Dry cleaning process and system using jet agitation

Details Dry cleaning process and system using jet agitation Dry cleaning process and system using jet agitation

1999-03-10

2001-04-10

Coe, Philip R. (Department: 1746)

Textiles: fluid treating apparatus

Machines

Combined

Reexamination Certificate

active

06212916

ABSTRACT:

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 a

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