The aim of the work is an experimental study of energy losses to the environment for the mesophilic mode of fermentation in order to increase the duration of substrate cooling and reduce energy costs for the process of biogas formation. To achieve the goals set, the following tasks have been solved: a methodological approach has been developed for conducting experimental studies; an experimental plant for a biogas reactor with an electrothermal-mechanical system with automatic control for mixing and heating the substrate was made; experimentally investigated energy losses to the environment for the mesophilic mode of fermentation; processing, analysis and comparison of the obtained experimental data were carried out. The working hypothesis of the research was that the use of an heating cable built into the stirrer paddles would provide a longer process of cooling the substrate to the heating switch-on temperature, which would reduce energy costs for the biogas formation intensification process. The most significant result of the study is to obtain the dependences of the change in the temperature of the heating cable, the substrate in the lower, middle and upper tiers of the reactor and the duration of the substrate cooling to the heating switch-on temperature in the operating biogas plant. The significance of the results of experimental studies lies in the fact that when placing a heating cable built into the stirrer paddles, the process of cooling the substrate to the heating switch-on temperature occurs later, on average, by 35 minutes, when the substrate is fermented in a biogas reactor with a volume of 40 liters. The implementation of the data obtained will increase the energy efficiency of the processes of intensification of biogas production and the profitability of further processing of biogas into heat and electricity.

The aim of the work is to experimentally study the energy consumption for the process of initial heating of the substrate to the fermentation temperature in order to increase the energy efficiency of the biogas formation process. To achieve the goals set, a preparation and a series of experimental studies of the indicators of energy consumption for the process of initial heating of the substrate to the fermentation temperature were carried out. The working hypothesis is that the use of a heating cable built into the stirrer paddles reduces the energy costs for the process of initial heating of the substrate, increasing thus the energy efficiency of the biogas production. The most important result of the study was to obtain the dependences of the temperature change in the heating cable, substrate, reactor walls and energy consumption for heating and mixing during the initial heating of the substrate. The significance of the research results presented in the work lies in the fact that when using a heating cable built into the stirrer paddles, the process of initial heating of the substrate to the fermentation temperature occured faster on average by 16 minutes, and the amount of energy spent was also decreased on average by 6.6% for heating and 5.3% for mixing the substrate in a 40-liter biogas reactor. The implementation of the data obtained experimentally increased the energy efficiency of biogas production and the profitability of further processing of biogas into heat and electricity.

The article is devoted to the study of energy losses of a biogas reactor into the environment during the fermentation of biomass in the mesophilic temperature regime. The article considers the influence of the presence of the insulating layer of the biogas reactor and the ambient temperature on the amount of energy losses and the required energy to recover these losses depending on the volume of the biogas reactor. The developed mathematical model allows to estimate the intensity of energy losses to the environment taking into account the amount of contamination of the inner wall of the biogas reactor, ambient temperature, average wind speed for the reactor location, surface area of the biogas reactor and its volume, material from which the biogas reactor is made, insulating layer and its material, mode of movement and frequency of biomass mixing. The following assumptions have been made for numerical studies: biomass fermentation takes place in the mesophilic temperature regime , biogas reactors with a volume of 50 to 200 liters, at ambient temperatures from to . It has been established that the heat loss to the environment for different volumes of biogas reactors, regardless of the ambient temperature and the presence or absence of an insulating layer, is not linear. Numerical research has shown that the use of an insulating layer of mineral wool with a thickness of 100 mm, depending on the volume of the biogas reactor and ambient temperature, reduces the amount of energy required to maintain the thermal regime by 55-63 times. Taking into account the amount of losses at the stage of design and manufacture of biogas reactors will reduce energy costs to maintain the required temperature, thereby increasing the profitability of the biogas plant.

To date, biomass fermentation in biogas plants is one of the most advanced, environmentally and economically viable solutions for energy production from waste. However, the process of anaerobic fermentation of waste is long, so one of the main ways to intensify biogas production is mixing and heating of biomass during fermentation. The article is devoted to the question of substantiation of creation of electrothermomechanical system for mixing and heating of biomass in a biogas reactor. The combination of two intensification processes in a combined system pays special attention to the energy efficiency of such a system, so the creation of the system requires in-depth study of heat fluctuations from speed and the presence of a contaminant layer on the heater surface and determine the optimal stirrer speed. The studies were performed for a cylindrical biogas reactor, assuming that the contaminant layer is evenly distributed on the surface of the blades and the shaft in which the electric heaters are installed. When determining the optimal frequency of biomass mixing, the criterion of optimality was taken to be the smallest value of the difference between the heat flux of the contaminated and uncontaminated surface of the heater. During the study it was found that at speed , the difference between the heat flux of the contaminated surface and uncontaminated is 40 %. At speed , the difference between the values is 26%. According to the selected optimality criterion, the optimal speed of the electrothermomechanical system taking into account the contaminant layer is in the range . The increase in heat flux from the stirring frequency is non-linear for both contaminated and non-contaminated heaters.

Purpose. Today, biomass fermentation in biogas plants is one of the most advanced, environmentally and economically viable solutions for energy production from waste. However, the process of anaerobic digestion of waste is long, so the main process of intensification is mixing. Analysis of well-known studies of domestic and foreign scientists indicates the urgency of reducing energy consumption for the mixing process. The aim of the study is to determine the energy-efficient speed of a paddle stirrer with blades set at an angle of 450 for small biogas reactors. Methodology. At the decision of the set tasks the general methods of physics, three-dimensional modeling, processing and visualization of the received results in the SolidWorks Flow Simulation and Wolfram Mathematica programs are applied. Results. Using 3D modeling, the influence of the stirrer speed on the picture of the distribution of the velocity vectors of the substrate flows in the biogas reactor was studied. Graphs of power consumption at the beginning of mixing for different stirrer speeds were obtained and analyzed, and the levels of energy consumed for mixing biomass during the start-up period and the whole mixing period were compared. A method for determining the energy efficient rotation speed of the stirring mechanism of the electromechanical system of biogas reactors is proposed. Practical value. The results can be used in the construction and modernization of biogas plants to reduce energy consumption of the substrate mixing process. Conclusion. Based on the research, it was concluded that for a paddle two-tier mixer with blades set at an angle of 450 energy-efficient speed, is 40 rpm. At this speed, careful and intensive mixing of the biomass is observed throughout the volume of the tank. The average velocity of flow vectors in the biomass volume is 0,273 m/s. The energy consumed per cycle of biomass mixing is 2471,3 J, and the percentage of energy consumed during the start-up period from the energy consumed during the entire mixing period is 0,62 %. References 19, figures 5.