U.S. patent number RE31,014 [Application Number 06/248,774] was granted by the patent office on 1982-08-17 for separation of multicomponent gas mixtures.
This patent grant is currently assigned to Air Products and Chemicals, Inc.. Invention is credited to Shivaji Sircar.
United States Patent |
RE31,014 |
Sircar |
August 17, 1982 |
Separation of multicomponent gas mixtures
Abstract
Multicomponent gas mixtures containing: (1) hydrogen as primary
component, (2) a secondary key component that is more strongly
sorbed by the adsorbent than hydrogen, and (3) a minor quantity of
one or more dilute components less strongly sorbed than the
secondary key component, are subject to selective adsorption in an
adiabatic pressure swing cyclic system for the separate recovery of
high purity hydrogen and of the secondary component. A given
example is the treatment of a shift converter effluent gas from a
hydrocarbon reformer plant, wherein hydrogen and carbon dioxide are
separately recovered as key components substantially freed of minor
dilute components such as methane, carbon monoxide and
nitrogen.
Inventors: |
Sircar; Shivaji (Allentown,
PA) |
Assignee: |
Air Products and Chemicals,
Inc. (Allentown, PA)
|
Family
ID: |
22940625 |
Appl.
No.: |
06/248,774 |
Filed: |
March 30, 1981 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
935435 |
Aug 21, 1978 |
04171206 |
Oct 16, 1979 |
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Current U.S.
Class: |
95/101; 95/130;
95/139; 95/140 |
Current CPC
Class: |
B01D
53/047 (20130101); C01B 3/56 (20130101); B01D
2257/102 (20130101); C01B 2203/043 (20130101); Y02P
20/156 (20151101); B01D 53/0476 (20130101); B01D
2257/7025 (20130101); B01D 2259/40015 (20130101); B01D
2259/403 (20130101); B01D 2257/502 (20130101); B01D
2259/4003 (20130101); B01D 2259/40052 (20130101); B01D
2259/40067 (20130101); B01D 2259/4062 (20130101); B01D
2259/40037 (20130101); C01B 2203/0465 (20130101); B01D
2259/40032 (20130101); C01B 2203/048 (20130101); Y02C
20/40 (20200801); Y02P 20/151 (20151101); B01D
2256/22 (20130101); C01B 2203/047 (20130101); Y02C
20/20 (20130101); B01D 2257/504 (20130101); Y02C
10/08 (20130101); B01D 2259/40001 (20130101); C01B
2203/0475 (20130101); Y02P 20/152 (20151101); B01D
2256/16 (20130101); B01D 2253/102 (20130101) |
Current International
Class: |
C01B
3/00 (20060101); C01B 3/56 (20060101); B01D
53/047 (20060101); B01D 053/04 () |
Field of
Search: |
;55/20,21,25,26,33,58,62,68,74,75,179,387,389 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Spitzer; Robert H.
Attorney, Agent or Firm: Ryder; Thomas G. Innis; E. Eugene
Simmons; James C.
Claims
What is claimed is:
1. In the separation of a multicomponent feed gas mixture with the
individual recovery of a primary key component and a secondary key
component present in such mixture, by selective sorption, wherein
said secondary key component is more strongly sorbed than the
primary key component and there is present in said mixture at least
one minor dilute tertiary gas component less strongly sorbed than
the secondary key component; the method which comprises, in an
adiabatic adsorption pressure swing cycle the steps of:
(a) passing such multicomponent gas mixture at initial
superatmospheric pressure and in selected flow direction through a
first sorbent bed (A) selective for preferential retention of said
secondary key component and then passing the effluent from said
first bed through a second sorbent bed (B) selective for retention
of said tertiary component(s) as opposed to said primary key
component, and discharging from said second sorbent bed unadsorbed
primary key component, said passing of the multicomponent gas
mixture being continued for a controlled time period until or short
of breakthrough of said secondary key component from said first
sorbent bed, while retaining all of the said tertiary components in
said second sorbent bed;
(b) thereafter discontinuing gas flow communication between said
first and second sorbent beds, and
(i) rinsing said first bed by flowing a stream of relatively pure
secondary key component therethrough at substantially the initial
feed pressure level for a controlled time period effective to purge
most of the void and displaced gases from the said first bed, and
during this time period (b),
(ii) lowering the pressure in said second bed to an intermediate
level by withdrawing a gas stream therefrom including void and
desorbed gases, and thereafter;
(iii) further depressuring said second bed to near ambient pressure
.[.followed by;.].
.[.(iv) purging the second bed at near ambient pressure with a
stream of primary key component.].;
(c) after said rinsing step in (b) above reducing the pressure in
said first bed to an intermediate level by desorption of gas
therefrom including previously sorbed secondary key component and
during this step (c), .Iadd.
(iv) purging the second bed at near ambient pressure with a stream
of primary key component and .Iaddend.repressuring the second bed
to an .[.immediate.]. .Iadd.intermediate .Iaddend.pressure level by
flow thereinto of gas essentially free of the secondary key
component;
(d) following step (c) above further desorbing gas from said first
bed to lower the pressure therein to substantially ambient level,
and thereafter;
(e) evacuating said first bed to subatmospheric level;
(f) after attaining the subatmospheric level in the said first bed,
introducing thereinto a gas stream substantially free of the
secondary key component to bring said first bed to an intermediate
pressure level, and thereafter;
(g) further repressurizing said first bed to initial
superatmospheric feed pressure level by flowing thereinto primary
key product gas via a second bed already pressurized to the
intermediate pressure level (step c), thereby bringing both beds to
the feed pressure level and making them ready to repeat the defined
sequence of steps beginning with the reintroduction of the
multicomponent feed gas mixture into the said first sorbent
bed.
2. The method as defined in claim 1, wherein said multicomponent
feed gas mixture comprises hydrogen as the primary key component,
carbon dioxide as the secondary key component and as tertiary gas
component at least one gas from the group consisting of methane,
carbon monoxide and nitrogen.
3. The method as defined in claim 2 wherein a carbonaceous solid
adsorbent is employed in at least said first bed.
4. A method as defined in claim 2 wherein the separation of the
multicomponent feed gas mixture is effected in a system comprising
a plurality of such first sorbent beds (A) operating sequentially
in parallel during a fixed cycle and a plurality of such second
sorbent beds (B), at least one of which second beds (B) is
selectively coupled in series with one or another first bed (A)
during the passage of the feed gas mixture into such first bed.
5. The method as defined in claim 4 wherein said rinsing of the
first bed at substantially feed pressure level during step (b)
above is effected in the same flow direction as that employed
during initial introduction of the multicomponent feed gas
mixture.
6. The method as defined in claim 5 wherein the effluent gas
discharged during said rinsing step is sent to another first bed
then receiving (step a) multicomponent feed gas for separation.
7. The method as defined in claim 4 wherein the defined pressure
lowering of said second bed to an intermediate pressure during step
(b) above is effected at least in part by transfer of gas withdrawn
therefrom to a previously evacuated first bed of the defined
system, thereby substantially equalizing pressure between said beds
involved in the transfer.
8. The method as defined in claim 7 wherein such withdrawal of gas
from the second bed for transfer to an evacuated first bed is
effected in a direction counter to the direction of passing of the
residual portion of the feed gas mixture therethrough at initial
substantially superatmospheric pressure.
9. The method as defined in claim 4 wherein the defined pressure
lowering of said second bed to an intermediate pressure during step
(b) above is effected in two sequential procedures, during the
first of which procedures withdrawn gas is transferred to a
previously evacuated first bed (A) of the defined system, and
during the second procedure the remainder of the withdrawn gas is
transferred to another second bed (B) of the system to equalize the
pressures between said second beds involved in the transfer.
10. The method as defined in claim 9 wherein such gas withdrawal
from said second bed is effected in a direction opposite to that of
initial passage of the multicomponent feed gas mixture into said
second bed.
11. The method as defined in claim 9 wherein said transfer of
withdrawn gas into the evacuated first bed is effected by flow of
gas into such first bed in a direction opposite to that of initial
feed gas flow therein.
12. The method as defined in claim 9 wherein said transfer of such
withdrawn gas into the evacuated first bed is effected by flow of
gas into such first bed in a direction concurrent to that of
initial feed gas flow therein.
13. The method as defined in claim 4 wherein the defined purging of
the said second bed at near ambient pressure during step (b) above
using part of the primary key component product is carried out in a
direction opposite to that of initial passage of the multicomponent
feed gas mixture into the said second bed.
14. The method as defined in claim 4 wherein the defined partial
repressuring of the second bed during step (c) above is effected by
introducing primary product gas into the bed in a flow direction
opposite to that of the initial feed gas flow therein.
15. The method as defined in claim 4 wherein the defined partial
repressuring of the second bed during step (c) above is effected in
two sequential procedures, during the first of which procedures
withdrawn gas from another second bed undergoing the pressure
reduction step (b) above is introduced into the said second bed in
a flow direction concurrent to that of the initial feed gas flow
therein and during the second procedure primary product gas is
introduced into the said second bed in a flow direction opposite to
that of the initial feed gas flow.
16. The method as described in claim 4 wherein the desorbed gas
during pressure reduction of said first bed as defined in step (c)
above is recompressed to feed pressure level and recirculated as
the rinse gas into another first bed of the system then undergoing
rinsing as defined in step (b) above.
17. The method as defined in claim 16 wherein the said desorption
step is carried out by flowing the gas in a direction opposite to
that of the initial feed flow through the bed.
18. The method as defined in claim 4 wherein the pressure reduction
of said first bed as defined in step (d) is effected in a direction
opposite to that of the initial feed gas flow through the bed.
19. The method as defined in claim 4 wherein said evacuation of the
first bed as recited in step (e) above is effected in a flow
direction therein opposite to that of the initial feed gas flow
therein.
20. The method as defined in claim 4 wherein said evacuation of the
first bed defined in step (e) is effected by pulling vacuum at an
intermediate level of said first bed.
21. The method as defined in claim 4 wherein the said partial
pressurization of the first bed during step (f) above to an
intermediate pressure level is effected by flowing the desorbed gas
from a second bed then undergoing the pressure reduction step
(b).
22. The method as defined in claim 4 wherein final pressurization
of a first and a second adsorbent bed to the initial
superatmospheric feed pressure during step (g) above is effected by
bringing a second bed in flow communication with a first bed, both
of which are previously pressurized to the same intermediate
pressure, and then flowing primary key product into the said second
bed in a flow direction opposite to that of the feed gas flow
through those beds.
23. The method as defined in claim 4 wherein during the aforesaid
rinsing step of said first bed as recited in step (b) above, at
least part of the effluent gas from said bed is added to the
multicomponent feed gas mixture.
24. The method as defined in claim 1 wherein during the aforesaid
rinsing step of said first bed as recited in step (b) above, at
least part of the effluent gas from said bed is added to the
multicomponent feed gas mixture.
25. In the separation of a multicomponent feed gas mixture with the
individual recovery of a primary key component and a secondary key
component present in such mixture, by selective sorption, wherein
said secondary key component is more strongly sorbed than the
primary key component and there is present in said mixture at least
one minor tertiary gas component less strongly sorbed than the
secondary key component; the method which comprises effecting such
selective sorption in a system comprising a plurality of first
sorbent beds (A) operated in parallel in timed sequence and a
plurality of second sorbent beds (B) operated in parallel in timed
sequence, said first beds containing said sorbent selective for
preferential retention of said secondary key component and said
second beds containing solid sorbent selective for retention of
said tertiary component(s) as opposed to said primary key
component; and wherein during a completed cycle each of said first
beds (A) undergoes a successive sequence of steps comprising:
(a) passage of the multicomponent feed gas mixture therethrough at
superatmospheric pressure in a selected positive flow direction;
with discharge therefrom of an effluent gas stream composed of the
unadsorbed portion of the feed gas mixture;
(b) discontinuing the passage of feed gas mixture into the bed and
discharge of effluent therefrom, followed by rinsing of the bed at
substantially initial feed gas pressure level by flow therethrough
of relatively pure secondary key component;
(c) after step (b) depressuring the bed to an intermediate pressure
level by gas withdrawal therefrom;
(d) further withdrawing contained gas from said bed to bring the
bed to substantially ambient pressure level;
(e) lowering the bed pressure to subatmospheric level by
evacuation;
(f) then again bringing the bed to an intermediate pressure level
by introduction therein of a product gas substantially free of
secondary key component;
(g) and finally bringing the bed to superatmospheric feed pressure
level by flow thereinto of substantially pure primary key
component; and during the time period for such complete cycle
undergone by each first (A) bed, each of the second (B) beds
undergoes twice in succession the steps of:
(h) receiving the previously unadsorbed effluent portion of the
initial feed gas mixture discharging from a first bed undergoing
step (a) above, with discharge therefrom of an effluent gas stream
composed of the unadsorbed portion of the primary key component of
the feed gas mixture;
(i) after discontinuing passage therein of said first bed effluent,
lowering the pressure of such second (B) bed by transfer of gas
therefrom into an evacuated first bed that has undergone step (e)
above;
(j) after step (i), further depressurizing such second bed by
transfer of gas therefrom into another second bed which has
undergone the purge step (l) below;
(k) after step (j) further depressurizing such second bed to or
near ambient pressure;
(l) purging such second bed at or near ambient pressure with
primary key component product;
(m) bringing such second bed to an intermediate pressure level by
introduction of desorbed gas from another second bed undergoing
step (j);
(n) and finally introducing substantially pure primary key
component into such second bed to bring the bed to substantially
feed gas pressure level.
26. The method as defined in claim 25 wherein said feed gas mixture
contains hydrogen as primary key component, carbon dioxide as a
secondary key component, and as tertiary component at least one gas
from the group consisting of methane, nitrogen and carbon
monoxide.
27. The method as defined in claim 26 wherein said adsorption
system is comprised of six first (A) beds and three second (B)
beds, each of said B beds being connected in flow communication
with a first bed (A) during at least the final repressurizing of
the latter bed to permit gas flow from the second bed to the
communicating first bed.
Description
RELATED APPLICATION
The present application is related to Applicants' companion
application Ser. No. 935,424 filed of even date herewith entitled
Separation of Multicomponent Gas Mixtures By Pressure Swing
adsorption.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to separation of gaseous mixtures
by selective adsorption and is more particularly concerned with an
adiabatic pressure swing adsorption system designed and operated
for separate recovery from a multicomponent gas mixture of a
primary key component and a secondary key component, each
substantially freed of the other key component and of the dilute
components present in minor quantity in the original gas mixture
subjected to treatment. To effect such separate recovery of desired
components of the feed gas mixture the system of the invention uses
separate beds of adsorbent in concurrent series gas flow
therebetween during the adsorption stage, yet designed for
independent operation during the regeneration or desorption
stages.
2. Prior Art
Pressure swing cyclic adsorption systems designed for fractionation
of gaseous mixtures by selective adsorption are well-known in the
art. In these systems one or more desired components of the feed
gas mixture are separately recovered at a yield and purity
depending upon the modes of the designed operation and their
efficiency.
Illustrative of typical systems indicated to be especially useful
in the recovery of hydrogen from gaseous mixtures with CH.sub.4
and/or CO.sub.2 are those described in U.S. Pat. Nos. 3,138,439;
3,142,547; 3,788,037. Other patents describe in general systems for
separation of essentially binary gas mixtures or of multicomponent
gas mixtures. Illustrative of these are the systems for separation
of essentially binary gas mixtures or of multicomponent gas
mixtures, asserted to be applicable in recovery of hydrogen from
such mixtures. Illustrative of these are the systems described, for
example, in U.S. Pat. Nos. 3,221,476; 3,430,418; 3,720,042. Also
among the systems described in the prior patent art are those
employing separate adsorbent beds operated in series flow and
designed for, or stated to be applicable in, separate recovery of
hydrogen and one or more other components present in a
multicomponent feed gas mixture. Typical among such systems are
those described in U.S. Pat. Nos. 3,102,013; 3,149,934; 3,176,444;
3,237,379; 3,944,400; and 4,000,990.
According to the present invention, a primary key component and a
secondary key component are recovered in separate streams at high
purity and in good yield from a multicomponent feed gas mixture,
each stream being substantially free of minor dilute contaminants
originally present in the feed gas mixture. Such separation and
recovery of the desired components are accomplished by the
hereinafter described sequence and mode of operation in a system
comprising a plurality of trains of adsorbent columns continuously
operated in timed cyclic sequence.
In U.S. Pat. No. 4,077,779, there are described adsorption systems
designed primarily for separation of binary gas mixtures which may
contain trace amounts of other impurities. While the systems
therein described can be successfully operated in the separation of
such binary gas mixtures, these systems cannot be efficiently
utilized in the individual recovery of two key components from a
multicomponent gas mixture containing in addition to these major
key components a minor quantity (more than trace amounts) of one or
more contaminating dilute components. The presence of such dilute
components may adversely affect the efficiency of gas separation of
pressure swing adsorption techniques designed for handling
essentially binary gas mixtures. However, the dilute components are
often present in such a small quantity that there is little
incentive for their separate recovery in highly enriched form. Thus
for many multicomponent gas mixtures confronted in industry for
separation therefrom of desired primary key and secondary key
components at high purity and yield, an impure tertiary stream of
the dilute components or their presence in the recovered secondary
product is often acceptable.
Multicomponent gas mixtures containing a bulk primary component, a
bulk secondary component and one or more dilute components,
generally encountered in industrial separation can be classified
into two different groups:
(1) Such mixtures in which the minor dilute components are less
strongly adsorbed than the secondary key component.
(2) Such mixtures in which the minor dilute components are more
strongly adsorbed than the secondary key component.
An example of a mixture of the first type is the gaseous effluent
from a shift converter in a hydrocarbon reforming plant. A typical
composition of such effluent may be 76% H.sub.2, 20% CO.sub.2, 3.5%
CH.sub.4, and 0.5% CO (each by volume). From such mixture CO.sub.2
is to be removed as the secondary key component and hydrogen
recovered as primary component in substantially pure state. The
dilute impurities such as CO and CH.sub.4, and N.sub.2 if present,
are less strongly adsorbed than CO.sub.2 on most commercial
sorbents such as activated carbons and certain molecular sieves. In
separation of this kind of gas mixture, a preferred plan may be to
obtain a stream of high purity H.sub.2 as the primary product, a
pure stream of CO.sub.2 as the secondary product, and a tertiary
stream containing the CO, N.sub.2 and CH.sub.4 impurities along
with some H.sub.2 which can be burnt as fuel.
An example of a mixture of the second type is the effluent gas from
a hydrodesulfurization plant after the removal of the sulfur
compounds, wherein it is desired to remove CH.sub.4 to recover high
purity recycle hydrogen. A typical desulfurized gas may contain for
example: 65% H.sub.2, 20% CH.sub.4, and 5% each of C.sub.2, C.sub.3
and C.sub.4 -C.sub.6 hydrocarbon components (each by volume). In
this instance also hydrogen constitutes the primary component. The
C.sub.2 + hydrocarbons are more strongly sorbed than the secondary
component (CH.sub.4). The dilute impurities containing C.sub.2
-C.sub.6 compounds in this case, may be tolerated in the secondary
product stream.
The present invention is particularly concerned with multicomponent
gas mixtures of the first kind hereinabove described. In such gas
mixtures high recovery of the primary key component (hydrogen) is
critical because any unrecovered hydrogen lost with the secondary
key component product, mainly CO.sub.2, cannot be efficiently
burnt.
Systems for handling gas mixtures of the second type
above-described is the subject of the aforesaid companion
application Ser. No. 935,424. In treating gas mixtures of the
second type, high recovery of the primary component is not as
critical economically since the hydrogen, which is not recovered in
the primary product, becomes a part of the secondary product mainly
containing CH.sub.4 and C.sub.2 + components which can be used as
fuel gas of high value.
Among the objectives obtained by practice of the present invention
is the economical individual recovery of both the primary and
secondary key components at high purity and improved product yields
as compared to the identified prior art systems.
SUMMARY OF THE INVENTION
In practice of the pressure swing adsorption method according to
the invention, a plurality of trains of adsorbent beds are operated
in parallel and in timed sequence, each such train comprising a
first bed containing an adsorbent selective for the retention of
the secondary key component of the feed gas mixture and a second
separate bed in series with said first bed, containing adsorbent
selective for retention of other dilute components of the feed gas
in preference over the primary key component. The adsorbent beds
and the time sequence are so arranged that only one second bed is
employed to serve two first beds. Thus a second bed and a first bed
form a train of two beds in series during the adsorption step of a
first bed at one part of the cycle, the same second bed provides
another train of two beds in series during the adsorption step of
another first bed at another part of the cycle. Consequently, the
total number of second beds used in the system is half the number
of first beds. Each train of adsorbent beds undergoes in its turn
during a cycle the following sequence of steps:
1. Adsorption. The feed gas mixture at superatmospheric pressure is
passed through a train of two adsorbent beds in series which have
been previously pressurized to the feed gas pressure, with the
withdrawal of an unadsorbed effluent comprising high purity
hydrogen from the exit end of the second bed, as primary purified
product. During this step the entire amount of the secondary key
component (CO.sub.2) from the feed mixture is retained in the first
bed and the entire amounts of the dilute components (CO and
CH.sub.4) are retained in the second bed.
2. High pressure rinse. At the end of step 1 the flow of feed gas
is switched to another train of adsorbent beds in the system which
has been brought to the desired adsorption pressure. The first bed
of the train that has undergone step 1, while substantially at its
initial high pressure, is now rinsed with pure secondary component
(CO.sub.2) by admitting the rinse gas at the initial inlet end of
that bed. During this step flow communication between the first and
second beds of the initial adsorption train is discontinued.
2a. Pressure equalization I. While the rinsing of step 2 is taking
place, the second bed of the train that has undergone step 1, is
connected to another first bed which has previously been evacuated
to lowest pressure level in the cycle. In this operation some of
the gas (void gas plus desorbed gas, if any) is being transferred,
thus lowering the pressure in the bed from which the gas flows.
2b. Pressure equalization II (optional). According to this mode of
operation, the pressure in the second bed that has been partially
reduced in step 2a is further lowered by gas transfer to another
selected second bed.
2c. Desorption. The bed that has undergone step 2a (or also 2b) is
further depressurized to or near ambient pressure.
3. Desorption I. The first bed that has undergone step 2 is now
brought to a first intermediate pressure level by withdrawal of gas
therefrom in a direction counter to that of step 1.
3a. Low pressure rinse. During step 3, the second bed that has been
brought to ambient pressure (step 2C) is rinsed with a part of the
high purity primary product (hydrogen).
3b. Pressurization. Flow of primary product gas into the second bed
that has been rinsed in step 3a is continued to bring that bed to
an intermediate pressure level and then to feed pressure level.
4. Desorption II. The first bed that has undergone step 3 is
further depressurized to about ambient pressure level, by
withdrawal of gas therefrom comprising chiefly the secondary key
component.
5. Evacuation. Following step 4, the first bed that has undergone
that step is now evacuated, withdrawing further quantities of the
secondary component (CO.sub.2).
6. Pressure equalization. Following evacuation in step 5 the first
bed is brought to an intermediate pressure level by the admission
thereto of the gas then being discharged (step 2a) from another
second bed of the series.
7. Pressurization. Primary product gas (H.sub.2) is then admitted
into the first bed following step 6 to bring that bed to adsorption
pressure level for start of a new cycle.
The operation of the invention will be fully understood and certain
of its advantages more fully appreciated from the detailed
description which follows read in connection with the accompanying
drawing illustrating a practical embodiment of a preferred system
in which the invention may be practiced.
The single FIGURE of the drawing is a flow diagram of a preferred
embodiment employing a group of six adsorbent vessels with
connecting conduits designed for operation in parallel in timed
sequence, each of these vessels being connected to a second group
of three adsorbent vessels through valved conduits designed to
enable vessels of said first group to be placed in series flow
communication with selected vessels of said second group.
DETAILED DESCRIPTION
Referring now to the drawing, the first group of vessels or
adsorption columns are labeled respectively 1A, 2A, 3A, 4A, 5A and
6A. The second group of vessels or adsorption columns are labeled
respectively 1B, 2B, 3B. The feed gas mixture to be separated may
be delivered to a selected initial column of the A group from a
feed gas manifold F, by opening the appropriate control valve 10,
11, 12, 13, 14, 15 in the branch line connecting manifold F to that
column.
At the inlet end (being the top in the illustrated embodiment as an
example) of each of the six vessels of the A group there is a gas
connecting line L through which under appropriate valve openings
gas can be selectively introduced and withdrawn from each of these
A vessels. A gas manifold G is connected to the outlet of
compressor C, whereby compressed gas can be introduced at the inlet
of the desired vessel of the A group through its line L, through a
valved connection between manifold G and that line by opening the
desired valve shown respectively at 20, 21, 22, 23, 24, 25.
The inlet of compressor C is connected to gas manifold H, which in
turn is connected to line L of each of the vessels of the A group
by a valved connection under control of valves 30, 31, 32, 33, 34,
35 respectively, by means of which gas can be selectively withdrawn
from the desired vessel into manifold H, compressed at C and
transferred into any one of the other vessels of the A group as
desired through manifold G on opening the appropriate valve in the
group numbered 20 to 25.
Each of the vessels of the A group is also connected to a gas
withdrawal manifold J through its line L under control of valves
40, 41, 42, 43, 44, 45 respectively. On opening the appropriate
valve in the 40-45 numbered group, gas will flow from its
associated vessel through its line L and into manifold J for
discharge therefrom or other desired disposition.
Each of the vessels 1A through 6A also is in flow communication
with a vacuum pump V through a manifold K, the manifold K being
connected to each of these A group vessels through line U and
through control valves 50, 51, 52, 53, 54, 55 respectively. Line U
may be connected to the A vessel at an intermediate level (as
shown) or at the feed inlet end of the vessel. Thus, by opening the
appropriate valve of the group numbered 50-55, the associated
vessel can be evacuated by operation of pump V and the gaseous
product withdrawn from that vessel discharged into manifold K. As
shown, the outlet of pump V is connected to discharge manifold J;
however, the evacuated gases may be separately disposed of, if
desired.
At the bottom of each of the columns 1A through 6A (hereinafter
sometimes referred to as the outlet end) is a connecting line M in
flow communication with a common gas receiving conduit N. Each of
the A group vessels can thus discharge gas into conduit N through
its associated line M by opening of the respective control valve
80, 81, 82, 83, 84, 85. Each of the vessels of the A group through
its associated line M, is also connected to a common gas withdrawal
conduit P under control of the respective valves 60, 61, 62, 63,
64, 65. Conduit P is in direct flow communication with manifold F
through a connecting conduit Q.
Each of lines M is also connected through a branch to a common gas
distributing conduit R under control of a valve 70, 71, 72, 73, 74,
75 respectively. By opening the appropriate valve of the 70-75
series, the associated A group vessel is brought into flow
communication with conduit R.
Each of the vessels 1B, 2B, 3B is provided at its upper end
(sometimes hereinafter called inlet end) with a gas line S
connected to common gas receiving conduit N under control of valves
90, 91, 92 respectively. By opening a selected one of these valves
90-92 gas will flow from line N into the associated vessel 1B, 2B,
or 3B through its line S.
Lines S also connect with a common tertiary gas product discharge
conduit T under control of valves 100, 101, 102 respectively. The
upper ends of vessels 1B, 2B, 3B are also in gas flow communication
with gas distributing conduit R. As shown, each of the lines S of
the group B vessels has a valve-controlled branch 200, 201, 202,
respectively, discharging into a common gas collecting conduit W in
direct flow communication with conduit R. By opening the selected
valve 200, 201 or 202, gas will be caused to flow from the B vessel
associated therewith into connecting conduit W and thence into
distributing conduit R. By opening a selected valve in the 70-75
group gas can be caused to flow upwardly from conduit R into the
associated vessel of the A group.
Each of the B vessels at its bottom end (sometimes hereinafter
referred to as outlet end) is in flow communication with a primary
product discharge manifold Z under control of a valved connection
300, 301, 302 respectively. By opening of any one of these valves
gas will be caused to flow from the associated B vessel into
manifold Z and thereby discharge unadsorbed primary products from
that vessel. A portion of the primary products in manifold Z can be
passed upwardly into any of the B vessels which is then at lower
pressure than that of the gas in manifold Z. This is accomplished
through valved connections 400, 401, 402 respectively. By opening
any one of these valves 400-402 associated with a vessel then at
lower pressure, primary gas product from manifold Z will be caused
to flow into the vessel associated with the thus opened valve.
As hereinafter more fully explained, the timed sequence of valve
openings and closings is so arranged that during an initial period
that the feed gas mixture to be separated is being introduced into
column 1A through open valve 10, valves 80, 90 and 300 are also
open, so that the portion of the gas that is not adsorbed by the
bed in Column 1A passes in series through Column 1B and the
effluent gas from Column 1B discharges through open valves 300 into
primary product discharge manifold Z. Thus, vessels 1A and 1B
constitute companion columns operating in series during this part
of the cycle and provide a train effective in selective adsorption
of components of the initial gas mixture charged. In the same way
columns 2A and 2B connected in series and 3A and 3B in series
respectively constitute similarly operating trains when these are
on the adsorption stage of their operating cycle.
The operating sequence is so arranged that each of the vessels 1B,
2B, 3B does double duty with respect to the A group of vessels.
During the time that vessel 4A is placed on adsorption by opening
valve 13, it is coupled in series with Column 1B through opened
valves 83, 90 and 300. Thus vessels 4A and 1B coupled in series,
constitute an adsorption train. In like manner vessels 5A and 2B,
6A and 3B respectively, operate as adsorption trains.
The sequence of process steps carried out in the illustrated system
of six beds (A group) for initial preferential adsorption of the
secondary key component (CO.sub.2), selectively coupled to one or
another of the three (B) beds of adsorbent for removal of the
tertiary minor components, is as follows:
1. Adsorption--Flow the feed mixture through a pair of sorption
vessels (say 1A and 1B in FIG. 1), connected in series through a
communicating valve 80 between them, both of which are previously
pressurized to the feed pressure level. Continue this step until
the secondary key component breaks through the exit end of vessel
1A or somewhat short of it. Withdraw the effluent gas during this
step from the exit end of vessel 1B as the purified primary product
at approximately the feed gas pressure (minus the losses in the
vessels and connecting lines). Vessel 1B is designed in such a way
that it retains all of the dilute impurities in the feed during
this step.
2. High Pressure Rinse--At the end of Step 1, flow a stream of
essentially pure secondary component of the feed mixture at the
feed pressure through the inlet end of vessel 1A. The communicating
valve between vessels A and B is closed during this step. Continue
this step until all of the void gas and any adsorbed primary
component from vessel A is purged out of the vessel. Recycle the
exit gas as feed into another A vessel undergoing step 1 during
this period.
2a. Pressure Equalization I--While rinsing vessel 1A in step 2,
connect vessel 1B with another A vessel which has previously been
evacuated to the lowest pressure level in the cycle. The purpose of
this step is to equalize the pressure between the two vessels,
thereby transferring some of the gas (void+desorbed if any) from B
vessel into A vessel. Pressure in vessel 1B decreases, while that
in 1A rises. The direction of gas flow in vessel 1B during this
step is countercurrent to that of step 1. The gas can be introduced
into A vessel either through the inlet or the exit end of that
vessel (FIG. 1 shows entry through the exit end).
2b. Pressure Equalization II--At the end of step 2a, connect vessel
1B with another B vessel which has been rinsed at low pressure with
primary effluent (step 3a) for a second pressure equalization,
thereby transferring more gas from vessel 1B into another B vessel.
The direction of gas flow in vessel 1B during this step is the same
as that in 2a, while the gas removed from 1B is introduced into
another B vessel in the same direction as that of feed (step
1).
It should be emphasized here that the extent of steps 2a and 2b
will be determined by various factors such as (i) feed pressure,
(ii) feed composition, (iii) desorption characteristics, (iv)
product purity, and (v) product recovery. It is conceivable that
step 2B is completely eliminated for a certain demand in operation.
In other words, the terminating pressure for the pressure
equalization steps will be governed by the above-mentioned
factors.
2c. Desorption--Depressurize vessel 1B countercurrent to the
direction of feed (step 1) further down to near ambient pressure
after the pressure equalization steps. The effluent during this
step consists of the dilute impurities of the feed mixture along
with some of the primary components. The duration of steps 2a plus
2b plus 2c is equal to that of step 2.
3. Desorption--Depressurize vessel 1A countercurrent to the
direction of feed (step 1) to an intermediate pressure level.
Recompress the desorbed gas, which is essentially pure secondary
key component of the feed mixture, to feed pressure level and
recirculate the compressed gas as the high pressure rinse gas (step
2) into another A vessel under going step 2 during this period.
3a. Low Pressure Rinse--While column 1A is undergoing step 3, rinse
column 1B countercurrent to the direction of feed (step 1) at near
ambient pressure using a part of the high purity primary product
gas. The effluent from this step may be mixed with the effluent
from step 2c and the mixed gas would constitute the tertiary
by-product stream from the process. The extent of this step will be
determined by the recovery and purity of the desired product.
3b. Pressurization--Pressurize vessel 1B with primary product gas
countercurrent to the direction of feed to the pressure level
achieved after step 2a. At this point, connect this vessel with one
of the A vessels which has undergone step 6 below and further
pressurize both vessels to the feed pressure. The direction of gas
flow through both vessels during this step is countercurrent to
that of the feed. The duration of steps 3a plus 3b equals to that
of step 3. Vessel 1B is now ready for a new adsorption step.
4. Desorption II--Further depressurize column 1A countercurrent to
the direction of the feed to ambient pressure level. Withdraw the
desorbed gas during this step as secondary by-product comprising
the secondary key component.
5. Evacuation--Evacuate vessel 1A to the lowest pressure level in
the cycle, by gas withdrawal from an intermediate level thereof or
at the feed inlet end thereof, countercurrent to the direction of
the feed. Withdraw the evacuated gas as additional secondary
by-product.
6. Pressure Equalization--Connect vessel 1A with one of the B
vessels which is undergoing step 2a for pressure equalization,
thereby pressurizing vessel 1A to an intermediate pressure
level.
7. Pressurization--Further repressurize vessel 1A to feed pressure
level using primary product gas by connecting it with one of the B
vessel undergoing later part of step 3b.
At this point, vessel 1A is at feed pressure and ready for a new
cycle starting from step 1. One of the B vessels is also ready to
undergo the adsorption step with the 1A vessel.
Operation of an embodiment of the invention according to one mode
(I) will now be explained in connection with an arbitrarily chosen
24 minute cycle, as set out in Table 1A (step 2B omitted).
TABLE 1A ______________________________________ PERFORMANCE OF THE
VESSELS ACCORDING TO I CONFIGURATION (Step 2b excluded) Time (min-
Vessels utes) 1A 2A 3A 4A 5A 6A 1B 2B 3B
______________________________________ 0-1 A PE E D.sub.2 D.sub.1 R
A P PE 1-2 A PE E D.sub.2 D.sub.1 R A P PE 2-3 A E D.sub.2 D.sub.1
R A PR D 3-4 A PR E D.sub.2 D.sub.1 R A PR D 4-5 R A PE E D.sub.2
D.sub.1 PE A P 5-6 R A PE E D.sub.2 D.sub.1 PE A P 6-7 R A E
D.sub.2 D.sub.1 D A PR 7-8 R A PR E D.sub.2 D.sub.1 D A PR 8-9
D.sub.1 R A PE E D.sub.2 P PE A 9-10 D.sub.1 R A PE E D.sub.2 P PE
A 10-11 D.sub.1 R A E D.sub.2 PR D A 11-12 D.sub. 1 R A PR E
D.sub.2 PR D A 12-13 D.sub.2 D.sub.1 R A PE E A P PE 13-14 D.sub.2
D.sub.1 R A PE E A P PE 14-15 D.sub.2 D.sub.1 R A E A PR D 15-16
D.sub.2 D.sub.1 R A PR E A PR D 16-17 E D.sub.2 D.sub.1 R A PE PE A
P 17-18 E D.sub.2 D.sub.1 R A PE PE A P 18-19 E D.sub.2 D.sub.1 R A
D A PR 19-20 E D.sub.2 D.sub.1 R A PR D A PR 20-21 PE E D.sub.2
D.sub.1 R A P PE A 21-22 PE E D.sub.2 D.sub.1 R A P PE A 22-23 E
D.sub.2 D.sub.1 R A PR D A 23-24 PR E D.sub.2 D.sub.1 R A PR D A
______________________________________ A = Adsorption R = High
Pressure Rinse D = Desorption D.sub.1 = Desorption D.sub.2 =
Desorption E = Evacuation PE = Press. Equal. P = Purging PR =
Pressurization
It is assumed that the train comprising columns 1A and 1B is
initially to be put on stream for removal of CO.sub.2 and other
contaminants from a hydrogen-containing gas mixture. The A columns
contain appropriate adsorbent materials, as hereinafter described,
for selective adsorption of CO.sub.2 (secondary key component) from
the feed gas mixture, while the B columns contain adsorbent
selective for adsorption of the minor diluents (such as CH.sub.4
and/or CO).
The feed gas mixture is introduced into adsorbers 1A and 1B (both
of which have been prepressurized to feed pressure) through valve
10 and the purified primary product stream is withdrawn through
valve 300. The interconnecting valves 80 and 90 between the two
vessels are kept open during this period. Valves 10, 80, 90 and 300
are closed when the secondary key component (CO.sub.2 in example)
is about to breakthrough the exit end of column 1A and the feed is
switched to vessel 2A by opening the appropriate valves. Valves 20,
60 and 200 are opened immediately thereafter. A stream of
essentially pure secondary key component at feed pressure is passed
through vessel 1A co-current to the direction of feed. The stream
is introduced through valve 20 and the exit void and displaced gas
from 1A is withdrawn through valve 60. The exit gas is mixed with
fresh feed and introduced into vessel 2A which is undergoing the
adsorption step. During the same period of time, the vessel 1B is
connected with vessel 3A which has been previously evacuated to the
lowest pressure level in the cycle. Gas from 1B flows out through
valve 200 and enters vessel 3A through valve 72. Optionally, when
the pressure levels between vessels 1B and 3A become equal, valve
72 is closed and valve 202 is opened for the second pressure
equalization between vessels 1B and 3B. If the second pressure
equalization step is not needed, the duration of first pressure
equalization step may be extended (see Tables 1A and 1B). Valve 200
is closed after the pressure equalization steps and vessel 1B is
depressurized to ambient pressure by opening valve 100. The
effluent through valve 100 constitutes part of tertiary product.
Valves 20 and 72 are closed when all of the void and displaced gas
from vessel 1A is purged out. Valve 30 is then opened and vessel 1A
is depressurized to an intermediate pressure level. The desorbed
gas during this step is recompressed and used to purge vessel 2A
undergoing the high pressure rinse step. Simultaneously, control
valve 400 is opened and a stream of high purity primary product is
introduced into vessel 1B at a controlled rate countercurrent to
the direction of flow in the sorption step. The exit gas flows out
of the vessel 1B through valve 100 and withdrawn as tertiary
product. After the required low pressure purge, valves 100 and 400
are closed, valve 200 is opened and vessel 1B is pressure equalized
with vessel 2B. Valve 400 is opened again while closing valve 200
and vessel 1B is further pressurized with the primary product gas
to the intermediate pressure level of A vessels at the end of step
6. Valve 200 is opened again along with valve 73 and vessels 1B and
4A are pressurized to feed pressure using primary effluent. In
absence of the second pressure equalization step, valve 400 remains
open during the entire period of low pressure purge and
pressurization. Valves 73, 200 and 400 are then closed. Vessel 1B
is now ready to go through a fresh cycle and engages with vessel
4A. The first desorption step of vessel 1A is completed during this
time and valve 30 closes. Valve 40 opens and vessel 1A is
depressurized to ambient pressure. The desorbed gas is withdrawn as
secondary product. Valve 40 is closed and valve 50 is opened for
evacuation of column 1A after the second desorption step. Valve 50
is closed after the evacuation step and valve 70 is opened for
pressure equalizing vessel 1A with vessel 2B. Valve 70 is then
closed for a period of time and reopened again for pressurizing 1A
to the feed pressure using primary effluent gas via vessel 1B and
valves 400 and 200. Column A is now ready to undergo another
cycle.
The position of the various valves during a single cycle in which
each of the adsorbent beds undergoes in timed sequence the steps
outlined in Table 1A is shown in Table 2A. The designation 0
indicates that the valve is open, while the blanks indicate closed
valves.
TABLE 2A
__________________________________________________________________________
TIME VALVES (MINUTES) 10 11 12 13 14 15 20 21 22 23 24 25 30 31 32
33 34 35 40 41 42 43 44 45
__________________________________________________________________________
0-1 0 0 0 0 1-2 0 0 0 0 2-3 0 0 0 0 3-4 0 0 0 0 4-5 0 0 0 0 5-6 0 0
0 0 6-7 0 0 0 0 7-8 0 0 0 0 8-9 0 0 0 0 9-10 0 0 0 0 10-11 0 0 0 0
11-12 0 0 0 0 12-13 0 0 0 0 13-14 0 0 0 0 14-15 0 0 0 0 15-16 0 0 0
0 16-17 0 0 0 0 17-18 0 0 0 0 18-19 0 0 0 0 19-20 0 0 0 0 20-21 0 0
0 0 21-22 0 0 0 0 22-23 0 0 0 0 23-24 0 0 0 0
__________________________________________________________________________
TIME VALVES (MINUTES) 50 51 52 53 54 55 60 61 62 63 64 65 70 71 72
73 74 75 80 81 82 83 84 85
__________________________________________________________________________
0-1 0 0 0 0 1-2 0 0 0 0 2-3 0 0 0 3-4 0 0 0 0 4-5 0 0 0 0 5-6 0 0 0
0 6-7 0 0 0 7-8 0 0 0 0 8-9 0 0 0 0 9-10 0 0 0 0 10-11 0 0 0 11-12
0 0 0 0 12-13 0 0 0 0 13-14 0 0 0 0 14-15 0 0 0 15-16 0 0 0 0 16-17
0 0 0 0 17-18 0 0 0 0 18-19 0 0 0 19-20 0 0 0 0 20-21 0 0 0 0 21-22
0 0 0 0 22-23 0 0 0 23-24 0 0 0 0
__________________________________________________________________________
TIME VALVES (MINUTES) 90 91 92 100 101 102 200 201 202 300 301 302
400 401 402
__________________________________________________________________________
0-1 0 0 0 0 0 1-2 0 0 0 0 0 2-3 0 0 0 0 3-4 0 0 0 0 4-5 0 0 0 0 0
5-6 0 0 0 0 0 6-7 0 0 0 0 7-8 0 0 0 0 8-9 0 0 0 0 0 9-10 0 0 0 0 0
10-11 0 0 0 0 11-12 0 0 0 0 12-13 0 0 0 0 0 13-14 0 0 0 0 0 14-15 0
0 0 0 15-16 0 0 0 0 16-17 0 0 0 0 0 17-18 0 0 0 0 0 18-19 0 0 0 0
19-20 0 0 0 0 20-21 0 0 0 0 0 21-22 0 0 0 0 0 22-23 0 0 0 0 23-24 0
0 0 0
__________________________________________________________________________
0 = Open Blank = Closed
In the alternative mode (II) of operation each of the B vessels
undergoes the second pressure equalization step described under
step 2b above, which is omitted in the sequence outlined in Table
1A. The process steps undergone in sequence in the alternative
operational mode is outlined in Table 1B and the valve positions
during such cycle as shown in Table 2B for an arbitrarily chosen 24
minute cycle.
TABLE 1B ______________________________________ PERFORMANCE OF THE
VESSELS ACCORDING TO II CONFIGURATION (Step 2b Included) Time (Min-
Vessels utes) 1A 2A 3A 4A 5A 6A 1B 2B 3B
______________________________________ 0-1 A PE E D.sub.2 D.sub.1 R
A P PE 1-2 A E D.sub.2 D.sub.1 R A PE PE 2-3 A E D.sub.2 D.sub.1 R
A PR D 3-4 A PR E D.sub.2 D.sub.1 R A PR D 4-5 R A PE E D.sub.2
D.sub.1 PE A P 5-6 R A E D.sub.2 D.sub.1 PE A PE 6-7 R A E D.sub.2
D.sub.1 D A PR 7-8 R A PR E D.sub.2 D.sub.1 D A PR 8-9 D.sub.1 R A
PE E D.sub.2 P PE A 9-10 D.sub.1 R A E D.sub.2 PE PE A 10-11
D.sub.1 R A E D.sub.2 PR D A 11-12 D.sub.1 R A PR E D.sub.2 PR D A
12-13 D.sub.2 D.sub.1 R A PE E A P PE 13-14 D.sub.2 D.sub.1 R A E A
PE PE 14-15 D.sub.2 D.sub.1 R A E A PR D 15-16 D.sub.2 D.sub.1 R A
PR E A PR D 16-17 E D.sub.2 D.sub.1 R A PE PE A P 17-18 E D.sub.2
D.sub.1 R A PE A PE 18-19 E D.sub.2 D.sub.1 R A D A PR 19-20 E
D.sub.2 D.sub.1 R A PR D A PR 20-21 PE E D.sub.2 D.sub.1 R A P PE A
21-22 E D.sub.2 D.sub.1 R A PE PE A 22-23 E D.sub.2 D.sub.1 R A PR
D A 23-24 PR E D.sub.2 D.sub.1 R A PR D A
______________________________________ A = Adsorption R = High
Pressure Rinse D = Desorption D.sub.1 = Desorption D.sub.2 =
Desorption E = Evacuation PE = Press. Equal. PR = Pressurization P
= Purging
TABLE 2B
__________________________________________________________________________
TIME VALVES (MINUTES) 10 11 12 13 14 15 20 21 22 23 24 25 30 31 32
33 34 35 40 41 42 43 44 45
__________________________________________________________________________
0-1 0 0 0 0 1-2 0 0 0 0 2-3 0 0 0 0 3-4 0 0 0 0 4-5 0 0 0 0 5-6 0 0
0 0 6-7 0 0 0 0 7-8 0 0 0 0 8-9 0 0 0 0 9-10 0 0 0 0 10-11 0 0 0 0
11-12 0 0 0 0 12-13 0 0 0 0 13-14 0 0 0 0 14-15 0 0 0 0 15-16 0 0 0
0 16-17 0 0 0 0 17-18 0 0 0 0 18-19 0 0 0 0 19-20 0 0 0 0 20-21 0 0
0 0 21-22 0 0 0 0 22-23 0 0 0 0 23-24 0 0 0 0
__________________________________________________________________________
TIME VALVES (MINUTES) 50 51 52 53 54 55 60 61 62 63 64 65 70 71 72
73 74 75 80 81 82 83 84 85
__________________________________________________________________________
0-1 0 0 0 0 1-2 0 0 0 2-3 0 0 0 3-4 0 0 0 0 4-5 0 0 0 0 5-6 0 0 0
6-7 0 0 0 7-8 0 0 0 0 8-9 0 0 0 0 9-10 0 0 0 10-11 0 0 0 11-12 0 0
0 0 12-13 0 0 0 0 13-14 0 0 0 14-15 0 0 0 15-16 0 0 0 0 16-17 0 0 0
0 17-18 0 0 0 18-19 0 0 0 19-20 0 0 0 0 20-21 0 0 0 0 21-22 0 0 0
22-23 0 0 0 23-24 0 0 0 0
__________________________________________________________________________
TIME VALVES (MINUTES) 90 91 92 100 101 102 200 201 202 300 301 302
400 401 402
__________________________________________________________________________
0-1 0 0 0 0 0 1-2 0 0 0 0 0 0 2-3 0 0 0 0 3-4 0 0 0 0 4-5 0 0 0 0 0
5-6 0 0 0 0 0 0 6-7 0 0 0 0 7-8 0 0 0 0 8-9 0 0 0 0 0 9-10 0 0 0 0
0 0 10-11 0 0 0 0 11-12 0 0 0 0 12-13 0 0 0 0 0 13-14 0 0 0 0 0 0
14-15 0 0 0 0 15-16 0 0 0 0 16-17 0 0 0 0 0 17-18 0 0 0 0 0 0 18-19
0 0 0 0 19-20 0 0 0 0 20-21 0 0 0 0 0 21-22 0 0 0 0 0 0 22-23 0 0 0
0 23-24 0 0 0 0
__________________________________________________________________________
EXAMPLE
The nine bed embodiment of the invention as illustrated in FIG. 1
will be more fully understood by the following example:
The system consists of six A beds, each packed with 96.7 lbs (44.0
kg) of BPL activated carbon, and three B beds, each packed with a
layer of 61.9 lbs (28.1 kg) of BPL carbon and a layer of 17.6 lbs
(8.0 kg) of 5 A molecular sieve. A feed gas comprising of 76.73%
H.sub.2, 18.71% CO.sub.2, 4.10% CH.sub.4 and 0.46% CO (by volume)
at 265 psia (18.0 bar) and a temperature of 100.degree. F.
(37.8.degree. C.) is introduced into one of the A columns connected
in series with one of the B columns, both of which are previously
pressurized to the feed gas pressure level. The feed flow rate is
11.3 lb moles/hour (5.1 kg moles/hour). A stream of essentially
pure H.sub.2 comprising of 99.99+% H.sub.2 (by volume) is withdrawn
through the exit end of the B column. A part of this stream is
withdrawn as product H.sub.2 at a rate of 7.90 lb moles/hour (3.6
kg moles/hour). The adsorption step is continued for four minutes
when the feed is switched to another A column. Then the
communicating valve between the A and the B columns is closed and
the column A is rinsed with a stream of 99.99+% pure CO.sub.2 at
about 265 psia (18.0 bar). The rinse gas is introduced into the A
column through the same inlet as that for the feed gas at a rate of
3.11 lb moles/hour (1.4 kg moles/hour). The effluent gas from the
first column during this step is withdrawn from the outlet end of
the A column at a rate of 1.18 lb moles/hour (0.54 kg moles/hour).
The effluent gas has essentially the same composition as feed gas
and it is recycled as feed to another column receiving fresh feed
gas. This step is continued for four minutes. While column A is
rinsed with CO.sub.2, column B is desorbed by connecting it with
another A vessel which is previously evacuated to the lowest
pressure level in the process. The pressure equalization step is
carried out for one minute and the pressure level in the two beds
at the end of this step is about 116 psia (7.9 bar). The B bed is
then further depressurized by connecting it with another B vessel
which is previously purged with H.sub.2 product gas. The second
pressure equalization is also carried out for one minute and the
pressure level in the two beds at the end of this step is about 58
psia (3.9 bar). The B bed is then further depressurized to near
ambient pressure level while withdrawing the effluent gas as the
tertiary product. This step is carried out for two minutes.
Column A is now depressurized for four minutes to a pressure level
of about 51 psia (3.5 bar). The effluent gas comprising of
essentially pure CO.sub.2 is recompressed to about 265 psia (18.0
bar) and recycled into another A column as the high pressure rinse
gas. While column A is desorbing, column B is first purged with a
portion of the high purity H.sub.2 effluent from the adsorption
step for a period of one minute. The effluent gas from column B
during the purge step is withdrawn as the tertiary product. The
combined flow rate of the tertiary product is 1.29 lb moles/hr
(0.59 kg moles/hour) and has a composition of about 59.0% H.sub.2,
36.0% CH.sub.4, 4.1% CO and a trace amount of CO.sub.2. The B
column is then connected with another B column, which other B
column is undergoing the pressure reduction step, in order to
pressure equalize both B columns to about 58 psia. This step is
carried out for one minute. The B column is then pressurized in one
minute to a pressure level of about 116 psia (7.9 bar) by flowing a
portion of the high purity H.sub.2 effluent from the adsorption
step. Finally the B column is connected to an A column which is
previously pressurized to about 116 psia (7.9 bar) and then both
columns are pressurized to about 265 psia (18.0 bar) by flowing a
portion of the high purity H.sub.2 effluent from the adsorption
step. The pressurization step is carried out in one minute. The B
column is now ready to undergo another cycle of operation according
to the scheme of the embodiment.
Column A is then further depressurized to near ambient pressure in
four minutes. The desorbed gas comprising of essentially pure
CO.sub.2 is withdrawn as the secondary key component product.
Next, column A is evacuated to a pressure level of 2.4 psia (0.16
bar) in four minutes. The evacuated gas is also withdrawn as
secondary product. The total flow rate of the secondary product is
2.11 lb moles/hr (0.96 kg moles/hour) and its composition is
99.99+% CO.sub.2.
Column A is then pressurized to a level of about 116 psia (7.9 bar)
by connecting it with a B column which is undergoing the first
pressure equalization step.
Finally the A column is pressurized to a level of about 265 psia
(18.0 bar) by connecting it with a B column which is already
pressurized to a level of about 116 psia (7.9 bar) and flowing the
high purity H.sub.2 effluent from the adsorption step. The A column
is now ready to undergo another cycle of operation according to the
scheme of the embodiment.
As a consequence of this operation, the feed gas is fractionated
into a primary product comprising of 99.99+% H.sub.2 by volume with
a hydrogen recovery from the feed gas of about 91.1%; a secondary
product comprised of 99.99+% CO.sub.2 by volume with a carbon
dioxide recovery from the feed gas of about 99.9+%; and a tertiary
product comprising essentially 59.0% H.sub.2, 36.0% CH.sub.4, 4.1%
CO by volume and a trace amount of CO.sub.2 with a very good fuel
value.
While the invention has been particularly described in connection
with the separation and recovery of hydrogen as the primary key
component and carbon dioxide as the secondary key component from a
gas mixture containing these accompanied by minor (tertiary)
components, it will be understood that the described system and
operation can be advantageously employed in the separation of other
multicomponent gas mixtures having present therein a major portion
of (1) primary key component which is not substantially adsorbed in
either of the adsorbent beds of a train, (2) a secondary key
component desired to be recovered and which is preferentially
adsorbed and (3) one or more dilute components which are less
strongly adsorbed than the secondary key component. Any sorbent
which is selective towards the secondary key component of the feed
mixture can be used in the A vessels. The sorbent in the B vessels
should be selective for the minor tertiary components of the feed
mixture or there may be employed in the B vessels a combination of
sorbents for that purpose. Thus, for the multicomponent gas mixture
of the illustrative example, comprising hydrogen (primary),
CO.sub.2 (secondary) and dilute impurities (tertiary) such as
CH.sub.4 and CO, the A vessels may contain a carbonaceous sorbent
such as BPL activated carbon or MSC-V carbon. In the B vessels a
combination of sorbents may be employed such as BPL carbon and 5
A.degree. molecular sieve zeolites. In general, the choice of the
particular sorbent is governed by the operating conditions (such as
temperature and pressure) employed in the separation process and
the composition of the feed gas and the nature of the impurities
sought to be removed and the nature of the product qualities and
recoveries demanded by the application.
The key benefits that can be achieved by operation according to
this invention are:
1. High purity of the primary product stream (e.g. hydrogen).
2. High recovery of the primary key component at such high
purity.
3. Recovery at high purity of an economically valuable secondary
product stream (e.g. CO.sub.2).
4. Very high yield of the secondary product at high purity.
5. Absence of significant amounts of the secondary key component in
the tertiary product stream. This may allow useful utilization of
that stream which may not be possible if the secondary key
component is present in that stream in substantial quantity. For
instance, the example given in the text will produce a tertiary
stream containing CO, CH.sub.4 and H.sub.2, substantialy free from
CO.sub.2, thus enabling the use of such stream as good quality fuel
gas.
6. Improved operational efficiency and improved process economics
as a result of:
(a) Continuous feeding of the charge gas mixture and continuous
withdrawal of product gas streams (primary and secondary) at
constant pressure and constant flow rates.
(b) Continuous operation of the compressors and vacuum pumps.
(c) Efficient utilization of the adsorbent beds.
(d) Efficient utilization of the available feed pressure
energy.
(e) Absence of large product surge tanks.
While in the drawing the feed gas is shown as being introduced to
flow downwardly through the A and B vessels, it will be understood
that the initial feed, if desired, may be introduced to flow
upwardly through these A and B vessels in that order. In that event
the directions of other gas flows will be changed to maintain the
same relative directions with respect to the flow of the feed
gas.
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