1. ESS Cryogenic System Design
Philipp Arnold
Section Leader Cryogenics
6th Internation Workshop on Cryogenic Operations
November 10-12, 2014

2. View of the Southwest in 2025
Max IV – a national research facility, under construction, opens up in 2015
Science City – a new part of town
Lund
( )
Malmö
( )
Copenhagen
( )
 MAX IV
- Linac comprising 43 cryomodules in baseline design, called optimus+ ; contingency space for 57 CMs
Rotating thungsten target with two cold moderators cooled with supercritical 17K hydrogen
Neutron instrument halls, comprising consumers of smaller quantities of LHe and LN2
 ESS

3. Outline System Overview Cryogenic Design Choices
Plant and process arrangement
Cryomodule cooling at 2K
ACCP plant staging
LN2 pre-cooling
Helium storage
Heat recovery
Control system
Procurement and Tender Evaluation

4. (1) ESS Cryogenic System
Pure Helium
Gas Storage 1
Standalone Helium Purifier
Helium Recovery System
Pure Helium
Gas Storage 2
Target Moderator
Cryoplant
Accelerator
Cryoplant
20 m3 LHe Tank
5 m3
LHe Tank
Test & Instrument Cryoplant
Target Distribution System
Test Stand Distribution System
ACCP: 2K, 40K, 270 l/h Liquefaction  special plant, power consumption in MW range, big industrial compressors, sophisticated CC system
TICP: 2K, 40K, 6 l/h Liquefaction  plant well in the standard range
TMCP: 16-19K  very large again, some challenges but not terribly sophisticated process, compared to ACCP
Large and sophisticated cryo-distribution system for all plants and their consumers
LHe Mobile Dewars
Cryogenic Distribution System
LN2 Storage Tanks
Hydrogen Circulation Box
LN2 Mobile Dewars
Instruments & Experiments
Cryomodule Test Stand
Hydrogen Moderator
Cryomodules

5. (2.1) Plant and process arrangement
1 coldbox building, 1 compressor building,
1 plant per job
Highest space and CAPEX savings
Schedule, budgeting and technical requirements
Maintainability
Combination of warm and cold sub-atmospheric compression for ACCP
High flexibility for load adaption
Optimal overall efficiency
Only warm sub-atmospheric compression for TICP
Natural decision for split in three cryoplants due to very different operation ranges and schedules
All plants at one space, start-up control room next door

6. (2.2) Cryomodule cooling at 2K
Production of 2 K helium in 2 K heat exchanger and a sub-sequent Joule-Thomson valve in each of the cryomodule–valve box assemblies
Heat load on CDS only on 4.5K, not 2K helium
independent warm-up / maintenance / cool-down of single cryomodules while the rest of the system is maintained in cold condition
One VBX per CM, all welded jumper connection
Vacuum barrier separating CM vacuum from CDS

7. (2.3) ACCP plant staging
Two sets of flow parts for cold rotating equipment
turbine expanders
cold turbo compressors
Variable frequency drive(s) in the warm LP compressor system
Stepwise upgrading of linac with CMs  ACCP long time well under max load
In case not all margins are needed later adaption possible
Acceptance testing: first with 2nd set of flow parts for full load, then 1st set for stage 1 load

8. WITHOUT 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
Much better plant fit with easy adapting when higher rate needed (switch pre-cooling on)
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
1st CM testing w/ LN2, 2nd Liquefaction for Neutron Instruments w/o LN2
LN2 usage makes most sense for liquefaction, less in refrigeration
LN2 usage also helps for cool-down
Thermal anchor 80K for adsorber beds more important in systems with less turbines

9. (2.5) Helium Storage
Helium inventory in CMs and CDS ~ 2 tons during normal operation
20 m3 LHe tank as second fill
Speed up re-cool-down
Facilitate helium management in transient modes
16 x 60 m3 warm tanks
Store helium when accelerator warm
A little more required for warm parts of ACCP and higher helium inventory during 4.5K standby mode / cool-down 3
Low design pressure of helium vessels in CMs  relief valves only for small flow  for bigger accidents burst disk  high helium loss
LHe tank used also for helium management in off-design operation cases, e.g. parts of the linac have to be warmed up 2 1

10. (2.6) Heat Recovery
25C
Middle temperature Return
37C
Middle temperature Supply
27C
25C
He to fine oil removal
Compr. motor
39C
83C
High temperature Return
32C
27C
Middle temperature Return
He from cold box
90C
85C
Helium compressor
Helium cooler
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
Clean up with rumors from last ICEC – no, we don’t intend to destroy our compressors right after first start-up, crack oil, reduce lifetime etc.
Quite straight-forward approach
Small dT on warm end side of the coolers with PFHX instead tube/shell HX
Closed secondary loop with own pumps
Oil vessel
90C
85C
32C
27C
Oil
cooler

11. (2.7) Control System Functional split between local PLCs and EPICS IOC
Safe operation even in case the EPICS IOC shuts down
ACCP control system is compatible with the other linac control
Advantages of an open control system
Deterministic control loops
Time critical and internal functions
Safety functions
Supervisory controls
High level batch operations
HMI incl. local SCADA
Alarm handling
Data archiving

12. (3) How do we get what we want?
Procurement procedures
open, restricted, negotiated, competitive dialogue
Scope split
clear interfaces (also during different phases of installation)
complex systems (rather one integrator) vs. simple systems
Small yet relevant qualitative part in the tender evaluation
verifiable with proposal
Thorough acceptance testing
Possibly incentive part for consumption
Sincere and transparent procurement process
For complex projects with many unknowns and long duration don’t do open bid but rather a negotiated procedure to find the best solution together with industry
Think thoroughly about where to split scopes – what must be managed for acceptance testing, what should be procured separately (obvious example: tanks)
Try to quantify quality in order to make offers comparable; the cheaper isn’t always the best but the most expansive also not
Bonus malus system to make bidders aware of importance of power consumption, motivate for optimized process but not too optimistic for sales – the requested has to be proven
Most important point; even for in-kind equipment free and unprejudiced competition, allow most market possible with few suppliers
Thank you for your attention