Refrigeration – Processes – Separating or preventing formation of undesirables
Reexamination Certificate
1999-08-12
2002-03-19
Doerrler, William C. (Department: 3744)
Refrigeration
Processes
Separating or preventing formation of undesirables
C062S149000, C062S292000
Reexamination Certificate
active
06357240
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of water chiller cleaning systems, and more particularly to a system for flushing and recharging a refrigeration system water chiller, especially after contamination.
BACKGROUND OF THE INVENTION
Mechanical refrigeration systems are well known. Their applications include refrigeration, heat pumps, and air conditioners used both in vehicles and in buildings. The vast majority of mechanical refrigeration systems operate according to similar, well known principles, employing a closed-loop fluid circuit through which refrigerant flows, with a source of mechanical energy, typically a compressor, providing the motive forces.
Typical refrigerants are substances that have a boiling point below the desired cooling temperature, and therefore absorb heat from the environment while evaporating under operational conditions. Thus, the environment is cooled, while heat is transferred to another location where the latent heat of vaporization is shed. Refrigerants thus absorb heat via evaporation from one area and reject it via condensation into another area. In many types of systems, a desirable refrigerant provides an evaporator pressure as high as possible and, simultaneously, a condenser pressure as low as possible. High evaporator pressures imply high vapor densities, and thus a greater system heat transfer capacity for a given compressor. However, the efficiency at the higher pressures is lower, especially as the condenser pressure approaches the critical pressure of the refrigerant. It has generally been found that the maximum efficiency of a theoretical vapor compression cycle is achieved by fluids with low vapor heat capacity, associated with fluids with simple molecular structure and low molecular weight.
Refrigerants must satisfy a number of other requirements as best as possible including: compatibility with compressor lubricants and the materials of construction of refrigerating equipment, toxicity, environmental effects, cost availability, and safety.
The fluid refrigerants commonly used today typically include halogenated and partially halogenated alkanes, including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HFCFs), and less commonly hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs). A number of other refrigerants are known, including propane and fluorocarbon ethers. Some common refrigerants are identified as R11, R12, R22, R500, and R502, each refrigerant having characteristics that make them suitable for different types of applications.
For example, R22 is of particular interest in that it is commonly used in commercial air conditioning systems, which often must be purged to conduct repairs. This R22 is collected in transfer vessels, also known as recovery cylinders, which hold about 30-50 pounds of refrigerant. This refrigerant is generally mixed with compressor lubricant oil, and may be contaminated with water, grit, or other materials. The transportation and logistics of recycling contaminated or used refrigerants typically compel careful use and disposition. Therefore, the art teaches that intentional contamination of refrigerants be strictly avoided, in order to reduce the amounts of refrigerants which must be purified. International treaties and regulations generally ban the disposal of refrigerant.
The mechanical compressor is subjected to operational stresses, and is subject to failure. Typically, the compressor is hermetically sealed within the refrigeration system, and failure of the compressor leads to high temperatures; burning and electrical arcing. These result in contamination of the refrigerant within the hermetically sealed space. Another mode of refrigeration system failure is breach of the hermetic seal, which may occur by accident, corrosion, or other cause. Often, this breach allows external environmental contaminants to enter the refrigeration system, also resulting in contamination.
During usage, it is important that the refrigerants be kept relatively free of contaminants, including foreign matter such as particulates, water and air, which may reduce system efficiency and/or cause wear or system failure. It is vital that hermetic integrity of the refrigerant system be maintained, both to retain the refrigerants and to prevent influx of undesired elements. When the refrigerants become contaminated, though influx of undesired elements, breakdown of refrigerant components, or internal contamination, such as by failure of a compressor motor, it becomes necessary to replace or purify the refrigerants, and often to completely clean the refrigeration system.
Contaminants within a refrigerant are thus substances that render the refrigerant impure. They include gaseous substances such as non-condensables, liquids such as water and solid particulates such as metal fillings. Contaminants also include chloride ions, acids, salts, and various other residues that result when hermetically sealed compressor motors fail while electrically charged, often with burned wire insulation. Contamination is generally measured via various laboratory instruments. Air conditioning/refrigeration original equipment manufacturers and standards organizations specify the percent of contamination allowable within equipment.
Another mode of failure of a refrigeration system, especially in a commercial chiller system, is a rupture or failure of a refrigerant-water heat exchanger. In this case, the refrigerant (with refrigerant oil) and water become mixed, contaminating both the primary and secondary heat exchange systems. The aqueous phase in a chiller is typically impure, and may have mineral salts and organic compounds as scale inhibitors, as well as scale. The solution may include, for example, calcium chloride brine. Thus, merely drying the system after such a failure is insufficient to repair the damage, as aqueous contaminants will remain in the refrigeration system, and nonvolatile refrigerant oil will remain in the water space. Further, even without hermetic failure of the chiller, the aqueous heat exchange system is subject to scale buildup, which reduces heat exchange efficiency, resulting in a need for periodic maintenance. Mechanical refrigeration systems thus periodically require servicing, either due to failure or for preventive maintenance. This servicing often includes the addition of refrigerant into the system to replace refrigerant which has escaped from the system. Other servicing often takes the form of repairs to, or replacements of components in the system such as compressors, evaporators, filters, dryers, expansion valves and condensers.
Before adding refrigerant, or repairing or replacing one or more components, it is often necessary to remove the refrigerant remaining in the system. Typically, this remaining refrigerant is removed and stored in transfer vessels. To avoid releasing these fluorocarbons into the atmosphere, devices have been constructed that are designed to recover the refrigerant from the refrigeration system. Examples of such a refrigerant recovery devices are shown in U.S. Pat. Nos. 4,942,741; 4,285,206; 4,539,817; 4,364,236; 4,441,330; 4,476,668; 4,768,347; and 4,261,178.
In this case, the refrigerant is normally transported to a recycler or reclaimer, who purifies the refrigerant for reuse. In this case, new refrigerant is used to charge the system when the repair is completed. Since refrigerant recycling is expensive, any cleaning or flushing of the system must be performed with disposable liquids, such as water or aqueous solutions, after the refrigerant is purged and before the refrigeration system is recharged.
It is believed that refrigerants, especially chlorofluorocarbons (CFCs), used in vapor compression cooling systems (i.e., refrigeration systems) have a detrimental effect on the ozone layer of the earth's atmosphere when released from the refrigeration system into the environment. To this end, Federal legislation has been exacted, commonly referred to as the Clean Air Act, that has mandated strict requirements directed toward eliminating the release
Mika Arthur R.
Zugibe Kevin
Doerrler William C.
Hudson Technologies Inc.
Milde Hoffberg & Macklin, LLP
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