High-pressure side separation of liquid lubricant for lubricating volumetrically working expansion machines

Abstract

The invention relates to a method for lubricating an expansion machine (30) in a thermodynamic cycle device, wherein the thermodynamic cycle device comprises the expansion machine, a feed pump (50), a lubricant separator (10) and a working medium containing a lubricant, and wherein the method comprises the following steps: The working medium is subjected to pressure by means of the feed pump. The pressurized working medium is delivered by the feed pump to the lubricant separator. At least part of the lubricant is separated from the working medium by means of the lubricant separator. At least part of the separated lubricant is delivered by the lubricant separator to the expansion machine. The invention further relates to a thermodynamic cycle device comprising a working medium that contains a working fluid and a lubricant, an expansion machine, a feed pump for subjecting the working medium to pressure, and a lubricant separator for separating at least part of the lubricant from the working medium, wherein the cycle device is designed to deliver at least part of the separated lubricant from the lubricant separator to the expansion machine.

Claims

1. Method for lubricating an expansion machine in a thermodynamic cycle device, wherein the cycle device comprises the expansion machine, a feed pump, a lubricant separator and a working medium including a working substance and a lubricant, and wherein the method comprises the following steps: pressurizing the working medium by the feed pump; supplying the pressurized working medium from the feed pump to the lubricant separator; separating lubricant from the working medium by the lubricant separator; and supplying at least a portion of the separated lubricant from the lubricant separator to the expansion machine; wherein the cycle device further comprises a condenser and an evaporator, and wherein the method further comprises the following steps: supplying the working medium from the expansion machine to the condenser; liquefying the working medium by the condenser; supplying the liquefied working medium from the condenser to the feed pump; supplying the working medium depleted of the lubricant from the lubricant separator to the evaporator; evaporating the working medium depleted of the lubricant in the evaporator; and supplying the evaporated working medium to the expansion machine; wherein only a portion of the lubricant is separated by the lubricant separator, such that lubricant remaining in the working medium depleted of the lubricant serves in the lubrication of parts of a working chamber of the volumetrically working expansion machine that roll upon or glide along one another.

2. The method according to claim 1, wherein the cycle device further comprises a feed container, and wherein the step of supplying the liquefied working medium from the condenser to the feed pump comprises the sub-steps of (i) supplying the liquefied working medium from the condenser to the feed container, and (ii) supplying the working medium from the feed container to the feed pump.

3. The method according to claim 2, wherein the supplying of the working medium from the feed container to the feed pump comprises the simultaneous suction of a lubricant-poor and a lubricant-rich phase of the working medium from the feed container, or a mixing of a lubricant-poor and a lubricant-rich phase of the working medium in the feed container.

4. The method according to claim 1, wherein the working medium liquefied by the condenser is available in the form of a suspension of working substance and lubricant.

5. The method according to claim 1, wherein on account of the pressurization, the separated lubricant flows to lubricating points of the expansion machine.

6. The method according to claim 1, comprising the further step: reducing a flow rate of the working medium in the lubricant separator.

7. The method according to claim 1, in which the working substance is provided in the form of an organic working substance.

8. The method according to claim 1, wherein no or only a slight dissolution of less than 15% of lubricant in the working substance takes place.

9. The method according to claim 1, wherein the separated lubricant flows to a bearing of the expansion machine, and wherein a controlling of a volume flow of the lubricant to the expansion machine is realized.

10. The method according to claim 1, wherein the working medium comprises a fluorinated hydrocarbon or is made thereof and/or the lubricant comprises a refrigerant oil or is made thereof.

11. Thermodynamic cycle device comprising: a working medium including a working substance and a lubricant; an expansion machine; a feed pump for pressurizing the working medium; and a lubricant separator for separating at least a portion of the lubricant from the working medium; wherein the cycle device is adapted to supply at least a portion of the separated lubricant from the lubricant separator to the expansion machine; the cycle device further comprising: a condenser for liquefying the working medium; and an evaporator for evaporating the working medium depleted of the lubricant; wherein the cycle device is adapted to supply the working medium from the expansion machine to the condenser, to supply the working medium depleted of the lubricant from the lubricant separator to the evaporator, and to supply the evaporated working medium to the expansion machine; wherein the lubricant separator is configured to separate only a portion of the lubricant, such that lubricant remaining in the working medium depleted of the lubricant serves in the lubrication of parts of a working chamber of the volumetrically working expansion machine that roll upon or glide along one another.

12. The cycle device according to claim 11, in which the cycle device further comprises a feed container, and wherein the cycle device is adapted to supply the liquefied working medium from the condenser to the feed container, and to supply the working medium from the feed container to the feed pump.

13. The cycle device according to claim 12, wherein a suction device is provided for sucking in the feed container at least a lubricant-rich phase of the working medium floating at the top, or wherein a suction device is provided for simultaneously sucking a lubricant-poor and a lubricant-rich phase of the working medium from the feed container, or wherein a mixing device is provided for mixing a lubricant-poor and a lubricant-rich phase of the working medium in the feed container.

14. The cycle device according to claim 11, in which the cycle device is an Organic Rankine Cycle device and/or in which the expansion machine is selected from the group consisting of a piston expansion machine, screw expansion machine, a scroll expander, a vane-type machine and a Roots expander.

15. The cycle device according to claim 11, further comprising a conduit in which the lubricant separated in the lubricant separator is conducted to lubricating points of the expansion machine.

16. Steam power plant comprising the device according to claim 11.

17. The cycle device according to claim 11, wherein the lubricant separated in the lubricant separator is conducted to a bearing of the expansion machine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a lubricating system for a volumetric expansion machine according to the state of the art.

(2) FIG. 2 illustrates by way of example a lubricating system for a volumetric expansion machine according to the present invention.

(3) FIG. 3 schematically represents different states of the working medium in the feed container.

(4) FIG. 4 illustrates a feed container including an suction lance for simultaneously withdrawing an oil-rich and an oil-poor phase.

DETAILED DESCRIPTION OF THE INVENTION

(5) As shown in FIG. 2, a lubricating system for a volumetric expansion machine in a thermodynamic cycle device according to an example of the present invention comprises a lubricant separator (by way of example referred to as an oil separator below) 10, which is arranged in the cycle between a feed pump 50 and an evaporator 20. The evaporator 20 generates a completely or partially evaporated working medium (live steam) which is suppled to an expansion machine 30 which is driven by the working medium and, in cooperation with a generator 40, serves in the generation of electric energy. The working medium is discharged from the expansion machine 30 in the form of a lubricant-working substance spray and flows to the condenser 60. In the condenser 60 the working medium is liquefied, wherein no or only an insignificant dissolution of lubricant in the working substance should take place. The liquefied working medium is preferably collected in a feed container 70. The feed pump 50 sucks the liquid working medium from the feed container 70, increases the pressure thereof and transports it into the lubricant separator 10. The suspension of lubricant and working substance is brought to live steam pressure. The working medium consists of the actual working substance and a lubricant. The separated lubricant is supplied from the lubricant separator directly, viz. without an additional pump, to the bearing of the expansion machine 30 for the lubrication and cooling thereof. The working medium depleted of lubricant is then resupplied to the evaporator 20, and the cycle is closed.

(6) While in the state of the art the lubricant is separated from the exhaust steam flow, i.e. on the low-pressure side, as was described above with reference to FIG. 1, according to the invention at least a portion of the lubricant is separated from the working medium mixed with the lubricant on the high-pressure side. For separating the lubricant from the working substance, preferably, the different densities of working substance and lubricant are taken advantage of. Internal attachments in the lubricant separator 10 as well as a widened cross-section and a reduction of the flow rate associated therewith encourage the phase separation. As a rule, the lubricant can be discharged in the upper area of the lubricant separator 10. As the discharged lubricant is provided on a high pressure level it may be conducted directly to bearing surfaces of the expansion machine 30, for instance through a conduit.

(7) Owing to the small solubility of oil in the working substance, a portion of the lubricant passes the lubricant separator 10 and is conducted, together with the working substance, to the evaporator 20. Here. too, the lubricant is discharged from the evaporator 20 in a liquid state, but at live steam temperature. The finely distributed lubricant present in the steam ensures a reliable lubrication of the flanks in the expansion machine 30.

(8) The following advantages of the invention should be mentioned. As a liquid is separated at a high density, a compact design of the lubricant separator 10 is obtained. The pressure losses are only insignificant. The lubricant (oil) has the temperature suited for the respective kind of use. Hot oil is used for the lubrication of flanks, and cool oil is used for lubricating and cooling the bearings. The liquid stock, being reduced in comparison with the state of the art, allows a faster start-up of the cycle device. As, according to the example described, the lubricating oil separated in the oil separator 10 is highly pressurized, allowing it to flow freely to the expansion machine 30 on account of the pressure, it is not necessary to provide another pumping device for the lubricant. Advantageously, a pressure reducing valve (flow control valve) may, however, be inserted between the oil separator and the expansion machine, for instance, to correct volume flow fluctuations of the lubricant occurring at different operating points.

(9) As opposed to the state of the art, it is another advantage that a smaller volume flows through the oil separator 10 per unit time so that same can be designed in a comparatively compact manner, resulting in the saving of space and a reduction of costs. In addition, the pressure loss downstream of the expansion machine 30 is reduced so that the pressure difference can be increased by means of the expansion machine 30, as compared with the conventional configuration comprising an oil separator 10 downstream of the expansion machine 30, thus allowing an efficiency increase of the expansion machine 30.

(10) In the constructive implementation of the invention a working medium should be used which has a sufficiently great miscibility gap. This means that an oil-poor phase and an oil-rich liquid phase develop, if, for instance, a pure refrigerant is used and oil is added, same can be dissolved in the working substance up to certain percentage, depending on the temperature. If the oil concentration is increased further, a two-phase mixture is obtained which consists of an oil-poor and an oil-rich liquid phase. If more oil is added a homogenous oil-rich phase is finally obtained.

(11) The working substance may be provided, for instance, in the form of a fluorinated hydrocarbon, e g. R134a, R245fa, and the lubricant in the form of a refrigerant oil. Suited refrigerant oils are produced, for instance, on a polyalphaolefin basis (PAO, base fluid for lubricants, e.g. Rensio Synth 68 of Fuchs Europe Schmierstoffe GmbH) or an alkylbenzene basis (e.g. Rensio SP 220 of Fuchs Europe Schmierstoffe GmbH). In general, the boiling temperature of the lubricant will be clearly higher than that of the working medium so that after passing through the evaporator 20, it will be contained in the working steam of the working medium in a liquid state, in the form of droplets.

(12) The start-up of a system in which the two-phase mixture was separated on account of the density differences in the feed container 70, e.g. after a longer standstill, or also owing to a fast separating speed during the operation, is problematical, however. In the right part of FIG. 3 such a phase separation (mixture separation) in the feed container 70 is shown schematically, with M1 designating the oil-poor phase and M2 designating the oil-rich phase, while the left part in FIG. 3 illustrates the two-phase mixture M1M2 during the operation. In a conventional feed container, as used for instance in refrigerating plants or also in ORC plants, the working medium is withdrawn at the bottom. In the case of a phase separation thus only the oil-poor phase M1 would be supplied to the feed pump. To overcome this problem the feed container may be extended by a suction device 71, e.g. a suction lance, as shown in FIG. 4. The suction lance has for instance, one or more upper and one or more lower bores by means of which the ratio of the volume flows of oil-rich and oil-poor phases can be defined. At the inlet openings of the suction lance exactly that flow rate will be adjusted which compensates the pressure losses in the suction lance. The ratio of the drawn in volume flows can be adjusted by the diameter of the bores and the number and arrangement thereof. In the lower conduit part of the suction lance leading to the feed pump the two phases are mixed, and are separated again from each other in the lubricant separator. If two phases are present the exemplary fixed suction lance 71 draws in same with an adjusting volume ratio.

(13) However, the suction device may also be constructed differently. In a mobile construction, in the presence of two phases, a floater can suck off at least the phase floating at the top. In the presence of two phases a switchable valve can suck off at least the phase floating at the top. The two phases may be mixed by a mixing wheel which is driven by the volume flow, so that in the presence of two phases same are drawn in mixed together. The two phases may also be mixed by a motor-driven mixing wheel so that, if two phases are provided same are drawn in mixed together.

(14) Summarizing, the invention relates to a device and a method for separating lubricant from the liquid working medium. To this end, a working medium-oil pairing is used in which the mutual dissolution of the oil and working medium is only insignificant. Therefore, the oil in a lubricant separator can be discharged for the lubrication and cooling of bearings in an expansion machine. As a mixture separation may occur in the feed container the device has to ensure that, in this case, both phases are drawn in, which may be realized, for instance, by a suction lance.