Information
-
Patent Grant
-
6260390
-
Patent Number
6,260,390
-
Date Filed
Wednesday, March 10, 199925 years ago
-
Date Issued
Tuesday, July 17, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Weingarten, Schurgin, Gagnebin & Hayes LLP
-
CPC
-
US Classifications
Field of Search
US
- 008 158
- 008 142
- 068 18 R
- 068 18 C
- 134 10
- 134 12
- 134 107
-
International Classifications
-
Abstract
A dry cleaning process and system for cleaning articles disposed in a cleaning chamber having a rotatable member therein, using carbon dioxide (CO2) from a storage tank. The process includes causing a pressure differential between the storage tank and the cleaning chamber, filling the cleaning chamber with a predetermined amount of liquid CO2 enabling flow of liquid CO2 from the storage tank to the cleaning chamber in response to the pressure differential, and rotating the rotatable member.
Description
FIELD OF THE INVENTION
The present invention relates to dry cleaning processes in general and, more particularly, to a dry cleaning process and system utilizing a solvent and having a rotatable container for agitating articles.
BACKGROUND OF THE INVENTION
Existing dry cleaning processes function by mechanically agitating articles to be cleaned, e.g., clothes, and a solvent. Typically, articles of clothing are placed in a container or basket with an amount of a chemical solvent that loosens dirt and dissolves staining matter from the clothes. The clothes are then agitated by movement of the basket to increase the effectiveness of the cleaning process. The agitation is often in the form of rotation, and rotation with an axis in the horizontal plane makes use of gravitational forces to further increase the amount of agitation.
Many chemical solvents are environmentally hazardous and present public health and safety risks. As a result, a number of solvents have been banned by law or heavily regulated. In addition, “environmentally friendly” alternatives have been sought. One such alternative is using liquid carbon dioxide (CO
2
) as a solvent.
Dry cleaning systems and processes using liquid/supercritical dense-phase gas such as carbon dioxide (CO
2
) are known in the art. In such processes, liquid CO
2
is pumped throughout the system using a heavy-duty positive displacement pump. Specifically, liquid CO
2
is pumped from a reservoir into a cleaning chamber where articles come into contact with the CO
2
. The articles are cleaned by agitation, such as by rotation of a container holding the articles, and finally, the liquid CO
2
is pumped back into the reservoir. The pump is also used during additional steps of the dry cleaning process as are known in the art.
The use of such a pump has a number of disadvantages that render prior art systems complex and/or cost-inefficient for many applications. One disadvantage is that the pump is a relatively expensive element of the dry cleaning system. Another disadvantage is that the pump requires a net positive suction head (“NPSH”). This head is generated by both the fluid level in whatever vessel is to be drained and the elevation of the vessel relative to the pump inlet. Configurations that provide adequate pressure such as tall vessels or mounting the vessel about the pump are not desirable because they result in a large machine. Furthermore, completely draining the cleaning chamber still may be difficult because NPSH decreases as the chamber empties.
Another method of providing adequate pump head is by using a distillation chamber. Gas is heated in the chamber, and the resultant pressure increase is used to provide the desired NPSH. However, the use of such a distillation chamber adds complexity and cost to the system.
Furthermore, the pump is susceptible to damage and wear from dirt suspended in the fluid, which reduces the pumping efficiency. Filters cannot be used on the suction side of the pump because they decrease the pressure at the pump inlet, adding to the problem of attaining adequate positive pressure head. Thus, in addition to equipment and operating costs, frequent maintenance is also necessary.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process and a system for efficiently supplying and/or recycling liquid carbon dioxide (CO
2
) in a dry cleaning system using a rotating basket. In accordance with the process of the present invention, pressurized liquid CO
2
is transported between a storage tank and cleaning chamber by means of a pressure differential produced between the tank and chamber, obviating the need for a pump. This eliminates the disadvantages typically associated with such pumps, such as high equipment cost, maintenance downtime and costs due to wear and low efficiency and, thus, expands the circumstances in which the present invention may be used.
In an embodiment of the present invention, the pressure differential is produced by a gas compressor which does not directly interact with liquid CO
2
and, thus, does not accumulate dirt suspended in the liquid CO
2
. This eliminates the problems associated with pumps used by prior arty systems, making the system of the present invention more cost effective and reliable. The compressor draws gaseous CO
2
from the cleaning chamber and injects it into the storage tank, or vice versa, to create either a positive or a negative pressure differential, respectively, between the storage tank and the cleaning chamber. A positive pressure differential enables flow of liquid CO
2
from the storage tank to the cleaning chamber. A negative pressure differential enables flow of liquid CO
2
from the cleaning chamber to the storage tank. The magnitude of the pressure differential may be controlled by varying the speed of the compressor motor or using a throttle valve.
The dry cleaning process of the present invention may also include a method of recovering heat from the compressed gas. In a vapor recovery step of the dry cleaning process, as described below, heat from the gaseous CO
2
is transferred to a heat sink, which may be in the form of heat exchanger immersed in a water bath, before cooling the CO
2
by a refrigeration system. This reduces the amount of energy consumed by the refrigeration system. The heat energy stored in the heat sink may subsequently be used to heat cold gas during a cleaning chamber warm-up step of the dry cleaning process, as described below, obviating or reducing the need for additional heating. Thus, the present invention utilizes a heat recovery cycle which improves the cost-efficiency of the dry cleaning process.
Except for specific aspects of the present invention, as described herein, the process and system of the present invention are compatible with existing dry cleaning processes and systems and may be used in conjunction with any cleaning chambers and/or baskets and/or other parts of dry cleaning systems that are known in the art.
A dry-cleaning system in accordance with an embodiment of the present invention includes a storage tank for storing CO
2
at a selectable pressure, a cleaning chamber having a pressure containment sufficient to keep CO
2
in a liquid state, means for providing a pressure differential between the storage tank and cleaning chamber, a rotatable basket within the cleaning chamber, and a rotational drive mechanism coupled to the basket. In some embodiments of the invention, the system may further include a vapor heat exchanger/recovery system, a refrigeration system, a lint trap/filtration system, and a cleaning chamber ventilation system. The pressure differential between the storage tank and cleaning chamber may be produced by a gas compressor, which may be an oil-less compressor.
A dry cleaning process in accordance with an embodiment of the present invention may include at least some of the following steps:
(a) Removing moisture-laden air from the cleaning vessel. The compressor may act as a vacuum pump to evacuate the air to the atmosphere.
(b) Equalizing pressure between the storage tank and the cleaning chamber in a controlled fashion to avoid clothes damage. CO
2
gas may flow from the comparatively higher pressure storage tanks to the comparatively lower pressure cleaning chamber until a predetermined pressure difference exists between the cleaning chamber and the storage tank.
(c) Filling the cleaning chamber with a predetermined amount of liquid CO
2
from the storage tank. CO
2
vapor may be drawn from the top of the cleaning chamber by the compressor and moved into the top of the storage tank, creating a pressure differential forcing liquid to flow from the bottom of the tank into the cleaning vessel.
(d) Agitating the articles being cleaned by rotating the basket.
(e) Draining used/contaminated liquid from the cleaning chamber. CO
2
vapor may be drawn from the top of the storage tank by the compressor and moved into the top of the cleaning chamber, creating a pressure differential forcing liquid from the bottom of the chamber into the bottom of the storage tank. The liquid may pass through a filter system located between the vessels.
(f) Recovering CO
2
vapor remaining in the cleaning chamber after drainage. CO
2
vapor may be drawn from the top of the cleaning chamber and pushed by the compressor, through a heat recovery system and/or refrigeration system that cools and condenses the vapor into liquid and into the storage tank.
(g) Heating the cleaning chamber. CO
2
vapor may be drawn from the top of the cleaning chamber and pushed by the compressor through a heat exchanger system that heats the vapor and into the bottom of the cleaning chamber.
(h) Venting the cleaning chamber. CO
2
vapor may flow out of the cleaning chamber through a cleaning chamber ventilation system, which may include a sound control muffler.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood and appreciated more fully from the following detailed description of a preferred embodiment of the invention, taken in conjunction with the accompanying drawings of which:
FIG. 1
is a schematic illustration of a dry-cleaning system during an air evacuation step of a dry-cleaning process in accordance with an embodiment of the present invention;
FIG. 2
is a schematic illustration of the system of
FIG. 1
during a pressure equalization step of a dry-cleaning process in accordance with an embodiment of the present invention;
FIG. 3
is a schematic illustration of the system of
FIG. 1
during cleaning chamber filling and agitation steps of a dry-cleaning process in accordance with an embodiment of the present invention;
FIG. 4
is a schematic illustration of the system of
FIG. 1
during a cleaning chamber draining step of a dry-cleaning process in accordance with an embodiment of the present invention;
FIG. 5
is a schematic illustration of the system of
FIG. 1
during a cleaning chamber vapor recovery step of a dry-cleaning process in accordance with an embodiment of the present invention;
FIG. 6
is a schematic illustration of the system of
FIG. 1
during a cleaning chamber warm-up step of a dry-cleaning process in accordance with an embodiment of the present invention;
FIG. 7
is a schematic illustration of the system of
FIG. 1
during a cleaning chamber ventilation step of a dry-cleaning process in accordance with an embodiment of the present invention; and
FIG. 8
is a schematic graphic representation of a dry cleaning process sequence in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Reference is now made to
FIGS. 1-7
which schematically illustrate a dry-cleaning system in accordance with an embodiment of the present invention during various stages of a dry-cleaning process in accordance with an embodiment of the present invention. The system includes a cleaning chamber
10
, for example an about 80-gallon cleaning chamber, having a basket
12
for holding articles to be cleaned. Cleaning chamber
10
is preferably designed to have high pressure containment capability, for example, a pressure containment of about 1,100 PSI, sufficient to maintain carbon dioxide (CO
2
) in a liquid state.
Basket
12
is rotatably mounted within cleaning chamber
10
and is coupled to a basket drive
14
via a coupling
16
, which may be of any type suitable for maintaining pressure integrity of cleaning chamber
10
, for example, a mechanical coupling with a high-pressure seal, as is known in the art. However, in a preferred embodiment of the invention, coupling
16
is a magnetic coupling which eliminates the need for an opening in chamber
10
, as required in the case of mechanical coupling. Rotational driving mechanism using magnetic coupling are well known in the art and are known in the art.
The system further includes at least one storage tank
20
having a predetermined volume capacity, for example, about 30-50 gallons. Storage tank
20
preferably has high pressure containment capability, for example, about 1,100 PSI, and is filled with a predetermined initial amount of CO
2
, for example, 100 gallons.
In a preferred embodiment of the invention, the system also includes a lint trap/filtration system comprising a lint trap
24
, for example, a 100 mesh lint trap, as is known in the art, and a filter
26
, for example, a 40 micron filter, as is known in the art.
In accordance with the present invention, the system includes means for providing a pressure differential between storage tank
20
and cleaning chamber
10
that comprises a gas compressor
30
, preferably an oil-less compressor. An important advantage of using a gas compressor such as compressor
30
, rather than a liquid pump (as used in prior art systems), is that gas flow does not suspend dirt and, thus, dirt is not carried into the compressor. This reduces wear and, consequently, operating and maintenance costs of the dry cleaning system.
Compressor
30
is preferably capable of producing partial vacuum duty and vapor recovery. In an embodiment of the present invention, compressor
30
is capable of decreasing the pressure in cleaning chamber
10
to less than 400 PSI, preferably less than 150 PSI, for example about 50 PSI. It should be appreciated that a low pressure in chamber
10
minimizes wastage of CO
2
during venting of the cleaning chamber, as described below. Further, in an embodiment of the present invention, compressor
30
is capable of increasing the pressure in storage tank
20
to more than 750 PSI, preferably more than 850, for example, 900 PSI. It should be appreciated that a high pressure in storage tank
20
maintains the CO
2
in liquid state with minimal cooling and, therefore, enables more energy-efficient dry cleaning. The magnitude of the pressure differential produced between storage tank
20
and cleaning chamber
10
may be controlled by varying the motor speed of compressor
30
or using a throttle valve, as is known in the art. An example of an oil-less compressor that may be used in conjunction with the present invention to provide the above described parameters is the Blackmer HDL 322 oil-less compressor, available from Blackmer, Inc., Oklahoma City, Okla.
The system preferably further includes a heat exchanger/recovery system
31
comprising a heat sink/water bath
28
and associated heat exchanger
32
in the embodiment shown. Heat recovery system
31
collects heat energy from hot gas in one step of the dry cleaning process and utilizes that heat energy to warm cold gas during another step, as is described below. Heat energy may be transferred to water bath
28
from CO
2
passing through heat exchanger
32
at certain times during the dry cleaning cycle, and water bath
28
may transfer heat to CO
2
at other times during the cycle. Preferably, an electric heater
40
is installed in water bath
28
to maintain it at a predetermined temperature, for example, 80° C., during idle periods of the dry-cleaning process.
In an embodiment of the present invention, a refrigeration system
35
with a heat exchanger
36
adapted for cooling CO
2
is included. Preferably, refrigeration system
35
possesses sufficient cooling capacity to condense CO
2
passing through heat exchanger
36
.
As clearly shown in the drawings but not individually referenced, the dry cleaning system includes piping as necessary for connecting between the different system elements of the system and various valves for controlling the operation of the system and CO
2
flow during different steps of the dry cleaning process. Some of these valves are specifically discussed below with reference to steps of the dry cleaning method of the present invention. However, the function of most of these valves will be apparent to persons of ordinary skill in the art of dry-cleaning systems. The system further includes a cleaning chamber ventilation system
41
with, preferably, a sound control muffler
46
that may be used during final venting of cleaning chamber
10
, as described below.
Reference is now made also to
FIG. 8
that schematically illustrates the different steps of a dry cleaning process according to an embodiment of the present invention and shows an exemplary duration for each step.
FIG. 8
is self-explanatory to a person skilled in the art. A detailed description of the different steps of the dry cleaning according to an embodiment of the present invention is provided below with reference to
FIGS. 1-7
.
FIG. 1
illustrates an air evacuation step of the dry-cleaning process in accordance with an embodiment of the present invention. The purpose of this step is to remove moisture laden air, thus reducing the amount of water that dissolves in the CO
2
. Compressor
30
acts as a vacuum pump with respect to cleaning chamber
10
. Compressor
30
is activated for a predetermined time period, for example, about 2 minutes, until a predetermined pressure is reached, for example, 20-25 inches Hg, as determined by a pressure transducer
42
. Once the desired pressure level is reached, compressor
30
is shut down.
FIG. 2
schematically illustrates a pressure equalization step of the dry-cleaning process in accordance with an embodiment of the present invention. During this step, the pressure between storage tank
20
and cleaning chamber
10
is generally equalized in a controlled fashion to avoid damage to the articles being cleaned. Gaseous CO
2
flows from the top of storage tank
20
to the top of cleaning chamber
10
through a valve
44
and an orifice
47
until the difference between the readings of pressure transducer
42
and a pressure transducer
48
in the storage tank
10
is below a predetermined threshold, for example a
10
percent pressure differential.
FIG. 3
schematically illustrates a step of partially filling cleaning chamber
10
with liquid CO
2
from storage tank
20
. Gaseous CO
2
is drawn from a top opening
18
of cleaning chamber
10
and is pushed by compressor
30
into the top of storage tank
20
. In this step, compressor
30
produces a positive pressure differential between storage tank
20
and cleaning chamber
10
, enabling the flow of liquid CO
2
from the storage tank to the cleaning chamber. Although heating of the CO
2
is not required at this stage of the process, the CO
2
flows through heat exchanger
32
in water bath
28
, thus utilizing the same piping scheme for different stages of the process. The flow of gas into storage tank
20
forces liquid CO
2
out of the bottom and into a bottom opening
38
of cleaning chamber
10
until the desired level of liquid CO
2
is reached. This level may be determined by a timer (not shown) and/or by a level sensor
50
associated with storage tank
20
.
Also referring to
FIG. 3
, after filling cleaning chamber
10
, the articles within basket
12
may be agitated by rotating the basket. As discussed above, any suitable rotational basket drive
14
may be used. If coupling
16
between basket drive
14
and basket
12
is a mechanical coupling, pressure integrity of cleaning chamber
10
may be maintained by a suitable high pressure seal. In the preferred embodiment, coupling
16
is magnetic so that pressure integrity is not an issue. The basket is agitated for an adequate time to clean the articles located therein, e.g., clothes. The time of the agitation may be dependent upon various factors, including the nature and amount of articles in the cleaning chamber, the composition, temperature and pressure of the solvent, the speed of rotation of basket during agitation, and the configuration of any structures within the basket, e.g., the height of paddles, as is known in the art.
Referring to
FIG. 4
, after agitation as described above, used/contaminated liquid is removed from cleaning chamber
10
. Gaseous CO
2
is drawn from the top of storage tank
20
and is pumped by compressor
30
into the top opening
18
of cleaning chamber
10
. This forces the used/contaminated liquid CO
2
out of bottom opening
38
of cleaning chamber
10
and into the bottom of storage tank
20
. Thus, in this step, compressor
30
produces a negative pressure differential between storage tank
20
and cleaning chamber
10
, enabling the flow of liquid CO
2
from the cleaning chamber to the storage tank. Preferably, the liquid flows through lint trap
24
and filter
26
before entering storage tank
10
. Also, the liquid preferably passes through refrigeration system
35
via its heat exchanger
36
, where it is cooled before entering storage tank
10
. The flow stops when a level sensor
57
on cleaning chamber
10
indicates it is empty.
FIG. 5
schematically illustrates a vapor pressure recovery step in accordance with an embodiment of the dry-cleaning process of the present invention. This step recovers CO
2
vapor remaining in cleaning chamber
10
after the drainage step described above. Gaseous CO
2
is drawn by compressor from top opening
18
of cleaning chamber
10
. The gas exiting compressor
30
is hot and needs to be cooled. The gas is directed first through heat exchanger
32
in water bath
28
, where some of the heat energy is transferred to water bath
28
and the CO
2
is somewhat cooled, and then into heat exchanger
36
in refrigeration system
35
. This cools and condenses the CO
2
gas back into a liquid state. The liquid CO
2
then flows into storage tank
20
. The flow stops when the pressure measured by pressure transducer
42
in cleaning chamber
10
reaches a sufficiently low threshold, for example, 50 psi.
FIG. 6
schematically illustrates a cleaning chamber warm-up step of the dry-cleaning process in accordance with an embodiment of the present invention. This step is implemented to warm up the interior of cleaning chamber
10
and the articles therein, thereby preventing water ice formation during vapor recovery. Cool CO
2
vapor is drawn from top opening
18
of cleaning chamber
10
and is pumped by compressor
30
through heat exchanger
32
in water bath
28
, where the CO
2
is heated at least in part by transfer of energy that was stored in water bath
28
during the vapor recovery step. The gas then flows through an opening
58
into the cleaning chamber
10
. The heated CO
2
warms-up cleaning chamber
10
and the articles therein. Heating element
40
may be utilized during this step to transfer heat to water bath
28
.
In an embodiment of the present invention, the cleaning chamber warm-up is utilized during vapor recovery. Recovery as described above continues until a first predetermined temperature is reached, for example, 35-40° F., as measured by a temperature sensor
55
in cleaning vessel
10
. At this point, vapor recovery pauses and warm-up begins and continues until a second predetermined temperature is reached, for example, a temperature greater than 50° F., which may also be measured by sensor
55
. Thereafter, vapor recovery is resumed. For example, the dry-cleaning process summarized in
FIG. 10
includes two vapor recovery steps, 3 minutes and 5 minutes, respectively, with an interceding two minute warm-up step.
FIG. 7
schematically illustrates a cleaning chamber venting step of the dry-cleaning process in accordance with an embodiment of the present invention. Remaining CO
2
vapor within cleaning chamber
10
, which may be at about 50 psi, is vented through cleaning chamber ventilation system
41
. When the pressure, measured by pressure transducer
42
in cleaning chamber
10
reaches a sufficiently low threshold, door
60
of cleaning chamber
10
may be safely opened and the clean articles removed. In an embodiment of the present invention, the CO
2
vapor may be released either to the system surroundings or outdoors via a venting pipe (not shown). Sound control muffler
46
and/or a throttling device (not shown) may also be utilized to control the venting rate.
While the embodiment of the invention shown and described herein is fully capable of achieving the results desired, it is to be understood that this embodiment has been shown and described for purposes of illustration only and not for purposes of limitation. Other variations in the form and details that occur to those skilled in the art and that are within the spirit and scope of the invention are not specifically addressed. Therefore, the invention is limited only by the appended claims.
Claims
- 1. Dry-cleaning apparatus for cleaning articles comprising:a storage tank for storing carbon dioxide (CO2); a cleaning chamber having a rotatable member therein; a rotation mechanism for rotating the rotatable member; a compressor for establishing a pressure differential between the storage tank and the cleaning chamber sufficient to transport liquid CO2 between the storage tank and the cleaning chamber; and a heat sink in thermal communication with a CO2 vapor flow between the storage tank and the cleaning chamber and operative to collect heat from relatively warm CO2 vapor and to transfer heat to relatively cold CO2 vapor, whereby part of the heat collected from the relatively warm CO2 vapor is transferred to the relatively cold CO2 vapor.
- 2. Apparatus according to claim 1 wherein the compressor is capable of raising the pressure in the storage tank to at least 750 PSI.
- 3. Apparatus according to claim 2 wherein the compressor is capable of raising the pressure in the storage tank to about 900 PSI.
- 4. Apparatus according to claim 1 wherein the compressor is capable of lowering the pressure in the cleaning chamber to less than 150 PSI.
- 5. Apparatus according to claim 4 wherein the compressor is capable of lowering the pressure in the cleaning chamber to about 50 PSI.
- 6. Apparatus according to claim 1 wherein the compressor comprises an oil-less compressor.
- 7. Apparatus according to claim 1 wherein the rotation mechanism comprises a rotation drive and a coupling between the rotation drive and the rotatable member.
- 8. Apparatus according to claim 7 wherein said coupling comprises a magnetic coupling.
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DE |
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DE |
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DE |
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DE |
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DE |
3906735 C2 |
Apr 1999 |
DE |
0518653 B1 |
Sep 1995 |
EP |
0530949 B1 |
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EP |
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WO |