Page 34 - Pressure Swing Adsorption

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8 PRESSURE SWING ADSORPTION INTRODUCTION

Table 1.2. Some Ma1or PSA Processes devoted to a cletai!ed description of some current PSA processes, while some
of the future trends in process development are discussed in Chapter 7 •
Process Product Adsorbent Type of SvsLern
H 2 recove1v from Ultrapure H ~ Act. C or zeolite Multiple"bed svstem
tuel gas References
J-leatless drier Drv air (for Act. Al O 3 Two-bed Skarstrom
2
1nstrumenrs) cycle (or vacuum- C. w. Skarstrom, U.S. Patent 2,944,627 (Feh. 1958) to Esso Research and Engineering
pressure swing cvde
Companv.
Air separation 0 2 (+Ar) 5A Zeolite Two-bed Skarstrom (Dec. 1957) to Air
2. p_ Guenn de Montgareuil and D. Domme, French Patent 1,223,261
cvcle
Air separation N (+Ar) CMS Two-bed self- Liquide. See also U.S. Patent 3,155,468 (1964) to Air Liquide.
2
purgrng cvde
.,. H. Kahle, Chemie lnR. Technik 23, 144 (1953).
Air separation N and 0 2 5A Zeolite Vacuum swmg
2
, or CaX sv::;tem 4. H. Kahle, Chemie Jng. Technik 26, 75 0954).
ISOSJV Linear /Branched SA Zeolite Molecular sieve separation 5. R. L. Hasche and W. N. Dargan, U.S. Pateni i,794,377 0931}
hydrocarbons with vacuum swing
Landfill gas CO and CH CMS Vacuum swmg 6. G. A. Perley, U.S. Patent 1,896,916 (1933).
2 4
separation 7. D. Finlavson and A. J. Sharp, U.K. Pateni 365,092 (Oct. 15, 1930) to British Celanese Corp.
c w Skarsirom "Heatless Frac11onat1on ot Gases over Solid Adsorbents," In Recent
8
· · · ' . 95 1116 N L. d CRC Press Cleveland
Devetovments In Separatwn Science, Vol. Il, pp. - , · 1 e -, ·
(1972).
misleading since the inmunty 1s almost entirely argon~which 1s adsorbed
with the same affinity as oxygen on most at1sorbents.
The largest-scale PSA processes are generally to be found m petroleum
refinery operat10ns-hydrogen purification and hydrocarbon seoaratt0n pro-
6
cesses such as Isos1v. In such processes product rates uo to 10 SCFH ( > 100
tons/day) are not uncommon. In the other mam areas of appiication (drying
and air separation) PSA umts are generally economic only at rat.her smaller
scales. For example, for large-scale Oh-ygen or nitrogen oroductmn ( > 100
tons/day) it 1s difficult to compete economically with cryogenic distillat1on.
However, there are many small-scale uses for both oxygen and nitrogen (e.g.,
home oxygen units for asthmatic patients and nitrogen units for purging
the fuel tanks of fighter aircraft or for ourgmg the interiors of trucks
and warehouses to prolong the shelf life of fruit and vegetables). For
such applications the robustness and portability of a PSA system provide
addit1onai advantages that reinforce the econom1c considerations. ln these
applications the most direct competition comes from small-scale membrane
systems, which offer many of the same advantages as a PSA system. A bnef
companson of these two classes of process ts included in Chapter 8.
To understand the process options and the factors mvoived m design and
optimization of PSA systems, some background m the fundamentals of
adsorption and the ctynan11c behavior of adsorption columns is reouired.
These aspects are considered m Chapter 2. A wide variety of different cycles
have been developed in order to mcrease energy efficiency, 1morove product
ounty, and improve the flexibility of the operation. The basic cycles and a few
of the more advanced cycles are reviewed in Chapter 3, while more detailed
aspects of process modeling are discussed m Chaoters 4 and 5. Chaoter 6 1s