Solar assisted biogas plants II: Energy balance of floating drum type biogas plants

Abstract

In the present paper, a mathematical model is developed to predict i the heat losses and gains from various mechanisms in a KVIC-type biogas plant as a function of slurry temperature and other parameters, ii transient performance of the conventional KVIC-type biogas plants, and iii transient performance of KVIC-type biogas plants covered by a greenhouse. Numerical calculations have also been made to predict the monthly performance of biogas plants of different sizes having digester volumes ranging from about 4 to 220 m3 for the climate of Delhi, India. The heat losses from the digester to the ground through the sides have been evaluated following Sodha et al. (1980) by assuming the digester to be an infinite cylindrical cavity in the ground. Computations have also been made to study the effect of a greenhouse, its size and night curtains on the performance of biogas plants. Results indicate that the heat losses from the slurry to ambient through the annular space left between the gasholder and the digester are very significant for smaller plants, whereas charging represents the largest single component of heat losses for larger plants.