Production method for producing cement and sulfuric acid from phosphogypsum

Abstract

The invention discloses a production method for producing cement and sulfuric acid by using phosphogypsum. The method comprises the following steps: carrying out pretreatment purification on phosphogypsum to reduce insoluble phosphorus, water-soluble phosphorus impurities and most free water in the phosphogypsum, kneading with a reducing agent, granulating, and directly feeding the material into a reductive decomposition integrated rotary kiln with fluidization preheating function; controlling a gas phase atmosphere to perform step-by-step heating, drying, dehydration and reductive decomposition under the combustion of the pulverized coal; sulfur dioxide gas generated after reductive decomposition is used for producing sulfuric acid after being subjected to dust removal and purification; and the reduced and decomposed material enters an oxidation calcining kiln for cement clinker sintering, and the gas-phase atmosphere is controlled under the combustion of pulverized coal for heating, mineralizing and sintering to obtain the cement clinker. Compared with the prior art, the production method for producing cement and co-producing sulfuric acid by using phosphogypsum has the advantages that the coal consumption for reduction and firing is reduced, the production efficiency and the product quality are improved, the device investment is saved, the economic benefit of producers is increased, and the environmental protection problem of phosphogypsum stacking treatment is eliminated.

Description

technical field [0001] The invention relates to a production method for co-production of sulfuric acid with cement produced from gypsum, in particular to a production method for co-production of sulfuric acid with phosphogypsum for production of cement. Background technique [0002] The production of phosphogypsum is produced by the precipitation and crystallization of phosphate rock and sulfuric acid during the production of wet-process phosphoric acid. The chemical reaction principle is as follows: [0003] Ca 5 F(PO 4 ) 5 +H 2 SO 4 +10H 2 O→3H 3 PO 4 +5CaSO 4 2H 2 O↓+HF↑ [0004] Production of one ton of wet-process phosphoric acid (P 2 o 5 %) to produce 5-6 tons of solid phosphogypsum. About 5 billion tons are stored on land in the world. A large amount of discharge of phosphogypsum requires a large amount of money and land to build a storage yard. Because phosphogypsum is soaked in rainwater for a long time, the soluble phosphorus and fluorine in it are tr...

AI Technical Summary

Problems solved by technology

Compared with natural gypsum or desulfurized gypsum, phosphogypsum has four major disadvantages: First, in the production of phosphorus chemical industry, in order to achieve the best utilization rate of phosphate rock, it is easier to filter and wash, and the phosphogypsum crystal particles need to be coarse, resulting in the use of phosphogypsum. When used in gypsum products, the specific surface area is low, and the activity is not good; the second is that some trace soluble components and residual phosphorus brought along with the liquid holding capacity of phosphogypsum, after entering the gypsum products, due to changes in the humidity in the air, salt frost and Mildew; the third is that due to the different mineral sources in phosphogypsum, in addition to the constant calcium, sulfur, and silicon components contained in it, the content of trace and ultra-trace impurities is different, resulting in differences in the morphology, specific surface, and reactivity of the produced phosphogypsum The changes are endless; the fourth is the impact of the original undecomposed phosphate rock particles and acid-insoluble particles brought about by the grinding fineness of phosphate rock in the production of wet-process phosphoric acid in the previous process of phosphogypsum production; the fifth is as the gypsum product itself Inherently low economic value and limited economic value due to transportation costs of plaster products are not profitable

[0022] Therefore, the cement clinker index cannot meet the basic requirements: the cement clinker control index requires free CaO (F-CaO) to be lower than 1.5% (the actual requirement is lower than or equal to 1.2), CaS is lower than 1.0%, SO 3 Less than 1.5%, while the actual production is free CaO1.89%, CaS1.53%, SO 3 2.42%, or even higher; high-quality cement clinker products cannot be produced, and the early strength index of cement "3 days, 28 days" is difficult to control stably

If the oxygen content is high, not only the decomposed SO produced at the kiln tail 2 The gas concentration is low, which is not conducive to the production of co-produced sulfuric acid, and the efficiency of the device is low

These shortcomings cannot be overcome by the current existing technology

This is also the difficulty that the existing phosphogypsum production technology of cement and sulfuric acid cannot be industrialized in the face of such a huge phosphogypsum output, environmental protection pressure and sustainable development and resource conservation requirements.

[0023] Therefore, in order to control the atmosphere of reduction decomposition and oxidative calcination, Chinese patents ZL201310437466.3 and ZL201410070462.0 adopt dry phosphogypsum powdered raw material as raw material, and carry out reduction decomposition after being suspended and preheated by a multi-stage suspension preheater Separated from the oxidation calcination burner, some progress has been made; however, there are three shortcomings: first, the high free water of phosphogypsum requires pre-drying to consume energy, and the residual phosphorus (including water-soluble phosphorus and insoluble phosphorus) in phosphogypsum is serious. Affect the cement firing reaction; second, dry phosphogypsum powder and reduced coal powder are mixed into the suspension preheater for preheating, resulting in ineffective combustion of the reduced coal powder on the heat transfer surface, expensive suspension preheater investment and production needs The power consumption increases, and the energy consumption is not optimal; the third is that the powder mixture material after entering the reduction and decomposition rotary kiln, as the rotary kiln rotates, the high-temperature gas is very easy to bring up the reduced coal powder on the surface of the exposed material and burn it rapidly. Not only the effect of reducing pulverized coal is not achieved, but a large amount of air is consumed

The same shortcomings of this process are: first, the process is long; second, phosphogypsum comes from phosphoric acid filter with high water content, and drying requires coal consumption, which is as insufficient as the drying of Chinese patents ZL201310437466.3 and ZL201410070462.0; third, fluorine in phosphogypsum High phosphorus content and phosphorus content are not removed in advance, but are passively removed at high temperature in an oxidation electric furnace. The heat source of the electric furnace is used as a secondary energy source with low efficiency and high energy consumption; the fourth is to use a stepping grid furnace, which has high mass transfer and heat transfer efficiency and large power consumption.

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