VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD
Modelling and Simulations of
PtG Plant Start-ups and
Shutdowns
The 9th Eurosim Congress on Modelling and
Simulation
Teemu Sihvonen
Content
Power-to-Gas (PtG) in general
Introduction to Power-to-Gas plant
Modelled PtG plant components
Control logics
Results
Conclusion
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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
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Power-to-Gas plant
Example plant configuration
CO2 capture
Storages
FG
O2
Electrical
grid
Grid connection
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Electrolysis
To gas
grid
Methanation
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Modelled PtG plant components
Power grid connection
Three 3 MW e alkaline electrolysers
Interim gas storages for H2, CO2 and O2
Methanation reactor
Synthetic natural gas (SNG) compression train
Built on Apros® process simulator platform
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Power-to-gas plant in Apros
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Power-to-gas plant in Apros – methanation
reactor
Reactor vessel
Electrical
heater
Concentration
distribution
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Heat transfer to
cooling circuit
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Control logics
Start-up
Initial state
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
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Control logics
Shutdown
Initial state
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
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Results: Methanation reactor
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Results: Electrolysers
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Results: SNG flow to the natural gas grid
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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
*T
0.014
total, U start-up and D shutdown
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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
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Thank you!
Any questions?
NEO-CARBON Energy project is one of the Tekes strategic research openings 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.
http://www.neocarbonenergy.fi