Patent Application
20220204403
This application claims priority to Chinese Patent Application No. 202011212325.7 with a filing date of Dec. 30, 2020. The content of the aforementioned applications, including any intervening amendments thereto, are incorporated herein by reference.
The present invention relates to a production method for producing cement and sulfuric acid from gypsum, and more particularly, to a production method for producing cement and co-producing sulfuric acid from phosphogypsum.
Phosphogypsum is produced by precipitation and crystallization of phosphorite and sulfuric acid subjected to a double decomposition reaction during wet-process phosphoric acid production, with a chemical reaction principle as follows:
Ca5F(PO4)5+H2SO4+10H2O→3H3PO4+5CaSO4.2H2O↓+HF↑
Production of 1 ton of wet-process phosphoric acid (P2O5%) generates 5 to 6 tons of solid phosphogypsum. There are about 5 billion tons of solid phosphogypsum stacked on lands in the world. A lot of capitals and lands are required to build a storage yard for massive discharge of the phosphogypsum. Since the phosphogypsum is soaked in rainwater for a long time, soluble phosphorus, fluorine, and the like in the phosphogypsum are transmitted to the environment through a water body as a medium, causing pollution of soil, water system and atmosphere, even causing a large number of environmental disasters due to collapse.
The phosphogypsum is a huge industrial solid by-product necessary to be generated under current technical conditions; and two chemical elements of calcium and sulfur contained in the phosphogypsum are necessary resources for life and production. Although there are many ways to utilize the phosphogypsum, such as directly using the phosphogypsum as a building material, and manufacturing the phosphogypsum into a gypsum board, a gypsum block, a gypsum putty, and the like, the phosphogypsum has four shortcomings compared with natural gypsum or desulfurized gypsum. Firstly, in phosphorus chemical industry production, in order to achieve a best phosphorite utilization rate and make filtration and washing easier, phosphogypsum crystalline particles need to be coarse, resulting in a low specific surface area and a poor activity when used in gypsum products. Secondly, some micro soluble ingredients and residual phosphorus brought by liquid holdup of the phosphogypsum may have salt efflorescence and mildew due to a change of a humidity in air after entering the gypsum products. Thirdly, except for constant calcium, sulfur and silicon ingredients contained in the phosphogypsum, contents of micro and ultra-micro impurities in the phosphogypsum are different due to different mineral sources, resulting in endless changes in differences in morphology, specific surface, and reactivity of the produced phosphogypsum. Fourthly, in wet-process phosphoric acid production which is a previous process of phosphogypsum production, a grinding fineness of the phosphorite brings influences of original undecomposed phosphorite particles and acid-insoluble particles. Fifthly, it is unprofitable due to an economic value limitation brought by a low inherent economic value of the gypsum products and a transportation cost of the gypsum products.
Therefore, sulfuric acid and cement are produced with calcium and sulfur elements in the phosphogypsum according to a principle of reduction, recycling, and reuse of a recycling economy. The sulfuric acid is recycled to a wet-process phosphoric acid device, so that sulfur resources are recycled, and the calcium element is used in cement production, which reduces exploitation of lime mine, and saves exploitation of primary calcium resources, thus being a best recycling economy method and a practical and effective way to maximize resource utilization. It is also a “knot” that people have diligently and continuously worked hard and failed in development of a generation technology in the past 100 years.
In 1915, German Müller used carbon as a reducing agent, and added Al2O2, Fe2O3, and SiO2 into the gypsum to decompose at a high temperature. Decomposed CaO reacted with an added oxide to form a cement clinker, and decomposed SO2 gas was used for producing the sulfuric acid. Afterwards, Kühne made a research and put it into industrial production on this basis. In 1916, Bayer Fuel Company of Germany built a plant for manufacturing sulfuric acid and cement from gypsum in Germany, and normal production was carried out in 1931. It is a technology called Müller-Küller method (M-K method) or a Bayer method for producing the cement and co-producing the sulfuric acid from the gypsum. In 1968, Linz Chemical Company of Austria used the phosphogypsum instead of natural gypsum to successfully operate on a 200 t/day sulphuric acid device by the Müller-Küller technology. In order to reduce energy consumption, a vertical cylindrical preheater was additionally arranged at a tail part of a rotary kiln in 1972, which achieved a good energy saving effect, and reduced heat consumption by 15% to 20%. It is a technology called an Osw-KPupp method (O-K method) for producing the cement and co-producing the sulfuric acid from the gypsum.
Although preheating outside the kiln is used in the Osw-KPupp technology, which utilizes sensible heat in tail gas of calcination and decomposition, coal consumption of a production device thereof is still high, a concentration of SO2 gas in the tail gas is low, a quality of the cement is poor, a production process is difficult to be controlled, and an efficiency of the production device is low. Compared with the production of the cement from limestone mine, an energy consumption index of an excellent cement producer is a heat quantity of 2926 KJ/Kg for producing every kilogram of cement clinker, wherein a heat quantity of 1580 KJ/Kg is needed to decompose calcium carbonate, accounting for nearly 70% of the energy consumption. However, a heat quantity of 1879.26 KJ/Kg is needed to decompose anhydrous gypsum, which is only 1.7 times of the heat consumption for decomposing the calcium carbonate according to calcium oxide per kilogram of cement clinker generated, while actual total energy consumption is more than 4 times higher.
A reaction principle of producing the cement and the sulfuric acid from the phosphogypsum is as follows:
CaSO4+2C═CaS+2CO2↑ (1)
3CaSO4+CaS=4CaO+4SO2↑ (2)
CaO+(SiO2,Al2O3,Fe2O3)→calcium silicate+calcium aluminoferrite, etc. (3)
CaSO4+3CaS=4CaO+4S (4)
C+O2═CO2↑ (5)
S+O2═SO2↑ (6)
The reaction formulas (1) and (2) are reduction and decomposition reactions, and the reaction formula (3) is a mineralization and sintering reaction for producing the cement, which is a main reaction needed in production, while the reaction formulas (4) to (6) are side reactions during production. The former two reactions and the latter two reactions determine a difficulty and a practical economy of the production device. In principle, the main reaction is a semi-reduction and decomposition reaction according to the reaction formulas (1)+(2), hexavalent sulfur in the calcium sulfate is reduced to tetravalent sulfur with elemental carbon, and a half molecule of carbon is needed for reducing one molecule of SO2. A combined reaction formula thereof is:
CaSO4+0.5C═CaO+SO2↑+0.5CO2↑ (7)
In the case of the side reactions, a deep reduction and decomposition reaction is carried out according to the reaction formulas (1)+(4)+(6), and one and a half molecules of carbon is needed to obtain one molecule of SO2, which is three times that of the main reaction. A combined reaction formula thereof is:
CaSO4+1.5C+O2═CaO+SO2↑+1.5CO2↑ (8)
If the side reactions are mainly focused, not only a production cost is high, but also a concentration of the sulfur dioxide gas of a production index and ingredients of the cement clinker are difficult to be controlled.
Moreover, according to a decomposition reaction condition of the phosphogypsum, the generated sulfur dioxide is related to a reaction temperature and a gas phase atmosphere of the reaction. As shown in
Therefore, a cement clinker index cannot meet a basic requirement: a cement clinker control index requires that free CaO(F—CaO) is lower than 1.5% (an actual requirement is lower than or equal to 1.2), CaS is lower than 1.0%, SO3 is lower than 1.5%, and actual production is 1.89% of free CaO, 1.53% of CaS, 2.42% of SO3, or even higher. It is impossible to produce high-quality cement clinker products, and early cement strength indexes of “3 days, 28 days” are difficult to be controlled stably. If the content of the oxygen is high, not only the concentration of decomposed SO2 gas generated from the kiln tail is low, but also the co-production of the sulfuric acid is unfavorable, so that an efficiency of the plant is low. These shortcomings cannot be overcome by an existing technology. It is also the difficulty that the existing production technology for producing the cement and the sulfuric acid from phosphogypsum cannot be industrialized in the face of such huge phosphogypsum output, an environmental protection pressure, and requirements of sustainable development and resource conservation.
Therefore, in order to control an atmosphere for reduction and decomposition as well as oxidizing calcination, Chinese patents ZL 201310437466.3 and ZL201410070462.0 feed powdered raw materials after drying phosphogypsum, which are suspended and preheated by a multi-stage suspension preheater, and reduced and decomposed to be separated from an oxidizing calcination combustor, and a certain progress is made. However, there are three shortcomings. Firstly, high free water of the phosphogypsum needs to be dried in advance, which consumes energy, and residual phosphorus (including water-soluble phosphorus and insoluble phosphorus) in the phosphogypsum seriously affects a cement sintering reaction. Secondly, dry phosphogypsum powder and reduced coal powder are mixed and enter the suspension preheater for preheating, resulting in ineffective combustion of reducing pulverized coal on a heat transfer surface, with high investment on the suspension preheater and increased power consumption required for production, and the energy consumption is not optimal. Thirdly, for a mixed powder material entering a reduction and decomposition ring kiln, with rotation of the rotary kiln, high-temperature gas is very easy to take up the reduced coal powder on a bare surface of the material and burn it quickly, so that not only an effect of reducing pulverized coal is not achieved, but also a lot of air is consumed.
U.S. Pat. No. 4,608,238 “Method for Treating Waste By-products of Phosphogypsum of Wet-process Phosphoric Acid” includes removing fluorine and phosphorus from the phosphogypsum, pre-drying, then reducing and decomposing at 1,050° C., heating a material at 1,200° C. to 1,250° C. with an excessive oxygen atmosphere, and then heating the material at 1,650° C. with an electric furnace to obtain silicate lime. The same shortcomings of the technology are as follows. Firstly, a process is long. Secondly, the phosphogypsum comes from a phosphoric acid filter with a high water content, and requires coal consumption for drying, which is as insufficient as the drying of the Chinese patents ZL201310437466.3 and ZL201410070462.0. Thirdly, the fluorine and the phosphorus in the phosphogypsum are high in content, and are passively removed by the oxidation electric furnace at a high temperature instead of removing in advance, and a heat source of the electric furnace is low in efficiency and high in energy consumption as secondary energy. Fourthly, a step grid furnace is used, with a high mass and heat transfer efficiency, and large power consumption.
According to a method of the U.S. Pat. No. 6,395,246 “preparation of calcium silicate and sulfur dioxide”, carbon is not used as a reducing agent to decompose the phosphogypsum, and the phosphogypsum is directly mixed with silicon dioxide, heated to 1,538° C., and sprayed with 2% to 5% water to generate “new ecological” hydrogen and oxygen, and the intermediate silicic acid is generated, and then decomposed with the phosphogypsum into the calcium silicate and the sulfur dioxide. Water has been vaporized before getting close to an object at a high temperature, thus being difficult to enter a semi-molten solid material, and a difficulty in generating new ecological silicic acid (H2SiOx) by hot melting the silicon oxide in solid is obvious.
In order to overcome the above shortcomings, the disclosure aims to provide a coupling production method for producing cement and co-producing sulfuric acid from phosphogypsum. The method includes: pretreating and purifying the phosphogypsum to reduce most insoluble phosphorus, water-soluble phosphorus, and large-particle silicon impurities (acid non-soluble substances) in the phosphogypsum, carrying out non-thermodynamic (mechanical) dehydration, then directly feeding the materials kneaded and granulated with a reducing agent into a reduction and decomposition integrated rotary kiln with fluidized preheating, drying and dehydration, and controlling to carry out step-by-step fluidized heating of reverse flow, fluidized drying, fluidized dehydration, reduction and decomposition in a low-oxygen-content atmosphere under pulverized coal combustion; using gas generated after reduction and decomposition to produce the sulfuric acid after dust removal and purification; making the materials after reduction and decomposition enter an oxidation calcining kiln for sintering a cement clinker, and controlling to heat and calcine cement clinker products in a high-oxygen-content atmosphere under the pulverized coal combustion. According to the method, in a process of removing phosphogypsum impurities in advance, mechanical dehydration is used, without separate drying to remove free water in the phosphogypsum, thus saving drying fuel, reducing consumption of reducing coal and sintering coal, improving a product quality of the cement clinker, and achieving purposes of energy saving, production cost reduction, production efficiency improvement, investment reduction, and economic benefit increase of a producer. An environmental protection problem of phosphogypsum stacking treatment is eliminated.
The disclosure has the technical solution that: a production method for producing cement and co-producing sulfuric acid from phosphogypsum includes: feeding phosphogypsum containing a large amount of free water discharged from a vacuum filter for phosphoric acid production into a pulping tank for pulping;
feeding pulp materials into a gravity classifier to separate coarse particles, and making the coarse particles return to an ore grinding system of the phosphoric acid production; making the materials with the coarse particles separated enter a filter press for filtration, pressure dehydration and blow drying, and recycling a filtrate to the phosphoric acid production as a process water supplement; feeding a filter cake into a granulator to be granulated with added reducing pulverized coal and supplemented auxiliary material;
using the granulated materials as cement raw materials to enter a reduction and decomposition integrated rotary kiln with a fluidized preheating device, and controlling to carry out fluidized heating of reverse flow, fluidized drying, fluidized dehydration, reduction and decomposition in a low-oxygen-content atmosphere under pulverized coal combustion; using decomposed gas sulfur dioxide generated after reduction and decomposition to produce the sulfuric acid after dust removal and purification; and
making the reduced and decomposed materials enter a cement clinker sintering kiln, controlling a high-oxygen-content atmosphere under the pulverized coal combustion, and increasing a temperature to heat and sinter the cement clinker products.
Preferably, a pulping ratio of the phosphogypsum to the water is 1:2 to 4, and preferably 1:2.5.
Preferably, after the phosphogypsum slurry is added into a gravity separator and separated, a total amount of separated coarse particles is 2% to 8%, and preferably 5%.
Preferably, the free water of the phosphogypsum subjected to the pressure dehydration is 8% to 15%, and preferably 10% to 12%.
Preferably, the filter cake of the dehydrated phosphogypsum is granulated with reducing pulverized coal and clay, and a kneading granulator is preferably used as a granulator.
Preferably, the reduction and decomposition integrated rotary kiln with fluidized preheating, drying and dehydration is an integral cylindrical rotary kiln, as shown in
Preferably, the material from a kiln outlet of the reduction and decomposition kiln directly enters the cement clinker sintering rotary kiln, and a diameter of the sintering rotary kiln is 0.5 to 0.7 times, and preferably 0.4 to 0.6 times a diameter ϕ of the reduction and decomposition rotary kiln.
Preferably, gas generated by sintering in the cement clinker sintering rotary kiln enters the reduction and decomposition rotary kiln; and the cement clinker enters a cooler and is cooled with air to prepare the cement.
Preferably, a temperature of the sulfur oxide gas discharged from a kiln tail of the reduction and decomposition rotary kiln after reduction and decomposition, fluidized preheating, drying, and dehydration is 320° C. to 400° C., and preferably 330° C. to 350° C. A content of O2 in the sulfur oxide gas is 0 to 1.0%, and preferably 0.2% to 0.6%.
Preferably, a temperature of the decomposition section of the reduction and decomposition rotary kiln is 1,000° C. to 1,200° C., and preferably 1,050° C. to 1,150° C.
Preferably, a temperature of the sintering section of the cement clinker sintering kiln is 1,250° C. to 1,450° C., and preferably 1,300° C. to 1,350° C.; and a content of O2 in outlet gas of the cement clinker sintering kiln is 1.0% to 4.0%, and preferably 2.0% to 3.0%.
Preferably, an excess air coefficient in the cement clinker sintering kiln is 1.06.
Preferably, the cement clinker is cooled from 1,150° C. to 110° C.-160° C., and preferably to 110° C.-130° C.
Compared with the prior art, the present invention has the principles and beneficial effects as follows.
According to the disclosure, the phosphogypsum containing high free water, water-soluble phosphorus and insoluble phosphorus separated by a vacuum filter in wet-process phosphoric acid production is directly added with the water for pulping, coarse-particle insoluble phosphorus in the phosphogypsum is separated by a gravity, and then the phosphogypsum is fed into the pressure filter for filtration separation, extrusion and air blowing, so that the contents of the free water and the water-soluble phosphorus in the phosphogypsum are reduced; then the phosphogypsum is kneaded and granulated with the reducing agent and the auxiliary material, so that the reducing agent and the auxiliary material are tightly kneaded with the phosphogypsum, which is beneficial for an oxygen deprivation reaction of the reducing carbon and a sulfate radical in gypsum; the granulated materials are fed into the reduction and decomposition integrated rotary kiln with fluidized preheating, drying and dehydration, which overcomes shortcomings of high reducing agent consumption, low thermal efficiency and high investment price of an original suspension preheater; and the reduced and decomposed materials enter an oxidation sintering rotary kiln with smaller specification and size, and the higher-oxygen-content atmosphere is controlled, so that the rotary kiln has a large filling coefficient, a thermal efficiency and a production efficiency are high, CaS in cement products is low, and a quality of products is high. Energy consumption for drying the free water of the phosphogypsum is saved, consumption of reducing coal and sintering coal is reduced, purposes of energy saving, production cost reduction, production capacity improvement, quality optimization of cement products, investment reduction, and economic benefit increase of a producer are achieved, and an environmental protection problem of phosphogypsum stacking treatment is eliminated.
According to the disclosure, pulping, purification, extrusion and blowing dehydration (non-thermodynamic dehydration) of the phosphogypsum are employed, the phosphogypsum is kneaded and granulated with the reducing agent, and a series of manners like the integrated rotary kiln for preheating, drying, dehydration, reduction and decomposition of fluidized materials and the oxidation sintering efficiency rotary kiln are used in the method for producing the cement and co-producing the sulfuric acid from the phosphogypsum, so that the existing technology for producing the cement and co-producing the sulfuric acid from the phosphogypsum is optimized and upgraded; by utilizing thermodynamic and kinetic characteristics of the reduction and decomposition of the cement sintering, and the optimum process parameters of kneading and granulation, fluidized preheating and drying, reduction and decomposition in the low-oxygen-content atmosphere, and mineralization and calcination in the high-oxygen-content atmosphere, the energy consumption of production is greatly reduced, the production capacity of the device is greatly increased, and the technological production is stable and easy to be controlled; a concentration of the gas sulfur oxide has small fluctuation, and the quality of the cement products is stable and excellent; purposes of saving energy, reducing the production costs, improving the production efficiency, reducing investment, and increasing economic benefits increase of a producer are achieved, and the environmental protection problem of phosphogypsum stacking treatment is eliminated. Therefore, the disclosure not only can use the phosphogypsum as a calcium and sulfur resource, but also has the advantages of low processing cost, remarkable economic and social benefits, and the like.
In the disclosure, the pulping ratio of the phosphogypsum from phosphoric acid production to the water is 1:2 to 4, and preferably 1:2.5; the total amount of separated coarse particles is 1% to 6%, and preferably 3%; the free water of the phosphogypsum subjected to the pressure dehydration is 8% to 15%, and preferably 10% to 12%; the filter cake of the dehydrated phosphogypsum is granulated with the reducing pulverized coal and the clay, and the kneading granulator is preferably used as the granulator; for the integrated rotary kiln for fluidized preheating, dehydration, drying, reduction and decomposition, a length L1 of the special-type shoveling plate for lifting is set to be 0.2 to 0.5 times, preferably 0.3 to 0.4 times the total length L of the kiln; the diameter of the sintering rotary kiln is 0.5 to 0.7 times, and preferably 0.4 to 0.6 times the diameter ϕ of the reduction and decomposition rotary kiln, with the length l of 0.4 L to 0.6 L; the temperature of the sulfur oxide gas discharged from the kiln tail of the integrated rotary kiln for fluidized preheating, drying, dehydration, reduction and decomposition is 320° C. to 400° C., and preferably 330° C. to 350° C., wherein the content of O2 in the sulfur oxide gas is 0 to 1.0%, and preferably 0.2°/o to 0.6%; the temperature of the decomposition section of the reduction and decomposition rotary kiln is 1,000° C. to 1,200° C., and preferably 1,050° C. to 1,150° C.; the temperature of the sintering section of the sintering rotary kiln is 1,250° C. to 1,450° C., and preferably 1,300° C. to 1,350° C., wherein the content of O2 in the outlet gas of the kiln is 1.0% to 4.0%, and preferably 2.0% to 3.0%; and the cement clinker is cooled from 1,150° C. to 110° C.-160° C., and preferably to 110° C.-130° C.
The disclosure solves a technical problem that people have been eager to solve for nearly 100 years, but have never achieved commercial success.
In
In
The disclosure is further described hereinafter with reference to the accompanying drawings.
As shown in
Reduced and decomposed high-temperature materials from the integrated rotary kiln K1 continuously entered the cement clinker sintering rotary kiln K2, and pulverized coal was fed into a pulverized coal injection combustor in the cement clinker sintering rotary kiln K2 by using a pulverized coal injection combustion fan V2 for combustion. A maximum temperature of materials in the cement clinker sintering rotary kiln K2 was controlled at 1,300° C., an excess air coefficient was controlled at 1.06 with matching secondary air of the pulverized coal injection combustion fan V2, and a concentration of O2 in a gas phase was 3.0%. The sintered clinker from the cement clinker sintering rotary kiln K2 continuously entered a cooler K3 and was cooled to 160° C. by using a cooling blower V3. 20,000 kg of cement clinker was obtained every hour, and fed for a cement grinding process to produce finished cement. Composition thereof refers to Table 3.
As shown in
Reduced and decomposed high-temperature materials from the integrated rotary kiln K1 continuously entered the cement clinker sintering rotary kiln K2, and pulverized coal was fed into a pulverized coal injection combustor in the cement clinker sintering rotary kiln K2 by using a pulverized coal injection combustion fan V2 for injection and combustion. A maximum temperature of materials in the cement clinker sintering rotary kiln K2 was controlled at 1,300° C., an excess air coefficient was controlled at 1.08 with matching secondary air of the pulverized coal injection combustion fan V2, and a concentration of O2 in a gas phase was 3.5%. The sintered clinker from the cement clinker sintering rotary kiln K2 continuously entered a cooler K3 and was cooled to 160° C. by using a cooling blower V3. 20,000 kg of cement clinker was obtained every hour. Composition thereof refers to Table 6.
Reduced and decomposed high-temperature materials from the integrated rotary kiln K1 continuously entered the cement clinker sintering rotary kiln K2, and pulverized coal was fed into a pulverized coal injection combustor in the cement clinker sintering rotary kiln K2 by using a pulverized coal injection combustion fan V2. A maximum temperature of materials in the cement clinker sintering rotary kiln K2 was controlled at 1250° C., an excess air coefficient was controlled at 1.08 with matching secondary air of the pulverized coal injection combustion fan V2, and a concentration of O2 in a gas phase was 3.5%. The sintered clinker from the cement clinker sintering rotary kiln K2 continuously entered a cooler K3 and was cooled to 160° C. by using a cooling blower V3. 40,000 kg of cement clinker was obtained every hour. Composition of the cement clinker refers to Table 6.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202011212325.7 | Dec 2020 | CN | national |
