In the dissertation, research was conducted with the aim of increasing the energy efficiency of biogas production intensification processes by using an electrothermomechanical system for mixing and heating the substrate in biogas reactors. The existing methods of calculation of mixing systems, electric heating and mathematical models of the process of anaerobic fermentation of the substrate and systems of automatic control of technological processes were analyzed. Existing shortcomings in the systems of mixing and heating the substrate were revealed. The expediency of reducing energy costs for the processes of intensification of anaerobic fermentation by integrating the processes of mixing and electric heating of the substrate is substantiated. The conducted theoretical studies made it possible to create an energy-efficient design of an electrothermomechanical system and methods of managing the processes of mixing and electric heating of the substrate in a biogas reactor. The rational design features of the electrothermomechanical system are defined, which ensure a reduction in energy consumption for heating and mixing. A mathematical model was developed, according to which the necessary energy costs for mixing the substrate in the biogas reactor during the working and starting moments of movement of various types of mechanical stirrers were determined. A comparative analysis of low-speed mechanical mixers was carried out. A rational type of mechanical stirring device was chosen to create an electrothermomechanical system. For the first time, 3D modeling was used to determine the energyefficient speed level of the stirring body of the electrothermomechanical system. The equation of the heat balance of the biogas reactor was developed in the presence of an electrothermomechanical system for mixing and electric heating of the substrate. It was found that the presence of contamination on the walls of the biogas reactor creates an additional obstacle for the passage of heat, both from the biogas reactor to the environment and vice versa. The amount of energy required for one substrate heating cycle, its duration and the temperature change of each object participating in the heat exchange were determined. Conducted theoretical and experimental studies have shown that the "rational" system – the use of an electric heating cable mounted in the paddles of a two-tier paddle mixer – is more energy efficient compared to the "classic" one – the electric heating cable is placed on the wall of the biogas reactor. An increase in energy efficiency occurs due to a decrease in the duration of the heating process, and accordingly, the mixing of the substrate. Corresponding savings in time for heating and mixing range from 1.9 to 20,2 %; energy savings for heating range from 8,4 to 27,2 %; for mixing – from 0,3 to 21 %, depending on the ambient temperature. The annual energy efficiency of the process of heating and mixing the substrate in the biogas reactor using an electric heating cable mounted in the paddle of a two-tier paddle mixer was calculated, which is 18,1 % (219,472 MJ), where, respectively, 13,1 % (195,072 MJ) is electric heating and 5,0 % (24,4 MJ) is mixing the substrate. Based on the obtained research results, methods of improving the system of electric heating and mixing of the substrate in the biogas reactor are proposed, which make it possible to increase energy efficiency and increase the profitability of biogas production. The design of an electrothermomechanical system for mixing and heating the substrate in a biogas reactor is protected by patents of Ukraine for an invention and a utility model.
