Is Natural Gas Renewable?

What Is Renewable?

The United States Energy Information Administration describes a renewable energy resource as one that is naturally replenished. Other definitions state that the resource must be replenished on a human timescale. Renewable energy resources include solar, wind, geothermal, hydro, wave and tidal action, and biomass.

Where Does Natural Gas Fit into This Mix?

Natural gas is burnt to produce energy in the form of heat – the main component of which is methane. The majority of the methane we use as natural gas comes from fossil fuel sources. However, there is another source of methane which we can use as a fuel. This methane comes from the gas released when biomass decays and is known as biomass gas or biogas. Furthermore, this source of natural gas is renewable and is becoming important in the energy mix.

A brief guide to natural gas is provided in the article: What is Natural Gas?

What Is Biogas?

Biomass is biological material from living or recently living organic organisms. This is a material (typically plant materials) that takes in carbon, in the form of carbon dioxide, from out of the atmosphere as it is growing. Biogas is produced when the biomass material breaks down in the absence of oxygen - this is termed anaerobic digestion - and produces methane and carbon dioxide. Typically, the biomass materials used to produce biogas include sewage, manure, green waste and landfill (municipal waste).

The process of anaerobic digestion takes place over several steps. The final step is methanogenesis, the formation of methane by microbes known as methanogens. The composition of the biogas depends on the initial biomass materials. Typical values of the major constituents of landfill-produced biogas are:

There are many environmental and cost benefits to controlling and utilising the biogas formed on landfill sites and other locations.

What Is Biogas Used For?

The composition of natural gas in the world’s supply lines is approximately 95% methane, with the other components being predominantly other alkanes. The biogas produced from landfill has a significantly lower methane level; consequently it cannot be added straight to the supply lines.

There are two main options for the use of biogas:

• Use a combined heat and power plant (CHP) at the biogas site to generate heat and electricity. The heat can be used in the biomass recycling process and the electricity can be transferred into the main electricity supply grid.
• Clean the biogas and concentrate the methane so it can be injected into the main gas supply.

Both of these options are used in different parts of the world. Biogas production and utilisation are becoming more important as governments look at methods of decreasing the reliance on gas imports. Additionally, regulations are limiting the release of biogas to the atmosphere to reduce emissions. An overview of the situation in Europe is given in this article: Biogas in Europe.