BIOLOGICAL METHANATION OF HYDROGEN:

A WAY TO INCREASE METHANE YIELD IN

BIOGAS PLANTS

20.10.2015Neocarbon Researcher Days

Tero TynjäläLappeenranta University of Technology

Biological methanation of hydrogen

• Biological methanation – methanogenesis• Microorganisms serve as a methane producing bio-catalyst• The process takes place in aqueuos solutions at

temperatures between 40-70 C• Limiting steps

– Stoichiometry 4moles of H2/mole of CO2

– Mass transfer of hydrogen from gas phase into the liquid.At 60 C CO2 is 25 times more soluble to water than H2

Power needed for hydrogen pumping and reactor stirring

Reaction paths in biogas reactorsAnaerobic digestion model (ADM1)

Batstone et al., WaterScience and Technology, 45 (2002) 65-73.

Hydrogenotrophic methanogenesisCO2 + 4H2 CH4 + 2H2O

Aceticlastic methanogenesisCH3COOH CH4 + CO2

Reaction paths in biogas reactors Anaerobic digestion model (ADM1)

Batstone et al., WaterScience and Technology, 45 (2002) 65-73.

In-situ biological methanation

• Biogas CO2 content up to 50 %• Hydrogenotrophic bacteria needed

for reaction present in biogasreactor possible to feed hydrogen directly into biogas reactor

• Biological limit – washout of themicrobial community due to hydrogen overloadmax H2 feed 4m3

H2/m3CO2

Bensmann et al. Applied Energy 134 (2014) 413 – 425.

In-situ biological methanation

Period (day) 0-10 11-43 44-73 74-96 97-135Gas injection rate(L/Lreactorday)

3 6 12 12 24

Gas retention time (h) 8 4 2 2 1Mixing speed (rpm) 500 500 500 800 800Biogas production rate(L/Lreactorday)

1.4 2.5 5.1 4.9 10.1

CH4 93.5 95.4 89.9 94.2 90.8CO2 4.2 0.7 2.6 1.9 2.2H2 2.3 3.9 7.5 3.9 7

Lab scale performance test of the thermophilic reactor under different operationconditions.

The quality of the upgraded biogas adequate for utilizationas natural gas. Source: Luo & Angelidaki, Biotechnology and Bioengineering (2012) DOI 10.1002/bit.24557.

Ex-situ biological methanation

Figure source: Götz et al. State of the art and perspectives of CO2methanation process concepts for power-to-gas applications, International Gas Union Research Conference, Copenhagen, 2014.

• External reactor for biological methanation increasesflexibility of the system

• Tailored micro-orgamisms concentrated only on hydrogenotrophic methanogenesis and appropriate nutrients can be used

• No disturbances to the base process• Increased Methane formation rate (Fv,CH4/VR)

Biological vs. thermochemical methanationReactor type BM (in-situ) BM (ex-situ) Fixed bed

Catalyst Buffer solution Nutrient solution, buffer solution

Ni-based

GHSV in 1/h FV,gas in/VR 0.05 – 1 56 – 112 2 000 – 5 000T in C 40 - 65 65 300 – 550p in bar 1 4 > 5 – 10Stage of development Lab scale/pilot Lab scale/pilot CommercialH2-conversion % 99 99 > 90Electricity demand in kWh/m3 SNG (16 bar)

1.8 0.4 – 0.8 < 0.4

Tolerance of impurities high high lowMinimum load % ? ~0 ? ~0 ~40

Götz et al. State of the art and perspectives of CO2 methanationprocess concepts for power-to-gas applications, International Gas Union Research Conference, Copenhagen, 2014.

Biogas production in municipal WWTP in Finland

Antti Holopainen, Carbon sources for PtG applications in the Finnish energy system, M.Sc. Thesis, LUT, 2015.

Biogas production in MSW treatment units in Finland

Antti Holopainen, Carbon sources for PtG applications in the Finnish energy system, M.Sc. Thesis, LUT, 2015.

Theoretical biogas potential in Finland –high utilization scenario

• Technically and economically utilizable maximumbiomethane production in Finland is 8.7 TWh (excludinglandfill gas) (Tähti & Rintala, 2010)

• Methane content 60 % 1 Mt of CO2

• Electrolyser power ~1 GW (4% of 23 GW in 100 % RES FIN2050)

• Increased biomethane production potential ~1.5 TWh (2583 PtG operation hours) and ~5 TWh if all CO2 is utilized for biomethane production

Antti Holopainen, Carbon sources for PtG applications in theFinnish energy system, M.Sc. Thesis, LUT, 2015.

Conclusions• Biomethanation offers feasible alternative to thermochemical

methanation at least in small and medium sized reactors+ tolerant to impurities+ integration possibility to biogas reactors+ flexible to load changes– (+) low temperature process, utilization of waste heat difficult– low reaction rate large reactor size– no large scale experienceBiocat project – largest biomethanation demoproject (2/2014 –10/2016, Denmark, Avedøre WWTP) 1 MW electrolyser power, ex-situ methanation http://biocat-project.com/

ReferencesBensmann et al. (2014) Biological methantion of hydrogen within biogas plants: A model-based feasibility study. Applied Energy vol. 134, pp. 413-425.Götz et al. (2014) State of the art and perspectives of CO2 methanationprocess concepts for power-to-gas applications. International Gas Union Research Conference, Copenhagen 2014.Hofstetter (2014) Biocatalytic methanation with methanogenic archaea for power-to-gas energy storage. Biomass for Swiss Energy Future Fonference2014.Holopainen (2015) Carbon sources for PtG applications in the Finnish energysystem, M.Sc. Thesis, LUT, 2015.Luo & Angelidaki (2012) Integrated biogas upgrading and hydrogen utilizationuin an anaerobic reactor containing enriched hydrogenotrophic metghanogenicculture. Biotechonolgy and Bioengineering vol. 109, pp. 2729-2736.Tähti & Rintala (2010) Biometaanin ja –vedyn tuotantopotentiaali Suomessa. Jyväskylän yliopiston bio- ja ympäristötieteiden laitoksen tiedonantoja 90.

NEO-CARBON ENERGY project is one of the Tekes strategic researchopenings and the project is carried out in cooperation with Technical Research

Centre of Finland VTT Ltd, Lappeenranta University of Technology LUT and University of Turku, Finland Futures Research Centre FFRC.