Biogas Power Generation 101


As gas-to-power specialists, SustainPower’s engineering team is experienced in natural gas and landfill gas, but biogas projects are a nostalgic look at where it all began for our company. Inspired by the vast number of biogas generators that abound across the length and breadth of Germany, SustainPower has actively pursued ways to show the Sub-Saharan Africa market what a fantastic business case biogas can offer.

But how is biogas used in power generation? Essentially, organic materials are broken down by bacteria in an oxygen-free environment, a process called anaerobic digestion. Biogas systems use anaerobic digestion to recycle these organic materials, turning them into biogas, which contains energy (gas).

Biogas contains between 50-70% methane, 30-40% carbon dioxide, and trace amounts of other gases. From a purely environmental standpoint, removing the abundant supply of animal manure and food waste from the environment prevents nitrogen pollution and runoff into water resources. Biogas also helps mitigate methane emissions that would have otherwise escaped from landfills or manure lagoons.

Of course, SustainPower seeks to harness energy wherever we can, and biogas can provide a clean, renewable, and reliable source of baseload power in place of South Africa’s coal-fired grid. It is a form of baseload power, which is electricity consistently produced to meet minimum power demands. Renewable baseload power such as biogas can complement more intermittent renewables, such as wind or Solar PV.

Like natural gas, biogas can also be used as a source of peak power that can be rapidly ramped up. Using stored biogas limits the amount of methane released into the atmosphere and reduces our dependence on fossil fuels.

If we had to look at the United States alone, the reduction of methane emissions derived from tapping all the potential biogas in America would be equal to the annual emissions of 11 million cars on the road. The New York Times has previously reported that New York City spends roughly $400 million each year to transport 14 million tons of waste to incinerators and landfills. Diverting that waste to anaerobic digestion would turn a cost into an opportunity, generating revenue from energy production and offsetting the need for more fossil fuels.

As to the question of how it all works? SustainPower uses biogas as a fuel source for our engines, and thus generate mechanical energy. Biogas is carefully mixed with the correct proportion of air and drawn into the biogas engine by the force of the engine pistons moving downwards, creating a vacuum. The air and biogas mixture is then compressed as the piston moves up. Biogas is a slow burning fuel, and a higher compression ratio engine is essential for efficient combustion. A high energy spark plug ignites the compressed air and biogas mixture. The burning biogas air mixture heats rapidly, expanding and then forces the piston down to create torque to rotate the engine. The biogas engine exhaust valve opens, releasing the spent air and fuel mixture into a heat exchanger to extract remaining combustion energy.

In this way, a biogas engine is simply another form of rotating equipment, but it is so much more. It is potentially the energy solution that makes the most economic and environmental sense to those who can harness it. Creating jobs, reducing pollution and powering developing economies.

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