HK1085007B - Oil recovery and lubrication system for screw compressor refrigeration machine - Google Patents

Description

Lubricating oil recovery and lubrication system for screw compressor refrigerating device

Technical Field

The present invention relates to a practical and efficient method for recovering lubricating oil and ensuring high viscosity oil for refrigerant compressors.

Background

In the prior art, the refrigerant cycle typically includes a compressor delivering compressed refrigerant to a condenser. From the condenser, the refrigerant passes to an expansion valve, and then to an evaporator. This refrigerant is returned from the evaporator to the compressor for compression.

The above-described compressors typically utilize a lubricant, such as a lubricating oil, to lubricate bearings and other running surfaces. This oil is mixed with the refrigerant so that the refrigerant leaving the compressor comprises a considerable amount of oil. This is somewhat undesirable because it sometimes becomes difficult to maintain a proper supply of lubricant to lubricate the compressor surfaces in the closed refrigeration systems described above. In the past, lube oil separators were employed immediately downstream of the compressor. Such lube oil separators can separate lube oil, but they do not always have fully satisfactory results. For example, the lubricant oil separated from such a separator is at a high pressure, and thus a significant amount of refrigerant may remain mixed in the lubricant oil. This reduces the viscosity of the lubricating oil. The use of a separator also results in a pressure drop of the compressed refrigerant, which is also undesirable.

Electric heaters are also employed to vaporize liquid refrigerant from the lubricating oil. The use of electric heaters requires the consumption of energy, which is also somewhat undesirable.

In some proposed systems, a mixture of lubricant and oil is contacted with a concentrator or vaporizer to evaporate liquid refrigerant from the oil. In the proposed system, a portion of the liquid refrigerant leaving the condenser passes through a concentrator into a heat transfer relationship with the combined liquid refrigerant/oil mixture. This refrigerant from the condenser causes the liquid refrigerant to evaporate and "boil" off of the combined liquid refrigerant/lubricant mixture.

The above system is not as efficient as it would be due to the reliance on refrigerant exiting the condenser for the majority of the liquid. Thus, the cooling that occurs in the concentrator is sensible cooling (non-phase change cooling). The temperature of the warmer refrigerant/lubricant mixture then approaches the temperature of the "cold" refrigerant discharged by the condenser. The result is a reduction in the average temperature of such heat exchangers, and thus an inefficient boiling of the refrigerant/oil mixture.

Disclosure of Invention

In the disclosed embodiments of the invention. The compressed gaseous refrigerant is preferably discharged upstream of the condenser and into the oil recovery vaporizer. The invention is preferably embodied in a screw compressor. The temperature of the refrigerant is much higher than in the prior art and thus the refrigerant is effectively vaporized from the liquid refrigerant/lubricant mixture. In addition, since the refrigerant is generally gaseous, the latent heat of condensation can be utilized to provide a large average temperature difference between the heat source and the refrigerant/oil mixture. In other words, this compressed gas is condensed from a gaseous state to a liquid state in the vaporizer, not just cooled to a lower temperature to extract heat, but condensed at a near constant temperature. An "orifice" or other flow control device for the discharged refrigerant is preferably disposed in the return line downstream of the vaporizer. The orifice plate generates a substantially constant pressure as the discharged refrigerant flows through the vaporizer. A higher average temperature difference is thus formed between the refrigerant discharged from the heat source and the oil/refrigerant mixture. The method thus more efficiently evaporates the refrigerant. The latent heat capacity of the discharged compressed gas is 1 to 2 orders of magnitude higher than what is possible in the prior art by sensible cooling of the refrigerant in the liquid state. The heat transfer coefficient associated with condensation is much higher than that associated with sensitive (no phase change) cooling. Thus, the present invention is much more effective in evaporating excess refrigerant from the mixture. It should be noted with respect to this feature that although it is preferred that the discharged refrigerant contain as high a percentage of gas as possible, there is always the possibility that some liquid may be entrained. Thus, when reference is made in this application to a discharged compressed gas, it should be understood that the discharged refrigerant need not be all gas.

In a preferred embodiment, the refrigerant is discharged immediately downstream of the compressor. In a second embodiment, the refrigerant is discharged into the last compression chamber or closed lobe of the screw compressor.

In at least some possible embodiments, the refrigerant can flow from the condenser as long as it is discharged from a point where it is still at a compressed pressure in the condenser and still has a high percentage of gas. In any of the above embodiments, the discharged refrigerant is substantially separated from the refrigerant/oil mixture within the vaporizer.

In order to provide additional heat to evaporate a portion of the refrigerant, the lubricant oil delivered to the compressor bearings is heated in the compressor and returned directly to the lubricant sump to further evaporate the refrigerant. This oil passes through the orifice plate before entering the bearings, where it is depressurized. This process causes a portion of the liquid refrigerant in admixture with the lubricant to rapidly evaporate into a gaseous state, further increasing the viscosity of the lubricant delivered to the bearings. The oil is heated during its cooling of the bearings and the warmed oil is used to further evaporate the refrigerant. The oil is removed from the sump and returned to the compressor for lubricating the compressor surfaces.

The basic system outlined above is advantageous over the prior art in that the separated oil is at a low pressure in relation to the evaporator. The lubricant/refrigerant mixture at low pressure is generally of higher viscosity than the mixture in prior systems employing separators. In such prior systems, the lubricant oil is at a high pressure and, in addition, the refrigerant is evaporated more efficiently than in the prior art using refrigerant gas heated in the compressor.

In other features of the invention, a restriction or valve is provided in the line leading from the evaporator to control the flow of liquid refrigerant/oil into the still or evaporator. There may also be a number of independently controlled lines from the evaporator to control the combined flow.

The above and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

Drawings

FIG. 1 is a schematic diagram of the system of the present invention.

Fig. 2 is a diagram of a second embodiment in the system of fig. 1.

Fig. 3 shows another embodiment.

Fig. 4 is a cross-sectional view taken along line 4-4 of fig. 3.

Fig. 5 illustrates yet another embodiment.

Fig. 6 shows yet another embodiment.

Detailed Description

Fig. 1 illustrates a refrigeration system 20 including a compressor 22. The present invention is particularly advantageous for screw compressors, although it may be equally advantageous for other types of compressors in some respects.

As is well known, the submerged evaporator 24 delivers refrigerant to the compressor 22 via a passage 26, with the refrigerant passing from the compressor 22 through a line 25 to a condenser 30. The compressed gaseous refrigerant is cooled in the condenser and converted to a liquid phase, which is passed through an expansion valve (not shown) on its way to the evaporator 24. In the evaporator 24, the environment to be cooled is cooled by the refrigerant therein. As shown, the liquid refrigerant 32 will typically precipitate from the refrigerant in the evaporator 24.

In general, the optimal viscosity range for a refrigerant will vary for a particular compressor, and one of ordinary skill in the art will recognize that in the case of refrigerants R-134a and 220 weighted POE oils, a peak viscosity occurs when the temperature of the refrigerant and oil mixture is about 4.44 ℃ (40 ° F) above the saturation temperature of the refrigerant corresponding to the pressure of the mixture. That is, at this mixture pressure, the refrigerant has a corresponding saturation temperature. The temperature of the mixture of refrigerant and lubricating oil is greater than 4.44 deg.C (40 deg.F) above the saturation temperature.

It is also known to supply lubricant, typically lubricating oil, to the compressor 22. This oil is mixed with the refrigerant so that the liquid refrigerant 32 in the evaporator 24 includes a large amount of oil. The present invention helps to separate this liquid refrigerant from the oil so that the oil returned to the oil sump 48 is almost free of refrigerant. This increases the viscosity of the lubricating oil, making it more advantageous to lubricate the surfaces of the compressor.

For this purpose, a return line 34 passes this mixture of liquid refrigerant 32 and lubricating oil to a still or vaporizer 38. A valve or choke 36 controls the flow from line 34. The flow back to the evaporator can be metered by a simple valve or choke 36 and a shut-off valve allows the controller 200 to make on or off control of the flow.

The controller 200 may also control the auxiliary line 134 and the valve 136. Valves 36 and 136 may be opened in series depending on the volume of the mixture of liquid refrigerant 32 and lubricating oil in evaporator 24 and the ability of the vaporizer to process and vaporize the liquid refrigerant 38. Although two manifolds and two valves are shown, even more manifolds and valves may be provided in accordance with the principles of the present invention.

Line 40 in the vaporizer receives hot, compressed gaseous refrigerant from a tap 42. Typically, the vaporizer is a heat exchanger having components that physically separate the hot, discharged refrigerant from the refrigerant/lubricant mixture. The line 40 schematically illustrated in the drawings is preferably a plurality of enhanced heat exchange copper tubes in practice. Alternatively, such a vaporizer may take the form of other heat exchangers, such as brazed plate or tube heat exchangers. Certain embodiments are illustrated below. Typically, the tapped refrigerant is cooled and condensed to a liquid state and causes evaporation of liquid refrigerant 32 from the mixture fed into the vaporizer 38 through line 34. Due to its higher temperature, the tapped refrigerant causes the liquid refrigerant 32 in the mixture to evaporate. The refrigerant/lubricant at evaporator pressure in the vaporizer ensures that the temperature of this mixture is lower than the temperature of the compressed gas used as the heat source. The refrigerant is returned to the mixture 32 downstream of the vaporizer 38 via a return line 44. An orifice or other flow restriction 300 is located in the return line 44 to ensure a near constant pressure and lower temperature of the refrigerant being discharged throughout the evaporator condensation process. As shown in fig. 1, the tap 42 is tapped upstream of the condenser and therefore the refrigerant is relatively hot, especially compared to the prior art. The mixture in the vaporizer that is contacted by the hot refrigerant via line 40 causes the refrigerant to vaporize from the mixture and return via line 43 to line 26 which leads to the compressor. Line 43 also acts as a vent to ensure that the refrigerant/oil in the vaporizer is at evaporator pressure. The refrigerant/oil in the vaporizer is at evaporator pressure to ensure that the temperature of this mixture is lower than the temperature of the compressed gas used as the heat source. This oil is returned to the oil sump 48 through line 46. From the sump 48, the oil passes through line 50 to an oil pump 52 and returns to the compressor through line 54. The lubricant oil that lubricates the inner surface of the compressor (not shown) is returned to the oil sump 48 through the lubricant return line 56. The returned oil is hot after lubricating the working surfaces of the compressor. This hot oil is then used to evaporate additional refrigerant from the oil in sump 48. That is, the still 38 will be used to remove a large amount of liquid refrigerant, but the returned hot lube oil 56 will remove even more refrigerant from the sump 48, and the removed liquid refrigerant will be returned to the line 43 and line 26 via line 58.

The present invention improves upon the prior art by utilizing a much hotter refrigerant to vaporize the liquid refrigerant from the fluid refrigerant/oil mixture. This allows for more efficient removal of the liquid refrigerant than in the prior art.

Fig. 2 shows another embodiment in which a branch 60 is inserted into the last closed lobe (lobe)62 of the screw compressor 22. That is, the refrigerant discharged into the vaporizer 38 is actually taken from the compression chamber here. The compression chamber is in a particularly hot position under most operating conditions. One desirable application of the above-described drainage operation is disclosed in co-pending U.S. patent application No.10/306326, filed on even date herewith. Entitled "alternative Flow of Discharge Gas to a Vaporizer for a Screwcompressor".

Fig. 3 illustrates yet another embodiment 100. The discharged refrigerant passes through the vaporizer tube 104 via the passage 102. The liquid refrigerant/oil mixture enters the vaporizer tube or still 104 via passage 106. One end 110 of the carburetor allows oil to enter an oil sump 112 surrounding the carburetor 104. The return lubrication line 114 leads to an oil pump. The separated liquid refrigerant is returned to the compressor inlet line via line 108.

Another embodiment 120 is illustrated in FIG. 5. Fig. 5 is similar in most respects to fig. 3, but with a lubrication oil passage 128 formed in the bottom of the carburetor 124, and a vent passage 132 formed through the outer wall 122 of the sump. A passage 137 is also formed through the sump to return more of the separated refrigerant. In addition, this liquid refrigerant/oil enters the vaporizer 124 via passage 130. The heated compressed refrigerant passes through line 126 and the separated oil is returned to the oil pump through line 136.

An electric heater may also be provided in association with the vaporizer to vaporize liquid cryogen when normal use of the heated cryogen is cut off or otherwise insufficiently supplied, as described in this application.

Although the preferred embodiments described above illustrate the discharge upstream of the condenser, it is also possible to discharge the hot, gaseous compressed refrigerant from the initial portion of the condenser. Fig. 6 schematically illustrates the condenser 30 receiving compressed refrigerant 28 from the compressor, with a tap 310 located at the beginning of the section where a large amount of gaseous compressed refrigerant may be available. One of ordinary skill in the art will know how to obtain such gaseous refrigerant from the beginning of the condenser 30.

Although a few preferred embodiments of the present invention have been disclosed above, those of ordinary skill in the art will recognize that many modifications may be made within the scope of the present invention. For that reason the following claims should be studied to determine the true scope and content of this invention.

Claims (24)

1. A refrigerant cycle comprising:

a refrigerant compressor for receiving refrigerant from the evaporator, compressing the refrigerant and delivering the refrigerant to the condenser, the refrigerant cycle flowing through the refrigerant cycle;

a lubricant circulation supplying lubricant to the compressor;

a passage for diverting the liquid refrigerant/lubricant mixture from the evaporator and into the vaporizer; and

discharging compressed refrigerant into a tap of the vaporizer from a location prior to the condenser, the compressed refrigerant heating the combined liquid refrigerant/lubricant mixture and causing liquid refrigerant to evaporate from the mixture, the compressed refrigerant subsequently flowing into the evaporator, the evaporated refrigerant evaporating from the liquid refrigerant/lubricant mixture flowing into an inlet line of the compressor, and lubricant separated from the liquid refrigerant/lubricant mixture being directed into the lubricant circuit.

2. A refrigerant cycle as set forth in claim 1, wherein there are two passages for delivering a combined liquid refrigerant/lubricant mixture to said vaporizer.

3. A refrigerant cycle as recited in claim 2, wherein a valve is provided on both of said passages.

4. A refrigerant cycle as set forth in claim 1, wherein a restriction is provided in a passage leading from said evaporator to said vaporizer.

5. A refrigerant cycle as set forth in claim 1, wherein said compressed refrigerant is discharged at a location between said compressor and condenser.

6. A refrigerant cycle as set forth in claim 1, wherein said compressed refrigerant is discharged from a location within the compression chamber of the compressor.

7. The refrigerant cycle as set forth in claim 6, wherein said compressor is a screw compressor and said compressed refrigerant is discharged from the last closed lobe of said screw compressor.

8. A refrigerant cycle as set forth in claim 1, wherein said lubricant is delivered from a sump to said compressor at a first temperature and returned from the compressor to said sump at a second temperature higher than said first temperature, said returned lubricant causing more refrigerant to evaporate from said liquid refrigerant/lubricant mixture, and said refrigerant evaporating from said sump being returned to the inlet line of the compressor.

9. A refrigerant cycle as set forth in claim 8, wherein said vaporized refrigerant is returned to an inlet line of said compressor, and a line for returning said vaporized refrigerant functions as a vent line to ensure that the portion of said vaporizer receiving said refrigerant/lubricant mixture is at the same pressure as the evaporator pressure in the evaporator.

10. A refrigerant cycle as set forth in claim 1, wherein said lubricant delivered to said compressor is delivered from an oil sump into which lubricant from said vaporizer is delivered.

11. A refrigerant cycle as set forth in claim 10, wherein said oil sump is disposed around said vaporizer.

12. A refrigerant cycle as set forth in claim 1, wherein said compressor is a screw compressor.

13. The refrigerant cycle as recited in claim 1, wherein said compressed refrigerant is gaseous.

14. A refrigerant cycle as recited in claim 1, wherein a return line is provided for returning said compressed refrigerant from said vaporizer to said evaporator, said return line including a fluid flow control device to ensure that the pressure of said compressed refrigerant flowing through said vaporizer is constant.

15. The refrigerant cycle as set forth in claim 1, wherein:

the compressor causes the refrigerant to flow from the condenser to the evaporator and from the evaporator back to the compressor, and the lubricant is delivered from the oil sump to the compressor via the pump, and the separated lubricant flows into the oil sump.

16. A refrigerant cycle as set forth in claim 15, wherein there are two passages for delivering a combined liquid refrigerant/lubricant mixture to said vaporizer.

17. A refrigerant cycle as recited in claim 16, wherein a valve is provided on both of said passages.

18. A refrigerant cycle as set forth in claim 15, wherein a restriction is provided in a passage leading from said evaporator to said vaporizer.

19. A refrigerant cycle as set forth in claim 15, wherein said compressed refrigerant is discharged at a location between said compressor and condenser.

20. A refrigerant cycle as set forth in claim 15, wherein said compressed refrigerant is discharged from a location within the compression chamber of the compressor.

21. A refrigerant cycle as set forth in claim 15, wherein said compressor is a screw compressor and said compressed refrigerant is discharged from the last closed lobe of the screw compressor.

22. A refrigerant cycle as set forth in claim 15, wherein said lubricant is delivered from an oil sump to said compressor and from said compressor back to said oil sump, said returning lubricant evaporating more refrigerant from said liquid refrigerant/lubricant mixture and said refrigerant evaporating from said oil sump being returned to an inlet line of said compressor.

23. A refrigerant cycle as set forth in claim 15, wherein said lubricant delivered to said compressor is delivered from an oil sump into which lubricant from said vaporizer is delivered.

24. The refrigerant cycle as recited in claim 15,

a return line is provided for returning said compressed refrigerant from the vaporizer to the evaporator, and includes a fluid flow control device to ensure that the pressure of said refrigerant flowing through said vaporizer is constant.