PpTek LtdOrchard Business Park,, North End Road Yapton,, Nr Arundel , United Kingdom

During the past 12 years PpTek has worked with leading Universities in the UK, including Imperial College London, to develop the regenerative media that is used in all their siloxane removal systems (SRS). This media is exclusive to PpTek and is non toxic, ozone friendly and Bio-degradable.

The final SRS have important key differences over existing products currently found in the filtration market, particularly activated carbon and graphite. The media used in ourSRS is not a general purpose filtration carbon based material and therefore has non of the traditional drawbacks of that material.

Particular downsides of carbon and graphite is their ability to absorb water, difficult and expensive to regenerate, expensive to dispose of, when saturated, and has a low percentage absorbency by mass.

By contrast the PpTek media repels water, can be regenerated on site with no disposal costs and absorbs 10x the amount of contamination of carbon or graphite.

The result is a SRS that lasts up to 5 years, before media replacement, can operate without drying the BioGas via a chiller, has no media disposal costs when finally renewed and has a small footprint. As the SRS unit is skid mounted it can be easily moved to alternative sites if required and takes a minimum of maintenance as there are very few moving parts on the unit.

PpTek can also "tune" the media mix to remove other VOC's found in BioGas such as chlorinated compounds, in addition to the targeted Siloxanes.

After extensive development the stainless steel constructed the SRS unit is now available for various gas flows of 50 m³/hr up to 4200 m³/hr in one single unit. Gas flows greater than this can be accommodated by utilising SRS's in parallel.

Volatile Methyl Siloxanes (VMS) in the landfill and sewage gas convert into silicon dioxide as combustion takes place in the engine. The silicon dioxide combines with other elements in the gas, and with the lubrication oil to form a hard matrix that accumulates on the combustion surfaces.

As the deposits accumulate, the engines efficiency falls causing detonation in the combustion chambers. The resultant unburned fuel contaminates the exhaust gas increasing emissions. 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.

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, tooth-pastes, skin care preparations, hair conditioners and as carriers in anti-perspirents. 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.

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 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 filter the Siloxanes from the gas before they reach the engine preventing the formation of deposits.

Active carbon filtration systems are available which filter the contaminants for a finite period, these can be large installations (sometimes requiring planning permission) and need manual removal of spent activated carbon and disposal of the contaminated medium.

Recently, derivatives of the active carbon principal have been developed which offer a cartridge / silo replacement and removal service of the spent carbon. Although this avoids some of the disposal and safety issues, it is costly and requires constant maintenance. Normally these installations have a large footprint and require site planning before commissioning.

The PpTek BioGas AK (BGAK) Siloxane Removal System is a small (1.8mx2.3mx4.1m) self-contained unit that automatically regenerates the filter medium and requires a minimum of ongoing maintenance. The siloxane filter units, under normal conditions, will absorb Siloxanes for up to 3 years before the medium requires replacement. The PpTek siloxane removal system is automatically regenerated at regular intervals, the resulting regenerated air is composed mostly of high boiling Siloxanes that are believed to be non-ozone depleting in the stratosphere and have negligible global warming potential due to their short atmospheric lifetimes (e.g. Swanson et al.,1996). The US EPA has granted VMS compounds exemption from regulation as VOC ozone precursors. Siloxanes have been shown to degrade rapidly in the presence of soil (Carpenter et al 1995) with more than 50% converted to a water soluble fraction after 4-6 weeks.

The PpTek BioGas AK 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.