U.S. patent application number 09/753612 was filed with the patent office on 2001-05-31 for system for energy recovery in a vacuum pressure swing adsorption apparatus.
Invention is credited to Schaub, Herbert Raymond, Sinicropi, Michael John, Smolarek, James.
Application Number | 20010001939 09/753612 |
Document ID | / |
Family ID | 25153310 |
Filed Date | 2001-05-31 |
United States Patent
Application |
20010001939 |
Kind Code |
A1 |
Smolarek, James ; et
al. |
May 31, 2001 |
System for energy recovery in a vacuum pressure swing adsorption
apparatus
Abstract
A VPSA apparatus includes a first adsorbent bed and a second
adsorbent bed, a feed blower for providing a flow of a gas mixture
at about atmospheric pressure to the beds, and a vacuum blower for
removing a flow of gas therefrom and venting the gas to a space at
atmospheric pressure. The VPSA process causes the first adsorbent
bed to be poised for evacuation by the vacuum blower and
concurrently, the second adsorbent bed is under vacuum conditions
and is poised for pressurization by the feed blower. A single motor
is coupled by a common shaft to both the feed blower and the vacuum
blower and operates both. A conduit/valve arrangement is operative
during at least a portion of a process time when the adsorbent beds
are in pressurizing/evacuation states, respectively, to couple the
feed blower to the second adsorbent bed when at vacuum and for
concurrently coupling the vacuum blower to the first adsorbent bed
which is to be evacuated. The feed blower is thereby caused to
operate in a gas expansion mode and imparts expansion energy, via
the common shaft, to the vacuum blower. During idling conditions, a
valve-conduit system is controlled to enable significant reductions
in pressure rise across the feed and vacuum blowers.
Inventors: |
Smolarek, James; (Boston,
NY) ; Sinicropi, Michael John; (Cheektowaga, NY)
; Schaub, Herbert Raymond; (East Amherst, NY) |
Correspondence
Address: |
PRAXAIR TECHNOLOGY, INC.
Law Department M1-557
39 Old Ridgebury Road
Danbury
CT
06810-5113
US
|
Family ID: |
25153310 |
Appl. No.: |
09/753612 |
Filed: |
January 4, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09753612 |
Jan 4, 2001 |
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09264812 |
Mar 9, 1999 |
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09264812 |
Mar 9, 1999 |
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08791308 |
Jan 30, 1997 |
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5912426 |
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Current U.S.
Class: |
96/115 ; 96/130;
96/133; 96/144 |
Current CPC
Class: |
B01D 2256/12 20130101;
B01D 53/0446 20130101; B01D 53/0476 20130101; B01D 2257/102
20130101; B01D 2259/40007 20130101; B01D 2259/40003 20130101; B01D
2259/402 20130101 |
Class at
Publication: |
96/115 ; 96/130;
96/133; 96/144 |
International
Class: |
B01D 053/047 |
Claims
1. A vacuum pressure swing adsorption (VPSA) apparatus for
producing a preferred gas from a gas mixture of said preferred gas
and a less preferred gas, through use of a separation process, the
VPSA apparatus comprising: at least a first adsorbent bed and a
second adsorbent bed, said separation process operative during a
predetermined process time, to cause said first adsorbent bed to be
poised for evacuation at a pressure which requires an input of
energy to a coupled vacuum blower to accomplish said evacuation,
and said second adsorbent bed is under a vacuum condition and is
poised for pressurization; feed blower means for providing a flow
of said gas mixture from a source at about atmospheric pressure,
via a feed conduit to either said first adsorbent bed or said
second adsorbent bed; vacuum blower means for removing a flow of
gas, via an exhaust conduit, from either said first adsorbent bed
or said second adsorbent bed and venting said gas via vent means to
a space at atmospheric pressure; a motor coupled to said feed
blower means and said vacuum blower means via a common coupling for
operating both thereof; and conduit/valve means, operative during
at least a portion of said predetermined process time, for coupling
said feed blower means to said second adsorbent bed and for
concurrently coupling said vacuum blower means to said first
adsorbent bed, so that said feed blower means is caused to operate
in a gas expansion mode and to impart expansion energy via said
common coupling to said vacuum blower means.
2. The VPSA apparatus as recited in claim 1, wherein said preferred
gas is oxygen and said gas mixture is air.
3. The VPSA apparatus as recited in claim 1, further comprising:
vent means connected to said vacuum blower means for venting a gas
to a space at atmospheric pressure; valve means for selectively
coupling said feed conduit to said vent means; and control means
operative during unload for opening said valve means to enable said
feed blower means to expel gas through said vent means.
4. A vacuum pressure swing adsorbent (VPSA) apparatus for producing
a preferred gas from a gas mixture of said preferred gas and a less
preferred gas through use of a separation process, the VPSA
apparatus comprising: adsorbent bed means for use in said
separation process; vent means for venting a gas to a space at
about atmospheric pressure; feed blower means for feeding said gas
mixture from a source at about atmospheric pressure, via a feed
conduit to said adsorbent bed means; vacuum blower means for
removing, via an exhaust conduit, a flow of gas from said adsorbent
bed means and for venting said gas through said vent means; valve
means for selectively coupling said feed conduit to said exhaust
conduit; and control means operative when said VPSA is in a
turndown state, to isolate said feed blower means and said vacuum
blower means from said adsorbent bed means, and for opening said
valve means to enable said feed blower means to expel gas through
said vent means.
5. The VPSA apparatus as recited in claim 4, wherein said valve
means further comprises; a first unload valve coupled between said
feed conduit and said exhaust conduit and vacuum blower means; a
second unload valve coupled between said exhaust conduit and said
vent means; and wherein said control means opens both said first
unload valve and said second unload valve during turndown to reduce
a pressure differential across said feed blower means and said
vacuum blower means.
6. The VPSA apparatus as recited in claim 5, wherein said valve
means further comprises; a third valve coupled between said feed
conduit and said vent means; and wherein said control means
additionally opens said third valve during turndown to reduce a
pressure differential across said feed blower means and said vacuum
blower means.
7. The VPSA apparatus as recited in claim 5, further comprising;
feed valve means for coupling said feed conduit to said adsorbent
bed means; exhaust valve means for coupling said exhaust conduit to
said adsorbent bed means; and wherein said control means additional
opens both said feed valve means and said exhaust valve means
during turndown to reduce a pressure differential across said feed
blower means and said vacuum blower means.
8. The VPSA apparatus as recited in claim 6, further comprising;
feed valve means for coupling said feed conduit to said adsorbent
bed means; exhaust valve means for coupling said exhaust conduit to
said adsorbent bed means; and wherein said control means additional
opens both said feed valve means and said exhaust valve means
during turndown to reduce a pressure differential across said feed
blower means and said vacuum blower means.
9. The VPSA apparatus as recited in claim 5, wherein said control
means causes both said feed blower means and vacuum blower means to
operate in an idling state.
10. The VPSA apparatus as recited in claim 5, wherein said
preferred gas is oxygen and said gas mixture is air.
11. A vacuum pressure swing apparatus (VPSA) for producing a
preferred gas from a gas mixture of said preferred gas and a less
preferred gas through use of a separation process, the VPSA
comprising: at least a first adsorbent bed and a second adsorbent
bed, said separation process operative during a predetermined
process time, to cause said first adsorbent bed to be poised for
evacuation at a pressure which requires an input of energy to a
coupled vacuum blower to accomplish said evacuation, and said
second adsorbent bed is under a vacuum condition and is poised for
pressurization; feed blower means for providing a flow of said gas
mixture from a source at about atmospheric pressure, to said first
adsorbent bed or said second adsorbent bed; vacuum blower means for
removing a flow of gas from said first adsorbent bed or said second
adsorbent bed and venting said gas to a space at about atmospheric
pressure; a motor/generator coupled to a source of electrical
supply for operating said feed blower means; a motor for operating
said vacuum blower means; and conduit/valve means, operative during
a turndown of said VPSA apparatus for coupling said feed blower
means to said second adsorbent bed so that said vacuum condition
causes said feed blower means to operate in a gas expansion mode
and to impart expansion energy to said generator to enable
generation of electrical energy into said source of electrical
supply.
12. The VPSA apparatus as recited in claim 11, wherein said
preferred gas is oxygen and said gas mixture is air.
Description
FIELD OF THE INVENTION
[0001] This invention relates to apparatus for separation of a
preferred gas, such as oxygen, from a mixture of the preferred gas
and other gases and, more particularly, to gas separation apparatus
which employs a vacuum pressure swing adsorption (VPSA) process and
recovers energy from blowers employed by apparatus that performs
the VPSA process.
BACKGROUND OF THE INVENTION
[0002] VPSA processes and systems are known in the art for
separating components of a feed gas mixture. Such a gas mixture
contains a more readily adsorbable component (i.e., a "more
preferred" gas) and a less readily adsorbable component (i.e., a
"less preferred" gas), and is passed through an adsorbent bed
capable of selectively adsorbing the more readily adsorbable
component at an upper adsorption pressure. The bed is thereafter
depressurized to a lower desorption pressure (e.g. a vacuum) for
desorption of the more readily adsorbable component and its removal
from the bed prior to introduction of additional quantities of the
feed-gas mixture. In a multiple bed VPSA system, the beds are
cyclically operated through the same series of process steps, but
the step sequence in one bed is offset from the same step sequence
applied to another bed. The step sequence offset is accomplished to
allow use of common feed and exhaust systems and to achieve process
and energy savings.
[0003] In conventional VPSA systems, multiple adsorber beds are
commonly employed, with each bed subjected to a VPSA processing
sequence on a cyclic basis so as to enable efficiencies to be
achieved. VPSA systems are often used to separate oxygen from an
input air stream. At certain times during operation of a VPSA
system, either a feed blower or a vacuum blower, or both, are
caused to operate in an "idle" mode, where they do not interact
with associated adsorbent beds to actively move feed or exhaust gas
through the system. Such operation is hereafter referred to as the
unload state. The term turndown state will hereafter be used and
will refer to the condition when: both the feed and vacuum blower
are set into the unload state (idling) for an extended period of
time; and the VPSA system is not producing product.
[0004] During the VPSA process, gas streams are frequently expanded
when pressure transferred during the process. Such gas transfer
takes place at both the product and feed ends of the adsorber bed.
Energy recovery from expanding gas streams in VPSA processes has
long been a goal in systems design.
[0005] Most present VPSA systems and, in particular, two-bed
systems incorporate process steps which throttle gas streams for
the purpose of pressure transferring the gas. The throttling
results in lost power and added inefficiencies. Energy recovery in
the prior art has also employed a natural aspiration of the feed
air during vacuum conditions, at the beginning of the VPSA cycle.
The natural aspiration method requires an additional air inlet
regulation system and results in only a modest reduction in the
feed gas compression requirement. Nor does the aspiration system
recover energy from the expanding stream, but rather merely
provides an air inlet without additional power consumption.
[0006] Other prior art teachings related to energy recovery in gas
separation systems are as follows. U.S. Pat. No. 5,429,666 to
Agrawal et al. describes a vacuum swing adsorption (VSA) process
which employs two beds that operate with product pressurization and
pressure equalization between the beds. Simultaneous operation of
the process steps, for the purpose of continuous utilization of
feed and vacuum blowers, is described. The Agrawal et al. process
employs a natural aspiration of feed air as an energy recovery
process. The system attempts to lower feed power by utilizing the
low adsorber bed pressure at the beginning of a cycle to allow for
some fraction of the feed air to be drawn directly into the bed,
without need for an air compressor. Such an ambient feed does
nothing to recover energy that is available from the expansion of
the feed air.
[0007] U.S. Pat. No. 4,995,889 to Abel et al. describes a method
for regulating product flow of an adsorption air separation system,
especially under conditions of discontinuous product flow that
result from variable customer demand. A control valve is connected
to the product line of the separation apparatus and controls flow
of the product through a variable or fixed orifice device that is
upstream of the control valve. A differential pressure controller,
which senses pressure upstream and downstream of the orifice
device, is used to operate the control valve.
[0008] U.S. Pat. No. 5,096,469 to Keefer details an adsorption air
separation process which utilizes oscillations of a liquid column
to change the volume of variable displacement chambers in order to
create cyclic pressure changes that are required for the pressure
swing process. In effect, the inertia of the oscillating fluid
provides an energy exchange between air separation chambers.
[0009] U.S. Pat. No. 5,183,483 to Servido et al. describes a
pneumatic control process for a pressure swing adsorption (PSA)
process. Adsorption, desorption and equalization phases are
connected through use of two 3-way valves and a single compressor.
By controlling the operation of the 3-way valves, the compressor
can be used for adsorption and desorption or can be allowed to
operate unloaded as well.
[0010] U.S. Pat. No. 5,518,526 to Baksh et al. describes a PSA
process which overlaps various steps to reduce total cycle time and
to achieve improved efficiency and productivity. A unique step is
described as being the simultaneous evacuation of a bed undergoing
an equalization rising step, while the other bed is undergoing an
equalization falling step. The next step in the cycle is
simultaneous product and feed pressurization at opposite ends of
the bed, followed by feed pressurization to the desired adsorption
pressure.
[0011] U.S. Pat. No. 5,042,994 to Smolarek (Applicant herein)
describes a method for controlling a PSA system by the monitoring
of a variable volume storage vessel during nitrogen production
applications. The process cycle contains two steps where the feed
blower and vacuum blower are idle. The first step is a
counter-current oxygen repressurization step of a previously
desorbed bed, while an adsorbed bed undergoes a blow-down of
product nitrogen. The second step when the process machines are
idled and not utilized occurs during a turndown step when the level
of the variable volume product storage vessel is monitored in order
to determine variations in customer demand. Thus, Smolarek teaches
that the measure of idle time is proportional to some measure of
customer demand. Smolarek further mentions that power reduction and
energy savings can be achieved under turndown conditions by idling
the machines proportionally with customer demand, while maintaining
product purity.
[0012] Notwithstanding the substantial development efforts that
have been directed at improvements of pressure swing adsorption
(PSA) and VPSA processes and systems, there is a continuing need
for efficiency improvements therein.
[0013] Accordingly, it is an object of this invention to provide a
pressure swing adsoption system which exhibits energy usage
efficiencies.
SUMMARY OF THE INVENTION
[0014] A VPSA apparatus includes a first adsorbent bed and a second
adsorbent bed, a feed blower for providing a flow of a gas mixture
at about atmospheric pressure to the beds, and a vacuum blower for
removing a flow of gas therefrom and venting the gas to an area of
atmospheric pressure. The VPSA process causes the first adsorbent
bed to be poised for evacuation by the vacuum blower and
concurrently, the second adsorbent bed is under vacuum conditions
and is poised for pressurization by the feed blower. A single motor
is coupled by a common shaft to both the feed blower and the vacuum
blower and operates both. A conduit/valve arrangement is operative
during at least a portion of a process time when the adsorbent beds
are in pressurizing/evacuation states, respectively, to couple the
feed blower to the second adsorbent bed when at vacuum and for
concurrently coupling the vacuum blower to the first adsorbent bed
which is to be evacuated. The feed blower is thereby caused to
operate in a gas expansion mode and imparts expansion energy, via
the common shaft, to the vacuum blower.
[0015] A further embodiment of the invention includes additional
conduits and valves which couple the feed conduit from the feed
blower to the exhaust conduit input to the vacuum blower. When the
system is in a turndown state, the adsorbent beds are isolated from
the vacuum blower and both the feed blower and vacuum blower are
idling and in the unload state. In such condition, the valving is
operated to enable the feed blower to exhaust its air flow via the
exhaust conduit, thereby resulting in a lower pressure drops across
both the feed and vacuum blowers.
[0016] A further, less preferred embodiment, uses independent
motors to power the feed and vacuum blowers but, during turndown,
couples the feed blower to the second adsorbent bed (which is at
vacuum), causing the feed blower to be operated in a gas expansion
mode. A generator is coupled to the feed blower motor and generates
electrical energy into the main, thereby creating a credit for
energy which is either later or concurrently used to power the
vacuum blower.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic diagram illustrating a VPSA system
embodying the preferred mode of the invention.
[0018] FIG. 2 is a block diagram of a VPSA system which embodies a
less preferred version of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0019] As will be hereafter understood, the preferred embodiment of
the invention shown in FIG. 1 is configured to enable a VPSA system
10 to recover energy that is associated with expanding air streams
and to deliver that energy directly to a vacuum blower. VPSA system
10 comprises a pair of adsorbent beds 12 and 14 which are coupled
to an output product tank 16 via control valves 18 and 20,
respectively.
[0020] It is to be understood that while the description hereafter
will only consider adsorbent beds 12 and 14, the system can be
configured with additional beds, as is known in the prior art.
Further, the system will be described in the context of an air
separation process, however, it is known that pressure swing gas
separation systems can be applied to other separations where a more
preferred gas and/or a less preferred gas is separated, and
provided as product, from a mixture of the more preferred gas and a
less preferred gas. In the example to be described below, it is the
less preferred gas (oxygen) that is output as product (with the
adsorbent beds being selective for nitrogen) Accordingly, the
invention is to be considered as applicable to all processes
wherein appropriate gases are separated.
[0021] A feed blower 22 is coupled via a feed conduit 24 and feed
valves 26 and 28 to beds 12 and 14, respectively. A vacuum blower
30 is coupled via an exhaust conduit 32 and exhaust valves 34 and
36 to adsorbent beds 12 and 14, respectively. A controller 38
enables operation of each of the aforesaid components in the known
manner to enable a separation of an inlet air feed 39 into an
oxygen output stream (via conduit 40) feed to product tank 16 for
storage.
[0022] Feed blower 22 and vacuum blower 30 are both operated by a
motor 50, which is coupled to both thereof by common shaft 52. By
this arrangement, as will be described in further detail below,
when feed blower 22 operates in an air expansion mode, the
expansion energy which results is transferred via shaft 52 to
vacuum blower 30, thereby enabling the electrical power input into
motor 50 to be reduced, while enabling vacuum blower 30 to maintain
its level of operation, albeit at a lower energy cost.
[0023] A first unload valve 54 is coupled between feed conduit 24
and exhaust conduit 32 and a second unload valve 56 further couples
exhaust conduit 32 to a vacuum silencer 58. Vacuum silencer 58 is
further provided with a gas flow from vacuum blower 30 via vent
conduit 60. Vacuum silencer 58 provides a vent action via vent
conduit 60 and enables venting of both vacuum blower 30 and feed
blower 22, when a control valve 62 is opened and couples feed
conduit 24 to vacuum silencer 58.
[0024] As will be hereinafter understood, the provision of motor 50
and common shaft 52 to connect feed blower 22 to vacuum blower 30
essentially creates an integral machine which enables vacuum blower
30 to be operated at reduced electrical power input as a result of
gas expansion energy imparted to feed blower 22 during a portion of
a VPSA cycle. The electrical power supplied to motor 50 during such
gas expansion time is lowered in direct proportion by controller
38.
[0025] Secondarily, the piping arrangement that includes unload
valves 54, 56 and 62 and their interconnection to vacuum silencer
58 allows feed blower 22 to be discharged to the suction created by
vacuum blower 30 during unload periods. This action results in a
decrease of the pressure rise across vacuum blower 30 and feed
blower 22 during times in the cycle when the blowers are not loaded
and reduces their resultant power draw.
[0026] As indicated above, VPSA systems commonly cause adsorbent
beds 12 and 14 to be respectively pressurized and at a vacuum,
during several process steps of the separation procedure. For
example, VPSA systems employ a purge and overlap equalization cycle
wherein continuous waste removal from one bed results in an
expanding feed stream which produces energy simultaneously with a
vacuum level waste stream requiring energy. During such action,
adsorbent bed 12, for instance, remains at vacuum conditions,
rising from 9-13 psi, while feed air is supplied to adsorbent bed
12 by feed blower 22. This action results in vacuum conditions
being present in feed conduit 24, thereby creating expansion of the
feed air during the entire step. The feed air rate must also be
limited during this period, hence extraction of work by limiting
the air feed flow by expansion through feed blower 22 is
advantageous from a process standpoint.
[0027] Concurrently, adsorbent bed 14 must be evacuated by the
operation of vacuum blower 30 through exhaust conduit 32 and vacuum
silencer 58 to vent pipe 70. At such time, waste nitrogen is
removed from adsorbent bed 14 and is vented via vent pipe 70 to the
atmosphere. During such time, adsorbent bed 14 experiences a
pressure fall into a vacuum condition (e.g., from about 16 to 13
psi).
[0028] Thus, when feed air is fed from feed air inlet 39 by feed
blower 22 into feed conduit 24, the feed air is expanded and the
expansion energy is imparted to feed blower 22 which, in turn,
supplies mechanical power via shaft 52 to vacuum blower 30. At such
time, controller 38 reduces the electrical power that is input to
motor 50 in accordance with the expansion energy input from feed
blower 22. Thus, motor 50 and common shaft 52 enable the expansion
gas to directly transfer energy, via feed blower 22, to vacuum
blower 30 which is concurrently operating in a compression mode to
extract gas via exhaust conduit 32 from adsorbent bed 14.
[0029] In addition to the energy savings achieved by the
aforementioned arrangement, a more compact plant layout is
achieved, while at the same time reducing capital costs of the
system through elimination of another drive motor and a motor
starter. The single motor arrangement also simplifies the start-up
controls. A common drive motor starts both blowers simultaneously,
eliminating any possibility of not starting both blowers at the
same time which could result in some undue loading on the machines,
causing unwanted wear.
[0030] At certain times during the VPSA cycle, plant unload may be
achieved by interrupting the cycling of adsorbent beds 12 and 14,
by isolating the beds and venting feed blower 22 and vacuum blower
30. During loaded operation, feed blower 22 and vacuum blower 30
are loaded by transfer of gas to and from adsorbent beds 12 and 14,
respectively. Feed valves 26 or 28 are either open or closed in
dependence on which bed is being adsorbed. The same is true for
exhaust valves 34 or 36, depending on which bed is being desorbed.
During loaded operation, unload valves 54, 56 and 62 may be closed.
Depending on the VPSA cycle, either or both of the feed and vacuum
blowers can be unloaded during portions of the cycle
[0031] When the VPSA cycle reaches a point where feed blower 22 and
vacuum blower 30 are to be unloaded, unload valves 54 and 56 are
opened and feed valves 26, 28 and exhaust valves 34, 36 are closed.
When this occurs, vacuum blower 30 operates in a recirculation
mode, while feed blower 22 discharges its gas (during unload), via
unload valve 54, into the recirculation loop employed by vacuum
blower 30 (i.e. vacuum blower 30, conduit 60, vacuum silencer 58,
unload valve 56 and exhaust conduit 32).
[0032] The system of FIG. 1, when in the unload state, is typically
operated with unload valves 54 and 56 open and third unload valve
62 closed. Under certain plant design conditions related to conduit
sizing, it may be beneficial to also open third unload valve 62 in
the unload state if a further pressure drop in the unload conduits
can be achieved. The additional reduction in overall pressure drop
will result in additional power savings.
[0033] The system of FIG. 1, when in the unload state, can be
operated with the bed feed and vacuum valves in a closed condition.
Under certain plant design conditions related to conduit sizing, it
may be beneficial to open these valves if a further reduction in
pressure drop in the unload conduits can be achieved. This
additional reduction in pressure drop will result in additional
power reductions. In such case, feed and vacuum valves 26, 34
and/or 28, 36 would be opened in addition to the opening of unload
valves 54, 56 and 62. Further, first unload valve 54 may be
eliminated from the system if the feed and vacuum valves are opened
as described.
[0034] The opening of the bed valves requires a design of the
control system that maintains the appropriate pressure levels in
the beds during the unload period. Those pressure levels are
controlled to be equal to the unload pressure to eliminate any flow
into or out of the adsorbent beds. The opening of the feed and
vacuum valves to augment pressure reduction in the unload conduits
can be employed in single and multi-bed systems.
[0035] As an example of how turndown/unload is achieved in a 60-ton
per day oxygen VPSA system, during normal cycle operation at full
production, first and second unload valves 54, 56 and third unload
valve 62 are closed. During unload, third unload valve 62 is opened
to unload feed blower 22, while unload valves 54 and 56 are kept
closed. During turndown periods, unload valves 54 and 56 are
opened, while unload valve 62 may or may not be opened as described
above. The unload discharge pressure drop for feed blower 22 is 0.5
psi, while the vacuum unload suction pressure drop is 1.0 psi for
the less preferred system of FIG. 2. Through implementation of the
invention as depicted in FIG. 1, the feed unload discharge pressure
drop reduces to 0.2 psi, while the vacuum unload suction pressure
drop is 0.3 psi. If plant flow is reduced to 66% of full flow, the
reduction in power consumption is calculated to be 5.0%.
[0036] The improvement under turndown conditions results from the
manner in which turndown control is implemented. When customer
demand is low, the system reacts by unloading its machinery and
idling the cycle for a period of time in inverse proportion to the
customer demand rate. Significant reductions in flow, therefore,
accentuate the benefits of the invention as the amount of time that
the machines are unloaded constitutes a larger fraction of the
entire cycle time. This improvement in power consumption, for
example at 33% of full flow, is 10%.
[0037] Energy recovery aspects of this invention that are achieved
by utilization of the expanding feed stream from feed blower 22 can
be practiced independently from the vent energy reduction aspects
of the invention (achieved through the use of unload valves 54 and
56 and other valves, as described above). Such energy recovery
system is applicable to any cycle which produces an expanding air
stream through a feed blower.
[0038] Turning now to FIG. 2, a less preferred embodiment of the
invention is illustrated wherein feed blower 22 and vacuum blower
30 are powered by independent motors 70 and 72, respectively. In
this instance, however, motor 70 includes a generator component 74
whose output is coupled to the electrical main via conductor 76. A
silencer 78 is coupled to feed blower 22 via feed unload valve
80.
[0039] Vacuum blower 30 is coupled to a silencer 58 via a vacuum
unload valve 82 and exhaust conduit 32 is coupled to silencer 58
via exhaust valve 84. When pressure in one adsorbent bed, in a
vacuum condition, is rising in pressure and in another bed, in a
vacuum condition, is falling in pressure, controller 38 connects
feed blower 22 to the adsorbent bed that is under vacuum condition
and rising in pressure. At such time, the expansion energy
experienced by feed blower 22 is transferred via motor 70 to
generator 74 which feeds power into the main, via conductor 76.
Accordingly, an energy credit is accumulated.
[0040] At the same time (or at some other time), vacuum blower 30
operates to remove a gas from the bed which is in a pressure
falling state. Under such conditions, the input energy to motor 72
can be supplied partially from the energy generated by generator 74
or can be taken, in its entirety from the main, with the credit
previously obtained being utilized to offset the costs of the input
energy. In such manner, energy savings are achieved. It is to be
understood, however, that this system is less efficient than the
most preferred system depicted in FIG. 1 as a result of the
mechanical-electrical-mechanical transformations which are
required, with their inherent energy losses which reduce the
overall energy savings.
[0041] It should be understood that the foregoing description is
only illustrative of the invention. Various alternatives and
modifications can be devised by those skilled in the art without
departing from the invention. Accordingly, the present invention is
intended to embrace all such alternatives, modifications and
variances which fall within the scope of the appended claims.
* * * * *