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PROCESS PHASE SEPARATION FOR METHANE ENRICHMENT
using microorganismsabilities for biogas upgrading
Flensburg, 12.09.2013Torsten Stefan, B.Sc. Bioprocess Eng.
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Table of Contents1. Motivation2. Idea and Theory3. Experiments4. Results5. Future aspects6. Summary
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Motivationcomponent formula heat of
combustion [kJ/Nm³]
Typical fraction in biogas [%]
methane CH4 39819 45-70
hydrogensulfide H2S 25336 <0,5
ammonia NH3 17177 <0,001
hydrogen H2 12750 0-1
carbon dioxide CO2 0 25-55
Water H2O 0 0-10
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Separation of CO2 and CH4 mixtures
• Water or polyglycol scrubbers
• Amine scrubbers
• Membrane systems
• Cryogenic processes
Economically feasable in large scale (>1 MWel)
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Biogas processHydrolysis
Acidogenesis
Acetogenesis
Methanogenesis
Monomers
Volatile fatty acids
Formic/acetic acid, CO2, H2
CO2, H2
H2S, NH3, N2
CO2, H2
CO2, CH4
Polymeric molecules
digestate
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Hydrolysis
Pictures:chemienet.info
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Acidogenesis
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Acetogenesis
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Methanogenesis
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Biogas process
Hydrolysis
Acidogenesis
Acetogenesis
Methanogenesis
Monomers
Volatile fatty acids
Formic/acetic acid, CO2, H2
CO2, H2
H2S, NH3, N2
CO2, H2
CO2, CH4
Polymeric molecules
digestate
IntermediateGas composition
methane [%] Carbon dioxide [%]
Formic acid 25 75
Acetic acid 50 50
Propionic acid 58,3 41,7
Butyric acid 62,5 37,5
Valeric acid 65 35
Lactic acid 50 50
Ethanol 75 25
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CO2 solubility in water
physical chemical
3 4 5 6 7 8 90.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
CO2 solubility in water, 38°C, p(CO2)=0,3 bar
pH [1]
chem
. Sol
ubili
ty [m
ol/L
]
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.000
0.005
0.010
0.015
0.020
0.025
CO2 solubility in water, 38°C
p(CO2) [bar]
phy.
Sol
ubili
ty [m
ol/L
]
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Biogas process
Hydrolysis
Acidogenesis
Acetogenesis
Methanogenesis
Monomers
Volatile fatty acids
Formic/acetic acid, CO2, H2
CO2, H2
H2S, NH3, N2
CO2, H2
CO2, CH4
Polymeric molecules
digestate
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Experiments
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Results Substrate: Sugar-Cellulose-Mixture
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Results Substrate: Sour cheese whey
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Results Substrate: Pig-Manure
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Results from LiteratureSubstrate: Soybean Processing Wastewater
Resource: Zhu, G.F. ; Li, J.Z. ; Wu, P. ; Jin, H.Z. ; Wang, Z.: The performance and phase separated characteristics of an anaerobic baffled reactor treating soybean protein processing wastewater. In:Bioresource technology 99 (2008), Nr. 17, S. 8027–8033
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Next steps
• Examine mixtures of manure and souring substrates• Investigate semi-aerobic hydrolysis• Upscaling to 200 L / 2 m³• Proove applicability to STR cascades
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Summary• Phase separation uses natural sequenced biogas process for
methane enrichment• Methane fraction up to 85%• Relatively simple and cheap technology• Enhances energy storage capacity through higher methane
content • Applicable to STR cascades• Problems: slowly hydrolysible substrates and substrates with
high alkalinity in mono-fermentation