GB2394004A

GB2394004A - Lubricant-cooled gas compressor

Info

Publication number: GB2394004A
Application number: GB0129341A
Authority: GB
Inventors: Terrence Edward Coker
Original assignee: Compair
Current assignee: Compair
Priority date: 2001-12-07
Filing date: 2001-12-07
Publication date: 2004-04-14
Anticipated expiration: 2021-12-07
Also published as: GB0129341D0; GB2394004A9; GB2394004B

Abstract

A lubricant cooled gas compressor 10 adapted to discharge a mixture of gas and lubricant having a separator 13 for separating the lubricant from the gas and a return means 16 to return the lubricant to the compressor. A temperature sensitive means is provided to vary the return flow of lubricant to the compressor such that the return flow of lubricant is restricted when the temperature of the lubricant falls and is increased when the temperature of the lubricant rises. The means for varying the flow may be a thermostatically controlled restrictor valve 22 having an axially slideable sleeve and having a temperature sensitive element incorporating wax which increases in volume as it liquifies in response to an increase in temperature.

Description

a a a e a a a a a a a 1. LUBRICANT-COOLED SCREW COMPRESSOR

This invention relates to an improved method of operas m g a lubricant-

cooled screw compressor and to an lubricant-cooled screw compressor adapted to carry out the method.

Air is compressed in a screw compressor between male and female helical rotors at the so-called "air-end". In a lubricant-cooled screw compressor lubricant such as oil is introduced to the air-end together with incom mg air and is then separated downstream of the air-end and recycled. me lubricant serves to cool the compressed air and the machinery of the Air end, to lubricate the bearings of the latter and to provide a seal between the rotors.

A major problem encountered in the operation of lubricant-cooled screw compressors is that of condensation of water from the indrawn air. It is not practicable to dry the incom mg air, which will precipitate when compressed unless temperatures are maintained high enough for the water to remain as vapour. During normal operation the temperature of the compressed air will be high enough to prevent substantial precipitation but at start up or when the compressor is idling (because of a temporary reduction in the demand for compressed air) temperatures will drop below the dew point of the compressed air so that water will collect in the separator and form an emulsion with the lubricant. When this is returned to the air-end lubrication will be adversely affected, causing high maintenance and a shortened life for the compressor.

A principal object of the present invention is to address the problem of condensation when operating a lubricant-cooled screw air compressor.

In accordance with one aspect of the present invention there is provided a method of operating a lubricant-cooled screw compressor having an Air- end which discharges a mixture of lubricant and compressed air, and means for separating the lubricant from the compressed air downstream of the air-end and for returning the separated lubricant to the air-end, wherein the return flow of lubricant to the air-end is controlled in accordance with the temperature of the lubricant such that said flow is restricted when said temperature is below a predetermined value and increased when said temperature is above said predetermined value.

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2. The said return flow of lubricant is preferably controlled to be proportional to variations of said temperature.

Preferably the temperature of the return flow of lubricant is sensed to determine the temperature of the lubricant.

In accordance with another aspect of the present invention there is provided a lubricant-cooled screw compressor comprising an air-end adapted to discharge a mixture of lubricant and compressed air and means for separating the lubricant downstream of the air-end and for returning the separated lubricant to the air end, wherein temperature sensitive means is provided for varying the return flow of lubricant to the air end in response to variation in the temperature of the lubricant such that the return flow of lubricant to the air-end is restricted when the temperature of the air end falls and is increased when the temperature of the lubricant rises. By this arrangement temperature rise of the air-end on start up will be accelerated and will not be allowed to fall proportionally to a reduction in the speed of rotation of the rotors during down time. The maintenance of high temperature substantially throughout the operation of the compressor will reduce the incidence of condensation and thus protect the rotating components of the assembly.

A thermostatically controlled restrictor valve may be located in the lubricant return line from the separating means to the air-end, the valve being adapted to control the flow of the returning lubricant according to the temperature sensed by the thermostat.

Preferably the thermostat is immersed in the return lubricant flow.

The restrictor valve may comprise a housing having a lubricant inlet and a lubricant outlet, the outlet communicating with a cylindrical chamber within the housing which is coaxial with, intermediate the ends of and of greater diameter than a bore within the housing communicating with the inlet, a sleeve moveable axially of the bore whereby an opening in the wall of the sleeve may be brought into or out of register with the chamber and a thermostatic device within the bore which will respond to changes in the temperature of lubricant passing through the housing thereby to displace

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the sleeve to vary the area of said opening which is exposed to the chamber. me thermostatic device may comprise q cylinder moveable with the sleeve, a piston fixed at one end relative to the housing and a wax within the cylinder at the free end of the piston, the wax being of the kind which increases in volume as it liquifies in response to an increase in temperature. By-pass means may be provided by passing the temperature sensitive means, the by-pass means being adapted to ensure a minimum return flow of lubricant from the scavenging means to the air-end independently of the temperature sensitive means.

me by-pass means may comprise a by-pass duct within the housing which directly communicates the inlet with said chamber.

me by-pass duct may have a restriction and the restriction may be adjustable.

A preferred embodiment of the present invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a screw compressor according to the present invention, and Figures 2 and 3 are similar sectional elevations of a thermostatically controlled restrictor valve used in the compressor of Figure 1 showing the restrictor valve respectively in a fully open and in a partially closed condition.

The screw compressor 10 illustrated in Figure 1 comprises a screw compressor 11 (known as the air-end) for compressing a gas such as air.

A motor 12 drives the rotors of the air end 11.

Air is taken into the air-end 11 via a gas intake filter 14. file quantity of air intake is controlled via a suction regulator 15 which is connected by a control line 15a to a reclaimer 13.

.e be: c: ce. e. be: À. . The discharge of the pressurized compressed air from the air-end 11 contains a large quantity of lubricant. m is lubricant has to be separated from the compressed air before the latter passes into use. me compressed air and lubricant mixture is therefore discharged from the air-end 11 to the reclaimer 13 via an appropriate duct 24.

me separation of the gas and lubricant is achieved in two stages; primary separation of the lubricant and gas is carried out within the reclaimer 13 and final separation is completed through a special filter 18 which in the example shown is integral with the reclaimer 13 although it may be fitted downstream of the reclaimer 13. As is known per se the line 16 between the reclaimer 13 and the air-end 11 passes through a lubricant cooler 28.

A by-pass 16A controlled by a thermostatic valve is provided which diverts the lubricant through the by-pass when the temperature of the lubricant from the reclaimer 13 is below a predetermined operating temperature.

The fully cleaned gas is subsequently passed through an after cooler 19 before passing to the plant discharge 20 and into use. A pressure transducer 26 responds to the pressure in the customer's gas main to energise the control system as and when required.

A small amount of the reclaimed lubricant is injected directly to the air end 11 through a scavenge pipe 27 but the bulk of the reclaimed lubricant returns from the reclaimer 13 and filter 13 to the air end 11 through the line 16.

In accordance with the present invention a thermostatically controlled restrictor valve 22 (Figures 2 and 3) is incorporated in the lubricant return line 16. The restrictor valve 22 comprises a housing 30 having a blind bore 31 communicating at its open end with an inlet 32 of the housing. An outlet 33 of the housing communicates with a cylindrical chamber 34 of greater diameter than the bore 31 and surrounding the same intermediate its ends. Axially slideable within the bore 31 is a sleeve 35 which has circumferential slit-like openings 36 and 36A in the same plane intermediate its ends. As shown in Figure 2, when the sleeve 35 is in a fully raised position within the bore 31 the openings 36 and 36A are fully in register with the chamber 34 and the flow of lubricant between the inlet 32 and the outlet 33 of the housing is substantially unrestricted by the sleeve 35. When the sleeve 35 is fully lowered in the bore 31 (Figure

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3) on the other hand it restricts the flow of lubricant into the chamber 34 from the inlet 32.

Movement of the sleeve 35 is under the control of a thermostatic device which comprises a cylinder 37 integral with one end region of the sleeve and a piston 38 fixed relative to the blind end of the bore 31. Between the free end of the piston 38 and the blind end of the cylinder 37 is a Q psule (not shown) of a wax which increases in volume as its temperature rises and it liquifies and decreases in volume as it solidifies as its temperature decreases. Bemuse the wax is located where it will be exposed to the temperature of the lubricant flowing between the inlet 32 and outlet 33 of the housing as the temperature of the 1ubriQ nt increases the sleeve 35 will be lifted from the position of Figure 3 to the position of Figure 2, thus increasing the flow of lubricant through the housing 30.

Conversely as the temperature of the lubricant falls and the wax solidifies and reduces in volume a compression spring 39 will urge the sleeve 35 from the position of Figure 2 to the position of Figure 3, thus restricting 1ubrim nt flow through the housing 30.

To ensure that there is always a minimum flow of lubricant through the housing 30 irrespective of the position of the sleeve 35 a by-pass line 40 is provided in the housing directly connecting the inlet 32 with the chamber 34. This safeguards against any malfunctioning or blockage of the sleeve 35 such as to cut off the flow of lubricant altogether or reduce it below a mi m mum level which will not adequately 1ubriQ te the air-end. If necessary the by-pass line 40 has a restriction 41, which may be adjustable.

Claims

. e À À eve À ÀÀ À. e e À... À. . À À À À À À e À a À He e r CLAIMS:

1. A method of operating a lubricant-cooled screw compressor having an air-end which discharges a mixture of lubricant and compressed air, and means for separating the lubricant from the compressed air downstream of the air-end and for returning the separated lubricant to the air-end, wherein the return flow of lubricant to the air-end is controlled in accordance with the temperature of the lubricant such that said flow is restricted when said temperature is below a predetermined value and increased when said temperature is above said predetermined value.

2. The method of claim 1, wherein the said return flow of lubricant is controlled to be proportional to variations of said temperature.

3. The method of claim 1 or claim 2 wherein the temperature of the return flow of lubricant is sensed to determine the temperature of the lubricant.

4. An lubricant-cooled screw compressor comprising an air-end adapted to discharge a mixture of lubricant and compressed air and means for separating the lubricant downstream of the air-end and for returning the separated lubricant to the air end, wherein temperature sensitive means is provided for varying the return flow of lubricant to the air end in response to variation in the temperature of the lubricant such that the return flow of lubricant to the air-end is restricted when the temperature of the air end falls and is increased when the temperature of the lubricant rises.

5. A compressor as claimed in claim 4, wherein a thermostatically controlled restrictor valve is located in the lubricant return line from the separating means to the air-end, the valve being adapted to control the flow of the returning lubricant according to the temperature sensed by the thermostat.

6. A compressor as claimed in claim 5, wherein the thermostat is immersed in the return lubricant flow.

7. A compressor as claimed in claim 5 or claim 6, wherein the restrictor valve comprises a housing having an lubricant inlet and an lubricant outlet, the outlet-communicating with an annular chamber within the housing

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À which is coaxial with, intermediate the ends of and of greater diameter than a bore within the housing communicating with the inlet, a sleeve moveable axially of the bore whereby an opening in the wall of the sleeve may be brought into or out of register with the chamber and a thermostatic device within the bore which will respond to changes in the temperature of lubricant passing through the housing thereby to displace the sleeve to vary the area of said opening which is exposed to the chamber.

8. A compressor as claimed in claim 7, wherein the thermostatic device comprises a cylinder moveable with the sleeve, a piston fixed at one end relative to the housing and a wax within the cylinder at the free end of the piston, the wax being of the kind which increases in volume as it liquifies in response to an increase in temperature.

9. A compressor as claimed in any one of claims 4-8, wherein by-pass means is provided by passing the temperature sensitive means, the by-pass means being adapted to ensure a minimum return flow of lubricant from the separating means to the air-end independently of the temperature sensitive means.

10. A compressor as claimed in claim 9 as appendant to claim 6 or claim 7, wherein the by-pass means comprises a by-pass duct within the housing which directly communicates the inlet with said chamber.

11. A compressor as claimed in claim 10, wherein the by-pass duct has a restriction. 12. A compressor as claimed in claim 11, wherein the restriction is adjustable.

12. An lubricant-cooled screw compressor substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

Amendments to the claims have been filed as follows CLAIMS:

1. A method of operating a lubricant-cooled gas compressor which discharges a mixture of lubricant and compressed gas, and means for separating the lubricant from the compressed gas downstream of the compressor and for returning the separated lubricant to the compressor, wherein the return flow of lubricant to the compressor is controlled in accordance with the temperature of the lubricant such that said flow is restricted when said temperature is below a predetermined value and increased when said temperature is above said predetermined value.

4. A lubricant-cooled gas compressor adapted to discharge a mixture of lubricant and compressed gas and provided with means for separating the lubricant downstream of the compressor and with means for returning the separated lubricant to the compressor, wherein temperature sensitive means is provided for varying the return flow of lubricant to the compressor in response to variation in the temperature of the lubricant such that the return flow of lubricant to the compressor is restricted when the temperature of the lubricant falls and is increased when the temperature of the lubricant rises.

5. A compressor as claimed in claim 4, wherein a thermostatically controlled restrictor valve is located in a lubricant return line from the separating means to the compressor, the valve being adapted to control the flow of the returning lubricant according to the temperature sensed by the thermostat. 6. A compressor as claimed in claim 5, wherein the thermostat is immersed in the return lubricant flow.

7. A compressor as claimed in claim 5 or claim 6, wherein the restrictor valve comprises a housing having an lubricant inlet and an lubricant outlet, the outlet communicating with an annular chamber within the housing

which is coaxial with, intermediate the ends of and of greater diameter than a bore within the housing communicating with the inlet, a sleeve moveable axially of the bore whereby an opening in the wall of the sleeve may be brought into or out of register with the chamber and a thermostatic device within the bore which will respond to changes in the temperature of lubricant passing through the housing thereby to displace the sleeve to vary the area of said opening which is exposed to the chamber.

9. A compressor as claimed in any one of claims 4-73, wherein by-pass means is provided by passing the temperature sensitive means, the by-pass means being adapted to ensure a m mimum return flow of lubricant to the compressor independently of the temperature sensitive means.

10. A compressor as claimed in claim 9 as appendant to claim 7, wherein the by-pass means comprises a by-pass duct within the housing which directly communicates the inlet with said chamber.

13. An lubricant-cooled gas compressor as claimed in claim 4 substantially as hereinbefore described with reference to and as shown in the accompanying drawings.