Patent Publication Number: US-6212916-B1

Title: Dry cleaning process and system using jet agitation

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 using a pressurized dense-phase gas such as carbon dioxide. 
     BACKGROUND OF THE INVENTION 
     Dry cleaning processes using pressurized carbon dioxide (CO 2 ) are well known in the art. Dry cleaning systems using liquid/supercritical dense-phase gas such as carbon dioxide are described, inter alia, in U.S. Pat. Nos. 5,267,455 and 5,412,958, 5,316,591, 4,012,194, 5,013,366, 5,456,759 and 5,339,844. In such systems, pressurized liquid CO 2  is pumped from a reservoir into a cleaning chamber, where articles to be cleaned, e.g., clothes, are suspended in the liquid CO 2 . Agitating of the articles and/or the CO 2  in the cleaning chamber provides the mechanical action required for cleaning. Some prior art systems use a mechanical rotation mechanism to provide the agitation necessary for cleaning. Other prior art systems use a plurality of injection ports to inject high-pressure liquid CO 2  jets into the cleaning chamber and, thereby, to provide the agitation necessary for cleaning. 
     Liquid CO 2  may be injected into the cleaning chamber via different sets of injection ports to provide agitation and, consequently, rotation of the articles within the cleaning chamber, in either a clockwise or counter-clockwise direction. In a standard CO 2  dry-cleaning process, the articles are alternately rotated in either direction by periodically stopping the injection through a first set of injection ports and resuming injection of the liquid CO 2  through a second set of injection ports that are positioned to inject the liquid CO 2  in a direction opposite that of the first set of ports. During the injection process, the continuous supply of liquid CO 2  forces the liquid CO 2  in the chamber to be continuously displaced out of the cleaning chamber and returned to the storage tank. After a desired number of agitation cycles are completed, the cleaning chamber is drained and the liquid CO 2  is transported back into the storage tank. A heavy-duty positive displacement piston pump is typically used to circulate the liquid CO 2  throughout the system, e.g. to provide a substantially continuous flow of liquid CO 2  through the cleaning chamber during agitation. 
     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 prior art 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 NPSH. However, the use of such 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 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 to provide a process and a system for efficiently supplying and recycling and draining liquid carbon dioxide (CO 2 ) in a dry cleaning system using jet agitation. In accordance with an embodiment of the present invention, pressurized liquid CO 2  is circulated throughout the dry cleaning system, specifically, liquid CO 2  is moved between one or two storage tanks and a cleaning chamber of the dry cleaning system, by means of pressure differentials produced between the storage tanks and the cleaning chambers, obviating the need for a pump. In an embodiment of the present invention, the pressure differentials are 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 art systems, making the system of the present invention more cost effective and reliable. 
     In an embodiment of the present invention, the compressor may draw gaseous CO 2  from the cleaning chamber and inject it into one of the storage tanks, 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 via jet ports, e.g., to fill the chamber. A negative pressure differential enables flow of liquid CO 2  from the cleaning chamber to the storage tank, e.g., to drain the cleaning chamber. The compressor may also draw gaseous CO 2  from one storage tank and inject it to the other storage tank to create a pressure differential between the two storage tanks. This pressure differential enables flow of liquid CO 2  between the two storage tanks via the cleaning chamber, to provide jet agitation within the cleaning chamber. The magnitude of the pressure differential may be controlled by varying the speed of the compressor motor or using a throttle valve. 
     In an embodiment of the present invention, first and second storage tanks are used to alternately supply liquid CO 2  to the cleaning chamber, thereby maintaining a periodically continuous flow of liquid CO 2  through the cleaning chamber. The flow of liquid CO 2  may be stopped periodically during the agitation cycle to switch between the first and second storage tanks being used for liquid CO 2  supply. 
     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 invention are compatible with existing dry cleaning processes and systems and may be used in conjunction with any cleaning chamber 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 cleaning chamber, which may include a basket, having jet inflow ports and a pressure containment sufficient to keep CO 2  in a liquid state, first and second storage tanks for storing CO 2  at a predetermined pressure, and means for providing a pressure differential between the first and second storage tanks and/or between the cleaning chamber and either the first or second storage tanks. In some embodiments, the system may further include a vapor heat exchange/recovery system, a refrigeration system, a filtration system, and a cleaning chamber ventilation system. The pressure differentials between the storage tanks and the cleaning chamber is preferably produced by a gas compressor, such as an oil-less compressor. The system may also include a heater to keep the heat sink water tank above a minimum temperature, a muffler for final venting of cleaning vessel, a lint trap and a filter. 
     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 and reducing the amount of water dissolved in the CO 2 . In this step, the compressor may act as a vacuum pump to evacuate moisture-laden air from the cleaning chamber to the outside environment. 
     (b) Equalizing pressure between the storage tanks and the cleaning chamber in a controlled fashion to avoid clothes damage. In this step, CO 2  gas may flow from the storage tanks to the cleaning chamber through appropriate valves, until the pressure difference between the cleaning chamber and the tank drops below a predetermined threshold. 
     (c) Filling the cleaning chamber with liquid CO 2  from the first or second storage tank. In this step, CO 2  vapor is drawn from the top of the cleaning chamber by the compressor and is compressed into the top of one of the storage tanks, preferably the storage tank having a higher fluid level. This creates a pressure differential sufficient to force liquid CO 2  out of the bottom of the storage tank into the bottom of the cleaning chamber until the cleaning chamber is completely full. 
     (d) Agitating the articles being cleaned by injecting liquid CO 2  through the jet ports causing rotation of the articles within the chamber. In this step, the compressor alternately draws CO 2  vapor from the top of the first or second storage tank and compresses the vapor into the top of the other storage tank. This creates a pressure differential between the first and second storage tanks sufficient to force liquid CO 2  out of the bottom of the compressed storage tank and into the cleaning chamber. The liquid CO 2  enters the cleaning chamber via the jet ports which are preferably positioned to provide agitation in a given direction, e.g., clockwise. Because the cleaning chamber is full, liquid CO 2  is displaced out of the cleaning chamber and is recycled back into the decompressed storage tank, optionally via filters and lint traps as are known in the art. The flow of liquid CO 2  in this direction may continue until the fluid level in the compressed storage tank drops below a predetermined threshold, or for a predetermined time period. Then, the direction of compression is reversed and agitation is resumed by flowing liquid CO 2  from the other storage tank into the cleaning chamber, preferably via a second set of jet ports, thereby providing agitation in an opposite direction, e.g., counter-clockwise. These alternate agitation cycles may be repeated a predetermined number of times to provide sufficient agitation. 
     (e) Draining used/contaminated liquid from the cleaning chamber. In this step, gaseous CO 2  is drawn from the top of the last-emptied storage tank and is compressed into the top of the cleaning chamber, forcing liquid out of the bottom of the cleaning chamber into the bottom of the last-emptied storage tank. This drainage is continued until the cleaning chamber is completely empty. 
     (f) Recovering CO 2  vapor remaining in the cleaning chamber after drainage. In this step, CO 2  vapor may be drawn from the top of the cleaning chamber and pushed by the compressor, through the water bath and/or refrigeration system which cools and condenses the vapor into liquid, back into the first and/or second storage tanks. 
     (g) Heating the cleaning chamber to prevent water ice formation on the articles being cleaned. In this step, the compressor draws cold CO 2  vapor from the cleaning chamber and pushes the vapor, via the water bath which heats the vapor, back to the cleaning chamber. Once the cleaning chamber is sufficiently warm, vapor recovery may be resumed. 
     (h) Venting the cleaning chamber to remove any remaining CO 2  pressure such that a door of the cleaning chamber may be opened and the clean articles removed. In this step, CO 2  vapor may flow out of the cleaning chamber, optionally via a sound control muffler, to the external environment. 
    
    
     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 following 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 a cleaning chamber filling step 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 an alternative cleaning chamber filling step in accordance with an embodiment of the present invention; 
     FIG. 5A is a schematic illustration of the system of FIG. 1 during a jet agitation step of a dry-cleaning process in accordance with an embodiment of the present invention; 
     FIG. 5B is a schematic illustration of the system of FIG. 1 during an alternative jet agitation step in accordance with an embodiment of the present invention; 
     FIG. 6A 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. 6B is a schematic illustration of the system of FIG. 1 during an alternative cleaning chamber draining step in accordance with an embodiment of the present invention; 
     FIG. 7 is a schematic illustration of the system of FIG. 1 during a pressure recovery step of a dry-cleaning process in accordance with an embodiment of the present invention; 
     FIG. 8 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. 9 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. 10 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. 1-9 which schematically illustrates 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 80 gallon cleaning chamber, having a basket  12  for holding articles to be cleaned and jet inflow port arrangements  14  and  16 . In an embodiment of the present invention, each of port arrangements  14  and  16  includes a plurality of hollow wands, each wand having a plurality of apertures through which liquid CO 2  may flow into cleaning chamber  10  in a predetermined direction. For example, each of port arrangements  14  and  16  may include two hollow, diametrically opposite, wands, each having 10-20 jet ports (e.g., apertures) which are oriented to provide liquid CO 2  inflow in a predetermined direction, e.g., clockwise or counterclockwise. In an embodiment of the present invention, as described in detail below, port arrangements  14  and  16  are designed to provide liquid CO 2  jet agitation in opposite directions, e.g., the ports of arrangement  14  may be oriented to provide clockwise jet agitation while the ports of arrangement  16  may be oriented to provide counter-clockwise jet agitation, or vice versa. 
     Cleaning chamber  10  is preferably designed to have high pressure containment capability, for example, a pressure containment of 1,100 PSI, sufficient to maintain carbon dioxide (CO 2 ) in a liquid state. The system further includes first and second storage tanks,  20  and  22 , respectively, having predetermined volume capacity, for example, 100 gallons each. Tanks  20  and  22  preferably have high pressure containment capability, for example, 1,100 PSI, and include predetermined initial amounts of CO 2  at a predetermined pressure. In a preferred embodiment of the invention, the system also includes 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 tanks  20  and/or  22  and/or cleaning chamber  10 . In an embodiment of the present invention, the desired pressure differential is provided by 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 either or both of storage tanks  20  and  22  to more than 750 PSI, preferably more than 850, for example, 900 PSI. 
     It should be appreciated that a high pressure in storage tanks  20  and/or  22  maintains the CO 2  in liquid state with minimal cooling and, therefore, results in more energy-efficient dry cleaning. The magnitude of the pressure differential produced between storage tanks  20  and/or  22  and/or 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 water bath  28  associated with a heat exchanger  32 , which act as a heat sink for heat storage and transfer, and a refrigeration system with heat exchanger  36  adapted for cooling CO 2 . An electric heater  40  is preferably installed in water bath  28  to maintain a predetermined temperature in the bath, for example, 80° C., during idle periods of the dry-cleaning process. When cold CO 2  from the cleaning chamber is transported through the heat exchanger, as described below, the temperature in the water bath drops because heat is transferred to the CO 2 . As clearly shown in the drawings, the dry cleaning system includes piping as necessary for connecting between the different system elements of the system various valves for controlling the operation of the system 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 sound control muffler  46  which may be used during final venting of cleaning chamber  10 , as described below. 
     Reference is now made also to FIG. 10 which schematically illustrates the different steps of a dry cleaning process according to an embodiment of the present invention, showing exemplary length of time for each step. FIG. 10 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. 1-9. 
     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 and, thus, to reduce the amount of water dissolved in the CO 2 . Compressor  30  acts as a vacuum pump with respect to cleaning chamber  10 . The compressor 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 tanks  20  and/or  22  and cleaning chamber  10  is equalized in a controlled fashion to avoid damage to the articles being cleaned. Gaseous CO 2  flows from the top of the storage tank to the top of the cleaning chamber through a valve  44  and an orifice  47  until the difference between the readings of pressure transducer  42  and a pressure transducer  48  is under a predetermined threshold, for example a 10 percent difference. 
     After pressure equalization is reached, cleaning chamber  10  may be filled with CO 2  from either storage tank  20  or storage tank  22 , both of which are full at this stage of the process. FIG. 3 schematically illustrates a step of filling cleaning chamber  10  with liquid CO 2  from storage tank  20 . In this step, 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 . Thus, compressor  30  produces a positive pressure differential between storage tank  20  and cleaning chamber  10 , enabling flow of liquid CO 2  from storage tank  20  to cleaning chamber  10 . 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. In response to the positive pressure differential, liquid CO 2  flows out of the bottom of storage tank  20  into a bottom opening  38  of cleaning chamber  10 , until the cleaning chamber is completely filled with liquid CO 2 . This may be determined by a timer (not shown) and/or by a sensor  50  which detects the presence of liquid CO 2  as it exits cleaning chamber  10  and/or by a level sensor  70  associated with storage tank  20 . 
     FIG. 4 schematically illustrates an alternative step of filling cleaning chamber  10  with liquid CO 2  from storage tank  22 . In this alternative step, gaseous CO 2  is drawn from top opening  18  of cleaning chamber  10  and is pushed by compressor  30  to the top of storage tank  22 . This forces liquid CO 2  out of the bottom of the storage tank  20  into bottom opening  38  of cleaning chamber  10  until the chamber is completely filled with liquid CO 2 , as described above with reference to FIG.  3 . Complete filling of cleaning chamber  10  may be determined by a timer (not shown) and/or by sensor  50  at the exit of cleaning chamber  10  and/or by a level sensor  72  associated with storage tank  22 . Because the arrangement of tanks  20  and  22  is generally symmetrical, either storage tank  20  or  22  may be used for the initial filling of cleaning chamber  10 . 
     After completely filling cleaning chamber  10 , the articles within chamber  10  may be agitated by a periodically continuous jet inflow of liquid CO 2  provided through either port arrangement  14  or  16 . In a preferred embodiment of the invention, port arrangements  14  and  16  are used alternately, to provide alternate clockwise and counter-clockwise agitation cycles. In this embodiment, port arrangement  14  may be used only for supplying liquid CO 2  from storage tank  22  and port arrangement  16  may be used only for supplying liquid CO 2  from storage tank  20 , as described below. The length of time of each agitation cycle may correspond to the amount of CO 2  in storage tanks  20  and  22 , whereby the direction of agitation may be reversed each time the level of CO 2  in the storage tank being used drops below a predetermined, low, level. This level may be detected by level sensors  70  or  72  of storage tanks  20  or  22 , respectively. The jet agitation causes rotation of the articles being cleaned in chamber  10 , as is known in the art. 
     FIG. 5A schematically illustrates jet agitation via port arrangement  14 . In this alternative, gaseous CO 2  is drawn from the top of storage tank  20  and is pushed by compressor  30 , via heat exchanger  32 , into the top of storage tank  22 . This forces liquid CO 2  out of the bottom of storage tank  22  via a valve  54  into port arrangement  14 , for example, two hollow wands located diametrically opposite each other in cleaning chamber  10  and each having a plurality of jet inflow ports. Excess fluid is continuously recycled, via lint trap  24  and filter  26 , via heat exchanger  36  of refrigeration system  34 , back into storage tank  20 . This produces a substantially continuous flow of liquid CO 2  via cleaning chamber  10 . 
     FIG. 5B schematically illustrates jet agitation via ports  16 . In this alternative, gaseous CO 2  is drawn from the top of storage tank  22  and is pushed by compressor  30 , via heat exchanger  32  in water bath  28 , into the top of storage tank  20 . This forces liquid CO 2  out of the bottom of storage tank  20  via a valve  53  into ports  16 , for example, two hollow wands located diametrically opposite each other in cleaning chamber  10  and each having a plurality of jet inflow ports. Excess fluid is recycled, via lint trap  24  and filter  26 , and optionally via heat exchanger  36  of refrigeration system  34 , back into storage tank  22 . 
     After agitation as described above, used/contaminated liquid is drained from cleaning chamber  10  into the bottom of either storage tank  20  or storage tank  22 , depending on the level of CO 2  in each tanks. Generally, cleaning chamber  10  is drained into the storage tank supplying liquid CO 2  for the last agitation cycle, because the last-used storage tank is at its minimum level at the end of last agitation cycle. FIG. 6A schematically illustrates draining of used/contaminated liquid into storage tank  20 . Clean gaseous CO 2  is drawn from the top of storage tank  20  and is pushed by compressor  30  into top opening  18  of cleaning chamber  10 . This forces the used/contaminated liquid CO 2  out of bottom opening  38  of the cleaning chamber, via filter  26  and heat exchanger  36  of refrigeration system  34 , into the bottom of storage tank  20 . Thus, filtered and cooled liquid flows into storage tank  20 . The flow stops when a level sensor  74  indicates a predetermined fluid level in storage tank  20  or when a low level sensor  56  associated with cleaning chamber  10  indicates that the cleaning chamber is empty. 
     FIG. 6B schematically illustrates draining of used/contaminated liquid into storage tank  22 . Clean gaseous CO 2  is drawn from the top of storage tank  22  and is pushed by compressor  30  into top opening  18  of cleaning chamber  10 . This forces the used/contaminated liquid CO 2  out of bottom opening  38  of the cleaning chamber, via filter  26  and heat exchanger  36  of refrigeration system  34 , into the bottom of storage tank  22 . Thus, filtered and cooled liquid flows into storage tank  22 . Drainage is terminated when cleaning chamber  10  as detected, for example, by low level sensor  56  or by a level sensor  76  associated with storage tank  22 . 
     FIG. 7 schematically illustrates a vapor recovery step in accordance with an embodiment of the dry-cleaning process of the present invention. This step is required in order to recover CO 2  vapor remaining in cleaning chamber  10  after the drainage described above. Gaseous CO 2  is drawn from top opening  18  of cleaning chamber  10  and is pushed by compressor  30 , via heat exchanger  32  in water bath  28 , where the CO 2  is somewhat cooled, into heat exchanger  36  in refrigeration system  34 . This cools and condenses the CO 2  back into a liquid state. The liquid CO 2  then flows into storage tank  20  and/or  22 . The flow stops when the pressure in cleaning chamber  10 , as measured by pressure transducer  42 , drops below a predetermined threshold, for example, 50 psi. 
     FIG. 8 schematically illustrates a cleaning chamber warm-up step of the dry-cleaning process in accordance with an embodiment of the of the present invention. This step is implemented to warm-up the interior cleaning chamber  10  and the articles therein, thereby to prevent water ice formation due to vapor recovery. In an embodiment of the present invention, vapor recovery as described above continues until a first predetermined temperature is reached, for example, 35-40° F., as measured by a temperature sensor  55 . At this point warm-up begins and remains in effect until a second predetermined temperature is reached, for example, a temperature greater than 50° F. which may also be measured by sensor  55 . After the warm-up step, a final vapor recovery may be resumed. For example, the dry-cleaning process summarized in FIG. 10 includes two vapor recovery steps, 3 minutes and 5 minutes, respectively, separated by a two minute warm-up step. The warm-up step may be performed as follows. gaseous CO 2  vapor is drawn from top opening  18  of cleaning chamber  10  and is pushed by compressor  30 , via heat exchanger  32  in water bath  28 , where the CO 2  is heated, into a side opening  58  of cleaning chamber  10 . The heated CO 2  warms-up cleaning chamber  10 . 
     FIG. 9 schematically illustrates a cleaning chamber venting step of the dry-cleaning process in accordance with an embodiment of the of the present invention. This step is implemented to vent the cleaning chamber of remaining CO 2  vapor pressure so that a door  60  of the cleaning chamber may be opened and the clean articles may be removed. In an embodiment of the present invention, the remaining CO 2  vapor, which may be at a pressure of about 50 psi, may be released either to the system surroundings, via sound control muffler  46 , or outdoors via a venting pipe  62 . 
     While the embodiment of the invention shown and described 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 which are within the spirit and scope of the invention are not specifically addressed. Therefore, the invention is limited only by the appended claims.