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The main energy costs for the needs of a biogas plant are the costs of low-potential thermal energy for maintaining the thermal regime of a biogas plant. When using modern heat-insulating materials, the cost of heat for heating the daily dose of the load to the process temperature comes first.
Figure 1 shows the calculated production and consumption of biogas for the own needs of a biogas plant with a working volume of 60 m3 operating in a thermophilic mode.
Figure 1. Structure of production and consumption of biogas
The biogas plant has thermal insulation made of mineral wool 300 mm thick and is located in the Moscow Region. The daily loading dose is 10% of the working volume of the digester and is equal to 6 m3 of cattle manure with a moisture content of 92% (Kovalev, 2014).
As can be seen from Figure 1, the main energy costs in a biogas plant are used to heat the daily loading dose, and only up to 40% of the biogas produced can be used for other purposes (Kovalev, 2014; Chen et al., 2014; Carrillo-Reyes et al., 2019).
In addition, the higher the process temperature, the narrower the range of its change, as for the mesophilic temperature regime (37 °C), the permissible temperature variation is 2,8 °C, and at a thermophilic temperature not more than 0,3 °C (Gunter& Goldfarb, 1991; Lindeboom et al., 2011).