Develop algorithms for calculating the heat transfer and temperature in simple and small biogas digesters buried into the soil

Abstract

Biogas digesters are used to produce methane from anaerobic digestion of animal manure in long lot of developing countries to replace wood as the traditional source of fuel to produce energy for domestic purposes. A variety of factors affect the rate of digestion and biogas production. One of the most important is temperature. Simple and small fixed dome digesters are partially or totally buried into the soil are widely used with more than 30 million having been constructed in Asia. For this reason, this study is focused on these. Temperature inside the digester is affected by many heat transfer phenomena which depend on of many parameters from the environmental conditions where the digester is installed: like ambient air temperature and soil temperature profiles. The algorithm developed takes into account these situations for simple and small digesters and in which input data required are easily available. To improve other studies of heat transfer models and temperature of heated lagoon digesters or floating drum digesters the algorithm includes some variations: the effect of the temperature of the slurry feeding, gas volume variations and soil temperature dependence on depth. The model elaborated is an acceptable first approximation of the model desired, as the model has been tested using data from Hanoi, Vietnam, cause the monthly average errors of computed temperatures are below 20%. To better understand how heat transfer phenomena are acting or which is the most influent or how much heat transfer is exchanged, more studies should be carried out using the model develop here because any remarkable conclusion cannot be deduced from obtained results.