A DEVICE FOR SEPARATING OIL FROM A REFRIGERANT

Abstract: Device for separating oil from a refrigerant comprising a separator (1) and a heat exchanger (2), said separator (1) having an inlet (3) passing through the heat exchanger (2) for refrigerant including oil from a compressor, and an outlet (13) for the separated oil to be returned to the compressor, whereby the separator comprises a primary and a secondary section, the primary section being located above the secon­ dary section and the oil-rich mixture of refrigerant and oil formed in the primary section being passed through the outlet (13) to the heat exchanger (2), where the refrigerant is evapo­ rated by the heat of the refrigerant and oil passing through the inlet (3) and whereby liquid refrigerant is continuously dis­ charged from the separator (1) through a line (8) and is returned to the inlet (3) on a constant amount.

Description: A device for separating oil from a refrigerant. The present invention relates to a device for separating oil from a refrigerant comprising a separator and a heat exchanger, in which separator the oil is separated from the gaseous refrigerant by gravity, partial condensation and dissolution in the liquid refrigerant, said separator having an inlet for refrigerant including oil from the compressor, an outlet for the gaseous refrigerant freed from oil to be passed to the condenser and an outlet for the separated oil to be returned to the compressor, and through which heat exchanger an oil-rich mixture of refrigerant and oil is passed in order to evaporate the refrigerant therefrom before returning the oil to the compressor, the heat of evaporation being supplied by the refrigerant passed to the separator upon discharge from the compressor. A similar device is known from the German Patent Specification Nr. 834,854. It is of common knowledge that for a good operation of the compressor in a refrigeration system oil should be supplied to the compressor. Together with the refrigerant, generally ammonia, part of this oil is carried to all other parts of the refrigeration system, such as the condenser and the evaporator,in which the presence of this oil is however undesirable because the heat transfer is affected unfavorably thereby. In the device for the removal of oil known from the German Patent Specification Nr. 834,854 the gaseous refrigerant discharged from the low pressure stage of the compressor, thus including much oil is passed to the separator, that is to say to apart thereof in which a pool of liquid refrigerant is present. Hence the heavily oil-laden gaseous refrigerant is washed and cooled in the bath of liquid.in the separator there occurs a settling of the oil and above the liquid in the separator an accumulation of gaseous refrigerant to be returned to the high pressure stage of the compressor. The separated oil yet contains quite some refrigerant and this refrigerant is separated from the oil by periodical evaporation in the said heat exchanger. The object of the invention is to provide a device exibitlng a yet better oil separation so that the gaseous refrigerant passed to the condenser is essentially free from oil while the oil content of the purified compressed gas amounts to less than 1 ppm. According to the invention this is attained in that the separator comprises a primary separating section and a secondary separating section, said primary separating section being located above said secondary separating 3section, the oil-rich mixture of refrigerant and oil formed in the primary section being passed to the heat exchanger for evaporation and the reTrigerant being passed to the secondary separating section and subsequently to the condenser and the liquid refrigerant being continuously discharged from the primary and the secondary separating section and being returned in a constant amour, to said inlet of the separator. Hence several measures are taken in order to attain the above object. In accordance with the first measure use is made of a primary and a secondary separating section, the primary separating section being located above the secondary separating section. In accordance with a second measure liquid refrigerant is continuously returned in a constant amount from the primary and the secondary separating section to the inlet of the separator accommodating the primary and the secondary separating section. An oil separator having a primary and a secondary separating section is known ner se from the Dutch Patent Application Nr. 73.02376, in particular Fig 2. However the primary section therein is present below the secondary section. The heavily oil-laden gaseous refrigerant discharged from the compressor is blown in the lower primary separating section, wherein the oil settles and from which the gas partially freed from oil is passed through a bath of refrigerant in the secondary separating section. The drawback of this arrangement of the separating sections is that when the refrigeration system has been out of operation for sometime i.e. in intermittant operation the refrigerant admixed with oil will flow back from the secondary section to the primary section due to the occurring pression differe.ntial so that when starting up one has to start with a heavily oil-laden mixture. In the device according to the Dutch Patent Application Nr. 73.02376 when in operation refrigerant will also be returned from the upper secondary separating section to the inlet of the sepa rator carrying the discharge from the compressor. The line between the secondary separating section and the inlet to the separator however includes an automatic valve which is governed by the temperature of the gaseous refrigerant. Furthermore the liquid refrigerant is returned to an injector unit in the inlet to the separator. The return of liquid refrigerant to the inlet of the separator according to the Dutch Patent Application Nr. 73.02376 is dependent on the temperature of the compressed gas discharged from the primary separating section of the separator. In accordance with the second measure of the inventionno regulation of the return is at stake at all. The liquid refrigerant is returned continuously and in a constant amount to the inlet of the separator. The goal thereof is to cauae as wet a condition as possible of the gaseous refrigerant discharged from the compressor. With certainty the partial pressure of the oil vapor will then be as low as possible while moreover liquid will be available for catching oil droplets. Preferably the returned amount of liquid refrigerant is that large that a wet mixture will reach the primary separating section under all operating conditions. Contrary to the device according to the German Patent Specification Nr. 838,854 in accordance with a further embodiment an oilrich mixture of refrigerant and oil is continuously passed to the heat exchanger in the device according to the invention from which the oil is periodically returned to the compressor after evaporation of the refrigerant therefrom. Furthermore the secondary separating section is preferably constructed as a tray column. It should be remarked that from the Dutch Patent Application Nr. 75.15207 an oil separator is known consisting of solely one section though also constructed as a tray column. The invention will be described in detail with reference to the diagrammatical drawing. The device according to the invention consists of a vertically arranged, for instance a cylindrical, vessel 1 and a heat exchanger 2. The line running from the n-ot shown compressor of the refriger ation system has been indicated by the reference numeral 3 and leads through the heat exchanger 2 to the vessel 1. Through= the vessel 1 the line 3 runs upwards to above a rigid tight bottom 4. The room above the bottom 4 constitutes the primary separating sectionand the room below said bottom the secondary separating section. The secondary separating section is constructed as a tray column known per se. By way of example two trays 5 and 6 have been represented in the drawing. A downcomer runs downwards from the primary separating section to below the tray 6 of the secondary separating section. A line 8 runs from a point at a certain distance above the bottom 4 and from a point just above the tray 6 and debouches in the line 3i The reference numeral 9 denotes the outlet of the vessel 1 through which the compressed gas freed from oil is passed to the (not shown) condenser. Through the junction 10 liquid refrigerant may be supplied for providing the maintenance of a certain liquid refrigerant level on the trays 5 and 6 governed by a level detector 11 by means of which a valve 12 in the junction 10 is operated. From a point just above the bottom 4 a line 13 runs to the heat exchanger 2. To the lower end of the heat exchanger2 there has been connected an oil discharge line 14 including a valve 15 said valve being operated by a temperature detector 16. When the refrigeration system is put in operation a layer of a certain depth of liquid refrigerant including oil is present on both trays 5 and 6 as well as on the bottom 4. An overflow-pipe 17 runs from the upper tray 5 to the lower tray 6. By means of line 3 warm refrigerant is supplied to the primary separating section. This refrigerant is laden with oil required for the operation of the compressor. Through the line 8 liquid refrigerant is fed to the line 3. This liquid refrigerant is fed continuously and in such a constant amount that the primary separating section is reached by the mixture of refrigerant and oil in liquid condition in the line- 3. Because of the wet condition of the refrigerant it is assured that the partial pressure of the oil vapor is as low as possible while moreover droplets of oil are caught in the refrigerant. In the primary separating section the oil will accumulate on the lower part on the bottom 4. The primary separation thus occurs on said bottom. The separation between oil and refrigerant has been indicated by a dash line. The gaseous refrigerant is present above the liquid and is fed through the downcomer 7 to the secondary separating section below the tray 6. The gas then bubbles upwards to the liquid on the trays 6 and 5 in order to remove the oil yet present as much as possible. The gaseous refrigerant freed from oil and containing less than 1 ppm of oil is discharged from the device according the invention by means of the line 9 and is fed to the not shown condenser. The oil on the bottom 4 will of course also include a certain content of refrigerant. This mixture is continuously fed to the heat exchanger 2 through the line 13. The heat of the compressed gas led through the line 3 is used for heating this mixture. The refrigerant is evaporated from the mixture and returned to the gas room in the primary separating section through a line 18. The oil accumulated in the lower part of the exchanger 2 is periodically discharged through the line 14 and returned to the carter of the compressor. This discharge is performed dependent on the temperature determined by means of the detector 16. When the refrigeration system is shut off there will however not be the danger of a back flow of oil-laden refrigerant from the primary separating section to the secondary separating section during the idle period. Upon starting up the system one will thus not commence with a refrigerant having too high an oil content as is the case in the device according to the Dutch Patent Application Nr. 73.02376. The device according to the invention is very simple and includes only two simple regulations, i.e. a level regulation 11, 12 of the trays 5 and 6 and a thermostatic regulation 15, 16 of the oil discharge through the line 14. The temperature of the oil'in the heat exchanger 2 will only increase after the evaporation of the refrigerant so that simple thermostatic regulation of the oil discharge is possible. The invention is in particular applicable to a refrigeration system operated with ammonia as the refigerant and to a refrigeration system operated by means of a compressor of the piston type. It will however be clear that the device according to the invention may also be uaed when employing other refrigerants and other types of compre8sors. (claims)

Claims: CLAIMS. 1. A device for separating oil from a refrigerant comprising a separator and a heat exchanger, in which separator the oil is separated from the gaseous refrigerant by gravity, partial condensation and dissolution in the liquid refrigerant, said separator having an inlet for refrigerant including oil from the c-ompressor, an outlet for the gaseous refrigerant freed from oil to be passed to the condenser and an outlet for the separated oil to be returned to the compressor and through which heat exchanger an oil-rich mixture of refrigerant and oil is passed in order to evaporate the refrigerant therefrom before returning the oil to the compressor the heat of evaporation being supplied by the refrigerant passed to the separator upon discharge from the compressor, c h a r a c t e r i z e d i n t h a t the separator comprises a primary separating section, said primary separating section being located above said secondary separating section, the oil-rich mixture of refrigerant and oil formed in the primary section--being passed to the heat exchanger for evaporation and the refrigerant being passed to the secondary separating section and subsequently to the condenser and the liquid refrigerant being continuously discharged from the primary and the secondary separating section and being returned in a constant amount to said inlet. 2.The device of claim 1 c h a r a c t e r i z e d i n t h a t the amount of liquid refrigerant is that large that a wet mixture will reach the primary separating eection under all operating conditions. 3. The device of claim 1 or 2 c h a r a c t e r i z e d i n t h a t an oil-rich mixture of refrigerant and oil is'continuously passed to the heat exchanger from which the oil is periodically returned to the compressor after evaporation of the refrigerant therefrom. 4. The device of claim 1, 2 or 3 c h a r a c t e r i z e d i n t h a t the secondary separating section has been constructed as a tray column.

Inventors: TEN HACKEN, JOHANNES GERARDUS
Applicants: GRASSO'S KONINKLIJKE MACHINEFABRIEKEN N.V.
Application year: 1980
Main classification: F25B43
IPC codes: F25B43