Experimental Investigation On Drying And Reaction To Produce Granular MAP In A Superheated Steam Fluidized Bed

According to the actual running condition of ammonium phosphate plants,problems such as serious scaling of ammonium phosphate slurry, long process flow,being difficult to treat waste gas, the difficulty of utilizing low-grade heat resources,serious pollution are existed. From the point view of energy saving, loweringconsumption, and reduction, a new process flow with short flow, low consume, littlepollution discharge, will be developed.The ammoniation of phosphoric acid is an instantaneous fast gas-liquid reactioncontrolled by gas-film mass transfer. According to the bi-film theory, the reactionoccurs at the gas liquid film, the total rate of reaction lies upon NH₃ mass transferratio in gas film. Therefore, in order to improve mass transfer ratio, we can increase thegas-liquid contact area and mass transfer coefficient.Fluidized-bed granulation is a process integration of particle formation, mixingand drying. It has the characteristics of larger gas-solid interfacial area and highrelative velocity, larger heat and mass transfer velocity was obtained ammoniationhappening in the fluidized bed, and reaction and drying can be finished at the sametime.Act as medium of fluidizing and drying, latent heat of superheated steam can berecovered and utilized by condensing, energy consumption was greatly decreased, and there was not the problem of tail gas treatmentAccording to the characteristics of fluidized bed, superheated steam drying, andphosphoric acid ammonization reaction, an integrated one-step-process technologyproducing granular ammonium phosphate employed a superheated steam fluidizedbed was suggested.Starting from crystallization of ammoniated phosphoric acid slurry, escape ofammonia, thermal stability of solid ammonium phosphate, according to heat andmass transfer mechanism of particles and gas-phase in fluidized bed, theory analysisof ammoniating reaction,drying and particle formation of surface of solid particle influidized bed was done. According to the experiment purpose and conditions, anexperimental process flow was suggested the design and calculation of the mainequipment and instruments of process flow was done. And installation anddebugging of equipment was done.Basing on theoretical analysis of ammonification, drying and particle formationin fluidized bed, experiment was done in the superheated steam fluidized bed toprepare MAP by reaction and drying. The following question was investigated in theexperiment. (1)Steady operational conditions of preparing ammonium phosphate inthe superheated steam fluidized bed was investigated, (2) the product mass ratio of Nto P₂O₅ and loss rate of NH₃ was affected by the feed mole ratio molar ratio of NH₃ toH₃PO₄, (3) the growth rate of fluidized particle diameter was investigated in order toinvestigate if product particles growing or not., (4) the effect of operationtemperature in fluidized bed on product mass ratio of N to P₂O₅ was investigatedThe experimental results indicate that: the feeding molar ratio of NH₃ to H₃PO₄does not have an obvious effect on the mass ratio of N to P₂O₅, and the product massratio of N to P₂O₅ is approximately equal to 0.198 of purity MAP when operatingtemperature is from 100℃to 130℃, there did not need excessive ammonia in theprocess. The product weight packed on the surface of fluidized particle increasedwith increasing reaction time, and the size of the particle increase continuously. Theproduct mass ratio of N to P₂O₅ decreases with rising of operating temperature in thefluidized bed. The basic rules of new integrated technology for preparing ammoniumphosphate by reacting and drying in one step in the superheated steam fluidized bed,the results were the basis for further research and development.