Method for preparing high-purity calcium oxide and co-producing sulfuric acid by decomposing hydrogen sulfide phosphogypsum

Abstract

The present application relates to phosphogypsum comprehensive utilization technical field, the present application is a kind of hydrogen sulfide decomposes phosphogypsum and produces sulfuric acid with high-purity calcium oxide method, comprising the following steps: S1, phosphogypsum is mixed with acid activator sufficiently;S2, aging;S3, complete aging phosphogypsum is added to multilayer pulse fluidized bed, and hydrogen sulfide gas is reacted;S4, drying separation;S5, sulfuric acid after absorbing water vapor is reused;S6, sulfur dioxide gas is sent into sulfuric acid generation equipment;S7, calcium oxide solid is taken out, and high-purity calcium oxide is obtained.The present application uses phosphogypsum waste residue and hydrogen sulfide as raw material, by improving the reaction characteristics of phosphogypsum and precisely controlling the proportion and temperature gradient of raw material, high-purity calcium oxide product is obtained in one step, by-product sulfur dioxide is connected to sulfuric acid device to produce sulfuric acid, process operation is simple, waste is turned into treasure, and energy consumption is low.High-purity calcium oxide produced provides high-quality raw material for downstream calcium product, and co-production of sulfuric acid can alleviate the shortage of sulfur resources in China, and has wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization technology of phosphogypsum, and in particular to a method for producing high-purity calcium oxide and sulfuric acid by decomposing phosphogypsum with hydrogen sulfide. Background Technology

[0002] Phosphogypsum is one of the main solid wastes generated by the phosphate chemical industry. With the rapid development of the phosphate chemical industry, the amount of phosphogypsum accumulated has increased year by year. Currently, my country's phosphogypsum stockpile exceeds 820 million tons, with an annual increase of approximately 80 million tons, and its comprehensive utilization rate is only about 50%. Phosphogypsum is mainly used in low-end building materials, such as building gypsum powder, roadbed materials, and ecological restoration agents. However, due to weak market competitiveness and severe homogenization, the comprehensive utilization of phosphogypsum faces numerous difficulties. Although phosphogypsum is classified as solid waste, it contains abundant sulfur and calcium, possessing recycling value and representing a potential resource for development and utilization.

[0003] Regarding the production of calcium oxide from phosphogypsum, CN101602518A discloses a production process for preparing calcium oxide and sulfur dioxide by decomposing phosphogypsum, using coke as a reducing agent and decomposing phosphogypsum in a fluidized bed. To increase the concentration of sulfur dioxide, CN101462699A discloses a method for the catalytic reduction of phosphogypsum by decomposing high-sulfur coal, using high-sulfur coal as a reducing agent and adding a catalyst to lower the decomposition temperature of phosphogypsum. CN101492177A discloses a method for the reduction and decomposition of phosphogypsum using yellow phosphorus tail gas, producing furnace gas with a sulfur dioxide gradient percentage content ≥15% and a solid calcium oxide content ≥70%. CN105036170A discloses a method for preparing calcium oxide by decomposing phosphogypsum, in which phosphogypsum is dried and ground, and then decomposed twice in a reducing atmosphere-oxidizing atmosphere cycle to generate CaO, with the reducing atmosphere being CO with a volume percentage content ≥99.9%.

[0004] Regarding the reduction of phosphogypsum by hydrogen sulfide, CN105129742A discloses a method for producing calcium sulfide from phosphogypsum by decomposing hydrogen sulfide tail gas. The main reducing agent is CO, and the addition of hydrogen sulfide tail gas enhances the reducing power of the reaction and reduces the need for hydrogen sulfide tail gas treatment. The calcium sulfide yield is greater than 85%. CN103130259A discloses a method for low-temperature decomposition of phosphogypsum, using hydrogen sulfide as the reducing agent and simultaneously adding calcium chloride to lower the decomposition temperature of phosphogypsum. The product is 55% calcium sulfide. CN101302002A discloses a method for producing sulfuric acid and cement clinker from gypsum, with the product being a solid mainly composed of calcium oxide.

[0005] In summary, the production of calcium oxide from phosphogypsum primarily relies on carbonaceous raw materials as reducing agents, resulting in high investment, high energy consumption, and the generation of large amounts of CO2 greenhouse gases. Furthermore, the reduction of phosphogypsum by hydrogen sulfide produces calcium sulfide or calcium oxide with low purity. Therefore, a method for the decomposition of phosphogypsum by hydrogen sulfide to produce high-purity calcium oxide and co-produce sulfuric acid is urgently needed to address these issues. Summary of the Invention

[0006] The purpose of this invention is to provide a method for producing high-purity calcium oxide and sulfuric acid by decomposing phosphogypsum with hydrogen sulfide, thereby solving the problems of high cost and low purity of calcium oxide in the prior art.

[0007] The solution of the present invention is:

[0008] A method for producing high-purity calcium oxide and sulfuric acid by decomposing phosphogypsum with hydrogen sulfide, characterized by comprising the following steps:

[0009] S1. Thoroughly mix phosphogypsum with the acidic activator;

[0010] S2. The mixed phosphogypsum is aged.

[0011] S3. The aged phosphogypsum is added to a multi-layer pulsed fluidized bed and hydrogen sulfide gas is introduced to react and generate calcium oxide solid, water vapor and sulfur dioxide gas.

[0012] S4. The water vapor and sulfur dioxide gas are drawn out by a fan and separated by absorption and drying with concentrated sulfuric acid.

[0013] S5. Use concentrated sulfuric acid that has absorbed water vapor as an acidic activator and reuse it in step S1.

[0014] S6. The dried sulfur dioxide gas is fed into the sulfuric acid generating equipment;

[0015] S7. Remove the generated calcium oxide solid and cool it to obtain high-purity calcium oxide.

[0016] As a preferred technical solution, the phosphogypsum in step S1 is one or both of dihydrate phosphogypsum and hemihydrate phosphogypsum.

[0017] As a preferred technical solution, the acidic activator in step S1 is one or more of sulfuric acid, hydrochloric acid, hydrofluoric acid, and phosphoric acid.

[0018] As a preferred technical solution, the mass concentration of the acidic activator in step S1 is 10% to 50%, and the amount of acidic activator added is 1% to 5% of the mass of the phosphogypsum.

[0019] As a preferred technical solution, the aging time in step S2 is 2 to 30 hours.

[0020] As a preferred technical solution, in step S3, the upper layer temperature of the multilayer pulsed fluidized bed is 300℃~600℃, the middle layer temperature is 700℃~900℃, the lower layer temperature is 1000℃~1200℃, the pulsation frequency is 0.5Hz~3Hz, the minimum fluidization velocity is 1.05 m / s~1.15 m / s, and the residence time is 1h~5h.

[0021] As a preferred technical solution, the hydrogen sulfide gas introduced in step S3 is at least one of the following: hydrogen sulfide tail gas from ammonia synthesis, hydrogen sulfide tail gas from phosphoric acid dehydrogenation, and hydrogen sulfide tail gas from phosphoric acid dehydrogenation, wherein the hydrogen sulfide content is ≥10%, and the molar ratio of hydrogen sulfide gas to phosphogypsum is 2-4:5.

[0022] As a preferred technical solution, in step S3, the water vapor and sulfur dioxide gas are separated by drying with concentrated sulfuric acid.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. The raw materials of this invention are phosphorus chemical wastes such as phosphogypsum, synthetic ammonia tail gas, and phosphoric acid de-stabilization tail gas, and the products are high-purity CaO and sulfuric acid, realizing high-value utilization of solid waste and tail gas at low cost;

[0025] 2. This invention first utilizes an acidic activator to disrupt the crystal structure of phosphogypsum, creating more defects and increasing its specific surface area, thereby enhancing the reaction kinetics of hydrogen sulfide reacting with phosphogypsum to form CaS. Second, by improving fluidization quality through a multi-layer pulsed fluidized bed, effectively disrupting particle clusters, enhancing heat and mass transfer efficiency between gas-solid and solid-solid phases, and precisely controlling the reduction temperature gradient, the reaction rate of CaS and phosphogypsum is greatly improved, resulting in an extremely short lifespan for the intermediate product CaS, thus achieving a one-step production of high-purity CaO.

[0026] 3. This invention uses hydrogen sulfide as a reducing agent to decompose phosphogypsum. By improving the reaction characteristics of phosphogypsum and precisely controlling the proportion of raw materials and temperature gradient, a high degree of material reaction can be achieved, thereby solving the problem of low product purity in existing technologies and producing high-purity calcium oxide (calcium oxide purity >99%). Co-producing sulfuric acid as a raw material for wet-process phosphoric acid has low production costs and broad application prospects. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0028] Figure 1This is a process flow diagram of the present invention. Detailed Implementation

[0029] This invention provides a method for producing high-purity calcium oxide and sulfuric acid by decomposing phosphogypsum with hydrogen sulfide, thereby solving the problems mentioned in the background art.

[0030] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0031] Example 1:

[0032] The main chemical components of phosphogypsum, by weight percentage, are: calcium oxide 34.62%, sulfur dioxide 40.33%, ferric oxide 0.03%, aluminum oxide 0.03%, magnesium oxide 0.06%, silicon dioxide 0.08%, fluorine 0.13%, phosphorus pentoxide 0.03%, and moisture 20.12%.

[0033] Add 2% by mass of 20% sulfuric acid to phosphogypsum, mix thoroughly, and age for 8 hours. Then, introduce phosphoric acid de-burden gas with a hydrogen sulfide content of 16%. Control the molar ratio of phosphogypsum to hydrogen sulfide at 5:3. The fluidized bed temperature is 300℃ for the upper layer, 700℃ for the middle layer, and 1000℃ for the lower layer. The pulsation frequency is 0.8Hz, the minimum fluidization velocity (Umf) is 1.05m / s, and the residence time is 2 hours for reduction decomposition.

[0034] During the reduction process, the induced draft fan is turned on to introduce water vapor and sulfur dioxide gas into the concentrated sulfuric acid drying system. The sulfuric acid that absorbs water vapor is returned for mixing and aging with phosphogypsum. Gas-phase sulfur dioxide is fed into the sulfuric acid unit (i.e., sulfuric acid generation equipment). The flue gas analyzer detects that the sulfur dioxide volume percentage is 15.37%.

[0035] After the reduction and decomposition reaction was completed, the calcium oxide solid was removed, and after natural cooling, a sample was taken for analysis. The calculated decomposition rate of phosphogypsum was 99.05%, and the purity of calcium oxide was 99.85%.

[0036] Traditional techniques for producing CaO involve a two-stage decomposition process: in the first stage (600℃~950℃), hydrogen sulfide reacts with CaSO4 to form the decomposition product CaS; in the second stage (1000℃~1300℃), CaS begins to decompose with CaSO4 to form CaO. Because the CaSO4 reaction in this stage is a parallel competition, both CaO and CaS decomposition products are produced simultaneously, ultimately resulting in CaO products containing CaS and exhibiting low purity. This invention first utilizes an acidic activator to disrupt the crystal structure of phosphogypsum, creating more defects and increasing its specific surface area, thereby enhancing the reaction kinetics of hydrogen sulfide reacting with phosphogypsum to form CaS. Secondly, a multi-layer pulsed fluidized bed improves fluidization quality, effectively breaks down particle clusters, enhances heat and mass transfer efficiency between gas-solid and solid-solid phases, and precisely controls the reduction temperature gradient, significantly increasing the reaction rate between CaS and phosphogypsum. The intermediate product CaS has an extremely short lifespan, achieving a one-step production of high-purity CaO.

[0037] Example 2:

[0038] The main chemical components of phosphogypsum, by weight percentage, are: calcium oxide 33.85%, sulfur dioxide 41.05%, ferric oxide 0.03%, aluminum oxide 0.02%, magnesium oxide 0.06%, silicon dioxide 0.12%, fluorine 0.12%, phosphorus pentoxide 0.02%, and moisture 20.41%.

[0039] Add 3% (by mass) of 25% hydrochloric acid to phosphogypsum, mix thoroughly, and age for 12 hours. Then, introduce phosphoric acid de-burden gas with a hydrogen sulfide content of 16%. Control the molar ratio of phosphogypsum to hydrogen sulfide at 5:4. Set the fluidized bed temperature to 400℃ for the top layer, 800℃ for the middle layer, and 1100℃ for the bottom layer. The pulsation frequency is 1.2Hz, the minimum fluidization velocity (Umf) is 1.1m / s, and the residence time is 4 hours for reduction and decomposition.

[0040] During the reduction process, the induced draft fan is turned on to introduce water vapor and sulfur dioxide gas into the concentrated sulfuric acid drying system. The sulfuric acid that absorbs water vapor is returned for mixing and aging with phosphogypsum. Gas-phase sulfur dioxide is introduced into the sulfuric acid unit, and the flue gas analyzer detects that the sulfur dioxide volume percentage is 15.56%.

[0041] After the reduction and decomposition reaction was completed, the calcium oxide solid was removed, and after natural cooling, a sample was taken for analysis. The calculated decomposition rate of phosphogypsum was 99.13%, and the purity of calcium oxide was 99.56%.

[0042] Example 3:

[0043] The main chemical components of phosphogypsum, by weight percentage, are: calcium oxide 34.51%, sulfur dioxide 40.56%, ferric oxide 0.02%, aluminum oxide 0.03%, magnesium oxide 0.05%, silicon dioxide 0.10%, fluorine 0.13%, phosphorus pentoxide 0.03%, and moisture 20.32%.

[0044] Hydrofluoric acid with a concentration of 10% and a mass fraction of 5% was added to phosphogypsum. After thorough mixing, the mixture was aged for 6 hours. Phosphoric acid de-burden gas with a hydrogen sulfide content of 16% was introduced. The molar ratio of phosphogypsum to hydrogen sulfide was controlled at 5:2. The temperature of the upper layer of the fluidized bed was 550℃, the middle layer temperature was 900℃, and the lower layer temperature was 1200℃. The pulsation frequency was 2Hz, the minimum fluidization velocity (Umf) was 1.15m / s, and the residence time was 3 hours for reduction decomposition.

[0045] During the reduction process, the induced draft fan is turned on to introduce water vapor and sulfur dioxide gas into the concentrated sulfuric acid drying system. The sulfuric acid that absorbs water vapor is returned to be mixed with phosphogypsum for aging. Gas-phase sulfur dioxide is introduced into the sulfuric acid unit, and the flue gas analyzer detects that the sulfur dioxide volume percentage is 15.24%.

[0046] After the reduction and decomposition reaction was completed, the calcium oxide solid was removed, and after natural cooling, a sample was taken for analysis. The calculated decomposition rate of phosphogypsum was 99.21%, and the purity of calcium oxide was 99.61%.

[0047] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents. Certainly.

Claims

1. A method for producing high-purity calcium oxide and sulfuric acid by decomposing phosphogypsum with hydrogen sulfide, characterized in that, Includes the following steps: S1. The phosphogypsum and acidic activator are thoroughly mixed; the mass concentration of the acidic activator is 10% to 50%, and the amount of acidic activator added is 1% to 5% of the mass of the phosphogypsum; S2. The mixed phosphogypsum is aged for 2–30 hours. S3. The aged phosphogypsum is added to a multi-layer pulsed fluidized bed, and hydrogen sulfide gas is introduced to react and generate calcium oxide solid, water vapor, and sulfur dioxide gas. The upper layer temperature of the multi-layer pulsed fluidized bed is 300℃~600℃, the middle layer temperature is 700℃~900℃, the lower layer temperature is 1000℃~1200℃, the pulse frequency is 0.5Hz~3Hz, the minimum fluidization velocity is 1.05m / s~1.15m / s, and the residence time is 1h~5h. The introduced hydrogen sulfide gas is at least one of the hydrogen sulfide tail gas from ammonia synthesis and the hydrogen sulfide tail gas from phosphoric acid dehydrogenation, wherein the hydrogen sulfide content is ≥10%, and the molar ratio of hydrogen sulfide gas to phosphogypsum is 2~4:

5. S4. The water vapor and sulfur dioxide gas are drawn out by a fan and separated by absorption and drying with concentrated sulfuric acid. S5. Use concentrated sulfuric acid that absorbs water vapor as an acidic activator and add it to step S1 for reuse. S6. The dried sulfur dioxide gas is fed into the sulfuric acid generating equipment; S7. Remove the generated calcium oxide solid and cool it to obtain high-purity calcium oxide.

2. The method for producing high-purity calcium oxide and sulfuric acid by decomposing phosphogypsum with hydrogen sulfide as described in claim 1, characterized in that: The phosphogypsum mentioned in step S1 is one or both of dihydrate phosphogypsum and hemihydrate phosphogypsum.

3. The method for producing high-purity calcium oxide and co-producing sulfuric acid by decomposing phosphogypsum with hydrogen sulfide as described in claim 1, characterized in that: The acidic activator in step S1 is one or more of sulfuric acid, hydrochloric acid, hydrofluoric acid, and phosphoric acid.

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