Helium Recovery Plant Maintenance Improvement
Background
The University of Tennessee Institute for Advanced Materials and Manufacturing (IAMM) facility has numerous instruments and systems that require ultra-high vacuum and the
usage of liquid helium.
The total demand for liquid helium within IAMM was so high that they decided to install a Cryomech liquid helium recovery plant which allows them to recycle and reuse already purchased helium.
The system
New helium tanks can cost between $3,000 to $5,000/100L tank at current rates and orders can take weeks to be fulfilled. With existing users at IAMM using up to 100L in one
day, a more sustainable approach to meet their helium demands was required. The Cryomech helium recovery plant was subsequently installed. The recovery plant has a
storage tank capacity of 500L and can produce 50-60L of helium per day. Users are connected to the helium plant directly through network piping allowing the
used helium to be collected at the recovery plant directly. After collecting, the helium is first run through a purification process, then liquified through cooling. Helium liquifies
at 4K (-269°C) making the cleanliness of the helium stream critical and free of impurities. Everything in the stream that is not helium is solid at these temperatures and small, solid fragments, or an accumulation of small fragments, can damage both the regeneration plant and end users’ equipment.
Purification takes place in 2 steps:
- Moisture Trap: The helium stream is run through a sorbent/filter cartage to remove
any remaining water and moisture. - Nitrogen Cold Trap: Purpose is to remove condensable impurities such as O2, N2,
and/or other contaminants that can condense out.
IAMM’s system requires their traps be regenerated, on average, every 2 – 3 months to keep them working properly, specifically the moisture trap. To regenerate the moisture trap, it is first heated/baked to release trapped and absorbed impurities and then fine vacuum is used to both remove the released impurities and to assist in final drying of the trap. System purity is critical, so strong, reliable, and efficient fine vacuum is required. Any remaining impurities will easily re-absorb and re-freeze when the traps are re-installed if not fully removed.
Solution
The recovery plant was utilizing an oil-free scroll pump for the regeneration of their moisture trap. As the moisture trap has a high vapor load, however, the scroll pumps would become saturated causing them to stop effectively pulling vacuum and requiring them to be dried in order to continue processing. Drying was accomplished by opening the gas ballast located on the pump and running the pump. The gas ballast was released, introducing ambient air into the pumping chamber, and the vacuum depth and flow rate was monitored to determine if the pump was dry enough to continue the regeneration process. In total, trap regeneration took 2 weeks to complete on average with the usage of their scroll pump. The scroll pump would saturate frequently and required on-site personnel to continuously monitor the pump keeping them from other tasks. IAMM was introduced to BRANDTECH® and the VACUUBRAND VACUU.PURE® 10C screw pump was discussed. The VACUU.PURE 10C met their vacuum depth and flow rate requirements and unlike scroll pumps, the VACUU.PURE 10C screw pump can handle high vapor loads, even under vacuum. This eliminates the need to stop trap regeneration to dry pump internals. An on-site demo was held, and the scroll pump was subsequently replaced by the VACUU.PURE 10C screw pump.
Results
The VACUU.PURE 10C screw pump successfully handled the vapor load and cut trap regeneration time in half, reducing the process from 2 weeks to 5 days.
Furthermore, as the VACUU.PURE 10C can effectively handle the process vapor load without needing to be dried, continuous monitoring was no longer required
allowing on-site personnel to be better utilized for other projects and demands. The helium regeneration plant is critical to IAMM operations and to keep from
plant downtime they have 2 sets of traps. This allows them to continuously have one set of traps in operation, and one set of traps being regenerated. With the
scroll pump, while one moisture trap was being regenerated, they were forced to operate for 2 weeks without trap redundancy. Were an issue to arise, the plant
would no longer be operational until the off-line traps were fully regenerated. With the time savings realized by the VACUU.PURE 10C, IAMM also increased their
plant redundancy by 1 week, reducing the risk of plant down time.
“With the scroll pump, it was taking about 2 weeks to bake and pump the moist trap. With your pump, we can do it in about 5 days. It really pumps the moist air much better than a scroll pump.”
-Randy McMillan,
Science Instrument Maker III