  Page last updated 30/08/2018
Volume of a cylinder The drum plant is made as a brick lined cylindlical hole in the ground. The space between the bricks and the side of the hole is back-filled with earth, which is packed firmly in. The cylindrical shape is very strong, especially in compression. The pressure due to the liquid inside the digester is balanced by the pressure of the soil on the outside. The volume of a cylinder is given by the equation:
Design Equations for biogas plant designs
Volume of a section of a sphere (a cap) The dome plants are made as sections of a sphere (or close to that shape). A spherical shape is even stronger in compression than a cylinder. Again, soil is used to compress the outside of the masonry shape. This is then able to balance the pressures due to the liquid and gas inside the dome. The relationships between the different parameters shown in the diagram are given by the equations below:
where V is the volume enclosed by rotating the upper part of the diagram around the vertical line. R is the overall radius of the dome, while r is the horizontal radius of the section and h is the height of the section. Stress analysis suggests that a section of a dome is all under compression, as long at the half included angle (φ) is less than 51°. This is why most Janata (concrete dome) plants (such as the GGC 2047) use a cylindrical lower section and a dome section at the top, with a half-included angle (φ) of less than 51°. Deenbandhu (brick domes) are usually built as a hemisphere (R - h = 0) or (R = h). Larger plants to this design use a steel reinforced collar around the area where the dome is in tension.        Page last updated 30/08/2018
Volume of a cylinder The drum plant is made as a brick lined cylindlical hole in the ground. The space between the bricks and the side of the hole is back-filled with earth, which is packed firmly in. The cylindrical shape is very strong, especially in compression. The pressure due to the liquid inside the digester is balanced by the pressure of the soil on the outside. The volume of a cylinder is given by the equation: Volume of a section of a sphere (a cap) The dome plants are made as sections of a sphere (or close to that shape). A spherical shape is even stronger in compression than a cylinder. Again, soil is used to compress the outside of the masonry shape. This is then able to balance the pressures due to the liquid and gas inside the dome. The relationships between the different parameters shown in the diagram are given by the equations below: Design Equations for biogas plant designs
where: R is the radius of the sphere r is the radius of the cap h is the height of the cap φ is the included angle Diagram of a cylinder
Diagram of a section of a sphere       which gives: The volume is: Rearranging: The angle (φ) is: