Brief description of our concept for gas recovery
systems and power production technologies.
The company Deponigas
ApS was established in 1999 in recognition of the fact that the existing
landfill gas plants in Denmark used technologies that were too automated and
made use of expensive materials and technologies in a manner that was
completely unnecessary for the purpose. Consequently, the plants were too
expensive in construction and operation.
Our concept is therefore purpose designed with a low-tech approach and as a result, cheap and
Gas recovery system:
In the beginning we used ´ boreholes (wells)´ that were made with a battering
ram technique using a drill bit with a diameter of 150mm. Later we moved to
using auger drilling with diameter of 150 mm at a depth of typically 8-10
meters. Auger Drilling has the advantage that we can see the waste we drill in
and the waste around the borehole is not compacted making it easy to withdraw
Our philosophy is: many wells = large surface coverage .
Suction pipes consist of diameter 40 mm perforated PEL tubing with air-tight
seal on the upper 1 meter of borehole, to avoid air being sucked in.
Gas transmission is also done using PEL tubing,
typically by 25 to 40 mm in diameter piping depending on the amount of gas and
Boreholes are preferably used at landfills that are completed with a final
layer of clay and topsoil.
Gas collection from horizontal trenches:
They are used where there still is
landfilled being deposited. In this case a trench is dug and a drain hose of
diameter 80-110mm.is placed, then it is covered up again with the dug up waste.
The gas transmission pipe has a diameter 32-40mm. PEL hose. The transmission
pipe is inserted in to the drain hose a few meters into the drain hose and then
on its way to the manifold it is covered for protection against traffic.
The gas produced from each well or trench is piped to a manifold consisting of
manual ball valves. Here it is possible to adjust the suction from each pipe
separately. There are also outlets for analyzing gas with hand held gas
From the manifold the gas is sucked by a speed controlled suction pump and then
it is passed through a gas meter. By regulating the gas flow at the manifold
the amount of gas collection can be controlled. Thus it is possible to estimate
the energy potential of the landfill site and there by the size of the motor
power generator required.
In Denmark it is often only the electricity production that is
relevant. The heat is wasted as it requires a local consumption near the site.
The newest plants all have remote control.
Test pumping period is normally 2-3 months. This is sufficient to find the
balance between gas potential of the landfill and the amount of gas we can
harvest. In the case of a landfill site where waste is still being deposited it
is of less importance if deposited waste has a gas potential.
Motor generator technology:
Our other distinctive characteristic is that we use the dual-fuel principle
(diesel + landfillgas ) on our motor - generator sets . A small amount of
diesel fuel is used to ignite the gas and to cool the injector nozzles. This
avoids problems with unstable engine operation due to large fluctuations in gas
quality which is caused due to varying atmospheric pressure. This also allows
us to use gas with lower methane content. Spark ignition engines require high
methane content in order to run smoothly.
We regulate the diesel used to a minimum so that the entire electricity
production is propelled using the landfill gas. As mentioned the diesel amount
used is just enough to ignite the gas but not enough to produce power. By using
traditional diesel engines converted to duel fuel operation the investments are
also affordable. Diesel engines are normally cheaper to purchase than purpose
built gas engines with spark ignition.
The electricity production is normally sold through the public electricity grid
and we receive payment for it.
The motors generator sets are typically placed in a 20 ´ steel container
together with the control systems and the necessary alarms. Placed in the
container is also the gas pump , safety valves, pressure monitors and gas