Note: Descriptions are shown in the official language in which they were submitted.
1049937
B.~C~;GROUND OF TI~E ~NVENTION
.
Tl-is invention rclates to improvements in the
separation of gas mixtures, and more particularly to a process
for the separation of gas mixtures by selective adsorption.
Gas mixtures having selectively adsorbably components
can be separated by certain adsorbent materials, and this
technique for the separation of gases is generally known as the
pressure swing separation of gases. Commercially available
adsorbent materials with selective adsorption characteristics
are well known for these processes. Each adsorbent has unique
characteristics which adapt its use to various gas separation
systems. The various applications for such systems range from
the separation of complex organic and/or inorganic gas mixtures
to the purification of air by the removal of water and carbon
dioxide. The prior art is replete with examples of these
mixtures of gases which can be separated by the pressure swing
processes. For example, ethane, propane, ethylene or propylene
can be separated from each other or from higher gaseous paraffins
or olefins; sulfur oxides, hydrogen sulfide, carbon dioxide,
carbon disulfide and/or carbonyl sulfide can be removed from
natural gas, ethane, propane, butane, ethylene, propylene,
isoprene or butadiene; and carbon dioxide and/or nitrogen can
be separated from air so as to purify the air or provide an
oxygen enriched air. Although the present process is specifically
described and illustrated in relation to the application of
pressure swing adsorption to the fractionation of air as a means
of producing an oxygen rich stream, it is broadly applicable
to the separation of organic and/or inorganic gas mixturcs.
There have been many pressure swing adsorption systems
set forth as a means of separating air into basically an oxygen
rich stream and a nitrogen rich stream. The oxygen rich stream
is of greatest commercial interest due to its many and varied
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104993~
uses., The maln goal of these systems has been to conserve
oxygen and thereby obtain the highest possible oxy~en recovery
from the feed ~ir stream. This has been accomplished by
utilizing one or more adsorbent beds and on occasion, one or
more empty storage tanks connected and sequentially arranged
such that a minimum low purity oxygen stream is vented to the
atmosphere while a maximum of high purity oxygen is available
as a product oxygen stream.
One of the pressure swing adsorption systems is
described by Marsh et al in U.S. Patent No. 3,142,547. Marsh
et al provide a cyclic scheme of alternately diverting lower
pressure product oxygen from either one of two adsorbent beds
for storage in an empty tank for later use as a countercurrent
purge gas for the low pressure desorbing bed. This involves
the preparative repressurization of the non-adsorbing bed with
product oxygen from the adsorbing bed prior to switching the
feed stream to the purged repressurized bed. However, it is
limited in quantity of void gas recovery to that which can be
blown down before pressure equalization occurs between the
adsorption bed and the surge tank. Moreover, it diverts a low
purity oxygen stream to the atmosphere and delivers product
quality-oxygen only after the maximum adsorption pressure has
been reached.
U.S. Patent No. 3,738,087 to McCombs et al describes
several cycles wherein repressurization occurs partially with
feedgas after initial bed pressure equalization step(s).
Product quality oxygen is removed from the bed being re-
pressurized with feed air in McCombs et al, this being referred
to as variable pressure adsorption.
In U.S. Patent No. 3,788,036, Lee et al describes
a sequential pressure equalization technique where high pressure
in the adsorbent bed which is to commence a regeneration phase
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_ . = ~ . . _ . . .. _ . = , _ _ .. , . _ _, . .. .. , ,,, _ _ . .
iO49937
is conserved by a dual pressure equalization. Lee et al
conserve oxygen to a greater exten~ than McCombs and Marsh
et al by adding an empty tank to the system and using this
tank to supply the purge gas to the depressurized desorbing bed
and showedsignificantly improved performance over Marsh et al
and McCombs, but Lee et al cannot deliver continuous product
oxygen without adding a product surge tank, nor can Lee et al
continuously receive an uninterrupted flow of feed air.
Other pressure swing adsorption processes are also
described in the prior art. However, these systems also have
the same shortcomings as described supra and/or require four
or more adsorbent beds with concomitant piping and valving to
provide efficient separation of gases, uninterrupted flow of
product gas and/or continuous flow of feed air stream.
OBJECTS OF THE INVENTION
Accordingly, it is the primary object of this
invention to provide an improved process for separation and
; fractionation of gas mixtures by selective adsorption.
It is another object of this invention to provide an
improved process for conserving low purity product gases here-
tofore vented from swing adsorption process systems.
It is another object of this invention to provide
for the efficient separation of gases by a selective adsorption
process utilizing as few as two adsorbent beds directly exposed
to a feed gas stream.
Another object of this invention is to provide a
continuous, uninterrupted flow of product gas from adsorbent
beds which have selectively separated gases in a continuously
flowing feed gas stream while utilizing low purity product
gases for repressurization of regenerated adsorbent beds and
high purity product quality gas for purge gas to regenerate
adsorbent beds without sacrificing the integrity and quality of
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10~9937
the product gas.
Still another object of this invention is to provide
an improved process for separation of air by selective adsorption
to provide a product oxygen of desired purity without loss of
low purity oxygen normally vented as a waste gas.
Another object of this invention is to provide a
process for regenerating exhausted adsorbent beds and re-
pressurizing such regenerated beds with high quality non-product
oxygen and low purity oxygen fractions respectively, said
oxygen generally being diverted to other functions of lesser
importance or diverted to waste.
These and other objects and advantages will be
apparent from the ensuing disclosure and appended claims.
SUMMARY OF THE INVENTION
These and other objects of this invention are
accomplished by utilizing at least two adsorption beds and at
least one segregated storage tank having adsorbent material
therein and hereinafter referred to as the segregated storage
adsorption bed. It is critical in the processes of the present
invention that the segregated storage adsorption bed never be
exposed directly to the feed gas stream during fractionation
cycles.
Thus, in accordance with the present teachings, a
pressure swing process is provided for fractionating at least
one component from a gaseous mixture by selective adsorption
in each of at least two adsorption zones by sequentially passing
the gaseous mixture from a feed stream through a first
adsorption zone until low purity gas is obtained while
simultaneously purging and then pressurizing a second adsorption
zone and then through the second adsorption zone until low
purity product gas is obtained while simultaneously purging
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104993~
~nd then pressurizing the first adsorption zone. The product
quality gas is selectively collected and low purity gas which
is not of product quality is segregated in a storage adsorption
zone. The quality gas collected is selectively passed in a
segregated storage adsorption zone from one end of the segregated
storage adsorption zone as countercurrent purge gas to at least
contribute to the purge gas used to remove components adsorbed
in the bed of the adsorption zones. The low purity gas
collected in the segregated storage adsorption zone is
selectively diverted from the other end of the segregated
storage adsorption zone as repressurizing gas to the adsorption
zone after the adsorption zone has been purged with a counter-
current flow of purge gasat least part of which was contributed
by gas from the segregated storage adsorption zone to at
least contribute to the repressurization of that particular
adsorption zone. The segregated storage adsorption zone is
never exposed directly to the feed gas stream during
the fractionation cycles.
The segregated storage adsorption bed allows for the
withdxawal of high quality or high purity product gas therefrom
for product and/or purge gas from its one end, and low purity
gas which is not of product quality, can be withdrawn from the
other end to be used to aid in the feed end repressurization of
the adsorbent bed or beds to be used later as the adsorbing bed.
Low purity gas which is not of product quality, is diverted
from the particular bed which has just terminated adsorption,
without contaminating the product delivering end of the next
adsorbing bed. This low purity gas is used to replace the high
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1049937
~urity pro~uct gas in the upper portions of beds undergoing
depressurization in the particular vessel or tank head and
in associated piping resulting in lower product gas losses
during the subsequent countercurrent depressurization to
atmosphere and purge and a higher product gas recovery.
The lower product gas loss and high product gas
recovery is accomplished by passing the low purity product
gas from the adsorption bed to one end of the segregated
storage adsorption bed where it is adsorbed and later discharged
therefrom to aid in the feed end repressurization of the next
adsorbing bed. By using the low purity product gas stream to
repressurize at the feed end, there is only a minimal effect
(loss of adsorptive capacity) on the fractionation or separation
capacity of the adsorbing bed.
As used herein, low purity product gas refers to gas
which has passed through an adsorption bed in the final stages
of adsorption and having only minimal adsorptive capacity
whereby the gas has been fractionated to such an extent that it
is of higher purity or quality than the feed gas stream (gaseous
mixture to be fractionated).
In accordance with the present invention any gas
mixture may be separated by the proper selection of time,
pressure and adsorbent material.
As used herein, depressurizing or depressurization
refers to the reduction of pressure in a vessel and associated
piping and includes the complete removal of pressure from
vessels during certain steps. In accordance with the present
invention desorption and purging pressures may be subatmospheric
and may be manipulated by one skilled in the art. Pressurizing
or pressurization refers to the increase of pressure in a
vessel and associated piping. The various embodiments of the
present invention include product gas delivery at pressures less
, . . . .
'
9937
than about 2 p.s.i.g. ~nd up to about 40 p.s.i.g., however,
the present invention is not meant to be limited to the pressures
of the delivery gas or any other pressures, it being within
the purview of one skilled in the art to manipulate and adjust
pressures throughout the system to provide the desired delivery
or product gas pressure.
In general, the present invention is described and
exemplified in terms of a process utilizing a first adsorption
bed, a second adsorption bed and a segregated storage adsorption
bed. However, the process of the invention may be carried out
in a system having more than one first adsorption bed, more than
one second adsorption bed and more than one segregated storage
adsorption bed. The only limiting factor is the utilization
of at least one segregated storage adsorption bed which is
never directly exposed to the feed gas stream, which allows for
the withdrawa~ of product quality gas from its one end, and
which allows for the withdrawal of low purity product gas from
its other end.
As used herein "adsorption bed", "adsorption beds",
"first adsorption bed", "second adsorption bed", and "at least
one additional adsorption ~ed" refer to an adsorption bed
communicating with a feed gas stream or feed gaseous mixture
stream as opposed to "segregated storage adsorption bed" or
"segregated adsorption bed" which refers to an adsorption bed
which never directly communicates with a feed gas stream or
feed gaseous mixture streams.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram of a high pressure
product delivery embodiment,
Figure 2 is a cycle sequence chart for a high
pressure product delivery embodiment.
Figure 3 is a schematic diagram of a low pressure
.. , . _ _ .. _ _ _ . . .. . ...
1049937
product delivery cmbodiment.
Figure 4 is a cycle sequellce chart for a low pressure
product delivery embodiment.
Eigure 5 i5 a graphical representation showing a plot
of the percent oxygen recovery to the percent oxygen purity for
a high pressure delivery system and a low pressure deli~ery
system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Although the preferred embodiments of this invention
are illustrated by systems which separate or fractionate air to
provide a high purity product oxygen by the removal of nitrogen,
essentially any gas mixture may be separated in accordance
with the present invention by the proper selection of time for
each cycle or step and pressure for each cycle or step and by
the selection of a proper adsorbent material, adsorbent materials
or mixtures of adsorbent materials.
Adsorbent materials are well known in the art, and
one skilled in the art may select an adsorbent material(s) which
is commercially recommended for the separation or fractionation
of the particular gas to be purified. Examples of typical
adsorbent materials for use in adsorption beds include natural
or synthetic zeolites, silica gel, alumina and the like.
Generally, the adsorbent beds and segregated storage adsorbent
bed in the same system contain the same adsorbent material,
however, each bed may contain a different type of adsorbent
~ material or different mixtures of adsorbent materials as desired.
'; The particular adsorbent material or mixtures used are not
critical in the practice of the present invention as long as
. . .
- they separate or fractionate the desired components.
In general, the process of the present invention for -
continuously fractionating at least one component from a gas-
eous mixture by selective adsorption in each of at least two
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iO49937
adsorption ~cds or zon~s is carried out by ~rovidin~ ~ first
adsorption bed having a gas inlet and a gas outlet, a second
adsorption bed having a gas inlet and a gas outlet, the gas
inlets of said first and second adsorption beds being connected
to a feed gas stream, at least one segregated storage adsorption
bed having two inlet-outlet pipes, the first inlet-outlet
communicating with the gas inlets and gas outlets of said first
and second adsorption beds and the second inlet-outlet
communicating with the gas outlets of said first and second
adsorption beds and a product outlet, the product outlet also
communicating with the outlet of the first and second adsorption
beds, a waste outlet communicating with either the inlet or
both the inlet and outlet of said first and second adsorption
beds, and associated valves to isolate each of said elements.
In accordance with the present invention, there may be multiples
of each of the described elements, and there may be multiples of
the complete system connected in series as desired.
In a preferred embodiment for delivery of a product
gas at high pressures, there is provided a first adsorption bed
having a gas inlet and a gas outlet, a second adsorption bed
having a gas inlet and a gas outlet, the gas inlets of said first
and second adsorption beds being connected to a feed gas stream,
at least one segregated storage adsorption bed having two
inlet-outlet pipes, the first inlet-outlet communicating with
the gas inlets and gas outlets of said first and second adsorption
beds and the second inlet-outlet communicating with the gas out-
lets of said first and second adsorption beds and a product outlet
the product outlet also communicating with the outlet of the
first and second adsorption beds, a waste outlet communicating
with the inlet of said first and second adsorption beds, and
associated valves to isolate each of said elements. The process
of this embodiment may be referred to as an isobaric adsorption
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1049937
step with product gas available at or near the adsorption
pressure. This is the embodiment illustrated in Figures 1 and
2, and in accordance with the description found in Figure 2 the
product gas is approximately 40 pounds per square inch gage.
This particular embodiment as applied to air separation with its
elevated pressure product delivery is ideally suited for use in
gas-cutting or welding equipment. The process utilizing this
embodiment is described in more detail infra in relationships
to Figures 1 and 2.
In another preferred embodiment for delivery of a
product gas, such as oxygen, at low pressures, there is
provided a first adsorption bed having a gas inlet and a gas
outlet, a second adsorption bed having a gas inlet and a gas
outlet, the gas inlets of said first and second adsorption beds
being connected to a feed gas stream, at least one segregated
storage adsorption bed having two inlet-outlet pipes, the first
inlet-outlet communicating with the gas inlets and gas outlets
of said first and second adsorption beds and the second inlet-
outlet communicating with the gas outlets of said first and
second adsorption beds and a product outlet, the product outlet
also communicating with the outlet of the first and second
adsorption beds, a waste outlet communicating with the inlet
and outlet of said first and second adsorption beds, and assoc-
; iated valves to isolate each of said elements. The process of
this embodiment allows the continual removal of product oxygen
at low pressures from the uncontaminated end, that is, the
second inlet-outlet end, of the segregated storage adsorption
bed for discharge at the product outlet. This is the embodiment
illustrated in Figures 3 and 4, and in accordance with the
description found in Figure 4 the product gas has an approximate
pressure of less than about 2 pounds per square inch gage. This
particular embodiment as applied to air fractionation with its
~ 049937
low pressure product delivery is capable of a high performance
level and is sufficient, for example, for such applications
as breathing devices. The process utilizing this embodiment is
described in more detail infra in relationship to the
description of Figures 3 and 4.
The storage bed is referred to as having "inlet-outlet
pipes" for ease of description and to distinguish the flow of
gases into and out of the segregated storage adsorption bed
from the flow of gases into and out of the adsorption beds
connected directly to the feed air streams.
Referring to Figures 1 and 2, a specific high
pressure product delivery embodiment and cycle will now be
described. In Figure 1, A and C represent vessels containing
adsorbent materials and described generally as adsorbent
beds or zones. Both A and C communicate with the feed gas
stream designated in the drawing as "FEED". As used herein,
"A" defines a first adsorbent bed and "C" defines a second
adsorbent bed or at least one additional adsorbent bed. "B"
represents a vessel containing adsorbent material and is
described generally as the segregated storage adsorbent bed.
"B" does not communicate with the feed gas stream. Preferred
vessel construction of the adsorbent beds and segregated
storage adsorbent bed is an outer pressure shell with an inner
annulus. One skilled in the art can provide suitable pressure
vessels, piping or tubing, connectors, valves and auxiliary
devices and elements.
The following steps describe the high pressure
product delivery process in detail. Preferred times (in
seconds) for operation of each step, preferred pressures in
each vessel (shown parenthetically) for each step, and the
particular operation being carried out in each vessel during
each step are all shown in Figure 2.
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1049937
In all fi~ures, '`~D~" r~fers to adsor~ing or
adsor~tioll, "D~P" refers to depressurizing or de~rcssurizatioll,
"PURGE" refers to the introduction of purge gas or purging,
"REP" refers to repressurization or repressurizing to increase
the pressure in the vessel, "ISOL" refers to isolating or
isolation of the vessel from other vessels and systems, and
"PROD" refers to product gas, for example, oxygen, "WASTE" in
the drawings refers to the waste outlet for discharging unwanted
and/or undesirable gases to the atmosphere or to a proper trap
or scrubbing device.
Unless otherwise described iII reference to particular
drawings and embodiments, generally, the inlets of vessels A
and C are at the feed stream end of the vessel and the outlets
are at the opposite end thereof. The first inlet-outlet of
vessel B is the end which communicates with both the inlets
and outlets of vessels A and C and the second inlet-outlet of
vessel B is the end which communicates with the outlets of
vessels A and C and also with the product outlet.
PROCESS STEPS FOR HIGH PRESSURE PRODUCT
DELIVERY EMBODIMENT OF FIGURES 1 AND 2:
Step No. 1 Valve Af opens allowing nitrogen rich gas,
(air) to enter adsorbing bed A. Valve Ar opens allowing oxygen
rich gas to be taken as product through pressure regulator Rp
and throttle valve Hp. Regulator Rr opens allowing product
quality oxygen rich gas to enter the top of bed B, (the
segregated storage tank) through valve Hb. Valve Cb opens
allowing nitrogen rich gas to flow into the bottom of bed B.
In this step air separation has been initiated in bed A. Bed
B is conserving product quality oxygen by storage in its clean
top end. sed C is partially depressurized into the bottom end
of bed B. Nitrogen rich gas (low purity product) flows out
of the top of bed C and into the bottom end of bed B, flushing
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1049937
the interconnecting vessel head and piping of o~ygen rich gas
and storing it in bed B. Throughout this step and all other
steps there is continuous air flow into the system and continuous
proauct flow out.
The process of step 1 may be described as
simultaneously introducing the gaseous mixture into the gas
inlet of the first adsorption bed from the feed gas stream,
allowing the gaseous mixture to pass through the first adsorption
bed, releasing product gas from the outlet of the first
adsorption bed, and discharging the product gas from the
product outlet; and simultaneously therewith collecting product
gas in the segregated storage adsorption bed through the second
inlet-outlet pipe thereof while partially depressurizing the
second adsorption bed from the outlet thereof into the first
inlet-outlet pipe of the segregated storage adsorption bed,
until the gas flowing from the second adsorption bed into the
segregated storage adsorption bed is depleted of any product
value.
Step No. 2 Valve Af remains open allowing feed air
to enter bed A. Valve Ar remains open allowing product quality
oxygen rich gas to be taken as product through regulator Rp
and throttle valve Hp. Product quality oxygen rich gas continues to
flow through back pressure regulator Rr through valve Hb and
into the top end of bed B. Valve Cb has now closed. Valve
Cw opens, allowing nitrogen rich gas (waste gas) to be rejected
to the atmosphere. In this step bed A remains on adsorption,
separating feed air. Product quality oxygen rich gas is with-
drawn as product. Additional product quality oxygen rich gas
is stored in the top end of B. Bed C has been depressurized
to the atmosphere in a direction reverse to air separation in
the first step of waste nitrogen rejection to the atmosphere.
Throughout this step as before, there is continuous air flow
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into the system and product flow out.
The yrocess of step 2 may be described as
simultaneously terminating the depressurizing of step 1 from
the outlet end of the second adsorption bed and continuing
depressurizing thereof from the inlet end thereof to the waste
outlet while continuing adsorption of the feed gas mixture in
the first adsorption bed, discharging the product gas from the
product outlet and collecting product gas in the segregated
storage adsorption bed.
Step No. 3 Valve Af remains open as does Ar, Rp and
Hp. Cp now opens allowing product quality oxygen rich gas to
flow through Bed C and out valve Cw in a direction reverse to
air separation. In addition, part of the product quality gas
available at the top end of bed B flows through valve Hb and
valve Cp through bed C and out valve Cw to the atmosphere. In
this step bed A remains on adsorption, separating air. Product
quality gas is withdrawn as product. Product quality oxygen
;~ rich gas is taken from the adsorbing bed A and also some from
bed B to purge the nitrogen loaded bed C in reverse direction,
to reject unwanted impurity to the atmosphere. Throughout this
step as before, there is continuous air flow into the system
and product flow out.
The process of step 3 may be described as simulta-
neously continuing to discharge product gas from the product
outlet and diverting product gas from the outlet of the first
adsorption bed and from the product gas collected in the
segregated storage adsorption bed to the outlet end of the
second adsorption bed, passing said diverted product gas through
the adsorption bed t~ereof to purge waste gas from the bed to
the waste outlet.
Step No. 4 Valve Af remains open as does Ar, Rp
and Hp. Valves Cp and Cw close. Product quality oxygen rich
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1049937
g~s passes tllLough rc.~ulator Rr through ll~ rcsulating in low
purity o~ygen passing from thc bottom of bcd B, out valve Bc,
which is now open, and into the bottom, or feed ai~ end of bed
C. In this step bed A remains on adsorption separating air.
Product quality gas is withdrawn as product. sed s has pressure
equalized with bed C, to begin the necessary repressurization
of bed C. Bed B has been reverse purged with product quality
gas to reject the impurity at its bottom end introduced in
step 1. This impurity was introduced at the feed air end of bed
C during pressure equalization in this step (4) so as to have
minimal effect on the subsequent air separation capacity of bed
C. The minimal effect is due to the use of treated air which
has less nitrogen content than untreated air. In effect bed s
was reverse purged with product quality gas while pressure
equalizing with bed C.
The process of step 4 may be described as simulta-
neously continuing to discharge product gas from the product
outlet, terminating the flow of diverted product gas to the
second adsorption bed, terminating the discharge of purge gas
from the waste outlet and equalizing the pressures of the
segregated storage adsorption bed and the second adsorption
bed by passing gas collected in the segregated storage adsorption
bed in step number 1 by the partial depressurizing of the second
adsorption bed from the second inlet-outlet pipe of the
segregated storage adsorption bed to the gas inlet of the second
adsorution bed while passing product gas into the first inlet-
outlet pipe of the segregated storage adsorption bed, thereby
initiating repressurization of the second adsorption bed with
: a gas of greater product quality than the feed gaseous mixture.
Step No. 5 Valves Af, Ar, Rp, Hp and Rr remain
open. Valve Bc closes and Cp opens allowing product quality gas
to enter the top of bed C. Valve Hb closes isolating bed B. In
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1049937
t~is step bed A remains on adsorptio~ separating air. Product
quality ~as is ~ithdrawn as product. Bed C is pressurizcd with
product quality gas in preparation for the beginning of its
adsorption step. Bed B is isolated, waiting to accept and store
depressurization gas from bed A on the next step.
The process of step 5 may be described as
simultaneously terminating the initial repressurization of
step 4, isolating the segregated storage adsorption bed, and
completely repressurizing the second adsorption bed with product
gas diverted from the outlet of the first adsorption bed
whereby the second adsorption bed is prepared for the fraction-
ation of at least one component from a gaseous mixture by
selective adsorption, while continuing to discharge product gas
from the product outlet.
Steps 6 through 10 The next five steps are identical
to steps 1 through 5 except bed C now separates air while bed A
is regenerated by depressurization and reverse purge. Bed B
serves the same function as it did during steps 1 through 5.
When all 10 steps are complete, the process has come one full
circle and starts again at step 1. Throughout all 10 steps
there is continuous air flow into the system and product quality
oxygen flow out of the system.
Steps 6 through 10 are consecutively repeating steps
1 through 5 reversing the functions of the first adsorption bed
and the second adsorption bed, wherein the gaseous mixture to
be fractionated is introduced into and product gas is discharged
from the second adsorption bed and the first adsorption bed is
depressurized, purged and pressurized for the following sequence.
In accordance with the present invention the process
may be initiated at any one of the designated steps and there-
after follow the sequentially numbered steps. Thus, for example,
in the embodiment described above, the process may be initiated
,, . _ _ , . . _ _ _ _ . . . . .. . .
1049937
at step number 4 and continue consecutively through steps
5-10 and then 1-3 to complete one full circle.
PROCESS STEPS FOR LOW PRESSURE PRODUCrr
D~LIVERY EMBODIMENT OF FIGURES 3 AND 4-
Step No. 1 Valve Af is open introducing feed air
into bed A and partially repressurizing bed A. Bed ~,
(segregated storage adsorber) is depressurizing through regulator
Rp and throttle valve Hp to supply oxygen rich product gas.
Also, it is depressurizing to reverse purge bed C through
valve Cb and reject unwanted nitrogen to the atmosphere through
valve Cw. In this step continuous air flow has been maintained
through valve Af into bed A. Product quality gas has been
delivered as product at low pressure. Bed C has been reverse
purged with product quality gas in preparation for air separation.
The process of step 1 may be described as simulta-
neously introducing the gaseous mixture into the gas inlet of
the first adsorption bed from the feed gas stream to repressurize
the first adsorption bed, releasing product gas from the second
inlet-outlet of the segregated storage adsorption bed to
depressurize the segregated storage adsorption bed and
discharging part of th~ product gas from the product outlet
while passing product gas into the gas outlet end of the second
adsorption bed to reverse purge said bed, the purged gas from
said bed being removed at the waste outlet.
Step No. 2 Valve Af remains open. Valve Ab opens
allowing product flow through Rp and Hp. Valves Cw and Cb
~lose. Valve Bc opens allowing product quality gas to reverse
purge unwanted nitrogen impurity out of bed B into the feed air
end of bed C. In this step continuous feed and product flow
have been maintained and bed B has been purged of unwanted
nitrogen which has been introduced at the feed end of bed C
where it has minimal effect on air separation capacity, while
.
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10~9937
also partially repressurizing bed C. This is in e~fect, an
intermediate pressure level isobaric adsorption stroke.
The process of step 2 may be described as
simultaneously terminating the reverse purge and the removal
of purged waste gas from the second adsorption bed of step 1,
continuing to introduce the gaseous mixture into the inlet
of the first adsorption bed, allowing the gaseous mixture to
pass through the first adsorption bed, releasing product gas
from the outlet of the first adsorption bed and discharging
product gas from the product outlet; and simultaneously
diverting product gas from the outlet of the first adsorption
bed to the second inlet-outlet of the segregated storage
adsorption bed whereby the segregated storage adsorption bed
is reverse purged with product gas, the gas purged from the
segregated storage adsorption bed passing to the second
adsorption bed through the gas inlet thereof to partially
repressurize the second adsorption bed at its feed end.
Step No. 2A Valve Af remains open allowing air to
repressurize bed A to the set point of electrical pressure
switch Ps-l. Valve Ab is closed. Valve Bc is closed.
Regulator Rp and hand valve Hp deliver product quality gas
strictly from the segregated storage tank. In this step bed
A is pressurized to the optimum pressure level for this cycle.
Bed B delivers product quality gas until bed A is repressurized.
Bed C is isolated, awaiting further pressurization.
The process of step 2A may be described as
simultaneously terminating the delivery of product gas from
the first adsorption bed while continuing to introduce the
gaseous mixture into the first adsorption bed to repressurize
said bed to the desired pressure, isolating the sccond
adsorption bed and delivering product gas from the segregated
storage adsorption bed at low pressure to the product outlet
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whereby the depressurization of the segregated storage
adsorption bed contillues and product gas continues to be
discharged.
Step No. 3 After electrical pressure switch Ps-l
has functioned at its set point sed A depressurizes into bed
C through Ar and Cr. Valve Af is still open introducing air to
bed A even though bed A pressure is decreasing. Bed B continues
to supply product quality gas independent of beds A and C. In
this step bed A has conserved oxygen and helped repressurize
bed C and continual feed flow has been maintained and delivered
to the bed at the highest pressure level, bed A.
The process of step 3 may be described as simulta-
neously continuing to deliver product gas from the segregated
storage adsorption bed at low pressure to the product outlet
and further reducing the pressure of the segre ated storage
adsorption bed and continuing to introduce the gaseous mixture
into the first adsorption bed, passing gas from the gas outlet
of the first adsorption bed to the gas outlet of the second
adsorption bed whereby the second adsorption bed is repressurized
while the pressure of the first adsorption bed is reduced.
Step No.~ 4 Valve Cf is now opened introducing air
into bed C. Valve Af is closed. Valve Ar and Bp are openedallow-
ing nitroyen rich~gas to purge the valve head and piping and
enter the top of bed B through throttle valve Hb. Meanwhile
- bed B continues to deliver product quality oxygen from the
opposite end of the bed through regulator Rp and throttle valve
Hp. In this step bed C is now being pressurized with air. Bed
A is depressurizing in preparation for its waste rejection step.
It has depressurized in such a way as to get complete bed
utilization and purge the vessel head and piping with nitrogen
rich gas. The oxygen rich gas it displaced is stored in bed B.
Bed B continues to deliver product quality gas from the other
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end of bed B. This is a true segregation effect.
The process of step 4 may be described as
simultaneously discontinuing the introduction of gascous mixture
into the first adsorption bed, terminating the flow of gas
from the first adsorption bed to the second adsorption bed,
introducing the gaseous mixture into the gas inlet of the
second adsorption bed to continue the pressurization of the
bed, passing gas from the gas outlet of the first adsorption
bed to the first inlet-outlet pipe of the segregated storage
adsorption bed and into said bed whereby the first adsorption
bed is partially depressurized and the segregated adsorption
bed is repressurized, releasing product gas from the second
inlet-outlet end of the segregated storage adsorption bed and
discharging the product gas from the product outlet.
Step No. 5 Valve Cf remains open. sed B continues
to deliver product quality gas through Rp and Hp. Valve Aw
opens, depressurizing bed A to the atmosphere in a reverse
direction to feed air flow. In this step bed C continues to be
repressurized with air. Bed A has depressurized to the atmos-
phere in a reverse direction to feed flow as part of its waste
rejection step. Bed B continues to deliver low pressure gas asproduct.
The process of step 5 may be described as simulta-
neously terminating the flow of gas from the first adsorption
bed to the segregated storage adsorption bed, continuing
introducing gaseous mixture into the second adsorption bed to
continue pressurization of the bed, continuing releasing
product gas from the second inlet-outlet of the segregated
storage adsorption bed whereby the segregated storage
adsorption bed begins depressurization, and discharging product
gas from the product outlet.
Steps 6-10 The next five steps are identical to
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steps 1-5 except beds A and C reverse roles while bed B repeats
the same function. When all ten steps are complete, the process
has come a full circle and begins again at step one. Through-
out all ten steps there is continuous air flow into the system
and product quality oxygen flowing out of the system.
Steps 6 through 10 are consecutively repeating steps
1 through 5 reversing the functions of the first adsorption bed
and the second adsorption bed, wherein the gaseous mixture to
be fractionated is introduced into and product gas is discharged
from the second adsorption bed while the first adsorption bed
is purged, isolated and repressurized and the segregated storage
adsorption bed provides a reservoir for the continuous discharge
of product gas from the product outlet. ~`
This process may be initiated at any one of the
designated steps and thereafter follow the sequentially numbered
steps.
Referring to Figure 5, the graph represents the
performance levels of schemes I and II as a function of oxygen
purity and recovery when the processes are used in the air
fractionation or separation made. Scheme I represents the high
! pressure product delivery cycle and is designated in the graph
by squares. Scheme II represents the low pressure product
delivery cycle and is designated in the graph by circles. Data
points are included for operation with pressure equalization
solely at the product end of the adsorber for both schemes.
EXAMPLES
The following examples are intended to further define,
describe and compare exemplary processes of this invention and
to illustrate various preferred embodiments.
All testing was accomplished with apparatus suitable
for testing all cycles and is essentially illustrated in Figures
1 and 3. Each of the two adsorbent beds contained about 140
--~0--
1049~3~7
pounds o type SA mol~cular si~v~ material. The segregatcd
stora~ ta~ colltain~d 70 ~OUII~S oE th~ s~lm~ material. A
summary of operating characteri-ctics of each of the cycles
tested is shown in Table I bclow:
TA~LE I
Test Oxygen Amb. sed Storage Equal Product
Ave. Rec. Temp. Length Tank Press
Purity ~ (C) (Meters) Prod.Feed (psig)*
1 82 13.7 7 1.22 empty x 40
2 92 15.2 8 2.44 empty x 40
3 87 24.2 5 2.44 full x 40
4 87 25.9 'g 2.44 full x 40
4 88 29.3 7 2.44 full x 40
63 41.4 13 2.44 full x 40
6 68 42.2 6 2.44 full x 40
7 75 41.4 9 2.44 full x 40
8 80 31.2 3 2.44 full x 40
9 87 29.0 6 2.44 full x 40
18.9 9 2.44 full x 40
11 88 45.5 10 2.44 full x 2
12 80 51.9 10 2.44 full x 2
13 95 29.2 10 2.44 full x 2
* 1 p.s.i.g. = 0.070307 kg/cm2
In accordance with the stated objects there has been
demonstrated a process for providing a continuous, uninterrupted
flow of product gas from adsorbent beds which have selectively
separated gases in a continuously flowing feed gas stream. Low
purity product gases have been used for repressurization of
regenerated adsorbent beds without sacrificing the quality of
the product gas and actually improving recovery.
30 While the invention has been described with respect
to preferred embodiments, it will be apparent that certain
modifications and changes can be made without departing from
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the spirit and scope of the invention and therefore, it is
intended that the foregoing disclosure be limited only by the
claims appended hereto.
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