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