Biomass Energy and Biogas in Australia
What if we could take organic waste; everything from sewage to leftover food products to organic matter in landfills, and use it to power homes and cars with zero carbon emissions? That’s exactly what bioenergy is. By breaking down organic matter (known as biomass), and creating a mixture of methane, carbon dioxide, and hydrogen sulfide known as biogas, we have the ability to power everything from home heating to vehicles, to home cooking, and industrial processes. But what exactly is biogas and what are its advantages and disadvantages? Read more below to learn about bioenergy and how biogas could be the future of renewable energy in Australia.
Biomass, biogas, and bioenergy - What’s the difference?
Biomass, biogas, and bioenergy can be difficult to differentiate but essentially all three are different pieces of the same process: The transformation of organic material into fuel that is used for energy.
What is biomass?
Biomass is the raw, organic, once-living material that is used to create biogas. This organic matter is broken down creating a mixture of methane and carbon dioxide with trace amounts of hydrogen sulfide, moisture, and siloxanes, that has huge energy potential.
Biomass can include:
- Agricultural waste
- Municipal waste
- Plant materials
- Green waste
- Food waste
- Energy crops
When biomass is turned into biogas, it also creates digestate - the leftover material after the organic matter is broken down. Digestate is incredibly nutritious and can be used as fertilizer for farming.
What is biogas?
Biogas is the mixture of methane and carbon dioxide, as well as hydrogen sulfide, moisture, and siloxanes that are formed when organic matter is broken down in the absence of oxygen. There are many different ways to produce unpurified biogas but before it can be used for residential or industrial purposes it first needs to be purified.
What is bioenergy?
Bioenergy (or biomass energy) is the energy generated from living or once-living organisms. A simple way to think about bioenergy is burning wood (biomass) to create heat (bioenergy). On a big scale, biomass energy can either be burned, like the wood in a campfire, to create heat or converted into electricity for residential and commercial use.
The production of bioenergy from biomass to biogas
Biogas, while not as widely known as other energy alternatives, has huge potential thanks to its high energy potential and low greenhouse gas emissions. It can be used for a number of applications and, since it can be produced using organic waste that would otherwise pollute water and landfills, can reduce the amount of garbage that ends up in landfills and sources of water.
How is biogas made?
Biogas is produced using a number of technologies in a multi-step process, but the most important step is the use of microbes that feed on the biomass (organic material) which creates the methane gas used for energy generation. The steps for creating biogas are:
Crushing the organic material into small pieces (under 10mm) which is then slurrifed, by adding liquid to the biowaste, for easier digestion. Any inorganic material (such as plastic packaging or glass) is removed.
As the microbes need a warm environment, the biowaste slurry is heated to around 37 Celcius.
The biowaste slurry is stored in large tanks for about three weeks. Through anaerobic digestion (the breakdown of the material in a space devoid of oxygen), biogas is formed as the microbes consume the organic material.
The gas is purified to remove impurities and carbon dioxide
The digestate (residual materials) are then stored in tanks for use as fertilizer. Often, the solid and liquid parts of the digestate are separated, with the liquid digestate being used in the slurrification process of biogas at the beginning of production.
How is biogas purified?
Unpurified biogas consists of mostly methane and carbon dioxide, with a few other compounds found in small quantities. In order to be used in industrial and residential settings, the biogas needs to be purified (also known as “upgraded”). Upgrading biogas involves removing the carbon dioxide to make it as close to natural gas as possible and removing hydrogen sulfide to prevent corrosion of metallic parts once the biogas is burnt. There are a number of methods to upgrade biogas but the most common is through a process called water washing.
Water washing is, quite literally, washing the biogas with water. The biogas is filtered through columns where it is scrubbed by cascading water at a very specific temperature and pressure. Water is very efficient at absorbing carbon dioxide and other unwanted compounds found in raw biogas.
What is bioenergy and biogas used for?
Biogas has numerous applications, from powering cars to heating homes. As well as being used instantly, biogas can easily be stored and transported for use at any time. For hybrid power plants, where it can be difficult or impossible to store wind and solar energy, biogas is able to compensate for fluctuations in other renewable energy sources.
Other biogas applications include:
Combined Heat and Power: Energy-efficient power plants that not only generate electricity but capture the excess heat produced which would otherwise be wasted. The heat can then be used for space heating and cooling, hot water, and industrial processes.
Transportation: Properly purified and condensed biogas can be a more environmentally friendly fuel alternative to natural gas vehicles or dual-fuel vehicles. These can include cars, trucks, and trains. If, for example, a fleet of trucks run on biogas they can easily fill up at the biogas plant which then also reduces the cost of transporting the biogas to another location.
Injection into the natural gas pipeline: When biogas is properly purified (known as biomethane or Renewable Natural Gas) it can be injected into the natural gas pipelines to then be used for residential use such as heating, cooking, or to heat water.
How does biogas generate electricity?
Biogas is not only useful in its gas form, for everything from powering methods of transportation to heating water and household cooking, but can also be used to generate electricity. Currently, the most energy-efficient method of electricity generation through biogas is mechanical generation. Theoretically, biogas can be converted directly into electricity through the use of a fuel cell but currently, the process is not financially viable in most cases and not practical until technology improves.
Until fuel cell technology improves, however, biogas is most often used to fuel combustion engines where the gas is converted into mechanical energy, which then powers an electric generator to produce electricity. While a multi-step process, using biogas to fuel combustion engines, and then electricity generators, involves fairly simple and easy to find equipment.
Biogas & bioenergy advantages and disadvantages
Bioenergy is a very underrated resource; it’s not only carbon-neutral but actually removes organic waste from landfills where it would decompose, releasing toxic liquid into the ground and greenhouse gases into the air.
However, there really isn’t the same support for biomass energy as there is for solar panels, hydropower, or wind power. Government programs such as the solar feed-in tariff would help move biomass along. However, there isn’t as much time, energy, research, or money being invested into biogas research despite its potential to help Australia reach its renewable energy target sooner than other methods.
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Biomass energy in Australia and the future of biogas
Biomass energy and biogas is a small piece of the renewable energy transition in Australia, but one with huge potential. The latest Clean Energy Council 2021 Clean Energy Report lists biogas as one of the smallest sources of clean energy in the country, making up just 5% of the renewable energy profile.
However, the Federal Government’s completion of the national Bioenergy Roadmap, might change this. This roadmap signifies the “validity and value of the Australian bioenergy industry going forward” the 2021 Clean Energy Council report states and, even in the short time since this roadmap’s development, has already led to a significant increase in the level of interest and development of bioenergy projects in the past year.