(SANITIZED)UNCLASSIFIED SOVIET PAPER ONTHE USE OF NEW SORBENTS FOR THE SUPER DRYING OF GASES(SANITIZED)

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80-00247A002200130001-1
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 16
• Document Creation Date: December 27, 2016
• Document Release Date: February 19, 2014
• Sequence Number: 1
• Publication Date: July 15, 1964
• Content Type: REPORT

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50X1 -HUM
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The Use of New Sorbents for the Super Dryinft of Gases.
Z.A. Zhukovs, N.V. Kelitsev, I.P. Oglovlina,
N.S. Torooheshnikov.
Khimiohedkaya Propyahlennost' No.2 (1962) pp.24 ?.29. :
STAT
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Now that natural, casing head, oil refinery, ooking and
other gases are widely used, the choice of the best methods of drying them
is a matter of considerable importance. Cased can be dried to a dew
point of ?400. to ?7?C., or ?7'0. to ?30?C. or to below ?30?C., depending
on the use to which they are put.
Fbr drying gas to a dew point of ?4?C. to ?7?C. the most
economic method is to adsorb the moisture by a liquid adsorbent ? di? or
tri?ethylene glycol. This method is simple both in apparatus and in '
procedure, but it is not suitable for winter conditions. For drying to a.
dew point of ?7?0. to ?30?C. liquid and solid adsorbents are about equalli
suitable. For drying to a dew point below ?30?C. ? which is very
important for many chemical processes ? solid adsorbente are used, since
only with these can required dew points from ?50?0. to ?85?C. be obtained.
Silica gel, alumina and bauxite are widely so used.
Oas drying with solid adsorbents can take place under either
adiabatic or isothermal conditions. Table 1 (1) gives data for the drying
of air in an unCooled adsorber, height 800 mm, diaMeter 300 mm, filled with
activated alumina.
TABLE 1 ? Change in Temperature in Adsorber in
Adiabatic Drying of Air.
(air intake. ? 0.33 m.metresihr. per kg. of adsorbent,
temperature of adsorbent at start of trial 27?04
Distance from Inlet
of Adsorber ? mm.
Temperature 'O. drying after
* hour
2 hours ,
t
4*. hours
7 hours
.
11 hours
0 (inlet)
27 .
27
27
27 ,
27
75
92
58
53
50
:47. ?
300
.53
123
78 ?
64.
? 56 ?
525
51 -
81
120
.89
67
750 (outlet) ' .
50
52 .
103
117
94 .
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Carry over of moisture was first observed after 7 hours
at an outlet temperature of 117?C. Yet an hour after this the processed
gas contained only 4% of its original moisture. Increasing adsorbent
temperature reduces its period of activity and consequently adsorbers in ?
practice are cooled no that they work in isothermal conditions.
The most stable dew point in drying a gas is obtained with
a moving bed of adsorbent.
The wide use of adsorbent methods of gas drying has been
hindered until now by the lack of an adsorbent which combined great
meohanioal strength with high adsorptive capacity and the ability to dry
gases to a low dew point. A new type of adsorbent, synthetic zeolites
(molecular sieves) has these qualities: their structure and basio method
of action have been described in the literature (3 to 8).
? Our investigations into gas drying were carried out using a
static bed of synthetio granular zeolites types 4A and 54. In adsorptive
capacity, zeolites 4A and 5A are very little different: at 20?C.,
pressure 10 mm mercury, adsorptive oapactities are respectively 20.8 and
20.6 grams/I00 grams.
TO study the adsorption characteristics of these zeolites the
isotherms of adsorption of water vapour were obtained in a.vacuum adsorption
installation with quartz weights. The adsorbent was prepared for the
experiment in an evacuated system at a residual pressure of less than 10-5mm
Hg at 350?C. Readings were taken at temperatures from 00 to 3500. ?
Water vapour adsorption isotherms for synthetic zeolites are
shown in Figures 1 and 2. The isotherms are very curved in regions of low
partial pressure. At 2000. and a partial pressure of 0.4 mm Hg the adsorptive
capacity of the zeolites is new to saturation (14 ? 16 gm/100 gm). The
difference in adsorptive capacity between zeolites and other sorbents is
clearly seen in the lower part of their isotherms (Figure 3). Thus, at 2000.
and a pressure of 1 mm the amount of water vapour adsorbed on silica gel or
alumina is 5 gm/100 gm and on zeolite 5A about 17 gm/I00 gm, i.e. the zeolite
is almost three and a half times as active. This confirms the usefulness of
zeolites in drying gases oontaining small quantities of water. vapour.
In the adsorption of water vapour on zeolites there is little
relationship, between capacity and temperature, as can be clearly seen from
the adsorption isobars in Figure 4. At 100?C. pressure 10 mm lig adsorptive
capacity of zeolites is 14.5 gm/100 gm, at 200?C. it falls to 4 gm/100 gm:
but in this region the capacity of silica gel or alumina is practically nil.
The ability to dry gases at high temperature is especially desirable in those
oases where gas, taken from a reaction, is required to re?enter the reaction
after drying (for example, the regeneration of catalyst by the circulation of
hydrogen).
2.
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The use of zeolites instead of the normal sorbents often
avoids the need to 0001 a gas before drying with.a significant saving of
energy. Since the adsorptive oapaoity of zeolites is little affected by
increases in temperature, the heat released in the adsorptive process has
little effeot on their activity. The adsorber consequently does not
require cooling coils. Further, this slight relationship between
temperature and adsorptive oapaoity means a saving in time required to cool
the sorbent after regeneration; the working oyole of the drying installation
is consequently reduced and its productivity increased.
To ascertain the dynamic activity of the adsorbent, its
moisture capacity and speed of adsorption of water vapour as well as the
degree to which the gas was dried, a detailed study was made of the process
of gas drying on zeolites. The experimental apparatus is shown
sohematioally in Figure 5.
The basic piece of apparatus is the glass vertical adsorber,
1, internal diameter 1.3 am, filled with adsorbent partiole size 1 ? 2 mm;
the height of the sorbent bed is 62 cm. Outside the adsorber is a sleeve,
2, in which during the adsorption process circulates water from the
thermostat, 3. Around the outside of the adsorber is a niohrome coil, 8,
for heating. On regeneration the adsorber is connected to a vacuum pump.
Regeneration takes place at 400?C. to a residual pressure below 1 mm Hg,
after which the adsorbent bed is blown through at the same temperature with
nitrogen which has been dried on silica gel (this is not shown in the
diagram). Heating of the adsorbent is regulated by transformer, 5, controlled
by thermocouple, 7. Complete regeneration is demonstrated by a change in
the moisture content of the blown gas (nitrogen), measured by its dew point.
The gas then passes from the measuring ohamber with mirror, 9, where it is
cooled by the copper pin, 10, enolosed in the Dewar vessel, 11, with liquid
nitrogen. A thermocouple is immersed in a vessel of ice, 13.
The dew point is measured on this therm000uple at the moment
when a drop of moisture appears on the mirror. To exclude the possibility
that a drop of moisture Should enter from the surrounding air, the exit .
?bomber, 14, is packed with zeolite. Regeneration is regarded as complete
when the dew point of the outgoing nitrogen is reduced to ?40?C.
TO study the working basis of the drying process, air is
pumped through a bed of the sorbent at a speed determined by the flowmeter, .
16. At this point the dry gas and regeneration gas are identical. The air
is saturated in a Drechsler flask, 17. To investigate the effect of
incoming moisture on the adsorptive capacity of zeolites, a series of trials
was run in which the vessel, 17, was filled with sulphuric acid of a
determined oonoentration to'give the required degree of moisture to the drying
gas. The moisture oontent of gas entering the column was determined every
15 or 20 minutes by its dew point; additionally the moisture content of thi
outgoing air was periodically tested.
1
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These trials gave ourves Showing the relation between the
dew point of the dried gas and the duration of drying (Figure 6). As
will be seent.the dgree of drying remained almost constant throughout the
trial, the dew point was within the limits ?600 to ?65?C. Increase in
moisture content (in contrast to other adsorbents) oame suddenly and
quiokly at the and of the trial. This indicates that even a small bed of.
zeolite is nearly in equilibrium with gas under dynamic conditions. The
differenoe between dynamic and statics aotivity is not more than 10 ? 15%,
In Figure 3 the dotted curve shows dynamic activity; the points of this
curve were obtained by combining the results of trials with different final
air moisture contents. Change in temperature does not alter the shape of
curves in Figure 6. .
The results of experiments to determine the effect of .
drying temperature, speed of the gas stream and moisture content of the
intake gas on the drying process are given in Pablo 2. It will be seen from
the data in the table that with increasing temperature the low, stable
dew point of the dried gas is unaltered. Increase in temperature from
300 to 80?C. lowers the dynamic activity from 21 to 16 gm/100 gm, i.e. by 25%
and the quantity of gas dried per gram of sorbent accordingly drops from
11.8 to 8.4 litres.
4.
J
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TABLE 2. Effect of Temperature, Rate of Flow and Outlet
Humidity of Gas on the Drying Process
'
Temperature
?C.
Intake
Humillity
gm/M3
Dew point
of intake
gas ?C.
Gas flow
litres/
minute
Duration of
trial until
passage of
water vapour
hours
Dew point
of dried
gas
?C.
Dynamic
Aotivity
gm/100 gm
Amount of
gas dried
litres/gm.
30
18.3
+21.0
0.5
17
-62.0
21.0
11.8
50
17.3
+20.0
0.5
14
-60.0
17.4
9.8
80
18.3
+21.0
0.5
12
-63.0
16.0
8.4
50
? 17.3
+20.0
0.5
14 .
-60.0
17.4
9.8
50 .
19.4
+22.0
1.5
4
-62.0
17.5
9.4
50
17.3
+22.0
2.8
25S
-65.0
14.5
- 8.8
50
18.3
+21.0 -
0.5
18
-70.0
17.5
9.8 '
50
9.4
410.0
0.5
32
-67.0
16.1
17.3
50
3.8
- 3.0
0.5
80
-65.0
15.8
43.3
50
1.4
-16.0
0.5
195
-63.0
. 14.6
105.0
The working life of the bed (dew point -50?C.) was 12 to
17 hours, changes in the gas flow from 0.5 to 1.5 litres/minute (which
corresponds to a rate of 0.4 - 1.2 litres/minute in units industrial absorbers)
did not for practical purposes 1oweR the activity. Even at an air flow of
2.8 litres minute (over 2 litres/cm'/Minute) a sorbent bed of 60 mm ensured-
drying to a dew point of -65?G. at an adsorptive ?opacity of 14.5 gm/100 gm._
It is obvious that in plant scale adeorbers, where the depth of bed is
several times greater than in laboratory models, the reduction in dynamic
activity from increased rate of gas flow would be less. In adsorptip
drying installations using zeolites, therefore, speeds of 3 litres/cm'/minute
and more are easily practicable, since the limits are set by the capacity of:
the adsorbent and not by the process.
To study the effeot of intake humid4ty on the adsorption
process, humidity was varied from 18.3 to 1.4 gm/OP, corresponding to a change
in dew point from +21 to -16?C. This range of humidities, expressed as
partial pressures of water vapour, correspond with those portions of the
isotherm (of. Figure 3) where adsorptive oapaoity is almost independent of
moisture content and approximate .to accepted maxima of activity. As a result
of this, the useful life of the adsorbent and, consequently, the amount of gas
dried per kilogram of sorbent per cycle, is inversely proportional to the
5.
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intake moisture content. Reduction of humidity from 18.3 to .1.4 gm/63
(i.e. to ane?thirteenth) resulted in an insignifioant drop in dynamic
adsorptive capacity from 17.5 to 14.6 gm/i00 gm, but a greatly increased
yield of dried gas. Under these conditions the drying cycle lasted 8 days.
The main experiments to study the drying of gases with
zeolites were carried out with air. In order to establish the effect of
natural gas on the prooess of drying and to relate test conditions to real
conditions, one of the experiments was run with Stavropol natural gas at
50?C. speed of gas stream 0.5 litres/minute. Since this gas contains long
chain hydrocarbons, which affeot the determination of dew point for the
experiment, it was first passed through a cartridge of activated carbon.
The results of the experiment showed good agreement with those obtained for
air. In the experimental conditions a stable dew point of ?60?C. was
maintained throughout with a sorbent capacity of 17 gm/100 gm. The
selectivity of the adsorption with reference to water vapour was clearly
demonstrated since the pressure of other components (oxygen and nitrogen in
air, methane and ethane in natural gas) had practically no effect on the
extraction of moisture. The higher hydrocarbons (C3 and above) which cause
coking and premature failure of conventional solid drying materials, do not
penetrate the fine pore structure of adsorbent 4A (5) and its service life
is accordingly prolonged.
When drying gases on zeolites, special care must be given to
regeneration of the adsorbent. In these experiments oonsistent results
were obtained only when correct conditions of regeneration were observed.
The main factors which determine the degree of regeneration are the bed
temperature and the humidity of the purging gas. Zeolites will stand a
temperature of 600?C. without any sensible change in their s2rptive
characteristics. It is usually better to regenerate at 200" ? 350?C.
Figure 7 shows the relationship between minimum dew point and bed temperature
for various residual humidities. This graph allows the determination of
residual moisture on the sorbent (after regeneration by a gas of determined
humidity) for any given temperature and also for any residual moisture
content the determination of the minimum dew point which may be obtained in
the process of dryiEg. Thus, after regeneration at 200?C. with a purging
gas of dew point -7 C. the residual moisture on the zeolite is 3.1%. A
sorbent of the same moisture content which has been cooled to 40?C. will
give a minimum dew point of ?73?C. If regeneration were not complete and
residual moisture were 10.8% by weight, then the dew point of the dried gas
would be about ?40?C. Thus the regeneration of zeolites can be reckoned
as a thermal balance between the heat absorbed by the grains at a given .
temperature and the amount of moisture released during regeneration.
Conditions of regeneration (temperature, moisture content of the purging air).
can be selected in accordance with the equilibrium curves given in Figure 7
to suit production requirement*. The following data are required for the.
calculations speoifis heat of zeolites 0.25 eal/kg.?O., thermal conductivity
-
0.5 ?al/60u', hour, O. ,,,,hoiat of desorption of water 1000 cal/kg.
6.
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Heating of the sorbent bed for. regeneration may be effected
by internal heating tubes, eleotrio heating elements or a current of hot
gas. In all these methods, once the sorbent has reached the required
temperature, it must be blown with a gas (e.g. nitrogen or air) of low
moisture content.
It must be emphasized that the efficiency of drying depends
very much on the direction of flow of the gas to be dried and that of the
regeneration gas with external heat and a flow of cold regeneration gas, counter
current working is undesirable sinoe the frontal layer of sorbent is cooled
and regeneration is incomplete. This layer will be the last to be dried and
the gas passing over it may pick up moisture and its dryness thus reduced.
If thee regenerationand drying gas flow together any defioienoies in drying
of the frontal layer will be made good by the following layers.
Our experiments established that with the same direction of
flow the degree of drying is grsatly increased; the dew point is reduced to
-75?C. or sometimes even to -80 C. or lower. With counter flow the dew
point does not fall below -600 to -65?0. (of. Table 2). Uounter current flow
may be used where blowing is by heated gas.
The results of full scale trials of zeolites in the U.S.A. show
that their adsorptive oapaoity in gas drying falls some 15 to .30% over the
first 200 cycles and thereafter remains pretty well stable up to 2000 cycles.
As a result of our laboratory trials and full scale trials abroad, it is
therefore possible to say that zeolites have a number of advantages over other
desiccants, particularly in the drying of gases of low initial moisture oontent
and of gases at high temperature. For drying gases containing an appreciable
amount of water vapour (natural gases for example) it is most convenient to
remove the bulk of the moisture by means of the conventional, cheaper, and more
easily regenerated liquid or solid sorbents and to complete the drying on
zeolites.
In some processes super drying of gases must be combined with
the removal of impurities: for example, where it is necessary to provide a
neutral atmosphere for metallurgical processes with complete absence of
oxidising agents (water and carbon dioxide).0n our installation, described
above (Figure 5) we carried out trials of simultaneous drying and purification
in which both water vapour and carbon dioxide were present in the gas to be
used for the neutral atmosphere (74.2%112,5.7% Co, 6.5% 1129 6.0% H20 and
7.6% CO2). Nitrogen was the diluent. .The concentration of carbon dioxide
was measured at the outlet of the column by absorbing it in barium hydroxide
and titrating the excess barites with sulphuric acid. The addition of the
-CO2 to the wet gas stream was from a cylinder through a flow meter.
The results of the experiment show that water is preferentially
adsorbed on the first layers of zeolite in the gas flow and gradually
dislodges the 002 from the pores of subsequent layers. Removal of 002 takes
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readily while the dew point still remains below ?45?C. In an apparatus
with. 43.05 gms of zeolite, type 4A, gas flow 0.5 litres/cm2/minute and bed
temperature 30?C., 002 removal began after 76 minutes. With a moisture
content of inlet gas of 12.8 gm/m.4 dynamic activity with respect to CO2
is about 10 gm/100 gm sorbent, and moisture adsorbed 11.3 gm/100 gm.
Simultaneous drying and purification makes drying possible
in a "dry" system, i.e. where the gas stream does not carry over excess ?
moisture from the preliminary purification; moreover the adsorbent is not
loaded with the purifying solutions. Figure 8 gives a diagram 0 a
commercial installation designed to dry and 'remove CO2 from 60 m' of
generator gas per hour. CO2 concentration of the gas averages 12% by
volume, dew point ?500. The working cycle consists 'of three operational
cleaning and drying hour; regeneration hour; , cooling it hour.
Cleaning reduces CO2 content to 0.001% by volume, dew point is lowered to
?5000. Regeneration uses air heated to 31500. After regeneration the
adsorber is cooled by oiroulation of the cleaned. gas.
8.
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24
I
20
50 ?
BO
,
100
.. ., .
,
g0._
:
'?"="------"-------3,TO?
_
4 8 8 /0 12 /4 a
Partial Pressure of Water Vapour mm. Hg.
Fig. 1.
Isotherms of Adsorption
of water vapour on
synthetic zeolites, Type 4A
00
20
.
80
?
?
BO
100
450
? .
.
?250
. .
.
.
.
.
?
0
0
3500?
2 . 4
Partial treasure of ;alter Vapour mm. llg.
Fig. 2. Isotherms of Adsorption
of water vapour on
synthetic zeolitee, Type 5A
8 10
t2
9.
f4
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MOO
?????
Cf"
4
6'
.0 17
Partial Pressure of Vapour
:Fig. 3. Adsorption of water vapour
on various types of adsorbent.
Dotted linet dynamio activity
of zeolite type 5A. '
1. zeolite 5A
2. silica gel.
3. alumina
??????*111..
??????11????????????
200 300
Temperature
Fig. 4. Isobars of Adsorption
of water vapour at a
pressure of 10 mm: lig.
1. zeolite 4A
2. silica gel
3. alumina
in
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To vacuum pump
1.
adsorber.
Pig. 5.
Schematic of
2.
3.
thermostat sleeve.
thermostat.
installation for,
gas drying.
4.
manometer
5.
autotransformer.
6.
potentiometer.
7.
thermocouple.
8.
nichrome winding.
9.
measuring chamber with mirrow.
10.
copper rod.
11.
Dewar vessel.
12.
bridge potentiometer,
13.
glass of ice.
14.
zeolite cartridge.
15.
gas cylinder.
16.
flowmeter.
17.
Drexel bottle.
STAT
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-
"10
4650
-40
0
8 8 10 12 14 /6 18 20 a
Drying time hours
Fig. 6. Dependance of dewpoint of dried gas
on time of drying.
4
20
0
-80
-IC
1. Speed of gas in drying zone
1.15 litres/cm2/min. - -
2. Speed of gas in drying zone
0.4 litres/cm /min.
..1.~.........n..P.Tor.apyall?IA.....~111.MINIIMIP.
41 : 1
A weight
105-
14,8
;
i6
V
----
441111111"r
1,if
if,
1
:
ago
vor
--,
50 100 150
200 250 309
Bed temperature 'IC
Fig. 7. Dependance of minimum dew
point on bed temperature for
different residual moisture'
contents.
12.
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?
0
?
0101?? 111?11DOMIII?
dIDMIND?10.4111.1.?
Inlet and product gas
Air
Circulating gas
Fig. 8. Schematic of an instal-
lation for cleaning and drying
gas.
1-3. adsorbers for cooling,
cleaning and drying, and
regeneration stages re-
spectively.
4. gas generator
5. heat exchanger
617. oondensers
80 gas pumps.
STAT
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,.
REFERENCES
(Nos. 2 to 8 are in Russian)
1. A.L. Kohl, P.C. Riesenfeld, Gas Purifioation, NV 1960.
2, N.V. Kel'tsev. Gas. prom. No.11 (1956) p.32.
II II No. 9 (1957) p.38.
3. N.V. Kel 'taw,
4. R.P. Bering, LU. Dubinin, E.G. Mukovske,ya, V.V. Serpinskii,
Dok. Akad Nauk SSSR 131, No.4 ( 1961) p.865.
5. Ia. V. Mirskii. Dok. Akad Nauk SSSR 130, No.1 (1960) P.115.
6. N.V. Kelitsev. Gas. prom. No. 9 (1960) p.49.
7. V. Ia. Taitsishviti, I.E. Neimark, M.A. Piontkovskeya.
Uspekhi Khimii 29, No.9 (1960) p.1088.
8. 0.1. Tsitsishvili, T.O. Andronikashvili, Moleoular sieves,
supplement to Evil. Nauchno?Tekh Inform. Georgian ssa.
9. A. Piumara. La rivista dei oombustibili 13, No.3 (1959) P.217.
IA 14.
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