Recent years have seen a marked increase in the use of siloxane-containing products, a substantial amount passing through to waste products both in sewage and landfill sites.
As the gas produced from these sites is used to power biogas-to-energy units, a substantial increase in the effects of the siloxane contamination will be seen in the form of crystalline silicon dioxide (quartz/sand) building up on the combustion surfaces inside generating engines. As the deposits accumulate, the engine efficiency falls causing detonation in the combustion chambers. The resultant unburned fuel contaminates the exhaust gas, increasing emissions particularly of carbon monoxide and mono-nitrogen oxides (NOx).
At this point the engine may need to be "de-rated” (output reduced) to prevent significant engine damage and to reduce emissions. If run unchecked, severe damage can occur to valves, pistons, piston rings, liners, cylinder heads, spark plugs and turbochargers, necessitating premature servicing and costly repairs and overhauls.
Volatile Methyl Siloxanes (VMS) are a class of chemicals with an increasing range of applications.
They are widely used in personal care products such as deodorants, toothpastes, skin care preparations, hair conditioners and as carriers in antiperspirants. They are also used as effective cleaning agents of electronic circuitry.
Recently legislation has encouraged the dry cleaning industry to change from using chlorofluoro solvents to more environmentally friendly products, such as Siloxanes.
Even in the food industry, Siloxanes are used as an oil substitute to create low-calorie alternative food products such as potato chips, salad dressings and spreads.
The waste from these industries are frequently disposed of in landfill sites. As organic matter decomposes it produces methane and carbon dioxide. The Siloxanes blend with this and contaminate the gas which is used to fuel engines that produce electricity.
Sewage Treatment Works acquire Siloxanes via industrial and domestic discharges. This is often supplemented by road tankers adding waste directly into the treatment process. The contamination is similar to that experienced on landfill sites, with the resultant gas used to fuel engines.
The gas produced by these sites is frequently contaminated by Siloxanes particularly the cyclic D3, D4, D5 and the linear L2 all of which will decompose into silicon dioxide during the combustion process.
Various methods have been employed in an attempt to reduce the effect of the silicon dioxide deposits in engines used by the landfill and sewage industries.
Fluid injection systems do allow the silicon matrix to soften making removal easier, however in the long term it is preferable to remove the Siloxanes from the gas before they reach the engine preventing the formation of deposits.
Active Carbon filtration systems are normally non-regenerative and thus can only filter the contaminants for a finite period until replacement is necessary. These can be large installations (sometimes requiring planning permission) and need manual removal of spent activated carbon and disposal of the contaminated medium.
The Parker PpTek BioGas AutoKleen (BGAK) Siloxane Removal System is a small, self-contained unit that automatically regenerates thus requiring a minimum of ongoing maintenance. The regenerative properties of the Parker PpTek adsorption media allow Siloxanes to be removed for up to 5 years before the media needs to be replaced.
The Parker PpTek BGAK Siloxane Removal System is cost effective to operate, removes the problem-causing Siloxanes, is environmentally friendly and enables engines to be run to their full potential between service intervals and overhauls.
“PpTek’s expertise in combination with Parker Hannifin’s products and in-depth knowledge of gas treatment and dehumidification results in a powerful portfolio in the biogas conditioning market. We can now offer our customers holistic solutions to condition their gas to be used for combined heat and power, gas-to-grid and gas-to-vehicle installations. In addition, we will jointly develop new products for this emerging market.” Guido Fogolari, General Manager, Hiross Zander Division
Article contributed by Steven Scott, M.B.A., Market Development Manager - Biogas Applications, Hiross Zander Filtration Division / domnick hunter Filtration & Separation Division