Method and Device For Rapid Oil Heating For Oil-Lubricated Expansion Machines

Abstract

The present invention relates to a method for lubricant heating during starting up of a thermodynamic cycle device, wherein the cycle device comprises a working medium with a working substance and a lubricant, an evaporator for evaporating the working substance, a lubricant separator for separating at least part of the lubricant from the working medium which is supplied by the evaporator, an expansion machine which is to be lubricated with the lubricant, and a condenser device with a condenser, and wherein the method comprises the following steps: delivery of lubricant from the lubricant separator to the condenser device and/or to the evaporator during shutdown of the cycle device, as a result of which a working medium which is enriched with lubricant is provided in the condenser device and/or in the evaporator; and heating of the working medium which is enriched with lubricant in the evaporator during starting up of the cycle device. Furthermore, the invention relates to a thermodynamic cycle device which comprises means for delivering lubricant from the lubricant separator to the condenser device and/or to the evaporator during shutdown of the cycle device, as a result of which a working medium which is enriched with lubricant can be provided in the condenser device and/or in the evaporator.

Claims

1. Method for lubricant heating upon starting up a thermodynamic cycle device, wherein the cycle device comprises a working medium including a working substance and a lubricant, an evaporator for evaporating the working substance, a lubricant separator for separating at least a portion of the lubricant from the working medium supplied from the evaporator, an expansion machine to be lubricated with the lubricant, and a condenser apparatus having a condenser, and wherein the method comprises the steps of: supplying lubricant from the lubricant separator to the condenser apparatus and/or to the evaporator upon shutting down the cycle device so as to provide a working medium enriched with the lubricant in the condenser apparatus and/or in the evaporator; and heating the working medium enriched with the lubricant in the evaporator upon starting up the cycle device.

2. The method according to claim 1, wherein the supplying of lubricant from the lubricant separator upon shutting down the cycle device includes a reduction of the pressure in the lubricant separator.

3. The method according to claim 2, wherein the reduction of the pressure in the lubricant separator is realized after a standstill of the expansion machine.

4. The method according to claim 1, wherein the cycle device further comprises a bypass line between the lubricant separator and the condenser apparatus so as to bypass the expansion machine, and wherein the bypass line is opened and closed by means of a valve, in particular a solenoid valve, and wherein the step of supplying lubricant from the lubricant separator to the condenser apparatus includes the opening of the valve.

5. The method according to claim 1, comprising the further step of: stopping a supply of working medium to the evaporator upon shutting down the cycle device prior to the supply of lubricant from the lubricant separator to the condenser apparatus and/or the evaporator.

6. The method according to claim 1, wherein the condenser apparatus further comprises a feed container in which condensed working substance is collected, and wherein the cycle device further comprises a feed pump; and wherein the step of supplying lubricant from the lubricant separator to the condenser apparatus upon shutting down the cycle device comprises a supplying of lubricant from the lubricant separator to the feed container; and wherein the step of heating the working substance enriched with the lubricant in the evaporator upon starting up the cycle device comprises a pumping of working medium enriched with the lubricant from the feed container to the evaporator by means of the feed pump.

7. The method according to claim 4, comprising the further steps of: conducting evaporated working substance to the condenser, through the bypass line, upon starting up the cycle device; detecting a filling level of lubricant in the lubricant separator; and conducting the evaporated working substance to the expansion machine upon detecting a predetermined filling level, by closing the valve of the bypass line.

8. The method according to claim 7, comprising the additional step of: opening a valve, in particular a solenoid valve, in a lubricant conduit from the lubricant separator to the expansion machine.

9. Thermodynamic cycle device comprising: a working medium including a working substance and a lubricant; an evaporator for evaporating the working substance; a lubricant separator for separating at least a portion of the lubricant from the working medium supplied from the evaporator; to the evaporator when the cycle device is shut down, so that a working medium enriched with the lubricant can be provided in the condenser apparatus and/or in the evaporator.

10. The cycle device according to claim 9, in which the means for supplying lubricant from the lubricant separator to the condenser apparatus comprise a bypass line provided with a valve, in particular a solenoid valve, between the lubricant separator and the condenser apparatus for bypassing the expansion machine and/or the means for supplying lubricant from the lubricant separator to the evaporator comprise a lubricant conduit between the evaporator and the lubricant separator.

11. The cycle device according to claim 9, in which the condenser apparatus further comprises a feed container in which condensed working substance and lubricant from the lubricant separator can be collected, and wherein the cycle device further comprises a feed pump for pumping working medium enriched with the lubricant from the feed container to the evaporator.

12. The cycle device according to claim 9, in which means for detecting a filling level of lubricant in the lubricant separator are provided.

13. The cycle device according to claim 9, in which a lubricant conduit comprising a valve, in particular a solenoid valve, is provided between the lubricant separator and the expansion machine, wherein the lubricant separated in the lubricant separator can be conducted in the lubricant conduit to lubricating points of the expansion machine, in particular to a bearing of the expansion machine.

14. The cycle device according to claim 9, 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. Steam power plant comprising the device according to claim 9.

Description

DRAWINGS

[0028] FIG. 1 illustrates a lubricating system for a volumetric expansion machine according to an internal state of the art known to the applicant.

[0029] FIG. 2 illustrates by way of example a first embodiment of the thermodynamic cycle device according to the present invention.

[0030] FIG. 3 illustrates by way of example a second embodiment of the thermodynamic cycle device according to the present invention.

[0031] FIG. 4 illustrates by way of example a miscibility gap for a working substance and a lubricant.

[0032] FIG. 5 illustrates by way of example the viscosity and the percentage of working substance dissolved in the oil depending on the temperature.

EMBODIMENTS

[0033] As shown in FIG. 2 a first embodiment of the cycle device according to the invention (corresponding to the cycle device according to the internal state of the art as shown in FIG. 1) comprises an evaporator 20, an oil separator 10, an expansion machine 30, a generator 40, a condenser 60 and a feed pump 50, as well as an oil conduit 11 between the oil separator 10 and the expander 30. In particular, oil for the lubrication of bearings in the expander is conducted through this conduit 11. However, the first embodiment according to the invention additionally also comprises a bypass line 80 between the oil separator 10 and the condenser 60, wherein the bypass line 80 is closed and opened by a valve 81.

[0034] FIG. 3 illustrates a second embodiment of the cycle device according to the invention, which corresponds to the first embodiment and where identical reference numbers designate components that correspond to one another. In this second embodiment a feed container 70 is additionally provided in which condensed working medium from the condenser is collected. The working medium is then sucked by the feed pump 50 from the feed container and transported to the evaporator 20. The valve 81 is furthermore designed as a solenoid valve 81. In addition, a throttle valve 12 in the oil conduit 11 as well as a solenoid valve 13 are provided.

[0035] The following description shall apply correspondingly to both embodiments according to FIG. 2 and FIG. 3.

[0036] The diameter chosen for the oil conduit 11 and the throttle valve 12 permits the non-recurrent adjustment of the necessary oil volume flow to be supplied to the bearings. The oil separator 10 itself is constructed such that sufficient oil is supplied with the live steam to the flanks (movable contact points of the working chamber in the expansion machine). In operation it shows that the start-up is very difficult if the oil separator 10 and the oil are cold. The operating temperature of the oil differs significantly from the downtime temperature. In operation the oil has a temperature equal to the live steam temperature of approximately 100=C, while the temperature in downtimes can fall even to minus degrees. As the viscosity increases by several orders of magnitude at low temperatures the start-up turns out to be problematic: the oil no longer passes the throttle valve 12 to a desirable extent.

[0037] The method according to the invention solves the problem regarding the heating of oil after downtimes and cooling down in a novel and advantageous manner. After the system was shut down the oil is transported out of the oil separator 10 and in the direction of the condenser 60 and/or the evaporator 20. At the shut-down time of the system working medium still in a liquid state, in which the oil can be dissolved, is still located in both the condenser 60 and the evaporator 20. If the system is restarted, the strongly oil-containing working medium is already located in the evaporator 20 or is transported by the feed pump 50 into the evaporator 20. Due to the dissolution in the working substance having an extremely low viscosity the viscosity of the oil is reduced to an acceptable extent. The heat supply is realized in the evaporator 20, the cold working medium is heated, and evaporated entirely or in part, with the oil remaining liquid and being separated in the oil separator 10.

[0038] For moving the oil from the oil separator 10 into the evaporator 20 and/or condenser 60 when the system is shut down a procedural process is applied. If the pressure is reduced abruptly after shutting down the system, i.e. after the standstill of the expansion machine 30, the working substance dissolved in the oil evaporates. This process takes place very fast, and the oil is frothed up intensively at the same time. The process may be compared with the frothing of a shaken mineral water bottle. If the opening and, thus, the pressure reduction takes place slowly enough no foam will develop and the water remains in the bottle. If the opening takes place abruptly, however, the gas is liberated rapidly and carries a portion of the water with it out of the bottle. In the present case, the liberated working substance correspondingly carries with it a portion of the oil out of the oil separator 10.

[0039] The rapid pressure drop may be realized by opening the bypass line 80 by means of valve/solenoid valve 81, which bypasses the expansion machine 30 and connects the live steam conduit leading from the oil separator 10 to the expansion machine 30 to the condenser 60.

[0040] If an automatic control or the user now decides that the system should be shut down, the supply of working medium into the evaporator 10 is stopped, while steam is still being generated by the residual heat and expands in the expansion machine 30. Above a specific pressure ratio the expansion machine 30 stops the mechanical work. With R245fa as working medium and a condensation at ambient temperature this is approximately a pressure ratio of 2, which corresponds to a pressure of about 3 bar. Starting at this point in time the solenoid valve 81 in the bypass line 80 can be opened, followed by the rapid pressure drop as described above, accompanied by the frothing of the oil. Depending on the position of the conduits one portion of the oil flows to the evaporator 20, while the major portion of the oil flows to the condenser 60 and the feed container 70. To shut down the system oil and working substance are now present in the evaporator 20 and the condenser 60/feed container 70 in a dissolved form, while the oil-carrying conduit 11 and the oil separator 10 contain now only oil residues.

[0041] When the system is started the control automatically detects available heat and puts the feed pump 50 into operation, which may alternatively also be forced by the user. Working medium is now transported to the evaporator 20. If a sufficiently large volume flow of steam is generated, this steam entrains the oil in a spray form which is then separated in the oil separator 10. In this operating condition the live steam is passed through the bypass valve 81 directly to the condenser 60 where the steam and the developing condensate flush oil present there in the direction of the feed container 70/feed pump 50.

[0042] If a filling level monitoring device (not shown in the illustration) in the oil separator 10 detects a sufficiently high oil filling level the solenoid valve 13 in the oil conduit 11 is opened and the solenoid valve 81 in the bypass line 80 is closed. Pressure is now continuously built up. At the same time, the control adjusts the feed pump speed and the expansion machine speed in response to the available heat flow. A change to the throttle valve 12 in operation need not take place; it serves in the non-recurrent adjustment of the volume flow, and could also be replaced by a fixed throttle.

[0043] In the constructive implementation the working media used in an ORC system (thermodynamic cycle device based on the Organic Rankine Cycle) are normally hydrocarbons fluorinated in part or entirely (CFCs) (e.g. R134a, R245fa etc.). It is now necessary to find a lubricant which has good dissolving properties with respect to the CFCs in the cold state. To this end, oils from the synthetic ester group are suitable. Oils from the Reniso Triton SE/SEZ series by Fuchs may be cited here as product examples. As opposed to conventional refrigerant oils same are very well miscible with polar CFCs. No miscibility gap must occur in the range of the condensate temperatures (usually 0 to 60 C.) (see illustration 4, Fuchs Europe Schmierstoffe (Ed.): Product information RENISO TRITON SE 55. Mannheim: 2010). As a rule, temperature-independent miscibility gaps are observed with conventional refrigerant oils, with a phase separation undesirable for the method described taking place within certain concentration boundaries for each temperature.

[0044] In order to allow for the realization of the above-described effect of the oil discharge by means of frothing up, a sufficient amount of working medium has to be dissolved in the oil at a high pressure, while only little oil must be dissolved in the working medium at reduced pressure.

[0045] Illustration 5 (Fuchs. op. cit.) shows the dependency of viscosity and dissolved working substance on temperature and pressure. At higher pressures and a constant temperature more lubricant is dissolved in the working substance. At a constant pressure, with a rising temperature, the solubility of working substance in the oil is reduced. During the operation of the plant a certain amount of working substance is dissolved in the oil at a high pressure and a high temperature. After opening the bypass valve 81 in the shut-down process the pressure is reduced, a portion of the working medium evaporates leading to a temperature reduction. After the pressure drop some of the refrigerant is dissolved again in the residual amount of oil still present in the oil separator 10. This does not result in an increase of the viscosity, however. The isolines drawn in illustration 5 for concentrations and pressures as well as operating points should be regarded as exemplary.

[0046] Summarizing, the separation of oil from the high-pressure steam is advantageous as compared with the oil separation from the low-temperature steam, but especially the start-up of the cold oil cycle constitutes a problem. The method according to the invention permits the oil separator to be emptied when the ORC is stopped. The oil is discharged from the oil separator utilizing a solubility difference associated with a rapid pressure reduction. The oil flows to the condenser, respectively feed container. After having passed the evaporator it is separated in the oil separator as heated liquid oil and is available again to the lubricating circuit. A monitoring of the filling level of the oil separator permits a start-up of the machine after sufficient oil was separated.