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Study On A Cleaning Process Of Compound Fertilizer With Urea Sulfuric Acid

Posted on:2004-07-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:C H HouFull Text:PDF
GTID:1101360125957309Subject:Chemical processes
Abstract/Summary:PDF Full Text Request
Based on the current status of fertilizer industry in China, a new cleaning process of compound fertilizer by decomposing phosphate rock with urea-sulfuric acid (USC in brief) is proposed and a systematic theory study is performed. The principal results are as follow:1. Basic data of the system, such as density, viscosity, enthalpy of solution of urea at different mole ratio in sulfuric acid, specific heat, melting point, phase transformation heat of urea-sulfuric acid are determined. It is found that the viscosity (77) of urea-sulfuric acid solution has the correlation with temperature (T):η = η0+A1*exp(-T/T1)Because of the complexation reaction between urea and sulfuric acid, the viscosity changed irregularly with the composition.When the first mole urea is fed in 1 mol H2SO4, the enthalpy of solution is the maximum (51.92KJ/mol H2SO4), then with more urea fed, enthalpy of solution decreased obviously.2. Due to the widely application of the process of decomposing phosphate rock slurry with concentrated sulfuric acid in superphosphate in China, a new technique of decreasing phosphate rock slurry water is put forward. The factors affecting the phosphate rock decomposing rate, such as the reaction temperature, mole ratio of urea sulfuric acid, stirring speed, size of phosphate rock and consumption of acid, are studied and optimized3. On the two-stage fluorine absorption apparatus with a fluorine ionic selective electrode, the fluorine emission law is studied. The action of urea is the most important factor for the fluorine emission rate. In order to evaluate the effect of urea, the vapor pressure of H2SiF6, pH value of urea-sulfuric acid are measured. AXRD analysis on the product indicates that a new complex [CO(NH2)2H]2SiF6 is formed in the reaction system. There is O...H...O bond in the complexation between CO(NH2)2 and H2SiF6 which slowers the decomposition reaction of H2SiF6 and brings on the low fluorine emission rate. With the new process, fluorine emission rate is less than 7%, the operation environment greatly improved and the cost of fluorine absorption economized.4. Based on the X-ray diffraction study and chemical analysis, the reaction principle of the urea sulfuric acid decomposing PR is put forward. It is deduced that themain reaction combines two stages. In first stage, urea sulfuric acid decomposing phosphate rock CaSO4 4CO(NH2)2 and CO(NH2)2 H3PO4 are formed; In the 2nd stage, Ca(H2PO4)2 CO(NH2)2 mainly formed and some CaHPOA and .CO(NH2)2 H3PO4 also occurred.In the whole reaction ,the existence state of fluorine may be as follows:5. According to the reaction principle, the reaction kinetics of decomposing phosphate rock with urea sulfuric acid at the first stage is studied by using chemical pure agent. A reaction kinetic equation is obtained:Comparing with the traditional process of decomposing PR with sulfuric acid, the rate of action is lowered by urea and reaction order about one order.In a MSMPR crystallizer, the crystallizing experiment is carried out. The crystal forming time is prolonged by 50% because of addition of urea, but the growth rate of crystals increased. When an active agent (APA) is used, the density of suspension is increased by more than 50%, the crystal shape becomes wider, the nuclear forming rate decreased and the growth rate increased.6. Through the experiments with reaction temperature 339K-359K, PR size 0.110-0.174mm, mole ratio of urea to sulfuric acid is 2.0:1 to 3.6:1, a macro kinetics equation of decomposing Baokang PR with urea-sulfuric acid is established:The study results could be used as a basis for the design of reactor and the optimization of process operation indices in practice.
Keywords/Search Tags:urea sulfuric acid, acidulate agent, cleaning process, compound fertilizer, fluorine emission rate, crystallization kinetics, reaction kinetics.
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