Fast regenerating adsorption column

A fast regenerating absorption column including a high pressure outer vessel containing an inner vessel packed with adsorption medium the inner vessel thermally isolated from the outer vessel and including means to rapidly heat and cool the adsorption medium so that a single column can be used to purify an incoming gas and can be rapidly regenerated to eliminate the need for switching adsorbers.

TECHNICAL FIELD 
The present invention pertains to an apparatus for purifying a high 
pressure gas stream by adsorption of unwanted components from the gas 
stream and in particular to a fast regenerating adsorption column. 
BACKGROUND OF THE PRIOR ART 
Presently high pressure cryogenic purification systems used to continuously 
supply pure gas to a process require utilization of dual switching 
adsorbers. In the prior art units, one adsorber is processing gas (e.g. 
adsorbing unwanted components) while the other unit is being regenerated 
by removal of the components previously adsorbed from the gas stream being 
purified. Prior art systems with dual switching adsorbers usually are 
large, complex devices with complex control systems to assure the 
switching of the adsorbers so that the one regenerates while the other, 
having been regenerated, is purifying the flowing gas stream. 
In U.S. Pat. No. 2,450,289 patentee discloses a device for gas separation 
without thermally isolating the inner vessel for fast regeneration. 
Patentee's design is merely to provide a flow geometry for the gas being 
treated. 
British Pat. No. 707,093 and U.S. Pat. No. 2,790,505 disclose devices for 
drying gas streams wherein a layer of insulation around an inner vessel is 
used as a static barrier to heat conduction during steady state operation. 
U.S. Pat. No. 3,264,803, discloses an adsorber utilizing a pool of boiling 
cryogenic fluid to cool an adsorption bed. 
Other adsorbers are disclosed in U.S. Pat. Nos. 3,335,550; 3,469,375; 
3,683,589 and 3,734,293. 
BRIEF SUMMARY OF INVENTION 
The present invention provides a fast regenerating adsorption column which 
includes a high pressure outer vessel containing an inner vessel packed 
with adsorption medium, the inner vessel being thermally isolated from the 
outer vessel. The apparatus includes means to rapidly heat and cool the 
adsorption medium so that a single column can be used to purify a gas 
stream. The single column can be rapidly regenerated to eliminate the need 
for a second adsorber thus, allowing for an uninterrupted supply of pure 
gas while reducing the size and complexity and operating costs normally 
associated with a dual switching adsorber set up.

DETAILED DESCRIPTION OF THE DRAWINGS 
Dual switching adsorbers for purification of high pressure gas streams have 
been used effectively for a long period of time. However, as pointed out 
above, the prior art systems require complex control systems and dual 
adsorbers increasing not only the capital cost but the size and complexity 
of the purification system. In addition, the use of dual vessels requires 
a large consumption of cooling fluid (e.g. nitrogen) which is normally 
used to cool the adsorption bed. 
The present invention has for its objective, the supply of an uninterrupted 
high pressure purified gas, such as helium, by using an adsorber design 
which permits fast regeneration and sufficient capacity during 
purification to accomplish one of the two following objectives: 
1. Build enough over capacity into the purification unit so that a reserve 
supply of pure gas can be stored during the purification phase of the 
cycle such that this gas is of sufficient quantity to feed the downstream 
process during the time the adsorber is being regenerated; or 
2. Design the regeneration time of sufficiently short duration, in 
comparison to the purification run time, to keep the pure gas makeup 
requirements from other sources consistent with what would normally be 
required for such a process. 
In regard to objective No. 2 above, consider the helium gas recovery and 
purification requirements of a laboratory size helium liquefier such as 
Model HL280, sold by Air Products and Chemicals, Inc. of Allentown, Pa. 
under the Tradename HELIFIER. With this apparatus a recovery yield of 80% 
of the originally liquefied gas is considered typical. Thus, one would 
normally expect to supply pure makeup helium from a gas supplier or other 
source equivalent to about 20% of the liquefier output. Thus, if 
t.phi.represents the total purify cycle time, tr time required for 
regeneration, and, tp the time during which the purifier is actually 
processing impure gas, then 
EQU t.phi.=tr+tp (1) 
and on the basis of 20% makeup requirement one can tolerate a regeneration 
time as high as 
EQU tr=0.2 t.phi. (2) 
which would permit substitution of the pure helium from an alternate source 
during regeneration. Another way of looking at the time parameter which 
must be adhered to is by substituting equation 12 above into equation 1 
thus yielding 
EQU tr=1/4tp 
thus if the adsorption bed is sufficiently large to process impure gas for 
8 hours, the regeneration must be carried out in at least 2 hours. 
Referring to the drawings the requirements for fast regeneration of a high 
pressure adsorption column can be carried out with an apparatus as shown. 
In particular, the column shown generally as 10 in FIG. 1 includes a first 
or outer pressure vessel 12 being generally elongated and cylindrical in 
shape closed on either end by a pair of hemispherical ends shown as bottom 
14 and top 16, each of which are afixed to vessel 12 by circumferential 
welds 18 and 20, respectively. Ends 14,16 are adapted to receive a 
plurality of hermetically sealed feed throughs, the function of which will 
be explained more fully hereinafter. 
Disposed radially at convenient locations around the circumference of 
vessel 12 are a plurality of supports 22,24,26 (FIG. 4) which are utilized 
in mounting the adsorption column 10 into an apparatus so that it can 
perform its purification function. 
Disposed within outer vessel 12 is a second or inner vessel 30 fabricated 
of a highly conductive material such as aluminum. Inner vessel 30 is 
affixed to outer vessel 12 by a plurality of low thermal conductive 
supports 32,34,36 and 38. Supports 32,34,36 and 38 are preferably made of 
a stainless steel which is a poor thermal conductor. Supports 32,34,36 and 
38 are also fabricated to provide a standoff of inner vessel 30 from outer 
vessel 12 and to define a fluid tight annular space between vessel 30 and 
vessel 12. Annular space 40 is filled with an insulating material such as 
packed glass wool or vermiculite. The insulating material is used in a 
transient heat transfer sense, i.e. to reduce temperature response of the 
outer wall with respect to temperature changes in the central adsorbent 
space inside vessel 30. 
Disposed within the inner vessel 30 is a transfer apparatus shown generally 
as 42 (FIG. 4). Transfer means 42 includes a generally elongated 
cylindrical tube or mandrel 44 having disposed along its length a 
plurality of thermal conducting fins 46 each of which extends 
longitudinally for substantially the entire length of mandrel 44 and are 
radially disposed of around the mandrel 44. The heat transfer means 42 can 
be a single extrusion of aluminum or can be fabricated by welding 
individual fins to the center mandrel 44. The transfer apparatus must be 
of a highly thermal conductive material such as the aforementioned 
aluminum. On each of the fins 46 is disposed a conduit 48 (FIG. 4) in 
serpentine array (FIG. 1). Each of the conduits 48 terminates on the 
bottom end in a ring manifold 50 and on the top end in a ring manifold 52. 
Ring manifolds 50 and 52 include distributor heads 54,56, respectively 
which in turn communicate with an inlet conduit 58 and an outlet conduit 
60, respectively, the function of which will be hereinafter more fully 
explained. Inlet conduit 58 projects through bottom head 14 of outer 
vessel 10 by means of a suitable pressure and fluid tight fitting 62 and 
outlet conduit 60 projects through top head 16 by a like fluid and 
pressure tight fitting 64. 
Disposed within inner vessel 30 between fins 46 and around conduits 48 is a 
bed of an adsorption material such as activated charcoal 70. The activated 
charcoal 70 is kept within inner vessel 30 by a combination of a pair of 
spaced apart perforated plates and fine screening 72,74,76,78 on either 
end of inner vessel 30 and packed glass wool insulation 80,82. Disposed 
within the bed 70 is a gas purity sampling probe shown generally as 90 
which includes the requisite capillary 98 projecting through head 16 of 
vessel 10 by an appropriate capillary feed through 96 as is well known in 
the art. Electrical feed throughs 92,94 (FIG. 2) and conduits 98 are 
adapted to permit a temperature sensor (not shown) to be disposed within 
the bed. The temperature sensor and the gas purity sampling probe 90 are 
disposed approximately 85% of the way through the bed. 
Disposed within mandrel 44 is a longitudinal heating element 100 with its 
associated electrical conduits 102 projecting through a suitable fitting 
104 in head 16 of vessel 12. Heater 100 is included to provide the 
necessary heat to the bed 70 during regeneration. Heating element 100 is 
preferably installed with a highly thermally conductive powder such as 
copper or aluminum as a packing material between heating element 100 and 
mandrel 44 so as to provide minimum thermal response time between said 
heater and the adsorption medium. 
Vessel 10 includes an impure gas inlet fitting 105 and inlet conduit 107 
(FIG. 3) and a pure gas outlet 106 (FIG. 1 and FIG. 2) as well as a sample 
outlet 108. 
In operation fitting 105 is connected to a source of impure gas and fitting 
106 is connected to the apparatus which is to receive the purified gas 
(e.g. helium). Fitting 62 and conduit 58 are connected to a source of 
liquid nitrogen and fitting 64 and conduit 60 are connected to a 
receptacle for receiving the liquid nitrogen. In use the liquid nitrogen 
is caused to flow through conduit 58 header 50, conduits 48, through 
header 52 conduit 60 and into a storage receptacle thus cooling fins 46 
and the bed of activated charcoal 70 by forced convective boiling of 
liquid nitrogen. When the bed is brought to operating temperature, impure 
gas is admitted into the space below inner vessel 30 through fitting 105 
and caused to flow upwardly through bed 70 where the impurities are 
removed by adsorption. The purified gas removed through conduit 106 is 
then used to precool the incoming impure gas stream through heat exchange 
and is then taken to the point of use and a portion collected for use 
during regeneration of the adsorber 10. When the purity monitor connected 
to gas sampling probe 90 determines that the adsorber should be 
regenerated the source of impure gas and source of liquid nitrogen are 
turned off and heater 100 is energized to warm the charcoal bed 70 to thus 
desorb the impurities from the charcoal bed. The impurities are collected 
or vented through fitting 107 (FIG. 3) which has been disconnected from 
the impure helium supply. After the bed has been regenerated the column 10 
is reconnected for use in the purification mode as was described above. 
An apparatus according to the present invention was tested to see if 
thermal isolation of the adsorption bed from the outer pressure vessel was 
effective. An increase in the bed temperature of 300.degree. F. 
(149.degree. C.) resulted in an outer pressure vessel 12 wall temperature 
increase of 24.degree. F. (13.3.degree. C.) or about 8% of the bed 
temperature swing. The 300.degree. F. (149.degree. C.) bed swing is about 
the same as will be experienced during regeneration. Since the outer 
pressure vessel represents the greatest thermal mass in the system an 
appreciable savings in liquid nitrogen can be realized since the outer 
vessel need not be cooled down over the same temperature range as the 
central adsorber core. As is well known in the art, conventional dual 
switching absorbers provide for heating of the entire adsorber including 
the outer vessel in order to achieve regeneration. With an apparatus 
according to the present invention, outer vessel 12 is a heavy walled 
cylinder made to withstand an operating pressure of 1400 psi, an operating 
temperature range of 80.degree. F. (26.7.degree. C.) to -320.degree. F. 
(-196.degree. C.). The inner vessel 30 is made to operate at a pressure 
of 1400 psi (96 atmospheres) and an operating temperature range of 
+70.degree. F. (21.1.degree. C.) to -320.degree. F. (-196.degree. C.). 
STATEMENT OF INDUSTRIAL APPLICATION 
An apparatus according to the present invention will be incorporated into a 
helium liquefier for producing liquefied helium primarily for research 
applications. The research applications provide for reclaiming of the 
helium, thus effecting a net saving on helium cost. A column according to 
the present invention was designed to handle 10 SCFM helium with an 
impurity level of up to 2% air for a period of eight hours with a 
regeneration time of less than two hours. The purifier will handle up to 
20% air contamination by using an air condenser upstream of the adsorption 
column which removes all but 2% of the impurities. An apparatus according 
to the invention can supply pure helium gas at up to 1400 psig. 
Having thus described my invention what is desired to be secured by Letters 
Patent of the United States is set forth in the appended claims.