The basic biogas designs as used in China, India and Nepal have proved very successful.
The plants normally used in the UK and the rest of Europe are made from steel and
are much larger and more expensive. To make the best use of these plants, slurry
and other feed stocks (such as food processing residues) need to be trucked to a
large central unit.
The Kingdom Bioenergy approach seeks to adapt the Asian concept so it can be used
in UK. This means reducing the labour requirement for on-site construction and including
built-in insulation. This can be done with the use of pre-cast concrete SIPs (Structural
Insulated Panels), which can be fitted together easily in a hole dug in the ground.
The key to making a gas-tight container from concrete is to keep the concrete under
compression. The gas storage volume is made as a spherical or cylindrical section.
Mass is added above it, in the form of backfilled earth, to balance the gas pressure
that develops within the concrete dome as gas is stored. In this way, the concrete
remains under compression and will not crack and cause leaks.
The concrete dome remains fixed in the ground, so the gas is stored for a limited
time by allowing the slurry to be displaced into a reservoir. In Asia, the gas that
is generated by the slurry in the reservoir is allowed to escape. However, in the
proposed design, this gas is collected at low pressure and used.
