Biogas from agricultural digesters, landfill sites, sewage works, and food waste anaerobic digestion is increasingly used as a renewable energy source. Before the gas can be burned in engines, fed into the natural gas grid, or upgraded to biomethane, it must be cleaned to remove the trace contaminants that damage downstream equipment. Activated carbon is the dominant polishing technology used to remove hydrogen sulphide, siloxanes, mercaptans, and other contaminants from biogas and natural gas streams. As an activated carbon manufacturer and supplier, SorbiTech provides impregnated and non impregnated carbon grades engineered for the demands of biogas service.
Hydrogen Sulphide Removal from Biogas
Hydrogen sulphide is the most damaging trace contaminant in raw biogas. It corrodes engine components, attacks pipeline steel, and produces sulphur oxides during combustion. Iron impregnated and potassium hydroxide impregnated activated carbons capture hydrogen sulphide by chemical reaction, forming non volatile iron sulphide or potassium sulphide that remains fixed inside the carbon. Catalytic activated carbon takes this further by oxidising the hydrogen sulphide to elemental sulphur on the carbon surface, which gives a higher working capacity and a longer service life.
Siloxane Removal for Engine and Turbine Protection
Siloxanes are organic silicon compounds present in biogas from landfill and sewage sources. When biogas containing siloxanes is burned in an engine or turbine, the siloxanes oxidise to form silica deposits on valves, pistons, and turbine blades. The deposits build up over time, reduce engine efficiency, and eventually cause expensive failures. High surface area coconut shell activated carbon removes siloxanes by physical adsorption, with typical working capacities high enough to give months of reliable service before replacement.
A typical biogas treatment train uses a two stage carbon system. The first stage is impregnated activated carbon for bulk hydrogen sulphide removal. The second stage is high surface area coconut shell carbon for siloxane and trace organic removal. This two stage approach gives the best overall service life and protects the downstream engine, gas upgrading membrane, or pressure swing adsorption unit.
Biomethane Upgrading and Grid Injection
Biogas upgraded to biomethane must meet pipeline gas specifications before injection into the natural gas distribution network. Activated carbon polishing removes residual hydrogen sulphide, mercaptans, and trace organics that survive the primary upgrading step, ensuring the final product meets the specifications of the receiving network. The same polishing approach is used in industrial process water and elsewhere where activated carbon serves as the final barrier between treatment and distribution.
Natural Gas Sulphur Polishing
Natural gas processing plants use activated carbon as a final polishing step downstream of amine absorption units. The carbon removes residual sulphur compounds that escape the amine system, ensuring the gas meets pipeline and LNG specifications consistently. Refinery off gases and sulphur recovery unit tail gas are also polished with activated carbon when the residual sulphur level is too low for further amine treatment but too high for direct release.
Selecting Activated Carbon for Biogas Service
Carbon selection depends on the contaminant profile of the gas. For hydrogen sulphide dominated streams, the main choice is between iron impregnated, potassium hydroxide impregnated, and catalytic carbon. Iron impregnated grades work in a wide range of conditions and are the most common choice for biogas. Potassium hydroxide grades offer higher working capacity but are sensitive to carbon dioxide content. Catalytic grades give the longest service life on heavily loaded sewage gas duties.
For siloxane removal, the choice is high surface area coconut shell granular activated carbon, with particle size selected to match the existing vessel hydraulics. Pelletised grades are common in CHP and grid injection applications where low pressure drop is important. Pressure rating, operating temperature, and humidity all influence the final selection.
SorbiTech Activated Carbon for Biogas Purification
SorbiTech supplies impregnated granular activated carbon and activated carbon pellets for biogas, landfill gas, and natural gas purification. The product range includes iron oxide impregnated, potassium hydroxide impregnated, and catalytic carbon grades for hydrogen sulphide removal, plus high surface area coconut shell carbons for siloxane and trace organic removal. SorbiTech supports operators with bed sizing, breakthrough monitoring, and spent carbon disposal coordination. Contact the SorbiTech technical team to discuss your biogas treatment requirements and the right grade for your gas chemistry and operating cycle.