JP2010242642A - Reciprocating compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen compressor preventing fretting fatigue caused by repeated stress in a high-temperature and high-pressure environment and hydrogen embrittlement caused by working hydrogen gas; and besides preventing leakage of high-pressure gas. <P>SOLUTION: The plunger hydrogen compressor compressing hydrogen gas in a compression chamber formed between a plunger and a cylinder by the reciprocating motion of the plunger includes: a plurality of rod packings provided in a plunger axial direction in order to be slid while being brought into close contact with the peripheral surface of the plunger so that the hydrogen gas compressed in the compression chamber is prevented from being leaked from the peripheral portion of the plunger; and a plurality of rod packing cases storing the rod packings. The hydrogen gas compressed in the compression chamber is prevented from being leaked from the mutual contact surfaces of the rod packing cases. The rod packing cases are formed with a nitrided layer on the contact surfaces. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a reciprocating compressor that handles combustible gas and the like, and more particularly, to a reciprocating compressor suitable for compressing hydrogen gas used in a fuel cell vehicle.

  Currently, hydrogen fuel cell vehicles are required to have 70MPa of hydrogen gas filling pressure in the fuel tank in order to achieve the same cruising range as gasoline vehicles, and a reciprocating compressor excellent in boosting lightweight gas is selected. Has been. Conventionally, a cylinder of a high-pressure reciprocating compressor exceeding 40 MPa has a plurality of plungers, rod packings, and rod packing cases, and the rod packing case is made by contacting the rod packing case with a high-strength material. A structure is adopted in which the gas boosted in step 3 is not leaked to the outside. For example, as shown in Patent Document 1 and Patent Document 2, in order to prevent compressed gas from leaking from the outer peripheral portion of the plunger, a rod packing that slides in close contact with the outer peripheral surface of the plunger is arranged in the plunger axial direction. There are several. A plurality of rod packing cases for housing the rod packing are also provided in the plunger axial direction, and an O-ring (annular seal in Patent Document 1) is used to prevent the compressed gas from leaking to the contact surfaces of the rod packing cases. Is arranged.

Japanese Patent Laid-Open No. 8-200512 JP 2007-2893 A

  However, in Patent Documents 1 and 2 described above, a plurality of rod packings are provided for leakage from the outer peripheral portion of the plunger. However, for leakage from the contact surfaces of the rod packing cases, an O-ring and a rod are provided. The contact pressure between the packing cases corresponds, and is not sufficient. For this reason, in a reciprocating compressor that handles high-pressure gas exceeding 40 MPa, a high-strength steel material is used for the rod packing case, and a structure in which the contact surfaces are brought into contact with each other in a high surface pressure state is required. As the surface pressure for preventing the leakage, a considerably large value is required according to the gas pressure.

  However, since the reciprocating compressor has a pressure fluctuation in the compression chamber due to its unique operation, if repeated stress acts on the high pressure contact surfaces between the rod packing cases as described above, fretting fatigue (metal Micro-vibration of the mating surfaces repeatedly causes minute surface oxidation and peeling, causing a surface damage phenomenon that causes plastic deformation of the contact area. Fatigue cracks often occur and propagate from the damaged area, resulting in member destruction. As a result, the strength of the member is significantly reduced, and high-pressure gas may leak from the contact surface.

  In addition, when the working gas of the reciprocating compressor is hydrogen, the high-pressure and high-temperature hydrogen gas is easily absorbed into the metal from the contact surface between the rod packing cases and causes hydrogen embrittlement. (Ductility or toughness) may be reduced, leading to leakage of high-pressure gas at the contact surface. Hydrogen embrittlement is likely to occur in stress-concentrated parts, and the phenomenon is more pronounced with high-strength steel. Therefore, particularly in a rod packing case using high-strength steel in a hydrogen reciprocating compressor, the above-mentioned contact surface is flat. An effective measure for preventing leakage of high-pressure gas is desired in combination with fatigue.

  In view of the above-mentioned conventional problems, the present invention provides a rod packing case that is installed in a plurality of high-pressure cylinder structures of a compressor, fretting fatigue due to repeated stress in a high-temperature / high-pressure environment, and hydrogen embrittlement due to working hydrogen gas. A hydrogen compressor that prevents the leakage of high-pressure gas is provided.

  In order to solve the above problems, the present invention provides a plunger-type hydrogen compressor that compresses hydrogen gas in a compression chamber formed between a plunger and a cylinder by a reciprocating motion of the plunger, and the hydrogen gas compressed in the compression chamber is A plurality of rod packings arranged in the plunger axial direction so as to slide in close contact with the outer peripheral surface of the plunger so as to prevent leakage from the outer peripheral portion of the plunger, and a plurality of rod packing cases for storing each rod packing And a tightening mechanism that presses the contact surfaces to prevent hydrogen gas compressed in the compression chamber from leaking from the contact surfaces of the rod packing case, and the rod packing case is nitrided on the contact surface A layer is formed.

  Further, the present invention is characterized in that the rod packing case is fastened to each other with a high surface pressure by the fastening mechanism.

  In the invention, it is preferable that the tightening mechanism includes an inner cover and an outer cover of a cylinder sandwiching the plurality of rod packing cases together with the cylinder, and a cylinder tightening bolt for tightening the both covers.

  According to the present invention, by providing a nitrided layer by nitriding treatment on the contact surface between the high pressure side rod packing cases of the hydrogen compressor, effectively preventing hydrogen embrittlement in a high temperature / high pressure hydrogen gas environment, The leakage of high-pressure gas can be prevented, and the safety and reliability of the hydrogen compressor can be dramatically improved.

  Examples of the present invention will be described below. Figure 1 shows an external view of the hydrogen compressor. The hydrogen compressor includes a hermetic frame 4 serving as a crankcase, an oil pan, and a hydrogen gas receiver, a low pressure side cylinder 1 on the vertical axis, and high pressure side cylinders 2 and 3 on the horizontal axis.

  FIG. 2 is a longitudinal sectional view of, for example, a high-pressure side cylinder 3 in which a rod packing and a rod packing case incorporating the rod packing are arranged in a plunger reciprocating compressor. The compressor pressurizes hydrogen used in the fuel cell, and the pressure reaches 70 Mpa. Therefore, a leakage prevention device is provided for sealing high-pressure gas to prevent leakage outside the compressor.

  Reference numeral 5 denotes a compression chamber composed of a cylinder ring 13, a rod-like plunger 15, and a cylinder outer cover 16 (described later). The plunger 15 moves in the cylinder ring 13 in the axial direction thereof, so that the plunger 15 Hydrogen working gas is compressed at the tip. A reciprocating force is transmitted from the right end of FIG. 2 to the plunger 15 via a crankshaft connected to a drive source (not shown), a connecting rod connected to the crankshaft, and an intermediate rod connected to the connecting rod. It is done.

  An outer cover 16 of the cylinder is attached to the end surface of the cylinder 13 on the compression side (left end side) of the plunger 15, and an inner cover 10 of the cylinder through which the plunger 15 passes is attached to the right end side. In the axial direction of the plunger 15, a plurality of annular rod packing cases (described later) through which the plunger 15 passes are sandwiched and supported between the inner cover 10 and the cylinder ring 13.

  A valve unit 17 connected to the compression chamber 5 is built in the outer cover 16 of the cylinder. The valve unit 17 includes a hydrogen gas suction port 6 and a discharge port 7. By the movement of the plunger 15 in the right direction, hydrogen gas is sucked from the suction port 6 through a suction valve (not shown) inside the valve unit 17 and led to the compression chamber 5, and the plunger 15 is moved in the left direction. The hydrogen gas sucked in is compressed in the compression chamber 5, and the hydrogen gas compressed to an ultrahigh pressure is discharged from the discharge port 7 through a discharge valve (not shown) inside the valve unit 17, The required external storage tank (not shown) is supplied.

  Next, the structure of the seal portion (leakage prevention device) of the cylinder 12 will be described. The hydrogen gas compressed in the compression chamber 5 has an extremely high pressure and tends to flow to the hermetic frame side 4 through the gap between the sliding surface between the inner peripheral surface of the cylinder ring 13 and the outer peripheral surface of the plunger 15. . A plurality of annular rod packings 21 </ b> P to 30 </ b> P are disposed so as to be penetrated by the plunger 15, so as to be in pressure contact with the outer peripheral surface of the plunger 15 and disposed along the axial direction. Accordingly, the high-pressure hydrogen gas that tends to flow from the gap to the hermetic frame side 4 is gradually reduced in pressure by the plurality of rod packings 21P to 30P, and gas leakage occurs in the final stage rod packing 30P. Completely prevented. A plurality of rod packing cases 21 to 30 for housing the rod packing are arranged in the cylinder 12 in the axial direction of the plunger 15.

The rod packing cases 21 to 30 are formed in an annular shape, for example, of chromium molybdenum steel SCM435 material (hydrogen brittle material), and are sandwiched between the outer cover 16 and the inner cover of the cylinder 12, and are arranged in the radial direction of the rod packing cases 21 to 30. By tightening both covers with the cylinder tightening bolts 18 located on the outside, the neighbors are held at a high surface pressure of about 70 kg / mm ² . This surface pressure is a value sufficient to seal an ultrahigh pressure gas of 70 Mpa with a steel material. Ultra-high pressure hydrogen gas tries to leak directly to the outside in the radial direction from the gap between the contact surfaces of the rod packing cases through the gap between the sliding surface between the inner circumferential surface of the cylinder ring 13 and the outer circumferential surface of the plunger 15. However, since the rod packing cases are in contact with each other at a predetermined pressure as described above, the pressure is gradually reduced in the radial direction at the surface contact portion, and leakage is prevented.

  The rod packing cases 21 to 30 are subjected to nitriding treatment on the contact surfaces between adjacent cases to form a nitride layer on the surface, thereby suppressing hydrogen gas from entering and suppressing surface hydrogen embrittlement. In the nitriding treatment, an anti-nitriding agent is applied to the surfaces other than the surface that becomes the contact surface during assembly of the rod packing cases 21 to 30 in the component state before assembly. Next, the rod packing cases 21 to 30 are put in a gas furnace (not shown) containing ammonia to perform heat treatment. In the above gas furnace, nitriding treatment is applied to the surface where no anti-nitriding agent is applied, and elements such as chromium (Cr) and molybdenum (Mo) existing in the steel of the rod packing case are combined with nitrogen to form a hard nitrided layer. Is done.

  FIG. 3 shows a schematic diagram of the rod packing case after nitriding. In this figure, for example, the rod packing case 25 shown in FIG. 2 is enlarged, the contact surfaces of the adjacent rod packing cases 24 and 26 are indicated by 100, 101, 102 and 103, respectively, and 25P ′ is the rod packing. Indicates a space in which 25P is built. By the nitriding treatment, a nitride layer having a depth of about 0.45 mm is formed on the contact surfaces 100 to 103 of the rod packing case, and its hardness is about Hv (micro pickers) 480 to 550, and adjacent rods A similar nitride layer is also formed on the contact surfaces of the packing cases 24 and 26 with the contact surfaces 100 and 101 and 102 and 103.

  In the assembly process of the rod packing case, the rod packing cases 21 to 30 nitrided as described above are in contact with the nitride layers and stacked and assembled so as to incorporate the rod packings 21P to 30P. (Figure 2).

  The nitride layers of the rod packings 21P to 30P formed by the above nitriding treatment are set to the above-described film thickness and hardness, thereby suppressing the absorption of hydrogen into the metal even in a high temperature / high pressure hydrogen gas environment. Prevent hydrogen embrittlement. Therefore, even if repetitive stress is applied due to the operation specific to the compressor under high contact pressure, the fretting fatigue of the contact surface can be prevented by the action of preventing hydrogen embrittlement by the nitride layer, and the life of the rod packing case can be extended. Can be achieved.

In addition, since the contact surface is pressed to about 70 kg / mm ² , leakage of high-pressure hydrogen gas to the outside is effectively prevented, and the contact surface is extended as described above, so that leakage can be prevented. It will be maintained for a long time, and the safety and reliability of the hydrogen compressor will increase dramatically.

It is an external view of the hydrogen compressor main body of the Example of this invention. It is the longitudinal cross-sectional view of the high pressure side cylinder of a hydrogen compressor similarly. It is the model of the rod packing case after nitriding similarly.

  DESCRIPTION OF SYMBOLS 1 ... Low pressure side cylinder, 2/3 ... High pressure side cylinder, 4 ... Hermetic frame, 5 ... Compression chamber, 10 ... Inner cover of cylinder, 12 ... Cylinder, 13 ... Cylinder ring, 15 ... Plunger, 16 ... Outer cover of cylinder , 17 ... Valve unit, 18 ... Cylinder clamping bolt, 21-30 ... Rod packing case, 21P-30P ... Rod packing, 100, 101, 102, 103 ... Contact surface (nitriding layer) of the rod packing case.

Claims (3)

In a plunger-type hydrogen compressor that compresses hydrogen gas in a compression chamber formed between a plunger and a cylinder by reciprocation of the plunger,
A plurality of rod packings arranged in the plunger axial direction so as to slide in close contact with the outer peripheral surface of the plunger so as to prevent hydrogen gas compressed in the compression chamber from leaking from the outer peripheral portion of the plunger; A plurality of rod packing cases for storing the rod packing, and a tightening mechanism for pressing the contact surfaces so as to prevent hydrogen gas compressed in the compression chamber from leaking from the contact surfaces of the rod packing case. The rod packing case is characterized in that a nitride layer is formed on the contact surface.   2. The hydrogen compressor according to claim 1, wherein the rod packing case is fastened to each other at a high surface pressure by the fastening mechanism.   3. The hydrogen compressor according to claim 1, wherein the tightening mechanism includes an inner cover and an outer cover of a cylinder sandwiching the plurality of rod packing cases together with the cylinder, and a cylinder tightening bolt for tightening the both covers. A hydrogen compressor characterized by that.

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