Horizontal bulk oil separator

Abstract

A high separation efficacy, compact, bulk oil separator oriented horizontally and used with a scroll-type oil-lubricated compressor unit adapted to compressing helium. The horizontal bulk oil separator contains an integral oil reservoir and removes more than 99.9% of the oil from the helium that exits. The bulk oil separator contains successive chambers where oil separates from the gas by impingement.

Description

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram of an oil-lubricated helium compressor system illustrating the relation between the horizontal bulk oil separator of the present invention and other compressor system components;

FIG. 2 is a schematic diagram illustrating the horizontal bulk oil separator in accordance with the present invention;

FIG. 2A is a plane cut-out view of baffles 45a and 45b.

FIG. 2B is a plane cut-out view of baffle 45c.

FIG. 3 is a graphical representation of the amount of oil in the bulk oil separator of FIG. 2 vs. the depth of oil above the cut-out point for the oil level switch.

FIG. 4 is a schematic diagram illustrating an alternate embodiment of the horizontal bulk oil separator in accordance with the invention; and

FIG. 4A is a plane cut-out view of a baffle having an upper cut-out.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and more specifically to FIG. 1, there is shown the bulk oil separator 4 of the present invention in relation to the other essential components of compressor system 1. The shell 2 of a Copeland compressor that has a scroll set 12 with a displacement of 98 mL, is driven by motor 14 through drive shaft 13. The horizontal orientation allows cooling oil in sump 28 to flow by gravity in the scroll set along with helium, as designated by arrow 18. The shell 2 has a volume 3 at the return (low) pressure (about 0.8 MPa) and a volume 11 at supply (high) pressure (about 2 MPa).

The compressor is a type that is used for compressing refrigerants used in air-conditioning service and is typically vertically oriented with the scroll above the motor and the oil sump at the traditional bottom. The end of the drive shaft 13 below the motor 14 contains an oil pump 16 that picks up oil from the traditional sump, (when it is oriented vertically), to pump it through a hole in drive shaft 13 that has ports to lubricate a lower bearing, an upper bearing, and to inject some oil into the compression chambers in the scroll set. Copeland has modified their standard compressor so it can be operated horizontally, by adding port 15 that allows cooled oil to impinge on the inlet to pump 16.

Excess oil drops into sump 27 and flows through small passages in the motor windings to get to sump 28. The addition of an oil by-pass line 23 to bring oil directly into sump 28 reduces the amount of excess oil dropping into sump 27 where it backed up and caused increased power consumption and vibration as it flowed through the “air gap” in the motor. With oil by-pass line 23, oil levels in sumps 27 and 28 remain nearly constant during operation of the compressor, as determined by the height of the inlet to scroll set 12. At the design operating pressures, 2.0/0.8 MPa (high/low), an oil flow rate of about 7 L/m is needed to keep the helium temperature at a maximum of about 70° C. The sizes of orifices 24 and 26 set the flow rates at about 2 L/m to the bearings, through line 25 and port 15, and 5 L/m directly into sump 28.

With reference to FIG. 1, arrow 19 denotes the helium/oil mixture leaving the compression chamber and flowing into high pressure plenum 11. From there the mixture flows through line 20 to the bulk oil separator 4 where most of the oil leaves through a line 21 and less than 0.1% of the oil leaves with the helium through line 31. Both flow streams in lines 21 and 31 flow through after-cooler 6 which cools both streams by the counterflow of cooling water through 30. Cooled oil is split into a first stream that flows through line 25 and orifice 26 into port 15 where it provides lubrication for the bearings, and into a second stream that flows through line 23 and orifice 24 into sump 28. Cooled helium flows through line 32 to oil separator 8 which removes most of oil that is not separated in bulk oil separator 4. Separated oil collects in the bottom of 8 and returns to low pressure volume 3, in compressor 2, through line 36 and filter/orifice 38. From separator 8 the helium with only a trace of oil in the form of a mist flows through line 33 to adsorber 10 which removes all but oil vapor before it leaves through supply line 37. The adsorber traps and holds contaminants. Its primary purpose is to remove all traces of elements, such as water vapor, from the helium gas, but principally oil. Supply line 37 takes the helium to the expander (not shown). Helium returns from the expander at low pressure through line 39 and continues on through line 17 to flow into compressor volume 3. The system is protected from being over pressurized by atmospheric relief valve 34. During cool down, or operation without lines 37 or 39 connected, excess pressure difference between the high pressure and low pressure side of the system is limited by internal relief valve 35.

FIG. 2 indicates the details of construction of a preferred embodiment of the horizontal bulk oil separator of the present invention. The horizontal bulk oil separator 4 consists of shell 40, inlet tube 20, baffles 45a, 45b, 45c, oil outlet tube 21, gas outlet tube 31, and oil level sensor 46. Baffles 45a, 45b, and 45c are brazed into shell 40. The baffles divide the separator 4 into four sections, i.e., 44a, 44b, 44c, and 44d. Baffles 45a and 45b have cut-outs 48a and 48b, shown in the enlarged view 2A, above the centerline of separator 4 for gas to flow through them, and ports 47a and 47b, near the bottom of separator 4, for oil to flow from one section to the next. Baffle 45c has a single cut-out as shown in the enlarged view 2B that has lip 49 which maintains a minimum oil level in sections 44a, 44b, and 44c, at or above the level of this lip.

The term baffles as used herein refers to a plate or partition to impede the force or movement of the fluid. It is understood that any means so positioned in the bulk oil separator may be used to impede the force or movement of the fluid.

Oil that enters separator 4, along with helium, through line 20 is directed to impinge on the inside head of shell 40. This is frequently referred to as inertial separation, because the relatively light gas can turn easily while the dense oil continues on a straight path. Most of the oil is separated from the helium at this point. Oil is further separated from the gas as it impinges on the baffles. While several different types of packing, screens and scouring pads may be used in the sections between the baffles, an absence of packing was found to be the most effective. The inlet to gas outlet tube 31 is in close proximity to an area in baffle plate 45c, shown as 50, that causes the gas to turn 90° as it flows into the gas outlet tube. This is the final mechanism to separate oil from the gas. The end of tube 31 is spaced about ½ the inside diameter of 31 from baffle 50, and the area of 50 is about twice the inlet area of tube 31. The oil that drops into section 44a has a large amount of gas bubbles mixed with it. Most of these gas bubbles rise to the surface of the oil in sections 44a, 44b, and 44c, so the oil in section 44d is sufficiently free of bubbles that an opto-electronic oil level sensor functions normally or without error. The oil level in sections 44a, 44b, and 44c, denoted by dashed line 41, and the oil level in 44d, denoted by 42, have an initial level that is above lip 49. FIG. 2 shows the condition that exists as the oil level in section 44d has dropped below the level of lip 49. As can be observed, the horizontal bulk oil separator of the present invention is capable or rendering the helium virtually oil-free.

As used herein the term opto-electronic oil level sensor refers to electro-optic devices with built-in solid state switching electronics where optic technology detects the presence or absence of a fluid directly. It is understood that any other liquid level sensor known to those skilled in the art, either direct or indirect, including but not limited to, microprocessor-based sensors, fibro-optic or laser, electrochemical, optical, electronic, capacitance, float and conductance liquid level sensors may be utilized.

FIG. 3 is a calculated plot of the amount of oil that can leave the bulk separator of the present design, versus the height of the oil above the inside bottom of separator 4. The amount of oil that is put in a new system is such that after an initial start up period, e.g. about 20 hours, there is between 200 and 300 mL of oil above the cut-out point for sensor 46. That is, the oil level will drop from a maximum of 7.5 cm to 3.5 cm before level sensor 46 opens and shuts down the compressor. The initial level is above the center line of the separator and drops in the entire separator until it reaches the height of lip 49, then only the level in section 44d drops until sensor 46 opens. Initially it drops 115 mL/cm, and then to about 30 mL/cm at the cut-out point. This provides a high level of sensitivity at the cut-out point. That is, the separator has an increase in the sensitivity to a change in oil level when the oil level drops below the lip 49 relative to when it is above the lip 49 by a factor of between about 2 and about 4, preferably between about 2.5 to about 3.8.

The present assignees have already disclosed an invention which contributes to an improvement of this type of oil-lubricated compressor. The bulk oil separator 4 is shown as having oil level switch 46. Since the oil level in compressor 2 is nearly constant, the oil level in the bulk oil separator drops over a long period of time as oil collects in adsorber 10. This provides a means of making the compressor “fail safe” as described in U.S. Pat. No. 6,488,120. This patent specifies that the compressor will shut down before the adsorber becomes more than about 75% loaded, oil (mist) never leaving the adsorber. The nearly constant oil levels in the compressor makes it possible to add oil above the level at which an oil level sensor or switch 46 opens to shut down the compressor without having a large difference between the maximum amount of extra oil that can be added and have it open with less than adsorber 8 being 75% loaded, and the minimum amount of oil that might collect in adsorber 8 when level switch 46 opens. The difference in the maximum and minimum oil levels being due to a tolerance on the initial oil charge in the system and changes in oil level during operation at different temperatures and pressures.

FIG. 4 is an alternative embodiment drawing of an alternate design of a horizontal bulk oil separator/reservoir in accordance with the present invention that embodies the essential features the separator of FIG. 2 but does not include an oil level detector. The essential features are the outlet of tube 20 that brings an oil/gas mixture into separator 7 being directed to impinge on the inside head of shell 40, one or more baffle plates like 45 that have upper cut-out 48 for gas and lower port 47 for oil. The inlet of outlet gas tube 31 is within ½ the tube diameter of the end of shell 40 causing the gas to make a 90° turn as a final stage of separation. Oil level 41 is the same in all sections of separator 5 and may be above or below the centerline of shell 40. Cut-outs 48 are always above oil level 41 and ports 47 are always below oil level 41. The residence time of the gas is between about 0.1 to 1.5 seconds, preferably about 0.3 to about 1.0 seconds. The residence time of the oil is between about 2 to about 10 seconds, preferably between about 3 to about 7 seconds. High oil level results in shorter residence time for the gas in the bulk oil separator and thus there will be a slightly higher fraction of oil in the gas leaving through tube 31, while a low oil level results in a shorter residence time for the oil in the bulk oil separator and thus a slightly higher amount of gas in the form of bubbles in the oil leaving through tube 21. As can be appreciated from FIG. 4, the horizontal oil separator and reservoir maintains a very high performance (although less than that of the preferred embodiment), and is of compact design.

It is understood that while there is a specific bulk oil separator, equivalent performance can be obtained in smaller or larger sizes by using three scaling parameters, 1) gas residence time, 2) oil residence time, and 3) percentage of oil removed from the gas. A forth parameter, the amount of gas in the oil, is hard to quantify and as used herein is defined as being sufficiently low that an opto-electronic level sensor gives a reliable signal.

As used herein, gas residence time is defined as the average time that it takes for gas to flow through the bulk oil separator, i.e., the time available for oil to be removed from the gas.

As used herein, oil residence time is the average time it takes for oil to flow through the bulk oil separator, i.e., the time available for gas to be removed from the oil. The percentage of oil removed from the gas could alternately be expressed as the fraction of oil that leaves with the gas.

EXAMPLE 1

The bulk oil separator used in the present compressor system, as shown in FIG. 2, has an outside diameter of 10.15 cm (4.0″) and a length of 22.8 cm (9.0″). Oil occupied approximately 50% of the volume. The compressor had a displacement of 98 mL, 338 L/min on 60 Hz power, and an oil circulation rate of about 7 L/min. The gas was helium, and the oil was UCON LBX300™ (LBX Company, LLC). The results obtained for the design and performance of the present horizontal bulk oil separator operating near the limits of test conditions are shown in Table I.

	TABLE I
	Internal volume of bulk oil separator - L	1.6	1.6
	Test pressures - MPa	2.0/0.4	2.1/0.8
	Volume of oil in bulk oil separator - mL	500	800
	Gas flow rate - L/min	69	132
	Oil flow rate - L/min	8.9	7.1
	Residence time of gas - s	0.95	0.36
	Residence time of oil - s	3.3	6.7
	Oil in gas at outlet, max - mL/hr	150	150
	Oil removal efficiency - %	99.97	99.96
	Initial rate of oil level change - mL/cm		160
	Rate of oil level change at point where	60
	switch opens - mL/cm

When the measured rates of oil level change were compared with the calculated values shown in FIG. 3 the measured initial change of 160 mL/cm was higher than the 115 mL/cm that was calculated, and the measured change at cut-out of 60 mL/cm was greater than the calculated value of 30 mL/cm. Calculations assumed static conditions while the conditions during operation are very dynamic. The test results showed that the sensitivity to a change in oil level in section 44d increased by a factor of 160/60=2.7 when the oil level dropped below lip 49. The calculated increase in sensitivity was 115/30=3.8.

The minimum volume of oil in the bulk oil separator, 500 mL, is the oil in sections 44a, 44b, and 44c when oil level 42 is near the cut-out point. As indicated, the time available for gas bubbles to separate from the oil is the residence time of the oil in the bulk oil separator. Effective removal of gas from the oil has been demonstrated with a residence time of 3.3 seconds.

Example 1 and FIG. 3 demonstrate that the bulk oil separator is designed to allow up to 300 ml of oil to be transferred to the absorber before the level switch is tripped. This represents about 18% of the volume of the bulk oil separator, i.e. 300 ml/1600 ml.

Nothing herein is meant to limit the present invention. It is understood that the present invention may be used with other horizontal scroll compressors or other compressors such as the screw, reciprocating, centrifugal, vane and rotary wave types as well as other compression or noble gases, including natural gas and air.

While this invention has been described, it will be understood that it is capable of further modification, uses and/or adaptations, following in general the principal of the invention, and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains, and as may be applied to the essential features hereinbefore set forth, as fall within the scope of the invention or the limits of the appended claims. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.

It is also understood that the following claims are intended to cover all of the generic and specific features of the invention described herein.

Claims

1. Horizontal bulk oil separator and reservoir comprising: a shell having an inlet tube which directs an inflow mixture of oil and gas to impinge on a plate;one or more baffles fixedly installed within and dividing said shell into sections wherein said inflow mixture of oil and gas impinges upon;cut-outs on said one or more baffles above oil level for gas to flow through and below oil level for oil to flow through from section to section;a final baffle provided with a single cut-out for gas and oil wherein the oil is forced to spill over into a final section, said single cut-out having a lip that maintains a minimum oil level between the inlet head of the shell and said final baffle, the oil level in the final section between said final baffle and an outlet head of the shell optionally being lower than said lip; andan oil outlet tube which directs an outflow of oil.

2. The bulk oil separator and reservoir as in claim 1 wherein an oil level sensor is below said lip of said final baffle in said final section.

3. The bulk oil separator and reservoir as in claim 1 wherein oil in said final section is sufficiently free of bubbles that a opto-electronic oil level sensor will function normally.

4. The bulk oil separator and reservoir as in claim 1 further comprising a gas outlet tube with an inlet within ½ a tube diameter of a plate causing the out-flowing gas to make a 90° turn as it enters the gas outlet tube.

5. The bulk oil separator and reservoir as in claim 4 wherein said plate is part of the final baffle.

6. The bulk oil separator and reservoir as in claim 1 having an oil reservoir allowing a change in oil volume of at least approximately 18% of the volume of the separator.

7. The bulk oil separator and reservoir as in claim 1 having an increase in sensitivity to a change of oil level when the oil level drops below said lip relative to when it is above said lip by a factor of at least about 2 to about 2.7.

8. The bulk oil separator and reservoir as in claim 1 having an increase in sensitivity to a change of oil level when the oil level drops below said lip relative to when it is above said lip by a factor of at least about 2.5.

9. The bulk oil separator and reservoir as in claim 1 wherein residence time of the gas is between about 0.1 and about 1.5 seconds.

10. The bulk oil separator and reservoir as in claim 9 wherein residence time of the gas is between about 0.3 and about 1.0 seconds.

11. The bulk oil separator and reservoir as in claim 1 wherein residence time of the oil is between about 2 to about 10 seconds.

12. The bulk oil separator and reservoir as in claim 11 wherein the residence time of the oil is between about 3 and about 7 seconds.

13. The bulk oil separator and reservoir as in claim 4 wherein at least 99% of the oil is separated from helium exiting said separator.

14. The bulk oil separator and reservoir as in claim 13 wherein at least 99.9% of the oil is separated from helium exiting said separator.

15. The bulk oil separator and reservoir as in claim 1 wherein said plate on which the inlet flow impinges is the inside head of the shell.

16. The bulk oil separator and reservoir as in claim 2 wherein an inlet to an oil outlet tube is below said oil level sensor in said final section.

17. A horizontal bulk oil separator with an integral reservoir comprising: a shell;passages for an inflow mixture of gas and oil to flow from an inlet to an outlet end within the shell;an inlet tube that directs the inflow mixture to impinge on a plate;one or more baffles that have cut-outs for gas to flow above the level of the oil and ports for the oil to flow near a bottom of the shell;an outlet port for gas above the maximum oil level and an outlet port for oil near the bottom of the shell; anda uniform oil level that is above said outlet port for oil.

18. The horizontal bulk oil separator with an integral reservoir separator as in claim 17 wherein said impingement plate is the head of said shell.

19. The horizontal bulk oil separator with an integral reservoir as in claim 17 wherein an oil reservoir with a common level allows a change in oil volume that is at least about 18% of the volume of the separator.

20. The horizontal bulk oil separator with an integral reservoir as in claim 17 wherein the position of the inlet to the gas outlet tube effects a 90° turn of the gas as it enters.

21. The horizontal bulk oil separator with an integral reservoir as in claim 20 wherein a plate that effects the gas to make a 90° turn is part of the final baffle.

22. The horizontal bulk oil separator with integral reservoir as in claim 17 wherein a residence time of the gas is between about 0.3 and about 1 second.

23. The horizontal bulk oil separator with integral reservoir as in claim 22 wherein a residence time of the oil is between about 2 and about 10 seconds.

24. A method for separating oil from gas in a horizontal bulk oil separator and reservoir comprising the steps of: inputting a gas and oil mixture flow into a shell;impinging said mixture on an inlet head of the bulk oil separator;allowing the mixture to impinge upon one or more baffles fixedly installed within and dividing said shell into sections;separating the gas from oil by flowing said mixture through upper and lower cut-outs in said baffles, the upper cut-out for gas to flow through and the lower cut-out for oil to flow through from section to section;forcing oil to flow over a final baffle having a single cut-out and a lip that maintains a minimum oil level between the inlet head of the shell and said final baffle, the oil level in the final section between said final baffle and an outlet head of the shell optionally being lower than said lip; anddirecting an outflow of oil through an oil outlet tube.

25. A horizontal bulk oil separator with integral reservoir which comprises: a shell;a means for directing an inflow mixture to impinge upon an inlet head of the bulk oil separator;one or more baffles having means for gas to flow above a level of oil and means for oil to flow near a bottom of the shell;a means for directing an outflow of gas; anda means for directing an outflow of oil.