A method for temperature control in a calcium sulfate reduction reactor

Abstract

This invention discloses a temperature control method for a calcium sulfate reduction reactor, comprising the following steps: S1, feeding hydrated calcium sulfate raw material into a material drying and preheating system consisting of a dispersing dryer and / or a cyclone dust collector, using the exhaust gas discharged from the reduction reactor to remove free water or at least part of the crystal water, obtaining preheated material; S2, feeding the preheated material into the reduction reactor, reacting it with a non-sulfur-containing reducing agent to reduce calcium sulfate to calcium sulfide; S3, introducing air and low-oxygen industrial exhaust gas with an oxygen content of less than 12 vol% into the reduction reactor, controlling the peak temperature of the reaction zone below a preset upper limit; S4, performing gas-solid separation on the exhaust gas leaving the reduction reactor, returning the separated exhaust gas to the cyclone dust collector as a drying heat source. The advantage of this invention is that by using low-oxygen exhaust gas or exhaust gas recirculation to replace part of the air, the adiabatic temperature rise within the reactor can be reduced from the source, avoiding the generation of SO2 flue gas due to material decomposition caused by excessively high temperatures.

Description

Technical Field

[0001] This invention relates to the field of calcium sulfate reduction reaction technology, and in particular to a method for temperature control in a calcium sulfate reduction reactor. Background Technology

[0002] Currently, my country has a huge accumulated stockpile of industrial by-product gypsum, mainly including desulfurization gypsum, phosphogypsum, titanium gypsum, fluorogypsum, salt gypsum, borate gypsum, citric acid gypsum, and neutralized waste acid gypsum. The main component of this type of solid waste is calcium sulfate, which can be divided into three categories according to its water of crystallization content: dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum. Except for a small amount that is used in building materials, a considerable portion is still disposed of by stockpiling, which occupies a large area and poses a high risk of leachate and dust pollution, making resource utilization urgently needed.

[0003] The reduction of calcium sulfate to calcium sulfide is an important route for the high-value utilization of calcium and sulfur resources. The resulting calcium sulfide can be further reacted with residual or added calcium sulfate to produce sulfur dioxide, which is then used in the production of sulfuric acid. It can also be used to prepare hydrogen sulfide, thiourea, sodium sulfide, and sulfur, thus possessing high technological value. Industrially usable reducing agents include coke, anthracite, bituminous coal, lignite, CO, H2, CH4, NH3, biomass fuels, and their mixed reducing gases. The basic reduction reactions can be represented as: CaSO4 + 2C → CaS + 2CO2, CaSO4 + 4CO → CaS + 4CO2, CaSO4 + 4H2 → CaS + 4H2O.

[0004] However, the industrial-scale production of calcium sulfide from calcium sulfate faces two key challenges. First, how to efficiently integrate the dehydration, preheating, and reduction of wet gypsum to reduce system heat consumption; second, how to stably control the reactor temperature within the required range. For routes using non-sulfur-containing reducing agents, when air enters the reactor, the oxygen must first be depleted by the reducing agent to establish a strong reducing atmosphere. The heat released by the combustion of the reducing agent often causes the reactor temperature to exceed the expected reaction temperature. Taking the combustion of lignite under stoichiometric air conditions as an example, its adiabatic combustion temperature can be far higher than the upper temperature limit allowed for the reduction of calcium sulfate to calcium sulfide. Therefore, reaction temperature control becomes the core issue for the stable and economical operation of the plant.

[0005] At high temperatures, CaS reacts with CaSO4 to produce CaO and SO2 via a side reaction: 3CaSO4 + CaS → 4CaO + 4SO2. This side reaction results in sulfur loss and increases the burden on tail gas treatment. The publicly available literature, "Thermogravimetric Study of CaS Oxidation Reaction Characteristics," indicates that SO2 precipitation increases significantly in the 930℃–1150℃ range, suggesting a strong risk of sulfur release in CaS-containing systems within this temperature range. On the other hand, the literature, "Thermodynamic Analysis of a New Process for Sulfuric Acid Production from Phosphogypsum," suggests that replacing coke with CO, H2, or methane partial oxidation gas has the potential to reduce energy consumption; however, this type of reduction route also requires addressing the temperature control issues under industrial conditions.

[0006] Chinese patent CN116425123A discloses a method for preparing calcium sulfide by gypsum reduction using an externally heated rotary kiln, which mainly relies on externally heated high-temperature flue gas to maintain the temperature inside the rotary kiln at 850℃~950℃. While this method achieves isolated heating, it places high demands on the rotary kiln materials, heat transfer structure, and externally heated flue gas recovery and utilization. It also results in large equipment investment, a complex system structure, and limited single-line scale-up capabilities. For applications requiring coordination with large-scale sulfuric acid plants or other by-product tail gas systems, a more suitable temperature control method for large-scale industrial applications is still needed. Summary of the Invention

[0007] The technical problem to be solved by this invention is to provide a temperature control method for a calcium sulfate reduction reactor. This method makes full use of low-oxygen industrial tail gas, system tail gas recirculation, the heat absorption effect of water-containing materials, and the removal of excess heat by cooling water or cooling gas to control the peak temperature of the reduction reaction zone within a safe temperature range that suppresses sulfur release side reactions, while also taking into account the recovery and utilization of tail gas waste heat.

[0008] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0009] A method for temperature control in a calcium sulfate reduction reactor includes the following steps:

[0010] S1. The hydrated calcium sulfate raw material is fed into a material drying and preheating system consisting of a dispersing dryer and / or a cyclone dust collector. The free water or at least part of the crystal water is removed by the tail gas discharged from the reduction reactor to obtain the preheated material.

[0011] S2. The preheated material is fed into a fluidized bed, suspension, or rotary kiln reduction reactor, and a non-sulfur-containing reducing agent is added to the reduction reactor through a non-sulfur-containing reducing agent inlet, so that calcium sulfate is reduced to calcium sulfide in a reducing atmosphere.

[0012] S3. Temperature control is applied to the reduction reactor to keep the peak temperature inside the reduction reactor below a preset upper limit. The temperature control includes at least one of the following methods:

[0013] S31. Low-oxygen industrial tail gas with an oxygen content of less than 12 vol% is introduced into the reduction reactor through the low-oxygen industrial tail gas inlet, and the amount of air added through the air inlet and / or the amount of low-oxygen industrial tail gas added is adjusted.

[0014] S32. Add wet calcium sulfate and / or partially dehydrated calcium sulfate to the reduction reactor through the wet material bypass inlet;

[0015] S33. Heat is removed by an indirect heat exchange device installed in the reduction reactor;

[0016] S34. The reduction temperature is maintained by an indirect heating device using electromagnetic heating and / or microwave heating;

[0017] S4. The gas and part of the powder discharged from the reduction reactor are sequentially fed into the secondary cyclone preheater and the primary cyclone preheater to exchange heat with the calcium sulfate raw material. The exhaust gas after heat exchange is supplemented with air through the combustion air inlet to burn off the residual reducing components. The exhaust gas after combustion is then sent to the exhaust gas treatment system through the dispersion dryer, the drying heat exchanger, the cyclone dust collector and the fan, and / or a part of the exhaust gas is returned to the reduction reactor as low-oxygen industrial exhaust gas.

[0018] S5. The calcium sulfide obtained in the reduction reactor is discharged through the product outlet and either used as a product or sent to a subsequent rotary kiln for a second-stage reaction to produce SO2.

[0019] Wherein, when the reduction reactor is a rotary kiln, the preset upper limit is less than 1000°C; when the reduction reactor is a suspension reduction furnace or a fluidized bed, the preset upper limit is less than 900°C.

[0020] Furthermore, the calcium sulfate raw material includes one or more of dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum.

[0021] Furthermore, the non-sulfur-containing reducing agent is a solid carbonaceous reducing agent and / or a reducing gas; the solid carbonaceous reducing agent is one or more of coke, anthracite, bituminous coal, lignite, raw coal or biomass fuel, and the reducing gas is one or more of CO, H2, CH4, NH3, semi-water gas or methane partially oxidized gas.

[0022] Furthermore, the low-oxygen industrial tail gas is selected from one or more of the following: tail gas from the sulfuric acid absorption tower, low-oxygen tail gas discharged from this system, CO2 tail gas discharged from the ammonia synthesis unit, N2 gas discharged from the oxygen production unit, flue gas discharged from the combustion furnace, high-humidity tail gas discharged from the drying unit, or water vapor.

[0023] Furthermore, when the low-oxygen industrial tail gas is the tail gas exiting the sulfuric acid absorption tower, the oxygen content of the tail gas exiting the sulfuric acid absorption tower is less than 8 vol%, and all or part of it is introduced into the reduction reactor through the low-oxygen industrial tail gas inlet.

[0024] Furthermore, the wet calcium sulfate and / or partially dehydrated calcium sulfate added through the wet material bypass inlet continue to absorb heat through water evaporation and crystal water removal, thereby suppressing local temperature rise in the reduction reactor.

[0025] Furthermore, the indirect heat exchange device is a water-cooled wall and / or a serpentine coil heat exchange device, and uses cooling media such as cooling water, cooling gas or cooling liquid to remove excess heat from the reduction reactor; when cooling water is used to remove heat, the indirect heat exchange device also produces steam or hot water as a byproduct.

[0026] Furthermore, the indirect heating device is an electromagnetic heating device and / or a microwave heating device, and it works in conjunction with the low-oxygen industrial exhaust gas to control the reduction temperature of the reduction reactor.

[0027] Furthermore, when the calcium sulfide is used to further react with the remaining calcium sulfate to produce SO2 and then sulfuric acid, the calcium sulfide enters a subsequent rotary kiln for a two-stage reaction, and the reduction rate of the calcium sulfate in the first-stage reaction is controlled between 25% and 90%. The required reduction rate for the second-stage reaction can also be adjusted and controlled by adding calcium sulfate. When the calcium sulfide is used to produce H2S, thiourea, or other high-reducing sulfur-containing chemical products, the calcium sulfide is discharged as a product through the product outlet, and the reduction rate of the calcium sulfate is controlled to be greater than 90%.

[0028] The beneficial effects of this invention are:

[0029] (1) Replacing part of the air with low-oxygen tail gas can control the adiabatic temperature rise in the reactor from the source and avoid reactor overheating.

[0030] (2) Bypass humidification material heat absorption, heat exchange and heat transfer in the reactor, and electromagnetic heating can meet the temperature control needs of different levels of enterprises and improve the flexibility and stability of temperature regulation.

[0031] (3) The system exhaust gas is used for material drying and preheating, which improves heat utilization and reduces the need for new heat sources;

[0032] (4) It can effectively suppress the side reaction of CaS and CaSO4 to generate CaO and SO2 at high temperature, reduce sulfur loss and tail gas treatment load. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of the present invention;

[0034] Figure 2This is a process flow diagram of Example 1;

[0035] Figure 3 This is a process flow diagram for Example 2;

[0036] Figure 4 This is a process flow diagram for Example 3;

[0037] Figure 5 This is a process flow diagram for Example 4.

[0038] In the diagram, 1-raw material silo; 2-feeder; 3-dispersing dryer; 4-drying heat exchanger; 5-cyclone dust collector; 6-first-stage cyclone preheater; 7-second-stage cyclone preheater; 8-supplementary combustion air inlet; 9-reduction reactor; 10-indirect heat exchange device; 11-indirect heating device; 12-non-sulfur-containing reducing agent inlet; 13-wet material bypass inlet; 14-air inlet; 15-product outlet; 16-low-oxygen industrial exhaust gas inlet; 17-fan. Detailed Implementation

[0039] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0040] Reference Figure 1 The system shown in this embodiment mainly includes a raw material silo 1, a feeder 2, a dispersing dryer 3, a drying heat exchanger 4, a cyclone dust collector 5, a primary cyclone preheater 6, a secondary cyclone preheater 7, a supplementary combustion air inlet 8, a reduction reactor 9, an indirect heat exchange device 10, a non-sulfur-containing reducing agent inlet 12, a wet material bypass inlet 13, an air inlet 14, a product outlet 15, a low-oxygen industrial tail gas inlet 16, and a fan 17. All connections are made through pipelines, which can be easily understood by those skilled in the art based on existing technology or the accompanying drawings. Operating conditions, detection methods, and equipment configurations not specifically described can be implemented using conventional techniques in the field. In practice, conventional detection components such as thermocouples, infrared temperature measuring devices, O2 analyzers, and CO analyzers can be used to monitor the temperature and atmosphere at key locations, and the reducing agent dosage, valve opening, induced draft volume, return air volume, wet material addition amount, and cooling medium flow rate can be used as adjustment variables. This application can control production through various temperature control measures, such as total gas oxygen control, wet material bypass heat absorption, in-reactor heat exchange and heat transfer, or direct electromagnetic and / or microwave heating. The specific measures can be adopted individually or in combination depending on the different reactor types and product routes.

[0041] In this application, the discharge end of the raw material silo 1 is connected to the inlet end of the feeder 2, the discharge end of the feeder 2 is connected to the inlet end of the dispersing dryer 3, the discharge end of the dispersing dryer 3 is connected to the drying heat exchanger 4, the discharge end of the drying heat exchanger 4 is connected to the cyclone dust collector 5, the solid outlet of the cyclone dust collector 5 is connected to the feed pipeline of the primary cyclone preheater 6, the solid outlet of the primary cyclone preheater 6 is connected to the secondary cyclone preheater 7, and the solid outlet of the secondary cyclone preheater 7 is connected to the reduction reactor 9. The non-sulfur-containing reducing agent inlet 12, the wet material bypass inlet 13, the air inlet 14, and the low-oxygen industrial tail gas inlet 16 are respectively connected to the reduction reactor 9. The tail gas outlet of the reduction reactor 9 is sequentially connected to the secondary cyclone preheater 7, the primary cyclone preheater 6, the dispersing dryer 3, the drying heat exchanger 4, the cyclone dust collector 5, and the fan 17. The outlet of blower 17 is connected to the exhaust gas treatment system and can selectively connect to the low-oxygen industrial exhaust gas inlet 16 to return a portion of the low-oxygen exhaust gas to the reduction reactor 9. The reduction reactor 9 is provided with a product outlet 15 for discharging calcium sulfide-containing products. An indirect heat exchange device 10 is installed inside the reduction reactor 9 to remove excess heat from the reactor via a cooling medium.

[0042] Example 1

[0043] Reference Figure 2 Using gypsum dihydrate as raw material, the temperature of the reduction reactor 9 is controlled by using all the tail gas from the sulfuric acid absorption tower as low-oxygen industrial tail gas, and SO2 is produced by a two-stage reaction, which is then used to produce sulfuric acid.

[0044] After filtration and dehydration, the raw materials enter the raw material silo 1, are metered, and then fed into the dispersing dryer 3 via the feeder 2. After further direct heat exchange via the drying heat exchanger 4, they enter the parallel cyclone dust collector 5 for gas-solid separation. The separated gas is discharged into the tail gas treatment system via the fan 17. Solids enter the inlet pipe of the primary cyclone preheater 6 via pipes and a spreader. The solids separated by the primary cyclone preheater 6 enter the secondary cyclone preheater 7. The solids separated by the secondary cyclone preheater 7 enter the fluidized bed, suspended state, or rotary kiln reduction reactor 9. One or more non-sulfur reducing agents selected from anthracite, bituminous coal, lignite, raw coal, biomass fuel, CO, H2, CH4, NH3, semi-water gas, or methane are added to the fluidized bed, suspended state, or rotary kiln reduction reactor 9 via the non-sulfur reducing agent inlet 12.

[0045] The tail gas exiting the sulfuric acid absorption tower typically has an oxygen content of less than 8%, and may also contain small amounts of sulfuric acid mist, SO2, and nitrogen oxides. In this embodiment, all the tail gas exiting the sulfuric acid absorption tower is introduced as low-oxygen industrial tail gas through the low-oxygen industrial tail gas inlet 16 into the fluidized bed, suspended, or rotary kiln reduction reactor 9. By controlling the amount of air added through the air inlet 14, the peak temperature inside the reduction reactor 9 is stably controlled below 900℃, and the reduction rate of the first-stage reaction is controlled between 25% and 90%.

[0046] After completing the first stage of reaction, the gas and some powder material from the fluidized bed, suspended, or rotary kiln reduction reactor 9 sequentially enter the secondary cyclone preheater 7 and the primary cyclone preheater 6, etc., to exchange heat with the gypsum raw material. The temperature of the gypsum raw material gradually increases, while the temperature of the gas gradually decreases. The reaction product solid calcium sulfide obtained in the reduction reactor 9 is discharged through the product outlet 15 and all of it enters the rotary kiln. In the rotary kiln, a second-stage reaction occurs at a higher temperature to produce SO2.

[0047] The reducing agent gas exiting the primary cyclone preheater 6 is added to air through the combustion air inlet 8, causing the reducing agent to burn completely within the pipeline, achieving heat recovery and eliminating its hazards. The exhaust gas from the combustion and elimination of reducing substances passes through the dispersion dryer 3 and the drying heat exchanger 4, where it directly exchanges heat with the gypsum before entering the parallel cyclone dust collector 5 and fan 17, and is then sent to the waste gas treatment system. After treatment, it meets emission standards.

[0048] Conventional sulfuric acid plants typically desulfurize and demistate the tail gas from the sulfuric acid absorption tower before discharging. In this embodiment, all the tail gas from the sulfuric acid absorption tower is introduced as low-oxygen industrial tail gas through the low-oxygen industrial tail gas inlet 16 into a fluidized bed, suspended, or rotary kiln reduction reactor 9. Inside the reduction reactor 9, sulfuric acid can be decomposed into SO2 at high temperatures, and nitrogen oxides can be reduced in a reducing atmosphere. Simultaneously, the sulfuric acid tail gas is extremely dry; when used for raw material drying, its drying capacity is far superior to hot flue gas at the same temperature. This reduces investment in treatment equipment while effectively utilizing its drying potential and reducing overall waste gas emissions.

[0049] Example 2

[0050] Reference Figure 3 In this embodiment, hemihydrate gypsum and anhydrous gypsum are used as raw materials. The low-oxygen tail gas discharged from this system is partially circulated and the wet material addition is controlled to control the reactor temperature. Calcium sulfide is produced by fluidized bed, suspended state or rotary kiln reduction reactor 9, and H2S, thiourea or other high-reducing sulfur-containing chemical products are further produced.

[0051] After filtration and dehydration, the raw materials enter the raw material silo 1, are metered, and then fed into the dispersing dryer 3 via the feeder 2. After further direct heat exchange via the drying heat exchanger 4, they enter the parallel cyclone dust collector 5 for gas-solid separation. The separated gas is discharged into the tail gas treatment system via the fan 17. Solids enter the inlet pipe of the primary cyclone preheater 6 via pipes and a spreader. The solids separated by the primary cyclone preheater 6 enter the secondary cyclone preheater 7. The solids separated by the secondary cyclone preheater 7 enter the fluidized bed, suspended state, or rotary kiln reduction reactor 9. One or more non-sulfur reducing agents selected from anthracite, bituminous coal, lignite, raw coal, biomass fuel, CO, H2, CH4, NH3, semi-water gas, or methane are added to the fluidized bed, suspended state, or rotary kiln reduction reactor 9 via the non-sulfur reducing agent inlet 12.

[0052] In this embodiment, the low-oxygen exhaust gas discharged from the system is partially recycled and introduced into the fluidized bed, suspended state, or rotary kiln reduction reactor 9 through the low-oxygen industrial exhaust gas inlet 16. By controlling the amount of air added at the air inlet 14, the amount of circulating gas, and the amount of wet material added at the wet material bypass inlet 13, the peak temperature inside the reduction reactor 9 is stably controlled below 950°C, and the reduction rate is controlled above 90%.

[0053] After completing one stage of the reaction, the gas and some powder material from the fluidized bed, suspended, or rotary kiln reduction reactor 9 sequentially enter the secondary cyclone preheater 7 and the primary cyclone preheater 6, etc., to exchange heat with the gypsum raw material. The temperature of the gypsum raw material gradually increases, while the temperature of the gas gradually decreases. The reaction product, solid calcium sulfide, obtained in the reduction reactor 9, is discharged through the product outlet 15 as the product.

[0054] The reducing agent gas exiting the primary cyclone preheater 6 is added to air through the combustion air inlet 8, causing complete combustion of the reducing agent within the pipeline. This achieves heat recovery while eliminating its harmful effects. The exhaust gas from the combustion and elimination of reducing substances passes through the dispersion dryer 3 and the drying heat exchanger 4, where it directly exchanges heat with gypsum before entering the parallel cyclone dust collector 5 and fan 17. A portion is sent to the waste gas treatment system for treatment and emission compliance. The remaining portion is returned to the reduction reactor 9 as low-oxygen exhaust gas.

[0055] Example 3

[0056] Reference Figure 4 In this embodiment, gypsum dihydrate, gypsum hemihydrate, and anhydrous gypsum are used as raw materials. The reactor temperature is controlled by controlling the amount of wet material added and by setting up water-cooled walls and / or serpentine coil heat exchange devices in the reactor. Calcium sulfide is produced by fluidized bed, suspended state, or rotary kiln reduction reactor 9, and H2S, thiourea, or other high-reducing sulfur-containing chemical products are further produced.

[0057] After filtration and dehydration, the raw materials enter the raw material silo 1, are metered, and then fed into the dispersing dryer 3 via the feeder 2. After further direct heat exchange via the drying heat exchanger 4, they enter the parallel cyclone dust collector 5 for gas-solid separation. The separated gas is discharged into the tail gas treatment system via the fan 17. Solids enter the inlet pipe of the primary cyclone preheater 6 via pipes and a spreader. The solids separated by the primary cyclone preheater 6 enter the secondary cyclone preheater 7. The solids separated by the secondary cyclone preheater 7 enter the fluidized bed, suspended state, or rotary kiln reduction reactor 9. One or more non-sulfur reducing agents selected from anthracite, bituminous coal, lignite, raw coal, biomass fuel, CO, H2, CH4, NH3, semi-water gas, or methane are added to the fluidized bed, suspended state, or rotary kiln reduction reactor 9 via the non-sulfur reducing agent inlet 12.

[0058] In this embodiment, a water-cooled wall and / or a serpentine coil indirect heat exchange device 10 are provided inside the reduction reactor 9, and excess heat in the reduction reactor 9 is removed by cooling media such as cooling water, cooling gas, and cooling liquid. By controlling the amount of wet material added to the wet material bypass inlet 13 and the amount of air added to the air inlet 14, the peak temperature in the reduction reactor 9 is stably controlled below 900°C, and the reduction rate is controlled above 90%.

[0059] After completing one stage of the reaction, the gas and some powder material from the fluidized bed, suspended, or rotary kiln reduction reactor 9 sequentially enter the secondary cyclone preheater 7 and the primary cyclone preheater 6, etc., to exchange heat with the gypsum raw material. The temperature of the gypsum raw material gradually increases, while the temperature of the gas gradually decreases. The reaction product, solid calcium sulfide, obtained in the reduction reactor 9, is discharged through the product outlet 15 as the product.

[0060] The reducing agent gas exiting the primary cyclone preheater 6 is added to air through the combustion air inlet 8, causing the reducing agent to burn completely within the pipeline, achieving heat recovery and eliminating its hazards. The exhaust gas from the combustion and elimination of reducing substances passes through the dispersion dryer 3 and the drying heat exchanger 4, where it directly exchanges heat with the gypsum before entering the parallel cyclone dust collector 5 and fan 17, and is then sent to the waste gas treatment system. After treatment, it meets emission standards.

[0061] Example 4

[0062] Reference Figure 5 Using gypsum dihydrate as raw material, the temperature of the reduction reactor 9 is controlled by electromagnetic and / or microwave heating and a portion of the tail gas from the sulfuric acid absorption tower as low-oxygen industrial tail gas. SO2 is produced in a two-stage reaction, and sulfuric acid is further produced.

[0063] After filtration and dehydration, the raw materials enter the raw material silo 1, are metered, and then fed into the dispersing dryer 3 via the feeder 2. After further direct heat exchange via the drying heat exchanger 4, they enter the parallel cyclone dust collector 5 for gas-solid separation. The separated gas is discharged into the tail gas treatment system via the fan 17. Solids enter the inlet pipe of the primary cyclone preheater 6 via pipes and a spreader. The solids separated by the primary cyclone preheater 6 enter the secondary cyclone preheater 7. The solids separated by the secondary cyclone preheater 7 enter the fluidized bed, suspended state, or rotary kiln reduction reactor 9. One or more non-sulfur reducing agents selected from anthracite, bituminous coal, lignite, raw coal, biomass fuel, CO, H2, CH4, NH3, semi-water gas, or methane are added to the fluidized bed, suspended state, or rotary kiln reduction reactor 9 via the non-sulfur reducing agent inlet 12.

[0064] In this embodiment, an electromagnetic or / and microwave electric heating device 11 and an appropriate amount of sulfuric acid absorption tower tail gas added from the low-oxygen industrial tail gas inlet 16 are used as temperature control methods to stably control the peak temperature in the reduction reactor 9 below 900°C and the reduction rate above 90%.

[0065] After completing the first stage of reaction, the gas and some powder material from the fluidized bed, suspended, or rotary kiln reduction reactor 9 sequentially enter the secondary cyclone preheater 7 and the primary cyclone preheater 6, etc., to exchange heat with the gypsum raw material. The temperature of the gypsum raw material gradually increases, while the temperature of the gas gradually decreases. The reaction product solid calcium sulfide obtained in the reduction reactor 9 is discharged through the product outlet 15 and all of it enters the rotary kiln. In the rotary kiln, a second-stage reaction occurs at a higher temperature to produce SO2.

[0066] The reducing agent gas exiting the primary cyclone preheater 6 is added to air through the combustion air inlet 8, causing the reducing agent to burn completely within the pipeline, achieving heat recovery and eliminating its hazards. The exhaust gas from the combustion and elimination of reducing substances passes through the dispersion dryer 3 and the drying heat exchanger 4, where it directly exchanges heat with the gypsum before entering the parallel cyclone dust collector 5 and fan 17, and is then sent to the waste gas treatment system. After treatment, it meets emission standards.

[0067] The above embodiments demonstrate that the present invention is not limited to a single temperature control method. Low-oxygen tail gas oxygen control, wet material bypass heat absorption, in-reactor heat exchange and transfer, and electromagnetic heating can be used individually or in combination, depending on the type of raw material, the scale of the equipment, the reactor type, and the requirements of downstream products.

[0068] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. For example, increasing or decreasing the number of preheater stages, changing the location of the supplementary combustion air, changing the location and method of adding solid reducing agent, increasing reactor material circulation, changing the cooling medium for heat transfer, controlling the high reduction rate before adding calcium sulfate, and replacing part of the reducing agent with a portion of the waste-derived fuel RDF added to fluidized bed, suspended, or rotary kiln reduction reactors, etc., still fall within the protection scope of the present invention.

Claims

1. A method for temperature control in a calcium sulfate reduction reactor, characterized in that, Includes the following steps: S1. The water-containing calcium sulfate raw material is fed into a material drying and preheating system consisting of a dispersing dryer (3) and / or a cyclone dust collector (5), and the free water or at least part of the crystal water is removed by the tail gas discharged from the reduction reactor (9) to obtain the preheated material. S2. The preheated material is fed into a fluidized bed, suspension or rotary kiln reduction reactor (9), and a non-sulfur-containing reducing agent is added to the reduction reactor (9) through a non-sulfur-containing reducing agent inlet (12) so that calcium sulfate is reduced to calcium sulfide in a reducing atmosphere; S3. Temperature control is applied to the reduction reactor (9) to keep the peak temperature inside the reduction reactor (9) below a preset upper limit. The temperature control includes at least one of the following methods: S31. Low-oxygen industrial tail gas with an oxygen content of less than 12 vol% is introduced into the reduction reactor (9) through the low-oxygen industrial tail gas inlet (16), and the amount of air added through the air inlet (14) and / or the amount of low-oxygen industrial tail gas added is adjusted. S32. Wet calcium sulfate and / or partially dehydrated calcium sulfate are added to the reduction reactor (9) through the wet material bypass inlet (13); S33, heat is removed by an indirect heat exchange device (10) installed in the reduction reactor (9); S34. The reduction temperature is maintained by an indirect heating device (11) using electromagnetic heating and / or microwave heating; S4. The gas and part of the powder discharged from the reduction reactor (9) are sequentially fed into the secondary cyclone preheater (7) and the primary cyclone preheater (6) to exchange heat with the calcium sulfate raw material. The exhaust gas after heat exchange is supplemented with air through the combustion air inlet (8) to burn the residual reducing components. The exhaust gas after combustion is then sent to the exhaust gas treatment system through the dispersion dryer (3), the drying heat exchanger (4), the cyclone dust collector (5) and the fan (17), and / or a part of the exhaust gas is returned to the reduction reactor (9) as low oxygen industrial exhaust gas. S5. The calcium sulfide obtained in the reduction reactor (9) is discharged through the product outlet (15) and used as a product or enters the subsequent rotary kiln for a second-stage reaction to produce SO2. Wherein, when the reduction reactor (9) is a rotary kiln, the preset upper limit is less than 1000°C; when the reduction reactor (9) is a suspended reduction furnace or a fluidized bed, the preset upper limit is less than 900°C.

2. The temperature control method for the calcium sulfate reduction reactor according to claim 1, characterized in that, The calcium sulfate raw material includes one or more of dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum.

3. The temperature control method for the calcium sulfate reduction reactor according to claim 1, characterized in that, The non-sulfur-containing reducing agent is a solid carbonaceous reducing agent and / or a reducing gas; the solid carbonaceous reducing agent is one or more of coke, anthracite, bituminous coal, lignite, raw coal or biomass fuel, and the reducing gas is one or more of CO, H2, CH4, NH3, semi-water gas or partially oxidized methane.

4. The temperature control method for the calcium sulfate reduction reactor according to claim 1, characterized in that, The low-oxygen industrial tail gas is selected from one or more of the following: tail gas from the sulfuric acid absorption tower, low-oxygen tail gas discharged from this system, CO2 tail gas discharged from the ammonia synthesis unit, N2 gas discharged from the oxygen production unit, flue gas discharged from the combustion furnace, high-humidity tail gas discharged from the drying unit, or water vapor.

5. The temperature control method for the calcium sulfate reduction reactor according to claim 4, characterized in that, When the low-oxygen industrial tail gas is the tail gas exiting the sulfuric acid absorption tower, the oxygen content of the tail gas exiting the sulfuric acid absorption tower is less than 8 vol%, and all or part of it is introduced into the reduction reactor (9) through the low-oxygen industrial tail gas inlet (16).

6. The temperature control method for the calcium sulfate reduction reactor according to claim 1, characterized in that, The wet calcium sulfate and / or partially dehydrated calcium sulfate added through the wet material bypass inlet (13) absorb heat through water evaporation and crystal water removal to suppress local temperature rise in the reduction reactor (9).

7. The temperature control method for the calcium sulfate reduction reactor according to claim 1, characterized in that, The indirect heat exchange device (10) is a water-cooled wall and / or a serpentine coil heat exchange device, and removes excess heat from the reduction reactor (9) by means of cooling water, cooling gas or cooling liquid; when cooling water is used to remove heat, the indirect heat exchange device (10) also produces steam or hot water as a byproduct.

8. The temperature control method for the calcium sulfate reduction reactor according to claim 1, characterized in that, The indirect heating device (11) is an electromagnetic heating device and / or a microwave heating device, and works in conjunction with the low-oxygen industrial tail gas to control the reduction temperature of the reduction reactor (9).

9. The temperature control method for the calcium sulfate reduction reactor according to claim 1, characterized in that, When the calcium sulfide is used to further react with the remaining calcium sulfate to produce SO2 and sulfuric acid, the calcium sulfide enters a subsequent rotary kiln for a second-stage reaction, and the reduction rate of the first-stage reaction of calcium sulfate is controlled at 25% to 90%. The reduction rate required for the second-stage reaction can also be adjusted and controlled by adding calcium sulfate; when the calcium sulfide is used to produce H2S, thiourea or other high-reducing sulfur-containing chemical products, the calcium sulfide is discharged as a product through the product discharge port (15), and the reduction rate of calcium sulfate is controlled to be greater than 90%.

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