Device for oil separation and removal from an organic working fluid

Abstract

Device for oil separation and removal from a working fluid of an organic Rankine cycle plant, said plant having at least a supply pump (6), at least a heat exchanger (1,16), an expansion turbine (5), a condenser (4), wherein the device is provided with a separator (2) and collection means (3), located between the evaporator (1) and the condenser (4) or between the evaporator (1) and a regenerator (16) of the organic Rankine cycle plant.

Claims

1. A system for oil separation and removal from a working fluid of an Organic Rankine Cycle plant, said system comprising an Organic Rankine Cycle plant and a device; wherein said plant comprising at least a supply pump (6), at least a heat exchanger (1,16), an expansion turbine (5), a condenser (4), and wherein said device comprises: a separator (2), and collection means (3), configured to be located between the evaporator (1) and a condenser (4) inlet or a regenerator (16) of the Organic Rankine Cycle plant, a bypass line (7) configured to fluid connect the evaporator (1) and the condenser (4) inlet, said separator (2) being located along the bypass line (7) that further includes a first valve (8) upstream of the separator (2) and a second valve (9) downstream of the separator (2) for isolating the bypass line (7) from the Organic Rankine Cycle plant, the device further comprises a third valve (10) which is located upstream of the collection means (3) for injecting air or nitrogen under pressure, coming from a tank (11), when it is necessary to perform the discharge of the collection means (3); and wherein said separator (2) comprises a cyclone (19) which, in turn, comprises a coalescent filter (20) located in a terminal part of said cyclone (19).

2. The system according to claim 1, wherein said bypass line (7) is configured so as to connect a portion (1) of the evaporator (1) in which is present the vapor phase of the working fluid and the condenser (4).

3. The system according to claim 1 wherein said first valve (8) is configured to continuously control a bypass flowrate in a range between 1/10000 and 1/1000 of the total plant flowrate.

4. The system according to claim 1 wherein said second valve (9) is configured to adjust the pressure on the bypass line.

5. The system according to claim 1 wherein a calibrated hole disc is configured to determine a bypass flowrate.

6. The system according to claim 1 wherein a capillary tube is configured to determine a bypass flowrate.

7. The system according to claim 1 further comprising a fourth valve (15) which is located between the separator (2) and the collection means (3), said fourth valve (15) being configured to isolate said collection means (3) so that the separator continues working while making the discharge of the collection means (3).

8. The system according to claim 1, wherein said device is assembled on a head of the evaporator (1) by fastening means.

9. The system according to claim 1 wherein said collection means (3) is configured to be welded on a evaporator (1) head, so as to allow an easy control of the collecting working fluid temperature.

10. The system according to claim 1 wherein said collection means (3) is a separate device that is autonomously heated.

11. The system according to claim 1, wherein said separator (2) is configured for fractional distillation and receive a mixture of oil and working fluid from a portion (1) of the evaporator in which is present a liquid phase of the working fluid.

12. A method for oil separation and removal from a working fluid of an Organic Rankine Cycle plant by means of the system according to claim 1, wherein said method is comprising the following steps: oil and working fluid inlet in the separator (2); oil separating from the working fluid in the separator (2), oil conveying inside the collection means (3); collection means (3) discharging, wherein said discharge phase of the collection means (3) takes place by opening the valve (10) for injecting air or nitrogen under pressure, which pushes the oil towards the drainage (14) of the collection means (3).

13. The method according to claim 12 where said step of oil separating from the working fluid in a vapor phase in the separator (2) is performed by means of a centrifugal or inertial effect.

14. The method according to claim 12 further comprising, at the end of the separating phase, a coalescence phase of the oil droplets by means of a coalescing filter (20) at a separator (2) outlet.

15. The method according to claim 12 where said step of oil separating from the working fluid in a liquid phase in the separator (2), is performed by means of a fractional distillation.

16. The method according to claim 12, wherein said discharging phase of the collection means (3) is performed isolating the bypass line (7) by closing the first valve and the second valve (8,9) and opening a valve (13) located on the drainage (14) of the collection means (3).

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The different embodiments of the invention will be now described, by means of non-limiting examples, with reference to the enclosed drawings, wherein:

(2) FIG. 1 shows the basic scheme of an ORC cycle.

(3) FIG. 2 is the scheme of FIG. 1 for a regenerative ORC cycle.

(4) FIG. 3 shows a by-pass device, located between the evaporator and the condenser of an ORC cycle, according to a first embodiment of the invention.

(5) FIG. 4 shows the by-pass device of FIG. 3, located between the evaporator and the regenerator of an ORC cycle.

(6) FIG. 5 shows the by-pass device located between the evaporator and the condenser of an ORC cycle, according to a further embodiment of the invention, with an intercepting valve of the separator.

(7) FIG. 6 shows the by-pass device of FIG. 5, located between the evaporator and the regenerator of an ORC cycle.

(8) FIG. 7 shows a scheme, according to which the device is heated by the evaporator conduction.

(9) FIG. 8 shows a further device scheme, wherein the separator is autonomously heated.

(10) FIG. 9 schematically shows the assembly of the device, wherein the separator is based on fractional distillation.

(11) FIG. 10 schematically shows a centrifugal separator, having a coalescent filter.

DETAILED DESCRIPTION

(12) A first embodiment of the invention is a device for oil removal from the working fluid in a vapor phase of an ORC cycle (FIG. 1). As known, an ORC plant comprises at least a supply pump 6, at least a heat exchanger 1, typically an evaporator, an expansion turbine 5, a condenser 4 and, eventually, a regenerator 16 (FIG. 2). The related thermodynamic cycle, the organic Rankine cycle, comprises a feeding phase of an organic working fluid in a liquid phase, by means of the supply pump; then a heating and vaporization phase of said working fluid, then an expansion phase, an eventual regeneration phase and a condenser phase of the same working fluid follow.

(13) Oil separation and removal from the working fluid in a vapor phase is realized by means of a device, which is located between the evaporator 1 and the condenser 4, or alternatively, between the evaporator 1 and the regenerator 16. Such a device (FIGS. 3, 4) comprises a separator 2, for example, a cyclone type or centrifugal type (FIG. 10), having at its end a coalescent filter 20, which must be kept heated, to avoid the condensation of the organic fluid in a vapor phase. Oil separation is a physical phenomenon, due to the different centrifugal forces acting on the ORC fluid in a vapor phase and on the oil in a liquid phase. After entering the separator 2, the bi-phase fluid is forced to a whirling path, during which oil droplets, subjected to a greater centrifugal force, are separated by the vapor flow of the ORC fluid and coalesce inside a suitable coalescent filter 20, until reaching dimensions able to provide a gravity fall in collection means 3. The flow path through the cyclone 19 will have change of directions, to facilitate (due to inertia too) the separation of the oil droplets from the vapor, which will go back into the working cycle.

(14) Collection means 3 are a tank receiving oil particles, separated from the vapor flow, and can be located in contact with a high temperature evaporator portion, for example on the evaporator 1 head (FIG. 7), being the evaporator a shell and tube heat exchanger. In particular, the device can be assembled as retrofitting for existing plants, by means of fastening means, for example grasps. Moreover, the device can be directly welded on the evaporator head. Alternatively, the device can be a separate device, autonomously heated, for example electrically, being this solution suitable to easily control the temperature of the collected fluid. The device also comprises a by-pass line 7, fluid connecting the evaporator with the condenser. Inside said by-pass line the separator 2 and collection means 3 are installed. Typically, through the by-pass line flows about 1/1000 of the total plant flow-rate. As said, the separated oil is collected into the tank 3 (collection means), from which, after a predetermined amount of time, the oil must be discharged. According to a preferred embodiment, the discharge of collection means 3 can be performed by isolating the plant by-pass, closing a first and a second valve 8 e 9 (respectively, downstream of the evaporator and upstream of the condenser) and opening a third valve 10. The latter valve 10 is located upstream of collection means 3 for allowing the injection of air or nitrogen under pressure, coming from a tank 11, said air or nitrogen pushing the liquid towards the drainage 14 of collection means.

(15) According to an alternative embodiment, the discharge of collection means 3 can be performed by gravity, opening the valve 13, located on the drainage 14 of collection means 3. According to this embodiment the tank 11 for air or nitrogen and the related valve 10 are not anymore needed.

(16) According to a different embodiment, a fourth valve 15 can be available between separator 2 and collection means 3 (FIGS. 5, 6), said valve isolating collection means from the plant, so that the separator continues working and in the meantime collection means can be discharged, according to pressure or gravity effect.

(17) The by-pass flow-rate is determined by adjusting the first valve 8, downstream of the evaporator 1. Typically, the flow-rate can be continuously adjusted in a range between 1/10000 e 1/1000. To improve machining feasibility, the valve can be replaced by a disc, having one or more calibrated holes, or by a capillary tube or by other chocking means. All these means define a not adjustable by-pass flow-rate. The by-pass line pressure is determined by adjusting the second valve 9, located upstream of the condenser 4 or the regenerator 16.

(18) As shown in FIG. 9, a further actuation of the invention is a device for oil removal from the working fluid in a liquid phase. Said embodiment differs from the previous one in the separator, which is now based on a fractional distillation. As known, fractional distillation can separate two or more substances. As for binary distillation, the mixture components are separated, based on their different volatility (or boiling temperature): in fact, in the highest portion of the distillation column (so called head) there is a greater concentration of the most volatile substances, while in the lowest portion (so called tail) there is a greater concentration of the less volatile substances. The distillation column is called fractioning column. The fractional distillation is based on a wide series of vaporizations-condensations, taking place in the device. The temperature profile in the column is characterized by higher temperature values close to boiler (where the mixture boils) and lower ones close to the condenser.

(19) The oil separation, being the working fluid in a liquid phase can not be realized on-line, requiring batch cycles in the limited volume of the separator 2, configured as a distillation column. Said volume is filled by liquid working fluid, by means of the valve 8, located through a pipe coming from the evaporator and containing liquid. The fluid, charged in the separator 2, is heated by means of heating elements (e.g. heat exchanger with thermal carrier fluid or electrical resistances). The high-boiling component (oil) is accumulated in the separator 2, which can be intercepted and discharged, after injecting air or nitrogen.

(20) Other than the embodiments of the invention, as above disclosed, it is to be understood that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.