GB2360953A

GB2360953A - Oil cleaner for removing water and gases from oil

Info

Publication number: GB2360953A
Application number: GB0008074A
Authority: GB
Inventors: Robert Parsons
Original assignee: OIL PURIFICATION SYSTEMS Ltd
Current assignee: OIL PURIFICATION SYSTEMS Ltd
Priority date: 2000-04-04
Filing date: 2000-04-04
Publication date: 2001-10-10
Anticipated expiration: 2020-04-04
Also published as: GB0008074D0; GB2360953B

Abstract

An oil cleaner for removing entrained and dissolved water from contaminated oil comprises a holding reservoir 1 for batch 5 of contaminated oil. The oil is heated in the reservoir using immersion heater 6, and is pumped from the base of reservoir 1 through dividing valve 8 selectively to be returned to the reservoir or passed to separator 13 suspended in vacuum chamber 3. Oil passing to separator 13 passes first in heat exchange contact with walls and lid 12 of chamber 3 and the combination of the high oil temperature and low pressure in chamber 3 causes entrained and dissolved water to evaporate from the oil as it passes back into oil batch 5. Water vapour is removed from the low pressure air in chamber 3, by condenser 17 adjacent thereto. Oil in the cleaner undergoes batchwise processing until the desired low water content is achieved.

Description

2360953 TITLE Oil Cleaner

DESCRIPTION Field of the Invention

The invention relates to oil cleaning apparatus, for removing impurities including emulsified and dissolved water and gases from oil.

Prior Art

Oil cleaners exist which first remove solid contaminants from oil by filtration and then remove emulsified and dissolved water by a separation/evaporation process. Solid particulate comtaminants are removed by filtration, preferably at a later stage. The dissolved water is the most difficult contaminant to remove, and the efficiency of such cleaners is generally judged by the dissolved water content of the final cleaned oil, as well as by the time and power consumption required to achieve a target dissolved water content.

Among the best oil cleaners currently available is the Parker PVS-180 oil purification system, manufactured by Filter Technologies Inc of Washington, U.S.A. The PVS-180 claims to remove 99.95% of the water (that is, the final cleaned oil still contains 500 p.p.m. of dissolved water) and retains the removed water in a condensate holding tank. Water removal is achieved by drawing the cold contaminated oil by suction through a heat exchanger to a separator in a vacuum chamber. The separator is a plate filter or a coalescing filter, and as it passes through the filter the oil, heated by the heat exchanger and exposed to low pressure in the vacuum chamber, loses water by evaporation. A constant stream of air at low pressure is passed through the vacuum chamber to purge the vacuum chamber of its moist air, and the water vapour entrained in that moist air is removed in a condenser. The oil processing is a continuous oncethrough process, -2 although the PVS-180 does incorporate a holding tank so that the cleaned oil can be removed intermittently.

The efficiency of the PVS-180 purification system varies with changes in ambient temperature and humidity, as the apparatus uses ambient air to flush out the vacuum chamber. If the ambient air temperature is below the dew point subsisting in the vacuum chamber, then a mist of condensed water droplets can be formed in the vacuum chamber as the flushing air mixes with the water-laden vapour around the coalescing filter. This mist can contact the cleaned oil, and easily re-contaminates the cleaned oil.

Another oil cleaner is the UM-VAC oil cleaner made and sold by Sesco Systems Engineering and Sales Co., Inc., Indiana, USA. The UNI-VAC cleaner operates in a manner very similar to that of the PVS-180. That is to say, contaminated oil is pumped from a holding tank through a heat exchanger to a separator horizontally disposed in a vacuum chamber. The hot oil loses water by evaporation as it passes through the separator into the vacuum chamber. The UNI-VAC cleaner, like the PVS-180, is a continuous once-through cleaner, and claims to reduce up to 1% of water in a single pass. If greater purification is required, then a tank of cleaned oil would have to be collected, returned to the holding tank, and re-processed. That can be repeated, in theory at least, until the dissolved water content is as low as 10 p.p.m. In practice however that requires extremely high vacuum and a very large number of repeated processing passes, and involves a very high energy consumption.

It is an object of the invention to provide an oil cleaner which can remove impurities, including dissolved water and gases, from contaminated oil to purification limits at least as high as and preferably higher than those previously achievable without excessive energy consumption or processing times. That and other objects and advantages are achieved by the invention as described below.

The Invention The invention provides an oil cleaner for removing entrained and dissolved water and gases from contaminated oil by passing heated oil through a separator into a vacuum chamber where it loses water by evaporation, and removing the water vapour from the low pressure air in the vacuum chamber by condensation, characterized in that the oil cleaner is a batch cleaner comprising a holding reservoir for a batch of contaminated oil to be cleaned; the holding reservoir contains an immersion heater for heating the batch of oil contained therein; the vacuum chamber is a thermally insulated chamber immediately above the holding reservoir, the walls and lid of the vacuum chamber being heated to maintain a desired working temperature in the vacuum chamber; a pump is provided for pumping the heated oil from the holding reservoir to a flow dividing valve which is operable selectively to return the pumped oil to the holding reservoir to create movement of the oil in the holding reservoir or to pass the pumped oil through the separator into the vacuum chamber; and a vacuum pump is provided for establishing and maintaining a low pressure in the vacuum chamber and for drawing water vapour lost from the oil by evaporation at the separator through an exit passage through the heated walls or lid of the vacuum chamber to a condenser externally of the vacuum chamber.

The holding reservoir is preferably circular in section to promote a cyclic movement of oil therein, avoiding dead areas of static oil. The cyclic movement may be created by jetting the oil returned from the flow dividing valve obliquely into, or onto the surface of, the oil in the holding reservoir. Dead areas of static oil may be further reduced by building the holding reservoir with a circular or generally circular section, and optionally with a downwardly and inwardly tapering base, with an exit point for the pumped oil to be drawn from the reservoir being at the bottom centre of the base. A preferred shape of the holding reservoir is one with an upwardly an inwardly tapering upper surface as well as the downwardly and inwardly tapering base. The potential for dead areas of static oil is thereby reduced to a minimum. The holding reservoir is preferably of a heat insulated double skin construction.

The batch of oil in the holding reservoir is liable to be thick and viscous when cold. After initial heating using the immersion heater it is pumped and returned under pressure to the holding reservoir via the flow dividing valve. Eventually the batch of oil is raised to the desired operating temperature, and at that stage the flow dividing valve is actuated to divert some or all, but preferably only a proportion, of the pumped oil to pass through the separator to the vacuum chamber. The oil is preferably used to heat the walls and lid of the vacuum chamber to the operating temperature by passing it through one or more heat exchange passages in walls and the lid so that as it flows to the separator into the vacuum chamber above the batch of oil in the reservoir chamber it raises the temperature of the inner walls and lid to the operating temperature. oil passing through the separator, which may be a plate separator or a coalescing filter, crosses a decreasing pressure gradient and is exposed to reduced pressure in the vacuum chamber above the oil in the holding reservoir. At this reduced pressure it loses water by evaporation.

No mist is generated in the vacuum chamber because there is no crosscurrent of ambient air. Neither is there any significant condensation on the walls or lid of the reservoir chamber because the chamber is preferably heat-insulated and the walls and lid are heated. Instead, water vapour in the low pressure air in the vacuum chamber finds its way through the exit passage in the walls or lid and is condensed in the condenser externally of the vacuum chamber. The vacuum pump for establishing and maintaining the reduced pressure in the vacuum chamber may be in-line with the exit passage and condenser.

The circulation of the oil through the separator may be continued until the desired degree of water removal has been attained. It is possible to obtain oil with a final water content as low as 3 to 5 p.p.m. by prolonged recycling. As a generality, however, it is seldom necessary to clean the oil to a higher degree of purity than that which characterised the starting oil. For example, if an oil used in an installation had an initial water content when new of 100 parts per million (ppm).then it would be regarded as satisfactory if after contamination of that oil in use, the cleaner of the invention was used to return the oil to a water content of the order of 100 ppm again.

The energy consumption of the oil cleaner of the invention is very low because the oil can be recirculated in a thermally insulated cyclic path, without the repeated heating and cooling which is a characteristic of repeat processing techniques of the prior art.

Drawings Figure 1 of the drawings is a schematic circuit diagram of an oil cleaner according to the invention; and Figure 2 is a graph illustrating water contant vs. time in an oil cleaning process using ap apparatur according to Figure 1.

Referring first to Figure 1, a holding reservoir 1 is of thermally insulated double walled construction and comprises a reservoir tank portion 2 for holding a batch of contaminated oil to be cleaned, and a vacuum chamber 3 over that tank portion. The tank portion 2 is of circular section, and has an upwardly and inwardly tapering top communicating with the vacuum chamber 3, and a downwardly and inwardly tapering base leading to an exit port 4.

The contaminated oil batch, shown as 5 in the tank portion 2, is heated by an electric immersion heater 6 until it is sufficiently fluid to be pumped by a pump 7 to a flow dividing valve 8. Initially the flow dividing valve 8 returns all of the pumped contaminated oil to the holding reservoir 1 through a conduit 9 and a jet 10. The jet 10 directs the fluid tangentially of the fluid reservoir tank portion 2 so as to induce a circular f low of oil within the holding reservoir 1.

When the oil in the reservoir has attained the necessary treatment temperature, which is preferably 550C to 600C, the right hand branch of the flow dividing valve 8 opens so as to direct the pumped oil under pressure through a conduit 11 leading to the vacuum'chamber 3. At this stage the flow dividing valve may terminate flow of the pumped oil through the conduit 9, or it may continue to send a throttled flow through the conduit 9.

The oil flowing through the conduit 11 is taken through heat exchamge passages (not shown) in the walls and in a lid 12 of the vacuum chamber 3. The lid 12 and walls are heated by heat exchange contact with the flow of heated oil. As the pumped oil from the conduit 11 passes through the lid 12 and walls, the lid and walls are brought to the full operating temperature of the oil, being the temperature necessary for the efficient removal of water by evaporation, so as to maintain the temperature in the vacuum chamber 3 at the operating temperature. That temperature does, of course, depend on the pressure established in the vacuum chamber 3. The heated oil passes into a separator 13, which may be a plate separator or a coalescing filter. The oil passes through the separator as a thin film, and experiences a sharp decreasing pressure gradient before returning under gravity to the tank portion 2 of the holding reservoir 1. Over the surface of the thin film of oil, however, entrained and/or dissolved water is rapidly lost by evaporation into the vacuum chamber 3.

The necessary reduced pressure is maintained in the vacuum chamber 3 by means of a vacuum pump 14 pneumatically linked to the vacuum chamber 3 by conduits 15 and 16 and a condensing chamber 17. As the moisture -enriched air in the vacuum chamber 3 reaches the condenser 17 through the conduit 16, water is separated therefrom by condensation, and collects in a condensate tank 18. There is no cross-flow of ambient air through the vacuum chamber 3, and no consequent generation of a mist of condensed water droplets in the vacuum chamber 3 over the holding reservoir tank portion 2. The oil passing back into the reservoir tank portion 2 from the separator 13 mixes with the remainder of the oil batch, and is recycled by the pump 7 until the necessary degree of water purification has been obtained. The process is highly energy efficient, because the whole of the oil circulation route can be thermally insulated. Pump life is prolonged, because the pump 7 can be started only when the batch of oil has attained a reasonable fluid viscosity for pumping. Substantially higher degrees of water removal for a given expenditure of energy can be obtained than in current known oil cleaning equipment.

At the end of the processing cycle, the cleaned oil can be removed from the reservoir tank portion 2 either under gravity from a discharge tap (not shown) or by pumping. The pump 7 could be used for the discharge of the treated oil batch, for example by placing a diverting valve (not shown) in the conduit between the pump 7 and the f low dividing valve 8, for selective diversion of the pump output to a collection vessel. Similarly the pump 7 could be used for the initial loading of a new batch of contaminated oil for cleaning, for example by placing a diverting valve at the inlet side of the pump, so that it draws oil not from the reservoir tank portion 2 but from a source of contaminated oil, and pumps it through the flow dividing valve into the reservoir chamber. Oil level detectors can be incorporated to make the process of filling and emptying of the reservoir tank automatic, so that even though the oil cleaner works on a batch principle it may be incorporated in a production line for the continuous but batchwise cleaning of contaminated oil.

Particulate contaminants are best removed from the oil in a filtration stage as the otherwise cleaned oil is removed from the reservoir tank 2.

Figure 2 shows a typical cleaning/time relationship, from which it will be seen that the rate of water removal deceases with decreasing water content. In the conducted tests on which Figure 2 was based, it took about three hours for the contaminated oil to be returned to a water content approximating that of the starting oil before contamination. The actual test figures are shown in the Table below. The restoration of a 20- litre oil batch over three hours at an energy consumption of the order of lkW per hour (being the energy consumption of the heater) respresents a particularly good energy efficiency for this process).

TABLE

Fluid Hydraulic Mineral Oil 32 cSt Oil Volume 20 Litres Oil Temp. 55 deg C Vacuum 180,000 Pa Heater 1 kW TEST RESULTS Water in Oil ppm (1) % Oil Sample New Oil 160(2) 0.016 Water Contaminated to 20000 2.00 mins 10000 1.00 mins 8300 0.83 mins 5500 0.55 mins 3400 0.34 mins 2200 0.22 mins 230(2) 0.023 240 mins 180(2) 0.018 Note (1) ppm = parts per million.

(2) Water content measured by UCC water in oil monitor.

Results verified by an independent laboratory analysis using Karl Fischer method ASTM D 1744.

Claims

1. An oil cleaner for removing entrained and dissolved water and gases from contaminated oil by passing heated oil through a separator into a vacuum chamber where it loses water by evaporation, and removing the water vapour from the low pressure air in the vacuum chamber by condensation, characterized in that the oil cleaner is a batch cleaner comprising a holding reservoir for a batch of contaminated oil to be cleaned; the holding reservoir contains an immersion heater for heating the batch of oil contained therein; the vacuum chamber is a thermally insulated chamber immediately above the holding reservoir, the walls and lid of the vacuum chamber being heated to maintain a desired working temperature in the vacuum chamber; a pump is provided for pumping the heated oil from the holding reservoir to a flow dividing valve which is operable selectively to return the pumped oil to the holding reservoir to create movement of the oil in the holding reservoir or to pass the pumped oil through the separator into the vacuum chamber; and a vacuum pump is provided for establishing and maintaining a low pressure in the vacuum chamber and for drawing water vapour lost from the oil by evaporation at the separator through an exit passage through the heated walls or lid of the vacuum chamber to a condenser externally of the vacuum chamber.

2. An oil cleaner according to claim 1, wherein the flow dividing valve is temperature-responsive, passing the pumped oil to the separator only when the temperature of the oil in the holding reservoir exceeds a given threshold.

3. An oil cleaner according to claim 2, wherein the flow dividing valve acts to return a proportion of the pumped oil to the holding reservoir to create movement of the oil in the holding reservoir even when the temperature of the oil in the holding reservoir exceeds the given threshold.

4. An oil cleaner according to any preceding claim, wherein the oil returned to the holding reservoir to create movement of the oil contained therein is jetted obliquely into the oil in the holding reservoir to impart a circular movement thereto.

5. An oil cleaner according to claim 4, wherein the holding reservoir is of circular section.

6. An oil cleaner according to claim 5, wherein the holding reservoir has an upwardly and inwardly tapering top communicating with the vacuum chamber.

7. An oil cleaner according to claim 5 or claim 6, wherein the holding reservoir has a downwardly and inwardly tapering base, with an exit point for the pumped oil to be drawn from the reservoir being at the bottom centre of the base.

8. An oil cleaner according to any preceding claim, wherein the walls of the vacuum chamber are heated by heat exchange with the oil being pumped via the flow dividing valve to the separator.

9. An oil cleaner according to any preceding claim, wherein the holding reservoir is of heat-insulated double skin construction.

10. An oil cleaner according to any preceding claim, wherein the separator is a coalescing filter.

11. A method of cleaning a batch of oil by removing entrained and dissolved water therefrom, which comprises:

placing the batch of oil in the holding reservoir of an oil cleaner according to any preceding claim; heating the oil in the reservoir; pumping the heated oil through the f low dividing valve to be returned in its entirety to the holding reservoir to create movement of the oil batch therein until the temperature of the oil in the holding reservoir reaches a given value, and thereafter actuating the flow dividing valve to divert a portion of the pumped oil to the vacuum chamber through the separator; establishing and maintaining a low pressure in the vacuum chamber to cause evaporation of the entrained and dissolved water and gas in the oil passing through the separator; and removing water vapour from the low pressure air in the vacuum chamber by condensation in the condenser which is located externally of the vacuum chamber and which communicates therewith by the exit passage through the heated walls or lid.

12. An oil cleaner substantially as described herein with reference to the drawing.

13. A process for cleaning oil substantially as described herein with reference to the drawing.