WP1: Green gas production and gas conditioning

Nabin AryalPostDocAarhus University Danish Gas Technology Center

WP1 Gas Conditioning and grid operation

• Analyze existing and emerging technologies for biogas upgrading and syngas methanation.

• Focus is on development and characterization of gas supply and emerging gas technologies.

• New and unconventional sources such as syngas are investigated, especially in relation tohow these can best be conditioned for the existing gas infrastructure, addressing challengesas cost efficient methanation and upgrading to natural gas quality.

Fig:- Work Packages of FutureGas Project

FutureGas (WP1)-Task

Biogas Plant

Biogas

40–60% CH4

60–40% CO2

Upgrading

CH4

CO2 CO2 + 4H2 → CH4 + 2H2O X

CH4

Figure :- Biogas production process

Microbial Biogas upgrading

Fig:- Microbial Biogas upgrading strategies (Angelidaki et al., 2018) Fig:- Bioelectrochemical system for biogas upgrading (Aryal N et al., 2018)

• Microbial Biogas upgrading can be done either in-situ, ex-situ or hybrid • In-situ biogas upgrading allows efficiently use of anaerobic digester avoiding extra bioreactor for post gas treatment.• Bio-electrochemical biogas upgrading approaches utilize CO2 and electricity for methane production

H2 mediated biomethanation from lab scale to full scale

Upgraded biogas 90 % CH4

10 % CO2

Lab scale reactor Development of technologies to inject H2 in full-scale

+H2

Upscaling Lab scale reactor

Fig:- Biogas upgrading technology development

Bioelectrochemical System (Electromethanogenesis)

Fig:- Bioelectrochemical System (Aryal N. et al., 2017)

CnHn

• Bioelectrochemical system (BES) is an emerging technology for a clean and efficient production of biochemicals and biofuels from CO2, using energy derived from renewable sources

• Electromethanogens can either directly accept electron from electrodes or via H2 to produce CH4

• It is a type of artificial photosynthesis• Further carbon chain elongation or product selection is possible.

Fig:-Lab scale prototype

PEM

Reactor configuration

Fig:- Lab scale reactor Fig:- Granular electrode packed system

Methane production rate

• Continuous methane production in BES was successfully demonstrated • Average methane production rate was achieved 3.6 mL per day. (36 LCH4 d

-1m-3)

• 3.7 V cell voltage was maintained

A B

Fig:- A) Biofilm of electromethanogens (Geppert et al., 2019) B) VFA production

Current draw without microbes

• 3.7 V cell voltage was maintained• Methane production was not observed • Continuous hydrogen production was decrease with time• VFA was not detected • Either Electromethanogens or Hydrogenotrophioc methanogens was involved for gas production

Green gas production from biomass• Gasification and Anaerobic digestion could be coupled for biomethane production • Attractive alternative to use waste materials • Biological methanation from syngas via biomass based fluidized bed gasifier reactor and AD• Hydrogen mediated in-situ methane upgrading from syngas

Electrolyzer

Anode EM

H+

e- e-

H2

O

2H+ + O2

Cathode

V

2H+

H2

H2

Syngas

CH4 , CO, CO2, H2

Fluidized bed gasifier reactor Bioreactor

H2(g)CH4(g)CO(g) CO2(g)

CH4

H2 ??????????

Fig:- Gasification coupled with Anaerobic digestion

Straw gasification

• Straw gasification could be best alternatives to producethe syngas

• The Danish agriculture crop residues is dominated bywheat and barley straw

• There are more than 1300 straw utilizing facilities inDenmark for heat production.

• Unfortunately, operating heat recovery utilities are notefficient and sustainable

• However, straw gasification could be problematic due tohigh alkali and which perhaps causes slagging, fouling andagglomeration.

Fig:- Straw burning

Allothermal gasification

• 1.5 kw Laboratory scale allothermal gasifierwas used

• The gasification was performed selecting750 oC, 800 oC, 850 oC, 900 oC and 950 oCallothermal temperature

• Commercially available straw and woodpellet was used with 8 mm diameter

• The olivine (Mg²⁺, Fe²⁺)₂SiO₄ catalysis wasused as a bed material for supporting andenhancement of gasification.

Fig:- Laboratory scale allothermal gasifier (DGC)

Syngas compositionA B

C D

Fig: Syngas composition A) 750 oC, B) 800 oC C) 850 oC, D) 900 oC), & 950 oC

Key Points• The CO2 content was relatively higher in lower temperature.• The syngas composition of CO (9.38%), H2(3.42%) CO2

(69.96%) & CH4 (4.34%) produced from straw feedstock at750 oC.

• Straw gasification was problematic in higher temperature

E

Fig:- A) Straw pellet B) agglomeration of bed materials

Biological methantion

Fig: Syngas from gasifier Fig: Biological methantion

• The biological methane enrichment was done in 100 mL serum bottle • Mesophilic sludge from manure based biogas plant was used • Methane enrichment was periodically measure.

Methane Production from syngas

Microbial group Biocatalytic reaction ΔGo

(kJ/mol)

Carboxydotrophic hydrogenogens CO + H2O → CO2 + H2 − 20

Carboxydotrophic methanogens 4CO + 2H2O → 3CO2 + CH4 − 210.9

Carboxydotrophic acetogens 4CO + 2H2O → CH3COOH +

2CO2

− 165.4

Hydrogenotrophic methanogens CO2 + 4H2 → CH4 + 2H2O − 135.6

Homoacetogens 2CO2 + 4H2 → CH3COOH +

2H2O

− 104.6

Acetoclastic methanogens CH3COOH → CH4 + CO2 − 31

Table:- Possible pathways for methane formation

Table: Methane production rate from syngas

Gas composition

Rate of comsumption and removal

(mmol/day)

Hydrogen -0,168

Methane 0,0456

Carbon monoxide -0,1077

Carbon dioxide -0,179

Carbon dioxide -0,354

Carbon monoxide 0,045

Methane -0,283

Hydrogen injection

A

B

Fig:- Syngas methanation A) Rate & B) Hydrogen Injection

Trickle bed reactor configuration

Fig:- Trickle bed carrier material (Gylling J. 2018 Master thesis) Fig:- Lab scale reactor configuration

• Trickle-bed reactors are a viable option for overcoming mass transfer limitation for syngas upgrading

Methane production

Fig:- Rate of gas consumption

Gas compositionRate of consumption and removal

(mmol/day)

Hydrogen -2,54

Methane 340,85

Carbon monoxide -40,42

Carbon dioxide -644,58

Table:- Methane production rate

Key Points• The syngas composition of CO2 (50%), CH4(7%), CO(20%), and H2(23%) was used for methanation• In situ biomethanation by H2 injection in trickle bed reactor was optimized• Optimization of mass transfer and Carboxytrophic methanogens activities is necessary• Methane production rate 415 mmol/d/L was achieved

Biogas Upgrading • It has reported 25 biogas upgrading facilities available in Denmark, including 9-water

scrubbers, 8 -amine-based, and 8 -membrane-based

• Legislation demand biogas upgrading

Fig:- Wobbe Index of different gases (Aryal & Kvist 2018)Fig:- Wobbe Index from different sources (ENERGYNET)

Alternative of Biogas Injection into the Grid

Fig:- Aryal and Kvist, ChemEngineering 2018Fig:- Danish Gas grid (DGC)

Biogas Introduction into gas grid

Fig:- Gas consumption

Food industry

Yearly gas consumption in Million (m3/hr.)

Compression cost in Million (€)#

Upgrading cost in Million (€)&

Total cost (€) in Million

1 26.7 1.4 2.083.48

2 17.1 0.8 1.332.13

3 12.4 0.6 0.961.56

4 9.8 0.5 0.76 1.26

#cost is calculated based on € 0.05/m3 &cost is calculated based on € 0.078 /m3 for water scrubber (IRENA 2018)

Table :- Cost Analysis

Food industries might be best selection,however further research need to perform onappliances

Is biogas plant emission friendly?

16%

71.7%

21%

Methane loss from biogas plants and its environmental and economic consequences have been underlined, but not thoroughly researched

Methane emission control

Fig:- Emission control applying regenerative thermal oxidizerFig:- Methane emission (Kvist & Aryal 2019)

• Process related biogas emission was reported• Amine based upgrading has least emission compared to water scrubber • RTO significantly reduces the CH4 concentration from 6900 ppm to an average of 13 ppm• The cost of an RTO was 0.0067 € m-3 biogas, that is may be economical compared to the consequential penalties from

environmental regulation authorities (Kvist & Aryal 2019)

Acknowledgement

Torben KvistNiels Bjarne Rasmussen

Michael VW KofoedLars DM Ottosen

Mikkel OddeCecilie Bøgeholdt Petersen