Concepts for efficient hydrogen liquefaction · Hydrogen intercoolers. Hydrogen compressors. MR...
Transcript of Concepts for efficient hydrogen liquefaction · Hydrogen intercoolers. Hydrogen compressors. MR...
Concepts for efficient hydrogen liquefaction
David Berstad, Geir Skaugen and Øivind WilhelmsenThe Role of Large-Scale Hydrogen, Hyper closing seminarBrussels, 11-12 December 2019
Overview of the presentation
• A look at the present and beyond-present state-of-the-art for LH2 generation.
• Dissecting the loss of efficiency – where does it come from?
• How do we realize the potential of LH2generation? – the next steps
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Efficiency of hydrogen liquefier
Power requirement vs exergy efficiency of liquefier
State of the art (5–10 t/d blocks)
Long-term identified potential
In perspective:Full-scale LNG plants: 10 000–20 000 tLNG/dRational (exergy) efficiency: Up to 48 %
Minimum liquefaction work
• Main influence:• Feed pressure
• Key influences:• Final liquid storage pressure
• 1.3 bar (blue dotted)• 1.5 bar (black)• 1.7 bar (red dashed)
• Target para-hydrogen concentration
• Ambient temperature
Conversion of ortho to para-hydrogen
para-hydrogen ortho-hydrogen
Process overview
HX-7
Ejector
Boil-off from storage
LH2 to storage
HX-6
HX-1
HX-2
LPC-1LPC-2HPC-1HPC-2MRC-1 MRC-2
H2 feed
HX-4
HX-3
HX-5
Mixed refrigerant pre-cooling cycle
Hydrogen Claude cycle
Regenerative adsorption and adiabatic ortho-para conversion
• Assumed capacity: 125 t/d• Additionally 7.1 t/d BOG from storage
• Mixed-refrigerant "PRICO" precooling of feed hydrogen to 114 K
• Hydrogen Claude cooling to 30 K• Continuous ortho-para conversion in heat
exchangers between 114 K and 30 K • Expansion and BOG recompression to
1.85 bar with ejector• Condensing and subcooling before
transfer to final LH2 storage• Storage pressure: 1.50 bar
Overall liquefier efficiency
• Two independent ways to calculate the overall efficiency (and to verify the calculations):
• Overall, top-down. Based on exergy flows in and out of the system boundaries
• Detailed, bottom-up. Calculating the exergy destruction in each single process component
• The former method is sufficient for calculating the overall efficiency of the plant
• The latter method gives a full breakdown of all losses and gives directions as to where the improvement potentials lie
HX-7
Ejector
Boil-off from storage
LH2 to storage
HX-6
HX-1
HX-2
LPC-1LPC-2HPC-1HPC-2MRC-1 MRC-2
H2 feed
HX-4
HX-3
HX-5
Mixed refrigerant pre-cooling cycle
Hydrogen Claude cycle
Regenerative adsorption and adiabatic ortho-para conversion
Overall, top-down approach• Only considers exergy streams crossing
the system boundaries• Hydrogen feed flow exergy• BOG flow exergy• LH2 product flow exergy• Compression power• (Turbine power, assumed dissipated)• (Intercooler heat, assumed dissipated)
• Exergy efficiency:= (ELH2 prod – (EH2 feed + EBOG)) / Wcompr
= (14 361 kW / 36 729 kW)= 39.1 %
Boil-off from storage
LH2 to storage
Hydrogen feed
Compressor and pump power
Turbine power
WTURB
WCOMPR
Pre-cooling cycle to 114 K• Single, 5-component refrigerant mixture• Estimated stand-alone exergy efficiency for pre-
cooling to 114 K: 50.75 %• Further efficiency improvements can be made:
• Replacing throttling valve with a liquid expander, or expander in series with throttling valve
• Reduces entropy in expansion process and leads to savings other places in the process
• Dual-mixed refrigerant cycle:• Tailored refrigerant mixtures for two temperature
ranges instead of a single one• Allows even deeper precooling, possibly down to 80 K
HX-1
LPHPC-1HPC-2MRC-1 MRC-2
H2 feed
Mixed refrigerant pre-cooling cycle
Regenerative adsorption and adiabatic ortho-para conversion
Useful exergy output
Irreversibilities, HX-1
Irreversibilities, Compressor stage 1
Irreversibilities, Stage 1 intercoolerIrreversibilities, Throttling valve
Irreversibilities, Stage 2 intercoolerIrreversibilities, Compressor stage 2
Irreversibilities, Gas-Liquid Mixing
Irreversibilities, Pump
Compression power
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Detailed, bottom-up approach Calculating the irreversibility rate (exergy destruction rate) in each component (40+)
Cumulative
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Hydrogenturbines anddissipative
brakes
Cryogenic heatexchangers
Hydrogenintercoolers
Hydrogencompressors
Hydrogenejector
MR intercoolers MRcompressors
Hydrogen/JTliquid turbineand throttling
valve
MR throttling Mixers Adiabatic ortho-para conversion
Throttling tostorage
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Irreversibility [kWh/kg H2 feed]
Verification of top-down and bottom-up approaches
Exergy added to reliquefied BOG
Exergy added to hydrogen feed
Hydrogen turbines and dissipative brakes
Cryogenic heat exchangers
Hydrogen intercoolers
Hydrogen compressors
Hydrogen ejectorMR intercoolersMR compressorsHydrogen/JT liquid turbine and throttling valve
MR throttlingMixers
Adiabatic ortho-para conversion
Throttling to storage
Hydrogen compressors power
MR Compressors power
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Improved efficiency from recovering turbine power • Efficiency of the liquefaction process without power recovery:
• Exergy efficiency: 39.1 %• 7.05 kWh/kg scaled with hydrogen feed rate (125 ton per day)• 6.67 kWh/kg scaled with hydrogen feed rate + boiloff gas reliquefaction rate
• For these numbers, 2769 kW of hydrogen turbine shaft power is assumed to be dissipated• If, e.g. 80 % of this power is recovered with electric generators the improved efficiency
figures will be:• Exergy efficiency: 41.6 %• 6.62 kWh/kg scaled with hydrogen feed rate (125 ton per day)• 6.27 kWh/kg scaled with hydrogen feed rate + boiloff gas reliquefaction rate
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Efficiency of hydrogen liquefier
Power requirement vs exergy efficiency of liquefier
State of the art (5–10 t/d blocks)
Long-term identified potential
Investigated process
Further improvements• High capacity shifts the cost weighting more towards OPEX, hereunder energy cost,
while the impact of CAPEX decreases. This motivates for, and necessitates, more advanced and integrated process designs
• Precooling: Dual mixed refrigerant to also extend the range from 114 down towards 80 K. Will shift power consumption over from hydrogen to MR compression
• Feed expansion from 30 K: Possibility for a liquid expander upstream of the ejector• Subcooling process: Can be two-stage instead of single-stage to improve efficiency• H2 feed pressure: Autothermal reforming as well as some electrolysers can supply
hydrogen at e.g. 30–40 bar. There are several means for taking advantage of this for improving the efficiency
• Turbocompressors and novel cryogenic refrigerant: More easily scalable, boiling at low temperatures.
For more: See D. Berstad, Ø. Wilhelmsen, K. Banasiak. Hydrogen liquefaction. Influence of ejector and expander configuration. Hyper Technical Seminar. Trondheim, 15 May 2019
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Acknowledgements
This publication is based on results from the research project Hyper, performed under the ENERGIX programme. The authors acknowledge the following parties for financial support: Equinor, Shell, Kawasaki Heavy Industries, Linde Kryotechnik, Mitsubishi Corporation, Nel Hydrogen, Gassco and the Research Council of Norway (255107/E20).
Internationally outstanding