Facts about biogas and biomethane
Sources of raw biogas
There are three broad categories of biogas sources. Each has slightly different raw gas characteristics:
In each case, the basic process of biogas production is the same. Organic matter, or biomass, breaks down in the absence of oxygen. The bacteria produce methane and carbon dioxide (CO2) as a natural byproduct of breaking down the organic matter. The raw biogas, which contains methane and other compounds, can be captured because the waste is concentrated in one location. Once collected, it can be purified (or upgraded) into pipeline-quality biomethane—producing renewable natural gas.
Composed primarily of methane, biogas also contains between 25 and 50 per cent CO2 and small quantities of other gases. These gases are removed in the upgrading process to improve its heating value and safety. The upgrading process may vary from project to project, but the goal is to ensure the gas introduced into the system meets the same quality standards as natural gas.
The first step is to remove contaminant gases through a careful gas cleaning process that leaves only CO2. The CO2, which lowers the heating value of the gas, can then be removed using well-proven gas processing technology that has been used around the world. In fact, a made-in-BC technology called pressure swing adsorption (PSA) is used in Salmon Arm to perform the final cleaning step. Once the gas has been cleaned, only methane remains along with a small amount of nitrogen, making it almost impossible to distinguish from conventional natural gas. This purified, or upgraded, biogas that’s free from undesirable contaminants is called biomethane.
Interchangeability between natural gas and biomethane
Sure it’s clean, but is it safe? In co-operation with other major gas utilities, FortisBC undertook a study to determine if biomethane was a safe alternative to natural gas. Multiple gas sources were examined in numerous locations around North America and compared with conventional natural gas. Study results showed that upgraded biomethane is interchangeable with natural gas. In some cases, biomethane was actually more pure (contained fewer contaminants) than conventional natural gas. This means customers won’t see any difference in the quality of gas provided and you can rest easy that it meets the same safety standards as conventional natural gas.
Advantages of biogas and biomethane
Renewable natural gas is carbon neutral
The provincial government considers biomethane to be a carbon-neutral source of energy in its February 15, 2011 budget, and the BC Ministry of Energy, Mines and Resources considers renewable energy from biogas as playing an important role in helping BC achieve its greenhouse gas targets. FortisBC’s renewable natural gas has been certified by Offsetters Climate Solutions Inc. as a carbon-neutral product.1
Why is renewable natural gas considered carbon neutral? In essence, the creation of biogas does not deplete the earth’s non-renewable resources and facilitates a closed-loop carbon process. Without turning biogas into biomethane, the biogas created by the natural breakdown of organic matter would otherwise release methane into the atmosphere. By upgrading the biogas to usable biomethane, greenhouse gas emissions are captured instead of released. Since methane is considered to be 21 times more potent than carbon dioxide as a greenhouse gas,2 this is a significant reduction to our local greenhouse gas emissions. In addition, when a customer agrees to purchase renewable natural gas, this displaces conventional natural gas, thus preventing carbon stored by fossil fuels from being added to the atmosphere.
Helping provide a closed loop for our suppliers
The injection of biomethane into our natural gas system also creates a closed-loop process for our suppliers. Landfill operators reduce the odours and emissions from their landfills and other suppliers, such as farms and sewage treatment plants, are able to capture clean, solid nutrient byproducts that can be used as organic fertilizer. Local farmers become less reliant on chemical fertilizers, as the nutrient byproduct can displace chemical fertilizers.
More efficient energy conversion than electricity
Similar to electricity generated from biogas, biomethane is distributed using the existing gas system. However, much more of the energy from biogas actually reaches the distribution system as upgraded biomethane. Delivering biomethane directly to customers is more than two times as energy efficient as generating electricity from biogas.
In a case where biogas is burned directly to run an engine to generate electricity, the process is about 39 per cent efficient.3 That means 61 per cent of the energy from the biogas is lost as waste heat before it even enters the electricity grid. The electricity then has to be transmitted over power lines before being used for heating (e.g. electric baseboards).
In contrast, where biogas is purified and upgraded for injection into the natural gas system, about 90 per cent of the energy is kept during the purification process.4 In other words, much more of the energy from biogas reaches the distribution system as biomethane, which can be used in customers’ homes and businesses. This is one more way we can all benefit, through more efficient use of our limited resources, from projects that purify biogas and add it to our natural gas supply.
1See Biomethane greenhouse gas emissions review prepared by Offsetters.2Intergovernmental Panel on Climate Change’s (IPCC) Fourth Assessment Report (2007), Table 2.14, available at http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-10-2.html#table-2-14.3Based on the manufacturers’ stated electrical efficiency of a Caterpillar G3520C engine with SR4B generator, with no heat recovery.4 Based on parasitic load and loss estimate of 0.25kWhr/Nm3/hour of a 500 Nm/hour biogas upgrading plant using pressure swing adsorption.