Abstract:
An apparatus and method for treating raw water. The apparatus comprises a vessel having an inlet for the raw water and an outlet for the skimmed water, and wherein the vessel contains the raw water, and a rotor mechanism for creating a plurality of gas bubbles within the raw water. The apparatus further comprises a disperser device, operatively associated with the rotor mechanism, for dispersing the plurality of gas bubbles from the rotor mechanism within the vessel, and wherein the gas bubbles create an oily froth on the top of the raw water, and a skim tray, positioned about the rotor mechanism, is provided for removing the oily froth from the top of the raw water as well as a secondary skimmer positioned within the skim tray. In one preferred embodiment, an external skim tank that is configured to deliver a gas to the rotor mechanism and wherein the external skim tank is configured to receive the oily froth from the secondary skimmer.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to a fluid treatment device and method. More particularly, but not by way of limitation, this invention relates to an apparatus and method to recover hydrocarbons from fluid streams. 
         [0002]    In the course of producing and refining hydrocarbons, operators produce fluid streams that contain impurities. As those of ordinary skill in the art will recognize, produced streams contain hydrocarbons that require separation. Many times, an operator may wish to discharge the produced stream into a body of water, or inject the produced water into predetermined subterranean zones. Government regulations address the content of the discharge fluid streams. Also, operators do not wish to be the cause of pollution. Therefore, various types of prior art separation devices have been developed. However, prior art devices suffer from several deficiencies. For instance, in order to adequately separate the water from the hydrocarbons, large pieces of equipment are required. A large foot print (area occupied by the separation equipment) is needed. However, many times hydrocarbons are produced and/or refined in remote areas where space is a premium. 
         [0003]    Hence, there is a need for a device and method that will effectively and efficiently separate hydrocarbons and other impurities from an effluent. There is also a need for a device and method that can be used with various types of fluid streams. Also, there is a need for a device that can be used in conjunction with other type of prior art separation devices. There is also a need for a device and method that creates a small foot print. These and many other needs will be met by the following disclosure. 
       SUMMARY OF THE INVENTION 
       [0004]    An apparatus for treating a raw water is disclosed. The apparatus comprises a vessel having an inlet for the raw water and an outlet for the skimmed water, and wherein the vessel contains the raw water, and a rotor mechanism for creating a plurality of gas bubbles within the raw water. The apparatus further comprises a disperser means, operatively associated with the rotor mechanism, for dispersing the plurality of gas bubbles from the rotor mechanism within the vessel, and wherein the gas bubbles create an oily froth on the top of the raw water, and a skimming means, positioned about the rotor mechanism, for removing the oily froth from the top of the raw water. 
         [0005]    In one preferred embodiment, the apparatus further comprises an external skim tank that is configured to deliver a gas to the rotor mechanism and wherein the external skim tank is configured to receive the oily froth and gas from the skimming means. 
         [0006]    The apparatus may also contain a pump and centrifuge for separating a hydrocarbon component and a water component from the oily froth within the external skim tank, and wherein the water component from the centrifugal pump is directed to the vessel. A heat exchange method may also be included that is operatively associated with either the external skim tank or the primary process vessel so that heat is added to the oily froth or the process stream. 
         [0007]    The disperser means, in one preferred embodiment, comprises a disperser mechanism concentrically disposed about the rotor mechanism, and a draft tube assembly operatively connected to the disperser mechanism, wherein the draft tube assembly provides a path for the raw water into the disperser mechanism. 
         [0008]    In the most preferred embodiment, the skimming means includes an aeration skim tray positioned above the rotor mechanism. The skimming means may also include a secondary oil skimming device positioned within the aeration skim tray and configured to direct the oily froth from the vessel. In one preferred embodiment, the secondary oil skimming device comprises a cylindrical member with notches at a top end and wherein the oily froth is directed over the notches and into an internal portion of the cylindrical member. The rotor mechanism may include a shaft concentrically disposed within a standing pipe, wherein the standing pipe is attached to the internal portion of the vessel. 
         [0009]    In yet another preferred embodiment, an apparatus for treating a raw water is disclosed. The apparatus includes a vessel having an inlet for the raw water and an outlet for the skimmed water, a rotor mechanism for creating a plurality of gas bubbles within the raw water and a disperser means, operatively associated with the rotor mechanism, for dispersing the plurality of gas bubbles from the rotor mechanism. In this embodiment, a skimming means, positioned about the rotor mechanism, for removing an oily froth from the top of the raw water is also included. The apparatus further includes an external skim tank that is configured to deliver a gas to the rotor mechanism and wherein the external skim tank is configured to receive the oily froth and gas from the skimming means. The apparatus further includes a closed loop gas line for communicating a gas from the external skim tank to the vessel. 
         [0010]    A method of treating a raw water is also disclosed. The method comprises flowing the raw water into a treatment device. The treatment device includes a vessel containing the raw water, a rotor for creating a plurality of gas bubbles in the raw water, a disperser operatively associated with the rotor for dispersing the plurality of gas bubbles from the rotor, an internal skim tray for removing an oily froth from the top of the raw water within the vessel, an external skim tank configured to deliver a gas to the rotor and wherein the external skim tank is configured to receive the oily froth from the internal skim tray, and a closed loop gas line for communicating a gas from the external skim tank to the vessel. 
         [0011]    The method further comprises channeling the raw water through a draft tube into the rotor, creating a plurality of bubbles within the raw water, and directing the raw water through the disperser in order to disperse the gas bubbles. The method further includes producing an oily froth on a top surface of the raw water, collecting the oily froth in the internal skim tray, and skimming the oily froth from the skim tray into a secondary skimming device. 
         [0012]    The method further comprises channeling the oily froth through an output line to the external skim tank and exiting the skimmed water from the vessel. The method may include treating the process stream with carbon dioxide within the external skim tank. It should be noted that the step of treating the oily froth may consist of heating the oily froth within the external skim tank. 
         [0013]    In one preferred embodiment, the method also includes directing the oily froth from the external skim tank to a pump and centrifuge, separating the oily froth into an oily component and a water component, and then channeling the water component back into the vessel. 
         [0014]    Additionally, in one preferred embodiment, the step of creating the bubbles includes communicating a gas from the external skim tank to the vessel via a closed loop gas line. The method may further comprise directing the gas in the vessel back into the external skim tank via the output line so that the output line is cleaned. 
         [0015]    An advantage is that the present disclosure combines components of several novel separation techniques into a single cell apparatus. Another advantage is that the invention provides for a smaller footprint of equipment, which is particularly valuable in remote and/or exotic locations. 
         [0016]    Yet another advantage is the ability to recover oil from primary induced gas flotation machine rejects and hydrocyclone rejects. Still yet another advantage is the recovery of oil from produced water streams on a temporary basis while primary water treating equipment is either being serviced or is too large to be economically operated on the early production flow rates of the production facilities. 
         [0017]    A feature of the present disclosure is a rotor mechanism for creating a plurality of bubbles within the flotation process. Another feature is a disperser for dispersing the bubbles. Yet another feature is the aeration skim tray for skimming the oily froth from the top of the effluent. Still yet another feature is the secondary oil skimming device, operatively associated with the aeration internal skim tray, for directing the oily froth from the vessel. 
         [0018]    Yet another feature is the ability to introduce carbon dioxide make-up gas into the closed circulation gas eductor loop for the purpose of lowering the Ph of the produced water which will result in removing water soluble organic (WSO) content from the produced water. In other words, carbon dioxide or other acid gas source is delivered to the rotor mechanism either via the external skim tank or directly to the atmospheric space of the vessel for purpose of lowering the pH of the raw water and releasing water soluble organic content from the raw water and removing the organic content from the raw water by the flotation process. 
         [0019]    Another feature is the ability to return the effluent water from the external skim tank to (1) the inlet of the vessel or (2) with the addition of subsequent filtration, discharge the water overboard within acceptable government regulations and industry standards. Put another way, the process includes subsequent, additional separation device(s) to clean the skimmed water for overboard or other suitable disposal means. 
     
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0020]      FIG. 1  is a partial cross-section end view of the rotor assembly, stand-pipe, and internal skim tray within the vessel of the most preferred embodiment. 
           [0021]      FIG. 2  is a partial cross-section end view of the disperser, draft tube and secondary skimmer within the vessel of the most preferred embodiment. 
           [0022]      FIG. 3  is a partial cross-section side view of the vessel with the internal components of the most preferred embodiment. 
           [0023]      FIG. 4  is a partial top view of the vessel with internal components illustrated in  FIG. 3 . 
           [0024]      FIG. 5  is a schematic illustration of a second preferred embodiment of a vessel operatively associated with an external skim tank. 
           [0025]      FIG. 6  is a schematic illustration of a third preferred embodiment of the vessel operatively associated with an external skim tank and other components. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Referring now to  FIG. 1 , a partial cross-section end view of the rotor assembly  2  and stand-pipe  4  within the vessel  6  of the most preferred embodiment will now be described. The rotor assembly  2  is connected to a shaft  8  and wherein the shaft  8  is disposed through the flange cover  10 , and wherein the flange cover  10  is affixed to the internal portion of the vessel  6 . The shaft  8  is spun by a motor means (not shown). As those of ordinary skill in the art will appreciate, the rotor assembly includes a member capable of rotation within a cylindrical housing so that during rotation, gas bubbles are produced. Rotor assemblies are commercially available from Petreco International Inc. under the name Wemco Depurator Rotor Assembly. A gas inlet port  12  for allowing the introduction of a gas into the vessel  6  via the standpipe  4  and rotor assembly  2  is also shown. 
         [0027]    As seen in  FIG. 1 , the stand-pipe  4  comprises a first outer diameter portion  14  and a second outer diameter portion  16 , and wherein the portion  14  is larger than the portion  16 . The standpipe  4  is attached at one end to the flange cover  10  and at the second end is attached to the internal skim tray  18  (also referred to as aeration skim tray  18 ). As those of ordinary skill in the art will recognize, the rotor assembly  2  will generate a plurality of bubbles within the raw water which in turn will cause an oily froth to rise to the top of raw water volume within the vessel  6 .  FIG. 1  also depicts the internal skim tray  18 , which forms part of the skimming means. As shown in  FIG. 1 , internal skim tray  18  has a saucier type of shape and is disposed about the secondary skimmer  34  (as illustrated in  FIG. 2 ), which surrounds the standpipe  4  and the shaft  8  of the rotary assembly  2 . A skim outlet  20  is also shown, and wherein the skimming means is fluidly connected to the skim outlet  20 . The internal skim tray  18  will be attached to the sides of the vessel  6 . In one preferred embodiment, the bottom of the internal skim tray  18  will have open ports  21   a ,  21   b  for the purpose of limited liquid communication between the internal skim tray  18  and the vessel  6 . This feature prevents flooding of the internal skim tray  18  by allowing liquids at the bottom of the tray (mostly water) to re-enter the flotation process simultaneously as liquids at the top of the tray (mostly oil) are skimmed into the secondary skimmer  34 . 
         [0028]    Referring now to  FIG. 2 , a partial cross-section end view of the disperser mechanism  24  and draft tube  26  within the vessel  6  of the most preferred embodiment is shown. It should be noted that like numbers appearing in the various figures refer to like components. The disperser mechanism  24  is disposed about the rotor assembly  2  (not shown in this view). The disperser mechanism  24  disperses the plurality of bubbles created by the rotor assembly  2 . The disperser mechanism  24  is a cylindrical cage assembly. The disperer mechanism  24  is connected to the draft tube centralizer  28  which in turn is connected to the draft tube  26 . The draft tube  26  provides a passage for the raw water that is being drawn by the rotation of the rotary assembly  2 , as will be more fully explained later in the disclosure. 
         [0029]    The lower assembly support struts  32  are also shown. The purpose of the lower assembly support struts  32  is to support the secondary skimmer  34 , disperser  24 , draft tube centrailzer  28 , and draft tube  26 .  FIG. 2  also depicts the secondary skimmer  34 , wherein the secondary skimmer  34  is a rolled piece of metal (i.e. cylindrical) that has several overflow “V” notches (such as notches  36 ,  38 ,  40 ) formed thereon, wherein the skimmer  34  is placed within the skim tray  18  (not shown in  FIG. 2 ). An outflow line  42  is in communication with the secondary skimmer  34 , and wherein the outflow line  42  is also in communication with the skim outlet  20  for discharging the collected oily froth. It should be noted that the secondary skimmer  34  is placed within the internal skim tray  18 , so that the oily froth overflows from the internal skim tray  18  and into the secondary skimmer  34 . From the secondary skimmer  34 , the oily froth exits via the out flow line  42 . 
         [0030]    Referring now to  FIG. 3 , a partial cross-section side view of the vessel  6  with the internal components of the most preferred embodiment. More specifically.  FIG. 3  depicts the rotary assembly  2  connected to the shaft  8 . The disperser mechanism  24  is disposed about the rotary assembly  2  and wherein the draft tube  26  is connected to the disperser mechanism  24 , as previously noted. The internal skim tray  18  is disposed about the secondary skimmer  34 . 
         [0031]    The arrows A 1 , A 2  represent the circulation path of the raw water that is being sucked into the draft tube  26  (as noted by arrow A 3 ), which in turn will be drawn into the rotary assembly  2 . The raw water will then be forced from the rotary assembly  2  thereby creating gas bubbles within the raw water, and through the disperser mechanism  24 , as noted by flow arrows A 4  and A 5 . From there, the generated gas bubbles will cause the oily froth to rise to the top, and wherein the oily froth will be directed into the internal skim tray as illustrated by skim tray inlet  44  and skim tray inlet  46 . The oily froth will collect in the tray  18 , and then into the secondary skimmer  34  for removal via the skim outlet nozzle  48 .  FIG. 3  further depicts the raw water inlet  50  for the introduction of the raw water into the vessel  6 , as well as the skimmed water outlet  52 . The skimmed water which exits at the water outlet  52  has had the oily froth removed as per the teachings of the present invention. 
         [0032]    Referring now to  FIG. 4 , a partial top view of the vessel  6  with internal components illustrated in  FIG. 3  will now be described. The raw water inlet  50  is shown along with the clean water outlet  52  and skim (oily froth) outlet  20 . The top view seen in  FIG. 4  also depicts the outer limits of the internal skim tray  18 . The internal skim tray  18  is secured to the side walls of the vessel  6 . The contour of the flange cover  10  is shown. Also shown is the standpipe portion  16  that extends to the standpipe portion  14 . The rotor assembly  2  is shown disposed within the disperser mechanism  24 . In the most preferred embodiment, the rotor assembly  2  and standpipe  4  are mounted to the flange cover  10  that bolts to the top of the vessel  6 . The disperser mechanism  24 , draft tube  26  (not seen in this view), and secondary skimmer  34  (not seen in this view) are all built as a single piece for installation through the flange cover  10 . The gas induction nozzle  12  allows the entry of gas from the external skim tank (not seen in this view). 
         [0033]      FIG. 5  is a schematic illustration of a second preferred embodiment of the vessel  6  operatively associated with an external skim tank  60 . The schematic of  FIG. 5  depicts the rotary assembly  2  and the disperser mechanism  24  disposed within the vessel  6  as previously described. The raw water inlet  50  and the skimmed water outlet  52  are shown. The flow arrows A 1 , A 2 , and A 3  are included, as previously described. 
         [0034]    The external skim tank  60  has a gas induction return line  62  that is connected to the gas inlet port  12 . Hence, gas is drafted into the rotor assembly  2  from the external skim tank  60  via gas induction return line  62 . Additionally, the skim outlet  20  is directed via outlet skim line  64  to the external skim tank  60 . Besides allowing for a gas circulation path, the closed loop of gas circulation keeps outlet skim line  64  clean of the oily froth, which is a feature of the present invention. Make-up gas enters the system through the external skim tank  60  via the make-up gas line  65 . Make-up gas is delivered to the system via line  65  from an external gas source such as natural blanket gas available on the platform or an alternate blanket gas source. As per the teachings of this disclosure, make-up gas can be carbon dioxide (CO2), wherein the CO2 is added for Ph adjustment to release water soluble organics for removal via the flotation process to the content of the external skim tank  60 . 
         [0035]    A skim intermittently means  66  for intermittenly skimming the oily froth within the external skim tank  60  is also shown. One embodiment of the skim intermittently means  66  consist of controllers and timers that remove oil from the surface of the tank and water  67  from the bottom of the tank.  FIG. 5  depicts a water outlet  67  and associated outlet line  68  which directs the water phase component from within the external skim tank  60  to the vessel  6 . The outlet line  68  has operatively associated therewith the pump means  70  as well as the valve means  72  for directing the water back to the vessel  6 . As an alternative, the water from the external skim tank  60  may also be directed to the pump means  74 , and wherein for this configuration, the operator may wish to perform additional separation with different types of separation techniques on the water, or the operator may simply discharge the water in the event that the operator feels that the water has been treated adequately. 
         [0036]    Referring now to  FIG. 6 , a schematic illustration of the third preferred embodiment of the vessel  6  operatively associated with an external skim tank  60  and other components will now be described. The liquid component from the external skim tank  60  will be directed to the outlet line  80  which in turn is delivered to the centrifugal separator means  82  for separating the liquid output into a water component and into a oil component. The oil component is delivered to the oil tank  84 , and wherein the pump means  86  may be further included in order to pump the oil component to other appropriate holding tanks (not shown). 
         [0037]      FIG. 6  also shows where the water component exiting the centrifugal separator  82  is directed to a water tank  88 . A pump means  90  is fluidly connected to the water tank  88  so that the water component can be pumped and delivered to the vessel  6  so that the water component can be subjected to the separation system within the vessel  6 , as previously described. The water component from the pump means  90  is feed into line  92 , and wherein a valve means  94  is included in line  92  to direct the water to the vessel  6 . The operation of the vessel  6  and external skim tank  60  is the same as previously presented. In this embodiment, it is also possible to include a divert line  98  and valve  95  to additional separation devices  96  such as nutshell filters, sock filters, granular activated carbon filters  96 , diatomaceous earth filters, and other equivalent separation means. The additional separation device(s)  96  will discharge clean water through discharge line  97  to overboard or other suitable disposal means (not shown). 
         [0038]    While the present techniques of the invention may be susceptible to various modifications and alternative forms, the exemplary embodiments discussed above have been shown by way of example. However, it should again be understood that the invention is not intended to be limited to the particular embodiments disclosed herein. Indeed, the present techniques of the invention are to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.