Atlas Copco breaks down biogas and its potential for gasworld readers in this article, explaining how its compressors, oxygen generators, blowers, vacuum pumps and industrial chillers are utilized in turning waste into green energy. Atlas Copco has a RNG compressor rebuild shop in Dallas and packages systems in Houston.
What do we mean by biogas?
David Walters, CNG/RNG National Sales Manager – North America, Atlas Copco (DW): Biogas is the captured gas that comes naturally from the anaerobic digestion of raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, or food waste. Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen – on an industrial level specialized digesters are used to control and manage the process. Biogas is a mixture of gases, primarily consisting of methane and carbon dioxide, along with traces of other gases. It is classed as a renewable energy source.
Is biogas different to Renewable Natural Gas (RNG)?
DW: Yes, often the two phrases are used interchangeably but there is a difference. In simple-terms, Renewable Natural Gas is a type of biogas. A very pure type of biogas (up to 99% methane) which makes it suitable for applications that have typically relied on traditional natural gas. The level of treatment and process applied to the gas dictates the final purity levels. Some people would also think of bio-fuels when thinking about biogas, such as using refining waste fats and oils to power vehicles.
What’s the process to turn biogas into a useful energy resource?
DW: The inputs for biogas production are largely food and livestock waste, wastewater, and crops. Anaerobic digestion already occurs naturally in landfills and some livestock manure management systems. Management of this waste is already regulated in just about every industry. This waste product can then be optimized, controlled, and contained using commercial anaerobic digesters. It’s very different to beer production, but you can think of producing biogas in similar terms to brewing beer.
Some organic waste is more difficult to break down in a digester than others. Food waste, fats, oils, and greases are the easiest organic wastes to break down, while livestock waste tends to be the most difficult. Mixing multiple wastes in the same digester, referred to as co-digestion, can help increase biogas yields. Warmer digesters, up to 100 degrees Fahrenheit, can also help waste break down more quickly. After biogas is captured, it needs to be cleaned and compressed to become a useful energy source. Due to the high content of methane in biogas it can be highly flammable and also toxic, meaning it does need to be managed in a controlled, safe manner.
What (end-user) applications are powered by biogas?
DW: This falls into three main categories: fueling vehicles – if biogas is cleaned and compressed it can be used as a vehicle fuel; a replacement for natural gas – if biogas is cleaned up and upgraded to natural gas standards, it can be injected into your local gas companies’ pipelines and used for commercial use or cooking and heating our homes; and electricity – very clean biogas can be converted directly into electricity by using fuel cells.
Which areas of the world are most active in producing biogas and what does future growth look like?
DW: The International Energy Agency (IEA) published a report in 2018 which listed production as: Europe: ~18 million metric tons of oil equivalent (Mtoe); China: 7.5 Mtoe; US: ~4 Mtoe; and ROW: ~4 Mtoe.
According to the report, every part of the world has significant scope to produce biogas and the availability of sustainable feedstocks for these purposes is set to grow by 40% over the period to 2040. The Coalition for Renewable Natural Gas (RNG Coalition) who serve as the public policy advocate and education platform for the Renewable Natural Gas industry in North America believes RNG is a game changer because it reduces the impacts of organic wastes, while also fueling a greener future. Solid waste is expected to grow by ~70% by 2050 due to natural human activity.
The US currently has >2,200 operating biogas systems across all 50 states. The map opposite from the RNG Coalition shows a simple overview of the current RNG projects in the US.
Many conversations today are around the hydrogen economy. How does clean biogas fit in to this?
DW: The world does use and need a lot of hydrogen gas. The majority of hydrogen is produced from fossil fuels by steam reforming of natural gas, partial oxidation of methane, and coal gasification. Hydrogen generators are capable of using RNG or biomethane to create renewable ‘green’ hydrogen (RH2). Renewable hydrogen or green hydrogen is referred to by many as the ‘holy grail of energy’. This hydrogen is produced without emitting greenhouse gases as a by-product. It can be generated from renewable electricity by electrolysis, from biogas by steam reforming, and biomass through thermal conversion. The term ‘renewable hydrogen’ is most often associated with water electrolysis powered by renewable sources such as wind, solar or hydro. Biogas reforming is often overlooked as a pathway to renewable hydrogen but it has the potential to play a critical role in the global effort toward net-zero emissions. In fact, on-site hydrogen production from biogas is the only way to produce hydrogen with a negative carbon intensity.
How can green hydrogen be used?
DW: Green hydrogen can be used in industry and stored in existing gas pipelines to power household appliances. It can transport renewable energy when converted into a carrier such as ammonia, for example, which is a zero-carbon fuel for shipping. Hydrogen can also be used with fuel cells to power anything that uses electricity, such as electric vehicles and electronic devices. And unlike batteries, hydrogen fuel cells don’t need to be recharged and won’t run down, so long as they have hydrogen fuel.
What are some typical air and gas applications within biogas production?
DW: At the collect and clean stage there are multiple applications:
- Blowers for capturing the methane produced by the decomposition in the landfill.
- Oxygen generation for desulphurization.
- Aeration blowers for wastewater treatment.
- Air compressors for tooling, conveyancing, and general plant usage.
- Industrial chillers for cooling.
- When it comes to compressing the gas to a high-pressure that turns it into a useful energy form:
- Belt and direct drive air compressors for compressing the gas up to 4,500 PSIG.
- Compressors for grid injection.
- Compressors for tube trailer injection up to 3,600 PSIG.
- Pressure reducing systems to step the pressure down in stages.
- Fueling stations and dispensers for NGV vehicles.
What’s the future like for biogas?
DW: Biogas production and usage will only continue to gain in importance and momentum. As the world continues to grow, treating waste and needing fuel are two bi-products of this growth and biogas production offers one solution to this. You could say biogas is the ultimate circular economy product and takes a big problem – waste, and finds a big solution – fuel, which today takes a lot of greenhouse gases to produce. In addition, according to the RNG coalition, RNG is a proven economic driver and job creator. It’s a win-win for sustainability!