Textiles: fluid treating apparatus – Machines – Combined
Reexamination Certificate
1999-03-10
2001-07-17
Coe, Philip R. (Department: 1746)
Textiles: fluid treating apparatus
Machines
Combined
Reexamination Certificate
active
06260390
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 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 li
Coe Philip R.
Sail Star Limited
Weingarten, Schurgin Gagnebin & Hayes LLP
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