The types of biogas designs are quite numerous. The information here is drawn from a paper titled ‘Biogas Plants’ by Ludwig Sasse. The designs being discussed here are relatively simple in design and are directed more at domestic and smaller scale rural installations rather than large scale commercial designs.
In the first instance a distinction is made between batch and continuous plants. Batch biogas designs are filled completely and then emptied completely after a fixed retention time. Each design and each fermentation material is suitable for batch filling. Large gasholders or a number of digesters are required for uniform gas supply from batch plants.
Continuous biogas designs are filled and emptied regularly – normally daily. Each design is suitable for continuous operation, but the feed material must be flowable and uniform for these types of biogas designs. Continuous plants empty automatically through the overflow. The continuous types of biogas designs are more suitable for rural households as the necessary ongoing work fits better into the daily round. Gas production is constant, and somewhat higher than in batch plants. If straw and dung are to be digested together, these types of biogas designs can be operated on a semibatch basis. The slowly digested straw-type material is fed in about twice a year as a batch load. The dung is added and removed regularly.
Basic Types of Biogas Designs
Fig1. A – Floating drum plant B – Fixed dome plant C -Fixed-dome with separate gasholder. The gas pressure is kept constant by the floating gasholder. The unit can be operated as a continuous flow plant with no compensating tank. The use of an agitator is recommended. D – Balloon type of biogas design E – Channel typedigester with folia and sunshade.