Helium Recovery System
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General
Cryomech has developed a Helium Recovery System. The HRS is a complete system designed to recover the boil-off directly from liquid Helium cryostats and store it at atmospheric pressure. Then compress the Helium to a higher pressure for more efficient storage. And finally, purify the Helium so that it might be liquefied again.
The efficient use of liquid Helium requires the user to recover it. Recent price increases and reduced supply has interfered with research. In most cases liquefaction necessitates very pure, >99.95% pure, Helium or the Helium Liquefier will freeze up.
Operation:
Atmospheric recovery
The boil-off from the liquid Helium cryostat must be connected directly to an atmospheric recovery bag through a piping system. To reach the lowest temperature possible, 4.2K, the cryostat must be allowed to evaporate at the lowest possible pressure, in this case the atmospheric pressure. The bags used in the HRS are especially made to minimize the permeability for both H2O and Air, the most prevalent contaminants to the Helium. The standard bag Cryomech offers will store 8.5 cubic meters (300 ft3) of gaseous Helium, which is approximately 11 liquid Helium liters.
The bag has 2 level sensors to control the compressor package, the next component in the recovery system. One sensor turns the compressor package on when it is full, and when it is empty the switch turns the compressor package off. The bag also comes with a pressure relief valve which keeps the bag from over-inflating (overfilling), but will exhaust the Helium to the room.
We recommend that the recovery bag is mounted off the ground to protect it from possible damage. It is made of a synthetic rubber like material. It could be damaged by moving things across it or caustic cleaning material.
Compressor package and Helium “Tank” storage
The second component group in the Helium Recovery System is the Compressor Package and storage tanks. The storage of Helium at a high pressure is a more efficient use of space than finding the room for many atmospheric bags. We also need to compress the Helium to enable the Purification of the Helium.
At the present time Cryomech offers two options for the Helium Recovery Compressor Packages. One is for high pressure storage, and uses a three-stage Compressor Package from another supplier. This enables the user to store Helium Gas @ 135-140 Bar in high pressure cylinders. This option will store more Helium in a smaller space because of the high pressure storage. But it costs more and needs more routine maintenance.
The second option is a Cryomech 2 stage recovery compressor package. Cryomech has developed a two- stage compressor package, the CPHRS201, for this purpose. The CPHRS-201 uses the same technology as in the standard Gifford-McMahon Cycle cryocoolers that have been used throughout the world for 50 years. This compressor package takes the Helium from the recovery bag and compresses it to 350 psig. The 350 psig fills an assembly of tanks.
Cryomech provides four 400L refrigerant tank for storage helium. A 400L liter tank will store 13 liquid liters of Helium gas @ 350 psig. Cryomech supplies the fittings, connections and valves for connecting all parts of the system. It is important that the tanks are attached to the HRS are properly cleaned and the preparation procedures are followed precisely. It is important to remember that when one is recovering Helium, all other gases (anything for that matter) are a contaminant. The procedures are supplied by Cryomech when the system is purchased.
Helium Purifier:
The Helium Purifier (HP07) prepares the recovered Helium gas to be liquefied in the Cryomech LHeP12,18 or 55. The incoming Helium from the cylinders passes through the absorber, mounted on the outside of the HP to remove any residual H2O left in the Helium. The Helium then passes through a liquid nitrogen LN2 trap. (Cryomech has been using LN2 traps for 50 years to eliminate air from its cryocoolers, it is a production line proven technology.) The LN2 trap removes any air contaminants still in the Helium. The Helium should now be ready for the LHePs at >99.99%. A Helium Purity Sensor has been included in the HP07 to insure that impure Helium does not pass on to the LHeP. This sensor will close a solenoid valve stopping the Helium flow to the LHeP if the purity level drops below specification.
Operation:
For the proper performance of the HRS, proper layout of the system and proper connections must be made to ensure that contaminants do not enter the system. Routine maintenance must be performed for the adsorbers and LN2 traps to perform properly. Cryomech will assist in the training of local technical staff. Liquid Nitrogen (LN2) is consumed in the HP07, We have designed the HP07 for a refill of once every a week. The counter-flow heat exchanger is very efficient so the majority of the LN2 boil-off comes from the dewar boil-off rate. Cryomech includes (2) LN2 Trap Assemblies in the HP07 so that one can be operating while the other is regenerating. The regenerating procedure is to pump it down to 25 x 10-3 torr with a standard vacuum fore-pump, while heating with the Cryomech supplied heater blanket assembly, and recharging it with Helium from the HRS.