A system and method for producing cement and co-producing sulphuric acid by pre-decomposing gypsum outside a kiln

Abstract

The application discloses a system and method for producing cement and sulfuric acid by gypsum pre-decomposition outside a kiln, which comprises a kiln preheater, a rotary kiln, a cooler, a reduction decomposition furnace, a sulfur-rich flue gas furnace preheater, a carbon monoxide digestion furnace, a fluidized reduction gas generator and an acid production system. Raw materials enter the reduction decomposition furnace through the kiln preheater and the sulfur-rich flue gas furnace preheater respectively; the fluidized reduction gas generator converts fossil fuels into gaseous reducing agent containing CO and feeds it into the reduction decomposition furnace, calcium sulfate is decomposed in a reducing atmosphere, SO2-containing flue gas is discharged after passing through the sulfur-rich flue gas furnace preheater and then enters the acid production system after acid corrosion-resistant dust collection, and the kiln preheater flue gas is discharged after dust collection; air in the high-temperature section of the cooler enters the carbon monoxide digestion furnace to digest CO, and waste gas in the medium and low-temperature section enters the fluidized reduction gas generator. The application realizes the decomposition of calcium sulfate outside the kiln, the SO2 concentration reaches 15%-20%, the kiln head waste gas is zero discharged, the clinker quality is good, and the acid production cost is low.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization technology of gypsum resources, specifically relating to a system and method for pre-decomposition acid production and cement co-production outside a gypsum kiln. Background Technology

[0002] The chemical industry and desulfurization environmental protection sector generate large quantities of solid waste, including phosphogypsum, fluorogypsum, and desulfurization gypsum. Current mainstream stockpiling methods not only occupy significant land but also pose substantial environmental and safety risks. A sustainable, large-scale utilization pathway is needed for the comprehensive utilization of industrial by-product gypsum. The main component of industrial by-product gypsum is calcium sulfate (CaSO4). Besides silicon, calcium, and sulfur, it also contains trace amounts of iron, aluminum, phosphorus, and fluorine. Except for sulfur, phosphorus, and fluorine, the other elements are commonly used in cement raw materials. The high-temperature calcination process in cement production can release sulfur as gas, and this sulfur-containing flue gas can be used to produce sulfuric acid. Therefore, co-producing sulfuric acid and cement from gypsum is a feasible approach to realizing the resource utilization of gypsum.

[0003] Generally, calcium sulfate in gypsum begins to decompose at 900℃, reaches its maximum decomposition rate at 1100-1200℃, and complete decomposition occurs above 1300℃. This decomposition temperature is higher than that of calcium carbonate in limestone, which is one of the technical challenges in using gypsum to replace limestone in cement production. To lower the decomposition temperature, reducing agents or a reducing atmosphere are usually used. Commonly used reducing agents are divided into gaseous and solid states. Gaseous reducing agents mainly include CO, H2, and CH4, while solid reducing agents mainly include high-sulfur coal, anthracite, coke, and coal char. The mechanism of gypsum reduction and decomposition is relatively complex, especially after the addition of a reducing agent, where multiple chemical reactions occur simultaneously. Furthermore, the components such as potassium, sodium, and iron in industrial by-product gypsum interact, resulting in the following main chemical reactions: ① CaSO4→CaO+SO2+0.5O2 ② 2CaSO4 + C → 2CaO + 2SO2 + CO2 ③ CaSO4 + CO → CaO + SO2 + CO2 ④ CaSO4 + 4CO → CaS + 4CO2 ⑤ CaSO4 + 2C → CaS + 2CO2 ⑥ 3CaSO4 + 2CaS → 4CaO + 4SO2 The solid-state reaction ⑥ between CaSO4 and CaS has a positive Gibbs free energy below 1200℃, making it relatively difficult to occur compared to other reactions. However, when the reaction temperature exceeds 1200℃, a large amount of liquid phase appears, and the silicate solid-state reaction begins, easily solidifying unreacted CaS within the clinker, leading to a decrease in clinker quality. Therefore, to suppress the production of excess CaS, it is necessary to control the over-reduction reactions in reactions ④ and ⑤.

[0004] Phosphorus and fluorine are common elements in gypsum solid waste, a byproduct of industrial production. Phosphorus hinders the calcination of cement clinker, primarily because: after entering the dicalcium silicate lattice, phosphorus prevents the reaction between calcium oxide and dicalcium silicate to form tricalcium silicate mineral phase; phosphorus also increases the surface tension of the liquid phase, hindering the mass transfer of free calcium oxide in the liquid phase, making it difficult for free calcium oxide to be absorbed in the clinker and thus affecting clinker quality. The effect of fluorine on cement clinker calcination varies depending on its content: when the fluorine content is low, it can lower the temperature at which the liquid phase appears and the formation temperature of tricalcium silicate, accelerating the calcination process of cement clinker; however, when the fluorine content is excessive, it can easily lead to crusting and ring formation in the kiln, affecting the operation of the rotary kiln; furthermore, it can cause abnormal growth of tricalcium silicate crystals and the formation of calcium fluorosilicate minerals, resulting in insufficient early strength and subsequent strength reduction in the clinker.

[0005] In conventional gypsum calcination cement production processes, elements in the gypsum that affect clinker calcination, such as phosphorus and fluorine, are generally not pretreated; for example... Figure 1 As shown, a suspension preheater is used for preheating, and both the calcium sulfate decomposition and clinker calcination processes occur within the rotary kiln. Solid reducing agents, such as coke or coal char, are commonly used and are directly added to the feed pipe of the lowest-level suspension preheater, entering the kiln for calcination along with the hot raw materials. The above process has the following technical defects: 1) Elements such as phosphorus and fluorine in gypsum solid waste significantly affect clinker quality. If these elements in gypsum are not pretreated to limit their content, it is easy to cause clinker quality fluctuations that are difficult to control. 2) When the liquid phase is generated in the kiln, some of the incompletely decomposed calcium sulfate is encapsulated in the clinker, reducing the content of silicate minerals and causing a decrease in clinker strength; the degree of reaction of solid particles is difficult to control, resulting in excessive calcium sulfate being over-reduced to calcium sulfide (CaS), which in turn affects the stability of clinker. 3) The reducing atmosphere during calcination in the kiln can easily lead to yellow core material, which causes C3S to be reduced and f-CaO to increase, resulting in reduced clinker strength and poor stability; some solid reducing agents react with oxygen and burn after entering the kiln, thus limiting the reduction effect. 4) The decomposition of calcium sulfate and the calcination of clinker all occur in the rotary kiln. Compared with conventional cement production lines, the rotary kiln equipment needs to be larger under the same output conditions. 5) The SO2 concentration in the flue gas at the preheater outlet is low, resulting in high production costs for subsequent acid production processes. Furthermore, the kiln tail exhaust gas treatment system requires large-scale corrosion-resistant dust collection equipment, leading to high equipment purchase and operating costs.

[0006] Chinese Patent Publication No. CN120268319A discloses an external decomposition device and process for preparing sulfur dioxide flue gas and cement clinker. This method employs a parallel arrangement of a gypsum decomposition column and a corrector material homogenization column on both sides. The solid CaO produced by the gypsum decomposition column is mixed with preheated silica-alumina corrector material before being calcined in a rotary kiln. However, in this technical solution, the gypsum decomposition column and the corrector material preheating column operate in parallel. Excessive heat in the corrector material preheating column can easily lead to the generation of a large amount of liquid phase, affecting the stable operation of the system. Furthermore, the gypsum decomposition process uses a solid-solid reaction method with direct addition of fuel carbon. The limited contact area between CaSO4 and solid carbon results in a low CaSO4 decomposition rate, making it difficult to control the degree of reaction of solid particles and posing a risk of over-reduction to CaS. Simultaneously, this solution does not address the pretreatment of harmful elements fluorine and phosphorus in gypsum, nor does it include carbon monoxide elimination and zero-emission measures for kiln head exhaust gas. Therefore, the issues of clinker product quality fluctuations and flue gas emissions remain unresolved. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a system and method for co-producing cement by pre-decomposing gypsum outside a kiln to produce acid. In terms of raw material processing, it proposes targeted pretreatment schemes for different types of harmful elements in gypsum, controlling the content of harmful elements within acceptable ranges and ensuring clinker quality. In terms of clinker calcination, the process flow is optimized by using external decomposition of calcium sulfate in the kiln, and replacing solid reducing agents with gaseous reducing agents to avoid the problem of uncontrollable reduction effects. This achieves near-complete decomposition of calcium sulfate, improves the calcium sulfate decomposition rate, maintains an oxidizing atmosphere during calcination in the kiln, and ensures clinker quality. The system features high product quality, low energy consumption, low acid production cost, and good environmental performance, realizing the resource utilization of gypsum solid waste.

[0008] The present invention is implemented as follows: a system for pre-decomposition acid production and cement co-production outside a gypsum kiln, comprising a kiln preheater, a rotary kiln, a cooler, a kiln preheater dust collection system, a reduction decomposition furnace, a sulfur-rich flue gas furnace preheater, a carbon monoxide digester, a fluidized bed reducing gas generator, a furnace acid corrosion resistant dust collection system, and an acid production system. The discharge port of the kiln preheater is connected to the first feed port of the reduction decomposition furnace, the discharge port of the sulfur-rich flue gas furnace preheater is connected to the second feed port of the reduction decomposition furnace, and the discharge port of the reduction decomposition furnace is connected to the rotary kiln; the gas outlet of the kiln preheater is connected to the gas inlet of the kiln preheater dust collection system. The fluidized bed reducing gas generator is provided with a fuel inlet and a gas inlet. The gas outlet of the fluidized bed reducing gas generator is connected to the reducing gas inlet of the reduction decomposition furnace. The fluidized bed reducing gas generator is used to convert fossil fuels into a gaseous reducing agent containing carbon monoxide. The flue gas outlet of the reduction decomposition furnace is connected to the inlet of the sulfur-rich flue gas furnace preheater, the outlet of the sulfur-rich flue gas furnace preheater is connected to the inlet of the furnace acid corrosion resistant dust collection system, and the outlet of the furnace acid corrosion resistant dust collection system is connected to the inlet of the acid production system. The carbon monoxide digester is installed on the flue gas duct of the sulfur-rich flue gas furnace preheater, so that all the flue gas from the sulfur-rich flue gas furnace preheater passes through the carbon monoxide digester before entering the furnace acid corrosion resistant dust collection system; the high-temperature section air outlet of the cooler is connected to the air inlet of the carbon monoxide digester through the high-temperature exhaust air duct at the kiln head; the medium-low temperature section exhaust gas outlet of the cooler is connected to the gas inlet of the fluidized reducing gas generator through the medium-low temperature exhaust air duct at the kiln head.

[0009] In the above technical solution, preferably, the reduction decomposition furnace includes a furnace body, the lower part of which is provided with a tangential vortex structure, the inlet of which is connected to the outlet of a fluidized reducing gas generator, so that the gaseous reducing agent containing carbon monoxide enters the furnace body tangentially to form a spiral flow field; the middle part of the furnace body is provided with a multi-point feeding device, which is connected to the outlet of the kiln preheater and the outlet of the sulfur-rich flue gas furnace preheater respectively; the upper part of the furnace body is provided with a top vortex structure, which is used to prolong the residence time of materials and gases in the furnace; the outlet of the top vortex structure is provided with a downward pipe, the outlet of which is connected to the final stage cyclone of the sulfur-rich flue gas furnace preheater.

[0010] In the above technical solution, preferably, the flue gas from the kiln preheater and the flue gas from the sulfur-rich flue gas furnace preheater are independent of each other and enter the dust collection system of the kiln preheater and the acid corrosion resistant dust collection system of the furnace respectively; the dust collection system of the kiln preheater is a conventional dust collection system and the acid corrosion resistant dust collection system of the furnace is an acid corrosion resistant dust collection system.

[0011] In the above technical solution, preferably, the kiln preheater includes a multi-stage kiln cyclone separator connected in sequence, and the discharge port of the kiln preheater is located at the feed pipe of the second-to-last kiln cyclone separator; the sulfur-rich flue gas furnace preheater includes a multi-stage furnace cyclone separator connected in sequence, and the discharge port of the sulfur-rich flue gas furnace preheater is located at the feed pipe of the second-to-last furnace cyclone separator.

[0012] In the above technical solution, a further preferred embodiment is that the kiln tail flue of the rotary kiln is connected to the air inlet of the kiln preheater through the rising flue, the discharge port of the reduction decomposition furnace is connected to the rising flue, and the discharge port of the final kiln cyclone of the kiln preheater is connected to the rotary kiln.

[0013] In the above technical solution, a further preferred embodiment is that the discharge port of the final stage cyclone separator of the sulfur-rich flue gas furnace preheater is connected to the rotary kiln.

[0014] In the above technical solution, preferably, the high-temperature section air outlet of the cooler is also connected to the rotary kiln.

[0015] A method for co-producing cement from gypsum using the above system via pre-decomposition outside a gypsum kiln includes the following steps: The gypsum raw materials are pretreated to control the P2O5 content in the raw meal after batching to be ≤1.0% and the F content to be ≤1.05%. After the pretreated gypsum is mixed with other raw materials and ground, part of the raw meal is fed into the kiln preheater and then fed into the reduction decomposition furnace after multi-stage preheating; the other part of the raw meal is fed into the sulfur-rich flue gas furnace preheater and then fed into the reduction decomposition furnace after preheating. Fossil fuel is fed into a fluidized bed reducing gas generator, and waste gas from the low-temperature section of the cooler is introduced through the low-temperature exhaust air pipe at the kiln head to produce a gaseous reducing agent containing carbon monoxide, which is then introduced into the reduction decomposition furnace. Calcium sulfate in the raw material is decomposed in a reducing atmosphere in a reduction decomposition furnace to generate solid products containing calcium oxide and flue gas containing sulfur dioxide. The solid products after decomposition are fed into a rotary kiln after gas-solid separation. The flue gas with high sulfur dioxide content generated by decomposition is discharged through a carbon monoxide digester and a sulfur-rich flue gas furnace preheater outlet in sequence. After acid corrosion dust collection, it enters the acid production system for the preparation of sulfuric acid. The flue gas discharged from the kiln preheater enters the kiln preheater dust collection system before being discharged and is not used for the production of sulfuric acid; Fuel and combustion air are introduced into the rotary kiln for clinker calcination; air from the high-temperature section of the cooler is sent to the carbon monoxide digester through the high-temperature exhaust air duct at the kiln head to digest the carbon monoxide in the flue gas.

[0016] In the above technical solution, preferably, the pretreatment is as follows: when the fluorine and / or phosphorus content in the gypsum raw material makes the P2O5 content in the raw material > 1.0% and / or the F content > 1.05%, the gypsum raw material is washed with water using a low-concentration strong acid, and the acid solution is preheated to 40-60°C using the waste heat of the cement kiln system, so that after the gypsum raw material enters the acid solution, P2O5 is converted into H3PO4 and dissolved in the solution, the fluoride structure is destroyed, and the fluorine element is carried away by the solution in the form of fluoride ions.

[0017] In the above technical solution, preferably, the fuel feed ratio of the fluidized reducing gas generator to the rotary kiln is 2:8 to 3.5:6.5, and the outlet flue gas temperature of the fluidized reducing gas generator is 1050 to 1150°C and the CO concentration is 10000 to 20000 ppm.

[0018] In the above technical solution, preferably, the outlet flue gas temperature of the reduction decomposition furnace is 850-950℃, and the calcium sulfate decomposition rate in the reduction decomposition furnace is 90%-99%.

[0019] In the above technical solution, preferably, the SO2 concentration in the flue gas at the outlet of the sulfur-rich flue gas furnace preheater is 15% to 20%.

[0020] In the above technical solution, preferably, the high-temperature air of the cooler is also introduced into the rotary kiln as combustion air for clinker calcination. The high-temperature air used for clinker calcination, the medium- and low-temperature exhaust gas used for preparing gaseous reducing agents, and the high-temperature air used for carbon monoxide decomposition form a staged full utilization of cooler exhaust gas, achieving zero emission of kiln head exhaust gas.

[0021] The advantages and positive effects of this invention are: 1) This invention ensures that the content of P2O5 and F in the raw material is within an acceptable range by pretreating the fluorine and phosphorus elements in the gypsum raw material, and the quality of the clinker product produced after calcination meets the requirements, thus solving the technical problem of harmful elements affecting the quality of clinker.

[0022] 2) This invention separates the calcium sulfate decomposition process from the clinker calcination process through the process design of the reduction decomposition furnace, thereby improving the calcium sulfate decomposition rate and avoiding the problem of undecomposed calcium sulfate being encapsulated in the clinker by the liquid phase, resulting in low clinker strength; by adjusting the amount of fossil fuel, the CO concentration at the outlet of the fluidized bed reducing gas generator is controlled, thereby avoiding the situation of calcium sulfate being over-reduced to calcium sulfide.

[0023] 3) This invention uses CO prepared by a fluidized bed reducing gas generator as a gaseous reducing agent to replace the conventional solid reducing agent. The reduction process occurs inside the reduction decomposition furnace, where the solid material is in a suspended state, resulting in a large contact area and better reduction effect. Increasing the CO concentration can achieve almost complete decomposition of calcium sulfate. The flue gas from the reduction decomposition furnace enters the acid production system separately, with a sulfur dioxide content as high as 15%-20%, resulting in lower acid production costs. A carbon monoxide digester is set up to digest excess carbon monoxide in the flue gas from the reduction decomposition furnace using the kiln head exhaust gas, thus solving the CO emission problem.

[0024] 4) The reduction decomposition furnace of the present invention introduces gas with a high carbon monoxide content. The unique tangential vortex structure makes the gas enter the furnace tangentially, presenting a spiral flow field, so that the material and gas are fully mixed and the reduction reaction is fully carried out. The top vortex structure designed at the top of the furnace body further extends the residence time of the material and gas in the furnace, improves the calcium sulfate decomposition rate, and ensures that the calcium sulfate decomposition reaction is basically completed in the furnace.

[0025] 5) This invention can achieve calcination in an oxidizing atmosphere inside the kiln, with virtually no calcium sulfate decomposition process occurring inside the kiln. The kiln temperature is increased, and the quality of clinker calcination is improved. Compared with the traditional gypsum cement production process, the rotary kiln only undertakes the clinker calcination task, and the equipment size can be appropriately reduced. The decomposition process occurs in the reduction decomposition furnace and is a suspension calcination, resulting in lower system energy consumption.

[0026] 6) The exhaust gas from the kiln head cooler of the present invention is used for calcination, reducing gas preparation and carbon monoxide decomposition in the kiln. The kiln head achieves zero exhaust gas emission and does not require additional dust collection equipment, thus saving investment costs. Attached Figure Description

[0027] Figure 1 This is a process flow diagram for the co-production of cement from conventional gypsum acid production. Figure 2 The process flow for pre-decomposition acid production and cement co-production outside the gypsum kiln of the present invention is as follows: Figure 1 ; Figure 3 The process flow for pre-decomposition acid production and cement co-production outside the gypsum kiln according to the present invention is as follows: Figure 2 ; Figure 4 This is a schematic diagram of the reduction decomposition furnace of the present invention.

[0028] In the diagram: 1. Kiln preheater; 2. Rising flue; 3. Rotary kiln; 4. Cooler; 5. Kiln preheater dust collection system; 6. Kiln high-temperature fan; 7. Reduction decomposition furnace; 7-1. Tangential vortex structure; 7-2. Multi-point feeding device; 7-3. Top vortex structure; 7-4. Downward duct; 8. C6 kiln cyclone separator; 9. C7 kiln cyclone separator; 10. C8 kiln cyclone separator; 11. Carbon monoxide digester; 12. Kiln head high-temperature waste air duct; 13. Kiln head medium-low temperature waste air duct; 14. Fluidized reducing gas generator; 15. Kiln acid corrosion resistant dust collection system; 16. Acid production system; 17. Kiln high-temperature fan; 18. Waste air circulation duct. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0030] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0031] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] my country generates over 50 million tons of gypsum solid waste annually. The resource utilization of gypsum solid waste is a crucial project in my country's environmental protection campaign. Gypsum-to-acid and co-production of cement is a relatively stable, environmentally friendly, and high-demand treatment method. However, practical application has revealed that cement produced using traditional methods lags behind conventional cement production lines in terms of quality and strength. Optimizing the gypsum-to-acid and co-production cement process to obtain higher-quality cement products is a key technical challenge for the future large-scale application of this technology. This invention addresses key technical challenges in the gypsum-to-cement process, significantly improving system energy consumption and product quality.

[0033] Example 1 Please see Figure 2 The system for co-producing cement by pre-decomposition acid production outside the gypsum kiln provided in this embodiment includes a kiln preheater 1, a rotary kiln 3, a cooler 4, a kiln preheater dust collection system 5, a kiln high-temperature fan 6, a reduction decomposition furnace 7, a sulfur-rich flue gas furnace preheater, a carbon monoxide digester 11, a kiln head high-temperature waste air duct 12, a kiln head medium-low temperature waste air duct 13, a fluidized reducing gas generator 14, a furnace acid corrosion resistant dust collection system 15, an acid production system 16, and a furnace high-temperature fan 17.

[0034] The discharge port of the kiln preheater 1 is connected to the first feed port of the reduction decomposition furnace 7, the discharge port of the sulfur-rich flue gas preheater is connected to the second feed port of the reduction decomposition furnace 7, and the discharge port of the reduction decomposition furnace 7 is connected to the rotary kiln 3. The air outlet of the kiln preheater 1 is connected to the air inlet of the kiln preheater dust collection system 5.

[0035] The fluidized bed reducing gas generator 14 is provided with a fuel inlet and a gas inlet. The gas outlet of the fluidized bed reducing gas generator 14 is connected to the reducing gas inlet of the reduction decomposition furnace 7. The fluidized bed reducing gas generator 14 is used to convert fossil fuels into a gaseous reducing agent containing carbon monoxide.

[0036] The flue gas outlet of the reduction decomposition furnace 7 is connected to the inlet of the sulfur-rich flue gas furnace preheater. The outlet of the sulfur-rich flue gas furnace preheater is connected to the inlet of the furnace acid corrosion resistant dust collection system 15. The outlet of the furnace acid corrosion resistant dust collection system 15 is connected to the kiln high-temperature fan 6. The outlet of the furnace acid corrosion resistant dust collection system 15 is connected to the inlet of the acid production system 16. The outlet of the acid production system 16 is connected to the furnace high-temperature fan 17.

[0037] The carbon monoxide digester 11 is installed on the flue gas duct of the sulfur-rich flue gas furnace preheater, so that all the flue gas from the sulfur-rich flue gas furnace preheater passes through the carbon monoxide digester 11 before entering the furnace acid corrosion resistant dust collection system 15. The high-temperature section air outlet of the cooler 4 is connected to the air inlet of the carbon monoxide digester 11 through the kiln head high-temperature waste air duct 12; the medium and low temperature section exhaust gas outlet of the cooler 4 is connected to the gas inlet of the fluidized bed reducing gas generator 14 through the kiln head medium and low temperature waste air duct 13, using the medium and low temperature section exhaust gas as the gasification medium.

[0038] By optimizing the connection relationships of each part of the system, the decomposition of calcium sulfate and the clinker calcination process are separated. The decomposition of calcium sulfate is completed in the reduction decomposition furnace 7, while the rotary kiln 3 only undertakes the clinker calcination task. Compared with the traditional gypsum cement production process, the equipment size of the rotary kiln 3 can be appropriately reduced. The low-temperature section exhaust gas from the cooler 4 is introduced into the fluidized reducing gas generator 14 to prepare gaseous reducing agent, while the high-temperature section air is used for calcination and carbon monoxide decomposition in the rotary kiln 3, achieving full utilization and zero emission of kiln head exhaust gas. The high sulfur dioxide content flue gas generated in the reduction decomposition furnace enters the sulfur-rich flue gas furnace preheater. After CO is decomposed in the carbon monoxide decomposition furnace 11, the flue gas enters the acid corrosion resistant dust collection system 15 for dust collection and then enters the acid production system 16 to produce sulfuric acid, avoiding environmental pollution caused by CO emissions and increasing the sulfur dioxide content of the flue gas.

[0039] In this embodiment, the kiln preheater includes kiln cyclone separators C1 to C5 connected in sequence, and the discharge port of the kiln preheater is located at the feed pipe of kiln cyclone separator C4; the sulfur-rich flue gas furnace preheater includes kiln cyclone separators C6, C7, and C8 connected in sequence, and the discharge port of the sulfur-rich flue gas furnace preheater is located at the feed pipe of kiln cyclone separator C7 9.

[0040] The tail flue of rotary kiln 3 is connected to the inlet of kiln preheater 1 via rising flue 2. The outlet of reduction decomposition furnace 7 is connected to the inlet of rising flue 2. The discharge port of kiln preheater 1 (C5) is connected to rotary kiln 3. The discharge port of furnace preheater 1 (C8) is connected to rotary kiln 3. The air outlet of the high-temperature section of cooler 4 is also connected to rotary kiln 3.

[0041] The flue gas from kiln preheater 1 is independent of the flue gas from the sulfur-rich flue gas furnace preheater, and enters the kiln preheater dust collection system 5 and the furnace acid corrosion resistant dust collection system 15, respectively. The kiln preheater dust collection system 5 is a conventional dust collection system, while the furnace acid corrosion resistant dust collection system 15 is an acid corrosion resistant dust collection system. The flue gas from the kiln preheater 1 has a low SO2 concentration and is discharged after entering the conventional dust collection system; it is not used for sulfuric acid production. The flue gas from the sulfur-rich flue gas furnace preheater has a high SO2 content (15%-20%) and enters the acid corrosion resistant dust collection system 15. After dust collection, it enters the acid production system 16 for acid production, avoiding the dilution of the acid production feed gas by low-concentration flue gas, thus reducing acid production costs.

[0042] like Figure 4 As shown, the reduction decomposition furnace 7 includes a furnace body. A tangential vortex structure 7-1 is designed at the lower part of the furnace body. The inlet of the tangential vortex structure 7-1 is connected to the outlet of the fluidized reducing gas generator 14, allowing the gaseous reducing agent containing carbon monoxide to enter the furnace body tangentially, forming a spiral flow field. A multi-point feeding device 7-2 is installed in the middle of the furnace body, which is connected to the outlet of the kiln preheater 1 and the outlet of the sulfur-rich flue gas furnace preheater. A top vortex structure 7-3 is designed at the upper part of the furnace body to extend the residence time of materials and gases within the furnace. A downward pipe 7-4 is provided at the outlet of the top vortex structure, and the outlet of the downward pipe 7-4 is connected to the inlet of the C8 furnace cyclone separator 10 of the sulfur-rich flue gas furnace preheater.

[0043] After the reduction decomposition furnace 7 is introduced with gas containing high carbon monoxide, the unique tangential vortex structure 7-1 tangential air intake makes the gas present a spiral flow field in the furnace, so that the material and gas are fully mixed and the reduction reaction is fully carried out. The top vortex structure 7-3 designed at the top of the furnace body further extends the residence time of the material and gas in the furnace, improves the calcium sulfate decomposition rate, and ensures that the calcium sulfate decomposition reaction is basically completed in the reduction decomposition furnace 7.

[0044] The fuel feed ratio between the fluidized bed reducing gas generator 14 and the rotary kiln 3 is 2:8 to 3.5:6.5. The outlet flue gas temperature of the fluidized bed reducing gas generator 14 is 1050 to 1150℃, and the CO concentration is 10,000 to 20,000 ppm. The CO concentration at the outlet of the fluidized bed reducing gas generator 14 is controlled by adjusting the fossil fuel consumption to avoid over-reduction of calcium sulfate to calcium sulfide. The outlet flue gas temperature of the reduction decomposition furnace 7 is 850 to 950℃, and the calcium sulfate decomposition rate in the reduction decomposition furnace 7 is 90% to 99%. The SO2 concentration in the outlet flue gas of the sulfur-rich flue gas furnace preheater is 15% to 20%.

[0045] The fluidized reducing gas generator 14 consists of a blower and a fluidized grate. By feeding fossil fuel into it and introducing low-temperature exhaust gas from the cooler, high-temperature flue gas with high CO content is generated. This gaseous reducing agent is then introduced into the reduction decomposition furnace, replacing the solid reducing agent (coke or coal char) used in conventional gypsum cement production processes.

[0046] The preheated raw material is fed into the reduction decomposition furnace 7, where the reducing atmosphere and high temperature environment are used to decompose calcium sulfate. The flue gas with high sulfur dioxide content enters the acid production system 16 separately, which has high acid production efficiency and lower cost. A carbon monoxide digestion furnace 11 is set up to digest the excess carbon monoxide in the flue gas using high-temperature air.

[0047] An electric gate valve is installed on the low-temperature waste air duct 13 at the kiln head to provide gas input for the fluidized bed reducing gas generator; an electric gate valve is installed on the high-temperature waste air duct 12 at the kiln head to provide gas input for the carbon monoxide digestion furnace. Compared with the conventional gypsum cement production process, the originally discharged waste gas is reused, and dust collection equipment is not required at the kiln head.

[0048] When the gypsum kiln pre-decomposition acid production and cement co-production system of the present invention is running, part of the pre-homogenized raw material is fed into the kiln preheater 1. After multi-stage preheating and separation, it is fed into the reduction decomposition furnace 7 through the feed pipe of the C4 kiln cyclone separator. The other part of the raw material is fed into the connecting air pipe between the C7 kiln cyclone separator 9 and the C6 kiln cyclone separator 8. After two-stage preheating, it is fed into the reduction decomposition furnace 7 through the feed pipe of the C7 kiln cyclone separator 9.

[0049] Fossil fuel (pulverized coal) is fed into a fluidized bed reducing gas generator 14. Low-temperature exhaust gas (medium-temperature air) from the cooler 4 is drawn in through the low-temperature exhaust air duct 13 at the kiln head. The fluidized bed reducing gas generator 14 produces a high-CO-content gaseous reducing agent, which enters the reduction decomposition furnace 7. Inside the reduction decomposition furnace 7, the gaseous reducing agent comes into full contact with the suspended raw material. Calcium sulfate in the raw material is reduced and decomposed under a reducing atmosphere, generating solid products containing calcium oxide and flue gas containing a high concentration of SO2. Because a gaseous reducing agent is used instead of a solid reducing agent, and the reduction process occurs within the reduction decomposition furnace 7, the solid material is in a suspended state, resulting in a large contact area and better reduction effect; the calcium sulfate decomposition rate can reach 90%–99%.

[0050] The decomposed material enters the C5 kiln cyclone separator along with the gas rising from the flue 2. After cyclone separation, the material is fed into the rotary kiln 3 through the feed pipe, while the gas enters the carbon monoxide digester 11 through the C8 kiln cyclone separator 10. Fossil fuel and combustion air are introduced into the rotary kiln 3 for clinker calcination. Since the decomposition of calcium sulfate is essentially completed in the reduction decomposition furnace 7, calcination in an oxidizing atmosphere can be achieved in the rotary kiln 3, thus improving the quality of the calcined clinker.

[0051] The flue gas from the outlet of kiln preheater 1 is drawn into the kiln preheater dust collection system 5 by the kiln high-temperature fan 6, and is not used for sulfuric acid production. The flue gas with high SO2 content from the outlet of the C6 furnace cyclone 8 is drawn into the furnace acid corrosion resistant dust collection system 15 by the furnace high-temperature fan 17. After dust collection, the gas enters the acid production system 16 for sulfuric acid production.

[0052] A portion of the high-temperature air from the cooler 4 is introduced as secondary air into the rotary kiln 3 to calcine the clinker inside the kiln. Another portion of the high-temperature air enters the carbon monoxide digester 11 through the high-temperature exhaust air duct 12 at the kiln head to digest excess CO in the flue gas and solve the CO emission problem. The remaining low-temperature exhaust gas at the kiln head is introduced into the fluidized bed reducing gas generator 14 through the low-temperature exhaust air duct 13 at the kiln head. The cooled clinker is discharged from the cooler 4 and transported for storage.

[0053] Example 2 See Figure 3 The difference from Example 1 is that the gypsum kiln pre-decomposition acid production and cement co-production system provided in this example is equipped with the following: the exhaust air outlet at the tail end of the cooler 4 is connected to the blower inlet of the cooler 4 through the exhaust air circulation pipe 18 to realize the kiln head exhaust air circulation. When the exhaust air at the tail end of the cooler 4 cannot be fully utilized by the existing system, zero emission of kiln head exhaust air is achieved through exhaust air circulation.

[0054] In this embodiment, the high-temperature air of the cooler 4 is used to feed into the rotary kiln 3 for clinker calcination and into the carbon monoxide digester 11 for CO digestion, and the exhaust gas of the medium and low temperature section of the cooler 4 is used to feed into the fluidized reducing gas generator 14 to prepare gaseous reducing agent, so as to realize the full utilization of the cooler exhaust gas in stages and the zero emission of kiln head exhaust gas.

[0055] Example 3 This embodiment provides a specific method for co-producing cement from gypsum using the system of the present invention via external pre-decomposition in a gypsum kiln, including the following steps: The gypsum raw materials are pretreated to control the P2O5 content ≤ 1.0% and F content ≤ 1.05% in the raw meal after batching. If the fluorine and phosphorus content in the gypsum raw materials is too high, resulting in P2O5 content > 1.0% and / or F content > 1.05% in the raw meal, the gypsum is pretreated by washing the gypsum raw materials with a low-concentration strong acid. The acid solution is preheated to 40-60℃ using the waste heat of the cement kiln system. After the gypsum raw materials enter the acid solution, P2O5 is converted into H3PO4 and dissolves in the solution. The fluoride structure is destroyed, and fluorine is carried away by the solution in the form of fluoride ions. This controls the P2O5 and F content in the raw meal (P2O5 ≤ 1.0%, F ≤ 1.05%), achieving the effect of reducing the P2O5 and F content in the gypsum. The pretreated gypsum is then batched with other raw materials and fed into the raw meal mill system. After grinding, it enters the homogenization silo.

[0056] Phosphorus, upon entering the dicalcium silicate lattice, hinders the reaction between calcium oxide and dicalcium silicate to form the tricalcium silicate mineral phase. It also increases the surface tension of the liquid phase, impeding mass transfer of free calcium oxide, making it difficult for free calcium oxide to be absorbed in the clinker. Excessive fluorine leads to crusting and ring formation within the kiln, abnormal growth of tricalcium silicate crystals, and the formation of calcium fluorosilicate minerals, resulting in insufficient early-stage strength and subsequent strength reduction in the clinker. This invention, through pretreatment, controls the P2O5 content in the raw meal to ≤1.0% and the F content to ≤1.05%, effectively eliminating the adverse effects of harmful elements on clinker quality and ensuring that the quality of the clinker product after calcination meets requirements.

[0057] After pre-homogenization, part of the raw material is fed into the kiln preheater 1. After multi-stage preheating and separation, it is fed into the reduction decomposition furnace 7 through the feed pipe of the C4 kiln cyclone separator. The other part of the raw material is fed into the connecting air pipe between the C7 kiln cyclone separator 9 and the C6 kiln cyclone separator 8. After two-stage preheating, it is fed into the reduction decomposition furnace 7 through the feed pipe of the C7 kiln cyclone separator 9.

[0058] Fossil fuel (pulverized coal) is fed into the fluidized bed reducing gas generator 14, and waste gas (medium-temperature air) from the low-temperature section of the cooler 4 is introduced through the low-temperature exhaust air duct 13 at the kiln head. The gaseous reducing agent with high CO content generated in the fluidized bed reducing gas generator 14 is then introduced into the reduction decomposition furnace 7. The fuel feed ratio between the fluidized bed reducing gas generator 14 and the rotary kiln 3 is 2:8 to 3.5:6.5. The outlet flue gas temperature of the fluidized bed reducing gas generator 14 is 1050 to 1150°C, and the CO concentration is 10,000 to 20,000 ppm.

[0059] Using a fluidized bed reducing gas generator 14 to prepare CO as a gaseous reducing agent instead of a conventional solid reducing agent can avoid the problem of uncontrollable solid reducing agent dosage and reduction effect. By adjusting the fossil fuel dosage to control the CO concentration at the outlet of the fluidized bed reducing gas generator 14, the over-reduction of calcium sulfate to calcium sulfide can be effectively avoided. Since CO is a gaseous reducing agent, it has a large contact area with the suspended raw material, resulting in a better reduction effect.

[0060] Calcium sulfate (CaSO4) in the raw materials is basically decomposed in the reduction decomposition furnace 7 under a reducing atmosphere, generating solid products containing calcium oxide and flue gas containing high concentrations of SO2. The outlet flue gas temperature of the reduction decomposition furnace 7 is 850-950℃, and the calcium sulfate decomposition rate is 90%-99%. The decomposed solid products are fed into the rotary kiln 3 after gas-solid separation by the C5 kiln column cyclone separator. The high SO2 content flue gas generated by decomposition is discharged sequentially through the carbon monoxide digester 11 and the outlet of the sulfur-rich flue gas furnace column preheater. The SO2 concentration in the flue gas at the outlet of the sulfur-rich flue gas furnace column preheater is 15%-20%. The flue gas discharged from the sulfur-rich flue gas furnace column preheater is drawn into the furnace column acid corrosion resistant dust collection system 15 by the furnace column high-temperature fan 17. After acid corrosion dust collection, it enters the acid production system 16 for the preparation of sulfuric acid.

[0061] The calcium sulfate decomposition process is separated from the clinker calcination process by the reduction decomposition furnace 7. Calcium sulfate decomposes in a suspended state, achieving a decomposition rate of 90%–99%, far exceeding that of traditional processes. The SO2 concentration in the flue gas exiting the reduction decomposition furnace 7 is as high as 15%–20% (affected by raw material batching and the decomposition effect of the reduction decomposition furnace), which is significantly higher than the 10%–15% SO2 concentration at the preheater outlet of conventional gypsum cement production processes. This results in higher output for the acid production system and lower unit output cost.

[0062] The flue gas discharged from the kiln preheater 1 is drawn into the kiln preheater dust collection system 5 by the kiln high-temperature fan 6 and then discharged after dust collection. It is not used for the preparation of sulfuric acid.

[0063] Fuel and a portion of the high-temperature air from the cooler 4 are introduced into the rotary kiln 3 as combustion air for clinker calcination. After cooling, the clinker is discharged from the cooler 4 and transported for storage. The rotary kiln 3 is calcined in an oxidizing atmosphere, while the calcium sulfate decomposition reaction is completed in the reduction decomposition furnace 7. The rotary kiln 3 only undertakes the task of clinker calcination. The other portion of the high-temperature air from the cooler 4 is sent to the carbon monoxide digester 11 through the high-temperature exhaust air duct 12 at the kiln head to digest the CO in the flue gas.

[0064] In the cooler 4, the high-temperature air used for clinker calcination, the medium- and low-temperature waste gas used for preparing gaseous reducing agents, and the high-temperature air used for carbon monoxide decomposition are used in a graded manner to achieve zero emissions of kiln head waste gas.

[0065] Since the decomposition of calcium sulfate is basically completed in the reduction decomposition furnace 7, oxidizing atmosphere calcination can be achieved in the rotary kiln 3, thus improving the quality of clinker calcination. The exhaust gas from the kiln head grate cooler is used for calcination in the kiln, preparation of reducing gas, and carbon monoxide decomposition, achieving zero exhaust gas emissions at the kiln head and eliminating the need for additional dust collection equipment, thereby saving investment costs.

[0066] The clinker from the cooler of this invention has a 28-day compressive strength ≥52.5MPa, a stability test pass rate ≥99.8%, and a factory pass rate of 100%.

[0067] This invention tests the decomposition of calcium sulfate under different reaction temperatures and CO concentrations. The decomposition rate is used to determine the decomposition rate of calcium sulfate in the material fed through the cyclone separator of kiln C5. The SO3 content before and after gypsum decomposition is measured according to GB / T 5484-2000 "Methods for Chemical Analysis of Gypsum". The decomposition rate = The details are shown in Table 1 below: Table 1. Experimental data on the decomposition of calcium sulfate

[0068] As can be seen from the experimental data in Table 1, the decomposition rate of calcium sulfate can reach 92.13% at 1075℃ and a CO concentration of 14100ppm; and 96.49% at 1100℃ and a CO concentration of 15600ppm. This verifies that the present invention can achieve a high decomposition rate of calcium sulfate under different reaction conditions.

[0069] Comparative Example 1 Compared with Example 1, the difference is as follows: Figure 1As shown, a conventional gypsum cement production process is adopted. The decomposition of calcium sulfate and the clinker calcination both occur within the rotary kiln. A solid reducing agent (coke or coal char) is used, directly added to the feed pipe of the final stage cyclone separator of kiln preheater 1, and fed into the kiln for calcination along with the hot raw materials. The SO2 concentration in the flue gas at the outlet of kiln preheater 1 is 10%-15%, the 28-day compressive strength of the clinker at the outlet of cooler 4 is ≥45.5 MPa, and the stability test pass rate is ≥95.5%.

[0070] A comparison of the data from Example 1 and Comparative Example 1 shows that, compared with conventional gypsum cement production processes, the system and method for pre-decomposition acid production and cement co-production outside the gypsum kiln of the present invention has the following outstanding advantages: 1) The 28-day compressive strength of the clinker is significantly improved (≥52.5 MPa in this invention, ≥45.5 MPa in the comparative example), and the pass rate of stability testing is significantly improved (≥99.8% in this invention, ≥95.5% in the comparative example). The fundamental reason is that, through process optimization and adjustment, the decomposition of calcium sulfate is separated from the clinker calcination process. The calcium sulfate decomposition process is completed in the reduction decomposition furnace, while the clinker calcination process is completed in the rotary kiln. The complete decomposition of calcium sulfate normalizes the calcination regime in the rotary kiln, achieving calcination in an oxidizing atmosphere, improving the quality of clinker calcination, increasing the content of silicate minerals that mainly provide strength, and correspondingly improving the strength of the clinker. Almost no calcium sulfate or calcium sulfide remains in the clinker, ensuring its stability.

[0071] 2) The concentration of SO2 (generated by the decomposition of calcium sulfate) at the outlet of the sulfur-rich flue gas boiler preheater is significantly increased (15%-20% in this invention, 10%-15% in the comparative example). The increased concentration of SO2 generated by calcium sulfate decomposition results in higher output from the acid production system and lower unit output cost.

[0072] 3) The rotary kiln only undertakes the clinker calcination task, and the equipment size can be appropriately reduced. The decomposition process occurs in the reduction decomposition furnace and is a suspension calcination, resulting in lower system energy consumption.

[0073] 4) Zero emissions of kiln head exhaust gas are achieved, eliminating the need for additional dust collection equipment and saving investment costs.

[0074] In terms of raw material processing, this invention proposes targeted pretreatment schemes for different types of harmful elements in gypsum, controlling the content of harmful elements within an acceptable range without affecting clinker quality. Regarding clinker calcination, through process optimization and improvement, external decomposition of calcium sulfate can be achieved, increasing the decomposition rate; calcination is maintained in an oxidizing atmosphere within the kiln, consistent with conventional cement clinker calcination procedures, ensuring clinker quality; solid reducing agents are not used, avoiding the problem of uncontrollable reducing agent dosage and reduction effect; a reduction decomposition furnace is added to alleviate the calcination pressure of the rotary kiln, allowing for smaller equipment specifications and reduced equipment investment for the same output; low-concentration SO2 flue gas from the preheater outlet enters the conventional waste gas treatment system, while high-SO2 flue gas from the reduction decomposition furnace independently enters the acid production system, increasing the output of the acid production system and reducing operating costs.

[0075] In summary, this invention significantly improves the quality and strength of cement clinker products and reduces system energy consumption by optimizing and adjusting the existing process flow. At the same time, it allows for smaller rotary kiln equipment specifications, saving on equipment investment.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for pre-decomposition acid production and cement co-production outside a gypsum kiln, characterized in that, It includes a kiln preheater, rotary kiln, cooler, kiln preheater dust collection system, reduction decomposition furnace, sulfur-rich flue gas furnace preheater, carbon monoxide digester, fluidized bed reducing gas generator, furnace acid corrosion resistant dust collection system, and acid production system; The discharge port of the kiln preheater is connected to the first feed port of the reduction decomposition furnace, the discharge port of the sulfur-rich flue gas furnace preheater is connected to the second feed port of the reduction decomposition furnace, and the discharge port of the reduction decomposition furnace is connected to the rotary kiln; the gas outlet of the kiln preheater is connected to the gas inlet of the kiln preheater dust collection system. The fluidized bed reducing gas generator is provided with a fuel inlet and a gas inlet. The gas outlet of the fluidized bed reducing gas generator is connected to the reducing gas inlet of the reduction decomposition furnace. The fluidized bed reducing gas generator is used to convert fossil fuels into a gaseous reducing agent containing carbon monoxide. The flue gas outlet of the reduction decomposition furnace is connected to the inlet of the sulfur-rich flue gas furnace preheater, the outlet of the sulfur-rich flue gas furnace preheater is connected to the inlet of the furnace acid corrosion resistant dust collection system, and the outlet of the furnace acid corrosion resistant dust collection system is connected to the inlet of the acid production system. The carbon monoxide digester is installed on the flue gas duct of the sulfur-rich flue gas furnace preheater, so that all the flue gas from the sulfur-rich flue gas furnace preheater passes through the carbon monoxide digester before entering the furnace acid corrosion resistant dust collection system; the high-temperature section air outlet of the cooler is connected to the air inlet of the carbon monoxide digester through the high-temperature exhaust air duct at the kiln head; the medium-low temperature section exhaust gas outlet of the cooler is connected to the gas inlet of the fluidized reducing gas generator through the medium-low temperature exhaust air duct at the kiln head.

2. The system for pre-decomposition acid production and cement co-production outside the gypsum kiln according to claim 1, characterized in that, The reduction decomposition furnace includes a furnace body. A tangential vortex structure is provided at the lower part of the furnace body. The inlet of the tangential vortex structure is connected to the outlet of a fluidized reducing gas generator, allowing gaseous reducing agent containing carbon monoxide to enter the furnace body tangentially, forming a spiral flow field. A multi-point feeding device is provided in the middle of the furnace body, connected to the outlet of the kiln preheater and the outlet of the sulfur-rich flue gas furnace preheater. A top vortex structure is provided at the upper part of the furnace body to extend the residence time of materials and gases within the furnace. A downward pipe is provided at the outlet of the top vortex structure, connected to the final stage cyclone separator of the sulfur-rich flue gas furnace preheater.

3. The system for pre-decomposition acid production and cement co-production outside the gypsum kiln according to claim 1, characterized in that, The flue gas from the kiln preheater and the flue gas from the sulfur-rich flue gas furnace preheater are independent of each other and enter the dust collection system of the kiln preheater and the acid corrosion resistant dust collection system of the furnace respectively; the dust collection system of the kiln preheater is a conventional dust collection system and the acid corrosion resistant dust collection system of the furnace is an acid corrosion resistant dust collection system.

4. The system for pre-decomposition acid production and cement co-production outside the gypsum kiln according to claim 1, characterized in that, The kiln preheater includes multiple kiln cyclone separators connected in sequence, and the discharge port of the kiln preheater is located at the feed pipe of the second-to-last kiln cyclone separator; the sulfur-rich flue gas furnace preheater includes multiple furnace cyclone separators connected in sequence, and the discharge port of the sulfur-rich flue gas furnace preheater is located at the feed pipe of the second-to-last furnace cyclone separator.

5. The system for pre-decomposition acid production and cement co-production outside the gypsum kiln according to claim 4, characterized in that, The kiln tail flue of the rotary kiln is connected to the air inlet of the kiln preheater through the rising flue, the discharge port of the reduction decomposition furnace is connected to the rising flue, and the discharge port of the last kiln cyclone of the kiln preheater is connected to the rotary kiln.

6. The system for pre-decomposition acid production and cement co-production outside the gypsum kiln according to claim 4, characterized in that, The feed inlet of the final stage cyclone separator of the sulfur-rich flue gas furnace preheater is connected to the rotary kiln.

7. The system for pre-decomposition acid production and cement co-production outside the gypsum kiln according to claim 1, characterized in that, The high-temperature section air outlet of the cooler is also connected to the rotary kiln.

8. A method for co-producing cement from gypsum using the system described in any one of claims 1 to 7, characterized in that, Includes the following steps: The gypsum raw materials are pretreated to control the P2O5 content in the raw meal after batching to be ≤1.0% and the F content to be ≤1.05%. After the pretreated gypsum is mixed with other raw materials and ground, part of the raw meal is fed into the kiln preheater and then fed into the reduction decomposition furnace after multi-stage preheating; the other part of the raw meal is fed into the sulfur-rich flue gas furnace preheater and then fed into the reduction decomposition furnace after preheating. Fossil fuel is fed into a fluidized bed reducing gas generator, and waste gas from the low-temperature section of the cooler is introduced through the low-temperature exhaust air pipe at the kiln head to produce a gaseous reducing agent containing carbon monoxide, which is then introduced into the reduction decomposition furnace. Calcium sulfate in the raw material is decomposed in a reducing atmosphere in a reduction decomposition furnace to generate solid products containing calcium oxide and flue gas containing sulfur dioxide. The solid products after decomposition are fed into a rotary kiln after gas-solid separation. The flue gas with high sulfur dioxide content generated by decomposition is discharged through a carbon monoxide digester and a sulfur-rich flue gas furnace preheater outlet in sequence. After acid corrosion dust collection, it enters the acid production system for the preparation of sulfuric acid. The flue gas discharged from the kiln preheater enters the kiln preheater dust collection system before being discharged. Fuel and combustion air are introduced into the rotary kiln for clinker calcination; air from the high-temperature section of the cooler is sent to the carbon monoxide digester through the high-temperature exhaust air duct at the kiln head to digest the carbon monoxide in the flue gas.

9. The method for pre-decomposition acid production and cement co-production outside a gypsum kiln according to claim 8, characterized in that, The pretreatment is as follows: when the fluorine and / or phosphorus content in the gypsum raw material results in a P2O5 content > 1.0% and / or F content > 1.05% in the raw material, the gypsum raw material is washed with water using a low-concentration strong acid, and the acid solution is preheated to 40-60°C using the waste heat of the cement kiln system. After the gypsum raw material enters the acid solution, P2O5 is converted into H3PO4 and dissolved in the solution, the fluoride structure is destroyed, and the fluorine element is carried away by the solution in the form of fluoride ions.

10. The method for pre-decomposition acid production and cement co-production outside a gypsum kiln according to claim 8, characterized in that, The fuel feed ratio between the fluidized bed reducing gas generator and the rotary kiln is 2:8 to 3.5:6.5, and the outlet flue gas temperature of the fluidized bed reducing gas generator is 1050 to 1150°C, with a CO concentration of 10000 to 20000 ppm.

11. The method for pre-decomposition acid production and cement co-production outside a gypsum kiln according to claim 8, characterized in that, The outlet flue gas temperature of the reduction decomposition furnace is 850-950℃, and the calcium sulfate decomposition rate in the reduction decomposition furnace is 90%-99%.

12. The method for pre-decomposition acid production and cement co-production outside a gypsum kiln according to claim 8, characterized in that, The SO2 concentration in the flue gas at the outlet of the sulfur-rich flue gas furnace preheater is 15% to 20%.

13. The method for pre-decomposition acid production and cement co-production outside a gypsum kiln according to claim 8, characterized in that, The high-temperature air from the cooler is also used as combustion air and introduced into the rotary kiln for clinker calcination. The high-temperature air used for clinker calcination, the medium- and low-temperature exhaust gas used for preparing gaseous reducing agents, and the high-temperature air used for carbon monoxide decomposition form a staged full utilization of the cooler exhaust gas, achieving zero emissions of kiln head exhaust gas.

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