The present invention relates to a method and apparatus for producing methane gas from organic solid materials in existence in industrial and living wastes.
A conventional method for producing methane gas has been developed, in which a sewage waste water is treated aerobically and the methane gas is collected from a disposal residue. However, in this case, since a weight ratio of an organic material with reference to the water is extremely small, the concentration of the organic material flowing or dissolving in the water is small, and thus it may stay in a digestion or fermentation tank for a long time. Accordingly, in this embodiment, the digestive tank and supplementary equipments are enlarged, and hence the installation space of the apparatus becomes large. Therefore, the cost of the apparatus becomes high, and the gas is not produced effectively as well as it is difficult to maintain the apparatus.
Another conventional method for producing methane gas has been proposed, in which the organic material obtained from an industrial waste is treated anaerobically. However, in this case, the applicable organic materials are restricted to the special materials, for example, wastes of the food industry such as wastes produced by a brewage, and liquids obtained by filtering solids in excretions of cattle, and consequently this method cannot be applied to all organic materials, lack of universality. Further, in this embodiment it takes a quite long time to generate the gas and the produced gas is less. Further, it is widely well-known that the high temperature treatment at 53.degree. C. is effective in order to conduct the fermentation effectively, however, the digestive tank is enlarged. Hence, it is difficult economically to completely make an adiabatic surface to the digestive tank, and hence the effective production of the methane gas cannot be realized practically.
In addition, in case of a large-sized digestive tank, the installation cost of the apparatus is enlarged for the strength of the groundwork and for manufacturing the body of the digestive tank as well as the long construction period, with the result of the disadvantageous account balance.