Fluid separator for a displacement machine and a method for separating lubricant and working fluid in a displacement machine

Abstract

A displacement machine is for acting on a working fluid and is provided with a lubricant and working fluid separator. The fluid separator has a separator volume constrained by a shielding member, a first fluid channel providing fluid communication between a first and second inner volumes and the separator volume, a second fluid channel providing fluid communication between the separator volume and a working fluid return volume. The fluid separator, the first fluid channel and the second fluid channel are fully contained within a full volume of the displacement machine. A method is for separating lubricant and working fluid in a displacement machine.

Claims

1. A displacement machine arranged for acting on and expanding a working fluid in an organic Rankine cycle system, and being provided with a lubricant and working fluid separator, the displacement machine further comprising a displacer housing, a displacer arrangement displaceable within the displacer housing, a working chamber upon which the displacer arrangement acts to change its volume, at least one inner volume arranged for containing a lubricant and a working fluid, working fluid ports providing fluid communication between at least one volume external to the displacement machine and the working chamber, and a leakage path formed between the displacer arrangement and the displacer housing, wherein the fluid separator comprises a separator volume constrained by a shielding member, a first fluid channel providing fluid communication between the at least one inner volume and the separator volume, a second fluid channel providing fluid communication between the separator volume and a working fluid return volume, and wherein the fluid separator, the first fluid channel and the second fluid channel are fully contained within a volume defined by an outer boundary and completely sealed off from the environment wherein the displacement machine is geometrically fully constrained.

2. The displacement machine according to claim 1, wherein the at least one inner volume comprises a first inner volume and a second inner volume, and wherein the first inner volume is freely communicating with the second inner volume.

3. The displacement machine according to claim 1, wherein the shielding member is a baffle shielding a working fluid exit in the fluid separator.

4. The displacement machine according to claim 1, wherein the shielding member is a housing shielding a working fluid exit in the fluid separator.

5. The displacement machine according to claim 1, wherein the separator volume is defined in a housing containing a coalescence promoting material.

6. The displacement machine according to claim 1, wherein a working fluid exit in the fluid separator is provided with a valve arrangement arranged to prevent backflow or backpressure from the exhaust port propagating into the separator volume.

7. The displacement machine according to claim 6, wherein the fluid separator valve arrangement is a reed valve arrangement.

8. The displacement machine according to claim 1, wherein a fluid mixture inlet path into the separator volume and a lubricant return path into an appropriate lubricant return volume are provided in the first fluid channel.

9. The displacement machine according to claim 1, wherein the second fluid channel is extending in a sealed manner into the working fluid return volume through a bore in a cylinder head.

10. The displacement machine according to claim 1, wherein the second fluid channel is arranged in a cylinder head cover and is defined by a cover and a return pipe extending in a sealed manner from the cover into the working fluid return volume through a bore in a cylinder head.

11. The displacement machine according to claim 1, wherein the working fluid return volume is inside an exhaust port of an expander or a suction port of a compressor.

12. A displacement machine arranged for acting on and compressing a working fluid in a vapor compression heat pump system, and being provided with a lubricant and working fluid separator, the displacement machine further comprising a displacer housing, a displacer arrangement displaceable within the displacer housing, a working chamber upon which the displacer arrangement acts to change its volume, at least one inner volume arranged for containing a lubricant and a working fluid, working fluid ports providing fluid communication between at least one volume external to the displacement machine and the working chamber, and a leakage path formed between the displacer arrangement and the displacer housing, wherein the fluid separator comprises a separator volume constrained by a shielding member, a first fluid channel providing fluid communication between the at least one inner volume and the separator volume, a second fluid channel providing fluid communication between the separator volume and a working fluid return volume, and wherein the fluid separator, the first fluid channel and the second fluid channel are fully contained within a volume defined by an outer boundary and completely sealed off from the environment wherein the displacement machine is geometrically fully constrained.

13. The displacement machine of claim 1, wherein the at least one inner volume is evacuated of air.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following is described examples of preferred embodiments illustrated in the accompanying drawings, wherein:

(2) FIG. 1 shows a displacement machine in the form of a piston expander, with a fluid separator integrated within the displacement machine housing and specifically within the cylinder head;

(3) FIG. 2 shows the same displacement machine as in FIG. 1, wherein a coalescence promoting material is inserted into the fluid separator;

(4) FIG. 3 shows the same displacement machine as in FIG. 1, wherein a simplified separator is installed;

(5) FIG. 4 shows a simplified flow schematic of an organic Rankine cycle, with its most essential components; and

(6) FIG. 5 shows a simplified flow schematic of an organic Rankine cycle, where the expander is in the form of a piston expander.

DETAILED DESCRIPTION OF THE DRAWINGS

(7) For the following description, we first turn the attention to FIGS. 1 and 5. A fluid separator 10 is integrated within a displacement machine 1, here shown in the form of an expander of the piston type. The expander 1 is part of an organic Rankine cycle (ORC) system 100 (see FIG. 5). The expander 1 is illustrated on FIG. 1 with a certain level of detail. It should be noted that the invention is not specific to an expander of the piston type for an ORC system, as it applies to any type of system using any type of displacement machine that uses a working fluid and a lubricant.

(8) An evaporator 103 (see FIG. 5) provides working fluid in the form of superheated vapour at high temperature and high pressure to the expander 1 through a first fluid line 109a. The expander 1 expands the vapour from high pressure to low pressure, thus generating work, and then exhausts the expanded vapour into a condenser 104 through a second fluid line 109b.

(9) There may also exist a recuperator in the ORC system, but this is not shown, as it has no particular importance to the description of the invention.

(10) Downstream of the condenser 104 there is a working fluid reservoir 101 connected to the condenser 104 through a third fluid line 109c, the fluid reservoir 101 for example in the form of a closed tank, which serves as a buffer for working fluid primarily in the liquid phase, i.e. after it has been condensed. From the working fluid reservoir 101, a pump 102 draws liquid working fluid through a fourth fluid line 109d, and increases the working fluid's pressure, as it is fed into the evaporator 103 through a fifth fluid line 109e. The working fluid is then heated, evaporated and superheated in the evaporator, as this completes the full organic Rankine cycle. The fluid lines 109a-109e are typically in the form of pipes or hoses. The ORC system 100 encompasses further devices (for example electrics and a housing) external to the expander 1, but are not mentioned here for relevance reasons.

(11) Looking again at FIG. 1, the piston expander 1 is assumed to consist of conventional main components such as a crankcase 4, a cylinder head 2, a valve cover 3 and a lubricant reservoir in the form of an oil sump 6. The main components 2, 3, 4, 6 all have an outer boundary 99 with respect to the environment, for example outer surfaces in contact with the environment and/or interfaces such as the openings of an inlet port 21 and an outlet/exhaust port 25. Together, these boundaries define a full outer boundary for the expander 1, and thus define the full volume 9 of the expander.

(12) Within the expander 1, there are additional components, arrangements and sections such as a piston arrangement 40 comprised by a piston 41 and piston rings 42, a connecting rod 43, a crankshaft 44 and a cylinder 45. The cylinder head 2 contains at least one inlet valve 22 and at least one exhaust valve 26, as well as the fluid separator 10. The inlet valve 22 may be of any type suitable for the application, such as a poppet, rotary, slide or disk valve, and is therefore not illustrated as a particular type on the figures. The exhaust valve 26 is shown on the figures as a poppet valve, however, the exhaust valve may also be of any suitable type.

(13) Immediately above the piston 41, a working chamber 5 is defined. The lubricant reservoir (oil sump) 6 contains lubricant 61 and a lubricant heater 69, which serves to boil off working fluid that has been mixed into the lubricant.

(14) First and second inner volumes 90a, 90b are defined as inner cavities in the cylinder head 2 and the crankcase 4 respectively. It should be noted that on FIGS. 1-3, a portion of the first inner volume 90a shown on the left hand side in the cylinder head 2 is in free communication with a portion of the first inner volume 90a shown on the right hand side. Further, a passage 90c provides free communication in the form of a free flow path 90d for fluids between the first and the second inner volumes 90a, 90b. Thus, the inner volumes 90a, 90b of the expander 1 can be seen as one united inner volume in terms of fluids occupying these spaces, as the fluids are free to flow between either one. The passage 90c is typically present due to the space required for a valve drivetrain (not shown) connecting the crankshaft 44 to a valve actuating system (also not shown).

(15) At the same time, it should be noted that the exhaust port 25, which in FIGS. 1-3 is indicated to be on either side of the passage 90c, is also free from obstruction between the left and right hand sides of the passage 90c, as the passage 90c doesn't directly interfere with the exhaust port 25 itself. On the figures, the passage 90c shall be perceived as being in front of the port 25.

(16) In the following, FIGS. 1 and 5 are most relevant. Superheated vapour enters the expander 1 through the inlet port 21, wherein the inlet valve 22 controls the admission of working fluid into the working chamber 5. Together, the inlet port 21 and the inlet valve 22 provide a first, selectably open working fluid path 23 for the working fluid to enter the working chamber 5.

(17) As the working fluid is admitted into the working chamber 5 at a higher pressure than the pressure of the inner volumes 90a, 90b, some working fluid may, and in most cases will, leak past a small gap formed between the piston arrangement 40 and the cylinder 45, as there is a small sealing gap between them. This sealing gap provides a leakage path 49 for the working fluid, which escapes from the working chamber 5 and past the piston 41. This leakage is often referred to as blow-by within some industries. The amount of working fluid that is subject to blow-by will then end up in the second inner volume 90b of the expander.

(18) Due to that many valve types are not perfectly sealed, a small leakage path 29 may also be present in conjunction with the inlet valve 22, which may result in some working fluid typically also leaking into the first inner volume 90a of the expander 1. Likewise, a leakage path (not shown) may also be present in conjunction with the exhaust valve 26 and its corresponding valve actuation devices (not shown). A person skilled in the art would know how these devices are implemented, and they are therefore not shown on the figures.

(19) At some point, the working fluid that is present in the inner volumes 90a, 90b of the expander 1 may start to mix into the lubricant 61. When this happens to a large extent, the viscosity of the lubricant/working fluid mixture may decrease (i.e. diluted lubricant), and if the viscosity becomes too low, this will impair the quality of the expander lubrication.

(20) There are devices present, such as an oil pump (not shown) and lubricant distribution channels (not shown), to ensure proper lubrication of all regions in the expander 1 that need lubrication. An oil pump (not shown) draws lubricant/oil 61 from the oil sump 6 and distributes it to the respective regions. While some of the lubricant 61 is present in the oil sump 6, there will also be some lubricant 61 in other areas of the expander covering most inner surfaces in communication with the inner volumes 90a, 90b. Wherever there are lower temperatures, typically in lower sections (with respect to gravity) of the expander 1, chances are that the proportion of working fluid, which is mixed into the lubricant 61 is at the highest. This especially applies to the oil sump 6, and therefore a heater 69 may be added in order to boil off working fluid mixed with the oil 61 in here. This helps in maintaining a higher viscosity of the lubricant 61.

(21) As more and more working fluid would accumulate in the inner volumes 90a, 90b due to the potential leakages described above, the pressure would rise, and thus more working fluid would be mixed with the oil. It would then come to a point at which the lubricant properties would cause an undesired, more rapid wear of the expander. One purpose of the fluid separator 10 is therefore to satisfactorily return working fluid to a section of the ORC system 100 wherein it primarily belongs, e.g. to the condenser 104 ultimately.

(22) In the embodiment according to FIGS. 1 and 2, the fluid separator 10 comprises a shielding member in the form of a housing 10a, wherein a separator volume 11 is defined. A first fluid channel 12, which may be comprised by one or more physical channels (as shown on FIGS. 1 and 2) defines at least one fluid mixture inlet path 13, wherein a mixture of working fluid and lubricant primarily in the form of droplets, is admitted. A second fluid channel 14 formed in a cavity 39 in the valve cover 3 and defined by a fluid channel cover 14a connects the separator volume 11 to a working fluid return volume 15 via a return pipe 20 which is extending from the fluid channel cover 14a into a bore 20a in the cylinder head 2, the working fluid return volume 15 being part of the exhaust port 25. A seal 20b is provided between the return pipe 20 and the bore 20a. The second fluid channel 14 thus allows for working fluid to be returned to the condenser via the exhaust port, thus providing a working fluid return path 16 as shown on FIGS. 1, 2 and 3. If needed, a third fluid channel 17 may be provided, to make for a lubricant return path 19 into an appropriate lubricant return volume 18, which can typically be a more or less arbitrary but suitable section of the inner volumes 90a, 90b.

(23) On FIG. 1, a large fraction of the lubricant 61 will, as it enters the separator volume 11, fall down due to gravity, and return to the first inner volume 90a through the third fluid channel 17. The working fluid, being generally in its gaseous phase, will continue and escape the separator volume 11 through a working fluid exit 31 prior to a valve arrangement 30, here provided as a reed valve arrangement. The valve arrangement 30 prevents pressure pulses in the exhaust system or the inner volumes 90a, 90b of the expander 1 to cause backflow of working fluid from the exhaust port 25. After the reed valve arrangement 30, and due to pressure differences, the working fluid is forced into the exhaust port 25, in which it joins and mixes with working fluid being exhausted from the working chamber 5.

(24) Thanks to the invention, the fluids are separated and routed entirely within the full volume 9 of the expander. No external connections are needed between the separator 10 and devices placed externally from the expander 1. This eliminates several possible leakage points, as the need for external pipes, connections and fittings are eliminated altogether.

(25) It should be noted that in a simple construction the first fluid channel 12, through which the fluid mixture enters the separator volume 11, may be mutually used as a lubricant return channel, since the lubricant is meant to be returned to the inner volumes 90a, 90b of the expander 1 anyway. This is shown on FIGS. 2 and 3. Here, there is no dedicated physical third channel, as the lubricant may return from the separator volume 11 in just the same way that it got in there. The return of lubricant from the inner volumes 90a, 90b to the oil sump 6 is provided through means of gravity and appropriate geometrical design of the expander's 1 interior. The specific implementation of this is not important to the invention, and is therefore not further described herein.

(26) In still another embodiment (see FIG. 3), a shielding member in the form of a baffle 10b is constraining the separator volume 11, shielding the working fluid exit 31 and forming part of the lubrication return path 19.

(27) Since several components in the expander 1 are under constant and vigorous movement, for example the piston 41, crankshaft 44, connecting rod 43 and valves 22, 26, there will be a continuous and intense movement (flow) of the fluids that are contained within the inner volumes 90a, 90b. This applies to the working fluid as well as to the lubricant, which will be partly in droplet or aerosol form. Because of this constant and intense fluid movement, the fluid separator 10 is shaped so as to limit the amount of lubricant being directly exposed to the working fluid exit 31. This is done by shielding the working fluid exit 31 and hence the working fluid return channel 14 from the inner volumes 90a, 90b. The shielding is for example provided by the oil separator housing 10a or the baffle 10b (as shown on FIG. 3).

(28) In a specific embodiment of the invention, a coalescence promoting material 28 (as shown on FIG. 2) can be inserted into the separator volume 11 to further ensure that smaller lubricant droplets will coalesce and be returned appropriately (e.g. by gravity) to either of the inner volumes 90a, 90b.

(29) Further, the invention assumes that the expander's 1 full volume 9 is completely sealed off from the environment through the implementation of appropriate sealing devices and methods. The inner volumes 90a, 90b of the expander 1 are generally free from air and other non-condensable gases, as the expander 1 has been evacuated prior to starting operation.

(30) A compressor, for example acting as compressing means in a vapour compression based heat pump system, may use the exact same solution for fluid separation, only with the main difference that working fluid flow is effectively reversed relative to that of the ORC. In the vapour compression example, the working fluid return volume 15 would be part of a compressor suction port 25a rather than part of an expander exhaust port 25.

(31) The expander 1 in the description may also be used reversibly as a compressor, providing that appropriate means for adjusting the valve timing are provided, and in that case it is possible to use the very same fluid separator 10 as is, since the exhaust valve 26 can then act as an inlet (suction) valve instead, and therefore the working fluid return volume 15 would be part of the suction port as noted above.

(32) During cold start-up of the displacement machine 1, there may be more working fluid mixed with the lubricant 61 in the sump 6 than during normal operating conditions. There is therefore a method in place to limit the negative effects of excess oil dilution at start-up. The method involves in a first step to add heat to the lubricant 61 in the sump 6 by means of a heater 69 (see FIG. 1). Further, the method has a second step, which comprises to measure and detect a minimum temperature of the lubricant 61, and then to provide a ready signal to a control system, which then allows the displacement machine to be started.

(33) Lastly, other displacement devices acting the same way or at least having a similar application may also benefit from the invention. For example, a Wankel expander or Wankel compressor could in many cases benefit from the fluid separator solution described herein.

(34) It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.

(35) The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.