| Phosphoric acid,with the molecular formula of H3PO4,is not easy to decompose.Pyrophosphoric acid or metaphosphoric acid can be obtained by deliquescence in air.The production method is divided into wet process and thermal process.Wet process phosphoric acid production process is generally selected for industrial production.Our company uses phosphoric acid process to produce low concentration phosphoric acid by decomposing fluorapatite with concentrated sulfuric acid.According to the different types of calcium sulfate produced by sulfuric acid decomposing phosphate rock,it can be divided into dihydrate method(DH method),hemihydrate method(HH method)and other combined forms of recrystallization process.At present,the mainstream production method is two water method,accounting for about 85%.Two water method is the earliest and most extensive production process.However,with the construction of large-scale863 projects(800000 tons of sulfuric acid,300000 tons of phosphoric acid and 600000 tons of diammonium phosphate)in China,the production capacity of phosphate fertilizer tends to be seriously surplus.The solid waste calcium sulfate dihydrate also faces considerable environmental pressure.According to the spirit of relevant national documents,the gypsum utilization rate of phosphate fertilizer industry needs to be close to or more than 25%,and the company has carried out a lot of research According to the production load of phosphoric acid,the output of gypsum increases at a rate of million tons per year,which has laid a major hidden danger for the company’s production and operation.In addition,the annual maintenance cost of gypsum slag yard is increasing year by year.In short,the safety risk is prominent and the cost pressure is huge.Enterprises need to tap the potential from the perspective of product transformation,try to improve the efficient use of energy and reduce production costs.Through the research,the author will study the process of semi aqueous wet process phosphoric acid from the perspective of experiment and production.Based on the current two water process theory,this paper analyzes the related principles of two-phase process control by ternary phase diagram and quaternary phase diagram,summarizes other unfavorable factors by practical experience,and studies the reaction conditions and transformation links of semi-aqueous process by analogy,including the core control indicators,such as reaction temperature,solid content of slurry SS,excess sulfur trioxide,and so on Stirring speed,liquid phase phosphorus pentoxide,etc.,according to the phosphorus recovery rate to test and analyze,select the best index control range,provide technical reference for the subsequent transformation,and put forward the feasibility analysis of our company’s two water method technology transformation of semi water.From the experimental point of view,the concentration of phosphoric acid can be increased from 20-27% to 43-45%,and the recovery rate can be increased from 95% to 96%.The cost will be greatly reduced.At the same time,according to the advantages of semi hydrated gypsum,such as high gelation,high strength and low moisture content,the utilization rate of gypsum will be greatly improved. |
