Monday, April 23, 2012

He and LN2 Storage

LHe is made from high purity helium gas. The picture shows the trailer of tubes for the storage of helium gas. Immediately after a He gas delivery, these tubes are all filled with pure He gas. At various times after a delivery, some of these tubes may be filled with impure gas. A large part of gas management is shifting different regions of storage real estate between pure and impure storage.

In the foreground is the large dewar for liquid nitrogen.  LN2 is required for not only the He liquefier, but also for the SEM EDS detector, various deposition systems, and for the Titan TEM in the Biological Imaging Resource next door.

Helium Recovery Part 4: Compression

Gas recovered in the recovery bag will eventually trip a sensor causing the recovery compressor to pump the gas from the bag and store it in different tubes. The destination of this gas can be changed depending upon the immediate gas management needs.

Friday, March 23, 2012

Helium Recovery Part 3: Gas Collection

Helium recovered from different locations is temporarily stored in a large bag. This bag is a collapsible vinyl material that is not permeable to helium. As this bag fills, it eventually trips a photo-detector which triggers a recovery compressor to empty the bag into high pressure storage tubes. This impure gas can then be reconditioned through a gas purifier or through the purifier of the liquefier itself. The serpentine copper line allows cold gas to warm before entering the bag. In the case of a magnet quench or the venting of a cold dewar's vacuum jacket a considerable volume of cold gas can be returned for recovery. This serpentine line protects the bag in the event of these failures.

Helium Recovery Part 2: Metering

Helium recovered from the different labs are metered. This allows the assessment of efficiency of both He recovery as well as LHe transfer. It is also a useful diagnostic in determining problems in individual research stations. High He boil-off rates can indicate soft vacuum jackets in dewars and cryostats or malfunctioning gas vapor heaters, LHe level meters and magnet persistence switches. The data is digitally encoded allowing this data to be accessed through a LabView program.

Helium Recovery Part 1: Lab Recovery

Helium recovery is key to the efficiency of the CMMP LHe facility. We are able to recover up to 80% of He boil-off using appropriately designed recovery strategies. Pictured is a recovery manifold for a QD MPMS SQUID magnetometer. Multiple recovery lines allow recovery of the annulus gas and transport gas, and extra ports are available for recovery from the LHe dewar itself and the LHe transfer line.

Lab recovery varies from application to application. He is recoverable from the Keen, Collins and Dittmer buildings on FSU campus.

Herd of Dewars

100 liter LHe dewars on recovery. Some have been returned cold to be refilled. Others are filled and waiting to be delivered or taken by users. Recovery manifold is visible on the back wall. Small notebooks attached to each dewar log LHe level when delivered as well as when returned.

500 Liter Dewar

The output of the liquifier enters a 500 liter dewar through a vacuum jacketed remote delivery tube or RDT. Boil-off is recovered and LHe is transferred to smaller 100 liter dewars for delivery to different facilities. Differential changes in dewar weight-- the red LED's of the scale can be see in the top right of the image-- allow for the precise transfer and delivery of LHe.