Multi-stage gas compressing apparatus

Abstract

A compressed gas compressed by the first gas compressor is further compressed by the second gas compressor. The compressed gas from the first gas compressor is sent to a crank case of the second gas compressor in which the gas is further compressed. The gas is sent to a cylinder of the second gas compressor and compressed by a piston in the cylinder.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a multi-stage gas compressing apparatus, and particularly to a multi-stage gas compressing apparatus in which a compressed gas is compressed by a plurality of gas compressors gradually.

JP2003-97466A discloses an oilless gas compressor in which a compressed gas introduced in the cylinder from the inlet is compressed by the piston which reciprocates with rotation of the crankshaft via the connecting rod in the crank case and is discharged from the outlet into a storage tank.

Nowadays, it is necessary to use an oilless compressor providing high discharge pressure of more than 2 MPa.

The oilless compressor used under high pressure is expensive and poor in durability. It is free of oil. Grease-containing bearings and air seals are short in life. So it is required to use a number of parts for maintenance, and parts used under low pressure cannot be used.

In a booster compressor in JP2000-34980A, a compressed gas is introduced in the cylinder of the compressor body and stored in the storage tank. The compressed gas in the storage tank is introduced to the compressor body again via the bypass conduit. By repeating the compression, the compressed gas in the storage tank is compressed gradually.

In the booster compressor, the compressed gas in the storage tank is directly introduced in the cylinder of the compressor body. Thus, the inside of the crank case for actuating the piston is always kept at atmospheric pressure.

As the compression step becomes high pressure, the pressure difference between the cylinder and the crank case increases. Especially the piston returns more rapidly in the reciprocating step.

Parts such as bearings for the crankshaft is subjected to more load, thereby reducing its life.

SUMMARY OF THE INVENTION

In view of the disadvantages, it is an object of the invention to provide a multi-stage gas compressing apparatus that can be operated under high pressure, similar parts to those under low pressure being used, lives of parts being extended.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will become more apparent from the following description with respect to embodiments as shown in accompanying drawings.

FIG. 1 is a vertical sectional view of a booster compressor used in one embodiment of a multi-stage gas compressing apparatus according to the present invention.

FIG. 2 is a block diagram showing one embodiment of a multi-stage compressing process.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 is a booster compressor used in one embodiment of a multistage gas compressing apparatus according to the present invention.

In FIG. 1, the booster compressor 1 in this invention comprises a tightly sealed crank case 2; a cylinder 3 on the crank case 2; a sucking chamber 5 having an inlet 4; and a discharge chamber 7 having an outlet 6 partitioned by a wall 8 from the sucking chamber 5.

The sucking chamber 5 and the discharge chamber 7 communicate with the cylinder 3 with a sucking port 9 and a discharge port 10 respectively. The sucking port 9 and the discharge port 10 have check valves 11 and 12 respectively.

In the crank case 2, a driving shaft 14 integrally connected with a crankshaft 13 driven by power is rotatably supported with bearings 15,15 and a seal 16.

A connecting rod 18 is pivotally supported at one end 18a by the crankshaft 13 with a bearing 17.

The other end 18b of the connecting rod 18 is mounted to a piston 19 reciprocating in the cylinder 3.

To the crank case 2, an introducing conduit 20 for a compressed gas and a connecting conduit 21 are connected.

The compressed gas A is introduced in the crank case 2 through the introducing conduit 20 and sent into the sucking chamber 5 from the inlet 4.

The compressed gas A is introduced in the crank case 2 through the introducing conduit 20 from a plant pressure conduit system or an oilless compressor and sent in the sucking chamber 5 through the connecting conduit 21 via the crank case 2.

The compressed gas in the crank case 2 is compressed by the piston 19 reciprocating in the cylinder 3 and introduced in the sucking chamber 5.

The compressed gas A in the sucking chamber 5 is introduced in the cylinder 3 through the sucking port 9 by opening the check valve 11 with reciprocation of the piston 19. By closing the check valve 11 with reciprocation of the piston 19, the gas is compressed.

The compressed gas A is discharged from the outlet 6 via the discharge chamber 7 by opening the check valve 12 in the discharge port 10. After the gas A is cooled by an aftercooler 22, it is sent to an inlet of a crank case of another booster compressor or to a storage tank.

In the embodiment, the compressed gas A is introduced from the plant pressure conduit system or oilless compressor into the sucking chamber 5 via the crank case 2. At least part of the compressed gas A may be introduced into the crank case 2 of the booster compressor 1.

FIG. 2 is a block diagram showing one embodiment of a multistage compression process.

In the embodiment, there are a low-pressure oilless compressor 23 and two booster compressors 24,25 which comprises the structure which sustains discharge pressure of compressed gas in each of the compressing steps.

An outlet of the oilless compressor 23 is connected to an inlet of a crank case of the first booster compressor 24 via a drier 26 for removing moisture. An outlet of the first booster compressor 24 is connected in series to an inlet of a crank case of the second booster compressor 25 via an aftercooler 27 for cooling the compressed gas.

A compressed gas is compressed to a discharge pressure for 1.4 MPa by the oilless compressor 23 and introduced into the crank case of the first booster compressor 24 via the drier 26.

The compressed gas after cooling by the drier 26 is taken out at the discharge pressure for 1.4 MPa.

The compressed gas compressed by the oilless compressor 23 is compressed by the first booster compressor 24 to the discharge pressure for 1.5 to 2.8 MPa and introduced into the crank case of the second booster compressor 25 via the aftercooler 27.

The compressed gas cooled by the aftercooler 27 is taken out at the discharge pressure for 1.5 to 2.8 MPa.

The compressed gas compressed by the first booster compressor 24 is compressed by the second booster compressor 25 to the discharge pressure for 2.9 to 3.8 MPa and taken out.

The compressed gas compressed by the oilless compressor 23 to the discharge pressure for 1.4 MPa is introduced in a cylinder via the crank cases of the first and second booster compressors 24,25. The discharge pressure is increased by the first booster compressor 24 to 2.8 MPa and by the second booster compressor to 3.8 MPa.

Accordingly, the pressure difference between the cylinder and the crank cases of the booster compressors 24,25 can be reduced. Compared with conventional compression by a single gas compressor, resistance against discharge pressure of compressed gas in each compression step can be increased to allow operation under high pressure.

It enables load applied to parts such as bearings for the crankshaft to decrease in each compression step. Thus, their lives are increased. Parts used under low pressure can be used as well.

The foregoing merely relates embodiments of the invention. Various changes and modification may be made by a person skilled in the art without departing from the scope of claims wherein:

Claims

1. A multi-stage gas compressing apparatus comprising:

a first gas compressor comprising a first driving shaft, a first crank case, a first introducing conduit through which a compressed gas is introduced into the first crank case, a first driving shaft extending through the first crank case, a first crankshaft coupled to the first driving shaft to rotate with the first driving shaft, a first connecting rod rotatably mounted at one end to the first crankshaft, a first cylinder on the first crankcase, a first piston coupled at the other end to the first connecting rod in the first cylinder to move up and down with rotation of the first crankshaft, a first sucking chamber communicating with the first cylinder, a first connecting conduit connecting the first crankcase to the first sucking chamber, the compressed gas being introduced from the first crank case to the first sucking chamber through the first connecting conduit so that the compressed gas is compressed by the first piston in the first cylinder communicating with the first sucking chamber; and a first discharge chamber communicating with the first cylinder to allow the compressed gas to be discharged from the cylinder through the first discharge chamber; and

a second gas compressor comprising a second driving shaft, a second crank case, a second introducing conduit through which the compressed gas is introduced from the first discharge chamber of the first gas compressor into the second crank case, a second driving shaft extending through the second crank case, a second crankshaft coupled to the second driving shaft to rotate with the second driving shaft, a second connecting rod rotatably mounted at one end to the second crankshaft, a second cylinder on the second crankcase, a second piston coupled at the other end to the second connecting rod in the second cylinder to move up and down with rotation of the second crankshaft, a second sucking chamber communicating with the second cylinder, a second connecting conduit connecting the second crankcase to the second sucking chamber; the compressed gas being introduced from the second crank case to the second sucking chamber through the second connecting conduit so that the compressed gas is further compressed by the second piston in the second cylinder communicating with the second sucking chamber, and a second discharge chamber communicating with the second cylinder to allow the compressed gas to be discharged from the second cylinder through the second discharge chamber.

2. The multi-stage gas compressing apparatus of claim 1 wherein the first and second gas compressors comprise a booster compressor.

3. The multi-stage gas compressing apparatus of claim 1, further comprising an oilless gas compressor for sending a compressed gas to the first gas compressor.

4. The multi-stage gas compressing apparatus of claim 3 further comprising an aftercooler between the first compressor and the second compressor.

5. The multi-stage gas compressing apparatus of claim 4 further comprising a drier between the oilless gas compressor and the first booster compressor.

6. The multi-stage gas compressing apparatus of claim 5 wherein a compressed gas is taken out of the drier, a compressed gas being taken out of the aftercooler, a compressed gas being taken out of the second gas compressor.

7. The multi-stage gas compressing apparatus of claim 6 wherein a compressed gas of less than 1.4 MPa is taken out of the drier, a compressed gas of 1.5 to 2.8 MPa being taken out of the aftercooler, a compressed gas of 2.9 to 3.8 MPa being taken out of the second gas compressor.