A process for producing SO2 from iron-containing solid waste through the decomposition of phosphogypsum and coupled production of cement clinker.

Abstract

The application discloses a kind of process methods for preparing cement clinker by decomposing phosphogypsum with iron-containing solid waste and coupling production of SO2, comprising: the mixture of phosphogypsum, coal and Fe3O4-containing solid waste is sent into a circulating fluidized bed reactor, and the phosphogypsum is reduced to SO2 at high temperature and generates a large amount of dicalcium ferrite.The flue gas enters the combustion chamber after passing through two cyclone separators, and then enters the waste heat recovery boiler for heat exchange.The flue gas after heat exchange enters the acid production unit after passing through a high-temperature dust collector.The materials from the fluidized bed discharge port, the material returner outlet and the secondary cyclone separator outlet are directly sent into the rotary kiln, and limestone, clay and coal are simultaneously added into the rotary kiln.The rotary kiln is heated to high temperature by using the waste heat of the fluidized bed solid product and the heat released by coal combustion, and the high-temperature clinker enters the waste heat recovery boiler for waste heat recovery.The application improves the process flow, and for the first time, Fe3O4-containing solid waste is used to reduce phosphogypsum to prepare SO2 and cement clinker, and at the same time, the energy consumption is reduced by waste heat recovery.

Description

Technical Field

[0001] This invention belongs to the fields of chemical production and environmental protection, and in particular relates to a process for producing cement clinker by decomposing phosphogypsum from iron-containing solid waste to prepare SO2. Background Technology

[0002] Phosphogypsum is a byproduct of phosphoric acid production in phosphate chemical enterprises, but its comprehensive utilization rate is currently low. The main component of phosphogypsum is CaSO4·2H2O. It also contains many impurities, such as Si, Fe, Mg, Al, P, F, organic matter, and trace elements like Cr and Pb. The presence of these impurities limits the large-scale application of phosphogypsum. Currently, phosphogypsum is mainly disposed of through stockpiling. However, stockpiling not only occupies large amounts of land but also easily pollutes the atmosphere and groundwater. Therefore, effectively addressing the stockpiling problem of phosphogypsum has become a major challenge in wet-process phosphoric acid production.

[0003] Reducing phosphogypsum to SO2 and lime slag using thermochemical methods is a feasible approach. SO2 can be used to produce sulfuric acid, and lime slag can be used as a raw material for building materials. This method can eliminate the environmental pollution caused by phosphogypsum, turning waste into treasure, and can also, to some extent, replace sulfur in the production of sulfuric acid.

[0004] Currently, the thermal decomposition processes of phosphogypsum include one-step and two-step methods. One-step decomposition requires higher temperatures and results in lower SO2 yields. Two-step decomposition involves low-temperature reduction and high-temperature roasting, which lowers the reaction temperature, but requires more stringent process control and equipment investment. To address the high decomposition temperature of phosphogypsum, industrial processes typically employ the addition of reducing agents. Common reducing agents include carbon-based agents such as coal, bituminous coal, anthracite, high-sulfur coal, coke, coal gangue, and petroleum coke; sulfur-based agents such as sulfur, pyrite, and H2S; and gases such as CO and H2. The addition of reducing agents significantly lowers the decomposition temperature of phosphogypsum. However, the decomposition temperature of phosphogypsum remains high. Researchers have found that by adding additives, the decomposition temperature of phosphogypsum can be further reduced, and the decomposition rate and SO2 yield can be improved. Currently studied additives mainly include FeCl3, Fe2O3, iron-phosphorus slag, Al2O3, SiO2, calcium fluoride, potassium feldspar, and various transition metal oxides such as V2O5, MnO2, Cr2O3, CuO, CoCl3·7H2O, and Co2O3 / Co3O4. Fe-based additives are the most widely used, most extensively studied, and most effective in the thermal decomposition of phosphogypsum. However, the use of these Fe-based additives has led to increased economic costs. Therefore, from an economic perspective, it is necessary to find more economical new Fe-based additives to further reduce production costs.

[0005] Solid waste, primarily composed of Fe3O4, originates from the steelmaking process. Utilizing the Fe3O4 in this solid waste to replace conventional Fe additives in promoting the decomposition of phosphogypsum would not only facilitate its resource utilization but also conserve resources. Furthermore, the resulting iron-based solid products can replace iron ore in cement clinker production, enabling full-process utilization of solid products without resource waste. Therefore, there is an urgent need to design a process for decomposing phosphogypsum from Fe3O4-containing solid waste and coupling it with cement clinker production. Summary of the Invention

[0006] This invention provides a process for producing SO2 by decomposing phosphogypsum from iron-containing solid waste and then coupling it with the production of cement clinker. The process utilizes Fe3O4-containing solid waste to reduce phosphogypsum to produce SO2, while simultaneously using the resulting iron-based solid products to produce cement clinker. The improved process shortens the process flow, and the generated high-temperature waste heat can be recovered and reused, reducing energy consumption.

[0007] A process for producing SO2 from iron-containing solid waste through the decomposition of phosphogypsum, coupled with the production of cement clinker, includes the following steps:

[0008] (1) A mixture of coal, phosphogypsum and Fe3O4-containing solid waste is fed into a circulating fluidized bed reactor in a certain proportion; at the same time, air is preheated and fed into the circulating fluidized bed reactor, where coal and hot air undergo combustion and gasification to generate reducing gas, phosphogypsum is reduced to SO2, and Fe3O4 is oxidized to Ca2Fe2O5.

[0009] (2) The amount of circulating material is controlled by controlling the material distribution flow rate of the return material device, thereby controlling the residence time of the material in the circulating fluidized bed reactor to be 15-30 min;

[0010] The flue gas generated by the circulating fluidized bed reactor passes through a primary cyclone separator and a secondary cyclone separator before entering the fluidized bed combustion chamber. After the reducing gases in the flue gas are fully burned off, it is sent to the fluidized bed flue gas waste heat recovery boiler for heat exchange. The flue gas after heat exchange is rich in 10-15% SO2. After further dust removal by the fluidized bed high-temperature dust collector, it enters the acid production unit.

[0011] (3) The material from the slag discharge port of the circulating fluidized bed reactor, the outlet of the return feeder and the outlet of the secondary cyclone separator is directly fed into the rotary kiln. At the same time, limestone, clay and coal are fed into the rotary kiln in a certain proportion, mixed with the supplied air and undergoing a combustion reaction, and are burned into cement clinker at high temperature.

[0012] (4) After the reaction is completed, the cement clinker from the rotary kiln enters the slag discharge waste heat recovery boiler for heat exchange. After the heat exchange, the temperature of the cement clinker drops to 100-150℃ and is stored in the clinker warehouse.

[0013] (5) 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.

[0014] Preferably, in step (1), the molar ratio of coal to phosphogypsum is 0.2–2, and the molar ratio of Fe3O4-containing solid waste to phosphogypsum is 0.5–3. This setting allows the decomposition rate of phosphogypsum to reach over 90%.

[0015] Preferably, in step (1), coal undergoes a combustion gasification reaction with the supplied hot air, releasing heat and producing reducing gases CO and H2; phosphogypsum is reduced by CO and H2, and the reduction reaction is endothermic; simultaneously, Fe3O4 reacts exothermically with CaSO4 in the phosphogypsum, and after the three reach thermal equilibrium, the reaction temperature in the circulating fluidized bed reactor is maintained at 950–1200°C. This setup allows the volume concentration of SO2 in the gas phase to reach over 12%.

[0016] Preferably, in step (2), the temperature of the flue gas after heat exchange in the fluidized bed flue gas waste heat recovery boiler is 100-200°C, and the preheated air is sent into the circulating fluidized bed reactor during the heat exchange process. This setup improves the energy utilization efficiency of flue gas waste heat recovery and reduces energy consumption.

[0017] Preferably, no additional iron ore is needed, and the amount of limestone added is reduced. In step (3), limestone and clay are fed into the rotary kiln at a raw material ratio of 30-40% and 20-25%, respectively. The amount of coal added is 10-20% of the mass of cement clinker produced, and the amount of air required to pass through 1 kg of coal is 11-17 m³. 3 .

[0018] In order to ensure the stability of the quality and performance of clinker, especially the formation of C3S, preferably, in step (3), heat is provided by coal combustion, and the cement clinker (solid phases such as C2S and C3S) needs to absorb heat during firing. After the two reach thermal equilibrium, the reaction temperature of the rotary kiln is maintained at 1300-1500℃.

[0019] Preferably, in step (4), the temperature of the flue gas after heat exchange in the slag discharge 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 clinker waste heat, improving energy utilization efficiency while reducing energy consumption.

[0020] Preferably, in step (5), 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.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. Compared with the two-step decomposition method, this method only requires one step, which shortens the process flow and saves on equipment investment costs and process operating costs.

[0023] 2. Waste-to-waste treatment. SO2 is produced by reducing phosphogypsum with Fe3O4-containing solid waste. This process can treat both phosphogypsum and solid waste, and also produce SO2 as a byproduct, which is both environmentally and economically beneficial.

[0024] 3. The generated high-temperature waste heat is recovered and utilized, reducing coal consumption, greatly reducing energy consumption, and saving process costs.

[0025] 4. The iron-based solid products generated can be used to prepare cement clinker without the need for additional iron ore, thus saving resources. Attached Figure Description

[0026] Figure 1 This is a flow chart of a process for producing cement clinker by decomposing phosphogypsum from iron-containing solid waste using SO2. Detailed Implementation

[0027] 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.

[0028] like Figure 1 As shown, a process for producing SO2 from iron-containing solid waste through the decomposition of phosphogypsum, coupled with the production of cement clinker, includes the following steps:

[0029] S1. A mixture of phosphogypsum, coal, and Fe3O4-containing solid waste is fed into a circulating fluidized bed reactor in a certain proportion.

[0030] S2. Air, after being preheated by the induced draft fan, enters the circulating fluidized bed reactor. Coal and air undergo combustion and gasification to produce reducing gases such as CO and H2, releasing heat while maintaining the reduction furnace temperature at a certain level. Phosphogypsum is reduced to SO2, and Fe3O4 is oxidized to Ca2Fe2O5. The decomposition rate of phosphogypsum is controlled by adjusting the opening of the return feeder to regulate the residence time of the material in the reactor.

[0031] S3. The flue gas continuously passes through a primary cyclone separator and a secondary cyclone separator before entering the combustion chamber. Next, the flue gas enters the waste heat recovery boiler. After passing through a heat exchanger and an air preheater, its temperature decreases. The preheated air is then fed into the fluidized bed. The flue gas after heat exchange enters the high-temperature dust collector and then proceeds to the acid production unit. Material from the fluidized bed slag outlet, the return feeder outlet, and the secondary cyclone separator outlet is directly fed into the rotary kiln cement clinker roasting furnace. A mixture of clay, iron powder, and coal is simultaneously added to the rotary kiln inlet. The high-temperature waste heat from the solid products maintains the rotary kiln temperature at a certain level. Simultaneously, air is fed into the rotary kiln by a blower and after passing through an air preheater; the heat released from coal combustion maintains the rotary kiln temperature at a certain level.

[0032] S4. After the reaction is complete, the high-temperature clinker enters the slag discharge waste heat recovery boiler. After heat exchange, the clinker temperature decreases, and the preheated air is sent into the rotary kiln. Then the clinker is stored in the clinker silo.

[0033] S5. The high-temperature flue gas from the rotary kiln enters the combustion chamber. It then enters the flue gas waste heat recovery boiler, where its temperature decreases after heat exchange. The preheated air is then fed back into the rotary kiln. The heat-exchanged flue gas then enters the high-temperature dust collector before being discharged into the atmosphere.

[0034] Example 1

[0035] The specific process of this embodiment is as follows:

[0036] S1. A mixture of 5700 kg / h phosphogypsum, 1600 kg / h coal, and 1310 kg / h Fe3O4-containing solid waste was uniformly mixed and then fed into a circulating fluidized bed reactor. The chemical composition of the phosphogypsum and Fe3O4-containing solid waste is shown in Tables 1 and 3, and the industrial and elemental analysis of the coal is shown in Table 2.

[0037] S2.1875m 3 Air, after being preheated by an induced draft fan, enters the circulating fluidized bed reactor. Coal and air undergo combustion and gasification to produce reducing gases such as CO and H2, releasing heat while maintaining the reduction furnace temperature at 1100℃. Phosphogypsum is reduced to SO2, and Fe3O4 is oxidized to Ca2Fe2O5. By controlling the opening of the return feeder, the residence time of the material in the reactor is controlled to be 20 minutes, thereby controlling the decomposition rate of phosphogypsum to over 95%.

[0038] S3. Materials from the fluidized bed slag discharge port, the return feeder outlet, and the secondary cyclone separator outlet are directly fed into the rotary kiln. Simultaneously, limestone, clay, and other raw and auxiliary materials are also fed into the rotary kiln at rates of 3750 kg / h and 1250 kg / h respectively, along with approximately 570 kg / h of coal and 6850 m³ of other feedstock. 3 / h air mixes to produce combustion and other reactions, and the temperature is controlled at 1400℃, which is then used to burn cement clinker at high temperature.

[0039] S4. After the reaction is complete, the clinker enters the slag discharge waste heat recovery device, where it exchanges heat with a heat exchanger and an air preheater. After heat exchange, the clinker temperature drops to 120°C and is then stored in the clinker silo. The flue gas temperature after heat exchange is 150°C, and the air is preheated to 550°C before being sent into the rotary kiln.

[0040] S5. The high-temperature flue gas from the rotary kiln first enters the combustion chamber, where the reducing gases are burned off at 1400℃. It then enters the flue gas waste heat recovery boiler, where it exchanges heat with the heat exchanger and air preheater. The temperature of the flue gas after heat exchange is 150℃, and the air is preheated to 550℃ before being sent into the rotary kiln.

[0041] The results showed that the decomposition rate of phosphogypsum reached 99%, and the SO2 concentration in the flue gas at the outlet of the circulating fluidized bed was 12.3%. The physical properties of the cement clinker prepared by the method of this invention are shown in Table 4. These results indicate that the cement clinker prepared by this process has good performance and meets production requirements.

[0042] Table 1. Chemical composition of phosphogypsum (%)

[0043] <![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

[0044] Table 2. Coal quality analysis results (%)

[0045]

[0046] Table 3 Chemical composition of Fe3O4-containing solid waste / %

[0047] <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[SO3]]> <![CDATA[Fe2O3]]> CaO MgO <![CDATA[K2O]]> <![CDATA[Na2O]]> ZnO CuO PbO 21.63 7.85 1.48 45.66 5.07 2.64 1.03 4.09 5.99 0.44 1.14

[0048] Table 4 Physical properties of clinker

[0049]

[0050] 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 iron-containing solid waste through the decomposition of phosphogypsum, coupled with the production of cement clinker, characterized in that... Includes the following steps: (1) A mixture of coal, phosphogypsum, and Fe3O4-containing solid waste is fed into a circulating fluidized bed reactor in a certain proportion. At the same time, air is preheated and fed into the circulating fluidized bed reactor. The coal reacts with the hot air to undergo combustion and gasification, releasing heat and producing reducing gases CO and H2. The phosphogypsum is reduced to SO2 by CO and H2, and the reduction reaction process is endothermic. Fe3O4 reacts with CaSO4 in the phosphogypsum to release heat and is oxidized to Ca2Fe2O5. After the three reach thermal equilibrium, the reaction temperature in the circulating fluidized bed reactor is maintained at 1100 ℃. The molar ratio of coal to phosphogypsum is 0.2~2, and the molar ratio of Fe3O4-containing solid waste to phosphogypsum is 0.5~3. (2) The amount of circulating material is controlled by controlling the material distribution flow rate of the return material device, thereby controlling the residence time of the material in the circulating fluidized bed reactor to be 15~30 min; The flue gas generated by the circulating fluidized bed reactor passes through a primary cyclone separator and a secondary cyclone separator before entering the fluidized bed combustion chamber. After the reducing gases in the flue gas are fully burned off, it is sent to the fluidized bed flue gas waste heat recovery boiler for heat exchange. The flue gas after heat exchange is rich in 10~15% SO2. After further dust removal by the fluidized bed high temperature dust collector, it enters the acid production unit. (3) The material from the slag discharge port of the circulating fluidized bed reactor, the outlet of the return feeder and the outlet of the secondary cyclone separator is directly fed into the rotary kiln. At the same time, limestone, clay and coal are fed into the rotary kiln in a certain proportion, mixed with the supplied air to undergo a combustion reaction, and are burned into cement clinker at high temperature. (4) After the reaction is completed, the cement clinker from the rotary kiln enters the slag discharge waste heat recovery boiler for heat exchange. After heat exchange, the temperature of the cement clinker drops to 100~150℃ and is stored in the clinker warehouse. The temperature of the flue gas after heat exchange in the slag discharge 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. (5) 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 preparing SO2 from iron-containing solid waste through the decomposition of phosphogypsum according to claim 1, characterized in that, In step (2), the temperature of the flue gas after heat exchange in the fluidized bed flue gas waste heat recovery boiler is 100~200℃, and the preheated air is sent into the circulating fluidized bed reactor during the heat exchange process.

3. The process for preparing SO2 from iron-containing solid waste through the decomposition of phosphogypsum according to claim 1, characterized in that, In step (3), limestone and clay are fed into the rotary kiln at raw material ratios of 30-40% and 20-25%, respectively. The amount of coal added is 10-20% of the mass of cement clinker produced, and the amount of air required to pass through 1 kg of coal is 11-17 m³. 3 .

4. The process for preparing SO2 from iron-containing solid waste through the decomposition of phosphogypsum according to claim 1, characterized in that, In step (3), heat is provided by coal combustion, and cement clinker needs to absorb heat during firing. After the two reach thermal equilibrium, the reaction temperature of the rotary kiln is maintained at 1300~1500℃.

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