Our daily activities emit greenhouses gases (GHGs) such as carbon dioxide (CO2) and methane (CH4) into the atmosphere. These green house gases are responsible for global warming. GHGs do not stay within country boundaries where they are emitted in fact they contribute to the climate change that is felt globally irrespective of their origin. The earth’s climate system remains stable due to a balanced system of energy transfer and transformation. However during the last millennium increased concentration of GHGs by human activities has forced major changes in the climate system.
The seven greenhouse gases regulated under the Kyoto Protocol are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphurhexafluoride (SF6), nitrogen trifluoride (NF3). All these gases are long lived green house gases (LLGHGs) because they are chemically stable and remain in the atmosphere over a time scale ranging from a decade to centuries or longer.
Methane is the second most significant greenhouse gas, it contributes to approximately 18% of total radiative forcing by LLGHGs. The global warming potential of methane is 25 times more than carbon dioxide. Approximately 40% of methane is emitted by natural sources and 60% is emitted by human activities such as cattle breeding, rice agricultural, fossil fuel exploitation and landfills. Methane stays in the atmosphere for approximately 12 years and the concentration of CH4 has more than doubled since pre industrial times.
Biogas (Biomethane) – Biogas or Biomethane is 50%-80% methane and 20%-50% carbon dioxide, with traces of gases such as hydrogen, carbon monoxide and nitrogen. Biogas is a gaseous product formed by decomposing organic matter such as sewage, animal byproducts, agricultural waste, industrial waste and municipal waste. Biogas can be upgraded in quality similar to natural gas from fossil, which is more than 70% methane and rest are hydrocarbon and traces of carbon dioxide. Natural gas obtained by cleaning of biogas is known as renewable natural gas (RNG). Biogas can be recovered from landfills, livestock operation sites, waste water treatment etc and refined to RNG which can be used to generate electricity or power natural gas vehicles. Thus capturing biogas will prevent methane release into the atmosphere.
Gas turbine generators are used to convert biogas from landfills into electricity. Various kinds of anaerobic digesters are also used to produce biogas from organic wastes. Biogas digesters ranging from single household devices to industrial scale equipment which can generate large amount of power are available.
One of the most promising technology to transform waste steams into clean energy is by using fuel cell. Fuel cell produces electricity without combustion so the exhaust has no pollutants. When hydrogen rich fuel such as biogas enters fuel cell it reacts electrochemically with oxygen to produce electricity, heat and water. Waste water treatment facilities can utilize biogas from digesters to power fuel cell, one such biogas project is in Fountain Valley, California.
Apple has built a fuel cell farm in Maiden, North Carolina that powers its data center. Apple uses fuel cell from a Silicon Valley company called Bloom Energy. Biogas used in Apple’s fuel cell farm is produced by a landfill which is about three miles from the data center.
Along with electricity, biogas powered fuel cells also produces usable high quality heat which can be used to make steam or fed back into the digester. However top benefit of fuel cell is that it produces clean energy with zero pollutants due to the absence of combustion process.
Biogas can also be reformed in a fuel cell to produce hydrogen which is being explored as an environmentally friendly fuel with zero emissions.
These technologies allow harnessing biogas while preventing methane release into the atmosphere in an environmentally responsible way to meet world’s growing energy need. Regulations to reduce emissions and smart policies to support these technologies are required for a large scale adoption.