Landfill Gas to Power

Landfill Gas (LFG) which results from decomposition and bacterial actions of garbage dumps, contain large volume of methane gas in addition to carbon dioxide, moisture, oxides of nitrogen and sulphur. These gases are continuously released into the atmosphere and go up to form Green House Gases (GHG), one notorious contributor to Global Warming. Therefore, there are concerted efforts to use this gas appropriately to prevent its release into the atmosphere. But the main problem is the inadequate quantity of gas available at any particular time for efficient use in any industry. When the landfill dump is large, the volume of gas released is also comparatively; large and can be used in power generation or in industrial furnaces as fuel.

The conventional practice to collect and treat the gas is through well points. In this method, the entire area of the dump is traversed by vertically driven pipelines having small holes on the lengths called Well points, sunken into the garbage dump. The released LFG enters the vertical pipelines through these holes and move up into common manifolds which are set of horizontal pipelines into which the vertical well points terminate. These manifolds are connected to a master manifold which collects the entire gas produced from the dump .The schematics of this system is shown in the sketch below.

The disadvantage of this system is that the LFG collection is dependent on the pressure generated at each layer of the fill and as the bacterial action is maximum towards the bottom, the bottom pressure of the gas is more than the upper ones. As a result when this high pressure gas travels up the well points, there is tendency to expel some of the gas produced at upper layers at relatively less pressure. The net effect is loss of aggregate gas production from every well point areas. This is explained by the same sketch. It can thus be concluded that by this conventional collection system, large quantity of gas is lost back into the dump and then to the atmosphere and less gas available at the well points at substantially low pressure (Figure 1).

Figure 1: Conventional Method of LFG production.