Abstrict A method and system for controlling airflow in a desiccant drying
system having two desiccant beds. A first diverter valve (14A) communicates
with each of the desiccant beds, a regeneration air inlet (22A),
and a process air outlet (28A). A second diverter valve (16A) communicates
with each of the desiccant beds, a process air inlet, and a regeneration
air outlet. A first of the beds is regenerated by moving the first
diverter valve to a position which the first bed communicates with
the regeneration air inlet and a second of the beds communicates
with the process air outlet, and by moving the second diverter valve
to a position in which the first bed communicates with the regeneration
air outlet and the second bed communicates with the process air
inlet. The first bed is subsequently cooled by moving the first
diverter valve to an intermediate cooling position in which the
second bed communicates with both of the process air outlet and
the first bed, and closing the regeneration air inlet.
Claims What is claimed is:
1. A method for controlling airflow in a desiccant drying system
having two desiccant beds,
a first diverter valve communicating with each of said desiccant
beds, a regeneration air inlet, and a process air outlet, and
a second diverter valve communicating with each of said desiccant
beds, a process air inlet, and a regeneration air outlet, said method
comprising the acts of:
(a) regenerating a first of said beds by moving said first diverter
valve to a position in which said first bed communicates with said
regeneration air inlet and a second of said beds communicates with
said process air outlet, and moving said second diverter valve to
a position in which said first bed communicates with said regeneration
air outlet and said second bed communicates with said process air
inlet;
(b) subsequently cooling said first bed by moving said first diverter
valve to an intermediate cooling position in which said second bed
communicates with both of said process air outlet and said first
bed, and closing said regeneration air inlet.
2. A method according to claim 1 further comprising the acts of:
(c) regenerating said second bed by moving said first diverter
valve to a position in which said second bed communicates with said
regeneration air inlet and said first bed communicates with said
process air outlet, and moving said second diverter valve to a position
in which said second bed communicates with said regeneration air
outlet and said first bed communicates with said process air inlet;
and
(d) subsequently cooling said second bed by moving said first diverter
valve to an intermediate cooling position in which said first bed
communicates with both of said process air outlet and said second
bed, and closing said regeneration air inlet.
3. A method according to claim 1 wherein act (b) further comprises
moving said second diverter valve to an intermediate cooling position
in which said second bed communicates with both of said process
air inlet and said first bed.
4. A method according to claim 3 wherein act (b) further comprises
closing said regeneration air outlet.
5. A method for controlling airflow in a desiccant drying system
having two desiccant beds,
a first diverter valve communicating with each of said desiccant
beds, a regeneration air inlet, and a process air outlet, and
a second diverter valve communicating with each of said desiccant
beds, a process air inlet, and a regeneration air outlet, said method
comprising the acts of:
(a) regenerating a first of said beds by moving said first diverter
valve to a position in which said first bed communicates with said
regeneration air inlet and a second of said beds communicates with
said process air outlet, and moving said second diverter valve to
a position in which said first bed communicates with said regeneration
air outlet and said second bed communicates with said process air
inlet, each of said regeneration air outlet and said regeneration
air inlet being communicated with the ambient atmosphere;
(b) subsequently cooling said first bed by communicating said regeneration
air outlet and said regeneration air inlet with each other in a
closed circuit including a heat exchanger.
6. A method according to claim 5 further comprising the acts of:
(c) regenerating said second bed by moving said first diverter
valve to a position in which said second bed communicates with said
regeneration air inlet and said first bed communicates with said
process air outlet, and moving said second diverter valve to a position
in which said second bed communicates with said regeneration air
outlet and said first bed communicates with said process air inlet,
each of said regeneration air outlet and said regeneration air inlet
being communicated with the ambient atmosphere; and
(d) subsequently cooling said second bed by communicating said
regeneration air outlet and said regeneration air inlet with each
other in said closed circuit including said heat exchanger.
7. A desiccant drying system, comprising:
two desiccant beds;
a first diverter valve communicating with each of said desiccant
beds, a regeneration air inlet, and a process air outlet;
a second diverter valve communicating with each of said desiccant
beds, a process air inlet, and a regeneration air outlet;
each of said first and second diverter valves being movable between
a first bed regeneration position, at least one intermediate cooling
position, and a second bed regeneration position,
wherein in said first bed regeneration position, said first diverter
valve communicates a first of said beds with said regeneration air
inlet and communicates a second of said beds with said process air
outlet, and said second diverter valve communicates said first bed
with said regeneration air outlet and communicates said second bed
with said process air inlet;
wherein in said intermediate cooling position, said first diverter
valve communicates said second bed with both of said process air
outlet and said first bed, and said second diverter valve communicates
said second bed with both of said process air inlet and said first
bed; and
wherein in said second bed regeneration position, said first diverter
valve communicates said second bed with said regeneration air inlet
and communicates said first bed with said process air outlet, and
said second diverter valve communicates said second bed with said
regeneration air outlet and communicates said first bed with said
process air inlet.
8. A system according to claim 7 further comprising a first cutoff
valve controllable to close said regeneration air inlet when said
first diverter valve is in said intermediate cooling position, and
a second cutoff valve controllable to close said regeneration air
outlet when said second diverter valve is in said intermediate cooling
position.
9. A system according to claim 7 further comprising a heat exchanger
arranged between each of said first and second beds and said second
diverter valve.
10. A desiccant drying system, comprising:
two desiccant beds;
a first diverter valve communicating with each of said desiccant
beds, a regeneration air inlet, and a process air outlet;
a second diverter valve communicating with each of said desiccant
beds, a process air inlet, and a regeneration air outlet;
each of said first and second diverter valves being movable between
a first bed regeneration position, and a second bed regeneration
position,
wherein in said first bed regeneration position, said first diverter
valve communicates a first of said beds with said regeneration air
inlet and communicates a second of said beds with said process air
outlet, and said second diverter valve communicates said first bed
with said regeneration air outlet and communicates said second bed
with said process air inlet;
wherein in said second bed regeneration position, said first diverter
valve communicates said second bed with said regeneration air inlet
and communicates said first bed with said process air outlet, and
said second diverter valve communicates said second bed with said
regeneration air outlet and communicates said first bed with said
process air inlet;
a heat exchanger; and
a valve system operable to selectively communicate said regeneration
air inlet and said regeneration air outlet with one of (a) the ambient
atmosphere, and (b) each other in a closed circuit with said heat
exchanger.
11. A system according to claim 10 further comprising means for
controlling said valve system to communicate said regeneration air
inlet and said regeneration air outlet with the ambient atmosphere
during a regeneration phase, and (b) means for controlling said
valve system to communicate said regeneration air inlet and said
regeneration air outlet with each other in a closed circuit with
said heat exchanger during a cooling phase.
12. A system according to claim 10 wherein said valve system comprises
a first and a second dual poppet valve,
said first dual poppet valve being communicated with said regeneration
air outlet and including a first poppet valve selectively communicable
with the ambient atmosphere and a second poppet valve selectively
communicable with said heat exchanger,
said second dual poppet valve being communicated with said regeneration
air inlet and including a first poppet valve selectively communicable
with said heat exchanger and a second poppet valve selectively communicable
with the ambient atmosphere.
13. A system according to claim 10 wherein said valve system is
a dual chamber regeneration valve comprising:
a first chamber communicable with said regeneration air outlet
and communicable with the ambient atmosphere via an outlet check
valve;
a second chamber communicable with said first chamber, communicable
with the ambient atmosphere via an inlet check valve, and communicating
with said regeneration air inlet via said heat exchanger; and
a single valve selectively movable between a regeneration position
shutting off communication between said first and second chambers,
a diverter valve movement position shutting off communication between
said first chamber and said regeneration air outlet, and an intermediate
cooling position between said regeneration position and said diverter
valve movement position.
Description BACKGROUND OF THE INVENTION
This invention relates to a method and a system for controlling
airflow in a multiple bed desiccant drying system, particularly
in a twin tower desiccant dehumidifier, and particularly during
a regeneration phase, and during transition periods between phases.
Multiple desiccant bed systems used for drying a synthetic plastic
material are known, in which a moisture-laden gas stream is formed
as the exit gas from a hopper in which plastic granules are dried
by a stream of drying air. During an adsorption phase, the exit
gas is conducted through one or more drying vessels filled with
an adsorption medium, whereby the adsorption medium extracts the
moisture from the gas so that the resulting dry gas can be used
again as a drying gas for drying plastic granules.
When the adsorption medium in a drying vessel is saturated with
moisture, the drying vessel is transferred to a regeneration phase
in which heated ambient air is conducted through the adsorption
medium which takes up and carries away the moisture which was adsorbed
therein. The ambient air used to dry the adsorption medium typically
contains moisture, which increases the drying time required to regenerate
the adsorption medium.
During the regeneration phase, since the adsorption medium is heated
by the heated regeneration air, the adsorption medium is typically
subsequently cooled with a cooling air flow prior to a transition
to the adsorption phase. If moisture-laden ambient air is used as
the cooling air, the adsorption medium will adsorb the moisture
therefrom, reducing the efficiency (i.e. dryness) of the regeneration
process.
By using a multiple bed system, the drying process can be continued
essentially without interruption, by utilizing one or a portion
of the beds for adsorption, while simultaneously regenerating other
of said beds, by appropriately channeling the process air flow.
In commonly owned prior U.S. patent application Ser. No. 08/874654
to Crawford et al., the disclosure of which is expressly incorporated
by reference herein, a system and method of operation is disclosed
in which two towers are connected by a 4-valve system. The 4-valve
system is controlled such that the process air stream is progressively
moved from the saturated bed to the regenerated bed. In that invention
the terminal disruption of the dewpoint is minimized by any residual
heat that remains in the fresh tower being brought online.
In previously known drying systems, a problematic issue is disruption
of the process air temperature and dewpoint quality when changing
from the saturated tower to the freshly regenerated tower. Furthermore,
in previously known drying systems, bringing a heat exchanger online
at the appropriate time without undue complexity of valves is a
known problem. As an additional issue, previously known drying systems
may be contaminated by room air during diverter valve changes. In
addition, since the common instrumentation used to determine the
dryness of the process air stream may require from 30 to 60 minutes
to recover from the exposure to a high intermittent dewpoint, it
is difficult to determine and monitor the humidity level of the
process air in previously known drying systems.
SUMMARY OF THE INVENTION
In view of the above, there is a need for an improved method and
a system for controlling airflow in a multiple bed desiccant drying
system.
There is also a need for a method and a system which can be implemented
in existing multiple bed desiccant drying systems with a minimum
of components, effort, and cost.
These and other needs have been met according to the present invention
as discussed in the following.
The present invention utilizes a multiple position operator for
the pair of four way diverter valves which direct the process and
regeneration air to the desiccant towers, in conjunction with two
cutoff valves at the ambient connection ports for the regeneration
air. This allows the desiccant cooling of the regenerating tower
to utilize a slipstream of the dry process airflow, in order to
avoid loading the regenerated bed with moist ambient air. The existing
four way diverter valves are used to accomplish the diversion of
the process air for the closed loop cooling of the desiccant by
incorporating a multiple position actuator to seal the regeneration
side of the dryer during the purge cycle, and then open slightly
to allow some air to bypass through the regenerating desiccant tower
for cooling. This avoids undue complication and expense.
The present invention limits the disruption of the process air
dewpoint at tower change over. The present invention avoids the
possibility of ambient room air contaminating the dry air circuit
when open regeneration ports become connected to the dry air system
while the tower diverter valves are in operation. Furthermore, by
using a heat exchanger to remove some of the residual regeneration
energy, the present invention avoids the use of ambient room air
for desiccant cooling.
The present invention's ability to seal off the desiccant beds
from the ambient atmosphere has further advantages. By sealing the
desiccant beds off from the ambient atmosphere, the desiccant can
be maintained in usable (i.e., dry) form for extended periods of
time, for example while waiting to be moved on-line, or even when
the machine is shut down. This eliminates time delays during start-up,
which are required in conventional desiccant drying systems to dry
out the desiccant which is exposed to the atmosphere, and reduces
energy requirements.
By introducing a multi ported valve in the regeneration airflow
circuit, the present invention isolates the tower system from the
ambient air that would otherwise enter the drying system while the
diverter valves are in intermediate or indeterminate positions during
tower exchange.
The present invention also allows the use of a regeneration cooling
heat exchanger with only the multi port valve as the sole additional
operating device. The multi port valve may have a number of mechanical
arrangements, for example both directly operated poppets, and a
combination of check valves and poppet valves.
The present invention may be either incorporated into new, or retrofitted
to existing, twin tower desiccant dehumidifiers. The disruptive
effects of changing the tower diverter valves of a conventional
twin tower desiccant dehumidifier are substantially reduced. This
is accomplished through the use of a multi port valve applied to
the regeneration air circuit of the dehumidifier system.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in further detail hereinafter with
reference to preferred embodiments illustrated in the accompanying
drawings in which:
FIG. 1 shows a schematic view of a drying system according to a
preferred embodiment of the present invention;
FIG. 2 shows a view of a diverter valve in an intermediate position;
FIG. 3 shows a schematic view of a drying system according to a
preferred embodiment of the present invention; and
FIG. 4 shows a schematic view of a drying system according to a
preferred embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to FIG. 1 a first tower 10 and a second tower 12 of
a twin tower desiccant dehumidifier are schematically shown, each
of which contains an adsorption medium (i.e. desiccant) for removing
moisture from a process gas, for example process air used to dry
plastic pellets. Each of the first and second towers 10 12 communicate
with each of first and second 4-way diverter valves 14 16. The
4-way diverter valves 14 16 are controllable to a plurality of
positions in order to direct airflow. In the positions shown in
FIG. 1 the diverter valves 14 16 direct airflow such that the
first tower 10 is in a regeneration (i.e., drying) phase, while
the second tower 12 is in an adsorption phase.
A process gas inlet 18 communicates with the first 4-way diverter
valve 14 which valve 14 is controllable to direct flow into either
of the first tower 10 or the second tower 12. In the position shown
in FIG. 1 the first valve 14 directs moist process gas, for example
process air, entering the process gas inlet 18 into the second tower
12.
A process gas outlet 20 communicates with the second 4-way diverter
valve 16 which valve 16 is controllable to direct flow from either
of the towers 10 12 to said outlet 20. In the position shown in
FIG. 1 the second valve 16 directs dried process gas from the second
tower 12 to the process gas outlet 20.
As mentioned above, in FIG. 1 the second tower 12 is shown in the
adsorption phase. The process gas outlet 20 and the process gas
inlet 18 are connected in a circuit with a drying vessel, not shown,
for example a drying hopper containing a material to be dried such
as plastic pellets. The dried process gas exits the process gas
outlet 20 picks up moisture as it passes through the material to
be dried in the drying vessel, and returns via the process gas inlet
18 passing through the second desiccant tower 12 to be dried again.
As mentioned above, in FIG. 1 the first tower 10 is shown in the
regeneration phase. A regeneration inlet 22 communicates with the
second 4-way diverter valve 16 with a first cutoff valve 24 and
a heater 26 being interposed therebetween. Regeneration gas, for
example ambient air, entering the regeneration gas inlet 22 is heated
by the heater 26 and is directed by the second valve 16 in the
position shown in FIG. 1 into the first desiccant tower 10. The
heated regeneration gas picks up moisture from the moist adsorption
medium in the first desiccant tower 10 and is directed via the
first diverter valve 14 to a regeneration gas outlet 28 which may
communicate, for example, with the ambient atmosphere or with a
heat exchanger for recovery of heat energy. A second cutoff valve
30 is disposed between the first diverter valve 14 and the regeneration
gas outlet 28. During the regeneration phase, both of the first
and second cutoff valves 24 30 are open to allow gas to pass therethrough.
After the adsorption medium in the first tower 10 has been de-moisturized
to a desired extent, the adsorption medium needs to be cooled in
order to avoid temperature disruptions when switching the first
tower 10 to the adsorption phase. With regard to this regeneration
cooling phase, simply turning off the heater 26 and running regeneration
gas (e.g. moist ambient air) through the first tower 10 has the
above-noted disadvantage of moistening the adsorption medium therein
and consequently reducing the efficiency of the regeneration cycle.
In view of the above, in the present invention at least the first
cutoff valve 24 is closed to prevent regeneration gas (e.g. moist
ambient air) from entering the system during the cooling phase.
The second 4-way diverter valve 16 is moved to an intermediate position
shown in FIG. 2 in order to allow a portion of the dried process
air coming from the second tower 12 to pass into the first tower
10 which portion of dried process air cools the adsorption medium
in the first tower 10.
In the cooling phase, the first 4-way diverter valve 14 is also
moved to the intermediate position shown in FIG. 2 essentially
in parallel with the movement of the second diverter valve 16. The
second cutoff valve 30 is also moved to a closed position, essentially
in parallel with the movement of the first cutoff valve 24. These
movements of the first diverter valve 14 to the intermediate position
and of the second cutoff valve 30 to the closed position are necessary
in order to balance the pressures within the system.
Accordingly, during the cooling phase, both cutoff valves 24 30
are in a closed position and both 4-way diverter valves 14 16 are
in the intermediate position shown in FIG. 2. The portion of the
dried process gas which is diverted into the first tower 10 via
the second diverter valve 16 picks up heat from the adsorption medium
therein, and then passes via the first diverter valve 14 back into
the second tower 12. The complete closure of the first tower 10
off from the regeneration gas (e.g. moist ambient air) advantageously
prevents the adsorption medium contained therein from picking up
moisture during the cooling phase. However, the passage of this
heated process gas back into the second tower 12 results in a temperature
variation in the system. In order to reduce this temperature variation,
it is contemplated to install respective heat-exchangers into the
system between the towers 10 12 and the first diverter valve 14.
Alternatively, in order to reduce the above-mentioned temperature
variation, it is contemplated to control the cutoff valves 24 30
to close gradually (e.g., step-wise incrementally or continuously
over a period of time) during transition from the regeneration phase
to the cooling phase (i.e. after shutting off the heater 26). This
gradual closing of the cutoff valves 24 30 may be effected simultaneously
with or prior to movement of the 4-way diverter valves 14 16 from
the position shown in FIG. 1 to the intermediate position shown
in FIG. 2. This gradual closing of the cutoff valves 24 30 allows
an initial portion of the cooling gas (regeneration gas and/or dried
process air) to pass out of the system via the regeneration gas
outlet 28. While this gradual closing of the cutoff valves 24 30
reduces temperature variations by flushing the initial portion of
the cooling gas, which picks up the greatest amount of heat from
the dried adsorption medium, out of the system, this advantage is
a trade-off with the disadvantage of introducing some moisture into
the dried adsorption medium. Those skilled in the art will understand
that experimentation and testing may lead to a preferred range of
times and/or positions for gradual closing of the cutoff valves
24 30 depending upon process-specific parameters.
The cutoff valves 24 30 allow the desiccant beds to be completely
closed off from the ambient atmosphere. For example, when the machine
is shut down, the cutoff valves may be closed to prevent the desiccant
from picking up moisture from the ambient atmosphere. Accordingly,
the present invention allows the desiccant beds to be maintained
in a ready (i.e., dry) state for instant use, whereas in conventional
drying systems an additional start-up time is required for drying
out the desiccant which has been exposed to the ambient atmosphere,
which also requires additional energy. Likewise, when the drying
system is being run below design capacity (i.e., when the regenerating
tower is regenerated before the adsorbing tower is fully loaded),
the desiccant in the regenerated tower can be maintained in its
optimum dry condition by closing the cutoff valves 24 30 while
the adsorbing tower is extended to full load before switching over.
After the adsorption medium in the first tower 10 has been cooled
to a desired temperature, at which time the adsorption medium in
the second tower 12 may have become saturated, the first and second
diverter valves 14 16 are moved into the position shown in FIG.
3 such that the first tower 10 enters the adsorption phase and
the second tower 12 enters the regeneration phase. The first and
second cutoff valves 24 30 are opened, either simultaneously with
movement of the diverter valves 14 16 into the position shown in
FIG. 3 or subsequently thereto.
In FIG. 3 components which essentially correspond to the system
shown in FIG. 1 are appended with an "A". In the system
of FIG. 3 the regeneration gas outlet 28A and the regeneration
gas inlet 22A are connected in a circuit including a regeneration
valve system generally referred to as 32. The regeneration valve
system 32 includes four poppet-type valves 34 36 38 40. Each
of the poppet-type valves is movable between an open position allowing
fluid flow and a closed position blocking fluid flow, and may be
constructed, for example, similar to those shown in FIG. 1 of commonly
owned prior U.S. patent application Ser. No. 08/874654 to Crawford
et al.
In the system of FIG. 3 the diverter valves 14A, 16A are shown
in the position in which the first tower 10A is in the adsorption
phase, while the second tower 12A is in the regeneration phase.
During the heating portion of the regeneration cycle, poppet valves
34 and 40 are moved to an open position, such that an open circuit
is formed in communication with the ambient atmosphere via the intake
port at poppet valve 40 and the exhaust port at poppet valve 34.
Ambient air enters the open circuit at the intake port at poppet
valve 40 subsequently passing through regeneration gas inlet 22A,
heater 26A which is turned on, and second tower 12A via second diverter
valve 16A, where the heated air picks up moisture from the adsorption
medium. The moist air subsequently passes from the second tower
12A via first diverter valve 14A through regeneration gas outlet
28A, and returns to the ambient atmosphere via the exhaust port
at valve 34.
During the subsequent cooling portion of the regeneration cycle,
poppet valves 34 and 40 are closed, while poppet valves 36 and 38
are opened, such that a closed cooling circuit is formed which is
shut off from the ambient atmosphere. Cooling gas in the closed
cooling circuit (e.g. ambient air left in the system from the heating
portion of the regeneration cycle) passes through the regeneration
gas inlet 22A, the heater 26A which is turned off, and into the
second tower 12A via second diverter valve 16A, where the cooling
gas cools the heated dried adsorption medium. The then-heated cooling
gas subsequently passes from the second tower 12A via the first
diverter valve 14A through the regeneration gas outlet 28A, and
to a heat exchanger 42 via a port at poppet valve 36 where the
heated cooling gas is cooled. The cooled cooling gas leaves the
heat exchanger and is passed back to the regeneration gas inlet
22A via a port at poppet valve 38.
Since the closed cooling circuit is shut off from the ambient atmosphere,
no moisture enters the system, which would disadvantageously moisten
the dried adsorption medium. Furthermore, the heat exchanger advantageously
expels the heat added to the system by the heater 26A during the
heating portion of the regeneration cycle. Accordingly, the system
shown in FIG. 3 advantageously minimizes both humidity and thermal
disruptions of the system.
The diverter valves 14A, 16A are moved from the position shown
in FIG. 3 to the position shown in FIG. 1 in order to exchange the
adsorption and regeneration cycles of the towers 10A, 12A. During
this movement of the diverter valves 14A, 16A, all of the poppet
valves 34 36 38 40 are closed in order to avoid a disadvantageous
introduction of moist ambient air into the system.
It is contemplated to move the diverter valves 14A, 16A gradually
during the exchange between regeneration and adsorption phases,
for example stepwise incrementally, e.g. into one or more intermediate
positions as shown in FIG. 2 or continuously over a period of time.
This gradual movement of the diverter valves 14A, 16A further helps
to avoid disruptions in the quality (e.g. humidity and temperature)
of the process air during the exchange between towers and phases.
In the FIG. 3 embodiment, although the diverter valves 14A, 16A
need not be moved into the intermediate position (as shown in FIG.
2) during the cooling phase, as a further alternative, the movement
of the diverter valves 14A, 16A may be initiated during the cooling
portion of the regeneration process.
In FIG. 4 components which correspond to the system shown in FIGS.
1 and/or 3 are appended with a "B". The system of FIG.
4 operates similarly to that of FIG. 3. However, rather than using
four poppet-type valves, the system of FIG. 4 utilizes a dual chamber
regeneration valve system 32B with a single valve 44 and an inlet
check valve 46 and an outlet check valve 48 to control regeneration
airflow therethrough. The valve 44 is movable between at least three
positions 1 2 3 as shown in FIG. 4.
During the heating portion of the regeneration cycle, the valve
44 backseats into position 3 closing port 54 and opening port 56.
Inlet and outlet check valves 46 and 48 are forced open to form
an open circuit in communication with the ambient atmosphere. Ambient
air enters the open circuit at the inlet check valve 46 subsequently
passing through chamber 50 heat exchanger 42B, regeneration gas
inlet 22B, heater 26B which is turned on, and second tower 12B via
second diverter valve 16B, where the heated air picks up moisture
from the adsorption medium. The moist air subsequently passes from
the second tower 12B via first diverter valve 14B through regeneration
gas outlet 28B, and returns to the ambient atmosphere via port 56
and chamber 52.
During the subsequent cooling portion of the regeneration cycle,
valve 44 is moved into intermediate position 2 and inlet and outlet
check valves 46 48 are closed, such that a closed cooling circuit
is formed which is shut off from the ambient atmosphere. Cooling
gas in the closed cooling circuit (e.g. ambient air left in the
system from the heating portion of the regeneration cycle) passes
through the regeneration gas inlet 22B, the heater 26B which is
turned off, and into the second tower 12B via second diverter valve
16B, where the cooling gas cools the heated dried adsorption medium.
The then-heated cooling gas subsequently passes from the second
tower 12B via the first diverter valve 14B through the regeneration
gas outlet 28B, into chamber 52 via port 56 into chamber 50 via
port 54 and to a heat exchanger 42B, where the heated cooling gas
is cooled. The cooled cooling gas leaves the heat exchanger and
is passed back to the regeneration gas inlet 22B.
Since the closed cooling circuit is shut off from the ambient atmosphere,
no moisture enters the system, which would disadvantageously moisten
the dried adsorption medium. Furthermore, the heat exchanger advantageously
expels the heat added to the system by the heater 26B during the
heating portion of the regeneration cycle. Accordingly, the system
shown in FIG. 4 advantageously minimizes both humidity and thermal
disruptions of the system.
The diverter valves 14A, 16A are moved from the position shown
in FIG. 4 to the position shown in FIG. 1 in order to exchange the
adsorption and regeneration cycles of the towers 10B, 12B. During
this movement of the diverter valves 14B, 16B, the valve 44 forward
seats in position 1 closing port 56 and leaving port 54 open.
It is contemplated to move the diverter valves 14B, 16B gradually
during the exchange, for example stepwise incrementally, e.g. into
one or more intermediate positions as shown in FIG. 2 or continuously
over a period of time.
Furthermore, as a further alternative, the movement of the diverter
valves 14B, 16B may be initiated during a portion of the cooling
portion of the regeneration process.
The foregoing description and examples have been set forth merely
to illustrate the invention and are not intended to be limiting.
Since modifications of the disclosed embodiments incorporating the
spirit and substance of the invention may occur to persons skilled
in the art, the invention should be construed to include everything
within the scope of the knowledge of such persons and equivalents
thereof. |