Abstract:
A method and apparatus for separating water from oil includes creating a vacuum in a container so that oil which contains water and gas bubbles is drawn upward through a first section of the container. At the top of the first section, the oil impacts a baffle plate, thereby releasing water vapor. The oil then flows downward through an obstruction component in a second section of the container, thereby releasing additional water vapor.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method 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 disturb/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 in which it serves. 
     U.S. Pat. No. 5,211,856 discloses a method of separating water from oil, in which the oil to be separated is introduced in a heated condition at a predetermined temperature into a container subjected to a vacuum. 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absorbing water vapor which, together with the gas in the bubbles, is released in the upper part of the column and withdrawn from the top thereof. 
     SUMMARY OF THE INVENTION 
     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. In other words, in a simple manner, the process 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 apparatus as defined in the claims. 
     Admittedly, it is a well-known 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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in detail with reference to the corresponding schematic drawings in which: 
     FIG. 1 is a partial perspective view of an embodiment of the apparatus according to the invention; 
     FIG. 2 is a longitudinal sectional view of a first possible variant of the apparatus shown in FIG. 1; and 
     FIG. 3 is a longitudinal sectional view of a second possible variant of the apparatus shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1 numeral  2  refers to a vertical, preferably cylindrical 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 an oil reservoir or tank not shown. 
     Further, at the bottom of the first section  12  there is a gas inlet  30 , preferably in the form of a plurality of nozzles  32  disposed around the central oil inlet  16 . The gas inlet  32  is, via a gas 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 container  2 , which preferably is dome-shaped, is provided with a suction opening  42  for withdrawing gas and liberated water vapor. The suction opening  42  communicates, through a line  43 , with a condensing cooler  44 , vacuum pump  46  and gas filter  48  discharging to the atmosphere, 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 an obstruction component  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 obstruction component  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 gas control valves  24  and  36  respectively, the vacuum of column  2  will cause oil and gas (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 without 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 interference 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 by absorbing the water in the oil. 
     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 out in a radial layer or film  37  through the peripheral gap  33  between the baffle plate and the upper edge of the tube while the air bubbles in the oil burst. Thus, the water vapor-containing air is released into the upper space  53  of the container  2 , and 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 obstruction component (which, in this case, comprises packing) and thereby again achieves a very large interface toward the ambient vacuum atmosphere. This results in an effective evaporation of the remaining water contained in the oil and withdrawal of the water vapor through the opening  42 . 
     Upon having sunk through the packing obstruction component  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 second section of the container  14  in a fully processed condition, i.e., substantially liberated from water. 
     The above described two-stage process, in which tile 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 upper and lower level gauges  62 ,  64 , respectively. 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 vapor-containing gas withdrawn through opening  42  at the top of the column, is separated from water vapor 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 obstruction component  52  could be any 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, about 2,000 balls having a diameter of about 16 mm would be suitable. 
     The container  2  with tubular partition wall  10  could be made 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 favorable flow conditions for obtaining an optimum result. More particularly, the valves are preferably adjusted depending on a predetermined approximate value of the vacuum in the container, 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 container  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 1,000 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 container  2  can be about 250 mm 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 such an 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 32 cSt (32×10 −4 m ⅖) 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 due 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 0.08 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 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 obstruction component  52  for increasing the oil interface preferably is in the form of a packing material as described above, it is also within the scope of the invention to use other obstruction components that serve to expose the oil flowing downward in the second stage of the process to a large surface area. For example, instead of the packing shown in FIG. 1, the obstruction component could comprise a plurality of downwardly inclined annular disks  70  as in FIG.  2 . The disks  70  are arranged one below the 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. This will 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 container (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 container (i.e., the region 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 (i.e., inverted) 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 container  2 ′ are 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 past the obstruction component  52 ′ (in the case, packing) before being 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 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.