STRUCTURAL AND PARAMETRIC IDENTIFICATION OF THE GRAIN DRYER WITH HEAT PUMP AS A CONTROL OBJECT

Energy efficiency of grain drying systems is becoming particularly relevant due to the high energy costs during grain drying, in particular seed grain drying, as well as due to the increasing cost of energy carriers. Heat pump drying is considered a promising technology, however, to ensure the optimal ratio between energy efficiency and technical capabilities of the equipment, further improvement of control systems is necessary. An analysis of the literature showed that in existing studies of heat pump drying of agricultural products, insufficient attention is paid to studying the interaction of the main process parameters, the influence of external disturbances, and the dynamic properties of the heat pump and the drying chamber. This paper proposes an approach to solving the specified problem by conducting structural and parametric identification of the grain dryer as a control object. For this purpose, a technological diagram of the rapeseed heat pump drying process was developed based on a modernized continuous-flow grain dryer of French production. An experimental study of the drying process parameters was conducted. The mutual influence of the main process parameters was determined: the drying agent temperature and moisture content, the seeds temperature and humidity, as well as the initial conditions. Based on the experimental data, the static and dynamic characteristics of the control channels “drying agent moisture content - seed humidity” and “drying agent temperature - seed temperature” were obtained. It was shown that both channels have practically linear dependencies in the operating range of the controlled parameters, however, a significant cross-coupling effect is observed, especially from the side of the drying agent temperature. It was established that the initial seed humidity is a significant controlled disturbance that affects both the drying duration and the final temperature of the product. Based on the analysis, a generalized parametric diagram of the grain dryer with the heat pump was constructed, which includes the main control channels, cross-connections and disturbances. The obtained results create a basis for further development of a simulation model and synthesis of effective algorithms for automatic control of the heat pump drying process.