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HomeMy WebLinkAboutPPP Biogas scrubbing Biogas scrubbing: A New Alternative oJaty SPNl Tq 71 co 9 Rob Thompson r Director of Engineering W; THE ENyyP 1 1 • 1 1 , The Opportunity Digester Gas Contains Impurities • 65% Methane A • 34% Carbon Dioxide • 1 % Trace Contaminants , — Hydrogen Sulfide ' (AQMD Limits) — Siloxane (Poisons Catalyst, Coats Engine and Steam Systems, Causes Engine Wear) Current Practice Activated Carbon Scrubbing Add iron ( FeC13) to digesters to prevent hydrogen sulfide ( H2S) formation . — 3000 ppm (uncontrolled) 30 ppm — Current iron cost: $4 million/year (APT & H2S control) — Iron adds to biosolids leaving treatment plant Alternatives, Water Scrubbing A New Alter Clean Gas possible Benefits: No moving parts Water/Gas Plant water Separation Inexpensive p Venturi Vessel Vessel w chemicals °p °o ° No new Plant O o Water Better quality methane gas Digester Gas • Water with ® Input Dissolved Impurities compound 4 CH4 (methane) 300 HZS (hydrogen sulfide) COZ (carbon dioxide) 256 M fts gas per 1000 gal water 1 � A j Pilot Tests Test Sites : Clean Gas Discharge �nrlll • Carollo: 4 Texas locations • H2S removal only Degas Valves • OCSD • H2S and Siloxanes ,i. .i Gasmater Separator Blogas Inlet OCSD Results: / 1-12S (hydrogen sulfide) 100% Drain toAerati=nBasins with H,S and CO, Siloxanes 97% CO2 (carbon dioxide) 94% CH4 (methane) 0 - 10% n Orange County Sanitationfor you. Benefits of Scrubbing • Option to eliminate iron for digester H2S control • Extend activated carbon bed life when used as a guard or polishing step • Possibly lower cost for advanced primary treatment (e.g. , substitute alum for iron) • Chemical contract negotiation options (alternative to ferric chloride) Orange County SanitationDistrict Phase 2 Evaluation • Engineering study of full-scale system at OCSD • Design and cost of large capacity scrubbers • Effects on plant water supply and treatment • Engine performance with fuel composition change • Waste stream treatment options/impacts • Site Study n � • ' 1 1 � 1 1