| In recent years,the CPC and the government have attached great importance to energy conservation and environmental protection.As an essential process in the processing of agricultural products,drying consumes a lot of energy and often causes severe environmental pollution by burning fossil energy to provide thermal energy.Heat pump drying,characterized by energy saving,environmental protection,and easy control,has been widely used in the drying process of various cash crops.A multifunctional air source heat pump drying experimental platform is designed and manufactured.The influence of the style of hot air cycle and environmental conditions on the drying performance of the heat pump is discussed through experiment and theoretical analysis.The heat pump unit and control equipment of the 3-ton recirculation grain dryer were designed and manufactured according to the actual requirements of the drying operation of major grain crops in Jianghuai region.The main work and research results are as follows:（1）A multifunctional air source heat pump drying experimental platform was designed.The test bench can be equipped with three different hot air circulation modes:closed type,semi-open type,and open type,by adjusting the air duct valve,and the bypass rate of hot air circulation can also be adjusted.The equipment of the experimental platform was designed and calculated,including the selection of compressor,fen and heat pump system heat exchanger,etc.Siemens S7-200 PLC was used to build the data acquisition and control system of heat pump drying experiment platform,and PID algorithm was used to realize the closed-loop control of temperature,humidity and wind speed in the drying chamber.（2）The influence of hot air circulation mode and environmental conditions（temperature and humidity）on the drying effect of the heat pump is analyzed.Heat pump drying experiments with different air circulation modes under different environmental conditions were carried out on the heat pump drying test bench,and the experimental results were analyzed.Using the enthalpy-humidity diagram of circulating air,the theoretical model of energy consumption of the heat pump drying system with different ambient temperature and humidity and different hot air circulation mode is established.The energy consumption and drying efficiency are evaluated by using SMER and MER,which can provide theoretical support for the heat pump drying process in monsoon climate regions like Jianghuai region.（3）According to the climate characteristics and grain cropping system in Jianghuai region,EC-326R recirculation grain dryer was used,and the heat pump device and control system were designed and manufactured to dock with EC-326R.According to the actual production demand,a heat pump system composed of three heat pump units was designed and manufactured according to the actual production demand.Through the start-stop combination of the heat pump unit to adjust the air supply temperature and heat production,to improve the annual energy efficiency ratio（AEER）of the heat pump dryer.Enhanced vapor injection technology was adopted by the heat pump system to solve the problem of the low temperature of supplying air and COP in low-temperature environment.The heat recovery device absorbs the waste heat of the dryer to preheat the fresh air and improve the thermal efficiency of the dryer.A remote control system based on 4G communication technology and cloud platform is developed in order to make drying operators not work in the high-dust grain drying operation site.（4）The performance of the designed heat pump circulating grain dryer was tested.The experimental results show that AEER of the heat pump system is higher;the performance of heat pump system under cold environment temperature is better,when the environment temperature is 5℃,57℃ maximum for the temperature of supplying air;The heat recovery device has a better heat exchange effect when the ambient air temperature is lower.The heat pump drying experiments of wheat and rice were carried out by using the above dryer.The results show that the heat pump dryer has significant advantages in drying rate,quality,energy consumption,and economy,and can be applied to rice and wheat drying operations in the Jianghuai region. |
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