A process for producing SO2 from phosphogypsum and coupling it with cement clinker production.

Abstract

The application discloses a process method for preparing SO2 coupling cement clinker production by decomposing phosphogypsum, which comprises the following steps: feeding the mixture of phosphogypsum and coal into a reduction furnace through a feeding device, and partially reducing the phosphogypsum into CaS; feeding the material at the outlet of the reduction furnace into a roasting furnace, and reacting the CaS and CaSO4 at high temperature to generate CaO and SO2; directly feeding the high-temperature CaO from the roasting furnace into a rotary kiln, and simultaneously adding clay, iron powder and coal into the rotary kiln; heating the rotary kiln to high temperature by using the waste heat of the CaO and the heat released by the combustion of the coal; firstly passing the high-temperature flue gas generated by the rotary kiln through a burn-out chamber, and then passing the high-temperature flue gas into a flue gas waste heat recovery boiler to perform heat exchange; and discharging the flue gas after dust removal by a high-temperature dust remover. After the reaction is completed, the high-temperature clinker is fed into a slag discharge waste heat recovery boiler to recover the waste heat. By using the application, the energy consumption, production cost and carbon emission amount of the cement clinker production can be greatly reduced, and the efficient and clean comprehensive utilization of the phosphogypsum can be realized.

Description

Technical Field

[0001] This invention belongs to the field of phosphogypsum resource utilization, and in particular relates to a process for the decomposition of phosphogypsum to prepare SO2 coupled with the production of cement clinker. Background Technology

[0002] Phosphogypsum is an industrial byproduct of the wet phosphoric acid leaching process; producing 1 ton of phosphoric acid generates 4-6 tons of phosphogypsum. As of 2021, global phosphogypsum stockpiles exceeded 6 billion tons and continue to grow at a rate of approximately 200 million tons annually, yet the global utilization rate of phosphogypsum is only around 25%. With increasing concern about environmental issues, the utilization of phosphogypsum has become a crucial environmental protection concern. The main component of phosphogypsum is CaSO4·2H2O, mixed with various forms of calcium phosphate, silica, and a wide range of impurities such as iron oxide, magnesium, aluminum, sulfides, organic matter, and trace metal elements. These impurities mainly exist in phosphogypsum in the form of lattice doping, atomic substitution, surface adsorption, and interstitial filling. These impurities and lattice morphology severely limit the resource utilization of phosphogypsum.

[0003] With the increasing demand for building materials, cement, as one of the most important building materials, has become an indispensable part of the construction industry. Cement clinker is usually produced using a dry process. First, raw materials, including limestone, clay, iron ore, and coal, are crushed and mixed to form a uniform mixture. Then, the mixture is sent to a rotary kiln for sintering. During the sintering process, parameters such as kiln temperature and oxygen content need to be controlled so that the mixture reacts at high temperature to produce clinker. Finally, the clinker is ground into cement clinker. This process has the following disadvantages: (1) High energy consumption: Traditional cement clinker production equipment uses a dry process, which requires a large amount of coal and electricity for heating and coal grinding, resulting in high energy consumption; (2) Serious environmental pollution: Cement production generates a large amount of waste gas, wastewater, and solid waste, causing serious environmental pollution. In addition, greenhouse gases such as CO2 are emitted during the sintering process, which has a negative impact on climate change; (3) Large raw material consumption: Cement production requires a large amount of raw materials, such as limestone and clay. The mining and transportation of these raw materials consume a large amount of resources and energy. Therefore, people have been seeking more environmentally friendly and sustainable cement production methods.

[0004] Reducing phosphogypsum into high-SO2-concentration flue gas for sulfuric acid production can achieve sulfur resource recycling in phosphate fertilizer production, effectively alleviating the environmental problems caused by phosphogypsum. However, the CaO-rich material produced in this process has insufficient CaO purity, affecting its subsequent utilization. On the other hand, the traditional rotary kiln process for producing cement clinker requires the high-temperature calcination and decomposition of large quantities of limestone into CaO as a raw material for subsequent cement clinker production. This not only consumes a large amount of limestone resources but also requires a significant amount of energy and releases a large amount of CO2 gas during the high-temperature calcination and decomposition process. Therefore, if the high-temperature material rich in CaO produced by the reduction and roasting of phosphogypsum is directly used as a raw material for cement clinker production, it can not only replace the limestone raw material required for cement production but also avoid the energy consumption and large CO2 emissions required for high-temperature limestone calcination, thereby significantly reducing energy consumption, production costs, and carbon emissions in cement clinker production.

[0005] Therefore, there is an urgent need to design a process for the decomposition of phosphogypsum to prepare SO2 and coupled with the production of cement clinker, so as to achieve efficient and comprehensive utilization of phosphogypsum. Summary of the Invention

[0006] This invention provides a process for SO2 preparation from phosphogypsum in the production of cement clinker. The high-temperature material rich in CaO produced by the reduction and roasting of phosphogypsum is directly used as a raw material for cement clinker production, replacing the limestone raw material required for cement production. This avoids the energy consumption and large CO2 emissions required for the high-temperature calcination and decomposition of limestone, significantly reducing the energy consumption, production cost and carbon emissions of cement clinker production, and achieving efficient, clean and comprehensive utilization of phosphogypsum.

[0007] A process for producing SO2 from phosphogypsum and coupling it with cement clinker production includes the following steps:

[0008] (1) A mixture of coal and phosphogypsum is fed into a circulating fluidized bed reduction furnace. At the same time, air is preheated and also fed into the circulating fluidized bed reduction furnace. The coal and hot air undergo combustion and gasification reactions to generate reducing gas and semi-coke. The CaSO4 in the phosphogypsum is partially reduced to CaS by the generated reducing gas and semi-coke through gas-solid and solid-solid reactions.

[0009] By controlling the opening of the return feeder in the reduction furnace, the residence time of the material in the circulating fluidized bed reduction furnace is controlled, thereby controlling the decomposition rate of phosphogypsum and making the molar ratio of CaS and CaSO4 in the circulating fluidized bed reduction furnace 2 to 4.

[0010] (2) The mixed flue gas generated by the circulating fluidized bed reduction furnace passes through the first-stage cyclone separator and the second-stage cyclone separator of the reduction furnace in sequence and then enters the combustion chamber of the reduction furnace. The flue gas coming out of the combustion chamber of the reduction furnace enters the waste heat recovery boiler of the flue gas of the reduction furnace for heat exchange. After heat exchange, the flue gas enters the high-temperature dust collector of the reduction furnace and is then discharged into the air.

[0011] (3) The mixture of CaS particles and phosphogypsum particles from the circulating fluidized bed reduction furnace is fed into the circulating fluidized bed roasting furnace. Some of the CaS reacts with the air entering the furnace to generate heat through oxidation. At the same time, the unoxidized CaS and CaSO4 react at high temperature to generate CaO and SO2.

[0012] The high-temperature flue gas generated by the circulating fluidized bed roasting furnace is separated by the first-stage cyclone separator of the roasting furnace and the first-stage cyclone separator of the roasting furnace to produce flue gas with a SO2 volume concentration of 20-25%. After passing through the flue gas waste heat recovery boiler of the roasting furnace, it is sent to the subsequent acid production unit.

[0013] (4) The high-temperature material rich in 60-90% CaO from the slag discharge port of the circulating fluidized bed roaster and the outlet of the cyclone separator directly enters the rotary kiln cement clinker roaster; at the same time, clay, iron ore and coal are fed into the rotary kiln cement clinker roaster in a certain proportion, and are mixed with the supplied air to undergo a combustion reaction and the temperature is controlled at 1300-1400℃, and cement clinker is produced at high temperature.

[0014] (5) After the reaction is completed, the cement clinker enters the clinker waste heat recovery device for heat exchange. After the heat exchange, the clinker temperature drops to 100-150℃ and is then stored in the clinker warehouse.

[0015] (6) The high-temperature flue gas from the rotary kiln first enters the combustion chamber of the rotary kiln to burn off the reducing gases, and then enters the waste heat recovery boiler of the rotary kiln flue gas for heat exchange. After heat exchange, the flue gas is further dusted by the high-temperature dust collector of the rotary kiln before being discharged into the air.

[0016] Preferably, in step (1), the mass ratio of coal to phosphogypsum is 0.5–2. This setting allows the decomposition rate of phosphogypsum to reach over 80%.

[0017] Preferably, in step (1), the coal undergoes a combustion gasification reaction with the supplied hot air, releasing heat and producing CO and H2. Simultaneously, phosphogypsum is reduced by CO and H2. The reduction process is endothermic, and after the two reach thermal equilibrium, the reaction temperature in the circulating fluidized bed reduction furnace is maintained at 800–1000°C. This setup allows the CaS yield to reach over 80%.

[0018] Preferably, in step (3), the residence time of the material in the circulating fluidized bed roaster is controlled by controlling the opening of the roaster return feeder at the outlet of the primary cyclone separator of the roaster, thereby controlling the yield of CaO. At the same time, the molar ratio of CaS and CaSO4 in the reduction product can be controlled to be 1.5 to 2.

[0019] Preferably, in step (3), the roasting process in the circulating fluidized bed roasting furnace involves the solid-solid reaction between CaSO4 and CaS, as well as the oxidation reaction between CaS and air. The solid-solid reaction is endothermic, and the oxidation reaction is exothermic. When the molar ratio of CaS to CaSO4 is controlled at 3:2, the two reactions will reach thermal equilibrium, maintaining the reaction temperature in the circulating fluidized bed roasting furnace at 1000–1200°C. This setup allows the yield of calcium oxide to reach over 70%.

[0020] Preferably, in step (4), clay and iron ore are fed into the rotary kiln at a raw material ratio of 20-25% and 2-5% respectively, and the amount of coal added is 10-20% of the mass of cement clinker produced.

[0021] The raw materials for cement clinker include clay, iron ore, coal, and calcium carbonate. The main function of calcium carbonate is to decompose and prepare calcium oxide, but the calcium oxide in this invention is derived from the decomposition of phosphogypsum, so there is no need to add calcium carbonate.

[0022] Preferably, in step (5), the temperature of the flue gas after heat exchange through the clinker waste heat recovery device is 100-200°C. During the heat exchange process, the air is preheated to 500-600°C before being sent into the rotary kiln. This setup allows the clinker waste heat to be recovered, improving energy utilization efficiency while reducing energy consumption.

[0023] Preferably, in step (6), the temperature of the flue gas after heat exchange with the rotary kiln flue gas waste heat recovery boiler is 100-200°C. During the heat exchange process, the air is preheated to 500-600°C before being sent into the rotary kiln. This setup allows for the recovery of flue gas waste heat, improving energy utilization efficiency while reducing energy consumption.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. Using phosphogypsum as a raw material, a reducing roasting process is employed to decompose it, generating high-SO2 gas for acid production while simultaneously producing CaO-rich materials. This not only recovers the calcium and sulfur resources from phosphogypsum but also reduces its environmental pollution.

[0026] 2. The generated CaO can be used to replace the raw material for limestone decomposition required for cement production. This not only effectively avoids the mining of new limestone ore and saves the use of natural resources, but also does not produce a large amount of greenhouse gases such as CO2, reducing environmental pollution and significantly reducing carbon emissions in the cement production process.

[0027] 3. The generated high-temperature CaO is directly fed into the rotary kiln, which can effectively utilize the high-temperature waste heat of CaO, reduce coal consumption, greatly reduce energy consumption, and save process costs. Attached Figure Description

[0028] Figure 1 This is a structural principle block diagram of the present invention.

[0029] In the diagram: 1-Circulating fluidized bed reduction furnace, 2-Primary cyclone separator of reduction furnace, 3-Reduction furnace return feeder, 4-Secondary cyclone separator of reduction furnace, 5-Reduction furnace combustion chamber, 6-Reduction furnace flue gas waste heat recovery boiler, 7-Reduction furnace blower, 8-Reduction furnace high-temperature dust collector, 9-Reduction furnace induced draft fan, 10-Exhaust gas, 11-Return feeder discharge pipe, 12-Reduction furnace secondary cyclone separator discharge pipe, 13-Circulating fluidized bed roasting furnace, 14-Roasting furnace primary cyclone separator, 15-Roasting furnace return feeder, 16-Roasting furnace secondary cyclone separator, 17-Roasting furnace flue gas waste heat recovery boiler 18-Roasting furnace blower, 19-Roasting furnace high-temperature dust collector, 20-Roasting furnace induced draft fan, 21-Acid production unit, 22-Roasting furnace discharge pipe, 23-Roasting furnace primary cyclone separator discharge pipe, 24-Roasting furnace secondary cyclone separator discharge pipe, 25-Rotary kiln cement clinker roasting furnace, 26-Clinker waste heat recovery device, 27-Rotary kiln blower, 28-Clinker silo, 29-Rotary kiln combustion chamber, 30-Rotary kiln flue gas waste heat recovery boiler, 31-Rotary kiln blower, 32-High-temperature dust collector, 33-Rotary kiln induced draft fan, 34-Exhaust gas. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not constitute any limitation thereof.

[0031] like Figure 1 As shown, a process for producing SO2 from phosphogypsum coupled with cement clinker production includes the following steps:

[0032] S1. A mixture of phosphogypsum and coal is fed into a circulating fluidized bed reduction furnace 1, followed by the introduction of a certain amount of air. The coal and air undergo a combustion and gasification reaction to produce reducing gases such as CO and H2, releasing heat while maintaining the furnace temperature at a certain level. The phosphogypsum is partially reduced to CaS. The decomposition rate of the phosphogypsum is controlled by adjusting the opening of the return feeder 3 to regulate the residence time of the material within the furnace. The flue gas passes sequentially through the primary cyclone separator 2 and the secondary cyclone separator 4 before entering the combustion chamber 5. The flue gas exiting the combustion chamber 5 enters the waste heat recovery boiler 6. After heat exchange with water and air, the flue gas temperature decreases. The air is preheated and then fed into the circulating fluidized bed reduction furnace 1 by the furnace blower 7. The heat-exchanged flue gas enters the high-temperature dust collector 8 and is then exhausted by the furnace induced draft fan 9.

[0033] S2. The material from the return feeder of the reduction furnace and the material from the secondary cyclone separator of the reduction furnace enter the circulating fluidized bed roasting furnace 13 through the return feeder outlet pipe 11 and the secondary cyclone separator outlet pipe 12, respectively, and then a certain amount of air is introduced. The semi-coke reacts strongly with the air entering the furnace, releasing heat and maintaining the reaction temperature of the roasting furnace at a certain temperature. CaS and CaSO4 react at high temperature to produce CaO and SO2. The residence time of the material in the roasting furnace is controlled by controlling the opening of the return feeder 15, thereby controlling the yield of CaO. The flue gas passes through the primary cyclone separator 14 and the secondary cyclone separator 16 of the roasting furnace in sequence before entering the flue gas waste heat recovery boiler 17 of the roasting furnace. The air is preheated by the flue gas waste heat recovery boiler 17 under the action of the roasting furnace blower 18 and then sent to the circulating fluidized bed roasting furnace 13. After heat exchange, the flue gas enters the high-temperature dust collector 19 of the roasting furnace and then enters the subsequent acid production unit 21 through the induced draft fan 20 of the roasting furnace.

[0034] S3. High-temperature CaO from the discharge pipe 22 of the calcining furnace, the discharge pipe 23 of the primary cyclone separator of the calcining furnace, and the discharge pipe 24 of the secondary cyclone separator of the calcining furnace is directly fed into the rotary kiln cement clinker calcining furnace 25. A mixture of clay, iron powder, and coal is simultaneously added to the rotary kiln inlet. The high-temperature waste heat of the CaO is used to maintain the temperature of the rotary kiln at a certain level. At the same time, air is sent into the rotary kiln cement clinker calcining furnace by the rotary kiln blowers 27 and 31 after passing through an air preheater. The heat released from coal combustion maintains the temperature of the rotary kiln at a certain level.

[0035] S4. After the reaction is complete, the high-temperature clinker enters the clinker waste heat recovery device 26. After heat exchange, the clinker temperature decreases, and the preheated air is sent into the rotary kiln cement clinker roasting furnace 25. Then the clinker enters the clinker silo 28 for storage.

[0036] S5. The high-temperature flue gas from the rotary kiln cement clinker roasting furnace 25 passes through the rotary kiln combustion chamber 29. Then it enters the rotary kiln flue gas waste heat recovery boiler 30. After heat exchange, the temperature of the flue gas decreases, and the air is preheated before being sent into the rotary kiln cement clinker roasting furnace 25. After heat exchange, the flue gas enters the high-temperature dust collector 32 and is then discharged into the atmosphere by the rotary kiln induced draft fan 33 34.

[0037] Example 1

[0038] The specific process of this embodiment is as follows:

[0039] S1. A mixture of phosphogypsum and coal is fed into a circulating fluidized bed reduction furnace 1, wherein the amount of phosphogypsum is 6250 kg / h and the amount of coal is 3360 kg / h. The chemical composition of the phosphogypsum is shown in Table 1, and the industrial and elemental analysis results of the coal are shown in Table 2. 8639 Nm 3Air at a rate of / h is fed into the circulating fluidized bed reduction furnace 1. Coal and air undergo combustion and gasification reactions to produce reducing gases such as CO and H2, releasing heat while maintaining the furnace temperature at approximately 900℃. Phosphogypsum is partially reduced to CaS. The decomposition rate of phosphogypsum is controlled to approximately 80% by adjusting the opening of the return feeder 3. The flue gas passes sequentially through the primary cyclone separator 2 and the secondary cyclone separator 4 before entering the combustion chamber 5. The flue gas exiting the combustion chamber enters the waste heat recovery boiler 6. After heat exchange with water and air, the flue gas temperature drops to 120℃, and the air is preheated to 300℃ before being fed back into the circulating fluidized bed reduction furnace 1. The heat-exchanged flue gas then enters the high-temperature dust collector 8 and is discharged into the atmosphere 10.

[0040] S2. The material from the return feeder of the reduction furnace and the material from the secondary cyclone separator of the reduction furnace enter the circulating fluidized bed roasting furnace 13, while 2354 Nm 3 / h of air is fed into the roasting furnace. The semi-coke reacts strongly with the incoming air, releasing heat and maintaining the roasting furnace reaction temperature at around 1100℃. The CaO yield is controlled by adjusting the opening of the roasting furnace return feeder 15 to control the residence time of the material in the roasting furnace. The flue gas passes sequentially through the primary cyclone separator 14 and the secondary cyclone separator 16 before entering the roasting furnace flue gas waste heat recovery boiler 17. The air is preheated to 400℃ and then fed into the circulating fluidized bed roasting furnace 13. The SO2-rich flue gas, after heat exchange (approximately 22% by volume), enters the high-temperature dust collector 19 of the roasting furnace and then proceeds to the subsequent acid production unit 21.

[0041] S3. Approximately 1533 kg / h of high-temperature CaO from the discharge pipe 22 of the calcining furnace, the discharge pipe 23 of the primary cyclone separator of the calcining furnace, and the discharge pipe 24 of the secondary cyclone separator of the calcining furnace are directly fed into the rotary kiln cement clinker calcining furnace 25. 384 kg / h of clay, 31 kg / h of iron powder, and 224 kg / h of coal are simultaneously added to the rotary kiln inlet. The residual heat of the CaO is used to maintain the temperature of the rotary kiln at around 600℃. Meanwhile, 1200 Nm³ / h of... 3 The air is preheated to 600°C by a blower and air preheater before being sent into the rotary kiln. The heat released by coal combustion maintains the rotary kiln temperature at around 1450°C.

[0042] S4. After the reaction is complete, the high-temperature clinker enters the clinker waste heat recovery device 26. After heat exchange, the clinker temperature drops to 150°C, and the air is preheated to 600°C before being sent to the rotary kiln cement clinker roasting furnace 25. Then the clinker enters the clinker silo 28 for storage.

[0043] S5. The high-temperature flue gas from the rotary kiln enters the rotary kiln combustion chamber 29. It then enters the rotary kiln flue gas waste heat recovery boiler 30. After heat exchange, the flue gas temperature drops to 150℃, and the air is preheated to 600℃ before being sent to the rotary kiln cement clinker roasting furnace 25. The heat-exchanged flue gas then enters the high-temperature dust collector 32 before being discharged into the atmosphere 34.

[0044] The results showed that the decomposition rate of phosphogypsum reached 99%, and the SO2 concentration in the flue gas at the calciner outlet was 22.5%. The composition of the products from the reduction calcination of phosphogypsum is shown in Table 3, indicating that the calcium oxide content in the products was 65.48%. The physical properties of the cement clinker prepared by the method of this invention are shown in Table 4. These results demonstrate that the cement clinker prepared by this process has good performance and meets production requirements.

[0045] Table 1. Chemical composition of phosphogypsum (%)

[0046] <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[SO3]]> <![CDATA[Fe2O3]]> CaO MgO <![CDATA[K2O]]> <![CDATA[Na2O]]> 17.25 0.51 47.87 0.54 33.51 0.25 0.23 0.16

[0047] Table 2. Coal quality analysis results (%)

[0048]

[0049] Table 3 Chemical composition of phosphogypsum reduction roasting products

[0050] Loss <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO 0.76 21.63 5.42 2.87 65.48 1.26

[0051] Table 4 Physical properties of clinker

[0052]

[0053] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for producing SO2 from phosphogypsum and coupling it with cement clinker production, characterized in that, Includes the following steps: (1) A mixture of coal and phosphogypsum is fed into a circulating fluidized bed reduction furnace. At the same time, air is preheated and also fed into the circulating fluidized bed reduction furnace. The coal and hot air undergo combustion and gasification reactions to generate reducing gas and semi-coke. The CaSO4 in the phosphogypsum is partially reduced to CaS by the generated reducing gas and semi-coke through gas-solid and solid-solid reactions. By controlling the opening of the return feeder in the reduction furnace, the residence time of the material in the circulating fluidized bed reduction furnace is controlled, thereby controlling the decomposition rate of phosphogypsum and making the molar ratio of CaS and CaSO4 in the circulating fluidized bed reduction furnace 2~4. (2) The mixed flue gas generated by the circulating fluidized bed reduction furnace passes through the first-stage cyclone separator and the second-stage cyclone separator of the reduction furnace in sequence and then enters the combustion chamber of the reduction furnace. The flue gas coming out of the combustion chamber of the reduction furnace enters the waste heat recovery boiler of the reduction furnace for heat exchange. After heat exchange, the flue gas enters the high-temperature dust collector of the reduction furnace and is then discharged into the air. (3) The mixture of CaS particles and phosphogypsum particles from the circulating fluidized bed reduction furnace is fed into the circulating fluidized bed calcining furnace. Some of the CaS reacts with the air entering the furnace to generate heat, while the unoxidized CaS and CaSO4 react at high temperature to generate CaO and SO2. The roasting process in the circulating fluidized bed roasting furnace involves the solid-solid reaction between CaSO4 and CaS, as well as the oxidation reaction between CaS and air. The solid-solid reaction is an endothermic reaction, while the oxidation reaction is an exothermic reaction. When the molar ratio of CaS to CaSO4 is controlled at 3:2, the two reactions will reach thermal equilibrium. The reaction temperature in the circulating fluidized bed roasting furnace is maintained at 1000~1200 ℃. The high-temperature flue gas generated by the circulating fluidized bed roasting furnace is separated by the first-stage cyclone separator of the roasting furnace and the first-stage cyclone separator of the roasting furnace to produce flue gas with a volume concentration of 20-25% SO2. After passing through the flue gas waste heat recovery boiler of the roasting furnace, it is sent to the subsequent acid production unit; (4) The high-temperature material rich in 60-90% CaO from the slag discharge port of the circulating fluidized bed roasting furnace and the outlet of the cyclone separator directly enters the rotary kiln cement clinker roasting furnace; at the same time, clay, iron ore and coal are fed into the rotary kiln cement clinker roasting furnace in a certain proportion, and are mixed with the supplied air to undergo combustion reaction and the temperature is controlled at 1300-1400℃, and cement clinker is produced at high temperature; (5) After the reaction is completed, the cement clinker enters the clinker waste heat recovery device for heat exchange. After the heat exchange, the clinker temperature drops to 100~150℃ and is stored in the clinker warehouse. The flue gas temperature after heat exchange through the clinker waste heat recovery device is 100~200℃. During the heat exchange process, the air is preheated to 500~600℃ and then sent into the rotary kiln. (6) The high-temperature flue gas from the rotary kiln first enters the combustion chamber of the rotary kiln to burn off the reducing gases, and then enters the rotary kiln flue gas waste heat recovery boiler for heat exchange. After heat exchange, the flue gas is further dusted by the rotary kiln high-temperature dust collector and then discharged into the air. The temperature of the flue gas after heat exchange in the rotary kiln flue gas waste heat recovery boiler is 100~200℃. During the heat exchange process, the air is preheated to 500~600℃ and then sent into the rotary kiln.

2. The process for producing SO2 from phosphogypsum via decomposition and coupled with cement clinker production according to claim 1, characterized in that, In step (1), the mass ratio of coal to phosphogypsum is 0.5 to 2.

3. The process for producing SO2 from phosphogypsum via decomposition and coupled with cement clinker production according to claim 1, characterized in that, In step (1), the coal and the incoming hot air undergo a combustion gasification reaction, releasing heat and producing CO and H2. At the same time, phosphogypsum is reduced by CO and H2. The reduction process is an endothermic process. After the two reach thermal equilibrium, the reaction temperature in the circulating fluidized bed reduction furnace is maintained at 800~1000℃.

4. The process for producing SO2 from phosphogypsum via decomposition and coupled with cement clinker production according to claim 1, characterized in that, In step (3), the residence time of the material in the circulating fluidized bed roasting furnace is controlled by controlling the opening of the roasting furnace return feeder at the outlet of the primary cyclone separator of the roasting furnace, thereby controlling the yield of CaO.

5. The process for producing SO2 from phosphogypsum via decomposition coupled with cement clinker production according to claim 1, characterized in that, In step (4), clay and iron ore are fed into the rotary kiln at a ratio of 20-25% and 2-5% respectively, and the amount of coal added is 10-20% of the mass of cement clinker produced.

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