Design Of Grain Heat Pump Drying Process System And Evaluation Of Energy Efficiency

In recent years,the number of grain driers has been developed rapidly in China.From the increase of 1,500 units in the overall market in 2010 to about 22,000 units in 2017.The current mechanization of grain drying is only 18.2%.Compared with the developed countries that have reached more than 90% and achieved the level of automated operations,there is a wide gap.Compared with the level of comprehensive mechanization in China that has reached more than 70%,the development is very unbalanced.The popularization and application of grain drying equipment has the problems of high energy consumption,low efficiency,and poor environmental friendliness.With the accelerating process of agriculture and industrialization in our country,the consumption of energy is increasing,and non-renewable resources are decreasing.It is particularly important to explore alternative technologies that use coal and oil as heat sources for green energy-saving drying.As a green and environmental protection device,heat pump is expected to change the traditional grain drying technology model,for realizing high efficiency and energy saving.It has been highly valued by government agencies at all levels,popularization of the heat pump drying technology in the grain drying field also includes additional purchase subsidies.Despite this,large-scale applications are still very difficult.The reality of development has made us realize that the existing grain heat pump drying system has unreasonable energy utilization,unscientific evaluation of energy efficiency,and many congenital defects in the equipment system.It is difficult for users to obtain satisfactory benefits in the heat pump drying process,which is one of the essential reasons for promoting difficulties.For this reason,this study according to the train of thought “Heat Pump System Operating Range and Environmental Conditions?Technical Problems in Industrial Applications?SystemDesign and Technical Basic Theory Analysis?Heat Pump Drying System Energy Efficiency Evaluation”.Focusing on the realization of the goal of green and energy-saving mechanization drying,a systematic design of grain heat pump drying process system and evaluation of energy efficiency were carried out.The research work and innovation of the thesis are mainly reflected in the following aspects:1.The development of heat pump drying technology at home and abroad is analyzed,and sort out problems in process theory and evaluation methods for grain heat pump drying systems.In view of the characteristics of large regional differences and strong seasonality,environmental factors directly relate to the key problems of the efficiency of heat pump systems.Combining the actual application of production and application,evaluating the feasibility of heat pump application in different grain production areas,and indicating the ways to improve the technology.It is clear that the heat pump can be used in the industrialization of China's Central Plains and southern grain production areas.2.For the characteristics of the heat pump system(working medium was R600a),it was established that when the maximum drying temperature for grain was not higher than 75?,the minimum ambient temperature for effective heating should not be lower than 15?.3.In view of the higher environmental temperature of grain harvest period in Central Plains and southern China,ambient air has certain drying capacity for high humidity grain.High humidity grain storage dryer-heat pump drying combined drying process system was designed.The results showed that under conditions of ambient temperature 25?,relative humidity 80%,and initial grain water content of30%,the high-humidity grain storage dryer had a water removal rate of 1.25%w.b./h or higher,which enabled the subjective heat loss of the system to decrease by about67.2%;For grain below 20%w.b.of water content,compared with the traditional coal-fired hot air drying system,the use of heat pump drying can reduce the subjective heat loss of the drying system by about 11.28%.