Abstract:
Systems and methods for removing solids from a process stream being fed into a flash separator include a solids fluidization device and a solids removal device. The solids fluidization device at the bottom end of the fluid column of the flash separator introduces a swirling motive fluid within the fluid column, while the solids removal device located above the solids fluidization device removes the slurry created by the swirling motive fluid. Systems and methods for fluidizing solids in the fluid column of a flash separator include a solids fluidization device that introduces a swirling motive fluid within the fluid column, means to limit the upward movement of the swirling motive fluid, such as a valve, and removing the solid slurry produced by the swirling motive fluid.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application which claims priority to U.S. patent application Ser. No. 15/056,256 filed Feb. 29, 2016, which claimed priority to U.S. patent application Ser. No. 14/307,232 filed on Jun. 17, 2014 (U.S. Pat. No. 9,272,972), which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to processes designed to treat mono ethylene glycol (MEG) used in the oil and gas industry, especially in offshore locations, to control hydrates formation. More particularly, the present disclosure relates to MEG reclamation processes which are designed to remove salts and other contaminants from a wet MEG feed stream. 
         [0003]    In the oil and gas industry, dry (lean) MEG is used to control the formation of hydrates within the produced stream. The now wet (rich) MEG is, in turn, dried by way of a MEG reclamation process so the MEG can be used again in hydrate control. 
         [0004]    The unit used to recover MEG includes three sections: pre-treatment, flash separation, and MEG regeneration. Those sections can be followed by salt management and calcium removal sections. 
         [0005]    In the pre-treatment stage, the rich MEG containing some dissolved gas and hydrocarbon liquids must pass through a three-phase separator vessel. The gas is flashed and recovered hydrocarbon liquids are sent to the production separator. The rich MEG is sent to a flash separator. The rich MEG stream comprised of produced water and MEG is fed to the flash separator where it is brought into contact with a hot recycle stream of MEG. The flash separator operates under vacuum. The MEG and water components of the rich MEG stream are flashed and exit through the top of the flash separator where they are sent to the MEG distillation column for regeneration. The salt components of the rich MEG stream precipitate in the flash separator. 
         [0006]    The MEG regeneration section is a refluxed distillation column. The distillation column also operates under vacuum and distills the water from the MEG-water vapors coming off the top of the flash separator. Salt-free, lean MEG produced at the bottom of the distillation column is pumped to storage for reuse. The vaporized water passes overhead from the distillation column. The water is condensed and collected in the reflux drum. A small amount is returned to the distillation column as reflux, and the remaining is routed to treatment. 
         [0007]    The salt crystals that precipitate in the flash separator are separated by gravity to the bottom of the brine column, where they are transferred to the salt tank. There, the salts are concentrated before removal through a centrifuge. 
         [0008]    The salts in produced water cover a variety of species, but generally are categorized into monovalent salts (typically sodium and potassium), and divalent salts (typically calcium and magnesium). The divalent salts cannot be effectively precipitated in the same manner as the monovalent salts, so a separate calcium removal process may be installed. Effective calcium control is accomplished as the divalent salts are collected, reacted and removed through a centrifuge with the centrate overflow returning to the process. 
         [0009]    Current methods of removing the salt crystals from bottom of the brine column involves a lot of equipment, including but not limited to complicated and expensive centrifugal filters or de-sanding cyclones, centrifuge pump filtration systems, a salt tank, a centrate tank, and a density measurement device. Reducing the footprint of the system used to remove the salt crystals is important for making more efficient use of space, reducing off-shore construction costs, and increasing ease of system operation and maintenance. 
       SUMMARY 
       [0010]    In an embodiment, a system for removing solids from a process stream being fed into a flash separator includes a solids fluidization device and a solids removal device. The solids fluidization device is located at the bottom end of the fluid column of the flash separator and arranged to introduce a swirling motive fluid within the fluid column. The solids removal device is located above the solids fluidization device and arranged to remove the slurry created by the swirling motive fluid. 
         [0011]    In an embodiment, a system for fluidizing solids in the fluid column of a flash separator includes a solids fluidization device that is located at the bottom end of the fluid column and arranged to introduce a swirling motive fluid within the fluid column and means to limit an upward movement of the swirling motive fluid within the fluid column. The means for limiting the upward movement may be a valve that is located above the solids fluidization device. 
         [0012]    In an embodiment, a method of removing solids from a process stream being fed into a flash separator includes the isolation of a fluid in the fluid column of the flash separator from the upper end of the flash separator. A swirling motive fluid, which contacts the solid components of the isolated fluid, is introduced into the bottom end of the fluid column of the flash separator, and the solids slurry produced by the swirling motive fluid is removed. 
         [0013]    In an embodiment, a method of fluidizing solids to aid in solids removal includes the introduction of a swirling motive fluid into the bottom end of the fluid column of the flash separator so that the swirling motive fluid contacts the solid components of a fluid in the fluid column. The method also includes limiting the upward movement of the swirling motive fluid within the fluid column and removing the solid slurry produced by the swirling motive fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    So that the manner in which the above recited features can be understood in detail, a more particular description may be had by reference to embodiments, some of which are illustrated in the appended drawings, wherein like reference numerals denote like elements. It is to be noted, however, that the appended drawings illustrate various embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments. 
           [0015]      FIG. 1  is a schematic of an embodiment of a salt transport system for a MEG reclamation or recovery process. The system includes a solids fluidization device located at the bottom end of the brine column of a flash separator and an on-off valve located between the fluidization device and the MEG/brine transition zone of the flash separator. 
           [0016]      FIG. 2  is a front elevation view of the embodiment of the solids fluidization device of  FIG. 1 . 
           [0017]      FIG. 3  is top view of the solids fluidization device of  FIG. 2 . 
           [0018]      FIG. 4  is a cross-section view of the solids fluidization device of  FIG. 2 . 
           [0019]      FIG. 5  is a cross-section view of the solids fluidization device of  FIG. 2  taken along section line  5 - 5  of  FIG. 2 . 
           [0020]      FIG. 6  is an enlarged view of the solids fluidization device of  FIG. 1  and the removal device located directly above the solids fluidization device. 
       
    
    
     ELEMENTS AND NUMBERING USED IN THE DRAWINGS 
       [0000]    
       
           10  Salt transport system 
           20  Flash separator 
           21  Upper end 
           25  Rich (wet) MEG stream 
           27  Water and MEG vapor stream 
           29  Brine (fluid) or downcomer column or section 
           31  MEG/brine transition zone 
           33  On-off valve 
           35  Recycle loop 
           37  Bottom or lower end of  29   
           39  Upper end of  29   
           40  Sand removal device 
           41  Inlet 
           43  Upper end of  40   
           45  Slots 
           47  Inner bore 
           49  Produced or condensate (carrier or motive) water stream 
           51  Swirling motive fluid stream 
           53  Salt slurry stream 
           55  Removal device or slurry discharge head 
           60  Brine generation vessel 
           61  Agitator 
           63  Brine stream 
           65  Salt slurry (discharge) stream 
       
     
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0045]    In the following description, numerous details are set forth to provide an understanding of some embodiments of the present disclosure. However, it will be understood by those of ordinary skill in the art that the system and/or methodology may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
         [0046]    In the specification and appended claims, the terms “connect”, “connection”, “connected”, “in connection with”, and “connecting” are used to mean “in direct connection with” or “in connection with one or more elements”; and the term “set” is used to mean “one element” or “more than one element”. Further, the terms “couple”, “coupling”, “coupled”, “coupled together”, and “coupled with” are used to mean “directly coupled together” or “coupled together via one or more elements”. As used herein, the terms “up” and “down”, “upper” and “lower”, “upwardly” and “downwardly”, “upstream” and “downstream”, “above” and “below”, and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the disclosure. 
         [0047]    Referring first to  FIGS. 1 and 6 , an embodiment of a salt transport system  10  for a MEG recovery or reclamation process includes a flash separator  20  having a solids fluidization device  40  located at the bottom end  37  of the brine or downcomer column  29  and an on-off valve  33  located between the device  40  and the MEG/brine transition zone  31 . 
         [0048]    The flash separator  20  is of a kind well known in the art. In the separator  20  a rich (wet) MEG inlet stream  25  is brought into contact with a hot MEG recycle stream  35 . The MEG and water components of the rich MEG stream  25  are flashed and exit the upper end  21  of the separator  20  as a water and MEG vapor stream  27 . The salt components of the rich MEG inlet stream  25  precipitate in the brine (fluid) column  29  of the separator  20 . A MEG/brine transition zone  31  forms in the column  29  between the MEG and the brine. 
         [0049]    Solids fluidization device  40  is arranged at the bottom end  37  of the column  29 . The device  40  includes means which produce or cause a swirling (e.g., vertiginous, rotary or cyclonic) motion or flow  51  of the motive fluid as it exits device  40 . One suitable device  40  is a HYDROTRANS™ solids fluidization and removal device (Cameron Process Systems, Houston, Tex.). Any other device may be used as the fluidization device provided the device creates a swirling (e.g., vertiginous, rotating, or cyclonic) motive fluid flow when the flow exits the device. 
         [0050]    Referring to  FIGS. 2-5 , the HYDROTRANS™ device includes a plurality of spaced-apart slots  45  arranged tangential to, surrounding, and in communication with an inner bore  47  which receives a motive fluid stream  49  at the lower inlet end  41  of the device. Motive fluid steam  49 —which can be a produced water or condensate water stream (or some combination thereof)—exits the slots  45  of device  40  as a swirling motive fluid stream  51 . The swirling motion of the motive fluid stream  51  mixes with the fluid containing solid/salt already residing in the column  29  to fluidize the salt components, thereby creating a salt slurry stream  53 . By way of example, during the first five minutes of operation, the concentration of salt in the device  40  can be about 20 vol % on average. 
         [0051]    Unlike a desanding hydrocyclone—which produce a cyclonic flow within the device but a straight over- and underflow exiting the device (i.e., straight in, cyclonic within, and straight out)—the solids fluidization device  40  produces this type of flow external to the device (i.e., straight in and rotary or cyclonic out). 
         [0052]    The removal device  55 , which can be a slurry discharge head, resides just above the upper end  43  of solids fluidization device  40 . Removal device  55  carries the salt slurry stream  53  to a brine generation tank or vessel  60 . 
         [0053]    Because the brine in the column  29  is saturated with salt, adding produced water to it causes the lower density (not saturated) produced water  49  to flow to the upper end  39  of the column  29  and MEG to flow to the bottom end  37 . This causes MEG loss. To prevent this loss from occurring, system  10  limits upward movement of the fluid, which can be by way of isolation means such as on-off valve  33 , which may be a butterfly-type valve. When the valve  33  is in the off or closed position, it prevents the produced water from flowing to the upper end  39  of the column  29 . The valve  33  isolates the fluid or brine located above and below the valve  33  from one another. 
         [0054]    Once the salts are removed from the bottom end  37  of the column  29 , the saturated brine in the brine generation vessel  60  is pumped back to the column  29  below the on-off valve  33  to replace the produced water. Once the produced water is replaced with the saturated brine, the on-off valve  33  is put in the on or open position to allow the salt to settle below the valve  33  and into the bottom  37  of column  29 . 
         [0055]    If a 1″ HYDROTRANS™ is used as device  40 , a flow rate of about 4 m 3 /hr may be used to remove the salt from the bottom end  37 . For about the first five minutes of operation, about 0.33 m 3  of a salt slurry stream  53  (about 20 vol %) is transferred to the brine generation vessel  60 . Assuming a void space of 40% between the salt particles (i.e., the salt represents 60%), the total amount of salt removed in five minutes (0.083 hr) is 0.04 m 3  (4 m 3 /hr×0.083 hr×0.2×0.6). The salt density is 2,165 kg/m 3 . Therefore, the amount of salt removed in five minutes of operation (i.e., with the valve  33  closed) is about 87 kg. If the amount of salt settled at the bottom end  37  is higher (or lower) than in the example, the removal process can be adjusted accordingly. 
         [0056]    In some embodiments, system  10  does not use any centrifugal filters or desanding cyclones to remove salt from the brine column  29 , nor does it use centrifugal filtration, salt and centrate tanks, and density measurement devices. In other embodiments, system  10  uses less foot print than the prior art systems and methods, has lower construction costs, and is easier to operate and maintain. 
         [0057]    After the salt removal process is completed, an agitator  61  can be used to agitate and dissolve the salt in the liquid phase within the brine generation vessel  60 . The saturated brine solution can then be pumped as a saturated brine stream  63  to the column  29  to replace the produced water. Once this operation is complete, the valve  33  can be put in the on or open position to accumulate salt in the bottom end  37  of the column  29 . 
         [0058]    When the brine generation vessel  60  is filled with enough salt, agitator  60  will again be turned on to make a salt slurry stream  65  which is pumped to a water treating unit (not shown) or to overboard (if allowed). 
         [0059]    In embodiments of a method of removing salt from a rich MEG stream which makes use of system  10  includes:
       i. isolating fluid in the brine column  29  of the flash separator  20  by closing a valve  33  located above the bottom end  37  of the brine column  29  and below the upper end  39  of the column  29 ;   ii. introducing a swirling motive fluid stream  51  into the bottom end  37  of the brine column  29 , the swirling motive fluid stream  51  coming into contact with salt components residing in the column  29  and forming a salt slurry stream  53 ;   iii. removing the salt slurry stream  53  from the brine column  29  to a brine generation vessel  60 ;   iv. agitating the contents of the brine generation vessel  60  to form a saturated brine  63 ;   v. transferring the saturated brine  63  back to the column  29 ; and   vi. opening the valve  33  after the transfer of the saturated brine  63  to the column  29  is complete.       
 
         [0066]    Salt removal system  10  and the method for its use is an improvement over prior art systems and methods. The prior art makes use of complicated and expensive centrifugal filters or desanding cyclones to remove salt from the brine column  29  of the flash separator  20  along with centrifuge filtration, a salt tank, a centrate tank, and density measurement devices. 
         [0067]    Embodiments of the system and method may (1) eliminate complicated and expensive centrifugal filters and desanding hydrocyclones to remove salt; (2) eliminate centrifuge filtration, a salt tank, a centrate tank, and density measurement devices; and (3) use less foot print than the prior art systems and methods and have lower construction costs and be easier to operate and maintain than those prior art systems and methods. 
         [0068]    Although the preceding description has been described herein with reference to particular means, materials, and embodiments, it is not intended to be limited to the particulars disclosed herein; rather, it extends to all functionally equivalent structures, methods, and uses, such as are within the scope of the appended claims.