Refrigeration – Processes – Lubricant handling
Patent
1996-01-11
1997-02-11
Sollecito, John M.
Refrigeration
Processes
Lubricant handling
62 77, F25B 4302
Patent
active
056009593
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of replacing the lubricant present in the lubrication circuit of existing refrigeration systems while they are being converted to refrigerants which have no effect on atmospheric ozone. This involves changing the lubricant when the chlorofluorocarbon refrigerants present in these systems are replaced by fluorohydrocarbons refrigerants.
This problem of converting existing refrigeration systems is now a matter of urgency throughout the world. On the one hand, the chlorofluorocarbon compounds called CFCs, such as dichlorodifluoromethane or R12, are damaging to the ozone layer in the Earth's atmosphere. On the other hand, as these are causing damage, it was decided to cease manufacturing them by the year 1995 in the signatory countries of the 1987 Montreal Protocol.
Of course, extensive research has been undertaken in industry, whether in the fields of refrigeration or in those of air conditioning, in order to develop replacements for these chloro-fluorocarbon compounds, the required characteristics of which are to be both a good refrigerant and not to damage the ozone layer. The best products found and marketed are the fluorohydrocarbon compounds called FHCs, the most well-known being 1,1,1,2-tetrafluoroethane or alternatively R134a. They have therefore rapidly been used in all new equipment manufactured.
However, those skilled in the art have not yet completely solved the problem of replacing these obsolete refrigerants with the new products in existing equipment.
The reason for this is that, in refrigeration systems, the refrigerants are permanently in contact with a small amount of lubricant, coming from the lubrication circuit of the compressor in the refrigeration system. However, it has been found that the lubricants compatible with refrigerants of the CFC (chlorofluorocarbon) type were no longer suitable for the refrigerants of the FHC (fluorohydrocarbon) type and that they could cause the refrigeration systems to malfunction. Therefore, on account of the low miscibility of the lubricant/refrigerant pair, films of lubricant are deposited on the condenser pipe and on the internal walls of the evaporator, thus considerably decreasing the efficiency of the heat exchange, or else the absence of lubricant generates wear zones in the region of the moving parts of the compressor. It is therefore essential for the lubricant/refrigerant pair to be highly miscible if the cooling performance of the system is to be maintained.
Conventional lubricants based on mineral oil or synthetic oil, known for their miscibility with chlorofluorocarbon compounds such as R12, are therefore not suitable as regards miscibility with the new fluorohydrocarbon compounds such as R134a. However, it is known that the lubricants compatible with the FHCs are generally compatible with the preexisting CFCs. Therefore, before replacing the chlorofluorocarbon compounds by the fluorohydrocarbon compounds in the refrigeration circuit, the lubrication circuit of the compression system is completely drained for the purpose of removing any trace of lubricant incompatible with the fluorohydrocarbon compounds.
However, since the lubrication circuits of the refrigeration systems include inaccessible dead spaces, draining alone does not enable all the lubricant to be removed. Currently, those skilled in the art-carry out repeated flushing of the lubrication circuit with the new lubricant, the refrigeration system being run for at least forty-eight hours after each flushing operation, until the previous lubricant has been virtually completely removed, that is to say the residual concentration of the latter in the new lubricant is less than 1%.
However, it will very quickly be realized that, given the specificity of the lubricants used with the refrigerants, such flushing operations are very expensive on account of the volumes of lubricant which are necessary to drain these circuits.
Although many companies have sought new lubricant compositions compatible with the new fluorohydrocarbon refrigerants such as R13
REFERENCES:
patent: 5375426 (1994-12-01), Burgener
patent: 5437162 (1995-08-01), Eden
Gay Marie N.
Genet Nicole
Sanvi Pierre
Elf Antar France
Sollecito John M.
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