| The contradiction between resource’s supply and demand issue becomes more and more serious during rapid socio-economic development. With the gradual expansion of demands of phosphoric acid and related products from phosphate ore, a non-renewable mineral resource, how to use existing phosphate ore efficiently is becoming urgent.Phosphate rock is utilized by decompositing it to produce phosphoric acid. Currently, the production methods of phosphoric acid are wet-process phosphoric acid, furnace-process phosphoric acid and the kiln phosphoric acid (KPA). Although the requirements of equipments, energy and cost of wet-process phosphoric acid are lower, it must use high grade phosphate (P2O5≥28%) as raw material, and the concentration of phosphoric acid is low while the impurity content is high. Despite the method of furnace-process phosphoric acid can use medium and low-grade phosphate rock to produce phosphoric acid, the released heat of phosphorus oxidation is difficult to be coupled in the reduction of phosphate rock, which leads to excessive energy cost. In spite of the same problem can be overcomed in the kiln phosphoric acid, the problems of phosphate rock blocking and slag release hinders its application.In order to utilize medium and low-grades phosphate ores, taking into account the above technical difficulties and the advantages of the fluidization technology, our group developed the fluidization technology to produce phosphate acid from medium and low-grade phosphate rock directly.In the self-made fluidized reactor, cold-flow mode experiments were conducted with phosphate ore (particle size of54-200μm, density of2253-2265kg/m3) at different bed height-diameter ratio of0.75,1.25,1.75and2.25. The results showed that the bed height-diameter have great influence on the fluidization behavior of phosphate rock particles. The bed expansion ratio decreases gradually with the increase of bed aspect ratio increase. When the bed height-diameter ratio is1.75, the slugging and channeling phenomena are not occurred in the bed. The phosphate critical fluidization velocity has been obtained by traditional depressurization method, the minimum fluidization velocity correlations was obtained by compared the results with various minimum fluidization velocity correlations.The reduction process of phosphate rock is studied in the fixed bed reactor. The effect of reaction temperature, reaction time, the amount of activated carbon and calcium silicate molar ratio on the reduction ratio of phosphate rock were studied. The kinetic parameters of the reaction were also investigated. The results demonstrated that the time required to achieve the same reduction ratio was shorter with the increase of temperature. With the increase of calcium silicate molar ratio, the reduction ratio increases at first and then decreases afterwards and finally stabilize. The reduction ratio of phosphate rock increases with the coke when the coke amount reaches the1.6times of theoretical value, the reduction ratio of phosphate rock stabilized. On the basis of above experiments, the fixed-bed pyrolysis kinetics of phosphate reduction equation was derived as lnk=9.69-176024/RT.The reduction reaction of medium and low-grade phosphate rock particles was studied in the self-made fluidized bed reactor. The effects of N2flow, calcium silicate molar ratio, reaction temperature and reaction time were investigated using the same phosphate rock particles in the fixed bed. The results showed that the N2flow rate plays great impact on the flow quality and reduction ratio. When the N2flow rate is500L/h, the reduction ratio of phosphate rock reaches maximum. When the N2flow rate increased further, it is unfavorable to the reaction. The optimal condition of phosphate rock particles in the fluidized reduction is the following:reaction temperature1250℃, reaction time40min, silicon calcium molar ratio of3.0, and excessive coke coefficient1.6, N2flow rate500L/h. Under this condition the phosphate rock reduction ratio was98.6%. |
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