Numerical Modelling of a Water Scrubber Separating Biogas

In this study, biogas was cleaned through water scrubbing. Water scrubbing is a method of separating biogas using different solubilities of carbon dioxide and methane in water. In addition to carbon dioxide and methane, biogas may contain trace levels of other pollutants. Some pollutants can damage biogas processing machinery by generating mechanical wear and corrosion. Therefore, biogas must be cleaned before it can be used to comply with the appropriate standards and laws. A tank was drawn using AutoCAD Inventor and exported to Star CCM+, using commercial packages to generate a fluid domain and perform computational fluid dynamics. Gases were modelled using a low-pressure system of two-phased flow using fill percentages of 40% water, 60% air and 60% water, 40% air into the tank. Methane was added to these mixtures to track the volume fraction of methane that would come out of the mixtures. The water fill ratio of 40% gave a higher methane volume fraction than the 60% water fill ratio. It demonstrates that CH₄ efficiently breaks out at the same pressure settings with less water of 40%, as there is less hydrostatic pressure due to a low water column than 60%. As a result, it offers favourable circumstances since less water is consumed, which lowers the amount of contaminated water. Water replenishment, however, will also happen often. The limitations of this study are placed on small laboratory experiments under atmospheric conditions and low-pressure systems of most domestic use. The water fill ratio approach for the water scrubbing provides acceptable quality levels of methane purification at a meagre cost of implementation.