WO2008090582A1

WO2008090582A1 - Piston for reciprocating compressors, in particular for hydrogen gas5 and relating reciprocating compressors

Info

Publication number: WO2008090582A1
Application number: PCT/IT2008/000030
Authority: WO
Inventors: Iginio Benedetti
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-01-22
Filing date: 2008-01-21
Publication date: 2008-07-31
Anticipated expiration: 2009-07-22
Also published as: ITPI20070006A1; WO2008090582B1

Abstract

A piston (11) for reciprocating compressors is provided in its outer surface with at least a first annular slot (22) filled with hydraulic fluid. At least a second annular slot (25), also provided in its outer surface is apt to collect the hydraulic fluid possibly escaping from said first annular slot and lead it towards a fluid circuit (26, 29). Proper apertures (28, 30) for the communication of said annular slots with said fluid circuit are provided in the surface of the cylinder (12) housing said piston.

Description

PISTON FOR RECIPROCATING COMPRESSORS, IN PARTICULAR FOR HYDROGEN GAS₅ AND RELATING RECIPROCATING

COMPRESSORS Field of the Invention

The present invention relates to a piston for compressors and to the compressors comprising said piston.

In particular, but not exclusively, the invention concerns a piston for reciprocating compressors of hydrogen gas. Background of the Invention

Reciprocating compressors are, as known, machines for compressing gas, or vapour, comprising at least one cylinder in which a piston leaktight moves of reciprocating motion. Specific apertures, opened at the right time by a proper distribution system, put the cylinder in communication with the adduction pipe or the exhaust one. The gas is sucked in during the intake stroke when the piston is moving away from the head of the cylinder, then, during the following stroke, the gas is compressed and subsequently discharged out of the cylinder. Such compressors can have a single cylinder or more cylinders displaced according to various geometries and they can be single or multi stage as a function, mainly, of the compression ratio.

They are used in industrial plants when high: compression ratios and high final pressures have to be obtained, even if there is a detriment of the treated volumes that, due to the geometry and the functioning principle of this kind of compressors are inevitably much lower than the ones which can be obtained with rotary compressors.

In particular, reciprocating compressors are widely used to produce compressed air, for compressing gas for motor-vehicles such as natural gas or methane, for compressing hydrogen or hydrogen mixtures and for many more applications in which very high pressures have to be obtained, of several hundreds bar.

Due to the high pressures of the gas in the compression chamber, in this kind of compressors is severely felt the matter of the sealing between the piston and the cylinder.

Furthermore considering that these compressors are usually provided with non-lubricated cylinders as a consequence of the high temperatures reached close to the compression chamber, that could compromise the characteristics of the lubricant, the result is that, at present, in reciprocating compressors, the sealing between piston and cylinder is obtained or through labyrinth seals made in the outer surface of the piston and in the internal surface of the cylinder, or by covering the internal surface of the cylinder with a sleeve made of a ceramic / self-lubricating material on which slides the piston rings, other through self-lubricating piston rings. Nevertheless, especially when a gas having a low molecular weight has to be compressed, such has hydrogen gas, neither the use of many piston rings, nor the use of labyrinth seals helps avoiding leakage of gas, that, from pressures of few tens of bars on, reach such volumes to require the adoption of measures to recover the escaped gas from the shaft vane and from other possible ways of escape.

It is so very important to search for solution able to assure, for this kind of compressors, a perfect sealing of the coupling piston-cylinder. Summary of the Invention Main object of the present invention is to provide a piston for reciprocating 008/000030

compressors, in particular for compressing hydrogen gas, able to eliminate the sealing problems between piston and cylinder.

Further object of the invention is to propose an improved reciprocating compressor for compressing gas or vapours apt to assure the sealing between piston and cylinder.

Such objects and other more are obtained through a piston for reciprocating compressors comprising at least a cylinder housing a piston moving of reciprocating motion, said piston compressing gas, in particular hydrogen gas or its mixtures, contained in a compression chamber made within said cylinder, said piston and the compressor's head, said piston being characterized in that it comprises, made in its external surface, at least a first annular slot apt to be filled with an hydraulic fluid coming between said piston and said cylinder, so that it avoid leakage of the gas which is in the compression chamber. The hydraulic fluid adopted may advantageously be ionic oil or equivalent fluid which, in particular, does not react with hydrogen or the different gases that have to be compressed.

Still in the outer surface of the piston, under the first annular slot, with respect to the head of the piston, is preferably made a second annular slot apt to collect the hydraulic fluid possibly escaped from said first annular slot.

In the outer surface of the piston are provided further slots for sealing and/or oil-scraper rings. In particular, at least one slot housing a sealing piston ring is advantageously made over said first annular slot. A reciprocating compressor comprising a piston having the above described characteristics also comprises a circuit for the adduction of hydraulic fluid to said first annular slot. The above may be obtained even through an aperture made in the surface of said cylinder. In addiction, said circuit is advantageously put in communication, during the piston's stroke, with said annular slot, so that the hydraulic fluid possibly escaped from said first annular slot and recovered in said second slot, is put into circulation again in said circuit. The advantages of the above piston, and the reciprocating compressors thereof, concern and are clear as regards the increased efficiency of such compressors deriving from fixing the leakages between piston and cylinder. Further relevant advantage, still due to fixing the leakage of gas, consists of the fact that no gas recovering from the bottom part of the cylinder or from shaft vane other from different sections of the motor is needed. The use of an hydraulic fluid in reciprocating compressors also allow a greater speed of the compressors and then a greater amount of gas can be compressed which cannot absolutely obtained in other gas compressing means that use hydraulic fluids. Further advantages finally descend from the overall reliability of the proposed compressors and from the great noiselessness coming from the reduction of frictions. Brief Description of the Drawings

Anyway, for a better understanding of the characteristics and the advantages of the present invention, this will now be described by way of some embodiments with reference to the accompanying drawings, in which:

-Figure 1 schematically a section view of a part of a compressor according to the invention, relating to the piston and the cylinder thereof; -Figures 2 and 3 show section view analogous to the view of fig.1, relating to different embodiments of the piston and cylinder. Description of Preferred Embodiments

Referring to fig.1 , it is shown a section of a reciprocating compressor 10 comprising a piston, 11 , moving inside a cylinder, 12, of reciprocating motion thanks a rod, 13, connected at one end to the piston by means of a pin, 14, and at its opposite end to a crankshaft, not shown in figure. Through an adduction conduit, 15, and the adduction valve, 16, thereof, the gas to be compressed enter the compression chamber, 18, than, at the end of the piston's compression stroke, upon opening of the delivery valve, 19, it goes out the compression chamber, 18, through the delivery conduit, 20, made, together with the adduction conduit 15, in the head, 21, of the cylinder 12. From here the compressed gas id sent out of the compressor, for instance towards storing tanks, or to a following stage of the compressor, in case after having passed a cooling stage. The piston, 11, is provided with a first annular slot, 22, made in the outer surface, 23, near the head of the piston 11 itself. Over said first annular slot, 22, there are more slots housing piston rings, 24, for sealing and oil- scrapers, made according to known techniques. In the lower part of the piston 11 , still made in the outer surface 23 of the piston, is provided a second annular slot, 25, under which is housed, in its slot, a further piston ring, 24, of known technique.

A first conduit, 26, of an adduction and recirculation circuit for a hydraulic fluid is connected, through a fitting, 27, to an aperture, 28, made in the lateral surface of the cylinder, 12. A second conduit, 29, of said hydraulic circuit is connected to a further aperture, 30, of the cylinder's surface, said second conduit being located under said first conduit 26. At the end of the suction stroke, during which the valve 16 is open and the gas to be compressed pass from the adduction conduit 15 to^' the compression chamber 18, the first annular slot, 22, is in communication, by the aperture 28, with the conduit 26 of the hydraulic fluid's adduction circuit that, being under pressure, fill up said annular slot 22. After that, during the compression stroke of the piston towards the head 21, when the pressure of the gas raise, this last, even if there are the piston rings 24, is able to escape from the compression chamber 18 toward the lower part of the cylinder, 12. The presence of hydraulic fluid under pressure in the first annular slot 22 forms a leaktight seal preventing leakage of gas which is so completely restrained in the compression chamber 18 until the valve 19 of the delivery conduit 20 opens. During the compression stroke the hydraulic fluid under pressure which is in said annular slot, 22, tend to escape towards the bottom part of the piston's outer surface, due to the upper pressure of the gas, and also due to the mutual motion between piston 11 and cylinder, 21. The fluid itself, reaching the second annular slot, 25, tend to gather inside this last slot, also thanks to the lower piston ring, and the above occurs until the end of the following suction stroke when, being said second annular slot 25 in communication with the conduit 29, the fluid flows through this last towards the outer recirculation circuit. At the same time, the conduit 26, is in communication again with the first slot, 22, so that it can be filled up again.

It has to be noted the shape of the piston 11 and the arrangement of the adduction and recirculation apertures 28 and 30 of the cylinder 12, are such that the lower annular slot 25 is never in communication with the adduction conduit 26, as shown in fig.l, where the piston 11 is at its top dead centre. As regards the kind of hydraulic fluid used, it worth stressing that the characteristics of said fluid fit with the chemical properties of the gas to be compressed, so that contamination is avoided. In particular, in case the gas to be compressed is hydrogen or hydrogen's mixtures, as hydraulic fluid can advantageously work ionic oil, whilst, in case another kind of gas has to be compressed, which is not compatible with the use of ionic oil, a different kind of hydraulic fluid will be adopted apt to avoid chemical reaction with the gas and contamination of the same. The relevant advantages relating to sealing which come with the reciprocating compressor of the invention remain safe even in case of changes of modifications to what above described.

In figure 2 is shown, for instance, a piston, 11 ', whose outer surface provides, near the head, two annular slots, 22', and still a single annular slot, 25', for recirculation in its lower part. This embodiment shows a different number also of piston rings, 24'; due to the height of the piston a single piston ring is in fact provided over the two slots 22' and is no more provided the piston ring placed under the slot 25'. In a further embodiment of the invention, shown in figure 3, the piston, 11 ", is coupled, thanks to a thread 31, with a connection bar 32, bound at its opposite end to a rod, not shown in figure. In this case the piston 11 " is provided with a single annular slot 22", fed by the adduction conduit 26"; then, the hydraulic fluid that escape towards the bottom section of the piston goes into the lower chamber of the cylinder, 12", and, from here, or is recovered and flows again into the adduction circuit thanks to specific conduits, other it can mix with the lubricating oil which is in the crankshaft ' s vane .

Further modifications may obviously concern the adduction and recirculation circuit that can be located in whatever section of the compressor, it can be made of various kind of components such as pumps, filters and valves, and it can also be put into communication with said first and second annular slots, 22 and 25, in different ways with respect to the shown apertures 28, 30, of the cylinder 12.

For instance, specific conduits could be provided inside the piston rod, which could be put in communication with the slot 22 by proper holes made in the piston.

In this way we could have the further advantage that the adduction of fluid is not limited the parts of the stroke of the piston where said slot 22 is in front of the aperture 28. The adduction of fluid could be commanded, mechanically or electronically, to obtain the adduction itself during the desired parts of the piston's strokes, so granting in an even better way the sealing between piston and cylinder. It is clear that the adduction of fluid to the slot 22, 22', could take place at different values of pressure, suitable to the specific application and the kind of fluid. Also the adduction and delivery conduits 15 and 20 and the relating valves

16 and 19 could differ from the ones schematically shown in figures 1 and

3.

In particular the valve could be reed valves or other kinds of valve, new or of known technique, These and other modifications may be carried out, always within the limits of the invention as defined in the appended claims.

Claims

C L A I M S

1- Piston for reciprocating compressors comprising at least a cylinder housing a piston moving of reciprocating motion, said piston compressing gas, in particular hydrogen gas or its mixtures, contained in a compression chamber made within said cylinder, said piston and the compressor's head, characterized in that it comprises, made in its outer surface, at least a first annular slot apt to be filled with an hydraulic fluid coming between said piston and said cylinder, so that it avoid leakage of the gas which is in the compression chamber. - Piston (1 1) according to claim 1, characterized in that the hydraulic fluid adopted is ionic oil or equivalent fluid.

3- Piston (1 1) according to claim 1 or 2, characterized in that it comprises still in the outer surface (23) of the piston, under the first annular slot with respect to the head of the piston, a second annular slot (25) apt to collect the hydraulic fluid possibly escaped from said first annular slot (22).

4- Piston (1 1) according to the previous claim, characterized in that it comprises in its outer surface (23), further annular slots housing sealing and/or oil-scrapers piston rings (24). 5- Piston (1 1) according to the previous claim, characterized in that it comprises in its outer surface (23), over said first annular slot (22), at least one more slot housing a sealing piston ring (24).

6- Reciprocating compressor (10) for compressing gas or vapours characterized in that it comprises a piston according to at least one of the previous claims, and at least one circuit for the adduction of hydraulic fluid to said first annular slot (22) of said piston (1 1).

7- Reciprocating compressor (10) according to the previous claim characterized in that said cylinder is provided with an aperture (28) apt to put into communication said first annular slot (22) of said piston (1 1) with said hydraulic fluid adduction circuit. - Reciprocating compressor (10) according to claim 6 characterized in that said at least one annular slot (22) is put into communication with said hydraulic fluid adduction circuit by means of conduits made in the piston (1 1) and in the piston rod. - Reciprocating compressor (10) according to claim 6, 7 or 8 characterized in that said second annular slot (25) is put into communication, thanks to the stroke of the piston (11), with a second circuit (29) apt to the recirculation of said hydraulic fluid.