Reciprocating compressor with improved seals for low molecular weight gases
The reciprocating compressor design with a barrier chamber and reduced piston rings effectively seals low molecular weight gases and addresses bearing wear, enhancing sealing and efficiency while reducing costs and safety risks.
Patent Information
- Application Number
- JP2025550923
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-03-03
- Filing Date
- 2024-03-01
- Publication Date
- 2026-02-27
AI Technical Summary
Reciprocating compressors face challenges in sealing low molecular weight gases, particularly hydrogen, due to leakage through conventional containment systems, and uneven wear of connecting rod bearings, especially at high compression ratios, leading to increased manufacturing costs and safety risks.
A reciprocating compressor design with a slidable member and a barrier chamber using barrier fluid to enhance sealing, reducing the number of piston rings and minimizing gas leakage, while addressing uneven bearing wear by ensuring continuous engagement of the connecting rod bearing.
The design achieves improved sealing and reduced gas leakage, lowers manufacturing costs, and enhances compression efficiency, minimizing the risk of explosive atmospheres and wear-related issues.
Smart Images
Figure 2026507187000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a reciprocating compressor comprising at least one compression unit, such as a cylinder-piston unit or a plunger unit including a slidable member movably arranged in a cylinder to define a compression chamber, and an improved sealing system is provided between the compression units to prevent low molecular weight and / or high pressure gas, in particular hydrogen or hydrogen-containing gas mixtures, from leaking from the compression chamber. [Background technology]
[0002] As is well known, in recent decades hydrogen has been attracting increasing attention as a possible energy vector for limiting the widespread use of fossil fuels. In view of this, it is necessary to install hydrogen production plants, as well as hydrogen supply networks and hydrogen storage systems, which, in order to be economically viable, must operate at high pressures, even of the order of several hundred bar, which can be reached by using reciprocating compressors.
[0003] It is also known how difficult it is to provide a low molecular weight gas-tight seal system, especially for hydrogen-containing gases, due to the tendency of the gas to leak through conventional containment systems. Leaking even a small amount of hydrogen from equipment into the atmosphere is usually an unwelcome event. Aside from the loss of product value, the high cost of protective measures that must be adopted to comply with regulations regarding potentially explosive atmospheres must also be considered.
[0004] A possible solution to the problem of hydrogen leakage from reciprocating machines is to provide the piston with multiple piston rings as sealing elements around the end of the piston facing the compression chamber of the machine. However, this requires a longer piston-cylinder unit, thus increasing the manufacturing costs of the compressor. Similarly, plunger compressors must have a plunger long enough to act as a seal and prevent gas leakage.
[0005] A further problem with reciprocating compressors is uneven wear of the connecting rod bearings, especially at high compression ratios. As is well known, when the slidable members pass top dead center, i.e., when the thrust direction reverses after the compression stroke, the upper half of the connecting rod bearing remains fully loaded, while the lower half remains unloaded, causing uneven bearing wear. Single-acting compressors, including plunger compressors, are particularly susceptible to this problem because the thrust acting on the connecting rod due to the pressure of gas in only one compression chamber is not offset by the counterpressure due to gas present in the second, opposite compression chamber, as is the case with double-acting compressors.
[0006] European Patent Publication No. 2796719(A1), U.S. Patent No. 4,174,929, and U.S. Patent Application Publication No. 2018 / 051684(A1) describe particular compressor units. Summary of the Invention
[0007] It is therefore an object of the present invention to provide a reciprocating compressor that provides improved sealing with respect to leakage and outward loss of low molecular weight gases, particularly hydrogen-containing gases, relative to the most commonly used reciprocating compressors for the same type of gas and a given operating pressure.
[0008] It is also an object of the present invention to provide a high pressure reciprocating compressor, i.e., one operating at a discharge pressure of the order of 100 bar or more, which offers improved sealing with respect to gas leakage and outward losses with respect to the most commonly used reciprocating compressors for the same type of gas.
[0009] A particular object of the present invention is to provide such a reciprocating compressor comprising at least one piston-cylinder unit, which allows a certain level of tightness for the same type of gas and / or for a given operating pressure, while comprising a relatively small number of piston rings arranged around the piston end portion facing the compression chamber or having a relatively short plunger seal area of its own plunger unit.
[0010] Another specific object of the present invention is to provide a reciprocating compressor which overcomes uneven wear of the rod bearings caused by the upper half of the rod bearing not disengaging from the thrust when the thrust is reversed at top dead center.
[0011] Furthermore, it is an object of the present invention to provide a compressor that is capable of achieving better compression efficiency than the conventional reciprocating compressor when used to process low molecular weight gases.
[0012] These and other objects are achieved by a compressor configured to compress a low molecular weight gas to a predetermined discharge pressure, as set forth in claim 1. Advantageous embodiments of the compressor are defined in the dependent claims.
[0013] The compressor includes at least one compression unit including a cylinder and a slidable member disposed within the cylinder, the slidable member having a head portion and a rod portion integral with the head portion and disposed to cause the head portion to stroke within the cylinder; the cylinder has a proximal cylinder portion, a central cylinder portion, and a distal cylinder portion relative to the rod portion, the proximal cylinder portion and the distal cylinder portion having a first cylinder inner diameter; the head portion has a head portion proximal portion, a head portion central portion, and a head portion distal portion relative to the rod portion, the head portion proximal portion and the head portion distal portion having a head portion first outer diameter; the first inner diameter of the cylinder and the first outer diameter of the head portion are equal to a common nominal diameter of the cylinder and the head portion, except for a predetermined coupling tolerance; the cylinder central portion has a second inner diameter; the head portion central portion has a second outer diameter; a distal portion of the head portion having a compression surface opposite a central portion of the head portion; the compression surface defining a compression chamber within the cylinder, the compression chamber having an intake port and a discharge port for a low molecular weight gas; According to the present invention, the second inner diameter of the cylinder central portion is larger than the second outer diameter of the head portion central portion by a predetermined amount, i.e., a predetermined gap thickness, thereby defining an annular gap having a thickness equal to the predetermined amount between the head portion central portion and the cylinder central portion; The central cylinder portion has at least one inlet opening for barrier fluid in fluid communication with a source of barrier fluid configured to deliver the barrier fluid to the annular gap at a predetermined barrier pressure such that the barrier fluid occupies the annular gap and the annular gap forms a barrier chamber between the compression chamber and a space opposite the compression chamber relative to the head portion of the slidable member.
[0014] In the case of a compressor with a single-acting compression unit, such as a single-acting cylinder-piston unit or plunger unit, a sealing chamber exists between the compression chamber and the outside of the compressor, which is configured to contain a barrier fluid at a pressure always higher than or at least equal to the pressure of the compression chamber. This sealing chamber provides an additional sealing effect between the compression chamber and the outside, i.e., the proximal space adjacent to the proximal part of the head portion. In the case of the cylinder-piston unit 1 or 2, this additional sealing effect is in addition to the sealing effect provided by the piston rings 41, 45 of the cylinder-piston units 1 and 2. Alternatively, in the case of the plunger unit 3, this additional sealing effect is in addition to the sealing effect provided by the mutual contact surfaces of the proximal and distal parts 11, 15 of the cylinder 10, on the one hand, and the proximal and distal parts 31, 35 of the plunger 20, on the other hand.
[0015] In other words, the barrier chamber cooperates with the piston rings in the case of a single-acting cylinder-piston unit, or with the sealing portion of the cylinder-plunger connection in the case of a plunger unit, to contain the compressed gas within the compression chamber. Because the barrier fluid is less likely to leak than low-molecular-weight gases, a given sealing performance can be ensured with fewer piston rings in the case of a cylinder-piston unit, or with a shorter sealing portion of the cylinder-plunger connection in the case of a plunger unit. The fewer piston rings or shorter sealing portions allow the length of the compressor unit and the compressor itself, and therefore the overall dimensions, to be reduced, which simplifies the compressor configuration and reduces manufacturing costs.
[0016] The present invention provides a space- and cost-saving compressor that limits the loss of compressed gas to the environment and, in the case of double-acting compressor units, limits gas leakage between opposing compression chambers, as will be described later, thus improving compression efficiency. In this way, economic losses due to compressed gas leakage can be reduced. Furthermore, in the case of flammable gases such as hydrogen or certain mixtures thereof, the risk of forming an explosive atmosphere around the compressor can be similarly limited.
[0017] As used herein, expressions such as "in pneumatic communication" and "in hydraulic communication" between two spaces indicate the presence of a connection between these spaces, such as a duct, piping element, or the like, through which a gas or a liquid, respectively, can flow. Moreover, these gases and liquids are not limited to air and water, respectively, contrary to the common meaning of "pneumatic" and "hydraulic."
[0018] Preferably, the thickness of the annular gap between the center of the cylinder and the center of the head portion of the compression unit is at least 1 mm, in particular the thickness is at least 5 mm, more in particular the thickness is at least 10 mm.
[0019] In some embodiments of the present invention, the second inner diameter of the central cylinder section is equal to the first inner diameter of the distal and proximal cylinder sections, and therefore equal to a common nominal diameter; the second outer diameter of the central head portion of the slidable member is smaller than the common nominal diameter by said predetermined gap thickness, i.e. the difference between the common nominal diameter and the second outer diameter of the central head portion is equal to said gap thickness; the central portion of the head portion has a length at least equal to the stroke of the slidable member;
[0020] In other words, the annular gap, and therefore the sealing chamber, can be formed by using a piston or plunger whose middle portion has a diameter smaller than the nominal diameter, which can be obtained, for example, by simply removing material from a conventional piston or plunger having the same outer diameter over its entire length. These embodiments relate particularly to the use of the invention in existing compressors and their compression units, since the slidable member can be machined more easily than the inside of the cylinder.
[0021] In this case, the barrier chamber moves integrally with the slidable member as the slidable member performs its stroke within the cylinder.
[0022] However, in other embodiments of the invention, the annular gap, and therefore the sealing chamber, can be formed by using a cylinder with an intermediate portion whose diameter is larger than the nominal diameter, which can for example only be obtained by removing material from a conventional cylinder having the same inner diameter over its entire length. the second outer diameter of the central head portion of the slidable member is equal to the first inner diameter of the distal and proximal portions of the cylinder, and thus equal to the common nominal diameter; the second inner diameter of the cylinder central portion is larger than the common nominal diameter by the above-mentioned predetermined gap thickness, i.e. the difference between the second inner diameter of the cylinder central portion and the common nominal diameter is equal to the gap thickness; The central part of the cylinder has a length at most equal to the difference between the length of the central part of the head part and the stroke of the slidable member.
[0023] In particular, the compression unit is a cylinder-piston unit, the slidable member being a piston; the proximal and distal head portions each include at least two resilient piston rings spaced a distance from each other and arranged to slide within a cylinder; The central head portion is located between the resilient piston ring of the proximal head portion and the resilient piston ring of the distal head portion.
[0024] In one embodiment of the invention, the cylinder piston unit is a double-acting cylinder piston unit, i.e., the compression surface of the head portion is a first compression surface, the compression chamber is a first compression chamber, a proximal portion of the head portion has a second compression surface opposite the first compression surface relative to a central portion of the head portion, the second compression surface and the cylinder define a second compression chamber, and the rod portion is disposed through the entire length of the second compression chamber.
[0025] In this case, the barrier chamber remains defined between the two compression chambers, which always operate at different pressures. The barrier chamber always contains a fluid at a pressure higher than, or even at least equal to, the maximum pressure reached by each compression chamber. The barrier chamber, together with the piston rings, therefore contributes to sealing the compression chambers from each other, again limiting the number of piston rings and therefore the length of the piston head portion.
[0026] This limits the number of piston rings and therefore the length of the piston head portion, significantly limiting gas leakage between one compression chamber and the other, and thus making it possible to maintain high compression efficiency of the compressor.
[0027] Advantageously, the central part of the head portion of the slidable member has a shape whose diameter decreases from the proximal to the distal part of the head portion, in particular this shape is frusto-conical.
[0028] Thus, the resultant pressure force acting on the central part of the head portion due to the barrier fluid contained in the barrier chamber has a component directed away from the only compression surface in the case of a single-acting unit, or away from the compression surface on the opposite side of the rod portion, which component serves to position the connecting rod bearing in its seat so that the lower part of the bearing is compressed, i.e. the lower part of its bearing surface is engaged, once the slidable member has passed top dead center, i.e. during the subsequent stroke of the slidable member. By "bottom dead center" is meant the extreme position of the slidable member corresponding to the minimum size of the compression chamber defined by the only compression surface of the slidable member, or in either case, in the case of a double-acting cylinder piston unit, the minimum size of the compression chamber defined by the compression surface on the opposite side of the piston rod relative to the piston head itself.
[0029] In some embodiments, the central cylinder portion has at least one barrier fluid outlet opening in its intermediate portion, where the inlet and outlet openings are preferably formed in the same cross section of the cylinder, and the cylinder has a circumferential recess or groove in said cross section that communicates with the barrier fluid inlet and outlet openings, which allows for a uniform distribution of the barrier fluid within the barrier chamber.
[0030] In some embodiments of a compressor including a cylinder-piston unit, the annular gap providing the barrier chamber is a first annular gap providing a head portion annular chamber, the rod portion is provided with proximal and distal seals, and a second annular gap is defined between the proximal and distal seals and arranged to supply rod portion barrier fluid to provide the rod portion barrier chamber. This is a further improvement to the sealing system of a double-acting cylinder-piston unit against gas leakage to the environment, in addition to the improved seal provided by the head portion barrier chamber between the two compression chambers and the associated performance benefits described above.
[0031] In these cases, the rod portion barrier fluid may be similar to the piston head portion barrier fluid, and the head portion barrier chamber and the rod portion barrier chamber may be supplied by the same circuit.
[0032] In particular, the head portion barrier chamber and the rod portion barrier chamber, i.e., the first and second annular gaps, have an interconnection, and the interconnection is a parallel interconnect, wherein both the first and second annular gaps are arranged to receive a common barrier fluid directly from a barrier fluid supply; - a serial interconnection, in which the cylinder and the second annular gap also have respective barrier fluid outlet openings, the outlet opening of the cylinder being hydraulically connected to the inlet opening of the second annular gap or the barrier chamber.
[0033] In a variation of the above embodiment, the compressor unit may comprise a closed barrier fluid supply circuit including a barrier fluid supply source.
[0034] In one embodiment, such a supply circuit comprises a compensation vessel having a deformable diaphragm or membrane disposed therein to define a first variable volume chamber and a second variable volume chamber, the first variable volume chamber being in pneumatic communication with the compression chamber discharge port and the cylinder inlet opening, respectively, the second variable volume chamber being configured to contain a predetermined amount of barrier fluid, thereby enabling the barrier fluid to be delivered to the annular gap at a pressure dependent on the pressure of the low molecular weight gas at the discharge port.
[0035] In this way, a closed circuit containing a predetermined amount of barrier fluid is used in the barrier chamber, which requires only minimal or no barrier fluid to be delivered, while maintaining the pressure within the barrier chamber using the compression power of the compressor itself. Complete isolation of the sealing circuit from the process by the deformable membrane ensures that no gas leaks to the outside.
[0036] In an alternative embodiment, the compressor unit may comprise a cooling circuit configured to deliver cooling fluid at a predetermined cooling fluid pressure higher than the discharge pressure. In such a case, the inlet opening of the cylinder is advantageously in hydraulic communication with said cooling circuit, whereby the barrier fluid comprises a portion of said cooling fluid. In other words, the source of the barrier fluid is the cooling circuit of the compressor.
[0037] Again, the sealing system can be made without introducing any fluids and supply circuits other than those already "naturally" present in the compressor, thus limiting the manufacturing and operating costs of the system.
[0038] In one embodiment, the compressor includes multiple compression stages, i.e., multiple compression units arranged to operate at successive suction-discharge pressure ranges relative to one another. In this case, the inlet opening of the barrier chamber of a compression unit arranged to perform an earlier compression stage may be in air communication with the discharge port of the compression chamber of a compression unit arranged to perform a later compression stage, whereby the barrier fluid comprises the low molecular weight gas itself. A pressure reducing device may be provided along the duct provided to enable this air communication to optionally reduce the pressure of gas drawn from the discharge port of a unit performing a later, higher-pressure stage without entering that stage, to a value low enough to properly function as a barrier fluid in one or more subsequent stages. In this way, fluids unrelated to the process are prevented from being introduced into the barrier chamber, thereby preventing the risk of contamination by foreign process fluids. [Brief explanation of the drawings]
[0039] The invention will now be illustrated by way of example and not limitation by describing some embodiments with reference to the accompanying drawings, in which: [Figure 1] 1A and 1B are schematic partial vertical cross-sectional views of a single-acting cylinder-piston unit of a reciprocating compressor according to an embodiment of the present invention, with the pistons at top dead center and bottom dead center, respectively. [Figure 2] 1A and 1B are schematic partial vertical cross-sectional views of a single-acting cylinder-piston unit of a reciprocating compressor according to an embodiment of the present invention, with the pistons at top dead center and bottom dead center, respectively. [Figure 3] FIG. 3 is a schematic side view of a piston head portion of the cylinder piston unit of FIGS. 1 and 2. [Figure 4] 5A and 5B are schematic partial vertical cross-sectional views of a single-acting cylinder-piston unit of a reciprocating compressor according to another embodiment of the present invention, with the pistons at top dead center and bottom dead center, respectively. [Figure 5] 5A and 5B are schematic partial vertical cross-sectional views of a single-acting cylinder-piston unit of a reciprocating compressor according to another embodiment of the present invention, with the pistons at top dead center and bottom dead center, respectively. [Figure 6]FIG. 6 is a schematic vertical cross-sectional view of a cylinder of the cylinder-piston unit of FIGS. 4 and 5. [Figure 7] 5A and 5B are schematic partial vertical cross-sectional views of a plunger unit of a reciprocating compressor according to a further embodiment of the present invention, with the plungers at top dead center and bottom dead center, respectively. [Figure 8] 5A and 5B are schematic partial vertical cross-sectional views of a plunger unit of a reciprocating compressor according to a further embodiment of the present invention, with the plungers at top dead center and bottom dead center, respectively. [Figure 9] FIG. 9 is a schematic side view of the plunger of FIGS. 7 and 8. [Figure 10] 1A-1C are schematic partial longitudinal cross-sectional views of double-acting cylinder-piston units of reciprocating compressors according to two alternative embodiments of the present invention, in which the barrier chamber has a single barrier fluid inlet / outlet opening and is internally defined by a cylindrical surface and a frusto-conical surface, respectively; [Figure 11] 1A-1C are schematic partial longitudinal cross-sectional views of double-acting cylinder-piston units of reciprocating compressors according to two alternative embodiments of the present invention, in which the barrier chamber has a single barrier fluid inlet / outlet opening and is internally defined by a cylindrical surface and a frusto-conical surface, respectively; [Figure 12] 10A-10C are schematic partial longitudinal cross-sectional views of double-acting cylinder-piston units of reciprocating compressors according to two further alternative embodiments of the present invention, in which the barrier chamber has a barrier fluid inlet opening and a barrier fluid outlet opening separate from the barrier fluid inlet opening, and is internally defined by a cylindrical surface and a frusto-conical surface, respectively; [Figure 13] 10A-10C are schematic partial longitudinal cross-sectional views of double-acting cylinder-piston units of reciprocating compressors according to two further alternative embodiments of the present invention, in which the barrier chamber has a barrier fluid inlet opening and a barrier fluid outlet opening separate from the barrier fluid inlet opening, and is internally defined by a cylindrical surface and a frusto-conical surface, respectively; [Figure 14] FIG. 13 is a schematic longitudinal sectional view showing the double-acting cylinder piston unit of FIG. 12 in more detail. [Figure 15] 15A and 15B are vertical cross-sectional perspective views of the cylinder piston unit and the cylinder of FIG. 14, respectively. [Figure 16] 15A and 15B are vertical cross-sectional perspective views of the cylinder piston unit and the cylinder of FIG. 14, respectively. [Figure 17] 3 is a partial longitudinal cross-sectional view of the cylinder piston unit shown in FIG. 2, in which a barrier chamber is also provided in the piston rod portion. [Figure 18] 18 shows a supply diagram of the head portion barrier chamber and the rod portion barrier chamber of FIG. 17, where the two barrier chambers are arranged in parallel and in series with each other, respectively, so that the same barrier fluid is delivered. [Figure 19] 18 shows a supply diagram of the head portion barrier chamber and the rod portion barrier chamber of FIG. 17, where the two barrier chambers are arranged in parallel and in series with each other, respectively, so that the same barrier fluid is delivered. [Figure 20] 13 is a schematic partial longitudinal cross-sectional view of the cylinder piston unit shown in FIG. 12, in which the head portion barrier chamber and the rod portion barrier chamber are arranged to receive the cooling fluid of the cylinder piston unit as the barrier fluid. [Figure 21] 11 is a schematic partial longitudinal cross-sectional view of the cylinder-piston unit shown in FIG. 10, in which a barrier fluid supply circuit including a compensation container is provided. DETAILED DESCRIPTION OF THE INVENTION
[0040] 1-9, there is shown three compression units 1, 2, and 3 of a compressor configured to compress a low molecular weight gas to a predetermined discharge pressure. Compression units 1, 2, and 3 each include a cylinder 10 and a slidable member 20. Slidable member 20 includes a head portion 30 slidably coupled within cylinder 10 along a common longitudinal axis 5 along which cylinder 10 and head portion 30 extend.
[0041] The cylinder 10 and the head portion 30 comprise respective parts which are in mutual sliding contact with each other and have a common nominal diameter D and respective predetermined coupling tolerances which can be determined in a manner known to those skilled in the art according to the operating conditions of the compression unit.
[0042] In particular, compression units 1 and 2 are cylinder-piston units (FIGS. 1-3 and 4-6) in which the slidable member 20 is a piston, while compression unit 3 is a plunger unit (FIGS. 7-9) in which the slidable member 20 is a plunger.
[0043] In addition to the head portion 30, the slidable member 20 includes a rod portion 39 integrally connected to the head portion 30 and arranged to cause the head portion 30 to perform a stroke of length C within the cylinder 10. The rod portion 39 is typically a connecting rod connected, in a manner not shown, to a crankshaft which may be a common crankshaft of several compression units 1, 2 or 3 and their respective variants.
[0044] The rod portion 39 has a diameter D3, which in the cylinder-piston units 1 and 2 (FIGS. 1 to 6) is smaller than the nominal diameter D of the head portion 30 and is therefore the maximum diameter of the rod portion 39. Conversely, in the plunger unit 3 (FIGS. 7 to 9), the rod portion diameter D3 is substantially equal to the nominal diameter D of the head portion 30; in other words, the rod portion 39 forms an extension of the head portion 39 with the same nominal diameter D, which extension is oriented towards the compressor transmission (not shown).
[0045] The head portion 30 comprises a proximal portion 31, a central portion 33, and a distal portion 35 (FIGS. 1 and 3). Similarly, the cylinder 10 has a proximal portion 11, a central portion 13, and a distal portion 15 (FIG. 2). The terms "proximal" and "distal" refer to the location of the head portions 31, 35 and the cylinder portions 11, 15 relative to the rod portion 39. Moreover, as expected, the diameters of the proximal portions 11, 31 and the distal portions 15, 35 of the cylinder 10 and the head portion 30, respectively, are equal to the nominal diameter D, excluding respective coupling tolerances that allow the proximal portions 11, 31 and the distal portions 15, 35 to be in sliding contact with one another.
[0046] Opposite the central head portion 33, the distal portion 35 of the head portion 30 has a compression surface 36 that defines a compression chamber 12 within the cylinder 10, the compression chamber being provided with an intake port 14 for the gas to be compressed and an exhaust port 16 for the compressed gas.
[0047] In particular, in the cylinder piston unit of Figures 1 to 6, at least two piston rings 41, 45 are arranged on the proximal and distal portions 31, 35 of the head portion 30 of the piston 20 so as to contact and slide against the inner surface of the cylinder 10. On the other hand, in the plunger unit 3 of Figures 7 to 9, the proximal and distal portions 31-33 of the head portion 30 are smooth sealing portions, which are themselves arranged to contact and slide against the inner surface of the cylinder 10.
[0048] As shown, the cylinder central portion 13 has a second inner diameter D2 (FIGS. 1, 2, and 6), while the piston head portion central portion 33 has a second outer diameter D1 (FIGS. 3, 4, and 5). The second inner diameter D2 of the cylinder central portion 13 and the second outer diameter D1 of the head portion central portion 33 differ by a predetermined amount G=D2-D1, or more precisely, the cylinder second inner diameter D2 is larger than the head portion second outer diameter D1 by the predetermined amount G (FIGS. 1 and 4).
[0049] Thus, an annular gap or chamber 50 is defined between the cylinder central portion 13 and the head portion central portion 33. The annular gap 50 has a major diameter equal to the cylinder second inner diameter D2 and a minor diameter equal to the head portion second outer diameter D1.
[0050] A bore 17 is drilled through the wall of the cylinder center section 13 to provide an inlet opening for fluid into the annular gap 50. The bore 17 is preferably positioned to be at a first axial end 51 of the annular gap 50 when the slidable member 20 is at top dead center ( FIGS. 1 , 4 , and 7 ), and to be at a second axial end 52 of the annular gap 50 opposite the first axial end 51 when the slidable member 20 is at bottom dead center ( FIGS. 2 , 5 , and 8 ). The inlet opening 17 is in fluid communication with a source 8 of barrier fluid 9 ( FIGS. 7 and 8 ) and is configured to deliver barrier fluid 9 to the annular gap 50 at a predetermined barrier pressure.
[0051] The barrier fluid 9 therefore fills and occupies the annular gap 50, thus forming a barrier chamber 50 between the compression chamber 12 and the space 22 on the opposite side of the compression chamber 12 from the head portion 30 of the slidable member 20. The barrier fluid 9 and the barrier chamber 50 provide an additional sealing effect between the compression chamber 12 and the space 22 in addition to the sealing effect provided by the piston ring 41 of the cylinder piston unit 1 and the piston ring 45 of the cylinder piston unit 2, and in the case of the plunger unit 3, by the respective contacting surfaces of the proximal and distal portions 11, 15 of the cylinder 10 and the proximal and distal portions 31, 35 of the head portion 30 of the plunger 20.
[0052] In the figures, for clarity, the difference between the common nominal diameter D of the head portion central portion 33 and the second outer diameter D1, and the difference between the second inner diameter D2 of the cylinder and the common nominal diameter D nominal, are exaggerated; in other words, the thickness G of the annular gap 50 is shown without regard to scale. In a manner that can be easily understood by a person skilled in the art, the thickness G is preferably at least 1 mm, more particularly at least 5 mm, and more particularly at least 10 mm, depending on the operating pressure of the compression units 1-3.
[0053] 1-3 and 7-9 relate to an embodiment of the invention in which the second inner diameter D2 of the cylinder is equal to the first inner diameter of the proximal and distal portions 11, 15 of the cylinder 10 and is therefore equal to the common nominal diameter D of the cylinder 10 and the head portion 30, and the second outer diameter D1 of the head portion central portion 33 of the slidable member 20 is smaller than the first outer diameter of the proximal and distal portions 31, 35 and is therefore smaller than the common nominal diameter D by a gap thickness G. Thus, the annular gap 50 is included in the profile of the head portion 30.
[0054] In this case, the annular gap 50 can be obtained, for example, by removing a portion of material of a given length L1 from the central portion 33 of the head portion 30 of the slidable member 20. In particular, in the case of the cylinder-piston unit 1 of FIGS. 1 to 3 , the central portion 33 is located between the piston rings 41 and 45 of the head portion 30 of the piston 20 ( FIG. 3 ), and therefore the length L1 of the central portion 33 having the reduced (second) outer diameter D1 is shorter than the distance between the innermost piston rings 41 and 45 of the head portion 30. Moreover, as FIGS. 1 and 2 show, during the stroke C of the slidable member 20, the annular gap 50 moves together with the head portion 30, and the length L1 of the head portion central portion 33 is preferably equal to or at least greater than the stroke C of the piston 20. Thus, when the slidable member 30 is at top dead center (Figures 1 and 7) and bottom dead center (Figures 2 and 8) of its stroke C, respectively, the inlet opening 17 is located longitudinally at the first and second axial ends 51, 52 of the annular gap 50, and in each case is always located longitudinally within the length L1 of the annular gap 50.
[0055] 4 to 6 relate to an embodiment of the present invention, in which the second outer diameter D1 of the head portion central portion 33 is equal to the first outer diameters of the corresponding proximal and distal portions 31, 35 of the head portion 30, and is therefore equal to the common nominal diameter D of the cylinder 10 and the head portion 30, and the second inner diameter D2 of the cylinder central portion 13 is larger than the first inner diameters of the corresponding proximal and distal portions 11, 15, and is therefore larger than the common nominal diameter D by the gap thickness G. Thus, the annular gap 50 is included in the contour of the cylinder 10.
[0056] In this case, the annular gap 50 can be obtained, for example, by removing a portion of material of a given length L2 from the central portion 13 of the cylinder 10. In either case, the cylinder central portion 13 with the increased (second) inner diameter has a length L2 at most equal to the difference LC between the length L of the head portion central portion 33 and the stroke C of the slidable member 20, the head portion central portion 33 being understood as the area of the central portion 33 between the innermost piston rings 41, 45. During the stroke C of the slidable member 20, a fixed annular gap 50 always exists between the cylinder central portion 13 and the head portion central portion 33.
[0057] Similar considerations apply to a compression unit consisting of a plunger unit, the diameter of the plunger center being greater than the common nominal diameter of the plunger and cylinder.
[0058] 10-14 and 17-21 relate to double-acting piston-cylinder units 1a-1i according to advantageous embodiments of the piston-cylinder unit 1 of FIGS. 1 and 2, but may also relate to single-acting embodiments. In the double-acting piston-cylinder units 1a-1i, the proximal portion 31 of the head portion 30 has a second compression surface 32 opposite the first compression surface 36 with respect to the head portion central portion 33. The cylinder 10 and the second compression surface 32 define a second compression chamber 22, through the entire length of which a rod portion 39 is disposed. The second compression chamber 22 is provided with an intake port 24 for the gas to be compressed and a discharge port 26 for the compressed gas.
[0059] In the two embodiments shown in Figures 10 and 12, the head portion central part 33 of the piston-cylinder units 1a and 1c has a cylindrical shape with a diameter D1. Alternatively, in two advantageous embodiments shown in Figures 11 and 13, the head portion central part 33 of the piston-cylinder units 1b and 1d has a frusto-conical shape, or more generally a shape in which the diameter D1 decreases from a maximum value D1" near the head portion proximal part 31 to a minimum value D1' near the head portion distal part 33.
[0060] Figures 14 and portions of Figures 15 and 16 show the piston-cylinder unit 1c of Figure 12 in more detail, and in particular Figure 16 shows the cylinder 10 of the piston-cylinder unit 1c without the head portion 30 of the piston 20 in order to show the interior of the cylinder 10.
[0061] 12 to 16, the cylinder central portion 13 of the piston-cylinder unit 1c has an outlet hole or outlet opening 18 for the barrier fluid 9 in addition to the inlet opening 17. The outlet opening 18 is arranged along the cylinder 10 so as to be located at the first axial end 51 of the head portion central portion 33 when the piston 20 is at top dead center as shown in FIG. 1, and at the second axial end 52 of the head portion central portion 33 when the piston 20 is at bottom dead center as shown in FIG. 2. In this way, the barrier fluid 9 can pass through the annular gap 50 in addition to being pressurized. This feature can obviously be extended to the case of the single-acting cylinder piston unit 20 of FIGS. 1 to 3 and the case of the plunger unit 3 of FIGS. 7 to 9.
[0062] In particular, as shown in FIG. 16, the cylinder 10 has a recess or circumferential groove 19 in its cross section, preferably in which an input opening 17 and an output opening 18 communicating with the circumferential groove 19 are made.
[0063] 17 to 19 relate to three double-acting cylinder-piston units 1e, 1f, and 1g according to respective variants of an advantageous embodiment of the invention, in which the rod portion 39 is provided with proximal and distal seals (not shown), and between the proximal and distal seals a second annular gap is defined providing a rod portion barrier chamber, i.e. a chamber arranged to be supplied with rod portion barrier fluid 9 or 9′. In cylinder-piston unit 1f of FIG. 18 and cylinder-piston unit 1g of FIG. 19, both annular gaps, i.e. the head portion barrier chamber 50 and the rod portion barrier chamber, are arranged to receive the same barrier fluid 9 from a common barrier fluid source 8. In particular, the second annular gap of piston-cylinder unit 1g (FIG. 19) has an inlet opening 67 in hydraulic communication with the barrier fluid source 8, whereby both barrier chambers are arranged to receive the common barrier fluid 9 directly from the barrier fluid source 8, i.e. the barrier chambers are arranged in parallel with the barrier fluid source 8. Alternatively, the cylinder 10 and the second annular gap of the piston-cylinder unit 1f (Figure 18) have respective outlet openings 18, 68 for a common barrier fluid 9, and the outlet opening 18 of the head portion barrier chamber 50 is hydraulically connected to the inlet opening 67 of the rod portion barrier chamber, in other words the two barrier chambers are arranged in series with respect to a common barrier fluid supply source 8.
[0064] Although Figures 17 to 19 show only double-acting cylinder piston units 1e to g in which the barrier chambers are provided with separate inlet openings 17, 67 and outlet openings 18, 68, the scope of the present invention also covers single-acting or double-acting cylinder piston compression units in which, in addition to the head portion barrier chamber 50, a rod portion barrier chamber is provided, each barrier chamber having one inlet / outlet opening or separate inlet / outlet openings, which openings can be obtained by modifying what is shown in Figures 17 to 19 in a manner obvious to a person skilled in the art.
[0065] 20 illustrates a cylinder-piston unit 1h according to one embodiment of the present invention, in which a cooling circuit 70 is configured to deliver cooling fluid 7 available at a cooling fluid pressure higher than the discharge pressure of the compressor that includes the cylinder-piston unit 1h. Moreover, both the rod portion barrier chamber and the head portion barrier chamber can be hydraulically connected to the cooling circuit 70 in parallel with each other, as shown, or in an alternative variation of this embodiment not shown, in series with each other. Thus, a portion of the cooling fluid 7 contained within the cooling circuit 70 provides barrier fluid 9 to both the rod portion barrier chamber and the head portion barrier chamber, and the inlet opening 17 of the barrier chamber 50 is in hydraulic communication with the cooling circuit 70.
[0066] Although Figure 20 shows a double-acting cylinder piston unit 1h including both a head portion barrier chamber and a rod portion barrier chamber, and in which the barrier chambers are provided with both inlet openings 17, 67 and outlet openings 18, 68, the scope of the present invention also encompasses compressors including single-acting or double-acting cylinder piston units in which only a head portion barrier chamber is provided, as well as compressors including single-acting or double-acting cylinder piston units including single-acting or double-acting cylinder piston units with a head portion barrier chamber and optionally a rod portion barrier chamber, the chambers having a single inlet opening 17 or separate inlet and outlet openings 17 and 18 (respectively), and the chambers or chamber barriers being in hydraulic communication with the cooling circuit of the cylinder piston unit by modifications to Figure 20 that will be obvious to those skilled in the art.
[0067] 21 , in a piston-cylinder unit 1i of a compressor according to one embodiment of the present invention, the supply circuit 4 includes a compensator tank 40 having a deformable membrane 45 defining a first chamber 41 and a second chamber 42 having variable volumes. The first chamber 41 of the compensator tank 40 is in air communication with the discharge ports 16, 26 of the compression chambers 12, 22, and thereby contains a variable volume of low-molecular-weight gas handled by the compressor unit 1i at the discharge pressure of the compressor unit 1i during operation of the compressor unit 1i. The second chamber 42 is in communication with the suction ports 17, 67 of the annular gap or barrier chambers of the head portion 30 and piston rod portion 39 of the piston 20, and contains a predetermined amount of barrier fluid 9 at a pressure that depends on the pressure of the first chamber 41, i.e., the discharge pressure of the compressor unit 1i.
[0068] Although Figure 21 shows a double-acting cylinder piston unit 1h including both a head portion barrier chamber and a rod portion barrier chamber, the scope of the present invention also encompasses compressors including single-acting or double-acting cylinder piston units provided with only a head portion barrier chamber, as well as compressors including single-acting or double-acting cylinder piston units including single-acting or double-acting cylinder piston units with a head portion barrier chamber and optionally a rod portion barrier chamber, wherein a first chamber of the compensation vessel is in air communication with the discharge port of one or more compression chambers and a second chamber is in air communication with the suction port of the barrier chamber, by modifications to Figure 21 that will be obvious to those skilled in the art.
[0069] In an embodiment not shown, the compressor has multiple compression stages, i.e., comprises multiple compression units 1, 1a-g, 2, or 3 arranged in series as shown in Figures 1 to 21, and these compression units operate within successive suction-discharge pressure sections. In this case, the inlet opening 17 of the barrier chamber 50 of the upstream compressor unit arranged to perform the low-pressure compression stage may be in pneumatic communication with the discharge port 16, 26 of the compression chamber of the downstream compressor unit arranged to perform the high-pressure compression stage, whereby the barrier chamber 50 of the upstream low-pressure compression unit is supplied with a barrier fluid 9 containing low-molecular-weight gas processed by the downstream high-pressure compression unit.
[0070] The above description of embodiments of the present invention may illustrate the invention from a conceptual point of view so that others, using known techniques, may modify and / or adapt such specific embodiments for various uses without further investigation and without departing from the concept of the present invention; therefore, it is understood that such changes and modifications are considered equivalent to variations and specific embodiments. The means and materials for achieving the various functions described may be of various types without departing from the scope of the present invention. It is understood that the expressions or terms used are merely descriptive and therefore not limiting.
Claims
1. A compressor configured to compress a low molecular weight gas to a predetermined discharge pressure is provided, comprising at least one compression unit (1, 1a-i, 2, 3) comprising a cylinder (10) and a slidable member (20) arranged within said cylinder (10), said slidable member (20) having a head portion (30) and a rod portion (39) integral with said head portion (30) and arranged to cause said head portion (30) to perform a stroke (C) within said cylinder (10); the cylinder (10) has a proximal portion (11), a central portion (13), and a distal portion (15) relative to the rod portion (39), the proximal portion (11) and the distal portion (15) of the cylinder (10) having a first inner diameter; the head portion (30) has a proximal portion (31), a central portion (33), and a distal portion (35) relative to the rod portion (39), the proximal portion (31) and the distal portion (35) of the head portion (30) having a first outer diameter; the first inner diameter of the cylinder (10) and the first outer diameter of the head portion (30) are equal to a common nominal diameter (D) of the cylinder (10) and the head portion (30), except for a predetermined coupling tolerance; the central portion (13) of the cylinder (10) has a second inner diameter (D2); the central portion (33) of the head portion (30) has a second outer diameter (D1); the distal portion (35) of the head portion (30) comprises a compression surface (36) opposite the central portion (33) of the head portion (30); the compression surface (36) defining a compression chamber (12) within the cylinder (10), the compression chamber having an intake port (14) and a discharge port (16) for the low molecular weight gas; the second inner diameter (D2) is greater than the second outer diameter (D1) by a predetermined amount (G) such that an annular gap (50) having a thickness (G) equal to the predetermined amount (G) is defined between the central portion (33) of the head portion (30) and the central portion (13) of the cylinder (10); the central portion (13) of the cylinder (10) has at least one inlet opening (17) for a barrier fluid (9), the inlet opening (17) being in fluid communication with a source (8) of the barrier fluid (9) configured to deliver the barrier fluid (9) to the annular gap (50) at a predetermined barrier pressure, such that the barrier fluid occupies the annular gap (50), and the annular gap (50) forms a barrier chamber between the compression chamber (12) and a space (22) on an opposite side of the compression chamber (12) with respect to the head portion (30) of the slidable member (20).
2. 2. The compressor according to claim 1, wherein the thickness (G) of the annular gap (50) between the central portion (13) of the cylinder (10) and the central portion (33) of the head portion (30) of the compressor unit (1, 1a-i, 2, 3) is at least 1 mm, particularly at least 5 mm, and more particularly at least 10 mm.
3. - the second internal diameter (D2) of the central portion (13) of the cylinder (10) of the compression unit (1, 1a-i, 2) is equal to the common nominal diameter (D); - said second outer diameter (D1) of said central part (33) of said head portion (30) is smaller than said common nominal diameter (D) by said predetermined amount (G); A compressor according to claim 1, wherein said central portion (33) of said head portion (30) has a length (L1) at least equal to said stroke (C).
4. - the second outer diameter (D1) of the central part (33) of the head portion (30) of the compression unit (3) is equal to the common nominal diameter (D); - said second internal diameter (D2) of said central part (13) of said cylinder (10) is greater than said common nominal diameter (D) by said predetermined amount (G); A compressor according to claim 1, wherein the central part (13) of the cylinder (10) has a length (L2) at most equal to the difference between the length (L1) of the central part (33) of the head portion (30) and the stroke (C).
5. the compression units (1a-i) are cylinder-piston units, and the slidable members are pistons (20); the proximal portion (31) and the distal portion (35) of the head portion (30) each include at least two elastic piston rings (41, 45) spaced apart from each other by a distance, the elastic piston rings (41, 45) being arranged to slide within the cylinder (10); 2. The compressor of claim 1, wherein the central portion (33) of the head portion (30) is located between the elastic piston ring (41) of the proximal portion (31) of the head portion (30) and the elastic piston ring (45) of the distal portion (35) of the head portion (30).
6. 6. The compressor of claim 5, wherein the cylinder-piston unit is a double-acting cylinder-piston unit, the compression surface of the head portion is a first compression surface, the compression chamber is a first compression chamber, the proximal portion of the head portion has a second compression surface on an opposite side of the first compression surface with respect to the central portion of the head portion, the second compression surface and the cylinder define a second compression chamber, and the rod portion is disposed throughout the entire length of the second compression chamber.
7. 2. The compressor of claim 1, wherein the second diameter (D1) of the central portion (33) of the head portion (30) of the compression unit (1b, 1d) decreases from the proximal portion (31) to the distal portion (35) of the head portion (30).
8. 2. The compressor of claim 1, wherein the central portion (13) of the cylinder (10) of the slidable member (20) of the compressor unit (1c-h, 2, 3) has at least one outlet opening (18) for the barrier fluid (9).
9. 9. The compressor according to claim 8, wherein the inlet opening (17) and the outlet opening (18) are made in the same cross section of the cylinder (10), and the cylinder (10) has a circumferential groove (19) in the cross section, the circumferential groove communicating with the inlet opening (17) and the outlet opening (18).
10. 7. The compressor of claim 6, wherein the annular gap is a first annular gap, and the rod portion of the slidable member of the compressor unit is provided with proximal and distal seals, and a second annular gap of the rod portion is defined between the proximal and distal seals, and the second annular gap has at least one inlet opening arranged to be supplied with a rod portion barrier fluid.
11. The first annular gap (50) and the second annular gap (50) of the compressor units (1f-i) are arranged to receive a common barrier fluid (9) and have an interconnection, the interconnection comprising: a parallel interconnection, in which the first and second annular gaps are arranged in parallel with each other, i.e. both the first and second annular gaps are arranged to receive the common barrier fluid (9) directly from the source (8); a serial interconnection, in which the cylinder (10) and the second annular gap also have respective outlet openings (18, 68) for the common barrier fluid (9), the outlet opening (18) of the cylinder being hydraulically connected to the inlet opening (67) of the second annular gap.
12. 2. The compressor of claim 1, wherein the compressor unit (1h) comprises a cooling circuit (70) for the cylinder (10) and the slidable member (20), the cooling circuit being configured to deliver cooling fluid (7) at a predetermined cooling fluid pressure that exceeds the discharge pressure, and the inlet opening (17) of the cylinder (10) being in hydraulic communication with the cooling circuit (70).
13. the compression unit (1i) comprises a supply circuit (4), in which a compensation vessel (40) is provided, in which a deformable membrane is arranged to define first and second variable volume chambers (41, 42), the first and second variable volume chambers (41, 42) being in fluid communication with the discharge port (16) of the compression chamber (12) and the inlet opening (17) of the cylinder (10), respectively, the second variable volume chamber (42) being configured to contain a predetermined amount of the barrier fluid (9); The compressor of claim 10, whereby the barrier fluid can be delivered to the annular gap (50) at a pressure that depends on the pressure of the low molecular weight gas at the discharge port (16).