JPH0646031B2 - Single-stage oil-free screw compressor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a shaft seal device for an oil-free compressor, and in particular, when using an oil-free screw compressor or the like under no load, compression is performed using discharged gas. The present invention relates to a shaft seal device for an oil-free compressor, which is suitable for increasing the shaft seal effect around the rotary shaft of a machine.

[Conventional technology]

First, a conventional shaft seal device for an oil-free compressor will be described with reference to FIGS. 3 and 4.

Here, FIG. 3 is a cross-sectional view of a conventional single-stage oil-free compressor body, and FIG. 4 is a vertical cross-sectional view of the compressor body.

In the figure, reference numerals 1 and 2 denote a pair of male and female screw rotors that rotate in mesh with each other, which relate to a compression machine element, 1 is a male rotor, 2 is a female rotor, 3 is a casing, and 4 is a suction casing.

5 is a radial bearing provided on the suction side rotor shaft, and 6 is
A radial bearing 7 is provided on the discharge side rotor shaft, and a thrust bearing 7 supports the weight of the screw rotor and the load generated by the compression of air.

8 is a pinion for transmitting power to the male rotor 1, 9 is a timing gear attached to each rotor shaft end of the male rotor 1 and the female rotor 2, and by the meshing of the timing gear 9,
The rotation is transmitted from the male rotor 1 to the female rotor 2.

In this single-stage oil-free screw compressor, suction port 1
4, the air sucked into the pressure chambers in the casing 3 and the suction casing 4 is compressed by the rotation of the pair of male rotor 1 and female rotor 2 which mesh with each other, and the compressed air is discharged from the discharge port 15 to discharge the discharge piping system. It is supplied to the demand destination through (not shown).

Oil is supplied to the discharge side bearings and gears from the oil supply port 18B provided in the casing 3, and after performing necessary lubrication, is discharged from the discharge side oil discharge port 19B also provided in the casing 3. Similarly, oil is supplied to the suction side bearings and gears from the oil supply port 18A provided in the suction casing 4, and after performing necessary lubrication, the suction casing 4 is also subjected to the same lubrication.
The oil discharged from the oil discharge port 19A on the suction side provided in the oil is collected by an oil recovery device (not shown) connected to the oil discharge ports 19A and 19B.

Generally, all oil-free screw compressors rotate in non-contact with the exception of bearings and gears that require lubrication, and the male and female rotors related to the compression element are oil-free.

Therefore, in the compressor of this type, the suction side carbon ring 12 is discharged around the suction side rotor shaft as a shaft sealing means in order to suppress leakage of compressed air from the non-contact rotor shaft portion as much as possible. The discharge side carbon ring 13 is attached around the rotor side to form an air seal.

Further, as a shaft sealing means for preventing oil for lubricating each bearing and gear from entering the compression chambers in the casing 3 and the suction casing 4, a screw seal type oil removing device that generates sealing pressure by itself is used. A reference numeral 10 is a suction side oil drainer, and 11 is a discharge side oil drainer.

There is an opening to the atmosphere in the middle where the air seal related to the shaft sealing means and the oil removing device are provided side by side, 16 is a suction gas vent hole, and 17 is a discharge gas vent hole.

[Problems to be Solved by the Invention]

In the case of a single-stage oil-free screw compressor, the conventional oil removing device has a discharge side temperature as high as about 300 to 350 ° C., so that the gap between the discharge side oil removing device 11 and the rotor shaft is set to the thermal expansion of the rotor. Therefore, it cannot be kept small. For this reason,
The shaft sealing pressure is small and is about 20 to 30 mmAq, and there is a problem that the shaft sealing pressure is reduced particularly when the compressor is under no-load operation, and the effect of the oil removing device is insufficient.

Japanese Unexamined Patent Publication No. 52-144808 discloses that a medium-pressure air is supplied to a shaft seal device during load operation of a multi-stage compressor, optionally via a pressure reducing valve, and air is blown to a blow-off pipe during no-load operation. A technique for supplying pressure due to resistance to the shaft sealing device to increase the shaft sealing pressure is disclosed, but in this case, the desired pressure could not always be obtained. In addition, JP-A-50-5
Japanese Patent No. 3909 discloses a technique of supplying a part of the compressed and high-pressure gas as shaft-sealing air through a throttle valve during load operation or low load operation. No mention of the case.

The present invention has been made in order to solve the above-mentioned problems of the prior art, so that the lubricating oil can be prevented from entering the pressure chamber under any load condition of the compressor. It is an object of the present invention to provide a shaft seal device for an oil-free compressor capable of enhancing the oil draining effect by increasing the shaft seal pressure of the surrounding outlet side shaft seal means.

[Means for Solving the Problems]

The structure of the shaft seal device for an oil-free compressor according to the present invention includes a pair of screw rotors arranged in a casing with their axes parallel to each other and rotating in opposite directions to compress air, and the rotation of the screw rotors. A suction side bearing and a discharge side bearing that respectively support a shaft on the suction side and a discharge side of the screw rotor, a suction side shaft sealing means and a discharge side shaft sealing means arranged on the screw rotor side of each of the bearings, and the screw. In a single-stage oil-free screw compressor provided with a suction pipe system from the atmosphere to the rotor and a discharge pipe system to the load, the suction side shaft sealing means and the discharge side shaft sealing means are respectively screws around the rotating shaft. A seal type oil drainer, a carbon ring arranged between the oil drainer and the screw rotor to form an air seal, the carbon ring and the It is configured to include a space between the oil seal of the screw seal type and a gas vent hole communicating with the atmosphere, and the gap between the oil cut of the discharge side shaft sealing means and the rotating shaft is the suction side shaft. The gap between the oil drain of the sealing means and the rotary shaft is made larger, and a discharge valve is arranged in the discharge piping system, and the secondary side of the discharge valve and the discharge side shaft seal are A shaft-sealing pipe for connecting the gas vent hole of the means is provided, and a shaft-sealing pressure adjusting means is provided for the shaft-sealing pipe, and a compressed gas that releases the air to the atmosphere by opening the air-release valve when the compressor is unloaded. A part of the above is bypassed to the shaft-sealing pipe to be sealed in the discharge-side shaft-sealing means around the rotary shaft through the gas vent hole.

[Action]

With a single-stage oil-free screw compressor, the discharge temperature is 3
Since the temperature is as high as 00 to 350 ° C, the cap of the discharge side oil drainer mounting portion around the rotor shaft cannot be held small,
Therefore, the shaft sealing pressure decreases when the compressor is unloaded.

Therefore, it was considered that the pressure of a part of the compressed air discharged to the atmosphere when the compressor becomes unloaded is adjusted and then sent to the oil draining portion to increase the shaft sealing pressure.

In this way, a portion of the discharge air is sealed in the shaft seal portion after the pressure is adjusted only when there is no load, so sufficient shaft seal pressure is applied to the discharge side shaft seal means even during no load operation. The
It is possible to prevent oil from entering the pressure chamber in the casing without actually reducing the amount of discharge air required for supply to the customer, and to improve the reliability of the oil removing device.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

Here, FIG. 1 is a horizontal sectional view of a single-stage oil-free compressor according to an embodiment of the present invention, and FIG. 2 is a vertical sectional view showing a shaft seal device of the compressor. In the figure, those having the same reference numerals as those in FIGS. 3 and 4 above are the same parts as in the prior art, and therefore the description thereof will be omitted.

In the figure, 20 is a discharge pipe connected to the discharge port 15 for supplying compressed gas to a customer, 21 is a check valve, 22
Is an aftercooler, which constitutes the discharge piping system.

Reference numeral 23 is a discharge valve arranged in the discharge pipe system, 24 is a discharge pipe, and 25 is a discharge silencer, which constitute a discharge pipe system.

Further, 26 is a shaft-sealing pipe connected to the discharge gas vent hole 17 from the secondary side of the air discharge valve 23, and 27 is a shaft-sealing orifice provided in the shaft-sealing pipe 26 for shaft-sealing pressure adjusting means.

The shaft-sealing action of the single-stage oil-free screw compressor provided with such a shaft-sealing device will be described in more detail below in association with the problems of the prior art described above and the idea of solving the problems.

The single-stage oil-free screw compressor increases the discharge output to 7 kg / cm ² g in one stage, so the discharge air temperature is 30
The temperature rises from 0 to 350 ° C. For this reason, the temperatures of the suction-side oil drainer 10 and the discharge-side oil drainer 11 of the oil draining device portion are significantly different.

Normally, the gap between the suction side oil drainer 10 and the rotor shaft is about 4
Although the shaft sealing pressure is about 0 μm and about 80 mmAq, the gap between the discharge side oil drainer 11 and the rotor shaft is about 80 μm, and the shaft sealing pressure is low at 20 to 30 mmAq. The reason is that the temperature of the discharge side oil drainer 11 is higher than that on the suction side, and if the gap is not enlarged, it may come into contact with the rotor shaft and cause seizure when the temperature rises.

Regarding the discharge side oil drainer 11, when the compressor is fully loaded, the discharge end face of the casing 3 has a discharge pressure of 7 kg / cm ² g, and there is a slight amount of pressure between the rotor shaft and the discharge side carbon ring 13. Since there is a gap, part of the discharge air leaks through this gap and partly escapes to the atmosphere through the discharge gas vent hole 17, but part of it escapes through the oil drainer, so the pressure at the oil drainer part. Is raised to generate a shaft-sealing pressure of 20 to 30 mmAq, which secures the shaft-sealing pressure to prevent oil from entering the casing.

However, when the compressor is under no load, the suction throttle valve (not shown) arranged in front of the suction port 14 of the compressor is closed and the intake air amount is reduced. For this reason, a part of the discharge-side end surface of the casing 3 becomes negative pressure, and it is not possible to expect positive sealing pressure due to leakage from the carbon ring as in the case of full load. When there is no load on the compressor, in the oil-free screw compressor, the suction side becomes a vacuum, and if the pressure on the discharge side is 7 kg / cm ² g, the compression ratio becomes very high, so the discharge air temperature becomes abnormal. To prevent this, when no load is applied, as shown in FIG. 2, the discharge air is discharged by using the discharge valve 23 arranged in the discharge pipe 20 up to the check valve 21. The discharge pressure is lowered by discharging air to the atmosphere via the air pipe 24 and the discharge silencer 25 to prevent the discharge temperature from rising.

A shaft seal pipe 26 is connected to the discharge gas vent hole 17 as a bypass pipe of the air discharge pipe 24, and the discharge air is released to the atmosphere also from a shaft seal orifice 27 related to a pressure adjusting means provided in the shaft seal pipe. The shaft sealing pressure is adjusted.

By means of this shaft-sealing pipe 26, the air discharged from the compressor is enclosed in the discharge gas vent hole 17 only when there is no load to increase the shaft-sealing pressure in the discharge-side oil drainer 11, which is sufficient even when there is no load. As a structure capable of holding the shaft sealing pressure, oil used for lubricating the bearings and gears is prevented from entering the compression chamber inside the casing 3.

According to this embodiment, there are the following effects.

1) When no load is applied, so-called backup air is sealed in the discharge-side oil drainer 11 to increase the shaft sealing pressure, so that the oil draining effect is increased and the reliability of the oil drainer is improved.

In particular, it is effective when the temperature of the oil removing device on the suction side and the temperature of the oil removing device on the discharge side are significantly different as in a single-stage oil-free screw compressor, and the shaft sealing gap around the discharge side rotor shaft cannot be reduced.

2) A portion of the discharge air is used as a backup for the discharge side oil drainer only when there is no load, so there is no loss of discharge air at full load, and the amount of discharge air actually required for supply to the customer is Since it does not decrease and there is no change in the discharge performance of the compressor, it is particularly effective for small capacity oil-free screw compressors.

〔The invention's effect〕

As described above, according to the present invention, even when the compressor is in the no-load operation, a part of the air discharged from the discharge pipe to the atmosphere through the discharge valve is provided with the shaft sealing pressure adjusting means. The shaft-sealing pipe supplies the shaft-sealing means on the discharge port side to increase the shaft-sealing pressure of the shaft-sealing means, so that the lubricating oil is prevented from entering the pressure chamber.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a single-stage oil-free compressor according to an embodiment of the present invention, FIG. 2 is a vertical cross-sectional view showing a shaft seal device of the compressor, and FIG. FIG. 4 is a vertical sectional view of the compressor body, and FIG. 4 is a vertical sectional view of the compressor body. 1 ... Male rotor, 2 ... Female rotor, 3 ... Casing,
4 ... Suction casing, 5 ... Suction side radial bearing, 6
…… Discharge side radial bearing, 7 …… Thrust bearing, 10 ・ ・ ・
… Suction side oil drainer, 11 …… Discharge side oil drainer, 12 …… Suction side carbon ring, 13 …… Discharge side carbon ring, 1
4 ... Suction port, 15 ... Discharge port, 16 ... Suction gas vent hole, 17 ... Discharge gas vent hole, 18A ... Suction side oil supply port, 18B ... Discharge side oil supply port, 19A ... Suction side exhaust Oil port, 19B ... Discharge side oil drain port, 20 ... Discharge pipe, 21
...... Check valve, 23 ...... Air release valve, 24 ...... Air release piping, 26
…… Shaft-sealed pipe, 27 …… Shaft-sealed orifice.

Claims (1)

[Claims] 1. A pair of screw rotors arranged in a casing with their axes parallel to each other and rotating in directions opposite to each other to compress air, and a rotation shaft of the screw rotors on a suction side and a discharge side of the screw rotor. A suction side bearing and a discharge side bearing which respectively support, a suction side shaft sealing means and a discharge side shaft sealing means arranged on the screw rotor side of each of the bearings, a suction piping system from the atmosphere to the screw rotor, and a load. In a single-stage oil-free screw compressor having a discharge piping system, the suction side shaft sealing means and the discharge side shaft sealing means are respectively screw seal type oil drainers around the rotary shaft, and the oil drainers and the screw. A carbon ring disposed between the rotors to form an air seal, a space between the carbon ring and the screw seal type oil drainer, and the atmosphere. And a gap between the oil drain of the discharge side shaft sealing means and the rotating shaft is between the oil drain of the suction side shaft sealing means and the rotating shaft. And a discharge valve in the discharge pipe system, and a shaft sealing pipe connecting the secondary side of the discharge valve and the gas vent hole of the discharge side shaft sealing means. A shaft sealing pressure adjusting means is provided in this shaft sealing pipe, and when the compressor is unloaded, a part of the compressed gas that releases the air release valve to the atmosphere is bypassed to the shaft sealing pipe. The single-stage oilless screw compressor is characterized in that the discharge-side shaft sealing means around the rotary shaft is sealed through the gas vent hole.