Cryogenic helium purification and adsorption systems make cost-effective removal of impurities possible.

When processes require pure helium, it is inevitable that impurities introduced as part of the process will need to be addressed. What are your options besides purging the system and replacing the helium? A less costly solution may be a helium purifier.

The type of process helps direct users when selecting a helium purification system. Smaller systems may be well suited to a stationary pressure swing adsorption (PSA) process. In this solution, a small stationary system is provided to adsorb contaminants in one chamber while regenerating the adsorption material in a second chamber. The process cycles between the two chambers to continuously purify the process helium.

In larger or intermittent processes, a bigger portable adsorption system is the better solution. A larger single chamber is used with adsorption media for an extended purification cycle. When the purification process is complete, the purifier is removed from the process system for an extended regeneration cycle. This style of cryogenic liquid helium purifier or adsorption system is suited to remove impurities within helium gas used in a liquefier or refrigeration system where the system has become exposed to the atmosphere. The purifying process is effective at removing nitrogen, oxygen, moisture and other air gases, increasing production efficiency and saving time associated with pumping and purging the system. Adding a second purification system can provide redundancy while offering for extended or continuous operation capabilities when required.

With a portable adsorption system, contaminants are removed through a filter bed comprised of activated carbon or a molecular sieve material. Activated carbon, while slightly less expensive, can present the potential for ignition. Molecular sieve adsorption media removes contaminants while allowing for regeneration, and regular regeneration allows repeated use of the adsorption media.

The process adsorbs contaminant, which differs from absorbing. Adsorption accumulates or attracts air and moisture contaminants on the surface of the adsorbed material or media sieve. The adsorption material is selected for its microscopic surface texture and physical nature of attracting air and moisture. This is not to be confused with absorption, which attracts contaminants such as moisture but takes the contaminant into the media bed. This makes the contaminants a part of the media, and much like a filter, media that absorbs contaminants cannot be regenerated but must be replaced. 

The advantage of adsorption is its ability for the media bed to attract contaminants as well as to shed those same contaminates during regeneration. The regeneration process allows the system to be cycled and cleansed for reuse, extending service life. The adsorption process is used in a range of industries.

The ever increasing demand - about 5 to 10 percent annually during the past decade - continues to push the cost of helium higher. Helium doubled in price from 2002 to 2007, and increased another 50 percent in 2008. With helium purification you can connect to a system permanently or temporarily, extending the service life of the helium while reducing the cost associated to replacement. If new helium needs to be added, a helium purification system also serves as place to charge the system, as it purifies the charge being added to the system.

In large systems or where multiple systems must be serviced, a mobile solution may be more practical. This allows purification of the helium systems with a single purification system. Mobile systems operate by introducing helium gas into the purifier at 250 to 275 psi. The helium gas passes through a heat exchanger, where the gas is cooled and some residual water vapor is condensed. The helium gas, after exiting the heat exchanger, enters a liquid nitrogen cooled vessel where it is further cooled as it passes through a heat exchanger submersed in the liquid nitrogen bath. The cooled helium gas now enters the adsorber vessel, where it moves through the adsorber media, which removes the impurities from the gas. After leaving the adsorber, the helium gas passes though a heat exchanger, where it is warmed to near ambient temperature.

As the demand and price for helium continues to grow, the savings a helium purifier offers by purifying and reusing helium needs should be considered. PC

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