What is Biogas & Biomethane?
Alternative fuel and energy sources are becoming more important in combatting the effects of climate change on the planet. These eco-friendly and renewable alternatives can come in many forms, with some of the more common ones coming in the form of biomethane and biogas.
What is biogas?
Biogas is a renewable fuel and energy source that is produced in AD plants by using microbial communities to break down organic matter such as food and animal waste. Biogas can be used to create various other products, such as biomethane, but is primarily used in CHP (Combined Heat and Power) to create electricity and heat homes connected to the grid.
What is biomethane?
Biomethane is an eco-friendly source of energy that is produced from biogas. Biomethane has a variety of environmental benefits as it repurposes methane, which can be a harmful gas, as well as food waste and other organic material which otherwise would have been sent to landfill.
What’s the difference between biogas and biomethane?
Biogas and biomethane are similar in the fact that they are both renewable gases produced from organic waste, however, they both have some very key differences.
The primary difference between biogas and biomethane is that biogas is a composition of a range of gases including methane and carbon dioxide whereas biomethane has been through a purification process which removes any CO2, hydrogen sulphide, and water from the original biogas composition.
It is due to the ‘upgrading’ process that biomethane can be injected into the grid to produce heat and electricity for homes.
How is biogas made?
Biogas is made through a process called “Anaerobic Digestion”, this is process involves collecting organic material, which can include food and animal waste, for use as a feedstock. Once the feedstock has been procured it is fed into sealed vessels, known as reactors, where a reaction takes place in the absence of oxygen.
During the reaction, microorganisms break down and decompose the feedstock to produce two separate products, biogas and a sludge-like material known as digestate. The biogas is then captured for use in CHP engines and to be upgraded into biomethane and the digestate is collected and used for fertilizer.
It is extremely important to monitor and analyse the environment within the reactors in AD plants in order to properly manage and maintain the composition of the biogas within the vessel. This is to ensure that the reaction taking place remains stable and efficient.
How is biomethane produced?
Biomethane is produced by ‘upgrading’ biogas after is has been captured following the anaerobic digestion process. The process of upgrading biogas into biomethane involves taking advantage of the different properties of the various gases found within biogas to separate them into individual components, one of which is methane.
There are several ways in which the various gases within biogas can be separated. However, around 60% of biomethane production takes place through water scrubbing and membrane separation.
How does ‘upgrading’ biogas work?
In simple terms, ‘upgrading’ biogas means to separate methane from the gas composition of carbon dioxide and other compounds. Ultimately, this process produces biomethane – however, there are a number of different technologies and methods that can be employed to produce this outcome.
For example, the upgrading process can be achieved through; amine scrubbing, pressure swing absorption, water scrubbing, organic physical scrubbing, cryogenic distillation, and membrane scrubbing. Choosing the right technology process can be dependent on the required efficiency rates of the as each one has its own properties and rates of efficiency.
In many cases, the upgrading process takes place in four steps, these steps being; pre-treatment, compression, upgrading, and injection. During pre-treatment the biogas is processed to remove any impurities or excess reactants such as Volatile Organic Compounds (VOCs) and Hydrogen Sulphide (H2S). Next is compression where the gas is compressed to the appropriate pressure for the final stages of the process.
Once the compression stage of the organic process is complete, the biogas can then be upgraded using any of the technologies available. This is the step where the methane is removed from the biogas compound to be used for CHP. Once the methane has been extracted it can then be injected into the grid for domestic and commercial uses.