Siloxane Removal from Biogas

Siloxane removal from biogas: protecting engines and turbines from silica damage

Volatile Methyl Siloxanes (VMS) are among the most destructive trace contaminants found in biogas, landfill gas, and sewage digester streams. While methane provides renewable energy, siloxanes introduce severe operational hazards. During combustion inside a gas engine, turbine, or boiler, siloxanes oxidize into micro-abrasive silicon dioxide (SiO₂), essentially fine glass dust that coats internal engine components.

Left untreated, siloxane buildup leads to severe valve pitting, spark plug fouling, cylinder head cracking, and turbine blade erosion. This can reduce engine performance by more than 20% and void major OEM warranties (such as Jenbacher, Caterpillar, MAN, and MWM).

Where do siloxanes in biogas come from?

Siloxanes are organic silicon compounds widely used in personal care products like shampoos, cosmetics, deodorants, and industrial adhesives or sealants. Because these compounds do not degrade during anaerobic digestion, they vaporize directly into the raw gas stream.

Siloxane concentrations vary significantly depending on the feedstock source:

• Landfill gas (LFG): Landfills contain high concentrations of cyclic siloxanes (D3, D4, D5, D6) due to disposed consumer plastics, cosmetics, and construction sealants. Siloxane removal from landfill gas requires robust systems capable of handling heavy contaminant loads alongside high H₂S levels.

• Wastewater treatment plants (WWTP): Sewage sludge digesters experience persistent siloxane contamination from household detergents and personal hygiene products ending up in municipal wastewater.

• Organic food waste co-digestion: Food waste digesters that process commercial packaging or supermarket returns frequently encounter siloxane spikes from food-grade sealants and packaging coatings.

What happens inside an engine when siloxanes burn?

When biogas containing siloxane gas enters a combustion chamber, temperatures exceed 1,000°C. At these temperatures, the silicon-oxygen bonds break apart and combine with oxygen to form silicon dioxide (SiO₂).

This process creates a hard, abrasive ceramic crust that accumulates on critical engine parts:

• Cylinder heads and valves: Thick silica deposits prevent valves from seating properly, causing compression loss, valve burning, and cylinder misfires.

• Spark plugs: Non-conductive silica crusts bridge spark plug gaps, leading to frequent misfires and premature plug replacement.

• Turbine blades and heat exchangers: In microturbines and boilers, silica dust fouls heat transfer surfaces and erodes high-speed turbine blades, drastically reducing thermal efficiency.

• Catalytic converters: Silica coats exhaust gas catalysts, poisoning the active sites and causing non-compliance with local NOx and CO emission limits.

To protect multi-million euro CHP investments and maintain valid engine warranties, siloxanes must be reduced to levels below 1 mg/Nm³.

Gazpack engineering: the two-stage siloxane treatment approach

Simple activated carbon filters often fail at siloxane removal because moisture in raw biogas occupies the media pores, causing early siloxane breakthrough. Gazpack utilizes an integrated two-stage treatment approach to ensure long media lifespan and predictable performance.

Stage 1: Deep gas pre-cooling and dew point control

Relative humidity is the single biggest factor in siloxane adsorption efficiency. Water molecules compete directly with siloxane molecules for active adsorption sites. Gazpack integrates dedicated chilling and condensation modules upstream of the siloxane filters. By lowering the gas dew point, water vapor is knocked out first, allowing the downstream filter media to operate at maximum adsorption capacity.

Stage 2: The Gazpack Guard system with SILOXgo media

Key features of the Gazpack Guard system:

• Integrated downstream protection: Installed as a final polishing guard before gas enters engines, microturbines, or upgrading membranes.

• Differential pressure monitoring: Automated sensors continuously track pressure drop across the vessel, alerting operators before media saturation occurs.

• Non-hazardous disposal: Saturated SILOXgo media can be safely replaced and disposed of without complex hazardous material handling.

Industry applications for siloxane treatment

• Landfill gas recovery projects: Handle heavy, unpredictable siloxane and H₂S loads. Gazpack combines deep gas drying with high-capacity SILOXgo Guard vessels to keep landfill gas CHP engines running without unexpected silica downtime.

• Wastewater treatment plants (WWTP): Protect municipal sewage sludge digester engines. Our systems remove siloxanes and moisture from digester gas, ensuring steady power generation for water utility operations.

• Food and beverage waste digesters: Neutralize siloxane spikes caused by packaging residues in food waste. Gazpack pre-conditioning ensures clean combustion for on-site boilers and CHP units.

• Renewable gas plants (Bio-CNG and Bio-LNG): Protect delicate membrane separation units and high-pressure compressors. Removing siloxanes upstream prevents membrane fouling and ensures transport fuel meets ISO 15403 specifications.

• Engineering firms (EPCM): Specify a complete, factory-tested siloxane treatment skid. Gazpack units arrive pre-cabled and pre-programmed, eliminating integration guesswork and protecting client engine warranties.

Strategic comparison: siloxane removal techniques

Frequently asked questions about siloxane removal

Protect your engines from siloxane damage

Do not let silica buildup destroy your CHP investment or void your engine warranty. Contact Gazpack’s engineering team to design an integrated siloxane treatment system tailored to your gas composition.

• Request a gas composition audit: Send us your siloxane (D4, D5, VMS) and H₂S lab test results for a custom media calculation.

• Calculate SILOXgo media lifespan: Evaluate your current replacement frequency and discover the savings of upstream drying.

• Consult a specialist: Book a technical review with our process engineering team.