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Title:
SYSTEM OF PROTECTING COMPRESSOR FROM WATER IN LUBRICATING OIL
Document Type and Number:
WIPO Patent Application WO/2005/012728
Kind Code:
A1
Abstract:
There is disclosed a compressor arrangement comprising a compressor (11) for compressing a gas, separating means (13) for separating oil from a compressed gas before its discharge from the compressor (11), a reservoir (14) for receiving the separated oil (16), means (19) for measuring a parameter of fluid resting at a lower end of the reservoir (14), means (21) for removing water (18) collected in the lower end of the reservoir (14) and control means (20) for activating the water removal means when the measured parameter of the fluid differs from a predetermined value, and deactivating the water removal means when the measured parameter of the fluid substantially matches the predetermined value.

Inventors:
NICHOL PHILIP (GB)
Application Number:
PCT/GB2004/003306
Publication Date:
February 10, 2005
Filing Date:
July 30, 2004
Export Citation:
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Assignee:
COMPAIR UK LTD (GB)
NICHOL PHILIP (GB)
International Classes:
B01D17/00; B01D21/34; F04B39/16; F04C18/16; F04C18/344; F04C29/00; F04C29/02; F04B39/02; (IPC1-7): F04B39/16; F04C29/02
Foreign References:
DE19842484A11999-12-02
US4315822A1982-02-16
US3847810A1974-11-12
US5171130A1992-12-15
Other References:
PATENT ABSTRACTS OF JAPAN vol. 0080, no. 68 (P - 264) 30 March 1984 (1984-03-30)
PATENT ABSTRACTS OF JAPAN vol. 0070, no. 41 (M - 194) 18 February 1983 (1983-02-18)
PATENT ABSTRACTS OF JAPAN vol. 2000, no. 04 31 August 2000 (2000-08-31)
PATENT ABSTRACTS OF JAPAN vol. 1998, no. 01 30 January 1998 (1998-01-30)
PATENT ABSTRACTS OF JAPAN vol. 1999, no. 13 30 November 1999 (1999-11-30)
Attorney, Agent or Firm:
Bucks, Teresa Anne (Verulam Gardens 70 Gray's Inn Road, London WC1X 8BT, GB)
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Claims:
CLAIMS:
1. A compressor arrangement comprising a compressor for compressing a gas, separating means for separating oil from a compressed gas before its discharge from the compressor, a reservoir for receiving the separated oil, means for measuring a parameter of fluid resting at a lower end of the reservoir, means for removing water collected in the lower end of the reservoir and control means for activating the water removal means when the measured parameter of the fluid differs from a predetermined value, and deactivating the water removal means when the measured parameter of the fluid substantially matches the predetermined value.
2. A compressor arrangement as claimed in claim 1 in which the measuring means comprise a pair of surfaces located in the lower end of the reservoir and means for measuring the capacitance between the two surfaces.
3. A compressor arrangement as claimed in claim 1 in which the measuring means comprise a pair of electrodes projecting into the lower end of the reservoir and means for supplying a low voltage to the electrodes and measuring the conductivity of fluid in which the electrodes are immersed.
4. A compressor arrangement as claimed in claim 1 in which the measuring means comprise an optical sensor which measures the refractive index of fluid in the lower end of the reservoir.
5. A compressor arrangement as claimed in any one of the preceding claim in which the water removal means comprise a duct provided in the base of the reservoir and valve means, the operation of which is controlled by the controller to allow water to be drained from the lower end of the reservoir.
6. A compressor arrangement as claimed in any one of claims 1 to 4 in which the water removal means comprise a heating element, the operation of which is controlled by the controller to heat water in the lower end of the reservoir to cause its evaporation.
7. A method of removing water from lubricating oil in compressors, comprising measuring a parameter of fluid resting at a lower end of a reservoir which receives oil separated from a compressed gas before its discharge from the compressor, comparing the measured parameter against the predetermined value and activating water removal means when the measured parameter of the fluid differs from said predetermined value.
8. A method as claimed in claim 7 in which the capacitance between two surfaces located in a lower end of the reservoir is measured.
9. A method as claimed in claim 7 in which the conductivity of fluid in which a pair of electrodes are immersed is measured.
10. A method as claimed in any one of claims 7 to 9 in which water is removed by opening valve means to allow it to drain from the lower end of the reservoir.
11. A method as claimed in any one of claims 7 to 9 in which the water is removed by heating water in the lower end of the reservoir to cause its evaporation.
12. A method as substantially as hereinbefore described with reference to the accompanying drawings.
Description:
SYSTEM OF PROTECTING COMPRESSOR FROM WATER IN LUBRICATING OIL The invention relates to compressor arrangements, such as rotary screw and vane compressors, used to compress a gas such as air and the protection of such compressors from water in the lubricating oil.

Many compressors require the use of oil during their operation. The oil has three major functions within the scope of compressor arrangements; it cools the compressed gas, lubricates the bearings and seals the rotors in the air end (compression element). As a result the discharged compressed gas contains a large quantity of oil that is separated and returned to the compressor. A pressure vessel is generally used to extract the bulk of the oil from the compressed gas during a primary separation process. This pressure vessel is also known as a reclaimer and usually contains, or works in conjunction with, a filter or separator element to separate the oil from the compressed gas. The oil separated from the gas is then cooled and filtered and returned to the air-end. Oil collecting in the separator element is drawn back to the air end through a restrictor and non-return valve.

A major problem with this type of arrangement is that the oil becomes contaminated with water. The atmospheric air drawn into the compressor contains water vapour. Under unfavourable conditions such as

humid climate or a compressor that runs at low temperatures the amount of water may be considerable. As the oil mixed with the air, it picks up some water which then circulates with the oil causing damage to the bearings and corrosion to the compressor and associated vessels and pipework.

Normally the water is most noticeably deposited in the air/oil separator vessel.

Whilst the compressor is in operation it can be hard to detect the water, as it tends to be mixed thoroughly with the oil. Indeed some lubricants have a tendency to absorb water. When the machine is at rest, the water tends to separate from the oil and, because of its higher specific gravity, will sink to the bottom of the reservoir beneath the oil.

The water should be drained regularly via a drainage valve in the bottom of the reservoir. Unfortunately in practice, this is not always carried out, and in many cases is not practical. Furthermore, when a compressor is stopped, the air inside the vessel cools which may result in further condensation of water.

It is an object of the present invention to overcome this disadvantage and to provide a convenient means of detecting the presence of water in the oil reservoir and removing it without loss of oil.

According to one aspect of the present invention there is provided a compressor arrangement

comprising a compressor for compressing a gas, separating means for separating oil from a compressed gas before its discharge from the compressor, a reservoir for receiving the separated oil, means for measuring a parameter of fluid resting at a lower end of the reservoir, means for removing water collected in the lower end of the reservoir and control means for activating the water removal means when the measured parameter of the fluid differs from a predetermined value, and deactivating the water removal means when the measured parameter of the fluid substantially matches the predetermined value.

According to another aspect of the present invention, there is provided a method of removing water from lubricating oil in compressors, comprising measuring a parameter of fluid resting at a lower end of a reservoir which receives oil separated from a compressed gas before its discharge from the compressor, comparing the measured parameter against the predetermined value and activating water removal means when the measured parameter of the fluid differs from said predetermined value.

The invention will now be described, by way of example only, with reference to the accompanying drawing Fig. 1 which is a schematic representation of a compressor arrangement according to the present invention.

The compressor arrangement 10 comprises a compressor 11 (air end) for compressing a gas such as air, a motor which drives the air end 11 and a pressure vessel (or reclaimer) 12. The pressure vessel 12 includes filtering means 13 for separating oil from the compressed gas, and a reservoir 14 for collecting the separated oil 16. The pressure vessel 12 may be made from aluminium, iron, steel or any other suitable material.

Gas is taken into the air end 11 via a gas intake filter and compressed. During the compression process oil is mixed with the gas.

The discharged pressurised compressed gas from the air end 11 contains a large quantity of oil, typically 10 to 15 litres per minute for each cubic metre of free air compressed per minute. This oil has to be separated from the compressed gas before it passes into use. The compressed gas and oil mixture is therefore discharged from the air end 11 to the pressure vessel 12 via an appropriate duct 15.

The separation of the gas and oil is typically achieved in two stages; primary separation of the oil and gas is carried out due to centrifugal forces as the mixture enters the pressure vessel 12 and final separation is completed through a separator element 13 in the pressure vessel 12 or alternatively through a special filter fitted downstream of the pressure vessel.

The fully cleaned gas is subsequently passed through an after cooler before passing to the plant discharge and into use.

The reclaimed oil 16 is re-circulated from the reservoir 14 via a return pipe 17 through a filter 23 and cooling means 24, back to the air end 11.

Further oil which passes through the filter is scavenged back to the compressor by scavenge line 25.

Under conditions of high humidity and low compressor temperatures (below the pressure dewpoint), water 18 precipitates from the air during compression inside the air end 11 and is carried with the oil into the pressure vessel 12. Whilst the reclaimed oil 16 is resting in the lower end of the reservoir 14, the water 18 separates from the oil 16 and, because of its higher specific gravity, sinks to the bottom of the reservoir beneath the oil 16.

A sensing device 19 is attached to the base of the reservoir 14, which is connected to a controller 20. A duct 22 is also connected to the base of the reservoir 14 incorporating a valve 21, such as a solenoid valve. The controller 20 is also connected to the valve 21.

In one embodiment of the invention the sensing device 19 comprises a probe having two electrodes which protrude a short way into the fluid resting in

the lower end of the reservoir 14. A low voltage electrical supply is attached to the probe, such that when a low voltage is applied to the electrodes, the conductivity (or resistance) of the fluid in which the electrodes are immersed is measured. The measured conductivity is compared by the controller against a known reference. If the measured value is higher than the reference value, it can be ascertained that the electrodes are immersed in water 18 rather than oil 16, as the conductivity or water is significantly higher than that of oil.

When the controller 20 determines that water 18 is present in the lower end of the reservoir 14, it opens the valve 21 to allow the water to drain out via the duct 22. As the water 18 drains out, the measured conductivity of the fluid falls, and when the controller 20 determines that the measured value of the fluid in the lower end of the reservoir 14 corresponds to that of oil, the valve 21 is closed.

In another embodiment of the invention, the sensing device 19 comprises a sensor which measures the capacitance between two surfaces immersed in the fluid and compares the measured value to establish whether it differs from a predetermined reference value. Further embodiments may use an optical sensor to measure and distinguish between the two fluids having a different refractive index.

In a further embodiment of the invention, the duct 22 and valve arrangement 21 are replaced by a heating element located in the reservoir 14. When the controller 20 determines that water 18 is present in the bottom of the reservoir 14, the heating element is switched on, thereby causing the water 18 to evaporate.

The measurement should preferably be made when the user attempts to start the compressor 11 after it has been idle, to ensure that the oil and water have had time to separate.




 
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