Siloxanes Removal (Presentation)

Commercial Department comercial@atlasseis.com Siloxanes ? Subgroup of silica compounds containing Si–O bonds with organic radicals attached to the silica molecule, including methyl and ethyl groups, among others: ? The polydimethylsiloxanes (PDMS) are polymers composed by silica and oxygen units, repeated n times, with two methyl groups attached to the silica atom, wherein the terminations are composed of trimethylsilane. The value of n can range between 3 and more than 10,000. ? The PDMS are transformed by hydrolysis into smaller-chain compounds, called volatile methyl siloxanes (VMS) and these may have a linear or cyclic structure. ? Properties: high compressibility; low flammability; low surface tension; hydrophobic properties; high thermal stability. What are they? Sil(ica) + Ox(ygen) + (Meth)ane There are thousands of different siloxanes Siloxane sources ? There is no known biological process that establishes the connection between the silica atom and a methyl group and thus these compounds are synthesized by Man. ? Due to its properties, siloxanes are widely used in various industrial processes and often added to consumer products ? present in lotions, shampoos, paper products, paints, oils, etc.. ? The annual siloxanes production is estimated at over one million tons. ? Although most siloxanes are very volatile and disperse into the atmosphere, some siloxanes ultimate destination is often waste waters or landfills. ? In the activated sludge process, siloxanes are not decomposed during anaerobic process, they volatilise, remaining in the biogas. What do they do? ? The combustion gases containing silicon produces an abrasive microcrystalline silica, which has chemical and physical properties similar to glass. The hardness of this residue leads to abrasion of the engine surfaces. ? The volatile compounds of silica generate a fouling layer in engines, turbines, boilers, etc., contributing to the deterioration of engines and malfunctioning spark plugs, pistons, engine heads, ... ? It is important to remove the siloxanes to improve the biogas quality and protect the equipments. ? Even at concentrations below 0.5 ppm, siloxanes can cause significant damage. The siloxanes concentration tend to increase over time because they are very persistent. ? The damages lead to higher costs and lower equipments useful life. Siloxanes Reactor ? The reactor is built in stainless steal with one ore more chambers, with retention time, which is considered a huge safety reserve for possible concentration and flow rate peaks. ? The adsorbent used is doped activated carbon increasing about ten times its adsorption capacity. The principal characteristics are: ? Free accessible micropores; ? Effective performance in very short retention time; ? Water-insoluble active centres for catalyst adsorption; ? Large pore volume to yield high siloxanes concentrations; ? Intensive catalytic adsorption at room temperature (20-40ºC). ? The siloxanes concentration in the adsorbent is verified by: ? Gas sample analysis at the filter output; ? Engine lube oil analysis; ? Endoscopies to the engine parts. Prototype Case Study Sample date Total engine hours Partial engine hours Silicone concentration The concentration is close to the maximum limit (75ppm) Siloxanes concentration decreased after the reactor installation. Case Study Before After ? The damages lead to higher costs and lower equipments useful life; ? Need for replacement/cleaning after more working hours . Considerations ? Considering an increase in the production of these compounds it will also increase the siloxanes concentrations that reach both the waste water such as landfills, which causes problems regarding the energetic valorisation of the biogas. ? Since the implementation of a biogas valorisation system requires a high initial investment and some maintenance costs, it is vital to have an effective biogas pre-treatment regarding the removal of siloxanes. ? This prevents increased costs related to more frequent maintenances, constant stoppages, reduced engine useful life and decreased system efficiency. Siloxanes Removal Fore more information regarding biogas treatment, please visit us at: http://www.atlasseis.com/en/products-services/biogas/109-biogas-treatment.html R. Alfredo da Silva, Lote 2 – B 2785-656 S. Domingos de Rana Phone: +351 219 258 292 Fax: +351 219 258 297 E-mail: comercial@atlasseis.com www.atlasseis.com Siloxanes What are they? Slide Number 3 What do they do? Siloxanes Reactor Case Study Case Study Considerations Siloxanes Removal Slide Number 10