Methane from off gas from geothermal power plants

Guðmundur Gunnarsson

Georg Geothermal Workshop 2016Grand Hotel – Reykjavik

October 25, 2016Orkusjóður

Methane from CO2 and H2

• CO2 + 4H2 → CH4 + 2H2O ΔH = - 165 kJ/mol, ΔG = - 118 kJ/mol• Reaction shifted to right at low temperature• Large activation energy - catalysts needed

• Nickel based catalysts for operation at 200 – 300°C – catalytic methanation• Methanogenic archaea evolved 3,8 billion years ago to utilize this reaction – microbial methanation

• Geothermal gas always contains some CO2 (50 – 99%)• H2 content can be up 50%• H2 can be added to adjust H2/CO2 = 4

• Geothermal gas contains other less desirable components• H2S, N2 and O2

• How can we remove them? • Methane for cars should contain > 95% methane

• < 2 – 3 % N2 and no H2S and O2

Vol%H2S 1 - 30N2 1 – 10O2 0 - 3CH4 0 – 1

Microbial methanation• Can tolerate at least up to 6000 ppm H2S in gas

• Catalytic methanation requires < 0,1 ppm• Low temperature (65°C)• Very flexible

• Gas supply can be decreased or increased very rapidly• Can be operated at elevated pressure

• Very high yield – no side reactions• 98.5 % of CO2 to CH4

• Gas with 98% CH4 and 2% H2 obtained

• Being developed by several companies• Electrochaea, Microb Energy, Krajete…..

Electrochaeas pilot methanation reactorCapacity 1.2 million Nm3 of CH4 per year

Uses microorganism from a geothermal areaMethanothermobacter thermautotrophicusStrain Hveragerði (DSM 3590)

h = 9 md = 0.7 m

p = 9 bar

Sulfix process for removal of H2S from geothermal gas

5

Washing column

(vol%)H2S 3.3%CO2 51.5%H2 36.1%N2 6.6%O2 1.1%CH4 1.0%H2O 0.3%Sum 100%

Gas from Sulfix Simulations

Condensate

Cooling water

Cooling water

Water with H2S and CO2 to injection

7 000 – 8 000 t/year of H2S10 000 – 11 000 t/year of CO2

H2 rich gas to CH4 synthesis

15 °C

6 bar

Recent experience H2S 0.5%

Now: 60% of all H2S and 30% of all CO2 injected

Treatment of gas before methanation

• H2S content too high (3-4 %)• Remove with microbial

desulphurisation

• Too much N2 (7%) and O2 (1%)• Decrease N2 and O2 content with

membranes• Part of the CO2 lost as well as 10%

of H2

(vol%)H2S 0.01%CO2 48.4%H2 50.0%N2 1.0%O2 0.2%CH4 0.2%H2O 0.2%Sum 100%

From Sulfix II

Membrane

N2 rich gas

60°C

AirSlurry with S

Bioreactor

Gas from membrane

H2/CO2 = 1.0Increase from 0.7

Hydrogen addition and methane production• Add H2 from water

electrolysis• Adjust H2/CO2 to 4• 3.7 MW needed for

electrolysis• Gas to reactor

• 9 bar • Reactor cooled

• Exothermic reaction• Final purification

• Drying• H2S removal• CO2 removal

Reactor60 – 65°C

Methane > 95%

Purification

H2 from electrolysis

Gas from membranes

(vol%)H2S 0.00%CO2 0.00%H2 1.9%N2 2.0%O2 0.0%CH4 96.1%H2O 0.0%Sum 100%

Fulfills standards for vehicle gas

What about economics?

• Hydrogen production• 754 Nm3/h of H2

• 3.7 MW for electrolysis• Two 2.2 MW electrolyser

• Electric energy consumption• 4.9 KWh/Nm3

• With compression to 15 bar• Electric energy price 34,6 €/MWh

• Transmission cost included• Manufacturing cost 0.25 €/Nm3

• 68% of cost electricity cost

• Methane production, with desulphurization and membranes

• 263 Nm3/h of methane• 2.1 million Nm3/year

• Manufacturing cost 1.25 €/Nm3

• Hydrogen cost 58 %

• Higher than the price of biodiesel in Europe

• Can the cost of hydrogen be decreased?• Can lower price electricity be obtained

Low price electricity from the balancing energy market

• Balancing energy is used by Landsnet to balance production and consumption of electric power

• Electricity production = electricity consumption to keep frequency (f) constant at 60 Hz

• If el. production > el. consumption then f > 60 Hz

• Decrease el. production or increase el. consumption• Down-regulation needed

• Water electrolyser can increase el. consumption and buy balancing energy at low price from Landsnet

Price of balancing energy on Landsnet´s market Nov. 2015 – Oct. 2016

0 2000 4000 6000 80000

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Hour of the year

Pric

e (IS

K/M

Wh)

Up-regulation4253 h 7131 ISK/MWh

Down-regulation4507 h956 ISK/MWh

Hydrogen production with balancing energy

• Water electrolyser participating in Landsnet´s balancing energy market

• Can buy low price electricity for 4000 – 5000 h/year (down regulation)

• Hydrogen manufacturing cost can be decreased by 30 – 50%

• Could decrease methane cost

• Water electrolysers

• Alkaline: Can increase load from 20% to 100% in 10 minutes

• PEM electrolysers: Can increase load from 1% to 100% in seconds

How can methane´s production cost be lowered?

• Electricity for hydrogen production is obtained from balancing energy market

• Takes advantage of the large flexibility of microbial methanation• Hydrogen storage capacity probably beneficial

• What is the optimum H2 storage capacity?

• Gas with low content of H2S and N2 and O2 should be used• Eliminate leakage of air into off gas in design of power plants• High H2 content beneficial

• Increase capacity• Methane production technology that can use gas with 1 – 4% H2S

• Under development

Thank you