1. Modelling and Simulations of PtG Plant Start-ups and Shutdowns
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The 9th Eurosim Congress on Modelling and Simulation Teemu Sihvonen

2. Content Power-to-Gas (PtG) in general
Introduction to Power-to-Gas plant
Modelled PtG plant components
Control logics
Results
Conclusion

3. Power-to-Gas in general
Convert intermittent renewable electricity to gas
Hydrogen or methane (Synthetic Natural Gas), with high energy density
Re-convert to electricity
Lately also talk about Power-to-X, with X = NH3, MeOH, fuels, …
Evolving from energy storage to a sector coupling technology

4. Power-to-Gas plant Example plant configuration FG CO2 capture Storages
Electrical grid O2
To gas
grid
Grid connection
Electrolysis
Methanation

5. Modelled PtG plant components
Power grid connection
Three 3 MWe alkaline electrolysers
Interim gas storages for H2, CO2 and O2
Methanation reactor
Synthetic natural gas (SNG) compression train
Built on Apros® process simulator platform

6. Power-to-gas plant in Apros

7. Power-to-gas plant in Apros – methanation reactor
Reactor vessel
Electrical
heater
Concentration distribution
Heat transfer to cooling circuit

8. Control logics Start-up Initial state Routine
Methanation reactor is at room temperature and filled with H2
Alkaline electrolysers are at room temperature
Interim gas storage tanks are full of gas
Routine
Methanation reactor heated up to 275°C with electric heaters
H2 and CO2 feed to the reactor opens, recirculation and compression to the gas grid starts
Steam cooling starts when reactor highest temperature reaches 550°C
Power feed to the alkaline electrolysers starts when methanation reactor is at 230°C, which allows the electrolysers to heat up and start H2 production in time

9. Control logics Shutdown Initial state Routine
Methanation reactor at steady state with 0.06 kg/s of SNG production
Alkaline electrolysers operating with alternating power between 20 – 100% based on power grid frequency
Interim H2 storage has some level of gas based on previous power grid frequency
Routine
CO2 feed to the methantion stops, stopping the reactions
Recirculation and cooling steam flow stops
Reactor is filled with H2, leaving gasmixture is compressed to the gas grid
Electrolysers are operating until the interim H2 storage is full

10. Results: Methanation reactor

11. Results: Electrolysers

12. Results: SNG flow to the natural gas grid

13. Results
Higher CO2 and H2 concentrations flow to the natural gas grid during start-up and shutdown
Total masses and moles of gas components to the natural gas grid during the 10 hour simulation
Also specified amounts for CO2 and H2 during start-up and shutdown
CH4 CO
CO2 H2
H2O
Mass, kgT / kgU / kgD*
650.0
0.004
20.0 / 7.8 / 1.07
16.8 / 5.94 / 9.18
0.25
MoleT / moleU / moleD
40.5
0.0001
0.45 / 0.18 / 0.02
8.3 / 2.95 / 4.55
0.014
*T total, U start-up and D shutdown

14. Conclusion
Initial control logics for PtG plant star-up and shutdown has been presented
Simulations revealed needs in
Modelling
Alkaline electrolyser model need N2 purge dynamics
Effect of temperature in the alkaline electrolyser during start-up
Low guality SNG during star-up and shutdown
Need for extra volume to facilitate recycle?
Control logics
Compression to the natural gas grid reacts too fast causing temperature and pressure gradients in the reactor

15. Thank you!
Any questions?