Bioenergy 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.
What is biogas?
Biogas is, simply put, the gas produced through the breakdown of organic material in the absence of oxygen. This organic matter breaks down, creating methane, carbon dioxide, and trace amounts of hydrogen sulfide, moisture, and siloxanes which then has huge energy potential.
The organic matter used to create biogas can be:
- Agricultural waste
- Municipal waste
- Plant materials
- Green waste
- Food waste
- Energy crops
When biogas is produced it also creates digestate, the leftover material after the organic matter is broken down. This digestate is incredibly nutritious and can be used as a fertiliser for farming.
How does bioenergy work? What is biogas used for?
Biogas, while not as widely known as other energy alternatives, has huge potential thanks to its high energetic 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 which 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 slurrified, 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 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 advantages and disadvantages
Biogas is seen as an amazing resource, it’s carbon-neutral and actually helps the environment by taking organic waste out of landfills where the material would otherwise decompose, releasing toxic liquid into the ground and greenhouse gases into the air. However, there just isn’t the same interest in biogas as there is in solar, wind, or hydro power and as a result governments just aren’t investing enough time, research, or money into biogas generation.
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Bioenergy in Australia
Bioenergy and biogas is a relatively new energy source in Australia, but one with huge potential. Currently, bioenergy only makes up 1.5% of all energy generated in the country, compared to the more popular hydro, wind, or solar, and only 7.1% of renewable energy generation, according to the Clean Energy Council 2019 Renewable Energy Report. While dozens of solar and wind projects were completed in 2018, only a handful of bioenergy projects were developed and built.
This doesn’t mean that biogas doesn’t have a future in Australia. Even now, more and more energy providers, such as Energy Locals and Origin Energy, are using bioenergy to power residential homes across the country.
Energy Locals and bioenergyCarbon-neutral energy provider, Energy Locals, buys energy from power stations which use waste sugarcane to generate their electricity through bioenergy generation. Another byproduct of the sugar cane, bagasse, is used to make rum by the Lord Byron Distillery.
In addition, the Australian Renewable Energy Agency is in the process of developing a roadmap for bioenergy in the country, set to be completed by the end of 2020. This Bioenergy Roadmap will help to guide and develop how the country can best invest money and research into bioenergy, as well as outline future policy for bioenergy. To date, the Australian Government has already invested over $118 million to bioenergy projects such as biogas, biomass, and biofuels.