Research On Theoretical Performance Of Grain In-bin Drying System Based On Liquid Desiccant Dehumidification Driven By Heat Pump

Wet grain drying is a significant step in the grain production process.Grain in-bin drying,as an effective drying method integrated by drying and storage,is widely used in grain drying.Safe,efficient and economical new grain in-bin drying technology is a direction worth exploring at present.Therefore,a system of grain in-bin drying based on liquid desiccant dehumidification driven by heat pump is proposed,and related theoretical research are carried out in this paper.Firstly,the structure and working principle of the system are determined and the mathematical model of each component of the system is established and verified.Through experimental verification,it is found that the accuracy of the prediction of mathematical model of each component is relatively high.Moreover,the thermal equilibrium model that takes into account the respiration is used to predict the grain drying process more accurately.Secondly,research on low temperature grain drying performance based on layered model are studied.It is concluded that the simulation results of thermal equilibrium and non-equilibrium models are similar under low-temperature,low-relative humidity air conditions,which verifies the appropriateness of the thermal equilibrium model selection again.Moreover,using dehumidified air for rice in-bin drying shows a high potential for improving the drying rate and helps to improve grain quality index.In addition,it is determined that the air flow rate and the initial moisture of the grain are two important factors that affect the low temperature grain drying process.Thirdly,this paper examines the performance and energy consumption of the system according to the relevant factors that affect grain in-bin drying.The results show that the inlet air of grain bin is in a low-temperature and low-relative humidity states slightly lower than the outdoor air temperature.Moreover,the drying completion time meets the specification requirements under various weather conditions,which verifies that the system is feasible in terms of drying completion time.Weather conditions with relatively low temperatures are inferior in terms of drying rate and energy consumption,but better in terms of grain dry matter loss and whiteness value.At 30?of air temperature,each thin layer of rice can meet the dual specification requirements of dry matter loss(<0.5%)and unit energy consumption of the system(<2.5 k W·h/(1%·t)).In addition,the optimal air flow rate with low total energy consumption or unit energy consumption appears under the weather conditions in summer and autumn of Nanchang.It can better satisfy the rice at initial moisture of the grain M₀=0.2 and height of the grain pile h<3m,and the height of the grain pile is not recommended to be above 4m under Nanchang summer weather conditions.Finally,the system is applied to the layering study of rice in-bin drying and then compared with other drying methods.The moisture of the same layer of rice is basically the same after drying under the weather conditions in summer and autumn of Nanchang,but the whiteness value of the same layer of rice in Nanchang autumn is higher than summer and the dry matter loss value is lower than it.The drying rate of the system is close to that of heat pump,and the total energy consumption and the quality index of each thin layer of rice after drying are better,so the system is superior to heat pump.The research results described in this paper can provide a reference for the application of liquid desiccant dehumidification in the field of grain in-bin drying.