| Zriconium hydroxide is the important intermediate products of zirconium. ZrO2 power obtained by calcining zriconium hydroxide is an important oxide due to its high strength and toughness, good corrosion and abrasion resistance, high melting point, refractory and low thermal conductivity, while preparation of zriconium hydroxide is accomplished in the liquid. So moisture content generally above 70%, the drying is important to the quality of the zriconium products. The manganese-carbon alloy ball is a new carburization material. The most critical stage of manganese-carbon alloy processing is drying, as the minimum moisture standard (below0.5%) can only be achieved under specific controlled conditions. Conventional drying is still widely used for dewatering manganese-carbon alloy ball and zriconium hydroxide but it is not economical as it heats both matiral and water. During the conventional drying, heat is transferred from outside to inside, which is in the opposite direction to the steam diffusion, causing low drying efficiency. There are aslo other problems associated with conventional drying such as environmental problems,long process,labor-intensive operation. Thus searching for new techniques for drying of manganese-carbon alloy ball and zriconium hydroxide is a subject long studied for improving the present drying techniques. In this study, microwave drying is chosen for the treatment of them, as it offers many advantages over conventional drying methods.In this paper, the craft for drying of manganese-carbon alloy ball and zriconium hydroxide was brought out based on the review of a general overview of microwave applications, this thesis is primarily concerned with experimental and numerical analysis.(1) The optimum conditions for the process was determined using response surface methodology (RSM). Central composite experimental design (CCD) was employed to evaluate relationships between the input variables including drying temperature,drying time,the mass of material and the interaction on the corresponding relative dehydration rate. Over the range studied, the optimum conditions for zriconium hydroxide the of relative dehydration rate were as follow:drying temperature of 95℃, drying time of 12.8min, the mass of material of 149.7g, the dehydration rate was 90.32% with the surface area, respectively. The optimum conditions for the manganese-carbon alloy ball of relative dehydration rate were as follow:drying temperature of 90℃, drying time of 175.8s, the mass of material of 150.61g, relative dehydration rate of material is 93.96% with the surface area, respectively.(2) The drying behavior of matters was investigated. It can be observed that increasing drying time and decrease mass substantially increases the drying rate and thus decreasing drying time. While at less than 100g of manganese-carbon alloy ball, constant drying rateperiod is less evident. Newton's, Page's and Wang's models were used to discribe drying kinetics. Page's was found to be more suitable to predict microwave drying behavior of manganese-carbon alloy ball and zriconium hydroxide.(3) Effective moisture diffusivities were determined to be from 1.079×10-7 to 3.008×10-7 m2/s, and from 1.010×10-7 to 3.051×10-7 m2/s, at mass load of 20g-100g, at 85℃-100℃, for microwave drying of zriconium hydroxide, respectively. While effective moisture diffusivities of manganese-carbon alloy ball were determined to be from 7.7×10-8m2/s to 4.33x10-7m2/s and from 8.3×10-8 m2/s to 2.44×10-7m2/s at mass of 30g-100g, at 70℃-90℃, respectively.(4) Based on the result of laboratory experiments and kinetics, industrial scale were carried out with the use of the industrial microwave equipment with power of 54 kW. The relations between effects of drying time,temperature and moisture content were studied.The resules shows the energy efficiency of zriconium hydroxide and manganese-carbon alloy ball is 0.46 kg/kwh,0.56kg/kwh, when moisture content of the matirals gets to industrial grades. |
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