WO2004036048A1

WO2004036048A1 - Condensate elimination in compressor systems

Info

Publication number: WO2004036048A1
Application number: PCT/AU2003/001397
Authority: WO
Inventors: Anthony John Kitchener
Original assignee: Cash Engineering Research Pty Ltd.
Priority date: 2002-10-21
Filing date: 2003-10-21
Publication date: 2004-04-29
Also published as: AU2002952175A0

Abstract

An arrangement for eliminating contaminated waste condensate flow discharges from air compressor systems, includes heat exchange means (83) for passing the waste condensate flow (20) in heat exchange with a region of the compressor system at an elevated temperature, including the hot compressed gas discharge line (90) from the compressor system or a hot lubricant line (15) of the compressor system, in a manner sufficient to evaporate water in the waste condensate flow (20), and means (84) to separate the water vapour from at least one other material in the waste condensate flow (20), and means (87) to vent the separated water vapour to atmosphere.

Description

CONDENSATE ELIMINATION IN COMPRESSOR SYSTEMS

The present invention relates to air compression systems and particularly to the elimination of condensate produced by such systems.

International Patent Application Nos. PCT/AU01/00402 and PCT/AU01/00403 disclose air compression systems of various configurations aimed at providing clean dry compressed air to end users requiring same.

The present invention is particularly adapted for use with the air compression systems disclosed in the aforementioned International applications, however, it is not limited to these systems. Moreover, while the present invention is particularly useful for lubricant injected rotary screw compressors, it will also be capable of use with rotary vane and reciprocating piston type compressor systems. To dry compressed air produced by an air compression system, atmospheric humidity may be condensed by any suitable means to produce a condensate which may be removed from the system. In the above identified International applications, such a condensate is produced in a compressor after cooler. When such a condensate is produced, it is conventionally drained by a trap or similar to a sewer or other disposal system. In lubricated compressors, this condensate may contain residues of the lubricant also condensed in the after cooler (or similar). These residues may form a stable emulsion with the water in the condensate, which creates problems with water treatment.

It is desired from a cost and waste disposal perspective to discharge the condensate into a local sewer, however, environmental safeguarding laws are generally becoming increasingly strict and if the condensate does include any lubricant residue, it can only be disposed in this way with a costly pretreatment. The objective therefore of the present invention is an arrangement for use with air compressor systems and air compressor systems including such arrangements which will eliminate the condensate problem outlined above by returning the moisture to the atmosphere from whence it came.

According to a first aspect, the present invention provides an arrangement in an air compressor system producing a waste condensate flow of water and at least one other material, said arrangement including heat exchange means for passing the waste condensate flow in heat exchange with a region at an elevated temperature in a manner sufficient to evaporate water in said waste condensate flow to form water vapour, and means to separate said water vapour from said at least one other material, and means to vent said separated water vapour to atmosphere. Conveniently, the at least one other material is a liquid material. Preferably, the region at an elevated temperature is a region of said compressor system.

By providing such an arrangement, the at least one material, preferably a liquid material, may be collected and disposed of by any suitable means, or returned to the lubrication system for the compressor system and the water vapour may be returned for the atmosphere from where it originated. Preferred features of the aforesaid arrangement may be as defined in claims 2 to 8 and 20 to 26 inclusive as annexed hereto which are, by this reference thereto, made part of the disclosure of this specification.

According to a second aspect, the present invention provides an air compressor system including a compressor unit operable in association with a liquid lubricant, the compressor unit receiving atmospheric air to be compressed and discharging a mixture of compressed air, water vapour and entrained lubricant, and an after cooler being provided to condense the water vapour in said mixture into liquid water to provide a liquid condensate flow being a mixture of at least said liquid water and at least some of said lubricant, the air compressor system further including heat exchange means for passing the liquid condensate flow in heat exchange relationship with a region at an elevated temperature whereby the liquid water in said condensate flow is evaporated and formed into water vapour, and filter means being arranged to receive the condensate flow after passing through the heat exchange means to separate said water vapour from any remaining liquid component including said lubricant with said water vapour being vented to atmosphere.

Preferred features of the aforesaid compressor system may be as defined in claims 10 to 19 inclusive as annexed hereto which are, by this reference thereto, made part of the disclosure of this specification. Further preferred features and aspects of this invention will become apparent from the following description given in relation to the accompanying drawings, in which: Fig. 1 schematically illustrates a conventional type air compression system producing a condensate which must be disposed;

Figs. 2 to 8, 10, 11 , 12 and 13 schematically illustrate various exemplary air compressor systems embodying various preferred arrangements for eliminating condensate produced therein; and

Fig. 9 is a schematic detail of part of the systems shown in Figs. 7 and 8. Fig. 1 shows a conventional air compressor system of the lubricant injected type where atmospheric air is drawn into a compressor 10 driven by a motor 11 via an inlet valve 7 and inlet 12 with compressed air and entrained lubricant droplets being discharged via line 14 into a separator vessel 13. Lubricant collected in the base of the separator vessel 13 is returned to the compressor 10 via line 15 including a lubricant cooler 16 and a lubricant filter 6. Compressed air together with some remaining lubricant droplets and water vapour from the air pass upwardly and through a coalescent type filter 17 in which the remaining lubricant droplets are removed with some being collected and scavenged via line 29 back to the compressor 10. The compressed air and water vapour passes via a minimum pressure valve 18 in a discharge line 90 to an after cooler 19 in which the water vapour is condensed and collected in a trap 81 from which it may be discharged via line 20. The dry compressed air is discharged therefrom via line 21. The waste condensate flow 20 will retain minimal amounts of lubricant normally in unacceptable levels for being simply discharged into a municipal drain or the like.

Fig. 2 illustrates one possible preferred arrangement for eliminating a contaminated condensate flow produced by a gas compressing system, one example of which is shown in Fig. 1 and described above. In this arrangement a moisture eliminator 82 is installed between the separator vessel 13 and the lubricant cooler 16. The moisture eliminator 82 conveniently includes a heat exchanger 83 and a lubricant mist filter 84. The mist filter 84 may be a coalescing type filter such as filter 17 but any other filter that will allow gas or vapour to pass without permitting liquid to pass could also be used. Such liquid components should be collected in a zone or region from where they can be then discharged or directed as desired. Condensate caught by the trap 81 is delivered via line 20 to the heat exchanger 83. To minimize the loss of compressed air through this line, a restrictor orifice 86 is provided. The heat exchanger 83 in this instance may be operatively associated with the hot lubricant return line 15 leading via the cooler 16 and filter 6 back to the compressor unit 10. In this case heat is exchanged from the hot lubricant return line 15 to the flow in line 20. Other heat exchange relationships are possible including with the separator vessel 13 itself on the hot lubricant pool 80 maintained in the base region of the separator vessel 13. As the condensate is evaporated in the heat exchanger 83, a mixture of air, water vapour and lubricant droplets pass to the lubricant mist filter 84. The air and water vapour pass through and are discharged to the atmosphere via a vent or line 87 with the lubricant droplets being collected and drained at 88. This lubricant may be collected in a container for disposal or returned to an inlet region of the compressor 10.

Fig. 3 illustrates a potential preferred alternative to the arrangement shown in Fig. 2. In this arrangement, the condensate eliminator 82 is operatively associated with the compressed air discharge line 90 leading from the separator vessel 13 to the after cooler 19. In this case, the heat exchanger 83 is located in heat exchange relationship with the hot compressed air flow from the separator vessel 13 to evaporate the water in the condensate flow from the condensate trap 81. The waste condensate flow is passed via line 20 through a flow restrictor 86 from the trap 81 to the heat exchanger 83. The lubricant mist filter 84 and associated parts operate as described above with reference to Fig. 2.

Figs. 4 and 7 illustrate schematically compressor systems disclosed and described in International Patent Application No. PCT/AU01/00402 but including a condensate eliminator 82 generally as described above with reference to Fig. 3. Figs. 5 and 6 similarly illustrate schematically compressor systems disclosed and described in International Patent Application No. PCT/AU01/00402 but including a condensate eliminator 82 generally as described above with reference to Fig. 2. By this reference thereto, so much of the specification of International Patent Application No. PCT/AU01/00402 is included herein so as to understand the compressor system and parts thereof as shown in Figs. 4, 5, 6 and 7.

Figs. 8, 9 and 10 schematically show air compressor systems as disclosed in International Patent Application No. PCT/AU01/00403. Again by this reference thereto, so much of the specification of International Application No. PCT/AU01/00403 is included herein so as to understand the compressor system and parts thereof as shown in Figs. 8, 9 and 10. In this arrangement, a condensate eliminator 82 is provided in the hot liquid line 91 leading to the hot stripper 32. As with other embodiments already described, the condensate eliminator 82 receives condensate from the trap 81 via the restrictor 86 and line 20 and passes same in heat exchange relation with a hot liquid line 91 to evaporate the water therein. Thereafter, water vapour, a small quantity of air and entrained liquid droplets are delivered via line 88 to the hot stripper 32 where the liquid recombines with the liquid in the hot stripper and the air / water vapour is vented via filter 89 (Figure 9) and vent or line 35 to the atmosphere. It will of course be appreciated that the moisture eliminator 82 may be positioned elsewhere in the compressor system circuit where there is sufficient heat to evaporate the water in the condensate flow. One such location may be as shown in the embodiments of Figs. 3, 5 and 6, where the condensate eliminator 82 is operatively associated with the hot compressed air flow in line 90 from the compressor separator vessel 13.

Reference will now be made to Figs 11 and 12 which illustrate still further preferred arrangements. In these arrangements, a final coalescing type filter 26 is located in the compressed air discharge line 90 after the after cooler 19 with this filter element 26 being external of the compressor separating vessel 13. A mixture of compressed air, liquid lubricant and water passes via the minimum pressure valve 18, line 90 and after cooler 19 to the filter element 26. Clean (lubricant free) dry compressed air is discharged at 27. Water in liquid form together with a little liquid lubricant and some compressed air passes via a restrictor orifice 86 and line 92 to a coil 93 located in the hot liquid lubricant pool 80 in the base of the separator vessel 13. The water component in this flow is evaporated in the coil 93 and the flow then of compressed air, water vapour and some liquid lubricant passes to a mist filter element 94 which may also be of the coalescing type similar to 26. Any other type of filter element capable of carrying out a similar task might also be used. The filter element 94 allows the water vapour and any remaining compressed air to be discharged or vented to atmosphere at 87. Any liquid component (mainly liquid lubricant) is collected in the base of the filter element 94 and scavenged back to the compressor unit 10 via line 29. By locating the filter element 94 within the hot environment of the separator vessel 13, the element itself including any housing walls are maintained sufficiently hot (ie within 5°C of the water vapour temperature) to prevent any of the water vapour condensing within the filter element itself.

One possible difficulty with this arrangement is that if the orifice 86 is set at a size sufficient to cope with the most humid conditions possible for the atmospheric air to be compressed, then a significant amount of compressed air is bled from the discharge 27. This is particularly disadvantageous if the compressor system is then to be used in a less humid environment. Figure 12 illustrates one means for overcoming such a difficulty. In this case, the orifice 86' is adjustable such that a variable amount of compressed air might be bled from the discharge line 90 depending on atmospheric humidity conditions. The adjustable orifice 86' might be varied or adjusted in response to humidity levels sensed by a humidity sensor 95 located in the water vapour discharge line or vent 87. In this manner, only so much of the compressed gas that is needed is bled from the discharge line 90 ensuring higher efficiency levels.

A possible alternative to the main arrangements shown in Figs 11 and 12 may be as follows. The orifice 86 / 86' might be replaced by a float valve or other level control valve 96 located in line 92. This then prevents the loss of any compressed air from the discharge line 90, however, a source of compressed air is still required to propel the liquid components along the line 92 and through the coil 93. This may be achieved by bleeding a small amount of compressed air and liquid lubricant from the compressor unit 10, where the air is at a relatively low pressure but greater than atmosphere (for example, at about 1.5 bars), along line 97. Line 97 enters line 92 below the evaporation coil 93. If tapping into the compressor unit 10 is not considered desirable for any reason, then line 97 might be replaced by a small air pump 98 driven by a motor 99 to deliver low level compressed air (ie at about 1.5 bars) via line 100 into the line 92 before the evaporating coil 93.

Fig 13 illustrates another possible preferred embodiment where the compressor unit 10 is integrally mounted within the space provided by the separator vessel 13. Manufacturers of this compressor system arrangement include Hitachi and Rotorcom Verdichte and the present invention is equally applicable to this type of compressor system arrangement. Such arrangements may include a coalescing type filter element in the compressed air discharge line from the separator vessel 13 which conveniently is mounted externally of the separator vessel 13 by a threaded or other connection means. In accordance with a preferred aspect of the present invention this coalescing type filter element may be replaced by a unit 101 including a coalescent type filter 102 to enable water vapour to be discharged or vented from the system at 87. The unit 101 receives hot compressed air including entrained water vapour and lubricant droplets at 103 from within the separator vessel 13. This flow passes through the interior zones of the unit 102 to maintain same sufficiently hot to prevent water vapour condensing within the unit with the hot compressed air then passing at 104 into discharge line 90 controlled by a minimum pressure valve 18. As with other embodiments this flow passes through an after cooler 19 into a final coalescing type filter 26. Water vapour in the flow is condensed by the after cooler 19 and collected as liquid coated with entrained liquid lubricant therein. A small amount of compressed air is bled from the main flow exiting at 27 to return the liquid water and lubricant via a restrictor orifice 86 and line 92 back to the unit 101. Line 92 passes through heat exchanger 83 where the heat of the discharging compressed air in line 90 heats the flow in 92 to evaporate the water vapour in the line. Within the unit 102, the water vapour and minor amounts of compressed air pass through the filter element 102 and are discharged or vented at 87. Any remaining liquid lubricant is retained by the filter element 102 and scavenged via line 29 back to the inlet to the compressor unit 10. While Fig 13 illustrates an arrangement where heat in the discharging compressed gas line is utilized to heat and evaporate liquid water in line 92, it will be apparent that other sources of heat might be utilized for the same purpose including the hot lubricant return line 15 and the hot lubricant pool 80 maintained in the lower regions of the separator vessel. It will of course be apparent that the features illustrated and described above in relation to Figs 11 and 12 might also be utilized in the present invention.

It will be recognized that many other alternative arrangements are also possible falling within the scope of the annexed patent claims and such alternative arrangements are also considered to form part of the present invention. For example, while it will be less efficient, externally applied heat might also be used to evaporate liquid water to form water vapour in any of the above described embodiments before venting the water vapour to atmosphere.

Claims

CLAIMS:

1. An arrangement in an air compressor system producing a waste condensate flow of water and at least one other material, said arrangement including heat exchange means for passing the waste condensate flow in heat exchange with a region at an elevated temperature in a manner sufficient to evaporate water in said waste condensate flow to form water vapour, and means to separate said water vapour from said at least one other material, and means to vent said separated water vapour to atmosphere.

2. An arrangement according to claim 1 wherein said region at an elevated temperature is a region of said compressor system.

3. An arrangement according to claim 1 or claim 2 wherein said at least one other material is a liquid material.

4. An arrangement according to claim 1 or claim 2 wherein said means to separate said water vapour from said at least one other material includes a filter element.

5. An arrangement according to claim 4 wherein said filter element is separate from operative flow circuits within said air compressor system.

6. An arrangement according to claim 4 wherein said filter element is included in flow circuits of said air compressor system.

7. An arrangement according to any one of claims 1 to 6 wherein said region at an elevated temperature is heated by gas at an elevated temperature.

8. An arrangement according to any one of claims 1 to 6 wherein said region at an elevated temperature is heated by liquid at an elevated temperature.

9. An air compressor system including a compressor unit operable in association with a liquid lubricant, the compressor unit receiving atmospheric air to be compressed and discharging a mixture of compressed air, water vapour and entrained lubricant, and an after cooler being provided to condense the water vapour in said mixture into liquid water to provide a liquid condensate flow being a mixture of at least said liquid water and at least some of said lubricant, the air compressor system further including heat exchange means for passing the liquid condensate flow in heat exchange relationship with a region at an elevated temperature whereby the liquid water in said condensate flow is evaporated and formed into water vapour, and filter means being arranged to receive the condensate flow after passing through the heat exchange means to separate said water vapour from any remaining liquid component including said lubricant with said water vapour being vented to atmosphere.

10. An air compressor system according to claim 9 wherein the region at an elevated temperature is a region of the compressor system.

11. An air compressor system according to claim 9 wherein the region at an elevated temperature is heated by an external source.

12. An air compressor system according to any one of claims 9 to 11 wherein the liquid condensate flow includes a small volume of entrained compressed air, said compressed air being vented to atmosphere with said water vapour.

13. An air compressor system according to claim 9 or claim 10 wherein the heat exchange means passes said liquid condensate flow into heat exchange relationship with hot compressed gas flow immediately before said after cooler.

14. An air compressor system according to claim 9 or claim 10 wherein the heat exchange means passes said liquid condensate flow into heat exchange relationship with hot liquid flow in said compressor system.

15. An air compressor system according to any one of claims 9 to 14 wherein the filter means is separate from operative flow circuits within the air compressor system.

16. An air compressor system according to any one of claims 9 to 14 wherein the filter means forms an operative part of flow circuits of the air compressor system.

17. An air compressor system according to any one of claims 9 to 16 wherein the compressor unit comprises a liquid lubricant injected rotary compressor discharging compressed air, water vapour and entrained liquid lubricant droplets into a primary separator vessel for separating most of said liquid lubricant droplets from the compressed air and water vapour, said liquid lubricant being collected in said primary separator vessel and returned to a lower pressure region of said compressor.

18. An air compressor system according to claim 17 wherein the rotary compressor is of the screw or vane type.

19. An air compressor system according to claim 17 or claim 18 wherein the rotary compressor is mounted within said primary separator vessel.

20. An arrangement according to claim 1 wherein said means to separate said water vapour from said at least one other material is maintained at an elevated temperature.

21. An arrangement according to claim 19 wherein said means to separate said water vapour from said at least one other material is located within a separator vessel of said compressor system.

22. An arrangement according to claim 21 wherein said means includes a coalescing type filter element.

23. An arrangement according to claim 21 or claim 22 wherein said waste condensate flow is passed through an evaporator coil located in a collection zone for hot liquid lubricant in the separator vessel of said compressor system, liquid water in said waste condensate flow being evaporated to form water vapour before being passed to said means to separate said water vapour from said at least one other material.

24. An arrangement according to any one of claims 20 to 23 wherein said waste condensate flow originates from a filter element located in a compressed air discharge line from the compressor system.

25. An arrangement according to claim 24 wherein the filter element is located after an after cooler located in the compressed air discharge line.

26. An arrangement according to claim 24 or claim 25 wherein the filter element is a coalescing type filter element.