Page 531 - Mechanical Engineers' Handbook (Volume 4)

520 Cryogenic Systems

evaporated LNG must be reliquefied, for which purpose a small liquefier circuit is available
onboard.

7.3 Helium Recovery and Liquefaction
Helium exists in minute concentrations in air (see Table 12). However, this concentration is
well below the 0.3 vol % that is considered to be the minimum for economic recovery. It
exists at higher concentrations in a few natural gas deposits in the United States, as shown
in Table 14, and in like concentrations in some deposits in Russia, Poland, and Venezuela.
This fossil material is apparently the total world supply.
The vital role that helium plays in welding, superconductivity applications, space pro-
gram operations, medicine, in certain heat transfer and inert atmosphere needs, and in a wide
variety of research requirements lead to the demand that helium be conserved. This was
undertaken by the Bureau of Mines after World War II. A series of helium-separation plants
was built in the Southwest. Generally these produced an 80% helium stream from high He-
content steams of natural gas that would otherwise have gone directly to the municipal
markets. The processes used a modified Joule-Thompson cooling system that depended on
the methane accompanying the He. This crude He was stored in the Cliffside Field, a depleted
gas reservoir, from which it could be withdrawn and purified. Most of these plants shut down
during the 1970s because of shifting government policies and budgetary limitations. In 1995
the last of these plants was closed down, as was the Bureau of Mines itself. The fate of the
stored crude helium is being debated now (1996).
There are now about 30 billion standard cubic feet of crude He stored in the Cliffside
reservoir, more than enough to supply the U.S. government needs estimated, at 10 Bcf

Table 14 Helium in Natural Gases in the United States
A. Composition of Some He-Rich Natural Gases in the United States
Typical Composition (vol %)
Location CH 4 C 2 H 6 N 2 CO 2 O 2 He

Colorado (Las Animas Co.) 0 77.6 14.7 0.3 7.4
Kansas (Waubaunsee, Elk,
McPherson Cos.) 30 30 66.4 0.2 0 3.4
Michigan (Isabella Co.) 57.9 25.5 14.3 0 0.3 2.0
Montana (Musselshell) 54 30 16
Utah (Grand) 17 1.0 3.5 7.1

B. Estimated Helium Reserves (1994)
Location Estimated Reserve (SCF)
Rocky Mountain area 25 10 9
(Arizona, Colorado,
Montana, New Mexico,
Utah, Wyoming)
Midcontinent area (Kansas, 169 10 9
Oklahoma, Texas)
He stored in the cliffside structure 30 10 9
Total 224 10 9