Heating of a biogas reactor using a solar energy system with temperature control unit

Maintaining a temperature level of about 40 degrees C the optimum temperature for mesophilic bacteria's growth and activity, is crucial for obtaining the best results with respect to biogas production. This study investigates the utilization of solar energy for heating a bioreactor that was already developed at our laboratory and is currently in operation. For purposes of this study, a solar collector combined with a heat exchanger are designed, manufactured, and installed to provide the necessary heating requirements for a water jacket around the bioreactor. In addition, an inexpensive PID (proportional. integral, and differential) controller was also designed, installed, and tested to maintain a constant temperature of 40 degrees C in the water-jacket around the bioreactor. The theoretical efficiency of the solar collector was computed and found to be about 61%. The controller action was seen to be very effective and a prompt response for little variation in the temperature of the water jacket (Delta T = 1 K) was noticed. Moreover, the internal rate of return of the investment in such solar heating system was found to be 32.7%. which indicates that we have an attractive investment. (C) 2000 Elsevier Science Ltd. All rights reserved.