Design And Study On Paddy Fluidized Bed Drying System Based On Self-heat Recuperation Theory

Rice,a necessity for human survival,is one of the primary food crops in China and it is also a kind of sensitive material.Freshly harvest paddy contains high water moisture.In order to prevent mildew damage,it is necessary to reduce the water content to safe storage standards.The traditional fluidized bed drying system has disadvantages of high energy consumption,high drying temperature.At the same time,it can not guarantee the quality of paddy.Thus,it’s of great importance to design an energy-saving fluidized bed drying system which is applicable for paddy.A novel paddy fluidized bed drying system is designed by combining the self-heat recuperation theory and drying process.In the case of satisfying drying production,the operation parameters of fluidized bed are determined and the thermal calculation model of each equipment is established.Thermodynamic parameters of each state point in drying system are obtained by using mass and energy conservation equations on the whole system as well as each equipment.Then,thermal and economic characteristics of conventional and self-heat drying system are evaluated.Compared to the conventional drying system,energy consumption of the advanced one deceases 54.09% and 60.21%,COP is improved significantly and the drying temperature reduced from 103.2℃ to 86.7℃ under the conditions of constant drying rate and fixed drying temperature.The self-heat dying system reduces 29.71% cost per year and its investment payback period is 4.41 years.Meanwhile,the energy is analyzed by the “three link theory” and “T-H” diagram,the results show that the total energy recovery rate of the self-heat drying system reached 82.77%,while the conventional one is only 8.58%.Only 7.79% recycled energy is utilized and 92.21% energy comes from the external heat in the conventional drying system,while the advanced one just needs 48.68% external heat for the process.Above results show the self-heat drying system is more reasonable,energy-saving and economic than the traditional one.Next,energy saving characteristics of the proposed system is investigated by analyzing the influence of key parameters,including fluidization velocity,compressor efficiency,expander efficiency and pressor ratio,on the overall performance indices.Fluidization velocity increases,which means the drying rate will increase so dose the total energy consumption.The higher the compressor and expander efficiency,the smaller the system energy input,in the premise of meeting the drying rate,lower pressure ratio leads to more latent energy recovery in the heat exchanger which means high heat efficiency of the heat exchanger and a better performance in energy saving of the self-heat drying system.Finally,exergy loss model of each parts are established in two drying system,and the influence of fluidization and compressor efficiency on the system exergy efficiency are analyzed.The results indicated that the largest exergy loss exists in heater occupying 87.55% of the total exergy loss,and the exergy efficiency of the conventional drying system is 0.45% while the self-heat one is 5.89%.Low fluidization velocity and high compressor efficiency results in high exergy efficiency of the advanced drying system.