METHOD AND APPARATUS FOR SEPARATING WATER FROM OIL

Abstract: Oil to be freed from water is introduced together with a gas, preferably atmospheric air, at the bottom of a first section (12) of a container (2) the interior of which is exposed to a negative pressure of about 0,8 bar. The inflowing gas forms bubbles in the oil which, owing to the negative pressure, rises in the first section (12) of the container (2). The air in the bubbles are rapidly heated by the ambient oil and therefore expands while its relative humidity decreases, resulting in the air absorbing water vapour from the oil. A baffle plate (50) above the first section (12) acts to spread the oil across a second section (14) of the container, in which the oil falls down across a surface-maximizing device preferably in the form of a packing (52), while the oil releases additional water vapour. The liberated water vapour is withdrawn from the container (2) through an opening (42) at the top of the container while the oil, upon having passed through the packing (52) is pumped out from the bottom of the second section (14) of the container. The first and second sections (12, 14) of the container (2) are separated by a partition wall (10), preferably in the form of a tube (11).

Description: METHOD AND APPARATUS FOR SEPARATING WATER FROM OIL The invention relates to a method or process and apparatus for separating water from oil. Oils are prone to be strongly invaded by water from leaking coolers, condensate in reservoirs, cleaning and steam leakages. Water may reduce viscosity, cause defects of the structural composition of the oil and disturbe/destroy additives in the oil. This will result in an accelerating change of the oil (the oil forming water as a result of ageing) and bacterial growth and corrosion, resulting in reduced life of the oil and of the components it serves. US 5 211 856 discloses a method for separating water from oil, in which the oil to be separated is introduced in a heated condition to a predetermined level into a container subjected to a vacuum, while gas which is preheated to the tempera- ture of the oil is introduced into the oil in the container to form gas bubbles rising through the oil while absorbing water vapour which, together with the gas in the bubbles, are released in the upper part of the column and withdrawn from the top thereof. The object of the present invention is to provide a continuous separation process which, by means of a particularly simple and reliable apparatus, results in a higher efficiency than that of the above and other prior methods of this type, i.e. which, in a simple manner, enables larger amounts of water to be separated per unit time from a certain amount of oil. This object is achieved according to the invention, by a process and appa- ratus as defined in the appending claims. Admittedly, it is wellknown technique to promote evaporation of a liquid by causing it to flow across a large surface area such as packing in a column. However, the present invention provides a surprisingly simple and effective manner of combining the two above mentioned prior separating principles which, as far as the applicant knows, provides an unsurpassed efficiency in separating water from oil. The invention will also result in a correspondingly effective separation of air or other gaseous contaminations from the oil. The invention will now be described in detail with reference to the schematic drawing in which fig. 1 is a partial perspective view of an embodiment of the appa- ratus according to the invention, while figs. 2 and 3 are longitudinal sectional views of two possible variants of the apparatus. In figure 1 numeral 2 refers to a vertical, preferably cylindric closed container or "column" having side wall 4, top wall 6 and bottom wall 8. Spaced below top wall 6 the interior of the column is separated by a vertical partition wall 10 into a first section 12 and a second section 14, the latter section having a substantially larger cross sectional area than that of the first section. The partition wall 10 would normally be in the form of a tube 11 centrally or coaxially arranged in the column. In the embodiment shown the interior of tube 11 will then constitute the first section 12, while the annular space between tube 11 and side wall 4 constitutes the second section 14. Centrally at the bottom of tube 11 , i.e. in the first section 12, there is an inlet 16 for unprocessed (unseparated) oil, and at the bottom of the second section or annular space 14 there is an outlet 18 for processed (separated) oil. The inlet 16 is connected, via an inlet conduit 20 including a heating element 22 and closing or control valve 24, to an oil reservoir (not shown), such as in a lubricating oil system or hydraulic plant. The outlet 18 is connected, via outlet conduit 26 provided with motor 28, to oil reservoir or tank not shown. Further, at the bottom of the first section 12 there is a gas inlet 30, prefera- bly in the form of a plurality of nozzles 32 disposed around the central oil inlet 16. The gas inlet 32 is, via a supply conduit 34, provided with a flow control valve (such as throttle valve) 36 and cleaning/drying filter 38 connected to a gas source 40 which would normally be surrounded by atmospheric air at about 20°C. The top wall 6 of column 2, which preferably is dome-shaped, is provided with a suc- tion opening 42 for withdrawing gas and liberated water vapour. The suction opening 42 communicates, through a line 43, with a condensing cooler 44, vacuum pump 46 and gas filter 48 discharging to the ambience, for example. Spaced above the first section 12, i.e. above tube 11 , there is a circular, substantially horizontal baffle plate 50 having a diameter equal to or somewhat larger than that of tube 11. In the upper part of the second section or annular space 14 there is a device 52 having a large surface area serving to impart to the oil flowing across and through the device a correspondingly large surface facing the upper space 53 of the column. In the example shown in the figure the device 52 is in the form of packing such as commonly used in columns for evaporation or absorption purposes, supported on a horizontal or slightly downwardly inclined support plate 54 extending radially outward from tube 11 toward side wall 6, with a small gap or clearance 56 between the wall and the edge of the support plate. The packing, however, covers the cross sectional area of the annular space all the way out to side wall 6. Alternatively, the support plate 54 could also extend all the way out to side wall 6, and be provided with perforations permitting oil through-flow. The operation of the apparatus according to the invention as illustrated in fig. 1 is as follows. Vacuum pump 46 is adjusted to provide a vacuum or negative pressure of at least 0,8 bar in column 2. Upon opening of the oil and air control valves 24 and 36 respectively, the vacuum of column 2 will cause oil and air to be drawn in through respective inlets 16, 32 at the bottom of tube 11. The inflowing oil is heated by heating element 22 to a temperature which is as high as possible with- out harming the properties of the oil, e.g. about 60°C, while the inflowing air would be at ambient temperature such as about 20°C. As a result of the relatively high vacuum in the column the inflowing oil - as a first stage of the process according to the invention - together with air which while forming bubbles 32 enters through the nozzles 32, will rise as a turbulent, "effervescent" stream 35 through tube 11. The air in the bubbles will rapidly be heated to ambient oil temperature, i.e. a temperature increase of about 40°C, causing the bubbles to expand and thus to achieve a greater surface area or interface with the oil, while the relative humidity of the bubble air is reduced. Consequently, the air of the bubbles will have a drying effect on the oil rising in the inner tube 11 of the column. Thus, already under this first stage of the separating or drying process, a large proportion of the water contained in the oil will be extracted from the oil. Owing to its relatively high velocity, the upflowing oil 35 will impact or strike against the baffle plate 50 above tube 11 , causing the oil to be spread in a radial layer or film 37 out through the peripheral gap 33 between the baffle plate and the upper edge of the tube while the air bubbles in the oil burst, releasing the water vapour-containing air to the upper space 53 of the column from which it is withdrawn through suction opening 42 as indicated with arrows 39. Under the action of gravity the radially flowing oil layer 37 in the upper space 53 of the column - as a second stage of the separating process according to the invention - will fall down over the underlying packing 52 and thereby again achieve a very large interface toward the ambient vacuum atmosphere, resulting in an effective evaporation of the remaining water contained in the oil and withdrawal of the water vapour through the opening 42. Upon having sunk through the packing 52, the oil flows outward to the edge of support plate 54 and down through gap 56 as indicated with arrows 41 , to be collected in the lower part 58 of the column annulus 14 in a fully processed condi- tion, i.e. substantially liberated from water. The above described two-stage process, in which the oil is caused to present a continuously large interface toward a space exposed to a relatively high vacuum, will also act to effectively remove possible air or other fluid contaminations in the oil. The level 60 of the processed oil in the column is adjusted by means of upper and lower level gauges 62, 64. When the level reaches the upper level gauge 62, outlet pump 28 is activated to pump oil 43 from the column until the pump stops when the oil level reaches the lower level gauge 64. The water vapour-containing gas withdrawn through opening 42 at the top of the column, is separated from water vapour in condensation cooler 44 before reaching the vacuum pump 46, and the exhaust gas from the pump is preferably cleaned in the gas filter 48 before being released to the atmosphere. Alternatively it could go to a closed exhaust system. The vacuum in the upper space of the column can be monitored by means of a manometer 66. The packing 52 could be any piece material commonly used in chemical engineering for evaporation purposes, such as pall rings made of metal or plastics. However, ordinary "marble balls", i.e. balls of glass or ceramic material has been found to be a lowcost and effective and therefore preferred packing. Normally balls having a diameter of about 16 mm in a number of about 2000 would be suit- able. The column 2 with tubular partition wall 10 could consist of any suitable material, such as stainless steel. However, a transparent hard plastic, such as plexiglass® is preferred, since it permits observation of the process and adjustment of the oil and air control valves 24, 36 in a manner ensuring the most favour- able flow conditions for obtaining an optimum result. More particularly, the valves are preferably adjusted depending on a predetermined approximate value of the vacuum of the column, as described below in connection with an example of practical use of the invention. The inlet and outlet conduits 20, 26 of the apparatus will normally be connected to one and the same oil reservoir for continuous operation, such that the oil in the reservoir is maintained in an optimally water and airless condition. However, the inlet 20 may of course, if desirable, be connected to a separate reservoir for unprocessed oil while the outlet 28 discharges to another reservoir or tank for processed oil. The dimensions of column 2 will be adjusted to the capacity of the plant to be served by the oil. For an oil reservoir having a capacity of about 1000 litres, the tube 11 can suitably have an inner diameter of about 60 mm and a height of about 800 mm, while the diameter and total height of column 2 can be about 250 and about 500 mm respectively. The vacuum pump 46 should have a capacity of 20 m 3 /h, and provide a maximum vacuum of down to 0,99 bar (1 mbar absolute). An example of practical use of a such apparatus in the process according to the invention for processing oil containing about 2 percent by weight of water (20 000 ppm) and a viscosity of about 32cSt, is as follows. With closed oil and air valves 24 and 36 respectively, the vacuum pump 46 and heat element 22 is activated. When manometer 66 indicates a vacuum of about 0,92 bar, oil valve 24 is opened, permitting oil to flow into the column owing to the vacuum. The oil valve 24 is adjusted to provide a flow rate of about 10 l/min. (e.g. by measuring the time elapsed from the time when the upper level gauge 62 starts outlet pump 28 until the lower level gauge 64 stops the pump). When the flow rate reaches the desired value, the vacuum in the column has increased to about 0,92 bar owing to the oil flowing through the column. Now the air valve 36 is opened and adjusted such that manometer 66 indicates a vacuum of between 0,75 and 0,85 bar, preferably about 0, 80 bar. Inspection of processed oil from the process according to the above example showed that its content of water was reduced to about 0,008 percent by weight (80 ppm). If the oil has a viscosity different from that of the above example, different adjustments of the valves may be needed. Although the valves 24 and 36 according to the above example o are adjusted when the process is started, it is of course possible to provide the valves with a fixed optimum pre-adjustment for a particular type of oil. Although the device 52 for increasing the oil interface preferably is in the form of a piece material as described above, it is also within the scope of the in- vention to use other approaches that serve to expose the oil flowing downward in the second stage of the process to a large surface area. E.g., the packing could, as indicated in fig. 2, be replaced by a plurality of downwardly inclined annular disks 70 arranged below each other and alternately attached to the tube 11 and side wall 6 at the respectively inner and outer periphery thereof, to form gaps 72, 74 with the side wall and tube respectively, at the opposite peripheral edge of the disks, to cause the oil to flow "zigzag-like" in a thin layer down along the upper surfaces of the annular disks 70 before being collected at the lower part of the column. Also in other respects the configuration of the apparatus according to the invention is not limited to that shown in fig. 1 and described above. Specifically, the "first section" of the column, i.e. the region where the oil and gas flow upward during the first stage of the process according to the invention, and the "second section" of the column where the oil sinks down during the second stage of the process according to the invention, could be configured in many different ways. Fig. 3 indicates a variant in which the first and second sections are "changed around" as compared to the embodiment shown in fig. 1. In the example of fig. 3 the side, top and bottom walls 4', 6', 8' of column 2' if substantially similar to those of the embodiment according to fig. 1 , and the partition wall 10' is again in the form of a central tube 11'. However, tube 11' has a substantially larger diameter than that of tube 11 of fig. 1. Thus, in this alternative embodiment the relatively narrow annular space between tube 11' and column side wall 6' forms the apparatus first section 12' through which the oil flows up from oil inlet 16', while the interior of tube 11' forms the apparatus second section 14' through which the oil, upon impacting the annular baffle plate 50, flows down passed the packing 52' before be- ing collected at the lower part of the column and pumped out through the central oil outlet 18'. The air intake is here preferable in the form of an annular passage 30' provided with nozzles. The column and its two sections need not be circular cylindrical. Thus, a rectangular configuration could be contemplated having a straight partition wall near one of the side walls, dividing the container in a first section of small cross sectional area and a second section of large cross sectional area.

Claims: Patent Claims: 1. Process for separating water from oil, in which the oil to be separated is introduced in a heated condition to a predetermined level into a container subjected to a vacuum, while gas which is preheated to the temperature of the oil is introduced into the oil in the container to form gas bubbles rising through the oil while absorbing water vapour which, together with the gas in the bubbles, are re- leased in the upper part of the column and withdrawn from the top thereof, characterized in that the oil, in a first stage, is caused to flow up through a first part (12, 12') of the container (2; 2') under the action of the vacuum therein, while inserting a bubble-forming gas in the upward flowing oil, and in that the oil, in a second stage, is spread across a second section (14; 14') of the container (2; 2') to sink down through a device (52; 70) acting to maximize the surface area of the sinking oil before being collected in the lower part of the second section (14; 14'). 2. Process according to claim 1 , characterized in that the oil is introduced at the bottom of the container together with the gas. 3. Process according to claim 1 or2, characterized in that the vacuum in the container is maintained at at least 0,8 bar, preferably about 0,85 bar. 4. Process according to any one preceding claim, characterized in that the oil is heated to about 60°C before flowing into the container . 5. Process according to any one preceding claim, characterized in that said gas is ambient atmospheric air being introduced in the oil without pre- heating. 6. Apparatus for separating water from oil, comprising a container (2) having inlet (16) for unseparated oil, outlet (18) for separated oil, inlet (30) for introducing gas into the unseparated oil, and outlet (42) for withdrawing gas and water vapour near the top of the container, characterized by a substantially vertical partition wall (10) spaced below the gas withdrawal outlet (42) and dividing the interior of the container in a first section (12) and a second section (14), the section for unseparated oil and the gas inlet (30) being disposed near the bottom of the first section (12) while the outlet (18) for separated oil is disposed at the bottom (18) of the second section and, spaced above the first section (12), a baffle plate (50) adapted to sprβad oil flowing out from the top of the first section down across a device (52; 70) having a large surface area disposed in an upper portion of the second section (14). 7. Apparatus according to claim 6, characterized in that the partition wall (10) is in the form of a tube (11) preferably centrally arranged in the container. 8. Apparatus according to claim 7, characterized in that the interior of the tube (11 ) constitutes the first section (12) of the container (2). 9. Apparatus according to claim 7, characterized in that the interior of the tube (11') constitutes the second section (14') of the container (2'). 10. Apparatus according to claims 6-9, characterized in that the device (52) having large surface area is a packing material. 11. Apparatus according to claim 10, characterized in that the packing (52) is in the form of marble balls. 12. Apparatus according to claim 7, characterized in that the device (70) having large surface area is in the form of a plurality of annular downwardly inclined disks (70) alternately fixed to the tube (11) and inner wall (6) of the container (2), with a gap (72; 74) toward the side wall and tube respectively.

Inventors: GROETHEIM JENS, GROETHEIM, JENS
Applicants: GROETHEIM JENS, NOR INSTR AS, GROETHEIM, JENS, NOR INSTRUMENTS AS
Application year: 1999
Main classification: B01D17
IPC codes: B01D17