Comparative exergy and energy assessment of a biogas plant with biological purification process: A multigeneration system

Abstract

The improved systems of biogas production usually increase the energy consumption of biogas plants. Therefore, it is very important to determine an appropriate improvement system to increase plant efficiency. For this purpose, a biogas plant with a biological self-purification system was energetically and exergetically analyzed, and its performance was compared with that of a base plant. To keep the temperature of digesters up to 310.2 K, a solar water heater was used. It was able to maintain a high level of efficiency for both plants. The energy analysis of the plants indicated that the overall energetic efficiency of both plants was very close. The exergy analysis of the plants showed that the overall exergetic efficiency of the self-purification biogas plant (76.24%) was higher than that of the base plant (66.78%). This is due to the fact that the total exergy destruction rate of the self-purification plant was lower than that of the base plant and the exergy rate of biogas output of the self-purification plant was higher than that of the base plant. The exergy analyses of both plant components showed that although the highest exergy destruction rates were attributed to the principle digester and separation unit, they showed the highest exergetic improvement potential rates. These results confirm that the digesters in biogas plants have a great potential to be improved exergetically, and the self-purification system is a suitable improvement system to increase the plant efficiency exergetically.

A comparative evaluation of energetic and exergetic performance parameters in syrup purification and evaporation lines

“…The highest improvement potential was achieved with 48.74 kW for HE3 in the purification line and 22.79 kW for HE6 in the evaporation line (Figure 6). Similar trend is reported in literature (Mahmoodi-Eshkaftaki et al, 2022).…”

“…For the evaporation line, the highest and lowest exergy efficiency was calculated at 87.52% and 83.18% for HE7 and HE6, respectively (Figure 5). In addition, a similar trend is presented in the previous works (Khorasanizadeh et al, 2021;Mahmoodi-Eshkaftaki et al, 2022).…”

“…Also, the largest logarithmic average temperature difference was calculated with a value of 32.42°C for the HE1. A greater temperature difference produces more entropy and, as a result, more exergy destruction (Li et al, 2022; Mahmoodi‐Eshkaftaki et al, 2022).…”