To understand the working of bio-gas generator or biogas plant, please refer the figure below. Here are the various steps of working of bio-gas generator or biogas plant.
1) In the mixing tank the water and cattle dung are mixed together thoroughly in the ratio of 1:1 to form the slurry. This slurry is then transferred to the digester via inlet chamber up to the cylindrical portion level of the digester.
2) The fermentation of slurry starts in the digester and biogas is formed, which is accumulated at the top of the digester in the dome. Since the outlet gas valve is closed, the bio-gas exerts pressure on the slurry which starts moving in the inlet and outlet chamber due to which the level of slurry drops in digester and increases in the outlet chamber.
3) If the biogas outlet valve is further kept closed, the level of slurry further drops in the digester. Due to gas pressure the slurry reaches to highest possible level in the inlet and outlet chambers.
4) If the gas valve is still kept closed the bio-gas will further get accumulated in the dome and its pressure increases. Eventually, its pressure becomes high enough and it starts escaping through the inlet and outlet chambers to the atmosphere. During its escape the biogas creates bubbles in the slurry in inlet and outlet chambers and there is also formation of froth.
5) The increase in the volume of slurry in the inlet and outlet chambers helps you calculate the amount of biogas generated within the digester.
6) If you want to use the biogas, you can open the valve of the gas pipe and remove it as per the requirement for various applications. When the gas is taken out from the dome, the level of slurry in the digester increases while the level in inlet and outlet valves reduces.
7) When the gas is not being used from the dome of the digester, the levels of slurry in the inlet and outlet chambers will be high and the intake of the fresh slurry in the digester is reduced. When the gas is being taken out from the dome, the slurry from the outlet chamber is removed and equivalent amount of fresh slurry is inducted into the digester to continue the process of fermentation and the formation of the biogas. Thus more is the biogas required more continuous will be the fresh slurry of cow dung and water required. The size of the digester tank also decides the amount of the gas that can be generated by the biogas plant.
