The study aimed to evaluate the potential for minimizing the overall energy intensity of convective drying of commercial grain in industrial shaft and drum-type installations with capacities ranging from 2 to 50 t/h of the finished product by applying low doses of microwave energy to the product before loading it into the drying chamber of grain dryers. Experiments were conducted in 2024 at the Russian State Agrarian University—Moscow Timiryazev Agricultural Academy. The research object was an experimental drying unit that sequentially exposed the product to microwave radiation and convective thermal energy. Energy efficiency was assessed based on energy consumption per unit time. Wheat and rye seeds of varying layer thickness were used as the product in trays that were transparent to both microwave and convective thermal energy. The trays were mounted on a chain conveyor and moved by an electric drive sequentially through a microwave-heating chamber based on a ridge waveguide, into which microwave energy was supplied from two magnetron sources operating in pulsed mode in antiphase. Afterward, the trays moved into a convective air chamber, where warm air was supplied from below, simulating the convective drying mode of industrial installations. In the first series of experiments, a 3 kg product with 28–32% moisture content and a 4 cm layer thickness was placed only in the convective air chamber, where it was dried to 12%, in accordance with the state standard for grain storage. Grain moisture was determined thermogravimetrically. To evaluate the energy costs of drying, a series of experiments was conducted. During these tests, the heater power was established at 5 kW. Subsequently, the drying time and energy intensity of the process were determined, ranging from 8.5 to 9.5 kWh per kilogram of evaporated moisture. In the next series of experiments, an equivalent grain load was first exposed to microwave radiation at levels of 1–5% of the convective thermal energy. The tray with the product was then transported into the convective air chamber, where drying continued until the grain reached 12% moisture content. Using the constructed dependencies of product weight loss over drying time, the total energy intensity was calculated. When 1% microwave power relative to thermal energy was added to the drying process, the energy intensity ranged from 6.8 to 7.8 kWh/kg of evaporated moisture, and at 5%, it ranged from 6.2 to 7.0 kWh/kg. Thus, the average energy savings amounted to 19–27%. The observed effect of adding low doses of microwave energy to the grain drying process indicates the potential for using low-power microwave radiation in industrial grain drying installations.
Chetverikov et al. (Fri,) studied this question.