Method and apparatus for preparing calcium silicate aggregate, sulfuric acid and CO2 by oxygen-enriched high-temperature decomposition of phosphogypsum

Abstract

The application belongs to the technical field of solid waste resource utilization, and specifically discloses a method and device for preparing silicon-calcium aggregate, sulfuric acid and CO2 by phosphogypsum oxygen-rich high-temperature decomposition. The method uses the adsorption method to obtain pure nitrogen products and oxygen-rich combustion-supporting gas, and provides different reaction temperatures and reaction atmospheres for different reaction stages of the rotary kiln reactor through the multi-point combustion mode, thereby ensuring the controllable high-temperature environment and atmosphere in the kiln. The method improves the combustion efficiency, greatly reduces the amount of flue gas after decomposition, effectively improves the concentration of SO2 in the flue gas and the efficiency of the subsequent sulfuric acid preparation system, and realizes CO2 emission reduction and resource utilization by using the CO2-rich tail gas of the sulfuric acid preparation system for adsorption recovery. The application also provides a device for realizing the method, which combines gas adsorption, oxygen-rich combustion and rotary kiln multi-point combustion equipment, thereby ensuring the effective realization of the process.

Description

Technical Field

[0001] This invention belongs to the technical field of solid waste resource utilization, specifically relating to a method and apparatus for preparing silicon-calcium aggregate, sulfuric acid and CO2 by oxygen-enriched high-temperature decomposition of phosphogypsum. Background Technology

[0002] my country's phosphorus chemical industry is mainly located in phosphate rock producing areas, including Yunnan, Guizhou, Hubei, Chongqing and Sichuan, all along the Yangtze River. The process of preparing phosphoric acid from phosphate rock generates a large amount of phosphogypsum solid waste, which is mainly composed of calcium sulfate dihydrate. However, the incompletely decomposed phosphate rock, residual phosphoric acid, fluorides, acid-insoluble substances, organic matter and other substances contained in it will have an impact on the environment and urgently need to be treated.

[0003] Currently, the main uses of phosphogypsum include cement retarder, gypsum board, gypsum blocks, and gypsum mortar. Cement retarder is the largest user, requiring 3-5% gypsum addition to cement, with an annual demand of 50-60 million tons. However, power plants typically have cement grinding stations to locally utilize fly ash and desulfurized gypsum; therefore, the gypsum used in cement retarder is primarily desulfurized gypsum, where phosphogypsum has no advantage. Furthermore, due to the concentrated production and output of phosphogypsum, the low added value of gypsum building materials, and the small market radius, the expansion of the gypsum building materials market is severely restricted.

[0004] Currently, phosphogypsum is also used in mining backfill, road construction materials, soil conditioners, inorganic functional materials, and the decomposition of gypsum to produce cement and sulfuric acid. Among these, the technology for producing cement and sulfuric acid through gypsum decomposition is undoubtedly the most competitive. The decomposed sulfuric acid can be directly reused, forming a sulfuric acid cycle, and cement is the largest building material product with high demand. However, phosphogypsum decomposition technology currently suffers from several problems, including high heat loss in rotary kiln reactors, susceptibility to scaling, and low SO2 concentration. These issues result in high sulfuric acid production costs that are unaffordable for enterprises, limiting the widespread application of gypsum-based sulfuric acid production technology. Summary of the Invention

[0005] This invention provides a method and apparatus for preparing silicon-calcium aggregate, sulfuric acid, and CO2 by oxygen-enriched high-temperature decomposition of phosphogypsum. By adding oxygen-enriched gas for combustion and using multi-point combustion to provide heat to the rotary kiln, the efficiency is improved, the concentration of SO2 in the flue gas is increased, and the efficiency of the subsequent sulfuric acid preparation system is also improved. Furthermore, the CO2-rich tail gas from sulfuric acid preparation can be adsorbed and recovered, thereby achieving CO2 emission reduction and resource utilization.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing calcium silicate aggregate, sulfuric acid, and CO2 by oxygen-enriched high-temperature decomposition of phosphogypsum, comprising the following steps:

[0007] S1. After crushing the coke powder, mix it evenly with phosphogypsum and water to make a slurry. Then filter and dehydrate it. The filter residue is dried in a dryer to obtain a mixture of phosphogypsum and coke.

[0008] After preheating, the mixture of S2 and S1 is sent to a rotary kiln for high-temperature decomposition. At the same time, nitrogen is produced by using outside air, and the remaining gas is used to prepare oxygen. The oxygen-enriched gas is then sent to the rotary kiln, where the phosphogypsum is decomposed at high temperature under oxygen-enriched conditions to obtain calcium silicate aggregate.

[0009] The high-temperature flue gas discharged from the S3 and S2 rotary kilns is used to preheat the mixture obtained from S1. After heat exchange, it undergoes dust removal and purification treatment, and then enters the SO2 converter and sulfuric acid absorption tower for reaction and absorption to obtain sulfuric acid products. The tail gas after absorption enters CO2 adsorption to obtain CO2 products.

[0010] Furthermore, the particle size of the crushed coke is 100-200 mesh, including but not limited to 100 mesh, 120 mesh, 140 mesh, 160 mesh, 180 mesh, or 200 mesh. The mass ratio of phosphogypsum to coke is 10:1~2; including but not limited to 10:1, 10:1.3, 10:1.5, 10:1.6, 10:1.8, or 5:1. The fixed carbon content in the coke powder is greater than 80%, and the silica content is less than 10%.

[0011] The solid-liquid ratio for mixing with water is 1:2 to 3, including but not limited to 1:2.0, 1:2.2, 1:2.4, 1:2.6, 1:2.8, or 1:3.0. The drying temperature is 150-200℃, including but not limited to 150℃, 160℃, 170℃, 180℃, 190℃, or 200℃. The mixture is dried until the moisture content is 5-9wt%, including but not limited to 5%, 6%, 7%, 8%, or 9%.

[0012] Furthermore, the preheating treatment in S2 uses high-temperature flue gas discharged from the gas phase outlet of the rotary kiln, with a temperature of 400-500℃. After preheating, the moisture content of the mixture is below 3wt%, and the preheated flue gas is then purified by dust removal.

[0013] Furthermore, the calcination temperature within the rotary kiln is 1100-1300℃; for example, 1100℃, 1150℃, 1200℃, 1250℃, and 1300℃. The calcination time is 60-90 minutes. The high temperature of the rotary kiln is provided by the combustion of fuel within the kiln, with oxygen-enriched fuel introduced simultaneously. The oxygen content of this oxygen-enriched fuel is 70-80 vol%. The fuel required for the high-temperature reaction calcination is coal, natural gas, diesel oil, etc. Preferably, the combustion temperature is 1700-1800℃, for example, 1700℃, 1720℃, 1740℃, 1760℃, 1780℃, and 1800℃.

[0014] Furthermore, both fuel and oxygen enrichment are introduced from the kiln head and the middle section of the rotary kiln, with the amount of fuel introduced from the kiln head and the middle section each accounting for 50%, and the amount of oxygen enrichment added from the kiln head section being 80 vol% and the amount added from the middle section being 20 vol%.

[0015] Furthermore, steam is added to the kiln head at a rate of 5-10 vol% of the total oxygen-enriched gas. This indirectly increases the carbon monoxide and hydrogen content in the reactor, typically controlled at 0.1-0.5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%.

[0016] Furthermore, before the oxygen-enriched material enters the rotary kiln, it exchanges heat with the calcium silicate aggregate discharged from the rotary kiln; after the heat exchange, the temperature of the calcium silicate aggregate is 150~200℃, and the temperature of the oxygen-enriched material is 150~200℃.

[0017] The present invention also relates to an apparatus for preparing calcium silicate aggregate, sulfuric acid and CO2 by oxygen-enriched high-temperature decomposition of phosphogypsum using the method described above. The apparatus includes a slurry tank, a slurry filter, a dryer, a cyclone preheating system and a rotary kiln connected in sequence. The rotary kiln is provided with a fuel injection pipe and an oxygen-enriched injection pipe at the kiln head and in the middle. The kiln head is also provided with a calcium silicate aggregate outlet. The gas phase outlet at the kiln tail is connected to a dust collector after passing through the cyclone preheating system, and then connected in sequence to a sulfuric acid preparation system and a CO2 adsorber production system.

[0018] Furthermore, the device also includes an oxygen enrichment preparation system, which consists of an air compressor, an adsorption nitrogen generator, a residual gas collection tank, a residual gas compressor, an adsorption oxygen generator, and an oxygen enrichment collection tank connected in sequence. The gas in the oxygen enrichment collection tank enters the rotary kiln after heat exchange with the discharge cooler of the rotary kiln.

[0019] Furthermore, the cyclone preheating system is a multi-stage cyclone preheater connected in series.

[0020] The present invention has the following beneficial effects:

[0021] 1. In the processing of phosphogypsum, this invention incorporates coke powder as a reducing agent. By adding water to form a slurry, the phosphogypsum and coke powder can be thoroughly mixed and more tightly bound. Later, steam and oxygen-rich water are added to the rotary kiln, creating a controllable and more uniform reducing atmosphere in the reduction section of the kiln. This atmosphere facilitates a gas-solid reaction with the phosphogypsum, increasing the reaction rate. The crushed coke powder is then slurried together with the phosphogypsum filter cake. After slurrying, the material is filtered and dried, and then dehydrated at 150-200℃ to remove free water and water of crystallization, yielding a mixture of gypsum and coke particles.

[0022] 2. The gypsum and coke mixture particles are preheated in a cyclone preheater before entering the rotary kiln for calcination and decomposition.

[0023] 3. Both fuel and oxygen enrichment are added from the front and middle sections of the rotary kiln, with a larger amount of oxygen enrichment added in the front section and a smaller amount in the middle section. The purpose of adding excessive oxygen enrichment in the front section is to reduce the combustion temperature and avoid the impact of excessively high temperatures on the refractory materials inside the rotary kiln, thus preventing damage to the refractory materials. This achieves the use of multi-point combustion to provide different reaction temperatures and atmospheres for different reaction stages in the rotary kiln reactor. The oxygen enrichment in this invention is obtained by enriching the residual gas after nitrogen production from external air through an oxygen adsorption device. The obtained oxygen enrichment is first used as a cooling medium to cool the solid materials obtained from the decomposition of materials in the rotary kiln reactor, and then it is preheated itself. Then, it is fully mixed with the fuel in the rotary kiln and injected into the rotary kiln for combustion. At the same time, a portion of water vapor is introduced to adjust the temperature and regulate the atmosphere. The phosphogypsum and coke powder preheated in the rotary kiln reactor can be effectively decomposed under high-temperature reaction conditions to obtain silicon-calcium aggregate. This invention utilizes adsorption to obtain pure nitrogen products while simultaneously producing oxygen-rich combustion-supporting gas. This improves combustion efficiency, significantly reduces the amount of flue gas after decomposition, and effectively increases the SO2 concentration in the flue gas, thereby enhancing the efficiency of the subsequent sulfuric acid preparation system. The tail gas after sulfuric acid preparation is rich in CO2, which can be used as a high-quality raw material for CO2 production through adsorption, achieving both CO2 emission reduction and resource utilization.

[0024] 4. The rotary kiln reactor in this invention uses a fuel mixing pipe rotary joint to introduce fuel and oxygen-enriched oxygen into the fuel mixing pipe, which effectively avoids the impact of ultra-high temperature under oxygen enrichment on the refractory materials inside the rotary kiln and ensures controllability of the kiln atmosphere. Attached Figure Description

[0025] Figure 1 This is a process flow diagram from Example 1.

[0026] Figure 2 This is a schematic diagram of the device structure involved in the present invention.

[0027] The components include: 1. Coke crusher; 2. Mixing and slurry tank; 3. Mixing and slurry pump; 4. Slurry filter; 5. Filter cake crusher; 6. Rotary flash dryer; 7. Drying cyclone separator; 8. Drying bag filter; 9. Drying induced draft fan; 10. Mixing conveyor; 11. Primary cyclone preheater; 12. Secondary cyclone preheater; 13. Tertiary cyclone preheater; 14. Quaternary cyclone preheater; 15. Rotary kiln reactor; 16. Air compressor; 17. Adsorption nitrogen generator; 18. Nitrogen collection tank. 19. Waste gas collection tank; 20. Waste gas compressor; 21. Adsorption oxygen generator; 22. Oxygen-enriched collection tank; 23. Combustion fan; 24. Fuel mixing pipe rotary joint; 25. Fuel mixing rotary pipe; 26. Discharge cooler; 27. Electrostatic precipitator; 28. Sulfuric acid induced draft fan; 29. ​​Flue gas scrubber; 30. SO2 converter; 31. Sulfuric acid dryer; 32. Sulfuric acid absorption tower; 33. Tail gas dehydrator; 34. Tail gas compressor; 35. CO2 adsorber; 36. CO2 collection tank. Detailed Implementation

[0028] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0029] This invention relates to a method and apparatus for preparing calcium silicate aggregate, sulfuric acid, and CO2 by oxygen-enriched high-temperature decomposition of phosphogypsum. A schematic diagram of the apparatus is shown below. Figure 2 The specific process flow is as follows: Figure 1 .

[0030] The device includes a coke crusher 1, whose outlet is connected to the inlet of a mixing slurry tank 2. The outlet of the mixing slurry tank 2 is connected to the inlet of a slurry filter 4 via a mixing slurry pump 3. The liquid outlet of the slurry filter 4 is connected to the return port of the mixing slurry tank 2, enabling recycling. The solid outlet of the slurry filter 4 is connected to the solid inlet of a rotary flash dryer 6 after passing through a filter cake crusher 5. The outlet of the rotary flash dryer 6 is connected to the inlet of a drying cyclone separator 7. The gas from the drying cyclone separator 7 is connected to a drying induced draft fan 9 via a drying bag filter 8 and is finally discharged into the atmosphere.

[0031] The solid outlets of the drying cyclone separator 7 and the drying bag filter 8 are connected to the inlet of the mixing conveyor 10. The outlet of the mixing conveyor 10 is connected to the inlet of the primary cyclone preheater 11. The solid outlet of the primary cyclone preheater 11 is connected to the gas inlet pipe of the secondary cyclone preheater 12. The gas outlet of the secondary cyclone preheater 12 is connected to the inlet of the primary cyclone preheater 11. The solid outlet of the secondary cyclone preheater 12 is connected to the gas inlet pipe of the tertiary cyclone preheater 13. The gas outlet of the tertiary cyclone preheater 13 is connected to the inlet of the secondary cyclone preheater 12. The solid outlet of the tertiary cyclone preheater 13 is connected to the gas inlet pipe of the quaternary cyclone preheater 14. The gas outlet of the quaternary cyclone preheater 14 is connected to the inlet of the tertiary cyclone preheater 13. The solid outlet of the quaternary cyclone preheater 14 is connected to the solid inlet of the rotary kiln reactor 15.

[0032] The outlet of air compressor 16 is connected to the inlet of adsorption nitrogen generator 17. The nitrogen outlet of adsorption nitrogen generator 17 is connected to the inlet of nitrogen collection tank 18. The residual gas outlet of adsorption nitrogen generator 17 is connected to the inlet of residual gas collection tank 19. The outlet of residual gas collection tank 19 is connected to the inlet of residual gas compressor 20. The outlet of residual gas compressor 20 is connected to the inlet of adsorption oxygen generator 21. The outlet of adsorption oxygen generator 21 is connected to the inlet of oxygen-enriched collection tank 22. The outlet of oxygen-enriched collection tank 22 is connected to the inlet of combustion blower 23. The outlet of combustion blower 23 is connected to the inlet of discharge cooler 26 at the discharge port of rotary kiln. The gas outlet of discharge cooler 26 is connected to the inlet of fuel burner in rotary kiln reactor 15 and the inlet of fuel mixing pipe rotary joint 24. The outlet of fuel mixing pipe rotary joint 24 is connected to the inlet pipe of fuel mixing rotary pipe 25.

[0033] The gas outlet of rotary kiln reactor 15 is connected to the inlet of the fourth-stage cyclone preheater 14. The outlet of the first-stage cyclone preheater 11 is connected to the inlet of the electrostatic precipitator 27. The solid outlet of the electrostatic precipitator 27 is connected to the inlet pipe of the fourth-stage cyclone preheater 14. The outlet of the electrostatic precipitator 27 is connected to the inlet of the acid-producing induced draft fan 28. The outlet of the acid-producing induced draft fan 28 is connected to the inlet of the flue gas scrubber 29. The outlet of the flue gas scrubber 29 is connected to the inlet of the SO2 converter 30. The outlet of the SO2 converter 30 is connected to the inlet of the sulfuric acid dryer 31. The outlet of the sulfuric acid dryer 31 is connected to the inlet of the sulfuric acid absorption tower 32. The gas outlet of the sulfuric acid absorption tower 32 is connected to the inlet of the tail gas dehydrator 33. The outlet of the tail gas dehydrator 33 is connected to the inlet of the tail gas compressor 34. The outlet of the tail gas compressor 34 is connected to the inlet of the CO2 adsorber 35. The outlet of the CO2 adsorber 35 is connected to the inlet of the CO2 collection tank 36.

[0034] The phosphogypsum and desulfurization gypsum used in this invention are from a domestic company. The main components of the phosphogypsum are shown in Table 1 below.

[0035] Table 1

[0036]

[0037] The coke used in this invention comes from a domestic company, and its main components are shown in Table 2 below.

[0038] Table 2

[0039]

[0040] Example 1: Method and apparatus for preparing calcium silicate aggregate, sulfuric acid, and CO2 by oxygen-enriched high-temperature decomposition of phosphogypsum.

[0041] 60 kg of coke powder (100 mesh) pulverized by a coke pulverizer was added to a mixing slurry tank. 1000 kg of phosphogypsum filter cake (80% calcium sulfate content in solid form, 40% water content) was added to the mixing slurry tank equipped with an agitator. The mixing slurry tank was constructed of acid-resistant bricks. 2000 kg of industrial water was added to the mixing slurry tank, with a solid-liquid ratio of 1:2. The mass ratio of anhydrous phosphogypsum to coke powder was 10:1. The mixture was stirred and mixed for 60 minutes. Then, the material was pumped to a slurry filter equipped with a diaphragm press and air blowing system for solid-liquid separation to obtain filter cake and filtrate. The filtrate can be directly recycled or the phosphorus can be recovered and reused. The filter cake, a mixture of phosphogypsum and coke, is crushed by a filter cake crusher and then conveyed to a rotary flash dryer. It undergoes drying and dehydration through heat exchange with 400°C high-temperature flue gas. The dehydrated gypsum has a moisture content of 6%, essentially being hemihydrate gypsum. It then enters a series of cyclone preheaters (stages 1, 2, 3, and 4) for preheating before entering the tail of the rotary kiln reactor. Outside air enters an adsorption nitrogen generator to obtain 99.5% pure nitrogen. The remaining gas, with an O2 content of 30%, is buffered and then enters an adsorption oxygen generator to prepare oxygen-enriched gas. When the O2 content reaches 70%, it is first used as combustion air and undergoes countercurrent heat exchange with the solid reaction products of the rotary kiln in a cooler. The solid material is cooled to 180°C, yielding 300 kg of calcium silicate aggregate, containing 60% calcium oxide and 35% silicon dioxide. The sulfuric acid content is 0.9%, and the thermal decomposition rate of calcium sulfate reaches 99.4%. The temperature of the oxygen-enriched gas after heat exchange with the solid material is 200℃. It is injected into the rotary kiln reactor together with pulverized coal as fuel for combustion. The fuel amount in the burner at the kiln head is 50%, and the oxygen-enriched gas injection amount is 80%. The fuel combustion temperature is 1700℃, and the temperature at the kiln head of the rotary kiln is 1200℃. At the same time, 0.5 MPa of water vapor is injected together with the fuel. The amount of water vapor is 10% of the amount of combustion air. The increase in the amount of water vapor changes the calcination atmosphere and indirectly increases the CO + hydrogen content to 0.1%. 50% fuel and 20% oxygen-enriched gas enter the fuel mixing rotary pipe through the rotary joint of the fuel mixing pipe and are injected into the middle position of the rotary kiln reactor. The high-temperature flue gas containing SO2 is cooled to below 400℃ after heat exchange with a mixture of phosphogypsum and coke powder, with an SO2 content of 20%. It then enters an electrostatic precipitator, and is further purified by a wet scrubber by an acid-producing fan. After that, it enters a gas drying tower for dehydration, then enters an SO2 converter to become SO3, and finally enters a sulfuric acid absorption tower to obtain 320 kg of 98% sulfuric acid. The tail gas is further dried and then enters a CO2 adsorber to prepare pure CO2 with a content of 99%.

[0042] Example 2

[0043] 66.7 kg of coke powder with a fixed carbon content greater than 80%, a silica content less than 10%, and a coke pulverizer fineness of 120 mesh was added to a mixing slurry tank. 1000 kg of phosphogypsum filter cake with a calcium sulfate content (calcium sulfate content in solids) of 85% (moisture content of 40%) was added to a mixing slurry tank equipped with an agitator. This mixing slurry tank was constructed of acid-resistant bricks. 2500 kg of industrial water was added to the mixing slurry tank, resulting in a solid-liquid ratio of 1:2.5 and a solid-to-coke powder mass ratio of 9:1. The mixture was stirred and mixed for 60 minutes. Then, the material was pumped to a slurry filter equipped with a diaphragm press and air blowing system for solid-liquid separation to obtain filter cake and filtrate. The filtrate can be directly recycled or recycled after phosphorus recovery. The filter cake, a mixture of phosphogypsum and coke, is crushed by a filter cake crusher and then conveyed to a rotary flash dryer. It undergoes heat exchange with 450°C high-temperature flue gas to achieve drying and dehydration. The dehydrated gypsum has a moisture content of 4%, consisting primarily of hemihydrate and anhydrous gypsum. It then enters a series of cyclone preheaters (stages 1, 2, 3, and 4) for preheating before entering the tail of the rotary kiln reactor. Outside air enters an adsorption nitrogen generator to obtain 99.5% pure nitrogen. The remaining gas, with an O2 content of 32%, is buffered and then enters an adsorption oxygen generator to prepare oxygen-enriched gas. When the O2 content reaches 72%, it is first used as combustion air and undergoes countercurrent heat exchange with the solid reaction products of the rotary kiln in a cooler. The solid material is cooled to 200°C, yielding 320 kg of calcium silicate aggregate, with a calcium oxide content of 61% and a silicon dioxide content of 33%. The sulfuric acid content is 0.7%, and the thermal decomposition rate of calcium sulfate reaches 99.6%. The oxygen-enriched temperature after heat exchange with solid materials is 150℃. It is injected into the rotary kiln reactor along with pulverized coal as fuel for combustion. The fuel amount in the burner at the kiln head is 50%, and the oxygen-enriched amount is 80%. The fuel combustion temperature is 1720℃, and the temperature at the kiln head of the rotary kiln is 1220℃. At the same time, 0.5 MPa of water vapor is injected along with the fuel. The amount of water vapor is 8% of the amount of combustion air. The increase in the amount of water vapor changes the calcination atmosphere and indirectly increases the CO + hydrogen content to 0.12%. 50% fuel and 20% oxygen-enriched oxygen enter the fuel mixing rotary pipe through the rotary joint of the fuel mixing pipe and are injected into the middle position of the rotary kiln reactor. The high-temperature flue gas containing SO2 is cooled to below 400℃ after heat exchange with a mixture of phosphogypsum and coke powder, with an SO2 content of 22%. It then enters an electrostatic precipitator, and is further purified by a wet scrubber by an acid-producing fan. After that, it enters a gas drying tower for dehydration, then enters an SO2 converter to become SO3, and finally enters a sulfuric acid absorption tower to obtain 325 kg of 98% sulfuric acid. The tail gas is further dried and then enters a CO2 adsorber to prepare pure CO2 with a content of 99%.

[0044] Example 3

[0045] 65 kg of coke powder with a fixed carbon content greater than 80%, a silica content less than 10%, and a coke pulverizer fineness of 140 mesh was added to a mixing slurry tank. 1000 kg of phosphogypsum filter cake with a calcium sulfate content (calcium sulfate content in solids) of 90% (moisture content of 35%) was added to a mixing slurry tank equipped with an agitator. This mixing slurry tank was constructed of acid-resistant bricks. 3000 kg of industrial water was added to the mixing slurry tank, resulting in a solid-liquid ratio of 1:3 and a solid-to-coke powder mass ratio of 10:1. The mixture was stirred and mixed for 40 minutes. Then, the material was pumped to a slurry filter equipped with a diaphragm press and air blowing system for solid-liquid separation to obtain filter cake and filtrate. The filtrate can be directly recycled or recycled for phosphorus recovery and reuse. The filter cake, a mixture of phosphogypsum and coke, is crushed by a filter cake crusher and then conveyed to a rotary flash dryer. It undergoes drying and dehydration through heat exchange with 500°C high-temperature flue gas. The dehydrated gypsum has a moisture content of 3.6%, consisting primarily of hemihydrate and anhydrous gypsum. It then enters a series of cyclone preheaters (stages 1, 2, 3, and 4) for preheating before entering the tail of the rotary kiln reactor. Outside air enters an adsorption nitrogen generator to obtain 99.5% pure nitrogen. The remaining gas, with an O2 content of 35%, is buffered and then enters an adsorption oxygen generator to prepare oxygen-enriched gas. When the O2 content reaches 75%, it is first used as combustion air and undergoes countercurrent heat exchange with the solid reaction products of the rotary kiln in a cooler. The solid material is cooled to 200°C, yielding 335 kg of calcium silicate aggregate, with a calcium oxide content of 71.6% and a silicon dioxide content of 26%. The calcium sulfate content is 0.7%, and the thermal decomposition rate of calcium sulfate reaches 99.6%. The temperature of the oxygen-enriched gas after heat exchange with the solid material is 170℃. It is injected into the rotary kiln reactor together with pulverized coal as fuel for combustion. The fuel amount in the burner at the kiln head is 50%, and the oxygen-enriched gas injection amount is 80%. The fuel combustion temperature is 1730℃, and the temperature at the kiln head of the rotary kiln is 1240℃. At the same time, 0.5 MPa of water vapor is injected together with the fuel. The amount of water vapor is 10% of the amount of combustion air. The increase in the amount of water vapor changes the calcination atmosphere and indirectly increases the CO + hydrogen content to 0.20%. 50% fuel and 20% oxygen-enriched gas enter the fuel mixing rotary pipe through the rotary joint of the fuel mixing pipe and are injected into the middle position of the rotary kiln reactor. The high-temperature flue gas containing SO2 is cooled to below 400℃ after heat exchange with a mixture of phosphogypsum and coke powder, with an SO2 content of 25%. It then enters an electrostatic precipitator, and is further purified by a wet scrubber by an acid-producing fan. After that, it enters a gas drying tower for dehydration, then enters an SO2 converter to become SO3, and finally enters a sulfuric acid absorption tower to obtain 420 kg of 98% sulfuric acid. The tail gas is further dried and then enters a CO2 adsorber to prepare pure CO2 with a content of 99.2%.

[0046] Example 4

[0047] 70 kg of coke powder with a fixed carbon content greater than 80%, a silica content less than 10%, and a coke pulverizer fineness of 200 mesh was added to a mixing slurry tank. 1000 kg of phosphogypsum filter cake with a calcium sulfate content (calcium sulfate content in solids) of 95% (moisture content of 35%) was added to a mixing slurry tank equipped with an agitator. The mixing slurry tank was constructed of acid-resistant bricks. 3000 kg of industrial water was added to the mixing slurry tank, resulting in a solid-liquid ratio of 1:3 and a solid-to-coke powder mass ratio of 9:1. The mixture was stirred and mixed for 60 minutes. Then, the material was pumped to a slurry filter equipped with a diaphragm press and air blowing system for solid-liquid separation to obtain filter cake and filtrate. The filtrate can be directly recycled or recycled for phosphorus recovery and reuse. The filter cake, a mixture of phosphogypsum and coke, is crushed by a filter cake crusher and then conveyed to a rotary flash dryer. It undergoes drying and dehydration through heat exchange with 500℃ high-temperature flue gas. The dehydrated gypsum has a moisture content of 3.0%, consisting primarily of hemihydrate and anhydrous gypsum. It is then preheated in four stages of cyclone preheaters before entering the tail of the rotary kiln reactor. Outside air enters an adsorption nitrogen generator to obtain 99.0% pure nitrogen. The remaining gas, with an O2 content of 32%, is buffered and then enters an adsorption oxygen generator to prepare oxygen-enriched gas. Once the O2 content reaches 80%, it is first used as combustion air and undergoes countercurrent heat exchange with the solid reaction products of the rotary kiln in a cooler. The solid material is cooled to 200℃, yielding 350 kg of calcium silicate aggregate, with a calcium oxide content of 81.6% and a silicon dioxide content of 17.0%. The sulfuric acid content is 0.6%, and the thermal decomposition rate of calcium sulfate reaches 99.6%. The temperature of the oxygen-enriched gas after heat exchange with the solid material is 200℃. It is injected into the rotary kiln reactor together with pulverized coal as fuel for combustion. The fuel amount in the burner at the kiln head is 50%, and the oxygen-enriched gas injection amount is 80%. The fuel combustion temperature is 1700℃, and the temperature at the kiln head of the rotary kiln is 1160℃. At the same time, 0.5 MPa of water vapor is injected together with the fuel. The amount of water vapor is 6% of the amount of combustion air. The increase in the amount of water vapor changes the calcination atmosphere and indirectly increases the CO + hydrogen content to 0.10%. 50% fuel and 20% oxygen-enriched gas enter the fuel mixing rotary pipe through the rotary joint of the fuel mixing pipe and are injected into the middle position of the rotary kiln reactor. The high-temperature flue gas containing SO2 is cooled to below 400℃ after heat exchange with a mixture of phosphogypsum and coke powder, with an SO2 content of 23%. It then enters an electrostatic precipitator, and is subsequently sent to a wet scrubber by an acid-producing fan for further dust removal and purification. It then enters a gas drying tower for dehydration, and then enters an SO2 converter to become SO3. Finally, it enters a sulfuric acid absorption tower for absorption to obtain 440 kg of 98% sulfuric acid. The tail gas is further dried and then enters a CO2 adsorber to prepare pure CO2 with a content of 99.2%.

[0048] Example 5

[0049] 70 kg of coke powder with a fixed carbon content greater than 80%, a silica content less than 10%, and a coke pulverizer fineness of 160 mesh was added to a mixing slurry tank. 1000 kg of phosphogypsum filter cake with a calcium sulfate content (calcium sulfate content in solids) of 85% (moisture content of 40%) was added to a mixing slurry tank equipped with an agitator. This mixing slurry tank was constructed of acid-resistant bricks. 3000 kg of industrial water was added to the mixing slurry tank, resulting in a solid-liquid ratio of 1:3. The mass ratio of solid calcium sulfate to coke powder was 8.5:1. The mixture was stirred and mixed for 30 minutes. Then, the material was pumped to a slurry filter equipped with a diaphragm press and air blowing system for solid-liquid separation to obtain filter cake and filtrate. The filtrate can be directly recycled or recycled after phosphorus recovery. The filter cake, a mixture of phosphogypsum and coke, is crushed by a filter cake crusher and then conveyed to a rotary flash dryer. It undergoes drying and dehydration through heat exchange with 400℃ high-temperature flue gas. The dehydrated gypsum has a moisture content of 5.0%, consisting primarily of hemihydrate and anhydrous gypsum. It is then preheated in four stages of cyclone preheaters before entering the tail of the rotary kiln reactor. Outside air enters an adsorption nitrogen generator to obtain 99.3% pure nitrogen. The remaining gas, with an O2 content of 31%, is buffered and then enters an adsorption oxygen generator to prepare oxygen-enriched gas. The oxygen content reaches 72%, which is first used as combustion air and undergoes countercurrent heat exchange with the solid reaction products of the rotary kiln in a cooler. The solid material is cooled to 150℃, yielding 320 kg of calcium silicate aggregate, with a calcium oxide content of 65.6% and a silicon dioxide content of 30.2%. The calcium sulfate content is 1.2%, and the thermal decomposition rate of calcium sulfate reaches 99.2%. The temperature of the oxygen-enriched gas after heat exchange with the solid material is 150℃. It is injected into the rotary kiln reactor together with pulverized coal as fuel for combustion. The fuel amount in the burner at the kiln head is 50%, and the oxygen-enriched gas injection amount is 80%. The fuel combustion temperature is 1800℃, and the temperature at the kiln head of the rotary kiln is 1300℃. At the same time, 0.5 MPa of water vapor is injected together with the fuel. The amount of water vapor is 10% of the amount of combustion air. The increase in the amount of water vapor changes the calcination atmosphere and indirectly increases the CO + hydrogen content to 0.15%. 50% fuel and 20% oxygen-enriched gas enter the fuel mixing rotary pipe through the rotary joint of the fuel mixing pipe and are injected into the middle position of the rotary kiln reactor. The high-temperature flue gas containing SO2 is cooled to below 400℃ after heat exchange with a mixture of phosphogypsum and coke powder, with an SO2 content of 23%. It then enters an electrostatic precipitator, and is subsequently sent to a wet scrubber by an acid-producing fan for further dust removal and purification. It then enters a gas drying tower for dehydration, and then enters an SO2 converter to become SO3. Finally, it enters a sulfuric acid absorption tower for absorption to obtain 365 kg of 98% sulfuric acid. The tail gas is further dried and then enters a CO2 adsorber to prepare pure CO2 with a content of 99.0%.

[0050] Comparative Example 1

[0051] 1000 kg of phosphogypsum filter cake with a calcium sulfate content of 85% (moisture content of 40%) was dried until the moisture content was below 10%. 70 kg of coke powder (crushed to a fineness of 160 mesh using a coke pulverizer) with a fixed carbon content greater than 80% and a silica content less than 10% was mixed with the dried phosphogypsum. The mass ratio of solid calcium sulfate to coke powder was 8.5:1. The mixture was then fed into a rotary flash dryer where it was dried and dehydrated through heat exchange with 400℃ high-temperature flue gas. The dehydrated gypsum had a moisture content of 5.0%. The gypsum, primarily composed of hemihydrate and anhydrous gypsum, is preheated in four stages (primarily cyclone preheaters) before entering the rotary kiln reactor at the kiln tail. Outside air enters the adsorption nitrogen generator to obtain 99.3% pure nitrogen. The remaining air, with an O2 content of 31%, is buffered and then enters the adsorption oxygen generator to prepare oxygen-enriched gas, reaching an O2 content of 72%. This oxygen is first used as combustion air and undergoes countercurrent heat exchange with the solid reaction products of the rotary kiln in a cooler. The solid material is cooled to 150°C, yielding 400 kg of calcium silicate aggregate, containing 45.4% calcium oxide and 24.2% silicon dioxide. The sulfuric acid content is 20.5%, and the thermal decomposition rate of calcium sulfate reaches 83.7%. The temperature of the oxygen-enriched gas after heat exchange with the solid material is 150℃. It is injected into the rotary kiln reactor together with pulverized coal as fuel for combustion. The fuel amount in the burner at the kiln head is 50%, and the oxygen-enriched gas injection amount is 80%. The fuel combustion temperature is 1800℃, and the temperature at the kiln head of the rotary kiln is 1300℃. At the same time, 0.5 MPa of water vapor is injected together with the fuel. The amount of water vapor is 10% of the amount of combustion air. The increase in the amount of water vapor changes the calcination atmosphere and indirectly increases the CO + hydrogen content to 0.15%. 50% fuel and 20% oxygen-enriched gas enter the fuel mixing rotary pipe through the rotary joint of the fuel mixing pipe and are injected into the middle position of the rotary kiln reactor. The high-temperature flue gas containing SO2 is cooled to below 400℃ after heat exchange with a mixture of phosphogypsum and coke powder, with an SO2 content of 12%. It then enters an electrostatic precipitator, and is subsequently sent to a wet scrubber by an acid-producing fan for further dust removal and purification. It then enters a gas drying tower for dehydration, and then enters an SO2 converter to become SO3. Finally, it enters a sulfuric acid absorption tower for absorption to obtain 185 kg of 98% sulfuric acid. The tail gas is further dried and then enters a CO2 adsorber to prepare pure CO2 with a content of 99.0%.

[0052] Comparative Example 2

[0053] The specific method is the same as in Example 5, except that both fuel and oxygen are added from the kiln head, resulting in 360 kg of calcium silicate aggregate, with a calcium oxide content of 55.2%, a silicon dioxide content of 26.3%, a sulfate content of 10.6%, a calcium sulfate thermal decomposition rate of 92.0%, and an SO2 content of 18%. The aggregate is then fed into an electrostatic precipitator and then into a wet scrubber by an acid-producing fan for further dust removal and purification. It then enters a gas drying tower for dehydration, then enters an SO2 converter to become SO3, and finally enters a sulfuric acid absorption tower to absorb the sulfuric acid, yielding 283 kg of 98% sulfuric acid. The exhaust gas is further dried and then enters a CO2 adsorber to prepare pure CO2 with a content of 99.0%.

[0054] The above embodiments describe preferred embodiments of the present invention, but the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other way. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for preparing calcium silicate aggregate, sulfuric acid, and CO2 by oxygen-enriched high-temperature decomposition of phosphogypsum, characterized in that, Includes the following steps: S1. After crushing the coke powder, mix it evenly with phosphogypsum and water to make a slurry. Then filter and dehydrate it. The filter residue is dried in a dryer to obtain a mixture of phosphogypsum and coke. The mixture of S2 and S1 is preheated and then fed into a rotary kiln for high-temperature decomposition. Simultaneously, nitrogen is produced using ambient air, and the remaining gas is used for oxygen enrichment. This oxygen-enriched gas then enters the rotary kiln, causing the phosphogypsum to decompose at high temperature under oxygen-enriched conditions, yielding calcium silicate aggregate. The rotary kiln calcination temperature is 1100-1300℃, and the calcination time is 60-90 minutes. This high temperature is provided by fuel combustion within the rotary kiln, with oxygen-enriched gas introduced simultaneously. The oxygen content of the oxygen-enriched gas is 70-80 vol%. Both fuel and oxygen-enriched gas are introduced from the kiln head and middle sections, respectively. Fuel is introduced at 50% each from the kiln head and middle sections, while oxygen-enriched gas is introduced at 60-80 vol% of the total amount at the kiln head and 20-40 vol% of the total amount at the middle section. The high-temperature flue gas discharged from the S3 and S2 rotary kilns is used to preheat the mixture obtained from S1. After heat exchange, it undergoes dust removal and purification treatment, and then enters the SO2 converter and sulfuric acid absorption tower for reaction and absorption to obtain sulfuric acid products. The tail gas after absorption enters CO2 adsorption to obtain CO2 products.

2. The method according to claim 1, characterized in that: The particle size of the crushed coke is 100-200 mesh; the mass ratio of coke to phosphogypsum is 1~2:10; the solid-liquid ratio of the mixture with water is 1:2~3; the drying temperature is 150-200℃, and the mixture is dried until the moisture content is 5-9wt%.

3. The method according to claim 1, characterized in that: The preheating process in S2 uses high-temperature flue gas discharged from the rotary kiln gas phase outlet at a temperature of 400-500℃. After preheating, the moisture content of the mixture is below 3wt%. The preheated flue gas is then purified by dust removal.

4. The method according to claim 1, characterized in that: Steam is also added to the kiln head of the rotary kiln, at a rate of 5-10 vol of the total amount of oxygen-enriched gas added.

5. The method according to claim 4, characterized in that: Before the oxygen-enriched material enters the rotary kiln, it exchanges heat with the silicon-calcium aggregate discharged from the rotary kiln. After the heat exchange, the temperature of the silicon-calcium aggregate is 150~200℃, and the temperature of the oxygen-enriched material is 150~200℃.

6. An apparatus for preparing calcium silicate aggregate, sulfuric acid, and CO2 by oxygen-enriched high-temperature decomposition of phosphogypsum using any one of claims 1 to 5, characterized in that: The system includes a slurry tank, a slurry filter, a dryer, a cyclone preheating system, and a rotary kiln, which are connected in sequence. The rotary kiln has a fuel injection pipe and an oxygen enrichment pipe at the kiln head and in the middle. The kiln head also has a silicon-calcium aggregate outlet. The gas phase outlet at the kiln tail is connected to a dust collector after passing through the cyclone preheating system, and then connected in sequence to a sulfuric acid preparation system and a CO2 adsorber production system.

7. The apparatus according to claim 6, characterized in that: The device also includes an oxygen enrichment preparation system, which consists of an air compressor, an adsorption nitrogen generator, a residual gas collection tank, a residual gas compressor, an adsorption oxygen generator, and an oxygen enrichment collection tank connected in sequence. The gas in the oxygen enrichment collection tank enters the rotary kiln after heat exchange through the discharge cooler of the rotary kiln.

8. The apparatus according to claim 6, characterized in that: The cyclone preheating system is a multi-stage cyclone preheater connected in series.

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