JPS60166785A - Self-lubricating rotary compressor - Google Patents

Abstract

PURPOSE:To increase the discharge pressure without increasing the discharge temperature of an oil screw compressor by cooling discharged gas and jetting a portion of said cooled gas into a compression chamber immediately after the completion of suction cycle. CONSTITUTION:The gas inhaled into a screw compressor 1 is compressed in a compression chamber and discharged in the form having a high pressure and a high temperature. The discharged gas passes through a heat exchanger 4 for primary cooling, check valve 6, and a heat exchanger 5 for secondary cooling which are arranged in a discharge gas conduit 3, and is cooled nearly to a suction temperature. The cooled gas is jetted into the compression chamber immediately after the completion of the suction cycle of the screw compressor 1, and the effective capacity of the compressor is increased. Therefore, the same effect of increasing the amount of inhaled gas is obtained, and the gas can be pressurized to a high pressure.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an oil-free rotary compressor, and in particular to a single-stage rotary air compressor that is oil-free and has a high discharge temperature, and is capable of achieving high discharge pressure. The present invention relates to an oil-free rotary compression device suitable for obtaining the desired results.

[Background of the invention]

Conventional single-stage oil-free rotary air compressors, such as screw compressors, have been able to achieve a discharge pressure of 4k by improving the radius, the tooth profile of the male-meshing rotor, and improving the production method.
H/cm” B was changed to 7kg/c+n
” I was able to raise it to G.

However, the discharge pressure 8 required in the market, especially in the United States.
, 5 kg, 7cm” g to 8, 8 kg/c
In order to produce 2.0 m2g, simply increasing the pressure ratio will further increase the discharge temperature, which previously exceeded 350°C, making it difficult to suppress the thermal expansion of the rotor, etc. This was an extremely difficult problem to realize in terms of minimizing the dangers.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned developments in the prior art, and it is possible to achieve the following without increasing the discharge temperature of an oil-free rotary compressor from the current proven temperature, and with a simple equipment configuration. , 5 kg/c, ra” (< to 8
, 8 kg/am''g of discharge pressure.

[Summary of the invention]

The configuration of the oil-free rotary compressor according to the present invention is such that a cooling heat exchanger is disposed in a discharge gas pipe line that discharges gas compressed by the oil-free rotary compressor, and the cooled discharge gas is Return gas piping equipped with a flow rate control means so that a part of the gas is returned to the suction side of the rotary compressor to increase the suction pressure, thereby increasing the discharge pressure while maintaining a predetermined compression ratio. is branched from the discharge gas pipe line described in (A) and connected to the suction side of the rotary compressor.

Additionally, the idea behind developing the present invention is as follows.

Normally, to increase the discharge pressure of a rotary compressor, the design compression ratio is increased. That is, it is common to change the discharge pressure. However, in the oil-free rotary compressed material, there is a big problem with the discharge temperature. Therefore.

In the present invention, the idea was to obtain a high discharge pressure by increasing the suction pressure while keeping the compression ratio, which is designed to be roomy, as it is. Although it is possible to increase the pressure of suction gas using a blower, in the present invention, in order to simplify the configuration as much as possible, the discharge air of the compressor itself is returned to the suction side to increase the discharge pressure while maintaining the compression ratio. That's what I decided to do.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

The figure is a schematic configuration diagram of an air compressor according to an embodiment of the present invention.

In the figure, 1 is a single-stage oil-free rotary air compressor* (hereinafter referred to as a compressor), for example a screw compressor, 2 is a gas suction pipe, and 3 is a discharge gas pipe that discharges compressed gas. , 4 is a primary cooling heat exchanger disposed in the discharge gas pipe line 3, and 5 is a secondary cooling heat exchanger also disposed in the discharge gas pipe line 3, both of which circulate cooling water. It is something.

6 is a check valve.

Reference numeral 7 denotes a return gas pipe that branches off from a position past the secondary cooling heat exchanger 5 of the discharge gas pipe line 3 and is connected to the suction side of the compressor 1. A solenoid valve 8 is connected to the return gas pipe 7.
and a regulating valve 9 related to flow rate control means are provided.

The gas sucked into the compressor 1, for example, a screw compressor, is caused by the meshing of a pair of male and female rotors within the casing.
(not shown), the pressure increases due to the reduction in compression chamber volume. In an oil-free compressor, not only the rotor and the casing, but also the male and female rotors rotate at high speed with very small gaps between them. During compression, no cooling oil is injected into the compression chamber, so even if the casing is cooled with water, if a single-stage compressor is used to obtain a discharge pressure of kg/cm2g, the discharge temperature will be 32
The temperature is between 0 and 380 degrees Celsius.

The pressurized gas is transferred to a primary cooling heat exchanger 4, a check valve 6, and a secondary cooling heat exchanger 5 disposed in the discharged gas pipe line 3.
It is cooled down to near the suction temperature and then discharged.

In this embodiment, a small amount of the cooled discharge gas that has passed through the cooling heat exchangers 4 and 5 is returned to the suction side of the compressor 1.

Although not shown in the drawings, the position to which the discharged gas is returned is preferably the position immediately after the compression chamber 1 completes suction of the suction gas and is isolated from the suction pipe 2.

The return gas pipe 7 is provided with a solenoid valve 4 for cutting off the flow of the return gas during unloading operation. A regulating valve 5 is provided to regulate the flow rate of the return gas. The solenoid valve 4 is necessary to prevent deterioration in unloading efficiency due to pressure remaining on the suction side during unloading.

On the other hand, the discharge temperature Td of the compressor, which is a problem, is theoretically calculated as follows: TS: Suction temperature Pd: Discharge pressure Ps: Suction output γ: Adiabatic compression index m: Number of compression stages In order to obtain a high discharge pressure, the compression ratio Pd/Ps The usual method is to raise the value, but in this case.

It is clear from equation (1) that the discharge temperature Td increases. In addition, if only the discharge pressure is increased, the pressure difference between the compression chambers will increase, the leakage between the compression chambers will increase, and the discharge temperature will rise by more than the amount due to the increase in (Pd/Ps) in theoretical formula (1). Increasing the discharge pressure using this method is difficult to achieve in an oil-free rotary compressor because it is difficult to suppress the thermal expansion of the rotor tube.

In this embodiment, the discharge pressure P is increased by increasing the suction pressure Ps while keeping the compression ratio P d / P s constant.
d is increased, and if the temperature of the gas returned to the suction side is sufficiently low, the increase in the discharge temperature can be suppressed to a very small value using equation (1). For example, the current compression ratio is 7.8 (suction pressure is 1.033 kg/am).
a, discharge pressure d 8.033kg/c, n+” a)
While using the compressor, increase the discharge pressure to 8.5 α/cm2g.
That is, in order to obtain 9.533 kg/cm" a, the discharged gas is returned to the compression chamber immediately after being confined on the suction side, and the pressure rises to P s = P d, / 7, 8 = 1.22 kg/cm" a. Just do it.

The volumetric efficiency of the compressor decreases each time the discharged gas is returned to the suction side, but in a single-stage oilless rotary compressor, keeping the discharge temperature low is the top priority, and in that sense, this example The effect is great.

According to this embodiment, a single-stage, oil-free rotary air compressor is used, and the current compressor with a discharge pressure of ``g/cm2g or more'' is used as it is, and the rotor is damaged due to an increase in discharge temperature. 8.5 kg/cm2E or 8.8 kg/cm2E to 8.5 kg/cm2E or 8.5 kg/cm2E to 8.5 kg/cm2E or 8.5 kg/cm2E or 8.5 kg/cm2E or 8.5 kg/cm2E or
There is an effect that a discharge pressure of kg/cIIl"H can be achieved.

Note that in the above embodiment, an oil-free rotary compressor is explained as an example of an oil-free rotary compressor, but the present invention is not limited to screw compressors, but can be applied to any other oil-free rotary compressor that can be expected to have the same effect. It is a general-purpose type in the range of oil-fed rotary compressors.

〔Effect of the invention〕

As described above, according to the present invention, the discharge temperature of an oil-free rotary compressor can be increased to 8.5 k without increasing it from the current proven temperature, and with a simple equipment configuration.
g/cm” H to 8, 8 kg/cI112
Oil-free rotational pressure N1j that can obtain a discharge pressure of g
tq can be provided.

[Brief explanation of the drawing]

The figure is a schematic configuration diagram of an air compressor according to an embodiment of the present invention.

Claims (1)

[Claims] 1. A cooling heat exchanger is installed in the discharge gas pipe line that discharges the gas compressed by the oil-free rotary compressor, and a part of the cooled discharge gas is transferred to the suction side of the rotary compressor. A return gas pipe equipped with a flow rate control means is branched from the discharge gas pipe to increase the discharge pressure while maintaining a predetermined compression ratio by returning the gas to the discharge gas pipe and increasing the suction pressure. Oil-free % type % characterized by being connected to the suction side of the rotary compressor