Abstract:
A centrifugal, liquid-liquid separator relies on a sweep flow in excess of the flow rate naturally occurring in the heavy constituent or species being separated out from a lighter species, in order to prevent access by the long-chain polymers of the lighter species to solids that may separate out and make a durable composition of polymers and particles that adheres and compacts against the shell wall of the centrifuge.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of co-pending U.S. Provisional Patent Application Ser. No. 62/312,246, filed Mar. 23, 2016, which is hereby incorporated herein by reference in its entirety. This application also hereby incorporates herein by reference U.S. Pat. No. 9,433,877, issued Sep. 6, 2016; U.S. Pat. No. 9,527,012, issued Dec. 27, 2016; U.S. patent application Ser. No. 14/313,392, filed Jun. 24, 2014; U.S. patent application Ser. No. 14/336,220, filed Jul. 21, 2014; and U.S. patent application Ser. No. 14/476,041, filed Sep. 3, 2014. All the foregoing references are hereby incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to separators and, more particularly, to novel systems and methods for improving performance of oil dehydrators. 
         [0004]    2. Background Art 
         [0005]    Liquid separation, from initial settling to purification, is an activity required to meet various objectives. For example, waste water from industrial processes may require remediation before returning the basic water stream into a riparian flow, estuary, lake, sea, or other supply. Similarly, production water generated during production of petroleum, natural gas, or other petroleous materials may require remediation before disposal in any one of several ways. 
         [0006]    For example, oil needs to be removed from water before it is re-injected into a disposal well. Otherwise, fouling will reduce the life of the disposal well. Similarly, if industrial contaminants or production water is re-injected into a disposal well, potential ground water contamination may be a consideration requiring removal of certain species of contaminants in the water. 
         [0007]    On the other hand, oil may need to be dehydrated of water. Meanwhile, production or other water may contain valuable oil that should be separated from the water for inclusion in the production of a well. Accordingly, water, oil, or both may be separated from each other and purified to an extent specified by technical or market demands. For example, water separation from oil to a volume fraction of less than one percent or a mass fraction of less than one percent may be required to obtain optimum prices for crude oil. 
         [0008]    Technologies have been developed for separating species of liquids or disparate phases (where each species is considered to be a separate phase, even though both are in a liquid state). U.S. Pat. No. 6,607,473, herein incorporated by reference herein; discloses certain embodiments of liquid-liquid separators. 
         [0009]    As a practical matter, separation processes, specifically liquid-liquid separation processes, are a staple of chemical engineering practice. As a direct result, certain rules, formula, procedures, rules of thumb, and the like may typically be relied upon. Nevertheless, much of settling theory originates in static settling tanks or settling ponds. These are not actually static, but the pond or tank wall itself is static. The flow passes through as the effects of gravity on the differentials of buoyancy between constituents within the flow thereby separate them out, coalesce, or otherwise render them separable from one another. 
         [0010]    In the chemical engineering arts, much of settling theory applied to stationary tanks has also been applied to the extent deemed appropriate to rotating separators, such as cylindrical tanks. Cylindrical tanks may have a fixed wall with a moving rotor inside. Other cylindrical tanks may actually rotate in their entirety. 
         [0011]    However, prior art systems suffer limitations in actual operation. Cleaning is not the least of these problems. Fouling prevention is desperately needed to improve operations. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    In view of the foregoing, in accordance with the invention as embodied and broadly described herein, a method and apparatus are disclosed in one embodiment of the present invention as including a system, apparatus, and method for controlling the development of boundary layers and a dispersion band location. 
         [0013]    Accordingly, in an apparatus and method in accordance with the invention, the phenomena have been studied, experimental data have been collected, relationships have been posited and established by experimental data, and a scheme has been developed for keeping petroleum constituents like heavy or long chain hydrocarbons of a dispersion band away from walls. The principle applies to rotating separators in general. In one embodiment, a specific geometry is tested to demonstrate the general principles and the specific performance of that particular geometry. 
         [0014]    In certain embodiments, an apparatus in accordance with the invention may include a separator operating to separate out at least one first liquid from at least one second liquid. It may be characterized by an inlet receiving a mixture of the at least one first liquid and the at least one second liquid, where the second liquid is heavier than the first, but is a small fraction or percentage (e.g., 1%-5%, up to about 10%). A dispersion band therein develops between a bulk flow of the at least one first liquid and a bulk flow of the at least one second liquid. A sweep flow of the heavy liquid re-circulates through the separator to assure that a robust boundary layer remains along the entire outer wall. The sweep flow keeps the lighter first liquid away from the outer wall. 
         [0015]    In experiments, the separator was a rotating separator. It was shaped as a frustum of a cone, having a tapered wall. The wall extends in an axial direction from an inlet end to an outlet end, progressing from a smaller diameter proximate the inlet end to a larger diameter proximate the outlet end. 
         [0016]    The first liquid is measurably different in density from the second, and the more dense liquid of the two carries with it a flow of even heavier solid particles. Other solids of lower density could move to the opposite extreme, including remaining in the dispersion band, depending on their density. 
         [0017]    However, the first (lighter) liquid has a tendency to combine with solids to form a persistent fouling difficult to remove from the outer wall. The sweep flow resists by floating the lighter (e.g., oil, heavy hydrocarbons, etc.) away from the wall and the solids. 
         [0018]    A corresponding method may include providing a separator, operating to separate first and second liquids from one another, and characterized by an inlet receiving a mixture of the first and second liquids, a dispersion band developing between the first and second liquids, a first outlet discharging the first liquid, and a second outlet discharging the second liquid. Operation of a control system positions the dispersion band away from the outer wall by introducing a sweep flow of the second (heavier) liquid that forms a boundary layer bounding the first (lighter) liquid away from the outer wall. 
         [0019]    The dispersion band is held at a location away from the outer wall. Droplets of the second liquid migrate radially outward with the solids through the first liquid into the sweep flow layer. Solids continue migrating radially through the second liquid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The foregoing features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described with additional specificity and detail through use of the accompanying drawings in which: 
           [0021]      FIG. 1  is a side elevation, schematic, cross-sectional view of a separator in accordance with the invention; 
           [0022]      FIG. 2  is a side elevation view thereof under conditions lacking a sweep flow of heavier species (e.g., water); 
           [0023]      FIG. 3  is a side elevation, cross-sectional view of one embodiment of a heavy species pickup tube at the dispersion band for removing the heavy species (e.g., water), while also inducing an outflow of an intermediate species from the dispersion band; 
           [0024]      FIG. 4  is a chart showing production run data of a 100 gpm system in accordance with the invention under a 2 gpm sweep configuration; and 
           [0025]      FIG. 5  is a chart of production run data of the system of  FIG. 4  operating under a 10 gpm sweep fluid condition. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    It will be readily understood that the components of the present invention, as generally described and illustrated in the drawings herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the system and method of the present invention, as represented in the drawings, is not intended to limit the scope of the invention, as claimed, but is merely representative of various embodiments of the invention. The illustrated embodiments of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. 
         [0027]    Referring to  FIG. 1 , while continuing to refer generally to  FIGS. 1 through 5 , a system  10  may include a centrifuge  12 . The centrifuge  12  rotates about a central axis  13 . In the illustrated embodiment, the side-elevation, cross section is trapezoidal. This is not the only operational configuration, but does assist in moving sediments settling out of the input. 
         [0028]    The centrifuge  12  rotates about the central axis  13 , which is also the central axis  13  for a main shaft  14 , or rotor shaft  14  supporting the centrifuge  12  on bearings. 
         [0029]    An inlet  16  provides a place for a mixture to enter the centrifuge  12  for processing. Meanwhile, the inlet  16  leads into a port  18  or leads to a port  18  passing from inside the shaft  14  into the main cavity  20  of the centrifuge  12 . 
         [0030]    In operation, the centrifuge  12  operates by rotating at an angular velocity of from about 1,000 rpm to about 2,500 rpm. As a practical matter, mechanical constraints on the construction of the centrifuge  12  will typically render a suitable operating range from between about 1,500 rpm to about 1,800 rpm for optimal performance. The system  10  may operate at a different angular velocity (speed of rotation, rpm&#39;s, radians per second, etc.). The instant embodiment illustrated comports with specific field units constructed and operated within the foregoing parameters. 
         [0031]    Actual data was taken in a system having an outermost internal diameter of the rotor cavity  20  of about 37 inches, with the minimum diameter at the narrow end thereof of about 18 inches. The overall length of the internal cavity  20  was about 36 inches. In operation, a target throughput was about 100 gallons per minute. This throughput corresponds to approximately 1,000 barrels per shift of from about seven to about nine hours duration. This throughput is influent constituting a combination of production oil, some amount of water, and some amount of sediment. 
         [0032]    In one currently contemplated embodiment, the system  10  operates as a dehydrator. In such circumstances, the water constituent is already typically on the order of below ten percent, and often below five percent. In many cases, a dehydration process is desired to improve the quality of oil below one percent of water. 
         [0033]    Influent passing through the inlet  16  enters the cavity  20  through the port  18 . Following centrifugation, the liquid influent has been exposed to approximately 1,000 g&#39;s (units of gravity). This increased acceleration (radial acceleration instead of actual gravity), results in the heavier species, typically water in a production context for petroleum products, accumulating near the outermost diameter of the centrifuge  12  or cavity  20 . Accordingly, a pickup tube  32  is provided with an opening  33  or port  33  through which the heavier species (e.g., water) may exit the chamber  20  or cavity  20 . 
         [0034]    In contrast, the lighter species will accumulate closer to the shaft  14  near the central axis  13  of the centrifuge  12 . An output port  36  in the shaft  14  drains the lighter species out to an exit passage  38 . Thus, an outlet passage  34  carrying the heavy species out through the shaft  14 , and an outlet passage  38  for the lighter species may pass collinearly or coaxially out through the shaft  14  to their respective transport lines, line  124  for the heavy species and line  126  for the light species. 
         [0035]    As will become clear hereinbelow, a selected volumetric flow rate of the heavy species traveling through the line  124  will eventually be transported back to be reintroduced into the influent line  122 . Typically, the heavy species will be introduced, without undue or enforced mixing, at some point in the line  122 . This is best done downstream of any pumping of the content of influent line  122 . 
         [0036]    As has been discussed in the references incorporated hereinabove by reference, a dispersion band  150  develops in the centrifuge  12 . However, in a dehydration condition, operation, or system  10 , the dispersion band  150  is located very differently. Typically, a dispersion band  150  establishes itself at some radius  151  (see  FIG. 3 ) from the central axis  13 . However, an interesting character of an apparatus  10  in accordance with the invention is the existence of a completely transient condition within the different layers  270 ,  272 ,  280 . 
         [0037]    For example, the layer  270  is typically oil or the lighter species. The layer  272  is a layer of sediments  272  that will eventually accumulate at the outmost radius of the cavity  20 . Meanwhile, the layer  280  constitutes water or other comparatively heavier species separated out of the oil  270  constituting the majority of the influent  30 . 
         [0038]    In operation, a system  10  in accordance with the invention operates by introducing an influent  30  from an incoming line  122  into the cavity  20  by means of the ports  18  traversing between the inlet  16  and the cavity  20 . The influent  30  immediately begins to separate out into various species according to weight. Typically, the heaviest material is sediment, which may include silica, and is typically a fine clay  272 . 
         [0039]    The sediment  272  separates out closest to a wall  22  of the centrifuge  12 . In fact, the inner surface  24  of the wall  22  operates to halt radial flow of the sediment  272 . Moreover, if the centrifuge  12  is trapezoidal in cross section as illustrated, then the sediment layer  272  or its content  272  tends to drift toward the end wall  26  of the centrifuge  12 . Accordingly, an accumulation  274  of the sediment layer  272  tends to grow in the corner between the wall  22  and the end wall  26  or cap  26 . 
         [0040]    Meanwhile, the heavier hydrocarbons  276  found in the influent  30  will begin to accumulate as far from the central axis  13  of rotation as they can. That location is limited by the wall  22 , the heavy species  280 , either, or both. Accordingly, these will also begin to form an accumulation  278  near the outermost extent of the oil  270  or lighter species  270 . 
         [0041]    However, the heavier or water layer  280  is constituted by two types of water or sources of water. It divides or separates the heavy hydrocarbon layer  276  from the surface  24  of the wall  22  of the centrifuge  12 . For example, water  280  being separated out from the influent  30  will be lighter than the sediments  272 , but heavier than the oil  270  and the heavy hydrocarbons  276 . However, in an oil dehydration process, the amount of water  280  directly removable from the influent  30  may be characterized as something between barely significant, and problematic. 
         [0042]    For example, if insufficient water  280  is available to be separated out from the influent  30 , then the centrifuge  12  is operating off its design set points, and can neither fill the line  124  carrying the water  280  to the settling tank  290 , nor coat the inside surface  24  of the wall  22 . This creates several problems discussed immediately hereinbelow. 
         [0043]    In a better operational embodiment, the layer  280  of water  280  is augmented by pumping through a line  284  driven by a pump  286  from the settling tank  290 . This means that an amount of make-up water  280  may be added to create a sweep flow  280 . Thus, although the water layer  280  has been discussed so far as though it were all removed from the influent  30 , which it may be, it is not necessarily being removed from the influent  30  or separated from the oil  270  in the quantities or at the rate at which it flows and needs to flow through the line  284  into the inlet  16 . 
         [0044]    Rather, water  280  is accumulated in the tank  290  so that it can be cycled through from the inlet  16  to the retrieval line  124  at a rate much higher than it can be generated or separated out from the influent  30 . This permits several benefits. For example, the water layer  280  is established to be flowing at substantially all times during operation of the system  10 , and covers the wall  22  from the inlet  16  to the outlet port  33  of the pick up tube  32 . By providing a vigorous flow in an axial direction, at a significant velocity, the water layer  280  tends to urge the sediments  272  to move along the surface  24  of the wall  22 . Thus, the sediments  272  can accumulate near the cap  26  or end wall  26  of the centrifuge  12 . 
         [0045]    Moreover, the water layer  280  separates the oil  270 , including the heavy hydrocarbons  276  that tend to further separate out therefrom, away from the sediments  272 . These two constituents, sediments and heavy hydrocarbons, are not allowed to mix to forma fouling composition. 
         [0046]    Referring to  FIG. 2 , while continuing to refer generally to  FIGS. 1 through 5 , the system  10  may be operated without the use of sweep water or sweep fluid in the layer  280 . In such a case, the layer  280  actually is not a layer, and becomes rather a series of rivulets  294 . That is, the sediment  272  when permitted to be in contact with the heavy hydrocarbon layer  276  forms a clay-bitumen composition  292  that becomes very durable, very resistant to disruption, and very difficult to remove from its adhesion to the inner surface  24  of the wall  22  of the centrifuge  12 . 
         [0047]    The insets of  FIG. 2 , showing expanded views from an elevation view, cross sectional view, and a top plan view, illustrate that the oil  270  lies above the heavy hydrocarbon layer  278 . The water  280 , in a side elevation view shows up as a rivulet  294 , not a continuous layer. Accordingly, at some locations, the heavy hydrocarbon layer  278  is in direct contact with the sediment layer  292 . The sediment layer  292  is not the same as the sediment layer  272  of  FIG. 1 . Instead, the layer  292  is a composite clay-bitumen layer  292  that is very difficult to remove, or dissociate its constituents. 
         [0048]    Across the fold line  295  is seen the top view, in which the rivulets  294  and the composite layer  292  are both present. The rivulets  294  of water  280  are insufficient to completely cover the surface  24  of the wall  22 , thereby leaving opportunities for the sediments  272  to embed with the heavy hydrocarbons  278 , thus forming the problem layer  292 . 
         [0049]    One will note the system  10  of  FIG. 1  operating with sufficient sweep flow  280  or water layer  280  of sufficient depth to completely coat the sediment layer  272 . It immediately isolates the sediment layer  272  from becoming concreted together by contact with heavy hydrocarbons  276 . 
         [0050]    As an operational matter, the difference in density between the sediments  272  and the oil  270 , which constitutes the majority of influent  30 , is sufficiently great that the tremendous acceleration of the centrifuge  12  begins a separation of species immediately in the entrance area  28 . Sediments  272  and water  280  will immediately begin to separate out toward the wall  22 . However, the sweep layer  280  or the additional volume of water flow in the sweep layer  280  is now rendered sufficient, and its separation out is rapid, since it is not actually thoroughly mixed by any means in the influent  30 . Immediately separates out into the sweep layer  280 . 
         [0051]    Moreover, the sweep layer  280  separates out a sufficient volumetric flow rate (gallons per minute, cubic feet per minute, cubic centimeters per minute, etc.) to float the heavy hydrocarbon layer  276  radially inward toward the central axis  13  and shaft  14 . Thus, the opportunity is simply not available for the amalgamation of the sediments  272  and the heavy hydrocarbons  276 . 
         [0052]    Referring to  FIG. 3 , while continuing to refer generally to  FIGS. 1 through 5 , in one embodiment, a flow  296  of water  280  from the accumulation  282  passes into the pick up tube  32 . In the illustrated embodiment, a pick up tube  32  reaches to the water layer  282  or the water accumulation region  282 . To do so, the tube  32  must pass through the heavy hydrocarbon accumulation region  278  or heavy hydrocarbon accumulation  278 . 
         [0053]    The illustrated embodiment is well suited for the tube  32  to pass through the entire thickness  297  of the heavy hydrocarbon accumulation  278  (defined as that portion between the dispersion band radius  151  and outermost extent of the oil  270 ) and the innermost surface  300  of the water  282  accumulated. Accordingly, a flow  296  of the water from the accumulation  282  will enter the port  33  of the tube  32 . Maintaining the opening  33  near the surface  300  between the water accumulation  282  and heavy hydrocarbon accumulation  278  assures that another sweep  298  or another flow  298  of the heavy hydrocarbon accumulation  278  will also be drawn into the port  33 . 
         [0054]    A benefit of this removal of the heavy hydrocarbon layer  278  or accumulation  278  from the centrifuge  12  is that the dispersion band  150  cannot exceed the operational limits of the system  10 . The heavy hydrocarbon accumulation  278  always has a way out of the cavity  20 . Thus, the heavy hydrocarbon accumulation  278  does not grow to an unhealthy level to support dehydration of the oil  270  by removal of the water  282 . This solution improves over prior art systems, such as U.S. Pat. No. 8,794,448. 
         [0055]    As a practical matter, the heavy hydrocarbon accumulation  278  or the heavy hydrocarbon layer  276  is, in effect, a part of the dispersion band  150  between the oil  270  and the water layer  280 . The accumulation  278  may actually include chunks, liquids, and the like of the heavy hydrocarbons  276 , mixed with some amount of water  280 . Thus, odd shapes and sizes of heavy hydrocarbon accumulation  278  may easily be swept (e.g., by fluid drag) by the flow  296  and water  280  into the port  33 . The dispersion band radius  151  at which the dispersion band  150  is located can be completely controlled, as discussed in the references incorporated hereinabove by reference. The accumulation  278  of the heavy hydrocarbons  278  may be precisely controlled near the mouth  33  of the tube  32 . 
         [0056]    Referring to  FIGS. 4 and 5 , while continuing to refer generally to  FIGS. 1 through 5 , a chart  302  illustrates actual results from production runs of an apparatus  10  in accordance with the invention under conditions corresponding to  FIG. 2 . Meanwhile, the chart  304  corresponds to conditions illustrated in  FIG. 1 . 
         [0057]    For example, in the chart  302 , the heavy constituent  306  or heavy phase  306  is identified and associated with a series of values  305 . The values  305  are arranged in a matrix identifying the heavy phase  306 , the light phase  308  (e.g., oil), the amount of sweep fluid  310 , and the overall influent  312  before being augmented by the sweep fluid  310 . 
         [0058]    Along the top legend, the total flow rate  314  is displayed beside the oil flow rate  316  exiting, the water flow rate  318  exiting, and the other properties  320 , namely the basic sediments and water (BS&amp;W)  320  resulting in the flow  316  of oil  270  exiting. One will note, for example, in the chart  302 , that an influent of 100 gallons per minute contains about 95 gallons per minute of oil, mixed with five gallons per minute of water, constituting approximately five percent BS&amp;W  320 . Meanwhile, the values  305  of sweep fluid are zero. 
         [0059]    The resulting light phase  308  total  314  is 91 gallons per minute, of which the oil flow  316  is 90.3 gallons per minute. The water flow  318  is 0.7 gallons per minute. The resulting BS&amp;W content  320  is less than 0.8 percent. The heavy phase  306  or water  280  introduced was about nine gallons per minute. Of the total flow rate  314 , 4.7 gallons in the oil flow rate  316  is being sent overboard through the oil line  126  exiting the centrifuge  12 . 
         [0060]    Meanwhile, 4.3 gallons per minute of water flow  318  exit through the takeout line  124 , from the tube  32 . It passes into the outlet passage  34 , and ultimately to the line  124  feeding the settling tank  290 . Note, that the somewhat less than 0.8 percent of BS&amp;W  320  is captured within the light phase  308 , and may actually not be separable, due to its microscopic nature. For example, particle diameters of plate-like clay particles may be on the order of from about one to about five microns. 
         [0061]    It is worth noting that the 4.3 gallons per minute of water flow  318  need not actually go to a settler  290  or settling tank  290 . Such a system was inoperative in this example. 
         [0062]    Referring to  FIG. 5 , while continuing to refer generally to  FIGS. 1 through 5 , a chart  304  illustrates operation of the system  10  for a set of values  305  corresponding to approximately ten percent of the influent  312  being a sweep fluid  310 . Again, the references  306 ,  308 ,  310 ,  312  refer to the materials as identified in the charts  302 ,  304 . 
         [0063]    A total flow rate  314  of 100 gallons per minute of influent  312  is constituted by about 95 gallons per minute flow rate  316  of oil  270 , and about five gallons per minute flow rate  318  of water  280 . The BS&amp;W content  320  is about five percent. By adding a sweep fluid  310  or a flow  314  of ten gallons per minute of sweep water  280 , the oil flow rate  316  is not increased. The sweep fluid  310  does not contribute thereto. Rather, the sweep fluid  310  passes out with the water flow  318 , contributing its full ten gallons per minute. 
         [0064]    Meanwhile, the light phase  308  or oil  270  in the total flow  314  constitutes 94.5 gallons, while the flow rate  316  of oil  270  exiting the centrifuge  12  constitutes only 93.7 gallons. This means that the light phase  308  flowing out of the light port  36  and light passage  38  actually contains about 0.8 gallons per minute of water flow  318 . One will not that this still results in better than 0.8 percent BS&amp;W  320  in the outgoing passage  38  carrying oil  270 . 
         [0065]    Finally, one will note that the heavy phase  306  has a flow of about 15.5 gallons per minute of the total flow  314 , with 1.3 gallons per minute in the oil flow  316  exiting the centrifuge  12 , with 14.2 gallons per minute exiting with the water flow  318 . Accordingly, the charts  302 ,  304  show various improvements in performance. For example, in the oil flow rates  316 , and water flow rates  306  one will note that the chart  304  passes only 1.3 gallons per minute of oil in the water, while the chart  302  shows 4.7 gallons per minute of oil in the water flow rate  306 . Dehydration seeks to minimize the amount of the heavy phase (water) exiting in the oil flow  316  and minimize oil in the water flow  306 . The test using a seep flow decreased oil in the water by about two thirds. 
         [0066]    That is, the heavy phase  306  exiting out the line  124  carries 4.7 gallons per minute of entrained or mixed oil flow  316 . In contrast, the amount of the heavy phase  306  in the chart  304  passing through the line  124  carries only 1.3 gallons per minute of oil as a pollutant or recoverable material. 
         [0067]    Likewise, the chart  302  illustrates that the amount of the light phase  308  is 0.7 gallons per minute. Meanwhile, the water is 4.3 gallons per minute out the heavy phase  306  exiting. In contrast, the chart  304  illustrates that the amount of oil flow  316  exiting with heavy phase  306  is 1.3 gallons per minute, a reduction of more than two thirds. Moreover, the amount of water exiting with the heavy phase  306 , as a water flow  318  in the heavy phase  306 , is 14.2 gallons per minute, almost exactly the amount extracted before, plus the sweep flow amount. 
         [0068]    In a nutshell, the removal of water or the dehydration process thus removes very nearly the same amount of water (4.2 gallons, rather than 4.3 gallons, but results in two thirds less oil in the exiting water. Thus, less oil is wasted, and the dehydration process is completely effective. 
         [0069]    Moreover, the plating out or coating out of the clay-bitumen layer  292  no longer occurs. It has been found that the sediment layer  272  breaks up readily, since it actually contains only sediment  272 . Thus, the difficulty of cleaning is greatly simplified. Moreover, the sweep flow  280  of water  280  tends to sweep the free particles of the sediment layer  272  toward the sediment accumulation  274 . Thus, the sediments  274  may be readily removed through cleaning procedures near the cap  26  or through ports in the cap  26 . 
         [0070]    The present invention may be embodied in other specific forms without departing from its purposes, functions, structures, or operational characteristics. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.