1. Mathew C. Wright January 26, 2009
Improving Helium Refrigeration Plant Reliability at Jefferson Laboratory
Mathew C. Wright
January 26, 2009

2. Definitions Jefferson Lab Cryo Operations Three Cryo Plants
2.1K (Accelerator)
(Experimental Halls)
4.5K (Test Facility)
24/7/365 Continuous unattended operations
2K operations started in 1994
Typical major maintenance cycle every 5 years
Only once LINAC has been warmed up
Hurricane Isabel

3. Definitions Down-time
Any time loss to scheduled beam operations due to the cryogenics system and back to data collecting
Accounts for the restoration of the entire machine
The amount of time to recover from an outage is exponential to the amount of time that the cryogenic plant is down
Cryo down-time resulting in stopped physics
1999 through 2008 ~ 1.57% average down time
November 2008 major down time of ~60 hours
2008 down time ~ 2.6%
Main compressor failure without redundancy

4. History Original Conditions 4 GeV (235 g/s at 2K – design with margin)
Forced cryo plant to run at max design point
No redundant equipment (compressors or turbines)
Improvements made
Implemented Ganni cycle
Replaced the old 2K Cold Box with Jefferson Lab design (1998)
Added the Stand-by Refrigerator (SBR)
Present conditions
6 GeV max load (235 g/s)
4 GeV turn down (190 g/s)

5. Major Contributions to Down Time
Utilities Failures
Electrical Power
Power spikes
Phase imbalance
Cooling Water
Cooling tower accumulates debris
Pumping system failures
Instrument (control) air
Faulty / failure of pneumatic control valves due to moisture contamination

6. Major Contributions to Down Time
Control systems (CAMAC)
Old technology, uses lots of power, generates lots of heat (more heat, higher failure rates).
Laboratory grade hardware, not designed for industrial environment.
Highest failure rates in control system; electric valve cards, crate controllers, power supplies.
Replacement components are getting harder to find.
Aging system
Control cards
Carbon purification systems
Compressors
Carbon Steel components
Vacuum Jackets
Water Piping

7. Contamination Dirty Sources (mostly Air & H2O)
Helium introduced into the system is always scrubbed
Clean gas from vendors is not always clean
Contamination can be found in Liquid dewars
Liquid dewars have been used as a source of clean helium
Loads from different users
Magnets
Cryogenic targets (sometimes sub-atmospheric)
Sub-atmospheric cryomodules

8. Contamination Oil carryover Improperly sized oil coalescers
10 cm/s max velocity
Saturated carbon resulting in oil breakthrough to the cold box
Oil coats heat exchangers and reduces effectiveness
Can result in months to years of down time

9. System Cycle Ganni cycle reduces how hard the system has to run
Invalidates the traditional philosophy that the design (‘TS’) condition is the optimal operating condition for as-built hardware and load
The traditional philosophy
Controls to the design T-s condition by adding heat, throttling valves and/or bypass of flow to maintain a fixed (design) load.
Utilizes a floating pressure system
A constant pressure ratio system that maintains a constant efficiency for a variable load

10. Redundancy Up to 5.5 GeV using the Ganni cycle
SBR 2nd stage compressor (1/2 size of main compressor) can be used instead of one of the three main 2nd stage compressors
The SBR compressor can be run while maintenance on one of the main compressors is performed
Only two 1st stage compressors are required compared to the three needed to reach the operating condition
The SBR can be used to keep 4K liquid helium in the LINACs during scheduled physics down-time
Opportunity to replace charcoal in oil removal system of main machine and any other maintenance requiring the main machine to be down

11. Preventative Maintenance (PM)
Do not over maintain
The longer the process piping is open, the higher the probability of contaminating the system
Oil has a high affinity to absorb moisture from surrounding atmosphere
Mistakes can be made when performing PM
Jefferson Lab runs compressors for 74,000 hours between maintenance
Vendor recommends 25,000 hours on helium compressors

12. Conclusion To minimize down-time and keep reliability up
Keep system free of contamination
Do not over drive the system
Have redundant systems for backup
Do not over maintain the system
Pay your cryogenics operators more
Attention
Money
Compliments