EP4689366A1

EP4689366A1 - Device for continuous separation of oil in an organic rankine cycle plant

Info

Publication number: EP4689366A1
Application number: EP24718895.6A
Authority: EP
Inventors: Mario Gaia; Roberto Bini; Davide Colombo
Original assignee: Turboden SpA
Current assignee: Turboden SpA
Priority date: 2023-03-29
Filing date: 2024-03-25
Publication date: 2026-02-11
Also published as: IT202300006051A1; WO2024201269A1

Abstract

Device (20) for the continuous oil separation suitable for an organic Rankine cycle plant, equipped with: - a first line (2) in which a mixture of vapor from the organic working fluid and lubrication oil is present, - an oil separator (3), downstream of the first line (2) and in fluid communication with it, which separates the lubrication oil from the organic working fluid vapor, and - a discharge line (4) downstream of the oil separator (3), in which a first flow of vapor of the organic working fluid is present, which is deprived of the lubrication oil, - a second bleed line (6), in which there is a second flow of vapor of the organic working fluid, - an ejector (5) downstream and in fluid communication with the discharge line (4) and with the second bleed line (6), wherein the first vapor flow of the organic working fluid is the flow that the ejector (5) draws and the second vapor flow of the organic working fluid is the driving flow of the ejector (5), - a third line (7), downstream and in fluid communication with the ejector (5), in which there is a third vapor flow of the organic working fluid, the sum of the first and second vapor flows.

Description

DEVICE FOR CONTINUOUS SEPARATION OF OIL IN AN ORGANIC RANKINE CYCLE PLANT

DESCRIPTION

Technical sector of the invention

The present invention relates to a device for the continuous separation of oil in an organic Rankine cycle plant.

Background art

As is known, a thermodynamic cycle is defined as a finite succession of thermodynamic transformations (for example isotherms, isochores, isobars or adiabatics) at the end of which the plant returns to its initial state.

Such cycle can be direct, for example a direct Rankine cycle, in which a thermal source is used for the production of mechanical/electrical energy and heat at a temperature lower than that of the thermal source; the thermodynamic cycle can also be reversed, in which electrical/mechanical energy is used to transfer heat from a source at a lower temperature to one at a higher temperature.

In the case of direct cycles, an ideal Rankine cycle is a thermodynamic cycle composed of two adiabatic and two isobaric transformations . In the case of a direct cycle , its purpose is to trans form heat into work . This cycle is generally adopted especially in thermoelectric power plants for the production of electricity and uses water as a driving fluid, both in l iquid form and in the form of steam, with the so-called steam turbine .

More specifically, organic Rankine cycles ( ORC ) have been hypothesi zed and implemented which use high molecular mass organic fluids for the most di f ferent applications , in particular also for the exploitation of low-medium enthalpy thermal sources . As in other steam cycles , the plant 100 for an ORC cycle (with reference to figure 1 ) comprises one or more pumps 110 for feeding the organic working fluid, at least one heat exchanger 120 ( also called preheater or evaporator, depending on the function performed) to carry out the phases of preheating, vapori zation and possible overheating or heating in supercritical conditions of the same working fluid, a turbine 130 for the expansion of the fluid, mechanically connected to an electric generator 140 , a condenser 150 which returns the organic working fluid to the liquid state .

It is also known that in ORC cycles the use of organic fluids with high molecular mass very often involves the need to introduce downstream of the turbine and upstream of the condenser a further heat exchanger called "regenerator" 160 or "recuperator" which recovers a large portion of the sensible heat of the organic fluid vapor at low pressure , which heat is used to preheat the organic working fluid in liquid phase downstream of the cycle feeding pump and upstream of the preheater .

The cycle therefore comprises rotating means for the conversion o f the enthalpy of the working fluid into mechanical work, i . e . the turbine , and general ly also for the transport of the liquid fluid from the condenser to the heat exchange circuit with the hot source , i . e . the pump .

The ORC plant works with pressures di f ferent from the ambient one : to prevent contamination of the fluid in the environment , and vice versa, it is advisable to use rotating mechanical seals with the use of oil as a barrier between the internal environment and the external one of the components .

The contact area between the two components in relative mutual motion requires constant lubrication and conditions under pressure to guarantee perfect functioning and durability, as in fact , it limits a wear due to a direct contact between the two parts . In these plants there is a control unit that supplies the sealing means with pressuri zed oil . This control unit must have a signi ficant oil accumulation volume , typically 100-300 1/MW of electrical power, to comply with the lubrication of the sealing means and bearings of the turbine ( s ) .

The rotating seals are subj ect to physiological oil losses and, in some cases , even more serious losses can occur due to mechanical failure of the seal , due to technical problems , for example to thermal or mechanical overloads . The physiological losses in an ORC plant of several MW can range from a few deciliters per day in plants with excellent sealing, up to 1 liter per day, but there may be plants with particularly worn seals which introduce even a few liters per day of lubricating oil into the plant .

To limit and minimi ze the oil entry into the plant , the existence of "physical" oil separation plants is known, such as rotating rings , also called "oil throwers" , which once inserted inside the seal throw the oil towards the side wall of the seal itsel f , so facilitating its collection .

Another system could be to provide labyrinths between the rotating part and the fixed part of the seal , in order to channel the flow in a tortuous path in which the oil particles are forced to hit the walls of the labyrinth itsel f , changing many times their direction, so facilitating the oil accumulation on the outer walls of the labyrinth, for easier recovery .

In any case , such plants cannot guarantee the complete separation of the two flows .

In cases in which the oil is at a pressure higher than the operating pressure of the process , the oil flows inside the ORC plant and mixes with the working fluid, so altering its characteristics ; once it enters the plant , due to the drag caused by the motion of the working fluid, the lubricating oil could be found in any duct , typically either in atomi zed form along the walls of the tubes in which the speed of the working fluid is high, or in the liquid phase mixed with the working fluid itsel f where the speeds are low ( for example , in correspondence with sudden increases in section in collectors or vessels ) .

The consequences of this mixing are essentially : the variation of the thermodynamic characteristics of the organic working fluid, which minimally mixes with oil and varies its thermodynamic quantities , including its condensation pressure , as well as , and also signi ficantly, the points of the thermodynamic cycle ;

- the variation in the composition of the organic working fluid and the increase in the global flow rate ( sum of those of the ORC fluid and the oil ) : in the plant there will be consequences on the heat exchange coef ficients and on the cycle pressure to the detriment of the ef ficiency . Furthermore , a fluid will be processed in the turbine which does not exchange momentum with the turbine itsel f and does not generate power like the organic working fluid;

- in less favorable situations , oil can also concentrate in areas which are not easily drainable , escaping the action of an in line separator, or, especially in plants operating at high temperatures , it could undergo cracking forming compounds which are deposited on the surfaces of exchange by increasing its thermal resistance , or on the turbine blades . This phenomenon is known as a fouling, or a deposit of cracked oil films . In particular, in relatively small expanders this phenomenon can reduce the passage area of the working fluid by up to 20% ;

- furthermore , the presence of a solid deposit , although of minimal thickness , on the turbine blades inevitably alters their geometry, which gradually presents a shape that is increasingly different from the one according to the design, which was thought in order to maximize the exchange of quantities of motion with the vapor of the working fluid.

These deposits, created by oil escaping the action of an in line separator, can hardly be removed without invasive interventions that lead to a plant shutdown .

It has been verified in practice that the efficiency performance of an ORC plant drops by up to 10% compared to the maximum efficiency, with a significant percentage (up to approximately 10%) of oil circulating in the plant, compared to the flow rate of the working fluid.

There is therefore a first need to separate and remove oil from the working fluid inside the plant, in order to guarantee optimal efficiency of the plant over time.

European patent EP3055518 of the undersigned presents a solution to the problem here described, by describing an "in line" device, i.e. an oil separator 170 (as indicated in figure 1) which operates by separating the oil by taking and separating a flow rate at a point in the plant - which can be along the bypass line 180 between a portion of the evaporator 120 and the condenser 150 ( or, as in the case illustrated in figure 1 , the regenerator 160 ) - without necessarily having to shutdown the plant .

It is clear, however, that it is not suf ficient j ust to provide solutions that implement the separation of oi l once it enters the plant , in order to solve the problems related to its coexistence with the working fluid, but it is also essential to evaluate the position in which the separator itsel f must be inserted .

In the current state of the art , the entry of oil into the plant is allowed by accepting to separate it with " in line" solutions in points with pressure signi ficantly higher than the condensation pressure ( for example , on a special bypass line by withdrawing the mixture at the vapori zation pressure which is reached downstream of the evaporator 120 ) , in order to then rej oin the plant in areas with lower pressure , thus allowing the outflow . Normally the oil separator is inserted between the evaporator and the regenerator or condenser : the flow rate used to separate the oil therefore bypasses the turbine and rej oins the condenser . Although the plant correctly separates the lubricating oil from the working fluid, solving the problem described so far, this " in line" separation entails two disadvantages :

- the bleed flow rate does not contribute to the production of mechanical power in the turbine ;

- oil is allowed to flow into all the components of the plant as it is not separated at its inlet , i . e . in the area highlighted with the reference 190 near the bearings and seals of the turbine 130 , or the shaft of the turbine itsel f .

By operating in this way, while separating the oil , portions of the plant occur in which the oil itsel f circulates together with the working fluid before being separated . These are remarkable portions of the plant : the working fluid in the vapor and oil phase from the turbine 130 to the regenerator 160 and then to the condenser 150 ; then the working fluid in the liquid phase and oil from the condenser 150 to the pump 110 , then back to the regenerator 160 and the evaporator 120 . Only at the exit from the evaporator this mixture is able to arrive through the bypass line 180 up to the oil separator 170 . Therefore , the oil passes in particular through all heat exchangers , resulting in thermal and pressure stress . Regardless of where the mixture is taken, the separation system still acts on a small bypass f low rate and therefore it does not exclude the lubricating oil from remaining in circulation for a long time .

In plants operating at particularly high temperatures , oil can deteriorate forming solid compounds which, by depositing on the walls of the exchanger, af fect its performance .

There is therefore a further need, namely that of separating and removing oil from the working fluid inside the plant , at the moment in which the oil itsel f is introduced into circulation ( reference 190 , near the turbine 130 ) , in order to guarantee the correct functioning and high overall performance of the ORC plant over time .

This further technical problem cannot be solved with " in line" devices which process a small flow rate in bypass conditions according to known technique : in fact , the point of entry of the lubricating oil into the plant is inevitably at the seal of the turbine , connected to the shaft , in the area of low-pressure stages . This is an unfavorable area for the insertion of an oil separation device , as this area is at a pressure very close to that of condensation : the insertion of an oil separator in this area, which would be at the same time most suitable for the separation of the oil itsel f as it would avoid its flowing into the other components of the plant , is complicated by the lack of driving force ( i . e . a suf ficient pressure drop ) to generate the flow rate to be processed, as the pressure in this area, already very close to the condensation pressure , would be further lowered by the presence of the oil separator 170 (which introduces an although minimal load loss ) and above all by the presence of the piping and the valves for conduction and regulation of this bleeding into the oil separator 170 and from there to the plant .

Summary of the invention

The solution of all the technical problems referred to in the previous paragraph is obtained, according to the present invention, with a device for the continuous separation of oil in an organic Rankine cycle plant , comprising an oil separator and an ej ector, downstream of the expansion turbine .

The present solution allows the flow of working fluid and oil to be separated so the driving force can rej oin the turbine discharge , allowing the continuous separation of oil near its entry into the plant , preventing the problems that this entry would otherwise cause .

According to one aspect of the present invention, a device for the continuous separation of oil in an organic Rankine cycle plant is therefore described, having the characteristics set out in the independent product claim attached to the present description .

Further preferred and/or particularly advantageous embodiments of the aforementioned plant are described according to the characteristics set out in the attached dependent claims .

Brief description of the drawings

The invention will now be described with reference to the attached drawings , which illustrate some non-limiting exemplary embodiments of a regenerator for ORC plants , in which :

- figure 1 schematically illustrates an ORC plant with oil separator, according to the known technique ,

- figure 2 schematically illustrates a device for continuous oil separation in an organic Rankine cycle plant , according to a first and preferred embodiment of the present invention,

- figure 3 illustrates a diagram of an ej ector of the device of figure 2 , and figure 4 illustrates a diagram of the oil separator of the device of figure 2 .

Detailed description

With reference to figure 2 , a known turbine 1 of an ORC plant , which is also known and for which reference will continue to be made to figure 1 , is schemati zed together with an admission line 9 of the saturated or overheated vapor of the working organic fluid, coming from a heat exchanger ( known and therefore not shown in figure 2 , but still illustrated in figure 1 ) and to a discharge line 10 of the expanded vapor of the working fluid which leads it to the regenerator or, directly, to the condenser (both known and therefore not shown in figure 2 , but still illustrated in figure 1 ) .

According to the present invention, the device 20 for continuous oil separation in an organic Rankine cycle plant comprises :

- a first line 2 , exiting from the area of the turbine shaft , or downstream of a seal 8 of the turbine 1 and in fluid communication with it . In the first line 2 , all oil flow rate entering the plant flows through the sealing means 8 , positioned on the low pressure of the turbine 1 . Therefore , in this first line 2 there is a mixture of vapor of the working fluid and lubricating oil . By means of an ej ector 5 , as will be seen, a depression zone is created with respect to the turbine discharge pressure , which draws this flow rate right through the first line 2 and leads it inside an oil separator 3;

- a second line 6 for bleeding a vapor flow of the working fluid, the flow rate of which has a value between 0.1% and 0.2% of the total flow rate at the turbine inlet (i.e. through the admission line 9) , which acts as the "driving force" of the ejector 5 for the creation of a low-pressure area at the discharge of one of its convergent-divergent nozzles. The withdrawal point of this flow 6 is the result of an optimization between the lower pressure level available, which is sufficient for the operation of the ejector, and the maximum flow rate that can be bled (which influences the diameter of this duct) . Theoretically, the smaller the pressure drop created by the ejector, the greater its efficiency; the smaller its drop, however, the greater the flow rate necessary for the same useful effect, therefore the greater the sizing of the ejector plant will be;

- an oil separator 3, preferably coalescing, in fluid communication with the first line 2. Inside the separator (also with reference to figure 4) the flow of working fluid, contaminated by oil, enters through a nozzle 41. A first oil separation occurs as a result of the sudden drop in flow speed due to the great difference in section between the inlet nozzle 41 and a calm zone 40 at the separator inlet ; a second separation occurs due to the change in flow direction, and to a minimal extent , a separation occurs due to collision of the same with the walls 42 near the inlet . The separated oil is collected in the lower portion of the separator, whereas the working fluid in the gaseous state continues through the duct 43 which connects the inlet 41 with the outlet 45 by means of a coalescing filter 44 . The drops of oil collected by the filter membrane descend by gravity, accumulate in the lower portion of the filter and from here pass into a drainage line 11 , through which, optionally, they can return to the lubrication circuit of the turbine 1 . The puri fied flow is instead expelled from the outlet noz zle 45 . Advantageously, the oil separator 3 is heated with a thermal blanket or other heating means , to avoid condensation of the working fluid, which must remain in the gaseous state ;

- downstream of the oil separator 3 , a discharge line 4 leads to the ej ector 5 , to which two vapor flows of the working fluid are connected : a first low pressure flow, the one exiting the separator which runs along the discharge line 4 and a second flow at higher pressure which derives from the bleeding of overheated and pressuri zed working fluid from an intermediate turbine stage 1 and which flows along the second bleed line 6 ; the line 4 is conveniently equipped with a non-return valve 46 , to prevent the flow from returning to the separator 3 , should transitory conditions allow this to occur ;

- the ej ector 5 which, as is known, is a static compressor that exploits the Venturi ef fect produced by a convergent-divergent noz zle , to convert the energy given by a high-pressure driving fluid into an increase in its speed, so that it can draw in a second fluid, mixing it with the driving fluid, and compress it so that when it comes out of the ej ector this second fluid has a pressure greater than the suction pressure . For convenience , the innovative characteristics o f the ej ector 5 are described below; finally, a third line 7 downstream of the ej ector 5 brings the overall vapor flow, which is the sum of the flows coming from the bleeding from the turbine and from the oil separator 3 , back to the l ine 10 which from the turbine brings the vapor of the working fluid either to the regenerator or to the condenser .

By way of example , the pressures in the di f ferent lines under design conditions could be :

- line 6 : 10 bar - turbine outlet, start of line 2: 1 bar

- discharge line 4, ejector inlet: 0,7 bar

- start of line 7: 1,3 bar

The head necessary for the flow of the exhaust line 4 to return to the turbine discharge is generated by the ejector 5.

In an ideal plant, the overall oil flow rate entering the seal is conveyed from the first line 2, exiting the sealing means 8 of the turbine 1, to the oil separator 3. However, it is not certain, in some plant configurations, that the overall oil of the seals which contaminates the working fluid will be intercepted by the plant according to the present invention. In this case, it will be accepted to allow a small percentage of lubrication oil into the plant, then separating it with an appropriate in line separator, for example with the plant described in the writer's European patent already previously cite. Also in this case, however, the advantages described here would not be lost, as the flow rate of oil entering the plant would still be minimal, compared to a scenario with the same boundary conditions but without any ejector.

The low-pressure flow (for example, 0,7 bar) , after passing through the separator 3, enters the ejector 5 together with the flow coming from the bleeding of a high-pressure zone of the turbine 1 (for example 10 bar) .

The flow of the third line 7, which is at a higher temperature than the condenser 150, can conveniently be used to heat the separator 3, maintaining it at a temperature sufficient to avoid the condensation of the working fluid inside it.

With reference to figure 3, the ejector includes:

- a first entry section 4e of the working fluid flow at lower pressure, for example 0.7 bar. In practice, the first section 4e constitutes the terminal portion of the discharge line 4 which conveys the first vapor flow of the working fluid from the outlet of the oil separator 3 to the ejector 5;

- a second entry section 6e of the working fluid flow at higher pressure, for example 10 bar. This second section 6e constitutes the terminal portion of the second line 6, the one which conveys the second vapor flow of the working fluid, bled at an intermediate stage of the turbine 1;

- a nozzle 31 which is affected only by the second flow of the second inlet section 6e . This flow, in the nozzle 31, converts its pressure energy into kinetic energy, creating downstream of the same a region with high-speed motion, with a Mach number greater than 1 and a turbulent regime , so favoring its mixing . The noz zle 31 can take on the convergent- divergent shape should pressure drops be used which are higher than the critical one : in the exemplary case , in fact , the pressure in the second section 6e is much higher than the pressure in the first section 4e , at least ten times higher . For the correct functioning of the ej ector 5 , downstream of the noz zle , where the flows of the first section 4e and the second section 6e rej oin, an area with lower pressure must be created, compared to the pressure in the first section 4e , therefore the pressure drop with which the noz zle 31 must be operated is much greater than the critical one . The noz zle 31 in the convergent-divergent shape allows the critical pressure ratio to be overcome and the fluid, downstream of the noz zle , to reach a pressure lower than that of the first section 4e ;

- a third section 32 , substantially cylindrical and almost isobaric except for pressure losses , having the function of mixing and exchanging the momentum between the flows coming from the first section 4e and the second section 6e which essentially form a third vapor flow, which is the sum of the first and vapor steam flows ,

- a fourth divergent section 33 , which provides for the reconversion of kinetic energy into pressure energy, so that the third vapor flow of the working fluid arrives at the outlet 7e of the ej ector 5e , therefore at the third line 7 , with a pressure greater than the condensation pressure . In this way, the flow exiting the ej ector 5 , through the third line 7 , will be able to rej oin the flow of expanded vapor from the exhaust line 10 from the turbine 1 .

The device 20 for the continuous oil separation, according to the present invention, entails the following advantages :

- being separated immediately downstream of the turbine , the oil is not af fected by the thermal and pressure stress which it undergoes in the heat exchangers ; therefore , it does not deteriorate and does not form compounds harmful to the proper functioning of the ORC plant ;

- in practice , the oil does not enter almost at all into the ORC plant and, therefore , does not influence the thermodynamic cycle ;

- the oil , not undergoing any thermal stress , once separated can be recovered by returning it directly to the lubrication circuit of the ORC plant ; the high-pressure flow rate is not bled upstream of the f irst stage of the turbine , but in an intermediate region of the expansion and, therefore , after having already partially contributed to the generation of power in the turbine .

The device 20 according to the present invention can therefore conveniently be used in an organic Rankine cycle plant , for example like the one illustrated in figure 1 , comprising at least one feed pump, at least one heat exchanger, at least one expansion turbine and at least one condenser . Advantageously, the ORC plant can also be equipped with a regenerator .

The device according to the present invention can also be conveniently used in points di f ferent from the one previously described (downstream of the turbine ) . For example , the ej ector can also draw from other low-pressure points of the plant in which there may be a mixture of working fluid and lubricating oil : speed reducers communicating with the turbine through labyrinth seals , lubrication control units , etc .

In particular, in plants with turbines , the seal in the turbine may not be obtained mechanically but instead can be provided with labyrinths . Even in this variant , the solution of the device 20 for the continuous oil separation including the ej ector, as previously described, remains valid in all its elements . The only change is the suction point , which will no longer be in correspondence with the turbine shaft but near the lubrication control unit . In this case it is the working fluid, which is normally at a higher pressure than the oil , which overcomes the labyrinth and contaminates the oil , contrary to what happens in the previously described case . The function of the separation and of the ej ector, although being physically the same , in this application has the function of recovering the working fluid which would otherwise remain in the lubrication control unit .

Similarly to the use of the ej ector, a compressor could be used for the same purpose . The ej ector, however, unlike the compressor, has the notable advantage of being a static component and not needing any mechanical sealing, regulation or supply . Furthermore , due to the working conditions considered, the compressor should be placed in positions which are di f ficult to access , making the maintenance activities complicated . The advantages of the ej ector therefore appear evident : it is smaller in si ze than the compressor, is a static component and therefore is more reliable and cheaper . In addition to the embodiments of the invention as described above , it should be understood that numerous further variations exist . It must also be understood that said methods of implementation are only illustrative and do not limit neither the obj ect of the invention, nor its applications , nor its possible configurations . On the contrary, although the above description makes it possible for the skilled man to implement the present invention at least according to one of its exemplary configurations , it must be understood that numerous variations of the described components are conceivable , without thereby departing from the obj ect of the invention, as defined in the attached claims .

Claims

1. Device (20) for the continuous separation of oil suitable for an organic Rankine cycle plant, in which

- the plant is operated by an organic working fluid, and

- the plant comprises at least one turbine (1) , provided with low pressure sealing means (8) and with a first discharge line (10) of expanded vapor of the working organic fluid, the device (20) comprising:

- a first line (2) , downstream of the sealing means (8) of the turbine (1) and in fluid communication with it, in which there is a mixture of steam from the organic working fluid and turbine lubrication oil (1) ,

- an oil separator (3) , downstream of the first line (2) and in fluid communication with it, which separates the lubricating oil from the vapor flow of the organic working fluid, and

- a second discharge line (4) downstream of the oil separator (3) and in fluid communication with it, in which there is a first flow of vapor of the organic working fluid, deprived of the lubricating oil, the device (20) being characterized in that it is positioned downstream of the turbine (1) , and in that the device (20) comprises:

- a second bleed line (6) , in which there is a second flow of vapor of the organic working fluid, bled from an intermediate stage of the turbine (1) and at a higher pressure than the pressure of the first flow of vapor of the organic fluid work, an ejector (5) downstream and in fluid communication with the second discharge line (4) and with the second bleed line (6) , wherein the first vapor flow of the organic working fluid is the flow that the ejector (5) draws in and the second vapor stream of the working organic fluid is the driving stream of the ejector (5) , a third line (7) , downstream and in fluid communication with the ejector (5) , in which there is a third vapor flow of the organic working fluid, the sum of the first and second vapor flows, and in wherein the third line (7) is also in fluid communication with the first discharge line (10) of the vapor expanded in the turbine (1) .

2. Device (20) according to claim 1, wherein the ejector (5) comprises:

- a first inlet section (4e) for the first vapor flow of the organic working fluid, - a second inlet section (6e) for the second vapor flow of the organic working fluid,

- a nozzle (31) in fluid communication with the second section (6e) , in which the second vapor stream of the organic working fluid increases its kinetic energy, reducing its pressure energy, a third section (32) , substantially cylindrical and almost isobaric, configured so that the first vapor flow and the second vapor flow mix, generating the third vapor flow of the organic working fluid, the sum of the first and second flows of vapor,

- a fourth section (33) , diverging, configured so that the third vapor flow of the organic working fluid reduces its kinetic energy and increases its pressure energy until it reaches a pressure higher than the condensation pressure of the vapor expanded in the turbine (1) .

3. Device (20) according to claim 1 or 2, wherein the oil separator (3) is coalescing.

4. Device (20) according to claim 3, wherein the oil separator (3) comprises:

- an inlet nozzle (41) in fluid communication with the first line (2) ,

- an inlet calm zone (40) of the oil separator (3) , in which a first separation of the lubricating oil from the vapor of the organic working fluid takes place,

- a duct (43) comprising a coalescing filter (44) , on the membrane of which the lubricating oil is collected,

- an outlet (45) in fluid communication with the second discharge line (4) ,

- a drainage line (11) for the lubricating oil.

5. Device (20) according to claim 3, wherein the oil separator (3) comprises a thermal blanket which prevents the vapor condensation of the organic working fluid .

6. Device (20) according to claim 3, wherein the third stream of vapor of the working organic fluid of the third line (7) is used to heat the separator (3) , preventing the condensation of the vapor of the working organic fluid.

7. Device (20) according to any of the preceding claims, wherein the second discharge line (4) is provided with a non-return valve (46) .

8. Device (20) according to any of the preceding claims, wherein the second vapor flow of the organic working fluid, bled from an intermediate stage of the turbine (1) has a weight flow rate ranging between 0.1% and 0, 2% of the total weight flow rate of vapor entering the turbine (1) .

9. Organic Rankine cycle system comprising at least one feed pump, at least one heat exchanger, at least one expansion turbine and at least one condenser, characterized in that it is provided with a device (20) for the continuous separation of oil, according to any of the preceding claims.

10. System according to the preceding claim, further comprising a recuperator.