The Process Optimization Of Using Raffinate Acid To Produce Industrial-grade Monoammonium Phosphate And Numerical Simulation Of Ammoniation

With the environmental and energy problem becoming serious,the wet process phosphoric acid technology with low energy consumption and little pollution has been applied widely on the production of industrial phosphoric acid.Currently,the solvent extraction method is the only purification technology of wet-process phosphoric acid which can be used in industry.In this purification process,the by-products,raffinate acid,will be produced inevitably,of which the comprehensive utilization has been paid more attention by companies.The use value and economic value of raffinate acid can be improved by producing industrial grade monoammonium phosphate(MAP).The outer loop reactor has been mainly used to produce MAP by companies.The structure optimization of outer loop reactor is important to the production with low cost.The main research content of this article includes three parts.Firstly,the different preparation processes of MAP were optimized using raffinate acid as materials,including the purifying and removal magnesium of raffinate acid and the removal magnesium and supplement nitrogen of MAP mother liquid before concentration and crystallization.Secondly,the technological parameters were optimized by the single factor experiment after confirming the combined technology.Finally,the flow of gas and liquid in outer loop reactors was simulated using the computational fluid dynamics(CFD)and Fluent.The main obtained conclusions are as the following:(1)The impurity magnesium in the raffinate acid can be removed using chemical precipitation method and fluosilicic acid as precipitant.The optimal magnesium removal technology is 1:4 of the mass ratio of fluosilicic acid and raffinate acid,170r/min of stirring rate,45 minutes of reaction time at room temperature without concentration.(2)The removal magnesium and supplement nitrogen of MAP mother liquid can be realized using chemical precipitation method and ammonium fluoride as precipitant and nitrogen filling agent.The optimal technology is 1:0.03(ml/g)of liquid-solid ratio of the mother liquor and ammonium fluoride,135 r/min of stirring rate,30 minutes of reaction time at 50?.(3)The optimal combined technology is that after fluosilicic acid treatment,use the product dilution at the ratio of 1:1,the temperature of the first neutralization and stewing is 70 ?,the time of the first stewing is 3 h,then the obtain filtrate according to the obtained filtrate and liquid-solid ratio of ammonium fluoride at 1:0.01(ml/g),the temperature of the second neutralization and stewing is 60 ?,the time of the second stewing is 3 h,relative density of concentration is 1.38,crystallization temperature is 40 ?and crystallization time is 40 min.The average yield of MAP(in terms of P2O5)is 31.77% under the optimal conditions of process.The sample can meet all indexes of industrial-grade monoammonium phosphate?standards.(4)The flow characteristic of gas and liquid in outer loop reactors was simulated and calculated using software,including the pressure distribution,velocity of gas phase,velocity of liquid phase,gas fraction and so on.The effects of admission velocity on the property of outer loop reactor has been discussed and the results show that the gas holdup and the phase velocity in the reactor distributes unevenly,and the increase extent reduces with the continuing increasing of the admission velocity.There is a optimal gas velocity control range.