Siloxanes are manmade by-products created as a result of a variety of combustion processes. They are difficult and expensive to measure due to the complex and varying gas matrices. Those concerned with siloxane levels include landfills and wastewater treatment plants that use biogas to generate electricity or upgrade the biogas to Renewable Natural Gas (RNG) for direct injection into a natural gas pipeline or Compress Natural Gas (CNG) for use as vehicle fuel.
When combusted, siloxanes convert to SiO2, which deposits as essentially a layer of glass inside the engine cylinders used to produce electricity at biogas electricity generation facilities or RNG-fueled vehicles. These deposits degrade engine performance and will eventually cause damage to the engine if accumulation is left unchecked.
Siloxane in biogas used to produce electricity:
Biogas is used as a fuel for large engines that power generators, which in turn produce electricity for the grid. Siloxanes in the biogas convert to SiO2 when the gas is combusted. This produces a layer of what is essentially glass inside the engine cylinders. This accumulation of SiO2 will eventually force the engine to be shut down for expensive and time-consuming maintenance and repairs.
If this biogas comes from a landfill or wastewater treatment plant, it will be rich with siloxanes. It must, therefore, be treated with a large vessel of scrubbing material (which is often carbon, perhaps with other proprietary material blends). By installing a siloxane analyzer between the scrubber and the engines, a gas-to-power plant can monitor the concentration of siloxanes in the fuel, determine when the scrubber material has begun to allow breakthrough, and maximize the use of this expensive scrubbing material without the risk of damaging the engines.
Siloxane in Renewable Natural Gas (RNG):
Biogas can be upgraded to RNG by removing a majority of the non-methane components of the gas, thereby increasing the methane content and making it suitable for compression (creating CNG) or injection into the natural gas grid. RNG injected directly into the gas grid must meet utility quality specifications, which may include limits on maximum allowable siloxane concentrations. This is the case in California, and other utilities across the country may establish their own pipeline gas specifications as RNG production continues to grow. Whether the RNG is used as CNG for vehicles or is injected into the pipeline grid, an RNG production facility would benefit from having a siloxane analyzer that can provide continuous siloxane concentration data.
The Ei2300 Siloxane Monitoring System measures the concentration of individual siloxane species in a sample gas matrix, including TMS/MOH, L2, L3, L4, L5, D3, D4, D5, and D6. Detection limits range from 0.5ppb to 2.1ppb per species, with heavier species having higher detection limits. The analyzer reports the individual siloxane species concentrations, as well as Total Siloxanes concentration, Total SiO2, and Total Si.