Abstract:
The present invention relates to a process for separating an aqueous phase from an oil phase of an oil-water mixture ( 6 ), which has a pressurized dewatering system ( 14 ) having multiphase separation profiles ( 15 ). According to the invention, it is essential that the pressurized dewatering system ( 14 ) operates in a plurality of stages. In addition, the invention relates to an apparatus ( 8 ) for carrying out the process of the invention.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
     This application is a National Stage application which claims the benefit of International Application No. PCT/EP2007/064090 filed Dec. 17, 2007, which claims priority based on German Patent Application No. 102006059714.1, filed Dec. 18, 2006, both of which are hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a method and device for separating an aqueous phase from an oil phase of an oil-water mixture. 
     BACKGROUND 
     The separation of an aqueous phase from an oil phase, particularly of crude oil and oil products, can, in principle, be effected by means of physical, chemical or thermal methods. The latter two methods frequently entail the subsequent emergence of secondary contaminations in the form of an additional loading of the waste water with chemicals. On the other hand, thermal methods require large amounts of energy and therefore are likewise regarded as neither ecologically nor economically appropriate. In contrast thereto, physical methods represent an environmentally friendly alternative that is particularly important from the standpoint of increasingly stringent environmental requirements. 
     This method is, however, disadvantageous in that productivity of the method, that is to say a throughput rate amount per unit of time, is relatively low, resulting in a considerable amount of time being necessary for larger quantities of oil-water mixtures to be separated. 
     Document DE 102 41 518 A1 teaches of a method of the type in question for separating an intermittent secondary phase from an aqueous primary phase, in a first step water droplets of a predetermined controlled size being formed, which droplets are, in a second step, conducted on a multi-phase separator unit on which they coalesce, are directed into a sump trap, subsequent to which they are separated. The coalesced and separated water is collected in a water pocket from which it is drawn off. For further refining and separation, for example, it is possible to incorporate downstream a mechanical emulsifying breaker-stage as well as one or a plurality of hydrophobic membranes. 
     SUMMARY 
     The invention concerns the problem of providing for a method of the type in question an improved embodiment that will allow for large amounts of water and likewise large quantities of oil to be separated rapidly, simply and, especially, continuously. 
     This problem is solved according to the invention by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims. 
     The invention is based on the general idea of using a pressure discharge system, which works in multi-stages, with multi-phase separator units in order to separate an aqueous phase from an oil phase of an oil-water mixture, which pressure discharge system successively separates the water portions present in the oil-water mixture in multiple stages. In a first stage in a first flow generator, the separator units are designed as phase separator elements and are arranged in such a manner that turbulence is generated therein from the oil-water mixture flowing therethrough, thereby promoting the settling of water on the separator units. The separator units designed as phase separator elements preferably have a hydrophilic coating or are produced from a hydrophilic material, so that the water present in the oil-water mixture can be attracted by the separator units and settle thereon. By generating turbulence, the water droplets present in the oil-water mixture can join and can subsequently settle on the hydrophilic separators and be separated. At the same time, the turbulence in the flow cause so-called water pockets to break up, thereby facilitating a separation process. A water film that additionally behaves hydrophilically forms on the upper side, that is to say the inflow side, of the separator. 
     The separators, which are designed as laminar-phase separator elements, of the second flow generator in the second step generate a laminar, that is to say a steadied, flow of the oil-water mixture, thereby permitting larger droplets to form on the separators likewise designed to be hydrophilic. In the second flow generator, a considerably lower rate of flow exists than in the first flow generator since the flow cross-section is greater, more particularly a distance between the laminar-phase separators, than in comparison to the first stage. 
     In a third flow generator of a third stage, separators, which are designed as mechanical phase separators, are provided that are capable of separating even the smallest water portions, which are in the form of miniscule water droplets, still distributed in the oil-water mixture. The separators of the third stage are also designed to be hydrophilic so that the water portions that still remain in the oil-water mixture can coalesce and be separated. According to the invention, the solution to the problem addressed makes it possible to split even larger quantities of an oil-water mixture into its oil portions and its water portions and to separate the water from the oil phase. This is of considerable importance to modern refinement procedures since therein, large quantities of water are added to crude oil to improve its quality during a later process phase. These considerable quantities of water of up to 20% are indispensable to the refinement process, yet must be removed again from the oil-water mixture after refinement. Conventional methods, which are based almost exclusively on a separation of the water on the basis of gravitation, quickly reach the limit of their performance and are entirely unsuitable for large quantities. With the method according to the invention, it is, however, possible, even prior to refinement, to remove rapidly and simply large quantities of added water again, thereby permitting the refinement process to be conducted far more economically. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is furthermore based on the general idea that in order to conduct the method as described in the previous paragraph, a device must be used that has at least one pressure discharge system with multi-phase separators, the latter being formed from a hydrophilic material and/or having a hydrophilic coating. Such a hydrophilic coating or such a hydrophilic material can be steel, in particular polished stainless steel, and/or plastic, for example. Steel and plastic have hydrophilic surfaces that during the operation of the device according to the invention are continually coated with a water film. In contrast to water, hydrophilic surfaces have a contact angle that is less than 90°. Both steel as well as plastic are robust materials that can guarantee reliable operations and a long lifetime of the device according to the invention. 
       Advantageous embodiments explained in greater detail are each represented schematically in the drawings that show in: 
         FIG. 1  a schematic diagram of equipment having a device for carrying out the method for removing water from oils; 
         FIG. 2  a detailed design of the device according to the invention for carrying out the method according to  FIG. 1 ; 
         FIG. 3  a detailed view of a possible separator of a pressure discharge system of the device according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     According to  FIG. 1 , at the beginning of the method according to the invention, oil  4  is stored in an oil tank  1  and water  5  is stored in a water tank  2 . To improve the quality of the oil  4 , it is fed to a device  3 , in particular a refining device  3 , in which it is refined. Since the refining process requires that a substantial portion of water  5  be in the oil  4 , water  5  from the water tank  2  is then admixed with the oil  4  from the oil tank  1  so that an oil-water mixture  6  results that is intermediately stored in a tank  7  intended for that purpose. Proceeding from the tank  7 , the oil-water mixture  6  travels by way of the refining device  3  in which it is refined, to a device  8  in which the water portions are removed again from the oil-water mixture. Thereafter, the oil-water mixture  6  arrives in a special mixing unit  9  in which a water droplet spectrum, briefly also called a controlled-water drop (CWD), is generated. This water droplet spectrum necessary for the separation of the water from the oil  4  is indispensable for optimal water separation in the following device  8 . The device  8  may, according to its use, have a diameter of up to many meters and effect a continuous water separation that is so large it does not prevent a conventional process speed. In the device  8  according to the invention, the separated water  8  sinks in previously precisely defined trajectories, and collects in water collection chambers  10 ,  10 ′ provided therefor from which it can be guided to an additional water tank  2 ′. The oil  4  that has preferably been completely purified of the water portions arrives in an additional oil tank  1 ′ from which it is transported, for example, by ship  11  or overland  12  to a refinery that is not shown. The separated water  5 ′ can, for example, be processed in an oil removal system  13  and is either supplied anew to the entire process or is disposed of. 
     The device  8  according to the invention for separating the water phase from the oil phase of the oil-water mixture  6  comprises at least one pressure discharge system  14  that is schematically shown in  FIG. 2  and is shown in detail in  FIG. 3 . The pressure discharge system  14  has so-called multi-phase separators  15  in flow generators connected one after the other, which multi-phase separators are formed from hydrophilic material and/or have a hydrophilic coating. The mixing apparatus  9  is arranged on the input side of the device  8 , as can be seen in  FIGS. 1 and 2 , in which mixing apparatus controlled, precisely-defined water droplets (CWD—controlled water drops) are generated. From there, the oil-water mixture  6  arrives in an antechamber  16  of the pressure discharge system  14  that forms a quiet zone and, on the one hand, effects a uniform distribution of the oil-water mixture  6  over the entire cross-section of the device  8  and, on the other hand, serves to dissipate the momentum of the entering, turbulent flow. By means of a distribution device  17 , in particular by means of a dispersion distribution segment, the oil-water mixture  6  is distributed on a first stage of the pressure discharge system  14  that has three stages in total. 
     Separators  15  designed as phase separator elements  15   a  are arranged in the flow generator of the first stage and serve to both split the oil-water mixture  6  into water  5  and oil  4  as well as to generate a turbulent flow. Downstream from the separators  15  designed as phase separator elements  15   a  are separators  15  designed as laminar-phase separator elements  15   b  arranged in a second flow generator of the second stage, which separators serve to generate a laminar flow and to separate water  5  from the oil-water mixture  6 . The separators  15   a  already promote a coalescing of the water droplets by means of their composition, in particular by means of their hydrophilic surfaces and their own given geometry or arrangement. In the third generator of the following stage with the separators  15  designed as laminar-phase separator elements  15   b , during laminar flow the wetting characteristics or an affinity of the separators  15   b  to water  5  is used in order to thereby be able to optimally use their droplet formation in the subsequent separators  15 , in particular the separators  15  designed as mechanical phase separators  15   c , of the third stage. By calculating the water droplet size resulting therefrom, the density difference and the set flow rate are adjusted by means of sensors  18  of a separation layer  19  specific to the oil-water mixture  6 , which separation layer is held constant by a valve control, in particular an automatic valve control, in the water collection chamber  10 . The water collected in the water collection chamber  10  can be discharged proportional to the production process. 
     For additional improved water separation, a mechanical emulsion breaker  20  can be provided which is arranged downstream from the separator  15 . Such a mechanical emulsion breaker  20  is capable of separating the smallest water droplets that are in the μm-range. Moreover, a hydrophobic membrane  21  specifically intended for the specific application instance can optionally be provided directly before an installation outlet  22 . The water separated in the mechanical emulsion breaker  20  and/or in the hydrophobic membrane  21  is then collected in the water collection chamber  10 ′, which in this instance is arranged between both of the components  20 ,  21 , by way of example, and after collection is discharged, if need be, in a process-appropriate manner. In this manner, a water level can be monitored by a sensor  18 ′. 
     The device  8  according to the invention is completed by a control apparatus  28  that ensures fully-automated operation, a monitoring of the sensors  18 ,  18 ′, a monitoring of the pressures, rate of flow, heating, and pumps, the apparatus  8  being able to be manually as well as semi- or fully-automatically operated. Both the valves, which are not shown, on the water collection chambers  10 ,  10 ′ as well as at least one of the sensors  18 ,  18 ′ are connected with the control apparatus  28  so as to be able to communicate and in such a manner that said control apparatus can undertake the control of water discharge from at least one water collection chamber  10 ,  10 ′. As can likewise be seen in  FIG. 2 , a separation device  17 ′ for levelling the oil-water mixture  6  is arranged upstream from the mechanical emulsion breaker  20 . 
     The following will explain in greater detail the separation layers  15  flow generators of all of the three stages one after the other of the pressure discharge system  14  using  FIGS. 3   a  to  3   c.    
     According to  FIG. 3   a , the first flow generator in the first stage of the pressure discharge system  14  is shown as separators  15  designed with phase separator elements  15   a . The phase separator elements  15   a  serve, on the one hand, to separate the oil-water mixture  6  into water  5  and oil  4  as well as to generate a turbulent flow. The separators  15   a  of the first stage have a flow-against surface  23  inclined at an angle α of approximately 50° to 60°, preferably 55°, with respect to the horizontal, which flow-against surface  23  diverts the oil-water mixture  6  upward. Moreover, separators  15   a  have a flow-off surface  24  inclined at an angle β of approximately 30° to 35°, preferably 33°, with respect to the horizontal, which flow-off surface  24  diverts or redirects the oil-water mixture  6  downward. An entire length l 1  of the separator  15   a  in the direction of flow  26  is preferably about 70 mm. A substantially horizontally extending joining surface  25  is provided between the flow-against surface  23  and the flow-off surface  24 , both the profiles  15   a  as well as the profiles  15   b  and  15   c  being formed from a hydrophilic material and/or having a hydrophilic coating. Steel, preferably polished stainless steel, and/or plastic can be used as a hydrophilic material and/or as a hydrophilic coating. A vertical h 1  distance between the individual separators  15   a  is approximately 10 mm to 20 mm, preferably 14 mm. It is conceivable that a plurality of separators  15   a  are combined into a common cartridge  27 , a plurality of cartridges  27 ,  27 ′ being in turn designed so as to be assembled into a cross-section that can be flowed through in a parallel manner and/or so as to be arranged one following the other.  FIG. 3   a  shows, by way of example, two rows, each of which has five separators  15   a  arranged one after the other in the direction of flow  26 , a distance d 1  of preferably 15 mm being maintained between the two cartridges  27  and  27 ′. A length l 1a  of the joining surface  25  in the direction of flow  26  is between 15 mm and 25 mm, preferably in the area of 20 mm. By means of the geometric design and the arrangement of the profiles  15   a , a breaking-up of water pockets can be achieved, a water film existing on the flow-against surfaces  23 , the joining surfaces  25 , and the flow-off surfaces  24 , which water film itself, in turn, attracts water  5  from the oil-water mixture  6  and brings about its attachment to the corresponding surfaces  23 ,  24 ,  25 . 
     According to  FIG. 3   b , the second flow generator of the second stage of the pressure discharge system  14  has separators  15  designed as laminar-phase separator elements  15   b , which separators are designed to generate a laminar flow and to separate water from the oil-water mixture  6 . The separators  15   b  of the second stage have a flow-against surface  23 ′ inclined at an angle α′ of approximately 30° to 35°, preferably 33°, with respect to the horizontal, which flow-against surface  23 ′ diverts the oil-water mixture  6  upward, and said separators moreover have a flow-off surface  24 ′ inclined at an angle β′ of approximately 30° to 35°, preferably 33°, which flow-off surface  24 ′ diverts the oil-water mixture  6  downward. In contrast to  FIG. 3   a , the angle α′ is equally as large as the angle β′. A substantially horizontal extending joining surface  25 ′ is provided between the flow-against surface  23 ′ and the flow-off surface  24 ′, a vertical distance h 2  between the individual separators  15   b  of the second stage being larger than that between the separators  15   a  of the first stage. The length l 2  in the direction of flow  26  is approximately 70 mm; the length l 2a  of the joining surface  25 ′ in the direction of flow  26  is likewise approximately 20 mm. The vertical distance h 2  of approximately 16 mm is, however, greater than the vertical distance h 1  of the individual separators  15   a  of the first stage. A distance d 2  between individual separators  15   b  in the direction of flow  26  is preferably 30 mm, depending on the type of oil used. It goes without saying that the number or the direction of the separators  15   b  according to  FIG. 3   b  as well as of the other separators  15   a  or  15   c  according to  FIGS. 3   a  and  3   c , respectively, is to be understood purely as an example, which is to say that another device or number or arrangement of the separators  15  is also intended to be comprised by the invention in so far as the separation of water  5  from the oil-water mixture  6  is thereby benefited. 
     According to  FIG. 3   c , the third flow generator of the third stage of the pressure discharge system  14  is represented with separators  15  designed as mechanical phase separators  15   c , which separators serve to separate the water portions that still remain by causing them to coalesce. The measurements l 3  or h 3  or the angles α″ and β″ correspond substantially to those of the separators  15   b  of  FIG. 3   b , a vertical distance h 3  between the individual separators  15   c  of the third stage being less than that between the separators  15   a  of the first stage. The vertical distance h 3  is preferably in a range between 5 mm and 10 mm, more particularly at 8 mm. A distance d 3  in the direction of flow  26  between individual separators  15   c  is in a range between 5 mm and 15 mm, preferably at approximately 10 mm. 
     Overall, with the separators  15   a  to  15   c  of the pressure discharge system  14 , a separation degree of over 95% of the water present in the oil-water mixture  6  can be achieved. 
     All of the features represented in the description and in the following claims can be pertinent to the invention individually and collectively in arbitrary combination.