Preheating and predecomposing device and method outside phosphogypsum acid-making and co-production cement kiln

Abstract

The invention discloses a pre-heating and pre-decomposing device and method for co-production of acid from ardealite and outside a cement kiln, and the device is characterized in that pretreated ardealite, a siliceous raw material and an aluminum raw material are prepared into a raw material according to a specific proportion, the raw material is fed into a pre-heating system, and the raw material and hot flue gas from a decarburization and desulfurization furnace are subjected to countercurrent suspension pre-heating; the preheated mixture enters a decomposing furnace, is subjected to suspension reductive decomposition with reductive hot flue gas from a gasification furnace, and then is mixed and oxidized with high-temperature and high-oxygen air from a kiln head, so that a hot raw material with relatively high calcium oxide content is obtained; and the hot raw material enters the rotary kiln and is further subjected to mineralization reaction with the silicon-aluminum correction material to generate cement clinker. According to the method for co-producing acid from ardealite and preheating and pre-decomposing outside the cement kiln, preheating and decomposing of ardealite are completed in a suspended state, decomposing of ardealite in the kiln is converted into decomposing outside the kiln, and the effects of being high in heat and mass transfer efficiency, high in reducing agent utilization rate, high in production efficiency, low in system energy consumption, cost-reducing and efficiency-increasing can be achieved.

Description

Technical Field

[0001] The invention relates to solid waste utilization in the building materials industry, and in particular to a high-efficiency phosphogypsum acid-making and cement kiln preheating and predecomposition device and method. Background Art

[0002] Phosphogypsum is the main solid waste generated in the production process of wet phosphoric acid, and its main component is calcium sulfate dihydrate (CaSO4·2H2O). Therefore, the resource utilization of phosphogypsum has become a major issue of global environmental protection and sustainable development. The technology of acid production and cement production by phosphogypsum is an important way to realize its large-scale resource utilization. The core of this technology is to decompose phosphogypsum through high-temperature reduction of coke, and the generated SO2 gas is used to make sulfuric acid, and the generated calcium oxide (CaO) is combined with silicon-aluminum raw materials to calcine into cement clinker. The research on this technology began in the early 20th century, and the process scheme exploration has gone through several stages such as hollow long kiln, preheating system kiln, kiln decomposition, fluidized bed, etc. The preheating system kiln process is still the one that realizes industrial production. However, this process has many problems such as small scale, large investment, high energy consumption, difficult operation, unstable production, poor product quality, and low economic benefits, which makes this technology face great difficulties in the process of promotion.

[0003] In recent years, domestic and foreign researchers have proposed a variety of improvement plans to reduce the decomposition temperature, increase the SO2 concentration in flue gas and optimize thermal efficiency. For example, based on the process technology with suspended preheating as the main feature, Sinoma International Engineering Co., Ltd. (Nanjing) has increased the SO2 concentration in flue gas to more than 12% by optimizing and improving high-efficiency low-resistance preheating and expanding kiln functions, and the firing heat consumption has also been greatly reduced to 1250kal / kg clinker. CN101456542A proposes to use carbon monoxide (CO) as a reducing agent and add composite admixtures (such as Fe2O3, CaCl2, etc.) to increase the decomposition rate to more than 98%, and decompose phosphogypsum in a nitrogen atmosphere at 750-850°C. In order to further optimize the decomposition reaction efficiency, CN104828784A proposes an off-kiln suspension decomposition process, which uses a U-shaped reaction tube to extend the material residence time, and introduces sulfur and coal mixed fuel, supplements heat through sulfur combustion and increases the SO2 concentration in the flue gas to 11%, and uses a four-stage preheating system to recover waste heat and reduce energy consumption. CN105152141A uses a step-by-step treatment strategy to partially reduce the phosphogypsum raw material with CO in a pre-reduction furnace to generate CaS (20% to 35%), and then completes the oxidation reaction of CaS and the remaining CaSO4 in a rotary kiln. This method alleviates the atmosphere contradiction in the kiln by separating the reduction and oxidation steps. CN101172582A uses a reducing agent such as CO generated by the oxygen-poor combustion of coal in a decomposition furnace to partially reduce calcium sulfate to CaS, and then sends it to a rotary kiln for subsequent production.

[0004] In general, although the existing technology has made great progress in reducing energy consumption and improving decomposition rate, the following bottlenecks still exist: (1) The utilization rate of reducing agent is low, and the high consumption of coke leads to rising costs; (2) The solid-solid mass transfer thermal efficiency in the rotary kiln is low, the reaction time is long, the kiln output per unit volume is small, the kiln body heats up, and the energy consumption is high; (3) The atmosphere of the rotary kiln is difficult to control, and the clinker quality fluctuates greatly; (4) The SO2 concentration is lower than 12%, which increases the acid production cost. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a preheating and predecomposition device outside the cement kiln for acid production and co-production of phosphogypsum with high heat and mass transfer efficiency and simple operation.

[0006] Another object of the present invention is to provide a method for preheating and predecomposing phosphogypsum acid-making and cement kiln outside the kiln, which has high heat and mass transfer efficiency, high reducing agent utilization rate, high production efficiency, low system energy consumption, and cost reduction and efficiency improvement.

[0007] Technical solution: The preheating and predecomposition device outside the phosphogypsum acid production and cement kiln of the present invention comprises a preheating system, a decarbonization and desulfurization furnace, a decomposition furnace, a rotary kiln and a tertiary air duct; the preheating system comprises N cyclones, N is 4, 5 or 6, and the cyclone comprises a feed pipe, a material spreading box, a flap valve, and a connecting air duct; the material-carrying air flow outlet at the top of the decarbonization and desulfurization furnace is connected to the gas-solid separation cyclone, the lower interface is connected to the tertiary air duct, and the bottom is connected to the outlet of the gas-solid separator;

[0008] The outlet of the decomposition furnace is connected to the gas-solid separator at the bottom of the decarbonization and desulfurization furnace, and a multi-point and multi-layer access port for the N-1-level cyclone discharge pipe is provided in the middle;

[0009] The kiln head of the rotary kiln is connected to the kiln head cover and the burner, and the kiln head cover is connected to the clinker cooling device;

[0010] The bottom of the decomposition furnace is connected with a gasification furnace, the lower part of the gasification furnace is connected with the smoke chamber outlet of the rotary kiln, and the gasification furnace is provided with coal powder and sulfur nozzles and a hot raw material inlet.

[0011] Preferably, the operating temperature of the decarbonization and desulfurization furnace is 850-1100°C, and the flue gas residence time is 5-8 seconds.

[0012] Preferably, the operable temperature of the decomposition furnace is 900-1100° C., and the residence time of the flue gas is 10-20 seconds.

[0013] Preferably, the operating temperature of the gasifier is 900-1100° C., and the smoke residence time is 10-20 seconds.

[0014] The method for preheating and predecomposing phosphogypsum acid-making and cement kiln using the device comprises the following steps:

[0015] (1) Batching and preheating: The pretreated phosphogypsum, siliceous raw materials and aluminum raw materials are mixed into raw materials according to a specific ratio and then sent to the preheating system for countercurrent suspension preheating with the hot flue gas from the decarbonization and desulfurization furnace;

[0016] (2) Reduction and oxidation: The preheated mixed material obtained in step (1) enters the decomposition furnace, is suspended and reduced and decomposed with the reducing hot flue gas from the gasification furnace, and is then mixed and oxidized with the high-temperature and high-oxygen air from the kiln head to obtain a hot raw material with a high calcium oxide content;

[0017] (3) The hot raw material enters the rotary kiln and further reacts with the siliceous and aluminous correction materials to produce cement clinker.

[0018] Preferably, in the hot flue gas described in step (2), the volume content of CO is 5-10%, and the volume content of O2 is less than 0.5%.

[0019] Preferably, the reducing hot flue gas described in step (2) is a mixed gas including CO and H2 gases.

[0020] Preferably, the temperature of the reduction and oxidation reaction in step (2) is 900-1100°C.

[0021] Preferably, the decarbonization and desulfurization furnace is used to remove sublimated sulfur and excess reducing gas generated at the outlet of the decomposition furnace, and the temperature in the furnace is 850-900°C.

[0022] Preferably, the decomposition furnace is used to decompose phosphogypsum into calcium sulfide in a reducing atmosphere, and is also used to oxidize calcium sulfide into calcium oxide in an oxidizing atmosphere. Calcium sulfate reacts with reducing gases such as C, CO, and H2 in the decomposition furnace to generate CaS, which is oxidized into CaO at the outlet of the decomposition furnace, i.e., the reduction and oxidation reaction of step (2). The temperature in the furnace is 900°C-1100°C, and the reaction in the lower part of the decomposition furnace is:

[0023] CaSO4+4CO=CaS+4CO2(g)

[0024] CaSO4+S2(g)=CaS+2SO2(g)

[0025] The reaction in the upper part of the decomposition furnace is:

[0026] CaS+1.5O2(g)=CaO+SO2(g)

[0027] The side reactions that may occur in the decomposition furnace mainly include:

[0028] CaS+2O2(g)=CaSO4

[0029] CaSO4+CO→CaO+SO2+CO2;

[0030] CaSO4+H2→CaO+SO2+H2O;

[0031] CaS+H2O→CaO+H2S.

[0032] Preferably, the gasifier is used for high-temperature oxygen-deficient gasification of bituminous coal, anthracite, lignite, coke, and sulfur; the generation reaction of reducing gases such as CO, H2, and S2 occurs in the furnace, and the reaction temperature is 1000-1100°C; the specific reactions are: C+0.5O2→CO; C+CO2→2CO; C+H2O→CO+H2; 2S→S2.

[0033] Principle of the invention: The present invention provides a method for preheating and predecomposition outside a cement kiln for efficient acid production from phosphogypsum. The reducing gas required for the decomposition reaction of the phosphogypsum is firstly gasified, and the solid-solid accumulation reduction reaction in the rotary kiln in the traditional process is converted into a suspended fluidized decomposition reaction with both gas-solid and solid-solid properties, and the decomposition in the kiln is converted into decomposition outside the kiln, thereby effectively improving the heat and mass transfer efficiency.

[0034] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention provides a method for preheating and predecomposing phosphogypsum acid and cement outside the kiln for high efficiency, so that the phosphogypsum can complete the preheating and reduction decomposition reaction in a suspended state, which not only reduces the energy consumption of the system, but also improves the production efficiency, and greatly improves the single-line production capacity of rotary kilns of the same specifications; (2) The method provided by the present invention gasifies the solid reducing agent into high CO / H2 and carbon particle reducing flue gas through an online gasification furnace, converts the decomposition in the kiln into decomposition outside the kiln, and converts the solid-solid reduction agent in the rotary kiln of the traditional process into decomposition outside the kiln. The stacked reduction reaction is converted into a suspended fluidized decomposition reaction with both gas-solid and solid-solid properties, which improves the heat and mass transfer efficiency; (3) The preheating, predecomposition, and online gasification processes in this method are all completed in a suspended state, with high heat and mass transfer efficiency, which can effectively reduce the specifications of dynamic equipment such as rotary kilns and their surface heat dissipation. The system has low heat consumption and high output, and can effectively expand the production capacity of rotary kilns of the same specifications. According to tests, taking a 1000t / d clinker production line as an example, the heat consumption is 70% to 80% of that of a preheating system kiln, and the production capacity is 120% to 160% of that of a preheating system kiln. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the overall appearance of the present invention. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is further described below in conjunction with embodiments.

[0037] like Figure 1As shown, the preheating and predecomposition device outside the phosphogypsum acid-making and cement kiln co-production of the present invention comprises a preheating system 1, a decarbonization and desulfurization furnace 2, a decomposition furnace 3, a gasification furnace 4, a rotary kiln 5 and a tertiary air duct 6; the preheating system 1 comprises 5 cyclones, and the cyclone comprises a feed pipe, a material spreading box, a flap valve, and a connecting air duct; the material-carrying air flow outlet at the upper part of the decarbonization and desulfurization furnace 2 is connected to the gas-solid separation cyclone C5, the lower interface is connected to the tertiary air duct 6, and the bottom is connected to the outlet of the S1 gas-solid separator; the outlet of the decomposition furnace 3 is connected to the S1 gas-solid separator at the lower part of the decarbonization and desulfurization furnace 2, and the bottom is connected to the gasification furnace 4 through the S2 gas-solid separator, and a multi-point and multi-layer access port of an N-1-level cyclone feed pipe is provided in the middle; the lower part of the gasification furnace 4 is connected to the smoke chamber outlet of the rotary kiln 5, and the gasification furnace 4 is provided with a coal powder and sulfur nozzle and a hot raw material access port; the kiln head of the rotary kiln 5 is connected to the kiln head cover and the burner, and the kiln head cover is connected to the clinker cooling device.

[0038] The process of using this device to preheat and predecompose phosphogypsum acid and cement kiln is as follows:

[0039] (1) Batching and preheating: Phosphogypsum with a particle size of 80 μm and a sieve residue of 10%-20%, coke, silica sandstone, bauxite, and mineralizer are mixed evenly in a ratio of 89:6:2:1 to prepare raw meal powder, which is then sent to the C2 cyclone outlet pipe by the elevator. Under the action of the airflow, the raw meal powder is dispersed and suspended in the airflow, and enters the C1 cyclone with the airflow. After gas-material separation, the raw meal powder enters the C3 cyclone gas outlet pipe through the flap valve, and enters the C2 cyclone with the airflow. In a similar manner, the raw meal powder is subjected to four-stage heat exchange in the C1, C2, C3, and C4 cyclone connecting pipes, and then is preheated in countercurrent suspension with the hot flue gas from the decarbonization and desulfurization furnace 2, and is fully preheated.

[0040] (2) Reduction and oxidation: A portion of the preheated mixed material obtained in step (1) enters the decomposition furnace 3 (the other portion enters the online gasification furnace 4 to control the temperature in the furnace), where it comes into contact with the hot flue gas containing CO and carbon particles at 1100° C. from the outlet of the gasification furnace 4, and the calcium sulfate is partially or completely reduced and decomposed into calcium sulfide in the furnace in a suspended state; high-temperature tertiary air is introduced from the kiln head into the upper part of the decomposition furnace 3 to partially or completely oxidize the calcium sulfide into calcium oxide, which enters the C6 cyclone with the air flow for gas-material separation, thereby obtaining a hot raw material with a high calcium oxide content.

[0041] (3) The hot raw material enters the rotary kiln 5 and further reacts with the silicon-alumina correction material to form cement clinker.

[0042] (4) The hot flue gas from the outlet of C6 cyclone enters the decarbonization and desulfurization furnace 2, is fully mixed with the high-temperature tertiary air from the kiln head, and completes the combustion of excess CO and sublimated sulfur in the decarbonization and desulfurization furnace 2. Then, it enters the cyclone of the preheating system 1 in turn to fully exchange heat with the raw material powder, and then passes through the high-temperature dust collector for dust removal, and is used to prepare sulfuric acid.

[0043] The bituminous coal is sprayed into the gasifier 4 above the kiln tail smoke chamber for gasification reaction, in which the volatile matter and part of the fixed carbon are converted into reducing gases such as CO and H2 and coke particles under high temperature and oxygen-deficient conditions. This reaction is an exothermic reaction, and the material discharged from the preheater C4 cyclone is partially distributed to the gasifier 4 for temperature control.

[0044] Wherein, in the hot flue gas of step (2), the volume content of CO is 5-10%, and the volume content of O2 is less than 0.5%.

[0045] Among them, the decarbonization and desulfurization furnace 2 is used to remove excess reducing gases such as CO in the flue gas and the sublimated sulfur produced in the decomposition furnace 3, so that they undergo an oxidative combustion reaction with a reaction temperature of 850-900°C. The specific reaction is: S+O2→2SO2; 2CO+O2→2CO2; 2H2+O2=2H2O.

[0046] Among them, calcium sulfate undergoes decomposition and oxidation reaction with reducing substances such as C, CO, H2, S2 in the decomposition furnace 3 to generate CaO; the temperature in the furnace is 1000-1100℃, and the overall reaction in the furnace is: CaSO4+CO→CaO+SO2+CO2; CaSO4+H2→CaO+SO2+H2O.

[0047] Among them, the online gasification furnace 4 is provided with coal powder and sulfur nozzles and a hot raw material inlet, and the formation reaction of the reducing agent used in the reduction reaction of step (2) occurs in the furnace. The temperature in the furnace is 1000-1100°C, and the specific reaction is: C+0.5O2→CO; C+CO2→2CO; C+H2O→CO+H2.

[0048] The formation reaction of cement clinker minerals occurs in the rotary kiln 5. The temperature in the kiln is 1100-1500°C. The reaction in the kiln is:

[0049] 12CaO+2SiO2+2Al2O3+Fe2O3=3CaO·SiO2+2CaO·SiO2+3CaO·Al2O3+4CaO·Al2O3·Fe2O3.

[0050] According to calculations, taking a 1000t / d clinker production line as an example, the heat consumption is 70% to 80% of the preheater kiln, and the production capacity is 120% to 160% of the preheater kiln. Raw material preheating, pre-decomposition, and online gasification furnace are all completed in a suspended state, with high heat and mass transfer efficiency, small equipment specifications, less system heat dissipation, and low heat consumption.

Claims

1. A preheating and predecomposition device outside a cement kiln for acid production with cogeneration of phosphogypsum, comprising a preheating system (1), a decarbonization and desulfurization furnace (2), a decomposition furnace (3), a rotary kiln (5) and a tertiary air duct (6); the preheating system (1) comprises N cyclones, N being 4, 5 or 6, the cyclone comprising a feed pipe, a material spreading box, a flap valve and a connecting air duct; the upper part of the decarbonization and desulfurization furnace (2) is connected to the gas-solid separation cyclone, the lower interface is connected to the tertiary air duct (6), and the bottom is connected to the outlet of the gas-solid separator; The outlet of the decomposition furnace (3) is connected to the gas-solid separator at the bottom of the decarbonization and desulfurization furnace (2), and a multi-point and multi-layer access port for an N-1-level cyclone discharge pipe is provided in the middle; The kiln head of the rotary kiln (5) is connected to a kiln head cover and a burner, and the kiln head cover is connected to a clinker cooling device; It is characterized in that The bottom of the decomposition furnace (3) is connected to a gasification furnace (4), the lower part of the gasification furnace (4) is connected to the smoke chamber outlet of the rotary kiln (5), and the gasification furnace (4) is provided with coal powder and sulfur nozzles and a hot raw material inlet.

2. The device according to claim 1, characterized in that The operating temperature of the decarbonization and desulfurization furnace (2) is 850-1100°C, and the smoke residence time is 5-8 seconds.

3. The device according to claim 1, characterized in that The operable temperature of the decomposition furnace (3) is 900-1100°C, and the smoke residence time is 10-20 seconds.

4. The device according to claim 1, characterized in that The operating temperature of the gasifier (4) is 900-1100°C, and the smoke residence time is 10-20 seconds.

5. A method for preheating and predecomposing phosphogypsum acid and cement kiln using the device according to claim 1, characterized in that: The following steps are involved: (1) Mixing and preheating: The pretreated phosphogypsum, siliceous raw material and aluminum raw material are mixed into raw meal in a specific ratio and then fed into a preheating system (1) to be preheated in a countercurrent suspension with the hot flue gas from the decarbonization and desulfurization furnace (2); (2) Reduction and oxidation: The preheated mixed material obtained in step (1) enters the decomposition furnace (3), is suspended and reduced and decomposed with the reducing hot flue gas from the gasification furnace (4), and is then mixed and oxidized with the high-temperature and high-oxygen air from the kiln head to obtain a hot raw material with a high calcium oxide content; (3) The hot raw material enters the rotary kiln (5) and further reacts with the silicon-aluminum correction material to form cement clinker.

6. The method according to claim 5, characterized in that In the hot flue gas described in step (2), the volume content of CO is 5-10%, and the volume content of O2 is less than 0.5%.

7. The method according to claim 5, characterized in that The reducing hot flue gas described in step (2) is a mixed gas including CO and H2 gases.

8. The method according to claim 5, characterized in that The temperature of the reduction and oxidation reaction in step (2) is 900-1100°C.

9. The method according to claim 5, characterized in that The decarbonization and desulfurization furnace (2) is used to remove sublimated sulfur and excess reducing gas generated at the outlet of the decomposition furnace (3), and the temperature in the furnace is 850-900°C; the decomposition furnace (3) is used to decompose phosphogypsum into calcium sulfide under a reducing atmosphere, and is also used to oxidize calcium sulfide into calcium oxide under an oxidizing atmosphere, and the temperature in the furnace is 900-1100°C.

10. The method according to claim 5, characterized in that The gasifier (4) is used for high-temperature oxygen-deficient gasification of bituminous coal, anthracite, lignite, coke and sulfur; a reaction of generating reducing gases such as CO, H2 and S2 occurs in the gasifier, and the reaction temperature is 1000-1100°C.

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