Biogas upgrading is the process of turning Biogas into Biomethane. Converting Biogas into Biomethane removes carbon dioxide, hydrogen sulphide, water and contaminants from the biogas. The resulting Biomethane can then be used for vehicle fuel or for injection into the natural gas grid network. Learn more about how biogas is produced.
How is Biogas upgraded?
Biogas upgrading can be achieved using a number of methods, the four main methods are: water washing, pressure swing adsorption, selexol absorption, and amine gas treating.
Water Washing
Water washing uses high pressure water to absorb the carbon dioxide CO2 from the biogas and therefore purifying it and creating biomethane. The carbon dioxide dissolves in the pressurised water along with any hydrogen sulphide found within the gas. The methane is not absorbed in the water and instead passes through the system. Water washing can achieve rates of 98% methane and is a very effective way to upgrade biogas to biomethane.
Pressure Swing Adsorption (PSA)
Pressure swing adsorption uses pressure between 4-10 bar and an adsorbent material to retain the CO2. The adsorbent material used is a porous solid with a high surface area. The CO2 is adsorbed by the porous material and therefore separates from the methane resulting in biomethane. The adsorbent material needs to be monitored and replaced on a regular basis as it can only collect so much CO2 before needing to be replaced. Materials such as activated carbon, silica gel, alumina, resin and zeolite are used in the PSA process to separate the CO2 from the biogas.
Selexol Absorption
Selexol Absorption is the process of using Polyethylene Glycol to absorb the carbon dioxide and hydrogen sulphide whilst the methane gets left behind. This process is similar to water washing but using Polyethylene Glycol instead. The advantages of using Selexol which is the trade name for Polyethylene Glycol over water is that it is more absorbent of CO2 and hydrogen sulphide which means less pumping is needed to purify the biogas. In addition to this the Selexol removes additional contaminants including water and hydrocarbons.
Amine Gas Treating
Amine Gas Treating is the process of removing CO2 and hydrogen sulphide using various alkanolamines, which are often referred to as amines. The amine gas combines with the carbon dioxide and hydrogen sulphide to separate these gasses from the methane in the biogas. The lighter methane can then be extracted from the top of the chamber whilst the heavier combination of amine, carbon dioxide and hydrogen sulphide can be extracted from the bottom.
What is the result of Biogas upgrading?
Biogas upgrading results in Biomethane. Biomethane has a methane concentration of over 90% or greater and is chemically identical to the natural gas found underground. This gas can be used the same as natural gas and therefore has many applications including fuel for vehicles, generating electricity, heating water, cooking and much more. Find out more about the applications of biogas.
Monitoring and Analysing Biogas and Biomethane
Biogas analysers and monitoring equipment improves the return on investment from biogas upgrading by maximising the energy produced and validating the purity of the biogas upgrading process. They also help to prevent and reduce leakage of greenhouse gasses and flaring. QED has a number of Biogas monitors including the Biogas 5000 and Biomethane 3000 both of these products help improve the efficiency of the biogas upgrading process.
