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Processing 101: Gas Cleanup

Biogas to RNG Vehicle FuelgJeff Cook

i @ iacrion@acrion.com

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BioGas CompositionBioGas CompositionDigester and LFG

Methane (CH4) 45%- 65%Carbon Dioxide(CO2) 30% -45%Carbon Dioxide(CO2) 30% 45%Nitrogen (N2) 0% - 20%Oxygen (O2) 0% - 2%Oxygen (O2) 0% 2%Hydrogen Sulfide (H2S) from ppm’s to %’sVOC’s (Si Cl F S) 100’s of ppm’sVOC s (Si,Cl,F,S) 100 s of ppm sWater Saturated (2% to 6%)

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These Aren’t Bank Deposits

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CNG (gas @3600psi)

CARBCNG

Pipeline EngineMf.

CH4 88% min # 65

CO2 1-2%CO2 1 2%

Inerts,(N2,CO2)

1.5-4.5% 4% 16,100BTU/lb LHV(N2,CO2) BTU/lb LHV

H2S 16 ppm 4 ppm

H2O Amb-10F 7 lb/MMscfO b 0dew pt

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LNG or LBM

Stored at BP of -260°F (-162°C)Density 3 5 lb/galDensity 3.5 lb/galCO2 50 ppmWater 1 ppmNitrogen 1%Nitrogen 1%

AcrionAcrion TechnologiesLandfill LNG (-259°F)

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Landfill Snow (d i 109°F)Landfill Snow (dry ice, -109°F)

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CO2 and VOC Removal Processes

• Condensation + Freezing of CO2Membranes (CO2)• Membranes (CO2)

• Physical Absorption• Chemical Absorption• Pressure Swing Absorption (PSA)• Pressure Swing Absorption (PSA)• Thermal Swing Absorption (TSA)

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( ’ )

Refrigeration

CH4, CO2 (no VOC’s)

RefrigerationLiquid CO2

(no VOC’s)(no VOC s)

Dry, Compressed Landfill Gas with VOC’swith VOC s

Liquid CO2 and VOC’s

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Membranes

Fast > Slow H2>H2O>CO2>H2S>O2>N2 CH4H2>H2O>CO2>H2S>O2>N2,CH4

• Cellulose Acetate CO2/CH4=10Spiral Wound Sheets

• Polyimide CO2/CH4=20• Polyimide CO2/CH4=20Hollow Fiber,

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Solvent Absorption

• PHYSICALRegeneration by Pressure Reduction,Regeneration by Pressure Reduction, Vacuum and Stripping GasWater, Selexol, Methanol, ,

• CHEMICALRegeneration by Heating + Pressure g y gReductionAmines (MEA)Fouled by Oxygen and LFG Contaminants

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Properties of Physical Solvents

Water Selexol MeOHCO2 Solubility 0 56 3 63 13 5CO2 Solubility 0.56 3.63 13.5

V/V @T(C) 25 25 -25

CO2 CH4 14 3 15 2 19 6CO2:CH4 14.3 15.2 19.6

BP C 100 275 65

Sp Gr 1.0 1.03 0.79

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Solid Adsorption

• PSA (Pressure Swing)Cycle time: 10’s of sec to 10’s ofCycle time: 10’s of sec. to 10’s of min.Vacuum Regeneration

• TSA (Thermal Swing)TSA (Thermal Swing)Cycle time: hoursHigh temperature Regeneration

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Nitrogen Removal

• Address at Source ( e.g. Landfill)PSA (N2 selective adsorbent)• PSA (N2 selective adsorbent)

• Cryogenic

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Conclusion

• All of the processes have been used to produce RNG from biogasto produce RNG from biogas

• RNG Vehicle Fuel: high value product

• Smaller Scale than Pipeline Projects

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LNG Fueling StationLNG Fueling Station