flue gas discharged from the top of the furnace is cooled and absorbed by multi-stage countercurrent spraying to obtain ammonium bicarbonate fertilizer. After the vertical shaft furnace is continuously fed and discharged for 1 hour, samples are taken for analysis. The obtained roasted sand is anhydrous calcium chloride with a CaCl2 content of 99.1%, of which the CaCO3 content is <0.1%.

[0030] Example 3

[0031] First, limestone ore with a CaCO3 content of 95.8% is crushed and ground to 450 mesh. Then, limestone powder and ammonium chloride crystals are mixed at a molar ratio of ammonium chloride to calcium carbonate of 2:1. Next, coke powder is added according to the maximum roasting temperature of 680℃, and bentonite is added as a binder at a ratio of 0.6%. Water is added to form ore agglomerates with a particle size of 3.5-6.5 cm. After the ore agglomerates are naturally dried, they are loaded into a vertical kiln similar to a lime kiln and ignited. During the roasting process, the residence time of the ore agglomerates in the kiln is controlled to be ~1.5 hours. The roasted ore is discharged from the bottom of the kiln. The flue gas discharged from the top of the kiln is cooled and absorbed by multi-stage countercurrent spraying to crystallize and precipitate ammonium bicarbonate crystals. After the equipment is continuously fed and discharged for 2 hours, samples are taken for analysis. The obtained roasted ore is anhydrous calcium chloride with a CaCl2 content of 96.2% and a CaCO3 content of <0.3%.

[0032] Example 4

[0033] First, the light calcium carbonate powder obtained from wastewater purification is mixed with ammonium chloride crystals at a molar ratio of 2:1 (ammonium chloride to calcium carbonate). Then, coke powder is added according to the maximum roasting temperature of 650℃, and clay is added as a binder at a ratio of 2.5%. After mixing with water, the mixture is pressed into ore balls with a diameter of 25cm using a honeycomb briquette press. After drying, the ore balls are placed in a vertical tube furnace, and the furnace bottom is ignited to allow them to self-heat and roast from bottom to top. The roasting flue gas is absorbed by water and used as agricultural fertilizer. After the flame in the furnace is extinguished, the mixture is cooled to room temperature, and samples are taken from the furnace. The resulting roasted sand is a foamy anhydrous calcium chloride with a CaCl2 content of 95.7%, which can be directly used as a snow melting and de-icing agent.

Claims

1. A method for preparing anhydrous calcium chloride by chlorination roasting of calcium carbonate agglomerates, characterized in that: Calcium carbonate is blended with auxiliary materials to form ore pellets. After drying, the ore pellets are placed in a vertical reactor and roasted with ammonium chloride pyrolysis gas to obtain the final product. Alternatively, calcium carbonate, ammonium chloride, and auxiliary materials are blended with ore pellets to form ore pellets. After drying, the ore pellets are placed in a vertical reactor and roasted to obtain the final product. The auxiliary materials include water and a binder. The binder in the auxiliary materials is at least one of hydrated lime, bentonite, clay, perlid, and modified starch; the auxiliary materials also include coke powder; the particle size of the ore agglomerates is 0.3~30cm; the amount of binder added in the auxiliary materials is 0.3~3% of the total mass of the ore agglomerates; the ore agglomerates are added from the top of the vertical reactor after drying, and discharged from the bottom after roasting. The flue gas generated during roasting is automatically discharged from the top of the reactor, while the roasted material gradually moves downward under the action of gravity, causing the gas and solid phases to move towards each other in the reactor.

2. The method for preparing anhydrous calcium chloride by chlorination roasting of calcium carbonate agglomerates according to claim 1, characterized in that: The calcium carbonate is at least one of the following: natural minerals containing calcium carbonate, heavy calcium carbonate, light calcium carbonate, calcium carbonate reagents, and artificial calcium carbonate; the particle size of the calcium carbonate is -250 mesh.

3. The method for preparing anhydrous calcium chloride by chlorination roasting of calcium carbonate ore according to claim 1, characterized in that: During the roasting process, the molar ratio of Ca to Cl is 1:1.9~2.

1.

4. The method for preparing anhydrous calcium chloride by chlorination roasting of calcium carbonate agglomerates according to claim 1, characterized in that: The roasting process is carried out at a temperature of 330~680℃ for a time of 0.5~2.5h.

5. The method for preparing anhydrous calcium chloride by chlorination roasting of calcium carbonate agglomerates according to claim 1, characterized in that: The flue gas generated during the roasting process also needs to be treated by multi-stage countercurrent liquid phase absorption.

6. The method for preparing anhydrous calcium chloride by chlorination roasting of calcium carbonate agglomerates according to claim 5, characterized in that: The multi-stage countercurrent liquid phase is water or calcium chloride solution.