Device for recovering compressor lubricating oil

Abstract

The present invention relates to a device (100) for recovering compressor lubricating oil in a compressor (10), comprising a pressure relief line (102) which is coupled to a crankcase (14) of the compressor (10) in such a way that compressed gas from the crankcase (14) can escape through it, a filter unit (106) which is accommodated in a filter housing (104) and which is arranged in such a way that the gas escaping from the crankcase (14) is conducted through the filter unit (106), and which is designed to separate compressor lubricating oil present in the gas, and which compressor lubricating oil is collected in the filter housing (104), a return line (108) for the compressor lubricating oil collected in the filter housing (104), which return line runs from the filter housing (104) back to the crankcase (14), and a ventilation opening (110), which is arranged downstream of the filter unit (106) and through which the filtered gas is discharged from the filter housing (106). The invention further relates to a compressor equipped with a device of this type and to a method for operating such a compressor.

Description

[0001] Device for recovering compressor lubricating oil

[0002] Description

[0003] The present invention relates to a compressor with a device for recovering compressor lubricating oil in the compressor, as well as a method for operating such a compressor.

[0004] Piston compressors operate by feeding a gas to be compressed into a compressor or compression cylinder, where it is compressed by a piston moving back and forth, and then expelled at a correspondingly increased pressure. The compression pistons of such compressors are driven by mechanical drive devices, usually a crankshaft rotating in a crankcase. The rotational movement of this crankshaft is transmitted to the piston by an eccentrically mounted piston rod, driving it in the aforementioned linear back-and-forth movement within the corresponding cylinder.The crankcase used in this context usually contains a certain amount of compressor lubricating oil, which must not fall below a specified minimum level within the crankcase to ensure the correct functioning of the corresponding compressor.

[0005] However, during operation of such compressors, it becomes apparent that due to the never completely perfect seal between the compression piston and the inner wall of the compression cylinder, some of the gas to be compressed or already compressed can flow past the outside of the piston and thus enter the crankcase. The term "blow-by" has become established in expert circles for this effect, whereby an excess pressure will arise within the crankcase compared to the atmospheric environment, which must be released from the crankcase in a controlled manner, as the crankcase is not designed to be gas-tight due to the expected manufacturing effort. This problem is even more pronounced in compressors that already operate with a pre-pressure, i.e. so-called "booster compressors."

[0006] In the prior art, simple pressure relief devices were provided for this purpose, from which the gas that has entered the crankcase can escape back into the environment, or, in the case of a gas that cannot be released into the environment for safety reasons, can be collected and processed in another way.

[0007] However, it has been shown that the interaction of the gas entering the crankcase with the compressor lubricating oil contained therein creates a gas / oil mist, so that when the pressurized gas is released from the crankcase, a certain amount of compressor lubricating oil is always carried out of the crankcase. This, however, poses the risk that the level of compressor lubricating oil within the crankcase will gradually drop below its specified minimum level, which, in extreme cases, could cause damage to the compressor in question. In any case, this would require shorter maintenance intervals or additional steps such as regularly refilling the crankcase with compressor lubricating oil.

[0008] To overcome these disadvantages known from the prior art, the object of the present invention is to provide a compressor operated with a pre-pressure, in which it can be prevented that compressor lubricating oil is lost when gas under excess pressure is discharged from a crankcase, so that time intervals between maintenance work on the crankcase of a compressor and / or refilling of compressor lubricating oil can be significantly extended, which in turn significantly reduces ongoing operating costs and at the same time prevents oil losses and the associated contamination. To achieve this object and to overcome the above-mentioned disadvantages of the known prior art, the invention provides a compressor with an oil-lubricated mechanical drive device, which comprises a crankcase in which compressor lubricating oil is contained, at least one compression cylinder,in which a compression piston is movably guided, which is driven by the drive device, and a device for recovering compressor lubricating oil in a compressor is proposed, which device comprises a pressure relief line which is coupled to a crankcase of the compressor in such a way that gas under excess pressure can escape from the crankcase through it, a filter unit accommodated in a filter housing, which is arranged such that the gas escaping from the crankcase is passed through the filter unit, and which is designed to separate compressor lubricating oil present in the gas, which is collected in the filter housing, a return line for the compressor lubricating oil collected in the filter housing, which runs from the filter housing back to the crankcase, and a vent opening downstream of the filter unit,through which the filtered gas can be discharged from the filter housing, wherein the device is coupled to the crankcase of the drive device by means of its pressure relief line and the compressor is designed to be operated with a pre-pressure.

[0009] Accordingly, a closed circuit for compressor lubricating oil is created in the compressor according to the invention, reliably preventing this compressor lubricating oil from escaping from the compressor. Accordingly, this lubricating oil is automatically recovered and returned to the crankcase, so that during normal operation of the corresponding compressor, no lubricating oil is lost due to blow-by, and maintenance interventions or interventions to check for a sufficient level of lubricating oil in the crankcase can be significantly reduced.

[0010] Different designs of the corresponding filter unit are conceivable; for example, injection-molded parts with a suitable filter material incorporated within them can be used. In particular, it is desirable to design the filter unit in such a way that the pressure difference between the pressure relief line and the return line is as small as possible, in particular a pressure difference of less than 20 millibars, which allows the separated oil to be easily returned to the crankcase.

[0011] To further facilitate this process of returning the compressor lubricating oil to the crankcase, the filter housing can be arranged vertically above the crankcase or at least above a designated oil level within the crankcase, so that the compressor lubricating oil will flow back into the crankcase solely by the effect of gravity once it has been separated into the filter housing.

[0012] Depending on the type of gas to be compressed, the vent opening of the device according to the invention can allow the filtered gas to be released into the environment, for example, when harmless gases such as air or nitrogen are compressed using the corresponding compressor. However, if the gas is problematic in any way and cannot be released directly into the environment, another processing device can of course be located downstream of the vent opening, in which the filtered gas is collected or further processed.

[0013] Furthermore, a pressure regulating valve can be provided which is associated with the vent opening, i.e. is arranged at the outlet of the filter, which enables more effective separation of the oil.

[0014] Furthermore, the compressor according to the invention can be provided with a bypass device that connects a point downstream of the filter unit with a point upstream of the filter unit, while a valve element is also provided that releases the bypass device above a predetermined threshold pressure. Such a bypass device acts as a safety function to bypass the filter, for example, if it is saturated and consequently venting through the filter is no longer possible.

[0015] Furthermore, in the compressor according to the invention, at least one seal can be provided in the area of ​​the filter housing, which seal is preferably made of an FKM / FPM material, i.e., a fluororubber or VITON. Such materials are particularly suitable for the present application, since high oil compatibility of the corresponding seals is required.

[0016] Although the device for recovering compressor lubricating oil used in the compressor according to the invention is also suitable for retrofitting to existing compressor systems, since only minor modifications and in particular the provision of a pressure relief line on the crankcase and a return line for compressor lubricating oil into the crankcase are required, the invention provides for newly manufactured compressors to be directly equipped with such a device.Accordingly, as mentioned, the present invention relates to a compressor comprising an oil-lubricated mechanical drive device which comprises a crankcase in which compressor lubricating oil is contained, at least one compression cylinder in which a compression piston is movably guided, which is driven by the drive device, and a device according to the invention of the type described above, which is coupled to the crankcase of the drive device by means of its pressure relief line and its return line.

[0017] Different types of compressors can be considered here, and in particular, the corresponding compressor can comprise a plurality of compression cylinders connected in parallel and / or in series, whose respective compression pistons are jointly driven by the drive device, so that only a single crankcase is provided in the compressor. Of course, however, the present invention could also be applied to compressors in which several independent crankcases are provided for a plurality of compression cylinders, in which case each corresponding crankcase would then be equipped with either its own device according to the invention or several pressure relief lines would converge to a single filter housing.

[0018] In particular, the invention envisages multi-stage compressors, each of which gradually increases the compression pressure of the gas to be compressed. A specific embodiment could, for example, be designed such that two or more first compression stages, each with its own compression cylinder, are connected in parallel, each supplying the correspondingly compressed gas to a common second compression stage for further compression. The number of compression stages connected in series is initially freely selectable; however, the prior art particularly includes corresponding compressors with three to five compression stages connected in series. These compressors may differ, for example, in the size of their compression cylinders, in order to accommodate the compression-related reduction in the volume of the gas to be further compressed.

[0019] Furthermore, the compressor according to the invention can be equipped with a lubricant pump arranged within the crankcase, so that it can be a pressure-oil-lubricated compressor. Although the present invention could also be implemented, for example, in the context of centrifugal pin-lubricated compressors, pressure-oil-lubricated compressors are characterized by the fact that, due to their lubrication characteristics, they are particularly suitable for use with a downstream filter of the type used in the present invention.

[0020] As already described above, the compressor according to the invention is designed to be operated with a pre-pressure, i.e., to be supplied with gas already under pressure for further compression. The term "booster compressor" has become common in technical jargon for such compressor designs, and it is customary to supply gas to be further compressed to the first compressor stage of such compressors at a pressure of approximately 0.3 bar to 16 bar. In such compressors, it is particularly not possible to feed gas purified by the filter unit back to the inlet of at least one compression cylinder, since, due to operational reasons, the respective pressure conditions at the corresponding points of the compressor are incompatible.

[0021] According to a further aspect of the present invention, it relates to a method for operating such a compressor, comprising driving the at least one compression piston by means of the mechanical drive device, discharging gas under excess pressure in the crankcase through the pressure relief line, and returning the compressor lubricating oil collected in the filter housing to the crankcase. As already noted, in such a method, the gas to be compressed is already supplied to the first stage of the compressor at an excess pressure, for example, in the range of approximately 0.3 bar to 16 bar.

[0022] Although any gases and gas mixtures can initially be compressed using the compressor just described in a process according to the invention, the compression of nitrogen is particularly suitable. In this case, as already indicated above, the filtered air exiting the filter housing can simply be released back into the environment. The corresponding nitrogen can be obtained using known suitable processes, in particular in a nitrogen membrane generator or a nitrogen generator with pressure swing adsorption.

[0023] Further features and advantages of the present invention will become more apparent from the following description of an embodiment thereof, when considered together with the accompanying Figure 1. This Figure 1 shows a schematic view of a compressor according to the invention with a device for recovering compressor lubricating oil.

[0024] The compressor according to the invention, schematically illustrated in Figure 1, is generally designated by reference numeral 10 and comprises an oil-lubricated mechanical drive device 12, which in turn comprises a crankcase 14 and a crankshaft 16, which is driven into rotation by a motor not further illustrated in Figure 1. The type of motor of the compressor 10 is not important, and both electrically and internal combustion engine-driven variants could be implemented in practice.

[0025] A compression piston 20 is connected to the crankshaft 16 by an eccentrically arranged piston rod 18, which can be moved up and down within the corresponding compression cylinder 22 by converting the rotational movement of the crankshaft 16 into a translational movement by means of the piston rod 18.

[0026] By providing and operating an inlet valve 24a and an outlet valve 24b in a manner coordinated with the movement of the compression piston 20, gas fed into the compression cylinder 22 can now be compressed and subsequently expelled again, as indicated in Figure 1 by the two arrows in the region of the valves 24a and 24b. It is conceivable that several such compression stages are connected in parallel and / or in series in the compressor 10 shown here; however, for reasons of clarity, only a single such stage is shown in Figure 1. It is clear, however, that corresponding compressor stages could, for example, be jointly driven by the mechanical drive device 14 shown here, and accordingly only the single crankcase 12 shown here would be included in the compressor 10.

[0027] Furthermore, it should be noted that the compressor 10 is of a pressure oil lubricated type, since a lubricant pump 26 is arranged within the crankcase 14, which pumps compressor lubricant S upwards from the sump of the crankcase 14 to a suitable position in the region of the compression cylinder 22.

[0028] Furthermore, during operation of the compressor 10, it becomes apparent that, due to the never completely perfect seal between the outer surface of the piston 20 and the inner wall of the cylinder 22, gas from the compression chamber of the cylinder 22 can enter the crankcase 12, as indicated in Figure 1 by the wavy arrows B. This gas entering the crankcase creates an overpressure compared to the environment at this point, which must be released again in a controlled manner. This shows that the gas entering the crankcase 12 and its interaction with the compressor lubricating oil S provided in the crankcase 12 for lubricating the corresponding components creates a gas / oil mist, which is indicated by the arrows N in Figure 1.

[0029] To prevent the loss of this compressor lubricating oil due to its discharge into the gas / oil mist N, the compressor 10 is further equipped with a device 100 for recovering the aforementioned compressor lubricating oil. This device 100 comprises a pressure relief line 102, which is coupled to the crankcase 12 of the compressor 10 in such a way that the pressurized gas can escape from the crankcase 12 through it.

[0030] The pressure relief line 102 opens at its end opposite the crankcase 12 into a filter unit 106 accommodated in a filter housing 104, which is arranged such that the gas-oil mixture emerging from the crankcase is passed through the filter unit 106. The filter unit 106 is configured such that compressor lubricating oil present in the gas-oil mixture is separated, which is accordingly collected in the filter housing 104, as indicated by the wavy line S2. Furthermore, the device 100 comprises a return line 108 for the compressor lubricating oil S2 collected in the filter housing 104, which in turn runs from the filter housing 104 back to the crankcase 12.Due to the arrangement of the filter housing 104 vertically above the crankcase 12, the separated lubricating oil S2 collected in the filter housing 104 will flow back into the crankcase 12 solely by the effect of gravity, as indicated by the arrow R in Figure 1.

[0031] Furthermore, it should be noted that the device 10 has a vent opening 110 downstream of the filter unit 106 with a pressure regulating valve 110a, shown only schematically, through which the filtered gas can be discharged from the filter housing 104. The separation of the compressor lubricating oil in the filter unit 106 ensures that no lubricating oil is discharged from the compressor 10. Accordingly, the provision of the device 100 ensures that a sufficient level of compressor lubricating oil S is contained in the crankcase 12 of the compressor 10 at all times, whereby refilling of lubricating oil and corresponding maintenance interventions can be carried out with reduced frequency.

[0032] Finally, it should be noted that a bypass device 112 is provided in the compressor 10, which connects a point downstream of the filter unit 106 with a point upstream of the filter unit 106. A valve element 114 is assigned to the bypass device 112, which, above a predetermined limit pressure, releases the bypass device 112 for the flow of the gas-oil mist N. The bypass device 112 acts as a safety function to bypass the filter unit 106 if it is clogged or saturated and, consequently, venting through the filter unit 106 is no longer possible.

Claims

Claims 1. Compressor (10), comprising: - an oil-lubricated mechanical drive device (12) comprising a crankcase (14) in which compressor lubricating oil is contained; - at least one compression cylinder (22) in which a compression piston (20) is movably guided, which is driven by the drive device (12); and - a device (100) for recovering compressor lubricating oil in a compressor (10), comprising: o a pressure relief line (102) which is coupled to a crankcase (14) of the compressor (10) in such a way that gas under excess pressure can escape from the crankcase (14) through it; o a filter unit (106) accommodated in a filter housing (104), which is arranged such that the gas escaping from the crankcase (14) is passed through the filter unit (106), and which is designed to separate compressor lubricating oil present in the gas, which is collected in the filter housing (104); o a return line (108) for the compressor lubricating oil collected in the filter housing (104), which runs from the filter housing (104) back to the crankcase (14);and o a vent opening (110) downstream of the filter unit (106), through which the filtered gas is discharged from the filter housing (106), wherein the device (100) is coupled to the crankcase (14) of the drive device (12) by means of its pressure relief line (102), and the compressor (10) is designed to be operated with a pre-pressure.; 2. Compressor (10) according to claim 1, wherein the filter unit (106) is designed such that a pressure difference of less than 20 mbar occurs between the pressure relief line (102) and the return line (108).

3. Compressor (10) according to one of the preceding claims, wherein the filter housing (104) is arranged vertically above the crankcase (14) or above a provided oil level within the crankcase (14).

4. Compressor (10) according to one of the preceding claims, wherein the vent opening (110) allows the filtered gas to be discharged to the environment.

5. Compressor (10) according to one of the preceding claims, further comprising a pressure regulating valve (110a) associated with the vent opening (110).

6. Compressor (10) according to one of the preceding claims, further comprising a bypass device (112) which connects a point downstream of the filter unit (106) to a point upstream of the filter unit (106) and comprises a valve element (114) which releases the bypass device above a predetermined limit pressure.

7. Compressor (10) according to one of the preceding claims, wherein at least one seal is provided in the region of the filter housing (104), which seal is preferably made of an FKM / FPM material.

8. Compressor (10) according to one of the preceding claims, comprising a plurality of compression cylinders (22) which are connected in parallel and / or in series and whose respective compression pistons (20) are jointly driven by the drive device (12).

9. Compressor according to one of the preceding claims, further comprising a lubricant pump (26) arranged within the crankcase (14).

10. A method for operating a compressor (10) according to any one of the preceding claims, comprising: Driving the at least one compression piston (20) by means of the mechanical drive device (12); Discharging gas under excess pressure in the crankcase (14) through the pressure relief line (102); and Returning the compressor lubricating oil collected in the filter housing (104) to the crankcase (14).

11. Method according to claim 10, wherein gas to be compressed is supplied to the first stage of the compressor (10) already at an overpressure.

12. The method according to claim 10 or 11, wherein the gas to be compressed is nitrogen.

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