EP0314133B1

EP0314133B1 - Oil cooled fluid compression apparatus

Info

Publication number: EP0314133B1
Application number: EP88117931A
Authority: EP
Inventors: Hiroyuku Matsuda; Taisuke Torigoe; Shiro Yoshihara
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1987-10-28
Filing date: 1988-10-27
Publication date: 1992-02-26
Anticipated expiration: 2008-10-27
Also published as: EP0314133A2; EP0314133A3; DE3868586D1; JPH01113586A; KR930006376B1; KR890006978A; JP2728409B2

Description

This invention relates to a fluid compressor, and more particularly to a safety device suitable for an oil cooled type air compressor.
In an oil cooled type air compressor, for example an oil cooled screw compressor, lubricating oil is supplied to the compression section. This lubricating oil, which provides the double function of lubrication and sealing, cools the compressed air whose temperature has risen because of the heat of compression, and moves to an oil separator. After being separated from the compressed air by the oil separator, the lubricating oil is cooled by water or air and then supplied to the compression section again. As this cycle is repeated, the lubricating oil is deteriorated through oxidization due to the heat of compression. Part of the lubricating oil is carbonized and the thus carbonized components move to the oil separator with the lubricating oil. The carbon components are then separated from the lubricating oil and accumulate on a filter of the oil separator. The accumulation amount of the carbon components gradually increases when the compressor is used for a long period of time, which may spontaneously ignite owing to the heat of compression under the effect of thermal accumulation of the carbon. Japanese Patent Laid-Open No. 59-115493, for example, discloses a device for detecting such spontaneous ignition. In this device, a detection member made of a material which fuses with heat is provided in an oil separating element of the oil separator, so that the ignition may be detected through the fusion of the detection member caused by the heat of ignition of the oil separating element.
Thus, in the prior art, a secondary or resultant temperature rise after the combustion of the carbon is sensed by means of a temperature detector, so that the ignition is detected only after the combustion has advanced to a considerable degree. Accordingly, no consideration is given to a danger of other sections catching fire through extension of the combustion, the prevention of such ignition from occurring or the extinction thereof at an early stage. Further, since the temperature sensing is made under the pressure of the compressed fluid, the detection end of the detector has to be covered by a protection tube, which involves the problem of low responsiveness in detection.
Accordingly, it is an object of this invention to make it possible to detect any burning or combustion in the oil separator of an oil cooled compression apparatus at an early stage and to effect an emergency stop of the compression apparatus for fluid so that the flow of fluid therein may be stopped to extinguish the fire as soon as possible and avoid any secondary ignition.
The above object is attained by connecting an auxiliary piping to a main piping which is connected to a secondary side section of the oil separator, and by providing in the auxiliary piping with a gas detector for detecting a gas which is generated, increased or decreased at an early stage of any burning in the oil separator, the gas detector outputting a signal for opening an emergency stop circuit of an operation control of the compression apparatus to effect an emergency stop thereof.
Thus, upon detecting the gas generated, increased or decreased by the burning in the oil separator, the gas detector generates a detection signal by means of which the compression apparatus is stopped.

Fig. 1 is a schematic diagram illustrating the compression system according to an embodiment of this invention;
Fig. 2 is a sectional view showing in detail a gas detector which is used in the system shown in Fig. 1; and
Fig. 3 is a schematic diagram illustrating the compression system according to another embodiment of this invention.

An embodiment of this invention will now be described with reference to Figs. 1 and 2. In this case, the invention is embodied as an oil cooled screw compressor system. The air serving as the working fluid is sucked by a compressor 7 through a suction throttle valve 6. The air is compressed in the compressor 7 to a predetermined pressure and is then discharged to an oil separator 8 through a piping 21. The oil separator 8 includes an element 9 which is adapted to separate an oil injected into the compressor during the compression process, from the compressed air. The material of this element 9 may be glass wool, for example. The air which has passed through this element 9, i.e. the air which is discharged from the oil separator 8, is delivered to a pressure regulator valve 10 which has a check valve and is provided in a main piping 22. The air which has passed through this pressure regulator valve 10 flows through the main piping 22 and is discharged as the supply air. Further, the air which has passed through this element 9 serves to control the throttle amount of the above-mentioned suction throttle valve 6 through the intermediary of an air discharge valve 11, thereby controlling the suction amount.
An auxiliary piping 23 branches off the main piping 22 at a position on the downstream side of the pressure regurator valve 10. A part of the discharge air is supplied, as a sample, to this auxiliary piping 23 through a pressure reducing valve 12 or an orifice so that the gas detection may be effected. This sampling air for the gas detection is regulated to a certain flow rate and pressure by the pressure reducing valve 12 and is delivered to a sensor unit 13. The sensor unit 13 includes a filter 14, a gas detector 2, an electronic circuit 3, a relay contact 4, and an orifice 16. In this sensor unit 13, the above-mentioned air for the gas detection flows through the filter 14 to the gas detector 2. The gas detector 2 includes, for example, as shown in Fig. 2, a container 15 which receives a CO gas sensor 1 and is sealed by means of an O-ring 30. The discharge air for sampling is supplied in the container through an inlet 31. The CO gas sensor 1 is arranged in the flow of the discharge air such that a CO gas density in the air flow may be detected with high accuracy. After the gas detection, the air flows out through an outlet 32 and is discharged in the atmosphere through the orifice 16 as shown in Fig. 1. The CO gas sensor 1 is of a thermal conduction type which detects any change in its thermal and electrical conduction due to the absorption of gas as a change in its resistance and transforms the detected change into an electric signal by means of the electronic circuit 3. The sensor then operates the relay contact 4 of the sensor unit, which contact is arranged in the operation circuit of a starting unit 5 provided for controlling the operation of the compressor. The starting unit 5 includes a relay 88 for operating the compressor 7, an activating contact BS and a stopping contact BSS for the compressor 7 as well as a normally opened contact 88a of the relay 88, the above-mentioned relay contact 4 being connected in series to the relay 88. When, for example, the CO gas density in the air exceeds several hundred ppm, the relay contact 4 which is normally ON is turned OFF, thereby cutting off the operation circuit. If the CO gas sensor 1 is of a type which can be used under pressure, it may be arranged directly in the main piping 22 on the outlet side of the pressure regulator valve 10. Alternatively, the system may be constructed as shown in Fig. 3, wherein an orifice 24 and the detector 2 are arranged in the branch piping 23 for detecting gas, and a plate 17 is fixed to the container of the gas detector by means of screws for securing the CO gas sensor 1 so that the sensor may withstand the pressure of the discharge gas. After the gas detection, the air is returned to the suction inlet of the compressor 7 through a return piping 25 so that pressure differential may be developed across the sensor unit, or to the main piping 22 for the compressed air through a return piping 26. This arrangement enables a constant amount of air to flow through the gas detector 2, thereby performing the detection of CO gas. In this embodiment, the sensor unit cuts off operation circuit of the starting unit for the compressor in the same manner as described with reference to the embodiment shown in Fig. 1.
In the embodiments described above, any ignition or combustion can be detected within one minute after its occurring, so that the compressor can be stopped before smoke and flames are generated. With a conventional temperature sensor, it takes about three and half minutes at the earliest to detect such ignition, and the burning would be developed to a considerable degree. The safety device according to this invention can be installed in any compressor system solely by providing a branch piping on the secondary side of the oil separator. Accordingly, it is easy to apply the invention to a compressor which has already been in practical work. Additionally, since no conventional temperature sensor has to be provided, the reliability of the device can be improved. Furthermore, as the CO gas detection is performed with a constant air flow rate, the gas sensor involves no erroneous operation due to loading and unloading, so that a high accuracy in detection and a long service life of the device are ensured. The device may also be used as a sensor for detecting oil deterioration as well as for detecting time for replacing the element of the oil separator with a new one. Consequently, the device will contribute much in improving the reliability of devices of this kind and developing a maintenance-free system for the future.
Thus, the above-described embodiments of this invention make it possible to detect any burning or combustion of the element in the oil separator more quickly than any other temperature sensor, thereby eliminating one of the factors causing a fire. Further, since the safety device according to the invention can also serve as an alarm for oil deterioration and element replacement, the device may find its use as a highly reliable maintenance device.
As described above, the present invention makes it possible to detect any ignition or burning in the oil separator at an early stage and to effect an emergency stop of the fluid compressor, thereby avoiding a secondary ignition in other sections of the system.

Claims

An oil cooled fluid compression apparatus comprising fluid compressor means (7) for compressing a working fluid sucked therein through an inlet to a predetermined pressure and discharging the compressed working fluid through an outlet, oil separator means (8) for separating oil injected into said compressor means (7) during compression process from the compressed working fluid, main piping means (22) for communicating said oil separator means (8) with a compressed fluid service end, characterized by auxiliary piping means (23) branching off said main piping means (22), and a sensor unit (13) provided in said auxiliary piping means (23) for detecting the density of a gas in the working fluid which density changes when burning takes place in said oil separator means (8) and stopping said compressor means (7) upon detection of change in the gas.
An apparatus according to claim 1, characterized in that said auxiliary piping means (23) communicate with either a suction side of said compressor means (7) or a portion of said main piping means (22) which is closer to said compressed fluid service end than the portion of said main piping means (22) at which said auxiliary piping (23) branches off.
Apparatus according to claim 1 or 2, characterized in that the safety device on the discharge side of the oil separator (8) comprises gas detector means (2) for detecting the density of a gas which density changes when burning takes place in said oil separator (8), circuit means (3) for transforming a detection signal of said gas detector means (2) into an electric signal, and control means (5) for controlling driving and stopping of said compression means (7) in accordance with an output signal of said circuit means (3).
An apparatus according to one of the claims 1 to 3, characterized in that the working fluid is air and in that the sensor unit (13) is provided in said auxiliary piping means (23) for detecting CO gas produced in the compressed air when burning takes place in said oil separator means (8) and stopping said compressor means (7) upon detection of the CO gas.
Apparatus according to claim 4, characterized in that the CO gas detecting device arranged in a piping (23) for detecting a density of CO gas in air flowing through the piping (23) comprises a container (15) having an air inlet (31) and an air outlet (32), and a CO gas sensor (1) airtightly arranged in said container (15), the air inlet (31) and the air outlet (32) of said container (15) and said CO gas sensor (1) being arranged in such a manner that said CO gas sensor (1) is positioned in an air flow in the piping (23).