Monday, 14 August 2023 13:34

Biogas and Biomethane

Biogas is a renewable energy source produced by the breakdown of organic matter, such as sewage, livestock, agricultural and food waste. Biogas contains between 45 and 75% methane, CO2 and small quantities of other gases produced by anaerobic digestion of organic matter in an oxygen-free environment.

To enable the use of biogas in the gas network or as a transport fuel, it is required to go through a purification and upgrading process where it becomes biomethane (~95% methane). The purification process requires energy and can produce emissions. Biogas can also be used directly to produce electricity and heat or as an energy source for cooking.

Diagram of Biogas Production
Source: Environmental and Energy Study Institute

Biogas production process

The production of Biogas is the result of anaerobic digestion which takes place in a sealed vessel called a reactor. A reactor can be designed and constructed in various shapes/sizes and contains complex microbial communities that break down (or digest) the waste in absence of oxygen and produce:

  • Biogas
  • Digestate (the solid and liquid material) which is discharged from the reactor.

Multiple organic materials can be combined in one reactor using a practice called co-digestion. Co-digestion can increase biogas production from difficult-to-digest organic waste such as:

  • manure
  • food waste
  • crop residues
  • fats, oils, and greases (FOG) typically from restaurant grease traps

Digestate is the residual material left after the digestion process which, with an appropriate treatment, can be used in many beneficial applications such as:

  • animal bedding (solids)
  • nutrient-rich fertilizer (liquids and solids)
  • foundation material for bio-based products (e.g., bioplastics)
  • organic-rich compost (solids)
  • soil amendment (solids)

Biogas processing, transport and use

Biogas produced by the process of anaerobic digestion is water-saturated and often contains small amounts of other gases like:

  • Hydrogen Sulfide (H2S)
  • Siloxanes H(OSiH2)nOH and (OSiH2)n
  • other contaminants

Biogas is submitted to a conditioning process to remove water and hydrogen sulfide. Most of the conditioned biogas is then used to generate electricity or heat in buildings. A fraction of the Biogas produced is submitted to a further process to remove siloxanes and carbon dioxide where it becomes Biomethane.

Unfortunately, only around 35% of primary energy is converted into usable electricity from the power generation process, the rest is released into the atmosphere as heat and CO2 emissions. Even more energy is lost as electricity travels through the grid to reach its destination. Co-generation is a process that integrates the production of usable heat and electricity from a fuel source (either natural or biogas).

Biogas Consumption Graph
Source: IEA (2020), Outlook for biogas and biomethane: Prospects for organic growth, IEA, Paris

Energy content

The energy content of biogas can vary from 16 to 28 megajoules per cubic meter (MJ/m3) while biomethane can reach 38 MJ/m3. Biomethane is indistinguishable from natural gas and can be used without any modification in the transmission and distribution infrastructure or end-user equipment. Biomethane is also fully compatible for use in natural gas vehicles.

Comparison of Average Density of Common Fuels

Biomethane in Australia

Currently around 3.5 million tonnes of oil equivalent (MTOE) of biomethane are produced worldwide and the vast majority of production lies in European and North American markets.

Biogas and biomethane today account for less than 3% of total bioenergy demand and represent an even smaller 0.3% share of total primary energy.

The Australian biogas industry is emerging. In 2017 there were 242 plants in the country, half of which were landfills, and the electricity generation was about 1,200 Giga Watt per hour (GWh) –  equivalent to 0.5% of the national electricity generation.

The total estimated biogas potential in Australia is 103,000 GWh, which is comparable with current biogas production in Germany and ­equivalent to almost 9% of Australia’s total energy consumption in 2017.

Zetco Valves

Zetco Valves have been serving the Australian and global market for over 50 years, and we understand how critical quality is to any business operation. Low quality valves and incorrect material selection can result in impactful failures across systems and equipment, and result in high business losses due to delays and costly replacements.

We understand that for many organizations globally, the quality of the material and parts you source for your equipment can form a crucial bedrock for the successful operation of machinery and equipment involved in processing, transport and use of Biogas.

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