Phosphogypsum decomposition co-production cement system and its reduction decomposition furnace and method

Abstract

The application provides a phosphogypsum decomposition co-production cement system, a reduction decomposition furnace and a method. The reduction decomposition furnace comprises a central strong reduction bin and a ring-shaped micro-oxidation bin. The bottom and the top of the central strong reduction bin are provided with openings. The bottom opening of the central strong reduction bin is communicated with a kiln tail smoke chamber of a rotary kiln. The central strong reduction bin is provided with a pulverized coal nozzle and a hot raw material inlet. The ring-shaped micro-oxidation bin is sleeved outside the central strong reduction bin and completely wraps the central strong reduction bin. The bottom and the top of the ring-shaped micro-oxidation bin are provided with openings. The ring-shaped micro-oxidation bin is provided with a hot raw material inlet and a tertiary air pipe air inlet. The bottom opening of the ring-shaped micro-oxidation bin is communicated with the kiln tail smoke chamber of the rotary kiln. The reduction decomposition furnace realizes the strong reduction gas-solid reaction through the inner bin and realizes the micro-oxidation through the residual oxygen of the kiln tail. The structure itself realizes the internal self-absorption and conversion of sulfur and carbon, realizes the efficient pre-decomposition of the phosphogypsum, reduces the decomposition load of the rotary kiln, and greatly improves the system processing capacity and the production efficiency.

Description

Technical Field

[0001] This invention relates to the field of cement production technology, and in particular to a phosphogypsum decomposition and cement co-production system, its reduction decomposition furnace and method. Background Technology

[0002] Phosphogypsum is a major solid waste generated during the wet-process phosphoric acid production process, and its main component is calcium sulfate dihydrate (CaSO4·2H2O). Currently, the comprehensive utilization rate of phosphogypsum is low, and large-scale stockpiling not only occupies land resources but also poses serious environmental risks. Utilizing phosphogypsum to decompose and produce acid and co-produce cement is an effective way to achieve its large-scale resource utilization.

[0003] Traditional phosphogypsum decomposition for sulfuric acid production and cement co-production typically involves directly feeding a mixture of phosphogypsum, corrective raw materials, and fuel into a rotary kiln for a solid-solid reaction at high temperatures. The phosphogypsum decomposition rate depends on a long residence time and high reaction temperature. However, this process has the following drawbacks: 1) Low solid-solid reaction efficiency, with a phosphogypsum pre-decomposition rate usually below 20%, resulting in a heavy decomposition burden in the kiln and limited production capacity; 2) Uneven temperature distribution within the rotary kiln, easily leading to localized overheating or under-burning, affecting cement clinker quality; 3) Difficulty in controlling the reducing atmosphere within the kiln, affecting sulfuric acid reduction efficiency and SO2 concentration in the tail gas. An external preheating decomposition process is also used. This process, to address the completely opposite requirements of the atmosphere properties in the "reduction" and "oxidation" stages, usually requires the parallel installation of independent online reducing agent gasification furnaces, suspension decomposition furnaces, and post-furnace decarbonization and desulfurization furnaces (such as CN119983819A). This complex "three-furnace parallel" structure has the following technical drawbacks: 1) High system resistance and heat dissipation. The furnaces are connected by numerous large flues and independent gas-solid separation cyclones, resulting in a large system footprint, high investment, and significant heat loss from equipment surfaces, leading to high energy consumption. 2) Insufficient thermal efficiency: After the high-temperature reducing gas generated by the gasifier reacts with the materials, the residual CO and sublimated sulfur need to be introduced into a subsequent independent decarbonization and desulfurization furnace for secondary combustion and heat release. Heat transfer is delayed in time and space, and cannot be directly radiated and supplied to the upstream endothermic reduction decomposition reaction. Therefore, there is an urgent need to develop a new process for the co-production of cement from phosphogypsum decomposition, which is highly efficient, energy-saving, and has a high processing capacity. Summary of the Invention

[0004] The main objective of this invention is to provide a cement co-production system for phosphogypsum decomposition, as well as its reduction decomposition furnace and method, which aims to achieve efficient pre-decomposition of phosphogypsum to reduce the decomposition load of the rotary kiln, thereby improving the system's processing capacity and production efficiency.

[0005] To achieve the above objectives, the present invention provides a reduction decomposition furnace for a phosphogypsum decomposition and cement co-production system, comprising: The central strong reduction chamber has openings at both the bottom and top. The bottom opening of the central strong reduction chamber is connected to the kiln tail flue chamber of the rotary kiln. The central strong reduction chamber is equipped with pulverized coal nozzles and hot raw material inlets. The annular micro-oxidation chamber is fitted outside the central strong reduction chamber and completely encloses it. It has openings at the bottom and top. The annular micro-oxidation chamber is equipped with a hot raw material inlet and a tertiary air duct inlet. The bottom opening of the annular micro-oxidation chamber is connected to the kiln tail flue chamber of the rotary kiln.

[0006] Preferably, the reduction decomposition furnace of the phosphogypsum decomposition and cement co-production system further includes a material overflow baffle located inside the chamber of the annular micro-oxidation chamber and above the top opening of the central strong reduction chamber, the bottom end face of the material overflow baffle being inverted conical.

[0007] Preferably, the annular micro-oxidation chamber is provided with multiple tertiary air inlets, which are arranged tangentially to form a vortex.

[0008] Preferably, the walls of the central strong reduction chamber and the annular micro-oxidation chamber are made of silicon carbide-silicon nitride composite ceramic or high chromium-nickel heat-resistant steel, and their inner walls are provided with an acid corrosion resistant layer, which is resistant to SO2, SO3 and H2S gases.

[0009] The present invention also proposes a phosphogypsum decomposition and cement co-production system, including the reduction decomposition furnace of the above-mentioned phosphogypsum decomposition and cement co-production system, and further including a preheating device, a rotary kiln and a tertiary air duct. The outlet of the preheating device is connected to the hot raw material inlet of the reduction decomposition furnace through a pipeline. The rotary kiln is connected to the bottom end of the reduction decomposition furnace. The two ends of the tertiary air duct are respectively connected to the reduction decomposition furnace and the rotary kiln.

[0010] Preferably, the phosphogypsum decomposition and cement production system further includes an airlock device located between the reduction decomposition furnace and the rotary kiln. The top outlet of the reduction decomposition furnace is connected to the gas-solid separation cyclone, and the airlock device is used to prevent flue gas backflow.

[0011] This invention also proposes a method for a cement co-production system based on the above-mentioned phosphogypsum decomposition, comprising the following steps: Phosphogypsum, siliceous raw materials, and aluminous raw materials are mixed in proportion to form raw meal powder, which is then fed into a preheating device for multi-stage countercurrent suspension preheating. A portion of the preheated raw meal powder is introduced into the central strong reduction chamber of the reduction decomposition furnace. The carbonaceous fuel is injected through the pulverized coal nozzle and the gasification reaction under high temperature and oxygen deficiency conditions produces reducing flue gas rich in CO and H2. The meal powder undergoes a reduction decomposition reaction in a suspended fluidized state to generate calcium sulfide. After the reaction in the central strong reduction chamber, the gas-solid mixture flows down through the material overflow baffle from the top opening into the annular micro-oxidation chamber. At the same time, high-temperature oxygen-containing tertiary air is introduced into the annular micro-oxidation chamber of the reduction decomposition furnace through the tertiary air duct. The material, in a suspended state, oxidizes calcium sulfide into calcium oxide and releases SO2 gas. Meanwhile, unburned coal powder and residual CO gas carried by the airflow from the central strong reduction chamber are fully oxidized and burned off in the annular micro-oxidation chamber. After the gas-solid mixture at the top of the annular micro-oxidation chamber is discharged, it enters the gas-solid separation cyclone. At the same time, the calcium oxide-rich hot raw material separated is fed into the rotary kiln and calcined with the correcting material to produce cement clinker. The SO2-rich flue gas separated by the gas-solid separation cyclone is sent to the acid plant to produce sulfuric acid after heat exchange by the preheating device.

[0012] Preferably, the flue gas residence time in the central strong reduction chamber is controlled to be 10-20 seconds, and the flue gas residence time in the annular micro-oxidation chamber is controlled to be 5-10 seconds.

[0013] Preferably, the firing temperature in the rotary kiln is 1250℃ to 1350℃; the coal gasification reaction temperature inside the central strong reduction chamber is 1000℃ to 1100℃; and the coal gasification reaction temperature inside the annular micro-oxidation chamber is 900℃ to 1100℃.

[0014] Preferably, the carbonaceous fuel is one or more of pulverized coal, coke, and biochar; the fuel supplemented in the rotary kiln is one or more of pulverized coal, coke, and biochar; and the volume content of CO in the gas atmosphere inside the central strong reduction chamber is controlled at 5%-10%, and the volume content of O2 is less than 0.5%.

[0015] The phosphogypsum decomposition and cement co-production system proposed in this invention has the following beneficial effects: 1. By organically integrating the three furnaces of "gasification furnace + decomposition furnace + decarbonization and desulfurization furnace" into a coaxial integrated furnace, the multi-section high-temperature connecting flue and the large gas-solid separator in the middle are eliminated, the overall system resistance is reduced by 15%-20%, the heat dissipation area of ​​the equipment surface is reduced by more than 30%, and the overall heat consumption of the system is significantly reduced. 2. The large amount of heat released by the oxidation and combustion of unburned CO and carbon particles in the annular micro-oxidation chamber can be directly radiated and conducted to the central strong reduction chamber through the intermediate coaxial lining wall, directly supplementing the strong endothermic heat source required for the calcium sulfate reduction reaction in the central chamber, and realizing the efficient in-situ self-balancing conversion of energy inside the furnace body.

[0016] 3. Extremely precise atmosphere control: The composite flow field design of coaxial central jetting and outer ring convection is adopted. The dynamic sealing of the "gas-liquid-solid" flow field is achieved by using the top overflow deflector structure. This ensures both the absolute strong reducing atmosphere in the inner chamber and the full oxidation and burnout in the outer chamber, completely solving the problems of difficult atmosphere control and clinker quality fluctuation in rotary kilns.

[0017] 4. Significantly improved pre-decomposition efficiency: By replacing the traditional solid-solid reaction with a gas-solid reaction, a pre-decomposition rate of 40% to 50% of phosphogypsum is achieved in a dedicated decomposition furnace. This decomposition rate is much higher than that of the static solid-solid reaction in traditional processes (generally less than 20%), reducing the decomposition load on the rotary kiln and greatly improving the reaction rate and system efficiency.

[0018] 5. Reduce decomposition pressure in the kiln: By pre-decomposing 40%~50% of the phosphogypsum, the heat load and decomposition load of the rotary kiln are significantly reduced, allowing more phosphogypsum raw materials to be processed in the kiln, and the system capacity can be increased by 30-50%.

[0019] 6. Adaptable to high temperature and corrosive environment: The decomposition furnace is made of special materials that are resistant to high temperature of 1100℃ and acidic gas (such as SO2, SO3, H2S, etc.) corrosion, which ensures the long-term stable operation of the equipment in a strong reducing and highly acidic atmosphere. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the phosphogypsum decomposition and cement co-production system of the present invention; Figure 2 This is a schematic diagram of the reduction decomposition furnace in the phosphogypsum decomposition and cement co-production system of the present invention.

[0021] In the diagram, 1-reduction decomposition furnace, 11-central strong reduction chamber, 12-annular micro-oxidation chamber, 13-material overflow baffle, 2-preheating device, 3-rotary kiln, 4-tertiary air duct.

[0022] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0023] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0024] It should be noted that in the description of this invention, the terms "lateral," "longitudinal," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used solely for the convenience of describing the invention and for 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 the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0025] This invention proposes a cement co-production system based on the decomposition of phosphogypsum.

[0026] Reference Figure 1 and Figure 2 In this preferred embodiment, a phosphogypsum decomposition and cement co-production system includes a reduction decomposition furnace 1, a preheating device 2, a rotary kiln 3, and a tertiary air duct 4. The outlet of the preheating device 2 is connected to the hot raw material inlet of the reduction decomposition furnace 1 via a pipe. The rotary kiln 3 is connected to the bottom end of the reduction decomposition furnace 1. The two ends of the tertiary air duct 4 are connected to the reduction decomposition furnace 1 and the rotary kiln 3, respectively. (Refer to...) Figure 2 The reduction decomposition furnace 1 of the phosphogypsum decomposition and cement co-production system includes a central strong reduction chamber 11 and an annular micro-oxidation chamber 12. The central strong reduction chamber 11 has openings at both its bottom and top. The bottom opening of the central strong reduction chamber 11 is connected to the kiln tail flue of the rotary kiln 3. The central strong reduction chamber 11 is equipped with pulverized coal nozzles and hot raw material inlets (both are located at the lower part of the central strong reduction chamber 11). The annular micro-oxidation chamber 12 is fitted around the central strong reduction chamber 11 and completely encloses it. The annular micro-oxidation chamber 12 has openings at both its bottom and top. The annular micro-oxidation chamber 12 is equipped with a hot raw material inlet and a tertiary air duct inlet. The bottom opening of the annular micro-oxidation chamber 12 is connected to the kiln tail flue of the rotary kiln 3.

[0027] Furthermore, referring to Figure 2 The reduction decomposition furnace 1 of the phosphogypsum decomposition and cement co-production system also includes a material overflow baffle 13 located inside the annular micro-oxidation chamber 12 and above the top opening of the central strong reduction chamber 11. The bottom end face of the material overflow baffle 13 is inverted conical. The top overflow baffle structure achieves dynamic sealing of the "gas-liquid-solid" flow field, ensuring both an absolutely strong reducing atmosphere in the central strong reduction chamber 11 and sufficient oxidation and burnout in the annular micro-oxidation chamber 12. This completely solves the problems of difficult atmosphere control and clinker quality fluctuations in the rotary kiln 3.

[0028] Furthermore, the annular micro-oxidation chamber 12 is provided with multiple tertiary air inlets, which are arranged tangentially to form a swirling flow.

[0029] Specifically, in this embodiment, the walls of the central strong reduction chamber 11 and the annular micro-oxidation chamber 12 are made of silicon carbide-bonded silicon nitride composite ceramic or high-chromium-nickel heat-resistant steel (forming a fire-resistant and heat-insulating inner lining wall), and their inner walls are provided with an acid-resistant corrosion-resistant layer, which is resistant to SO2, SO3 and H2S gases. The central strong reduction chamber 11 and the annular micro-oxidation chamber 12 are separated by a fire-resistant and heat-insulating inner lining wall. The lining wall of the central strong reduction chamber 11 is used for high-temperature heat conduction between the chambers, so that the exothermic reaction heat in the annular micro-oxidation chamber 12 directly compensates for the endothermic reaction in the central strong reduction chamber 11.

[0030] Furthermore, this phosphogypsum decomposition and cement co-production system also includes an airlock device located between the reduction decomposition furnace 1 and the rotary kiln 3, which is used to prevent flue gas backflow. The preheating device 2 is equipped with a multi-stage gas-solid separation cyclone separator; in this embodiment, a five-stage separator is used as an example for specific explanation. The top outlet of the reduction decomposition furnace 1 is connected to a gas-solid separation cyclone separator.

[0031] The phosphogypsum decomposition and cement co-production system proposed in this invention has the following beneficial effects: 1. By organically integrating the three furnaces of "gasification furnace + decomposition furnace + decarbonization and desulfurization furnace" into a coaxial integrated furnace, the multi-section high-temperature connecting flue and the large gas-solid separator in the middle are eliminated, the overall system resistance is reduced by 15%~20%, the heat dissipation area of ​​the equipment surface is reduced by more than 30%, and the overall heat consumption of the system is significantly reduced. 2. The large amount of heat released by the oxidation and combustion of unburned CO and carbon particles in the annular micro-oxidation chamber 12 can be directly radiated and conducted to the central strong reduction chamber 11 through the intermediate coaxial lining wall, directly supplementing the strong endothermic heat source required for the calcium sulfate reduction reaction in the central chamber, and realizing the efficient in-situ self-balancing conversion of energy inside the furnace body.

[0032] 3. Extremely precise atmosphere control: The composite flow field design of coaxial central jetting and outer ring convection is adopted. The top overflow deflector structure realizes the dynamic sealing of the "gas-liquid-solid" flow field, which not only ensures the absolutely strong reducing atmosphere of the central strong reducing chamber 11 (inner chamber), but also ensures the full oxidation and burnout of the annular micro-oxidation chamber 12 (outer chamber), which completely solves the problems of difficult atmosphere control and clinker quality fluctuation in rotary kiln 3.

[0033] 4. Significantly improved pre-decomposition efficiency: By replacing the traditional solid-solid reaction with a gas-solid reaction, a pre-decomposition rate of 40% to 50% of phosphogypsum is achieved in a dedicated decomposition furnace. This decomposition rate is much higher than that of the static solid-solid reaction in the traditional process (generally less than 20%), reducing the decomposition load of the rotary kiln 3 and greatly improving the reaction rate and system efficiency.

[0034] 5. Reduce decomposition pressure in the kiln: By pre-decomposing 40%~50% of the phosphogypsum, the heat load and decomposition load of rotary kiln 3 are significantly reduced, allowing more phosphogypsum raw materials to be processed in the kiln, and the system capacity can be increased by 30-50%.

[0035] 6. Adaptable to high temperature and corrosive environment: The decomposition furnace is made of special materials that are resistant to high temperature of 1100℃ and acidic gas (such as SO2, SO3, H2S, etc.) corrosion, which ensures the long-term stable operation of the equipment in a strong reducing and highly acidic atmosphere.

[0036] The present invention also proposes a reduction decomposition furnace 1 for a phosphogypsum decomposition and cement co-production system.

[0037] In this preferred embodiment, a reduction decomposition furnace 1 of a phosphogypsum decomposition and cement co-production system includes a central strong reduction chamber 11 and an annular micro-oxidation chamber 12. The central strong reduction chamber 11 has openings at both its bottom and top, and the bottom opening of the central strong reduction chamber 11 is connected to the kiln tail flue of the rotary kiln 3. The central strong reduction chamber 11 is equipped with a pulverized coal nozzle and a hot raw material inlet. The annular micro-oxidation chamber 12 is fitted around the central strong reduction chamber 11 and completely encloses it. It also has openings at both its bottom and top, and the annular micro-oxidation chamber 12 is equipped with a hot raw material inlet and a tertiary air duct inlet. The bottom opening of the annular micro-oxidation chamber 12 is connected to the kiln tail flue of the rotary kiln 3.

[0038] Furthermore, the reduction decomposition furnace 1 of this phosphogypsum decomposition and cement co-production system also includes a material overflow baffle 13 located inside the annular micro-oxidation chamber 12 and above the top opening of the central strong reduction chamber 11. The bottom end face of the material overflow baffle 13 is inverted conical.

[0039] Furthermore, the annular micro-oxidation chamber 12 is provided with multiple tertiary air inlets, which are arranged tangentially to form a swirling flow.

[0040] Furthermore, the walls of the central strong reduction chamber 11 and the annular micro-oxidation chamber 12 are both made of silicon carbide-silicon nitride composite ceramic or high chromium-nickel heat-resistant steel, and their inner walls are provided with an acid corrosion resistant layer, which is resistant to SO2, SO3 and H2S gases.

[0041] This invention also proposes a method for a cement co-production system based on the decomposition of phosphogypsum.

[0042] A method for a cement co-production system based on the above-mentioned phosphogypsum decomposition includes the following steps: Step S10: Phosphogypsum, siliceous raw materials and aluminous raw materials are mixed in proportion to form raw meal powder, which is then fed into preheating device 2 for multi-stage countercurrent suspension preheating. In step S20, a portion of the preheated raw material powder is introduced into the central strong reduction chamber 11 of the reduction decomposition furnace 1. The carbonaceous fuel is injected through the pulverized coal nozzle and the gasification reaction under high temperature and oxygen deficiency conditions produces reducing flue gas rich in CO and H2. The raw material powder undergoes a reduction decomposition reaction in a suspended fluidized state to generate calcium sulfide. In step S30, the gas-solid mixture after reaction in the central strong reduction chamber 11 flows down through the top opening, past the material overflow baffle 13, and into the annular micro-oxidation chamber 12. At the same time, high-temperature oxygen-containing tertiary air is introduced into the annular micro-oxidation chamber 12 of the reduction decomposition furnace 1 through the tertiary air duct 4. The material oxidizes calcium sulfide into calcium oxide in a suspended state and releases SO2 gas. Meanwhile, the unburned coal powder and residual CO gas carried by the airflow from the central strong reduction chamber 11 are fully oxidized and burned off in the annular micro-oxidation chamber 12. In step S40, the gas-solid mixture at the top of the annular micro-oxidation chamber 12 is discharged and enters the gas-solid separation cyclone. At the same time, the separated calcium oxide-rich hot raw material is fed into the rotary kiln 3 and calcined and mineralized with the correcting material to produce cement clinker. The SO2-rich flue gas separated by the gas-solid separation cyclone is sent to the acid plant to produce sulfuric acid after heat exchange by the preheating device 2.

[0043] Specifically, in step S10, the raw materials are mixed according to the proportion and ground until the residue on an 80μm square hole sieve is ≤10%, thus obtaining raw material powder.

[0044] In step S20, the hot raw material preheated by the pre-stage gas-solid separation cyclone is divided into two parts: the first part accounts for 60% to 80% of the total weight and is fed into the central strong reduction chamber 11 through the first hot raw material inlet. The endothermic decomposition reaction of CaSO4 in the material is used to stably control the coal gasification reaction temperature in the central strong reduction chamber 11 at 1000℃ to 1100℃; the second part accounts for 20% to 40% of the total weight and is fed into the upper part of the central strong reduction chamber 11 through the second hot raw material inlet.

[0045] Specifically, the flue gas residence time in the strong reduction chamber 11 of the control center is 10-20 seconds, and the flue gas residence time in the annular micro-oxidation chamber 12 is 5-10 seconds.

[0046] Furthermore, the firing temperature inside the rotary kiln 3 is 1250℃ to 1350℃; the coal gasification reaction temperature inside the central strong reduction chamber 11 is 1000℃ to 1100℃, thereby ensuring the conversion rate of calcium sulfate to calcium sulfide. The coal gasification reaction temperature inside the annular micro-oxidation chamber 12 is 900℃ to 1100℃, thereby ensuring the conversion rate of calcium sulfide to calcium oxide and sulfur dioxide.

[0047] Furthermore, in this embodiment, the carbonaceous fuel is one or more of pulverized coal, coke, and biochar; the fuel supplemented in the rotary kiln 3 is one or more of pulverized coal, coke, and biochar; in the gas atmosphere inside the central strong reduction chamber 11, the volume content of CO is controlled at 5%-10%, and the volume content of O2 is less than 0.5%.

[0048] The following specific embodiment illustrates the method for the co-production of cement from phosphogypsum decomposition.

[0049] Example 1 In this embodiment, the material of the reduction decomposition furnace 1 is a silicon carbide-silicon nitride composite ceramic plus refractory material. Phospholipid gypsum (CaSO4·2H2O content ≥85%), silica correcting material (fly ash), alumina correcting material (bauxite), and ferrous correcting material (iron ore powder) discharged from a phosphate fertilizer plant are used. By weight: 75 parts phospholipid gypsum, 12 parts fly ash, 8 parts bauxite, and 5 parts iron ore powder are mixed and ground to obtain raw material with 8% residue on an 80μm sieve.

[0050] After being preheated in four stages, the raw meal is fed into the lower part of the central strong reduction chamber 11 through the first raw meal inlet at a mass ratio of 70%. At this time, the 1100℃ high-temperature flue gas injected into the kiln tail flue chamber undergoes an oxygen-deficient oxidation reaction with the bituminous coal injected through the pulverized coal nozzle at the lower part of the central strong reduction chamber 11, producing a large amount of CO.

[0051] A strong reduction reaction occurs in the central strong reduction chamber 11: CaSO4 + 4CO → CaS + 4CO2. The airflow velocity in the central strong reduction chamber 11 is maintained at 5 m / s to 8 m / s to ensure that the material is in a good suspended fluidized state.

[0052] Subsequently, the gas-solid mixture rapidly rises to the constriction at the top of the central strong reduction chamber 11, and is ejected at a speed of approximately 12 m / s, impacting the hyperboloid material guide cone hanging at the top. The material and flue gas are uniformly deflected outwards and fall into the annular space of the annular micro-oxidation chamber 12.

[0053] At this time, high-temperature tertiary air (oxygen content of about 18%~21%) from the kiln head is blown tangentially into the lower part of the annular micro-oxidation chamber 12, forming an upward vortex rotating around the central strong reduction chamber 11 inside the annular micro-oxidation chamber 12. At the same time, the remaining 30% of the preheated raw material is fed in from the second raw material inlet at the upper part of the annular micro-oxidation chamber 12.

[0054] In the weakly oxidizing atmosphere of the annular micro-oxidation chamber 12, the material coming out of the central strong reduction chamber 11 is at an extremely high temperature and immediately undergoes an oxidative transformation: CaS + 1.5O2 → CaO + SO2.

[0055] Meanwhile, the very small amount of coal powder that failed to fully gasify in the central strong reduction chamber 11, as well as the excess CO gas, come into full contact with the newly added cold raw material powder in the annular micro-oxidation chamber 12 and the oxygen in the tertiary air, and undergo secondary combustion in situ within the annular micro-oxidation chamber 12, and are captured and absorbed by the surface of the raw material particles.

[0056] Finally, after desulfurization and decarbonization, some of the hot raw materials (CaO) fall into the discharge cone at the bottom of the annular micro-oxidation chamber 12 by gravity and slide directly into the rotary kiln 3 to be calcined into cement clinker; the flue gas rich in SO2 (concentration 13%) and hot raw materials is discharged from the top of the annular micro-oxidation chamber 12 and enters the next stage cyclone separator for gas-solid separation. The solid enters the rotary kiln 3 to be calcined into cement clinker, and the gas is sent to the acid production workshop after heat exchange. The decomposition rate of calcium sulfate in the raw materials reaches 45%.

[0057] The pre-decomposed material enters rotary kiln 3, where the temperature is controlled at around 1300℃, with a small amount of pulverized coal added at the kiln tail. The free calcium content of the clinker exiting the kiln is ≤1.2%.

[0058] The clinker is cooled to below 120°C using a grate cooler, and then 5% gypsum and 3% slag are added and ground together to a specific surface area of ​​350 m² / kg to obtain PO42.5 cement.

[0059] Industrial-scale numerical simulations and experiments show that the system in this embodiment has a processing capacity that is approximately 42% higher than that of traditional processes, while reducing heat consumption by approximately 10%. The 28-day compressive strength of the cement clinker is 48.6 MPa, which meets the GB 175-2007 standard. The SO2 concentration in the kiln tail flue gas remains stable at 12-15%, making it suitable for direct acid production. After six months of operation, the inner wall of the decomposition furnace showed no significant corrosion or deformation, and the equipment lifespan is significantly longer than that of ordinary heat-resistant steel.

[0060] Example 2 The difference between Example 2 and Example 1 is that the material of the reduction decomposition furnace 1 is high-chromium-nickel heat-resistant steel (Cr25Ni20Si2) with refractory castable lining and acid-resistant coating; at the same time, the staged feeding ratio is controlled, with the first part of hot raw materials accounting for 80% of the total and the second part accounting for 20% of the total. The oxygen-deficient combustion temperature in the inner silo is controlled at 1000℃. The pre-decomposition rate reaches 48%. The system capacity is increased by 38%, and the cement quality is qualified.

[0061] The method proposed in this invention uses a gas-solid reaction to replace the traditional solid-solid reaction, achieving a pre-decomposition rate of 40-50% for phosphogypsum in a dedicated decomposition furnace, which is far higher than the static solid-solid reaction of the traditional process (generally less than 20%), thus significantly improving the reaction rate and system efficiency.

[0062] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A reduction decomposition furnace for a phosphogypsum decomposition and cement co-production system, characterized in that, include: The central strong reduction chamber has openings at both the bottom and top. The bottom opening of the central strong reduction chamber is connected to the kiln tail flue chamber of the rotary kiln. The central strong reduction chamber is equipped with pulverized coal nozzles and hot raw material inlets. The annular micro-oxidation chamber is fitted outside the central strong reduction chamber and completely encloses it. It has openings at the bottom and top. The annular micro-oxidation chamber is equipped with a hot raw material inlet and a tertiary air duct inlet. The bottom opening of the annular micro-oxidation chamber is connected to the kiln tail flue chamber of the rotary kiln.

2. The reduction decomposition furnace of the phosphogypsum decomposition and cement co-production system as described in claim 1, characterized in that, It also includes a material overflow baffle located inside the chamber of the annular micro-oxidation chamber and above the top opening of the central strong reduction chamber, with the bottom end face of the material overflow baffle being inverted conical.

3. The reduction decomposition furnace of the phosphogypsum decomposition and cement co-production system as described in claim 2, characterized in that, The annular micro-oxidation chamber is equipped with multiple tertiary air inlets, which are arranged tangentially to form a swirling flow.

4. The reduction decomposition furnace of the phosphogypsum decomposition and cement co-production system as described in claim 2 or 3, characterized in that, The walls of the central strong reduction chamber and the annular micro-oxidation chamber are made of silicon carbide-silicon nitride composite ceramic or high chromium-nickel heat-resistant steel, and their inner walls are provided with an acid corrosion resistant layer, which is resistant to SO2, SO3 and H2S gases.

5. A cement co-production system for phosphogypsum decomposition, characterized in that, The reduction decomposition furnace of the phosphogypsum decomposition and cement co-production system as described in claim 4 further includes a preheating device, a rotary kiln, and a tertiary air duct. The outlet of the preheating device is connected to the hot raw material inlet of the reduction decomposition furnace through a pipeline. The rotary kiln is connected to the bottom end of the reduction decomposition furnace. The two ends of the tertiary air duct are respectively connected to the reduction decomposition furnace and the rotary kiln.

6. The phosphogypsum decomposition and cement co-production system as described in claim 5, characterized in that, It also includes an airlock device located between the reduction decomposition furnace and the rotary kiln. The top outlet of the reduction decomposition furnace is connected to the gas-solid separation cyclone. The airlock device is used to prevent flue gas from flowing back.

7. A method for a cement co-production system based on the phosphogypsum decomposition method of claim 6, characterized in that, Includes the following steps: Phosphogypsum, siliceous raw materials, and aluminous raw materials are mixed in proportion to form raw meal powder, which is then fed into a preheating device for multi-stage countercurrent suspension preheating. A portion of the preheated raw meal powder is introduced into the central strong reduction chamber of the reduction decomposition furnace. The carbonaceous fuel is injected through the pulverized coal nozzle and the gasification reaction under high temperature and oxygen deficiency conditions produces reducing flue gas rich in CO and H2. The meal powder undergoes a reduction decomposition reaction in a suspended fluidized state to generate calcium sulfide. After the reaction in the central strong reduction chamber, the gas-solid mixture flows down through the material overflow baffle from the top opening into the annular micro-oxidation chamber. At the same time, high-temperature oxygen-containing tertiary air is introduced into the annular micro-oxidation chamber of the reduction decomposition furnace through the tertiary air duct. The material, in a suspended state, oxidizes calcium sulfide into calcium oxide and releases SO2 gas. Meanwhile, unburned coal powder and residual CO gas carried by the airflow from the central strong reduction chamber are fully oxidized and burned off in the annular micro-oxidation chamber. After the gas-solid mixture at the top of the annular micro-oxidation chamber is discharged, it enters the gas-solid separation cyclone. At the same time, the calcium oxide-rich hot raw material separated is fed into the rotary kiln and calcined with the correcting material to produce cement clinker. The SO2-rich flue gas separated by the gas-solid separation cyclone is sent to the acid plant to produce sulfuric acid after heat exchange by the preheating device.

8. The method for a cement co-production system based on the decomposition of phosphogypsum as described in claim 7, characterized in that, The flue gas residence time in the central strong reduction chamber is controlled to be 10-20 seconds, and the flue gas residence time in the annular micro-oxidation chamber is controlled to be 5-10 seconds.

9. The method for a cement co-production system based on the decomposition of phosphogypsum as described in claim 7, characterized in that, The firing temperature inside the rotary kiln is 1250℃ to 1350℃; the coal gasification reaction temperature inside the central strong reduction chamber is 1000℃ to 1100℃; and the coal gasification reaction temperature inside the annular micro-oxidation chamber is 900℃ to 1100℃.

10. The method for a cement co-production system based on the decomposition of phosphogypsum as described in claim 7, characterized in that, The carbonaceous fuel is one or more of pulverized coal, coke, and biochar; the fuel added to the rotary kiln is one or more of pulverized coal, coke, and biochar; in the gas atmosphere inside the central strong reduction chamber, the volume content of CO is controlled at 5%-10%, and the volume content of O2 is less than 0.5%.

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