Microwave - Heat Pump Joint Characteristics Of Dry Ammonium Sulfate And New Technology Research

At present, in order to deal with massive low concentration SO2 exhausted by thermal power and metallurgy industry, majority enterprises adopt the ammonia desulphurization technology to realize the recycle of SO2. In the ammonia desulphurization technology, centrifugal dewatered ammonium sulfate usually contains high water ratio. However, in national standard (GB535-1995), there is a strict provision of the ammonium sulfate's moisture content, in which the moisture content of premium grades is less than 0.2%. For the reasons above, the following drying process is significant and necessary. Because of the high energy consumption in current ammonium sulfate drying process, the microwave and heat-pump drying technology is applied to ammonium sulfate drying in this research. In this article, ammonium sulfate's microwave drying characteristic was in-depth studied, and the drying dynamics model was established. Meanwhile under the study of the energy efficiency compared to different drying process, the heat pump-microwave combined drying craft of ammonium sulfate and the best technological conditions were determined, providing the important theory basis to realize the industrial production application of ammonium sulfate's microwave drying.Firstly, the research on microwave drying of ammonium sulfate technique was initiated.The drying behavior of ammonium sulfate was investigated and the thin-layer drying models are used for data processing. The results show that the modified page model (II) is more suitable than other models for simulation of microwave drying of ammonium sulfate. Under the condition of microwave power of 230-700W or material mass being 150-300g, application of Fick's second law results in an effective diffusion coefficient of thin-layer sludge subjected to microwave drying ranging from 1.48×10-7 to 4.33×10-7m2/s or from 3.61×10-7 to 6.59×10-7m2/s, respectively.Secondly, for realizing the low energy consumes under the basic conditions of microwave drying, ammonium sulfate technique is investigated, using the temperature-controlled microwave technology. It is indicate that the key factors, like drying temperature, microwave drying time, material weight and thickness, have an affect on the relative dehydration rate of ammonium sulfate. On the basis of single-factor experiment, the response surface central composite design was adopted to optimize microwave drying parameters of ammonium sulfate, by taking the relative dehydration rate of ammonium sulfate as response value. The obtained optimized technology parameters were:temperature of 86.05℃, the radiation time of 190.50s, material weight of 102.59g, thickness of 20.55mm. The corresponding relative dehydration rate of material is 99.29%. The deviation of experimental values and predicted values is only-0.43%, showing high reliability. The results show that the response surface central composite design plays good optimization and prediction roles. The technology of microwave drying of ammonium sulfate used is reasonable and feasible, which can provide reference and guide for future research. The contrast research with the conventional drying indicated that under the condition of the same temperature, material weight, thickness and achieves the same relative dehydration rate, The temperature-controlled microwave drying compared with the conventional drying save the time of 77.14%, and can obvious guarantee the quality of the product at the same time.Besides, the heat-pump drying experiment of ammonium sulfate was carried out to further reduce the energy consumption. The effects of material quality, drying time, material thickness on the relative dehydration rate and the energy efficiency ratio of ammonium sulfate were investigated. On the basis of single-factor experiment, the response surface central composite design was adopted to optimize heat-pump drying parameters of ammonium sulfate, by taking the relative dehydration rate and the energy efficiency of ammonium sulfate as response value. The obtained optimized technology parameters were: material quality 598.9g, heat pump drying time 56.75min, material thickness 15mm. The corresponding relative dehydration rate of material is 92.1%, the energy efficiency ratio is 0.292kg/kw·h. The regression analysis and the verification test have indicated the rationality and the feasibility of the response surface method. The contrast research with the conventional drying shows that under the condition of the same temperature, material weight, thickness and achieves the same relative dehydration rate, the heat pump drying not only has the obvious energy conservation superiority and also has certain timing superiority.On the basis of experiments above, the feasible horizontal extent of heat pump microwave combined drying craft was determined through the contrastive analysis of relative dehydration rate and energy efficiency ratio. And the response surface central composite design was adopted to optimize heat pump-microwave combined drying parameters of ammonium sulfate, by taking the relative dehydration rate and the energy efficiency of ammonium sulfate as response value. The obtained optimized technology parameters were:Material quality of 600g, heat pump time of 37.26min, microwave time of lmin. The corresponding relative dehydration rate of material is 91.7%, the energy efficiency ratio is 0.316kg/kw-h. The contrast research with The separate experiments of heat-pump and microwave drying shows that compared with the heat-pump drying, compared drying can enhances by 12.9% in the energy efficiency ratio, saving the time by 36.2%; Compared to microwave drying, can enhances 43.6% in energy efficiency ratio, simultaneously can guarantee the quality of the product.