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Siloxanes are silicone compounds found in products such as coatings, soaps, cosmetics, shampoos and lotions. In the anaerobic environment of a landfill or digester, they break down and contaminate the gas generated.
When the gas is used as a fuel the siloxanes are oxidized to silicon dioxide (quartz, sand), coating internal engine or gas turbine parts.
This contamination and coating leads to:
- Engines run hotter, reducing oil life.
- An abrasive is introduced to the engine or turbine.
- Turbine balance is affected.
The consequences are:
- Increased down-time
- Reduced efficiency
- Higher maintenance costs
- Difficulty meeting emissions standards
In one specific, but not unusual case, at a landfill generating electricity from landfill gas, engine rebuilds were required every three months, instead of the manufacturer’s recommended interval of two years, and oil changes were required after 700 hours. After the installation of a Venture Gas Conditioning Skid, engine rebuilds are on a two year schedule, and oil changes occur every 1500 to 2000 hours. At $25,000 – $75,000 per rebuild per engine, a week of down-time, and $800 per oil change the impact of siloxanes is clear.
Engine manufacturers recognize the impact of siloxanes and are limiting the siloxane concentrations entering their engines. Having levels too high may impact warranties.