The enrichment of biogas to the quality of natural gas through backwashing with pressurized water is the most flexible technology available for the treatment of biogas, regardless of quality and quantity. This technology is used to enrich biogas and separate the carbon dioxide and hydrogen sulfide in a single step through a completely automated process of utmost efficiency.
Biogas is compressed up to 7 bars and then washed in a countercurrent flow of water in a water scrubber. Carbon dioxide and hydrogen sulfide have much greater water solubility than methane and will dissolve in water.
To reduce the loss of methane in the process, the wash water is transferred to an expansion tank. A portion of the dissolved gases are re-gasified and compressed again. In a desorption column, wash water is regenerated by separating carbon dioxide and hydrogen sulfide in a countercurrent air flow thereby reducing fresh water consumption to a minimum. After cooling the wash water to low temperature it is reused in the water scrubber. After the wash, clean biogas is dried, first in a coalescing filter and then in two parallel adsorption columns to low dew points.
The air from the desorption column is loaded with carbon dioxide, hydrogen sulfide, and traces of methane; therefore it must be treated to comply with emission standards through regenerative thermal oxidation (RTO conforms emissions to standards in accordance with the technical instructions of air quality of adaptable control regulations of every country).
Uses of Biogas
The majority of biogas plants are equipped with cogeneration facilities that produce electricity and heat. Sometimes, not all excess heat can be utilized, therefore biogas plants are not used to their full potential. In these cases, the alternative is the production of biomethane that offers interesting economic variables.
Through the use of biogas enrichment technologies, CO is eliminated from the biogas very efficiently and biomethane is produced with a quality equivalent to that of natural gas (CH4 97-99%). Additionally, biomethane is a renewable gas of high quality that can be injected directly into existing natural gas. Some of its uses are:
- Combustion in facilities located far away from production (combined cycle)
- Biogas for direct consumption in households or industry
- Biofuels for vehicles
- Green energy
Advantages of Biogas Enrichment
- Plants are made in standard modules with different capacities and are easy to implement
- CO is removed from the biogas through scrubber technology using pressurized water
- No chemicals products are consumed
- No prior desulfurization is required
- No heat demand
- 99% recovery efficiency of methane
- High flexibility despite the variations of CH4 content