PROCESS PHASE SEPARATION FOR METHANE ENRICHMENT
using microorganismsabilities for biogas upgrading
Flensburg, 12.09.2013Torsten Stefan, B.Sc. Bioprocess Eng.
2
Table of Contents1. Motivation2. Idea and Theory3. Experiments4. Results5. Future aspects6. Summary
3
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
4
Separation of CO2 and CH4 mixtures
• Water or polyglycol scrubbers
• Amine scrubbers
• Membrane systems
• Cryogenic processes
Economically feasable in large scale (>1 MWel)
5
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
6
Hydrolysis
Pictures:chemienet.info
7
Acidogenesis
8
Acetogenesis
9
Methanogenesis
10
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
11
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
]
12
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
13
Experiments
14
Results Substrate: Sugar-Cellulose-Mixture
15
Results Substrate: Sour cheese whey
16
Results Substrate: Pig-Manure
17
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
18
Next steps
• Examine mixtures of manure and souring substrates• Investigate semi-aerobic hydrolysis• Upscaling to 200 L / 2 m³• Proove applicability to STR cascades
19
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
