1. Energy efficiency considerations in cryogenics Philipp Arnold Section Leader Cryogenics www.europeanspallationsource.se Proton Driver Efficiency Workshop March 02, 2016

2. Outline 1)Introduction 2)Cryogenic Design Choices – Some theory – Cooling below 4.5K – Thermal shield – Part-load operation – Staging – LN2 pre-cooling 3)Heat Recovery 4)Helium Inventory Management 5)Summary 2

3. (1.1) View of the Southwest in 2025 3 Max IV – a national research facility, under construction, opens up in 2015 Science City – a new part of town Lund (113 500) Malmö (309 000) Copenhagen (1 200 000)  MAX IV  ESS

4. (1.2) ESS Cryogenic System Pure Helium Gas Storage 1 20 m 3 LHe Tank Standalone Helium Purifier Helium Recovery System Pure Helium Gas Storage 2 Accelerator Cryoplant Test & Instrument Cryoplant 5 m 3 LHe Tank Target Moderator Cryoplant LHe Mobile Dewars Test Stand Distribution System Instruments & Experiments LN2 Storage Tanks LN2 Mobile Dewars Cryogenic Distribution System Cryomodules Cryomodule Test Stand Target Distribution System Hydrogen Circulation Box Hydrogen Moderator

5. (1.3) ESS Energy high level goals 5

6. Outline 1)Introduction 2)Cryogenic Design Choices – Some theory – Cooling below 4.5K – Thermal shield – Part-load operation – Staging – LN2 pre-cooling 3)Heat Recovery 4)Helium Inventory Management 5)Summary 6

7. (2.1) Power consumption - Theory – Remember Carnot (theoretical efficiency): 7 Desired cooling temperature Ambient temperature Heat load Electrical input power – Actual consumption: Efficiency of Carnot: depending on Q and T Normalising all heat loads to 4.5K load: ACCP ~ 250 W/W  P/Q = 66 W/W @ 4.5K

8. (2.1) Refrigeration vs. liquefaction 8 Figures from CERN Divisional Report CRYOGENICS FOR PARTICLE ACCELERATORS AND DETECTORS (2002), U. Wagner, Ph. Lebrun, L. Tavian et. al. 4.5K isothermal refrigeration Liquefaction

9. (2.2) Cooling below 4.5K – Cooling below 4.5K means sub-atmospheric pressures need to be created Vacuum pumps (rotary vane + roots) for smaller capacities Cold turbo compressors for bigger capacities – Impact on system reliability and operability Helium purity must be ensured (purification, helium guards) Serial rotating equipment Spares 9

10. (2.2) Cryomodule cooling at 2K 10 Production of 2 K helium in 2-4 K heat exchanger and a sub-sequent JT valve in each of the cryomodule–valve box assemblies  Heat load on CDS only on 4.5K, not 2K level

11. (2.3) Thermal shield Thermal shield pressures and temperatures depend not on ideal COP w.r.t. Carnot but on entire cryogenic system Temperature level where appropriate expansion stage is Shield Pressure = HP of cryoplant Temperature spread = expansion turbine temperature step 11 TypeTempMax. loadExergy CMs and CDS2 – 4 K3060 W79% Thermal shields33 – 53 K11 380 W11% Coupler cooling4.5 – 300 K9.0 g/s10% 300 K 115 K 70 K 53 K 33 K 24 K 9 K 6 K 4.5 K

12. (2.4) Part load operation 12

13. (2.5) Cryoplant staging 13 Two sets of flow parts for cold rotating equipment -turbine expanders -cold turbo compressors Variable frequency drives for SP and LP compressors

14. (2.6) LN2 pre-cooling TICP WITH LN2 PRE-COOLING -CM testing: “constant level liquefaction w/o internal freeze- out purification” -Liquefaction for LHe consumers: “rising level liquefaction w/ internal purification” -  Turbo-expanders can be optimized to perform efficiently in both operation modes -Much better plant fit with easy adapting when higher rate needed (switch pre-cooling on) 14 ACCP WITHOUT LN2 PRE-COOLING -~80% of the load is at 2K  with cold compression translated to 4-20K refrigeration -~20 tons of cold mass max do not impose tough cool-down requirements -No substantial CAPEX impact -Downsides of LN2 usage like dependency on regular supply and increased traffic at ESS more severe

15. Outline 1)Introduction 2)Cryogenic Design Choices – Some theory – Cooling below 4.5K – Thermal shield – Part-load operation – Staging – LN2 pre-cooling 3)Heat Recovery 4)Helium Inventory Management 5)Summary 15

16. (3.1) Oil flooded screw compressors Adiabatic compression 16 ESS high pressure stage: Suction pressure: 4 bar(a) Discharge pressure: 20.5 bar(a) NOT FEASIBLE! Quasi-isothermal compression by oil injection T>300°C for ESS HP stage discharge In fact: inlet ~40°C, outlet ~80°C

17. (3.2) Heat from screw compressors 17 ESS high pressure stage: Helium flow: 0.735 kg/s Oil flow: 19.285 kg/s Electrical consumption: 1.45 MW Heat into oil cooler: 1.13 MW

18. (3.3) Heat Recovery 18 No elevated oil or helium temperatures out of compressor suppliers specs Dedicated cooling water circuit for cryoplant (quality constraints of available cooling water in the building) Slow temperature control on cooling water side, fast temperature control on oil side Cooler design state of the art e.g. for Kaeser compressors Cooling function has priority over heat recovery return Compr. motor Middle temperature Return Middle temperature Supply Oil vessel Helium compressor Helium cooler Oil cooler He to fine oil removal He from cold box High temperature Return Middle temperature Return 27° C 30°C 39°C 71°C 39°C 83°C 49°C 74°C 40°C 69° C 37°C

19. Outline 1)Introduction 2)Cryogenic Design Choices – Some theory – Cooling below 4.5K – Thermal shield – Part-load operation – Staging – LN2 pre-cooling 3)Heat Recovery 4)Helium Inventory Management 5)Summary 19

20. (4) Helium Inventory Management 20 (1)Helium inventory in CMs and CDS ~ 2 tons during normal operation (2)20 m 3 LHe tank as second fill – Another 2 tons when 80% full – Facilitate helium management in transient modes (3)Battery of warm storage tanks Try to Never warm up the entire system Leave as much helium liquid as possible (less purification) Recover helium as much as possible Guard sub-atmospheric systems (less purification)

21. Outline 1)Introduction 2)Cryogenic Design Choices – Some theory – Cooling below 4.5K – Thermal shield – Part-load operation – Staging – LN2 pre-cooling 3)Heat Recovery 4)Helium Inventory Management 5)Summary 21

22. (5.1) Summary Conceptual phase Cryogenics is expensive and energy demanding Select carefully the operation temperature  by far the biggest impact Keep in mind that a large load portion is static  always substantial energy consumption regardless of beam Talk early to cryoplant vendors to define best technology (cold compression, LN2, 2K heat exchanger position) Consider heat recovery if clients are around 22

23. (5.2) Summary Purchasing the cryoplant Consider OPEX over several years Consider OPEX particularly for turn-down scenarios Define shield conditions w.r.t. overall efficiency Think about flexibility (VFDs, staging) Specify exactly LN2 and heat recovery set-up Consumption measurement and penalisation Acceptance tests of turn-down automation 23

24. (5.3) Summary Start up and operations Plan long acceptance testing Focus on stable controls, otherwise turn-down will be controlled with heaters for stability reasons Spend long time on initial drying and cleaning Try to adapt the plant to actual loads as good as possible (look for pressure drops, bypass valves, temperature mixing) Watch helium inventory closely (leaks) 24