| Phosphoric acid(PA)is one of the main basic raw materials of phosphorus chemical products,one of the main uses is to produce phosphorus compound fertilizer,such as superphosphate,TSP,ammonium phosphate,MKP,etc.At the same time,it is also the production raw material of industrial additives,food additives,feed additives and other phosphorus containing products.PA is widely used in metallurgy,petroleum,chemical industry,medicine,food,feed,electronic products and other fields.However,the main raw material of PA production is phosphate rock,which is rich in reserves in China,but most of them belong to medium and low grade mineral resources,with low reaction activity and high impurity content.Belongs to the low reaction activity phosphate rock with great difficulty in sorting.This kind of phosphate rock with low grade and high impurity content is suitable for the production and processing of wet-process PA,generally,industrial PA is produced by traditional thermal process,but the production of thermal process PA has the problems of high energy consumption,serious pollution and poor environment.At present,the majority of enterprises adopt INCRO technology in their ammonium phosphate plants,generally usethe process of p re-neutralization plus tubular reactor in reaction process to produce 64%nutrient superior DAP.Due to the high quality requirement of raw material PA to produce DAP,the PA produced by wet process PA plant generally needs to be aged and settled to meet the production demand,but a number of sludge acid will arise in this process.About the treatment of sludge acid,generally consider to consume sludge acid withabout 6.5%solid contentin DAP plant to produce GMAP product in the design.However,due to market demand and other factors,it is rarely organized to produce this product.In recent years,most of the sludge acid with about 17%solid content is used to produce first-class DAP product or any other ways to consume sludge acid such as export.The domestic fertilizer market is affected by overcapacity and other factors,limit the market demand offirst-class DAP f product and the sales volume of sludge acid,while cause the high storage of first-class DAP product and the expansion of sludge acid,which seriously affect the production balance and limit the operation of the plant.Therefore,the problem of sludge acid in PA production is need to be solved.Based the enterprise’s production plants,own work content and actual situation,this paper is mainly carried out the engineering research and tested on the treatment and application of sludge acid produced in the production process of wet-process PA,and participated in the small batch test of sludge acid application and fertilizer effectiveness.The results are as follows:(1)The recovery and treatment capacity of concentrated residue acid back to the main process is limited,and it is necessary to divert and treat concentrated residue acid with high impurity content in time.The filter press and its supporting auxiliary facilities are used to compress and filter the concentrated residue acid,realize liquid-solid separation and obtain the clear phosphoric acid and the filter cake with less moisture content and water-soluble phosphorus,solve the impact of the accumulation of slag acid on the production load of the wet phosphoric acid production device,reduce the frequency of device maintenance after the pipeline fouling caused by acid reflux,and solve the difficulty of the enterprise affecting the production balance operation due to residual acid.The residue acid press filter of phosphoric acid carries out targeted graded utilization of the product materials of the existing phosphoric acid plant,which plays the purpose of rational use of raw materials,and can also provide different raw materials for the diversification of products of subsequent devices.(2)The clear acid produced by sludge acid pressure filtration directly enters the existing clear acid distribution tank or dilute phosphoric acid settling tank,resulting in low solid content,and P2O5generally in the range of 41%.This part of the filtrate is mixed with the original clear acid,which basically does not affect the quality of the clear acid,could improve the production of the follow-up superior DAP product and promote the economic benefit of enterprises.(3)The addition amount of filter press sludgeof phosphoric acid and phosphate rock powder is controlled in a certain ratio range,fresh calcium product is obtained after reacting,stacking,curing,and add a certain amount of bitter soil to produce powdery "Magnesiumrich incalcium" new product,through the granulation process to further produce granular product.According to the needs of customers and the market of different specifications of "Magnesium rich in calcium" new products could bring better economic benefits;(4)Sulfuric acid is used to decompose the press filter sludge of PA,and the citric acid soluble phosphorus in the press filter sludge is converted into water-soluble phosphorus,which is then reacted with phosphate rock powder to produce high-quality calcium superphosphate.The decomposition rate of this calcium superphosphate could reach 90%above,and the physical properties could meet the requirements also,the indicatorsof high-quality calcium superphosphate product is better than the national standard(GB20413-2006)superior products.(5)Combined with the local high-quality humic acid resources,the fertilizer efficiency of phosphoric acid filter press sludge was studied after adding humic acid,production could meet the GB 15063 standardnutrients containing humic acid compound fertilizer products,which provides a new way for the comprehensive utilization of sludge from wet-process phosphoric acid processing.Through demonstration test and application promotion,the possibility of producing humic acid containing compound fertilizer from by-product sludge of wet-process phosphoric acid production after filter pressing is further determined,which accumulated resources for industrial production and marketing of the product. |
