A production method for increasing the SO2 concentration in a phosphogypsum sulfuric acid production device

Abstract

A production method for increasing the SO2 gas concentration in a phosphogypsum sulfuric acid production device comprises the following processes: raw material enters a suspension preheater, and exchanges heat with kiln gas separated from a firing kiln tail in the suspension preheater; after the raw material is heated to 700°C-1000°C by heat exchange, the solid phase enters the decomposition kiln tail, and the raw material is heated in the suspension preheater; the kiln gas exchanges heat with the raw material in the suspension preheater to cool it down, and takes away water in the raw material; after the raw material enters the decomposition kiln, it is gradually heated to 1150°C-1200°C to complete the first two steps of reduction reaction, and the solid phase enters the firing kiln; the solid phase undergoes a mineralization reaction from 1200°C to 1450°C in the firing kiln to generate cement clinker; after the firing kiln gas phase reaches the kiln tail from the kiln head, part of the heat enters the suspension preheater to provide the heat required for raw material drying, and the other part goes to the decomposition kiln to provide the heat energy required for decomposition of phosphogypsum; after the kiln gas at the tail of the decomposition kiln recovers heat energy through heat exchange, dust removal and purification are carried out, and then enters a sulfuric acid device to produce sulfuric acid. The advantage of the present invention is that it only requires simple improvements to the existing technology to increase the SO2 gas concentration by more than 70%.

Description

Technical Field

[0001] The invention belongs to the field of chemical technology and building materials, relates to the field of comprehensive utilization of phosphogypsum, and specifically relates to a production method for increasing the SO2 gas concentration in a phosphogypsum sulfuric acid production device in phosphogypsum sulfuric acid production. Background Art

[0002] Phosphogypsum is a solid waste produced during the wet process of phosphoric acid production. Each ton of wet process phosphoric acid produces about 4.8 to 5.5 tons of phosphogypsum. With the continuous development of the phosphate fertilizer industry, the emission of phosphogypsum is increasing day by day. The comprehensive utilization of phosphogypsum is a global problem. The global stockpile of phosphogypsum has exceeded 6 billion tons, and it continues to grow at a rate of about 200 million tons per year, but the global comprehensive utilization rate of phosphogypsum is only about 25%. The comprehensive utilization of phosphogypsum is imminent. The technology of making sulfuric acid from phosphogypsum can transform solid waste into resources and reduce the import of sulfur, which has broad prospects.

[0003] On April 5, 1996, Nanjing University of Chemical Technology applied for patent number CN96116877.3 for the "Production Process of Cement and Sulfuric Acid from Phosphogypsum". Specifically, the phosphogypsum is ground and dried, and the ingredients and phosphogypsum are mixed and processed before entering the rotary kiln. After passing through a cooler, cement and sulfuric acid can be prepared respectively. The processing process after the ingredients and phosphogypsum are mixed is first to pass through a ball forming system to form balls, and then enter the ball drying and preheating machine. At this time, the high-temperature exhaust gas from the rotary kiln is introduced into the drying and preheating machine to dry and preheat the balls and partially or completely decompose the phosphogypsum, so that the exhaust gas temperature is reduced, and then it is sent to acid production.

[0004] Hunan Xiangfu New Building Materials Co., Ltd. applied for patent number CN201110449184.6 for a method for preparing sulfuric acid and cement from phosphogypsum on December 29, 2011, which comprises the following steps: (1) mixing phosphogypsum, sand, coke, lime, crude salt and ferrous salt to obtain a mixture of phosphogypsum, sand, coke, lime, crude salt and ferrous salt; in the mixture, the weight percentages of phosphogypsum, sand, coke, lime, crude salt and ferrous salt are: 60-83%, sand 5-12%, coke 4-20%, lime 3-10%, crude salt 2-5%, ferrous salt 1-3%; the lime saturation coefficient KH of the mixture is 0.65-1.0, the silicate rate n is 3.0-3.4, and the iron rate P is 2.0-2.2; (2) adding the mixture obtained in step (1) into a grinding preheater for grinding, and the grinding particle size is 0.10mm sieve residue 13-17%; 0.20mm sieve residue is less than 1.5% ; While grinding, preheat the mixture obtained in step (1) at a preheating temperature of 500-650°C; (3) add the mixture treated in step (2) into a rotary kiln for calcination at a temperature of 850-1150°C, and introduce air containing hydrogen sulfide during calcination for 2-4 hours, and control the SO2 mass concentration of the gas in the rotary kiln to be 12-15%, thereby obtaining cement clinker; (4) cool the cement clinker obtained in step (3), and then add Fly ash slag equivalent to 3-5% by weight of cement clinker and cement retarder 4-6% are ground into powder to obtain a cement product; the particle size of the powder is less than 0.03mm and the specific surface area is greater than 350m2 / kg; (5) the exhaust gas containing SO2 is passed through a grinding preheater, and the mixture obtained in step (1) is preheated by the waste heat of the SO2 exhaust gas. After the temperature of the SO2 exhaust gas is reduced, the SO2 is oxidized to SO3, and then dedusted, cooled, washed, purified and absorbed to produce sulfuric acid.

[0005] In the phosphogypsum sulfuric acid technology represented by Lubei Chemical and Jinzhengda, the large amount of CO2 generated by coal combustion in the kiln and the free water and crystal water brought into the system by phosphogypsum result in low SO2 gas concentration, large investment in sulfuric acid equipment and high operating costs, which slows the promotion of phosphogypsum sulfuric acid technology;

[0006] 202111540790.9 discloses a sulfuric acid production system and production process based on the phosphogypsum furnace method. Although the SO2 gas concentration can be increased to 15%, the water is not discharged in time during the production process, the flue gas dew point is greatly increased, and the equipment is easily corroded. The reaction temperature is set at 1280-1600℃, and a large amount of liquid phase will appear. The liquid phase will enter the acid-making section with the air flow or adhere to the pipeline between the furnace and the acid-making purification to form a blockage. Obviously, the system and method cannot be industrialized.

[0007] This patent solves this bottleneck. Increasing the SO2 gas concentration makes the technology of producing sulfuric acid from phosphogypsum lower in cost and easier to promote. Summary of the invention

[0008] The purpose of the present invention is to provide a production method for increasing the SO2 gas concentration in a phosphogypsum sulfuric acid production device in view of the above situation. It only requires simple improvements to the existing technology to increase the SO2 gas concentration by more than 70%.

[0009] The technical solution for realizing the present invention is that a production method for increasing the SO2 gas concentration in a phosphogypsum sulfuric acid production device comprises the following process:

[0010] (1) The raw material enters the suspension preheater and exchanges heat with the kiln gas separated from the kiln tail in the suspension preheater;

[0011] (2) After the raw meal is heated to 700℃-1000℃, the solid phase enters the tail of the decomposition kiln. During the heating period of the suspension preheater, the CaSO4·2H2O and CaSO4·1 / 2H2O contained in the raw meal are dehydrated to become CaSO4, and the carbonate in the raw meal is decomposed into CO2;

[0012] (3) The kiln gas exchanges heat with the raw material in the suspension preheater to cool it down, and takes away the CO2, free water and crystal water in the phosphogypsum decomposed in the raw material;

[0013] (4) After the raw material enters the decomposition kiln, the temperature is gradually raised to 1150℃-1200℃ to complete the first two steps of reduction reaction, i.e. 2C+CaSO4→CaS+CO2, CaS+3CaSO4→4CaO+4SO2, and then the solid phase enters the firing kiln;

[0014] (5) The solid phase undergoes mineralization reaction in the firing kiln at a temperature of 1200°C to 1450°C to form cement clinker;

[0015] (6) Coal injection and air combustion at the kiln head provide the heat required for solid phase mineralization and maintain the solid phase temperature near the coal injection gun at 1450±10℃;

[0016] (7) After the kiln gas phase reaches the kiln tail from the kiln head, part of the heat enters the suspension preheater to provide the heat required for raw material drying, and the other part goes to the decomposition kiln to provide the heat energy required for the decomposition of phosphogypsum. The opening degree of valve A depends on the temperature of the raw material entering the decomposition kiln tail from the suspension preheater, which is controlled at 700℃-1000℃;

[0017] (8) The kiln gas at the tail of the decomposition kiln is heat exchanged to recover heat energy, and then dusted and purified before entering the sulfuric acid plant to produce sulfuric acid.

[0018] Furthermore, in step (1), the free water content of the raw material and the crystallization water content of the phosphogypsum are controlled within the range of 0.2%-4.5%.

[0019] Furthermore, the kiln gas tail washing in step (3) can be calcium washing, ammonia washing, hydrogen peroxide washing, or a new catalytic flue gas desulfurization technology, and the free water in the drying of phosphogypsum is ≤3%.

[0020] Furthermore, in step (4), coal is sprayed at the head of the decomposition kiln and air is burned to supplement the heat required for the decomposition of phosphogypsum and maintain the solid phase temperature at the head of the decomposition kiln between 1150°C and 1200°C.

[0021] Furthermore, in step (7), valve A is mainly used to control the solid phase temperature from the suspension preheater to the end of the decomposition kiln between 700°C and 1000°C, rather than mainly supplying heat to the head of the decomposition kiln.

[0022] Furthermore, in step (8), medium-pressure steam can be produced after heat exchange of the heat energy of the flue gas at the tail of the decomposition kiln.

[0023] The present invention has the following beneficial effects:

[0024] 1. The purpose of the present invention is to provide a production method for increasing the SO2 concentration in a sulfuric acid production device made of phosphogypsum. First, the free water and crystal water of the phosphogypsum are partially or completely removed (theoretically, all are removed, but in practice, only infinitely close to 0.2%) through a suspension preheater, thereby reducing the moisture of the materials entering the decomposition kiln and preventing the moisture in the phosphogypsum from reducing the SO2 concentration at the tail of the decomposition kiln. Second, in the suspension preheater, CO2 is carried out by the kiln gas during the preheating process and does not enter the decomposition kiln, thereby reducing the amount of CO2 and air entering the tail gas system, so that the SO2 concentration of the product can be increased by more than 15%, reducing the manufacturing and operating costs of the sulfuric acid device. Third, the utilization rate of thermal energy is increased and carbon emissions are reduced.

[0025] 2. The process of the present invention belongs to a fully closed cycle process system. The effluent and the heat energy contained therein are recycled and utilized by subsequent production units. No additional three wastes are generated, which is in line with the concept of green chemical industry.

[0026] 3. The present invention has simple production process, convenient operation, low production cost and good economic benefit. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the process flow of the present invention.

[0028] Figure 2 It is the prior art. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with implementation cases and drawings, but the implementation cases do not constitute a limitation to the present invention.

[0030] like Figure 1 As shown, Example 1:

[0031] The phosphogypsum enters the phosphogypsum drying section from the homogenization bin via a belt, and is dried to 120-130°C by the waste heat of the kiln flue gas at 490°C, removing free water and converting part of CaSO4·2H2O into CaSO4·1 / 2H2O. The flue gas after heat exchange enters the tail washing section at 150°C to treat the dust and SO2 carried in the flue gas. The dried phosphogypsum enters the semi-hydrated gypsum homogenization bin for homogenization. The auxiliary materials enter the auxiliary material homogenization bin after drying and crushing, and the raw coal and reduced coal enter the fuel coal bin and reduced coal bin after drying by the vertical mill. The auxiliary materials and semi-hydrated gypsum are discharged onto the belt and mixed in proportion and then enter the raw material homogenization bin. The homogenized material at 34°C and the reduced coal at 70°C are mixed on the belt at a C / S ratio of 0.65-0.75.

[0032] A production method for increasing the SO2 gas concentration in a phosphogypsum sulfuric acid production device comprises the following process:

[0033] (1) The raw meal enters the suspension preheater C. There are four suspension preheaters C, namely, suspension preheaters C1, C2, C3, and C4. After the raw meal exits the suspension preheater C, the free water content and the crystal water content of the phosphogypsum are controlled within the range of 0.2%-4.5%. The raw meal is heat exchanged with the kiln gas separated from the kiln tail of the firing kiln in the suspension preheater C;

[0034] (2) After the raw meal is heated from 35°C to 910°C in the suspension preheaters C1, C2, C3, and C4, the solid phase enters the tail of the decomposition kiln. During the heating period in the suspension preheater, the CaSO4·2H2O and CaSO4·1 / 2H2O contained in the raw meal are dehydrated to become CaSO4, and the carbonate in the raw meal is decomposed to become CO2;

[0035] (3) The kiln gas exchanges heat with the raw material in the suspension preheater to cool it down, and takes away the CO2 decomposed in the raw material, free water, and crystal water in the phosphogypsum. Preferably, the kiln gas tail washing can be calcium washing, ammonia washing, hydrogen peroxide washing, and new catalytic flue gas desulfurization technology. The free water content of the phosphogypsum dried is ≤3%;

[0036] (4) The temperature of the raw material in the decomposition kiln rises from 910°C to 1170°C, and the raw material undergoes a reduction reaction to generate CaO which enters the firing kiln, i.e., 2C+CaSO4→CaS+CO2, CaS+3CaSO4→4CaO+4SO2. After that, the solid phase enters the firing kiln. Coal is sprayed at the head of the decomposition kiln and air is burned to supplement the heat required for the decomposition of phosphogypsum.

[0037] (5) The solid phase temperature in the firing kiln rises from 1170°C to 1450°C, and a mineralization reaction occurs to generate C3S, C2S, C3A, and C4AF, i.e., 2CaO+SiO2=C2S, 3CaO+SiO2=C3S, 3CaO+Al2O3=C3A, 4CaO+Al2O3+Fe2O3=C4AF, and then the solid phase is cooled by a grate cooler and enters the clinker storage;

[0038] (6) Coal injection and air combustion at the kiln head provide the heat required for solid phase mineralization and maintain the solid phase temperature near the coal injection gun at 1450±10℃;

[0039] (7) After the kiln gas phase reaches the kiln tail from the kiln head, part of the heat enters the suspension preheater to provide the heat required for raw material drying, and the other part goes to the decomposition kiln to provide the heat required for the decomposition of phosphogypsum. The opening of valve A depends on the temperature of the raw material entering the decomposition kiln tail from the suspension preheater, which is controlled at 700℃-1000℃. Valve A is mainly used to control the solid phase temperature from the suspension preheater to the decomposition kiln tail between 700℃-1000℃, rather than mainly supplying heat to the decomposition kiln head. The gas phase ranges from 1600℃ at the kiln head to 1320℃ at the decomposition kiln tail, of which 40000m 3 / h calcining kiln flue gas enters suspension preheater C through valve A, and after heat exchange with raw materials in the suspension preheater, enters the phosphogypsum drying system as waste heat for drying phosphogypsum. At this time, the temperature is still 490-520℃. The remaining calcining kiln flue gas passes through the decomposition kiln to provide temperature for the decomposition reaction. Coal is sprayed at the head of the decomposition kiln to supplement heat. The gas phase temperature of the decomposition kiln tail is 950℃-1050℃;

[0040] (8) After heat energy is recovered through heat exchange at the tail of the decomposition kiln, the temperature of the kiln gas at the tail of the decomposition kiln is 250°C and the SO2 gas is 14.3%. After dust removal and purification, the gas enters the sulfuric acid device to produce sulfuric acid. After heat energy is recovered through heat exchange at the tail of the decomposition kiln, medium-pressure steam can be produced.

[0041] After adding oxygen at an O / S ratio of 1:1, the SO2 gas concentration is 8.81%. The conversion section can be realized without running an electric furnace, and the low-temperature waste heat recovery system in the acid-making section can produce low-pressure steam as a by-product. Even if the decomposition condition in the kiln is abnormal and the SO2 gas concentration decreases, the conversion heat can still maintain a balance. During the start-up period, an average of 79t / h of phosphogypsum was processed, 38t / h of sulfuric acid was produced, 4.7t / h of reduced coal (coke, containing 77%-82% residual carbon), and 13.7t / h of standard coal was converted into fuel coal and calcined coal.

[0042] Implementation 2:

[0043] The phosphogypsum enters the phosphogypsum drying section from the homogenization bin via a belt, and is dried to 120-130°C by the waste heat of the kiln flue gas at 490°C, removing free water and converting part of CaSO4·2H2O into CaSO4·1 / 2H2O. The flue gas after heat exchange enters the tail washing section at 150°C to treat the dust and SO2 carried in the flue gas. The dried phosphogypsum enters the semi-hydrated gypsum homogenization bin for homogenization. The auxiliary materials enter the auxiliary material homogenization bin after drying and crushing, and the raw coal and reduced coal enter the fuel coal bin and reduced coal bin after drying by the vertical mill. The auxiliary materials and semi-hydrated gypsum are discharged onto the belt and mixed in proportion and then enter the raw material homogenization bin. The homogenized material at 34°C and the reduced coal at 70°C are mixed on the belt at a C / S ratio of 0.65-0.75.

[0044] A production method for increasing the SO2 gas concentration in a phosphogypsum sulfuric acid production device comprises the following process:

[0045] (1) The raw meal enters the suspension preheater C. There are four suspension preheaters C, namely, suspension preheaters C1, C2, C3, and C4. After the raw meal exits the suspension preheater C, the free water content and the crystal water content of the phosphogypsum are controlled within the range of 0.2%-4.5%. The raw meal is heat exchanged with the kiln gas separated from the kiln tail of the firing kiln in the suspension preheater C;

[0046] (2) After the raw meal is heated from 35°C to 900°C in the suspension preheaters C1, C2, C3, and C4, the solid phase enters the tail of the decomposition kiln. During the heating period of the suspension preheater, the CaSO4·2H2O and CaSO4·1 / 2H2O contained in the raw meal are dehydrated to become CaSO4, and the carbonate in the raw meal is decomposed to become CO2;

[0047] (3) The kiln gas exchanges heat with the raw material in the suspension preheater to cool it down, and takes away the CO2 decomposed in the raw material, free water, and crystal water in the phosphogypsum. Preferably, the kiln gas tail washing can be calcium washing, ammonia washing, hydrogen peroxide washing, and new catalytic flue gas desulfurization technology. The free water content of the phosphogypsum dried is ≤3.2%;

[0048] (4) The temperature of the raw material in the decomposition kiln is raised from 900°C to 1160°C-1170°C, and the raw material undergoes a reduction reaction to generate CaO which enters the firing kiln, i.e. 2C+CaSO4→CaS+CO2, CaS+3CaSO4→4CaO+4SO2. After that, the solid phase enters the firing kiln, and coal is sprayed at the head of the decomposition kiln and air is burned to supplement the heat required for the decomposition of phosphogypsum.

[0049] (5) The solid phase temperature in the firing kiln is raised from 1160°C-1170°C to 1445°C-1455°C, where a mineralization reaction occurs to generate C3S, C2S, C3A, and C4AF, i.e., 2CaO+SiO2=C2S, 3CaO+SiO2=C3S, 3CaO+Al2O3=C3A, 4CaO+Al2O3+Fe2O3=C4AF, and then cooled by a grate cooler before entering the clinker storage;

[0050] (6) Coal injection and air combustion at the kiln head provide the heat required for solid phase mineralization and maintain the solid phase temperature near the coal injection gun of the kiln at 1450±10℃;

[0051] (7) After the kiln gas phase reaches the kiln tail from the kiln head, part of the heat enters the suspension preheater to provide the heat required for raw material drying, and the other part goes to the decomposition kiln to provide the heat required for the decomposition of phosphogypsum. The opening of valve A depends on the temperature of the raw material entering the decomposition kiln tail from the suspension preheater, which is controlled at 700℃-1000℃. Valve A is mainly used to control the solid phase temperature from the suspension preheater to the decomposition kiln tail between 700℃-1000℃, rather than mainly supplying heat to the decomposition kiln head. The gas phase ranges from 1600℃ at the kiln head to 1320℃ at the decomposition kiln tail, of which 40000m 3 / h calcining kiln flue gas enters suspension preheater C through valve A, and after heat exchange with raw materials in the suspension preheater, enters the phosphogypsum drying system as waste heat for drying phosphogypsum. At this time, the temperature is still 490-520℃. The remaining calcining kiln flue gas passes through the decomposition kiln to provide temperature for the decomposition reaction. Coal is sprayed at the head of the decomposition kiln to supplement heat. The gas phase temperature of the decomposition kiln tail is 950℃-1050℃;

[0052] (8) After heat energy is recovered through heat exchange at the tail of the decomposition kiln, the temperature of the kiln gas at the tail of the decomposition kiln is 250°C and the SO2 gas is 14.1%. After dust removal and purification, the gas enters the sulfuric acid device to produce sulfuric acid. After heat energy is recovered through heat exchange at the tail of the decomposition kiln, medium-pressure steam can be produced.

[0053] After oxygen is added at an O / S ratio of 1:1, the SO2 gas concentration is 8.8%, the conversion section can be realized without opening the electric furnace, and the low-temperature waste heat recovery system in the acid-making section can produce low-pressure steam as a byproduct. Even if the decomposition condition in the kiln is abnormal and the SO2 gas concentration decreases, the conversion heat can still maintain balance. During the start-up period, an average of 79t / h of phosphogypsum was processed, 38t / h of sulfuric acid was produced, 4.7t / h of reducing coal (coke, containing 77%-82% residual carbon), and 13.72t / h of standard coal was converted into fuel coal and calcined coal. Compared with Example 1, although the total coal consumption required by the system is balanced, the lower the temperature from the suspension preheater into the decomposition kiln, the higher the heat required in the decomposition kiln and the firing kiln, and the lower the kiln capacity. And the lower the sulfuric acid gas concentration, the lower the steam output of the acid-making section to recover the waste heat, and the higher the comprehensive energy consumption of the system. Considering the comprehensive investment cost, the preferred temperature is 700-100℃, which is on the upper limit control.

[0054] Existing technologies such as Figure 2 As shown: phosphogypsum enters the phosphogypsum drying section from the homogenization tank through the belt, and is dried to 120℃-130℃ by the independent heat source calcining furnace to remove free water and convert part of CaSO4·2H2O into CaSO4·1 / 2H2O. The dried phosphogypsum enters the semi-hydrated gypsum homogenization tank for homogenization. The auxiliary materials enter the auxiliary material homogenization tank after drying and crushing, and the raw coal and reduced coal enter the fuel coal bunker and reduced coal bunker after drying by the vertical mill. The auxiliary materials and semi-hydrated gypsum are discharged onto the belt and mixed in proportion and then enter the raw material homogenization tank. The raw materials 34℃ and reduced coal 70℃ after homogenization are mixed on the belt according to the C / S ratio of 0.65-0.75 and then sent to the suspension preheater C by the belt. The raw material enters the tail of the decomposition kiln through the suspension preheater, and the temperature rises from 35℃ to 780℃. The temperature in the decomposition kiln rises from 780℃ to 1170℃, and the material undergoes a reduction reaction to generate CaO, which enters the firing kiln, i.e. 2C+CaSO4→CaS+CO2, CaS+3CaSO4→4CaO+4SO2. The solid phase temperature in the firing kiln rises from 1170℃ to 1450℃, and a mineralization reaction occurs to generate C3S, C2S, C3A, and C4AF, i.e. 2CaO+SiO2=C2S, 3CaO+SiO2=C3S, 3CaO+Al2O3=C3A, 4CaO+Al2O3+Fe2O3=C4AF, and then enters the clinker storage after being cooled by a grate cooler. The gas phase enters the suspension preheater from 1600℃ at the head of the firing kiln to 1010℃ at the tail of the decomposition kiln. After heat exchange with the raw material in the suspension preheater, it enters the gas-solid separator from C1. When it leaves the gas-solid separator, the temperature is 326℃ and the SO2 gas concentration is 9.47%. The gas phase enters the conversion section of the sulfuric acid workshop after passing through bag dust removal, primary power wave, packing tower, two-stage electric demisting, and drying tower. After oxygen distribution according to the O / S ratio of 1:1, the SO2 gas concentration is 6.42%. The conversion section can only barely achieve the goal of not turning on the electric furnace and cannot produce steam. Once the decomposition condition in the kiln is abnormal, the SO2 gas concentration decreases, and the conversion heat fluctuates, it is necessary to prepare to turn on the electric furnace. During the start-up period, an average of 79t / h of phosphogypsum was processed, 38t / h of sulfuric acid was produced, 4.67t / h of reducing coal (coke, containing 77%-82% residual carbon), and 15.3t / h of standard coal was converted into fuel coal and calcined coal.

[0055] Conclusion: Both method 1 and method 2 have better actual production data than the current industrial production data, especially SO2 gas concentration, which is 70% higher than the existing SO2 gas concentration of 9.47%. The gas concentration has increased significantly after the transformation. The independent heat source calcining furnace has been removed and the heat of the calcining kiln flue gas has been used instead. A medium-pressure preheating system and a low-pressure waste heat system have been added to recover heat. The overall energy consumption of the system is lower, the production economy of the transformed device is better, and the investment in the construction of the acid-making device is also lower.

Claims

1. A method for increasing the concentration of SO2 in a phosphogypsum sulfuric acid production device, characterized in that The process includes the following: (1) The raw material enters the suspension preheater and exchanges heat with the kiln gas separated from the kiln tail of the firing kiln in the suspension preheater; (2) After the raw meal is heated to 700℃-1000℃, the solid phase enters the tail of the decomposition kiln. During the heating period of the suspension preheater, the CaSO4·2H2O and CaSO4·1 / 2H2O contained in the raw meal are dehydrated to become CaSO4, and the carbonate in the raw meal is decomposed into CO2; (3) The kiln gas exchanges heat with the raw material in the suspension preheater to cool it down, and takes away the CO2, free water and crystal water in the phosphogypsum decomposed in the raw material; (4) After the raw material enters the decomposition kiln, the temperature is gradually raised to 1150℃-1200℃ to complete the first two steps of reduction reaction, i.e. 2C+CaSO4→CaS+CO2, CaS+3CaSO4→4CaO+4SO2, and then the solid phase enters the firing kiln; (5) The solid phase undergoes mineralization reaction in the firing kiln at a temperature of 1200°C to 1450°C to form cement clinker; (6) Coal injection and air combustion at the kiln head provide the heat required for solid phase mineralization and maintain the solid phase temperature near the coal injection gun at 1450±10℃; (7) After the kiln gas phase reaches the kiln tail from the kiln head, part of the heat enters the suspension preheater to provide the heat required for raw material drying, and the other part goes to the decomposition kiln to provide the heat energy required for the decomposition of phosphogypsum. The opening degree of valve A depends on the temperature of the raw material entering the decomposition kiln tail from the suspension preheater, which is controlled at 700℃-1000℃; (8) The kiln gas at the tail of the decomposition kiln is heat exchanged to recover heat energy, and then dusted and purified before entering the sulfuric acid plant to produce sulfuric acid.

2. A method for increasing the SO2 concentration in a phosphogypsum sulfuric acid production device according to claim 1, characterized in that: In step (1), the free water content of the raw material and the crystal water content of the phosphogypsum are controlled within the range of 0.2%-4.5%.

3. A method for increasing the SO2 concentration in a phosphogypsum sulfuric acid production device according to claim 1, characterized in that: In step (3), the kiln gas tail washing can be calcium washing, ammonia washing, hydrogen peroxide washing, or a new catalytic flue gas desulfurization technology, and the free water content of the phosphogypsum dried is ≤3%.

4. A method for increasing the SO2 concentration in a phosphogypsum sulfuric acid production device according to claim 1, characterized in that: In step (4), coal is sprayed at the head of the decomposition kiln and air is burned to supplement the heat required for the decomposition of phosphogypsum and maintain the solid phase temperature at the head of the decomposition kiln between 1150°C and 1200°C.

5. The method for increasing the SO2 concentration in a phosphogypsum sulfuric acid production device according to claim 1, characterized in that: In step (7), valve A is mainly used to control the solid phase temperature from the suspension preheater to the end of the decomposition kiln between 700°C and 1000°C, rather than mainly supplying heat to the head of the decomposition kiln.

6. A method for increasing the SO2 concentration in a phosphogypsum sulfuric acid production device according to claim 1, characterized in that: In step (8), medium-pressure steam can be produced after heat exchange of the heat energy of the flue gas at the tail of the decomposition kiln.

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