Landfills naturally produce a substance called biogas as part of the process of breaking down the organic material found in the waste that is discarded by humans. This process is called anaerobic digestion. In some instances where the landfill does not produce enough gas it is burnt on site to stop it causing any harm by escaping into the atmosphere, this is known as gas flaring. However, there is an alternative use for this gas, if collected and processed in the right way it can be used as a source of electricity and gas to heat and power people's homes. In this article we take a look at the process of turning landfill gas into electricity.

Landfill Gas Collection

Firstly, the gas must be carefully collected in the landfill and not allowed to escape into the atmosphere. The gas contains methane and carbon dioxide along with a number of other substances. Both of these gases contribute to global warming. Methane is also highly flammable. Careful collection of landfill gas minimises the potential risk of explosions and accidents on landfill sites.

Pipes, also known as wells, are placed into the landfill site to collect the gas, these work by pulling the gas out of the landfill into a collection tank. When a landfill site produces enough gas for it to be used to create electricity or used in gas boilers then the gas is taken to a biogas upgrading facility. This can be done in several ways, some landfills have onsite biogas upgraders, in this instance the gas travels through a pipe to the upgrading plant. Other landfills without this facility transport the gas to a separate location where it is upgraded.

Biogas upgrading

Biogas upgrading is the process of removing contaminants from the biogas so it can be used to generate electricity more efficiently or be added back into the gas grid. Once this process is complete the gas becomes known as biomethane. Essentially the gas goes through several processes each to remove a different chemical or compound in the gas. Biogas contains methane, carbon dioxide, hydrogen sulfide, water and other contaminants. The main purpose of biogas upgrading is to remove every other component except methane. Methane can then be used to power vehicles, added to the gas supply or used to generate electricity.

There are several different ways of removing contaminants from the biogas. These include water washing, pressure swing adsorption, selexol absorption and amine gas treating. If you’re interested in more information on the biogas upgrading process you can read our article on biogas upgrading.

Fuel cell

Biogas can be directly converted into electricity using a fuel cell. However, this is very expensive and requires the gas to be very clean. This process is therefore not currently a viable way to convert biogas into electricity. More research is needed in this area for it to develop into a workable option.

Generator conversion

The main way that biogas is converted into electricity is through a generator. This is a two step process. The first step requires the biogas to be burnt in a combustion engine, this transforms the power into mechanical energy using compression, a spark and moving pistons. Mechanical energy is also known as the energy of motion or kinetic energy. In this instance the energy is pistons moving within the combustion engine as a result of burning biogas.

The second part of the process is taking this mechanical energy and turning it into electrical energy. This is done using an electric generator. The mechanical energy rotates an electric generator which takes this power and transforms it into electricity. Generators transform kinetic energy into electric energy in different ways. One of the most common ways this is done is through electromagnetic induction. One transformed into electrical energy the generator can be used to power electrical devices in peoples’ homes.

Landfill Gas Monitoring

Landfills naturally produce biogas which can be used as a source of gas or transformed into electrical energy. A key part of this process is landfill gas monitoring. Landfills need to be continuously monitored using surface emission monitors, these take readings of the landfill gas being emitted at the surface. If the landfill is emitting too much gas then it can be a cause for concern. There are strict regulations in place that require landfills to actively monitor and measure their gas production. Find out more about landfill gas management and how QED can help you monitor the gas produced at your landfill site.