HomeMy WebLinkAboutPPP Biogas scrubbing Biogas scrubbing:
A New Alternative
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Rob Thompson
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Director of Engineering
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THE ENyyP
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The Opportunity
Digester Gas Contains Impurities
• 65% Methane
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• 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
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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%
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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
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