The present invention relates to a method and to a device for separating water and products of degradation from lubricating oil in heat pumps or cooling machines.

In conventional refrigerant based systems, such as freon-based systems, i.e. systems in which the refrigerant and lubricating oil are in one and the same closed system, mineral oils are used for lubricating the motor and compressor. Earlier used lubricating oils are advantageous, because such oils are not hygroscopic and do not appreciably reduce the transfer of heat in the heat exchangers, i.e. evaporator and condenser.

Refrigerants which are free from freon and chlorine have begun to be used in heat pumps and cooling or refrigerating machines in recent times. When changing to more environmentally- friendly refrigerants of the type R 134 A, it has been found that the lubricating oils used earlier are less soluble in refrigerants of this kind, therewith impairing the heat transfer in the heat exchangers. On the other hand, it has been found that PAG oils and ester oils are readily dissolved in these refrigerants, meaning that the transfer of heat in the heat exchangers will not be impaired. On the other hand, these lubricating oils are very hygroscopic, which increases the water content of the lubricating oil in lubricating systems that are open to atmosphere, therewith impairing the lubricating properties of the lubricating oil.

There is therefore a strong need for the use of an oil which will easily dissolve in the refrigerant and which can be used in open lubrication systems without impairing the lubricating ability of the lubricant.

This need can be fulfilled by the present invention.

The present invention thus relates to a method for separating water and degradation products from lubricating oil in heat pumps or cooling machines comprising a closed circuit which includes a compressor, an evaporator and a condenser, wherein coolant is circulated in the circuit and wherein there is included an open lubricating oil system which contains lubricating oil which is soluble in the refrigerant and which is hygroscopic, wherein the lubricating oil is circulated to lubricate motor, compressor and gearing when present, said method being characterized by bringing the lubricating oil into contact with a water absorbent means during circulation of the oil, so as to remove water and degradation products dissolved in the lubricating oil.

The invention also relates to an arrangement of the kind having the main characteristic features set forth in the following Claim 4.

The invention will now be described in more detail, partly with reference to an exemplifying embodiment of the invention illustrated in the accompanying drawing, of which Figure 1 illustrates the application of an inventive arrangement schematically.

Figure 1 illustrates an arrangement for separating water and degradation products from lubricating oil in heat pumps and cooling or refrigerating machines which include a closed circuit having a compressor 1, an evaporator and a condenser. The evaporator and condenser are conventional and are not shown on the drawing. A refrigerant is circulated in a known manner in the refrigerant circuit, comprising compressor, evaporator and condenser. The reference numeral 14 in Figure 1 identifies a line extending from the compressor to the condenser, while the reference numeral 15 identifies a line extending from the evaporator to the compressor.

The arrangement includes an open lubricating system containing

a hygroscopic lubricating oil which is dissolvable in the refrigerant and which is circulated so as to lubricate a motor 2, the compressor 1 and gearing 3 when present. In systems of this kind, a certain amount of oil will leak into the refrig- erant circuit through the compressor shaft seals.

The lubricating system shown schematically in Figure 1 includes an oil sump 5, a line 6 which extends from the oil sump to a pump 7, and lines 8, 9, 10 which lead to lubricating points and the shaft sealing system, and return lines 11, 12, 13 which extend from the lubrication points to the oil sump 5.

Because the lubricating oil is circulated in a system which is open to the atmosphere, the oil will take-up water vapour from the surroundings, therewith impairing the lubricating properties of the oil.

In accordance with the invention, there is provided an absorption means 4 through which the lubricating oil is passed as it circulates in the lubricating oil circuit, this absorp¬ tion means including a water-absorbing agent for removal of water and degradation products dissolved in the oil.

The degradation products are products which have split or cleaved from the oil and which are dissolvable in water. More specifically, the water-soluble products that have split from the oil are products whose molecules are smaller than the molecules of the oil. These degradation products will thus be absorbed by the water-absorbing agent together with the water in the lubricating oil.

The absorption means 4 includes a vessel which contains a water-absorbing agent through which lubricating oil can flow and therewith come into contact with the water-absorbing agent. According to one embodiment, the vessel may have the form of a vessel which is closed, with the exception of inlet

and outlet lines 18, 19, and which can be filled completely or partially with a water-absorbent agent.

Alternatively, the water-absorbent agent can be submerged in the lubricating oil sump and therewith function in the same way.

The water-absorbent agent is in a solid state. It is preferred to use a crystal-like agent, such as the agent commercially available under the name "Monukular Sive" or some like agent. This has been found to function extremely effectively in conjunction with an oil designated ICI Emkarate RL 46S. This lubricating oil can be used together with the refrigerant R134 A.

The lubricating properties of the lubricating oil are retained by separating water and degradation products from the oil in this way.

According to one preferred embodiment, the arrangement includes a valve 21 and a line 22 provided in the flow direction downstream of the lubricating oil pump 7 provided in the lubricating oil circuit, so as to lead a part-flow of oil through the absorption means 4.

In the case of this embodiment, it is possible to control the amount of oil that shall pass through the arrangement so as to maintain the water content of the oil at a predetermined level, by means of a sensor (not shown) which detects the water content of the oil, and which is located, for instance in the oil sump, and a control circuit which functions to control a motor for adjusting the extent to which the valve 21 is open.

Alternatively, the water content of the lubricating oil can be checked by taking samples.

According to one alternative, preferred embodiment of the invention, the arrangement includes a separate oil pump 20 and a line 21 through which lubricating oil is passed from the lubricating oil sump 5, through the absorption means 4 and back to the oil sump. This embodiment is shown in broken lines in Figure 1. A sensor and a control circuit of the aforedescribed kind can be used in this embodiment to adjust the capacity of the pump 20, so that the water content of the lubricating oil will be maintained at a predetermined level.

Different embodiments have been described above with regard to the positioning of the absorption means 4. An exemplifying embodiment of the absorption means has also been described. It will be understood, however, that the structural design of the absorption means and its positioning can be varied in several ways obvious to the skilled person. For instance, the absorption means can be placed in the lubricating oil circuit so that all oil will flow through the absorption means.

The present invention is therefore not considered to be restricted to the aforedescribed and illustrated exemplifying embodiments thereof, since modifications can be made within the scope of the following Claims.