Abstract:
Systems and methods for improved column operation in offshore environments by using a co-current contactor system in floating production, storage and offloading (FPSO) systems.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The priority of U.S. Provisional Patent Application No. 61/837,169, filed Jun. 19, 2013, is hereby claimed and the specification thereof is incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not applicable. 
       FIELD OF THE DISCLOSURE 
       [0003]    The present disclosure generally relates to systems and methods for improved column operation in offshore environments. More particularly, the present disclosure relates to improved column operation in offshore environments by using a co-current contactor system in floating production, storage and offloading (FPSO) systems. 
       BACKGROUND OF THE DISCLOSURE 
       [0004]    Offshore processing of natural gas or oil associated gas is becoming a more and more attractive alternative to conventional land-based facilities. Marginal gas fields can be economically developed by means of the FPSO concept. Offshore processing plants on floating structures can be production units for liquefied natural gas (LNG), liquefied petroleum gas (LPG), methanol, gas to liquid (GTL), or ammonia. The ability to station the FPSO vessel directly over fields avoids expensive offshore pipelines. In addition, once the existing field is depleted, the production facility can be moved to a new location to continue production. 
         [0005]    One of the critical technical challenges for the FPSO concept is the influence of movement, acceleration and static tilt on the performance of distillation and absorption columns, such as demethanizer, deethanizer, depropanizer, glycol-based dehydration system, or acid gas removal absorber columns. For these units, the uniform countercurrent gas and liquid flow is disturbed by motion leading to reduced heat and mass transfer. Their efficiency is thus, often influenced by the deviations from the vertical position. 
         [0006]    Though amine-based acid gas removal is a well proven technology for onshore applications, offshore conditions may result in not contacting some of the untreated or insufficiently treated feed gas due to movement or tilt of the absorber. The problem is especially severe for floating LNG FPSO, since the liquefaction process requires CO 2  to be reduced to less than 50 ppm to avoid risk of the freeze out and blockage of heat exchangers at cryogenic temperatures. Even a small bypass may have an adverse impact on liquefaction system operation with off-specification (off-spec.) treated gas having an excess of CO 2  exceeding about 50 ppm, and may require the process to shut down resulting in production losses. 
         [0007]    Moreover, various studies have established that distillation or absorption column movement due to sea conditions can negatively affect separation efficiency in the column. In a 50 mm diameter distillation column, for example, a 50% reduction in efficiency at an inclination of 2.5 degrees was reported. In addition, a 16% reduction in efficiency at an inclination of 1.2 degrees for a 2 meter diameter one or two-pass tray column, and a 31% reduction in efficiency at an inclination of 1 degree for a 330 mm diameter one-path tray column were reported. 
         [0008]    These reported reductions in separation efficiency will have a significant impact on the equipment performance, and eventually the reliability of the operation. Availability of production will suffer due to process shut down triggered by the off-spec treated gas from the acid gas removal unit. Equipment may need to be over-sized to offset the reduction in separation efficiency at higher sea states. Alternatively, proprietary equipment may need to be used to alleviate the uneven distribution problem. 
       SUMMARY OF THE DISCLOSURE 
       [0009]    The present disclosure overcomes one or more deficiencies in the prior art by providing systems and methods for improved column operation in offshore environments by using a co-current contactor system in floating production, storage and offloading (FPSO) systems. 
         [0010]    In one embodiment, the present disclosure includes co-current contact system for operating an absorption column in offshore environments, which comprises: i) a solvent regeneration unit having a rich amine input opening in fluid communication with a rich amine output line connected to the absorption column and a lean amine output line in fluid communication with a lean amine input opening in the absorption column; a static mixer having a static mixer input opening in fluid communication with the lean amine output line, a treated gas input opening in fluid communication with a treated gas output line connected to the absorption column and a static mixer output line; and iii) a separator having a separator input opening in fluid communication with the static mixer output line, a separator liquid output line and a separator vapor output line. 
         [0011]    In another embodiment, the present disclosure includes a co-current contact system for operating a distillation column in offshore environments, which comprises: i) a static mixer having a first static mixer input opening in fluid communication with a reflux pump output line connected to a reflux pump, a second static mixer input opening in fluid communication with a distillation column output line connected to the distillation column and a static mixer output line in fluid communication with a condenser input opening in a condenser; and ii) a reflux drum having a reflux drum input opening in fluid communication with a condenser output line connected to the condenser, a first reflux drum output line in fluid communication with a reflux pump input opening in the reflux pump and a second reflux drum output line. 
         [0012]    In yet another embodiment, the present disclosure includes a method for operating an absorption column in offshore environments using a co-current contact system, which comprises: i) sending lean amine from a solvent regeneration unit to the co-current contact system, wherein the co-current contact system comprises a static mixer and a separator; ii) mixing the lean amine and a treated gas from the absorption column in the static mixer; and iii) separating the mixed lean amine and treated gas into a vapor and a liquid using the separator. 
         [0013]    In yet another embodiment, the present disclosure includes a method for operating a distillation column in offshore environments using a co-current contact system, which comprises: sending a reflux liquid from a reflux drum to the con-concurrent contact system, wherein the co-current contact system comprises a static mixer and a condenser; ii) mixing the reflux liquid and a vapor from the distillation column in the static mixer; and iii) condensing the mixed reflux liquid and vapor into a mixed condensate using the condenser. 
         [0014]    Additional aspects, advantages and embodiments of the disclosure will become apparent to those skilled in the art from the following description of the various embodiments and related drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The present disclosure is described below with references to the accompanying drawings in which like elements are referenced with like reference numerals, and in which: 
           [0016]      FIG. 1  is a schematic diagram illustrating one embodiment of a co-current contact system for use in a conventional acid gas removal system according to the present disclosure. 
           [0017]      FIG. 2  is schematic diagram illustrating another embodiment of a co-currrent contact system for use in a conventional acid gas removal system according to the present disclosure. 
           [0018]      FIG. 3  is a schematic diagram illustrating yet another embodiment of a co-currrent contact system for use in a conventional acid gas removal system according to the present disclosure. 
           [0019]      FIG. 4  is a schematic diagram illustrating yet another embodiment of a co-currrent contact system for use in a conventional acid gas removal system according to the present disclosure. 
           [0020]      FIG. 5  is a schematic diagram illustrating another embodiment of a co-current contact system that may be used in place of the co-current contact system illustrated in  FIGS. 1-4 , 
           [0021]      FIG. 6  is a schematic diagram illustrating yet another embodiment of a co-current contact system that may be used in place of the co-current contact system illustrated in  FIGS. 1-4   
           [0022]      FIG. 7  is a schematic diagram illustrating one embodiment of a co-current contact system for use with a distillation column according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    The subject matter of the present disclosure is described with specificity, however, the description itself is not intended to limit the scope of the disclosure. The subject matter thus, might also be embodied in other ways, to include different steps or combinations of steps similar to the ones described herein, in conjunction with other present or future technologies. Moreover, although the term “step” may be used herein to describe different elements of methods employed, the term should not be interpreted as implying any particular order among or between various steps herein disclosed unless otherwise expressly limited by the description to a particular order. While the present disclosure may be applied in the oil and gas industry, it is not limited thereto and may also be applied in other industries to achieve similar results. 
         [0024]    The following description refers to  FIGS. 1-7 , which includes systems and methods for improved column operation in offshore environments using co-current contactor systems to improve mixing between incoming streams. In  FIGS. 1-7 , various embodiments of a co-current contact system are illustrated in an exemplary acid gas removal system or with an exemplary distillation column. In each embodiment, the co-current contact system includes a static mixer insensitive to motion, which provides mixing between the incoming streams. A static mixer may include, for example, of a series of motionless elements installed in a pipe. These elements promote e mixing of two or more fluids, which flow through the pipe due to a pressure gradient. Where needed, multiple stages of such mixing can be utilized. When used with an absorption column, the co-current contactor system is positioned downstream of the absorption column to treat the vapor leaving the absorption column overhead. When used with a distillation column, the co-current contactor system is positioned downstream of the distillation column before the condenser. 
         [0025]    Referring now to  FIG. 1 , a schematic diagram illustrates one embodiment of a co-current contact system for use in a conventional acid gas removal system. The acid gas removal system includes an absorber  106  and a solvent regeneration unit  130 . The co-current contact system includes a static mixer  112  and a separator  120 . The absorber  106  has an input opening  104  located below the lower packed section adapted for fluid communication with a feed gas line  102 . The solvent regeneration unit  130  has a rich amine input opening  132  in fluid communication with a rich amine output line  128  at the bottom of the absorber  106  and a lean amine output line  134  in fluid communication with a lean amine input opening  108  near the top of the absorber  106 . The static mixer  112  has a static mixer input opening  116  in fluid communication with the lean amine output line  134 , a treated gas input opening  114  in fluid communication with a treated gas output line  110  from the top of the absorber  106 , and a static mixer output line  118 . For liquefaction applications, the treated gas output line  110  is generally specified to contain less than 50 ppm CO 2  and less than 5 mg/Nm 3 H 2 S. The separator  120  has a separator input opening  122  in fluid communication with the static mixer output line  118 , a separator liquid output line  124 , and a separator vapor output line  126 . 
         [0026]    Referring now to  FIG. 2 , a schematic diagram illustrates another embodiment of a co-currrent contact system for use in a conventional acid gas removal system. The acid gas removal system includes an absorber  106  and a solvent regeneration unit  130 . The co-current contact system includes a static mixer  112  and a separator  120 . The absorber  106  has an input opening  104  located below the lower packed section adapted for fluid communication with a feed gas line  102 . The solvent regeneration unit  130  has a rich amine input opening  132  in fluid communication with a rich amine output line  128  at the bottom of the absorber  106  and a lean amine output line  134  in fluid communication with a lean amine input opening  108  near the top of the absorber  106 . The static mixer  112  has a static mixer input opening  116  in fluid communication with the lean amine output line  134 , a treated gas input opening  114  in fluid communication with a treated gas output line  110  from the top of the absorber  106 , and a static mixer output line  118 . For liquefaction applications, the treated gas output line  110  is generally specified to contain less than 50 ppm CO 2  and less than 5 mg/Nm 3 H 2 S. The separator  120  has a separator input opening  122  in fluid communication with the static mixer output line  118 , a separator liquid output line  124 , and a separator vapor output line  126 . In this embodiment, a sufficient amount of lean amine from the lean amine output line  134  is sent to the static mixer  112  through the static mixer input opening  116  where it is mixed with the gas from the treated gas output line  110  as it enters the static mixer  112  through the treated gas input opening  114 . The resulting treated gas from the separator vapor output line  126  will meet acid gas specifications and semi-lean amine from the separator liquid output line  124  is combined with the lean amine from the lean amine output line  134  before entering the absorber  106  through the lean amine input opening  108 . 
         [0027]    Referring now to  FIG. 3 , a schematic diagram illustrates yet another embodiment of a co-currrent contact system for use in a conventional acid gas removal system. The acid gas removal system includes an absorber  106  and a solvent regeneration unit  130 . The co-current contact system includes a static mixer  112  and a separator  120 . The absorber  106  has an input opening  104  located below the lower packed section adapted for fluid communication with a feed gas line  102 . The solvent regeneration unit  130  has a rich amine input opening  132  in fluid communication with a rich amine output line  128  at the bottom of the absorber  106  and a lean amine output line  134  in fluid communication with a lean amine input opening  108  near the top of the absorber  106 . The static mixer  112  has a static mixer input opening  116  in fluid communication with the lean amine output line  134 , a treated gas input opening  114  in fluid communication with a treated gas output line  110  from the top of the absorber  106 , and a static mixer output line  118 . For liquefaction applications, the treated gas output line  110  is generally specified to contain less than 50 ppm CO 2  and less than 5 mg/Nm 3 H 2 S. The separator  120  has a separator input opening  122  in fluid communication with the static mixer output line  118 , a separator liquid output line  124 , and a separator vapor output line  126 . In this embodiment, a sufficient amount of lean amine from the lean amine output line  134  is sent to the static mixer  112  through the static mixer input opening  116  where it is mixed with the gas from the treated gas output line  110  as it enters the static mixer  112  through the treated gas input opening  114 . The resulting treated gas from the separator vapor output line  126  will meet acid gas specifications and semi-lean amine from the separator liquid output line  124  is sent to the absorber  106  through another lean amine input opening  304 . In this manner, the semi-lean amine will not dilute the lean amine from the lean amine output line  134 . 
         [0028]    Referring now to  FIG. 4 , a schematic diagram illustrates yet another embodiment of a co-currrent contact system for use in a conventional acid gas removal system. The acid gas removal system includes an absorber  106  and a solvent regeneration unit  130 . The co-current contact system includes a static mixer  112  and a separator  120 . The absorber  106  has an input opening  104  located below the lower packed section adapted for fluid communication with a feed gas line  102 . The solvent regeneration unit  130  has a rich amine input opening  132  in fluid communication with a rich amine output line  128  at the bottom of the absorber  106  and a lean amine output line  134  in fluid communication with a lean amine input opening  108  near the top of the absorber  106 . The static mixer  112  has a static mixer input opening  116  in fluid communication with the lean amine output line  134 , a treated gas input opening  114  in fluid communication with a treated gas output line  110  from the top of the absorber  106 , and a static mixer output line  118 . For liquefaction applications, the treated gas output line  110  is generally specified to contain less than 50 ppm CO 2  and less than 5 mg/Nm 3 H 2 S. The separator  120  has a separator input opening  122  in fluid communication with the static mixer output line  118 , a separator liquid output line  124 , and a separator vapor output line  126 . In this embodiment, a sufficient amount of lean amine from the lean amine output line  134  is sent to the static mixer  112  through the static mixer input opening  116  where it is mixed with the gas from the treated gas output line  110  as it enters the static mixer  112  through the treated gas input opening  114 . The resulting treated gas from the separator vapor output line  126  will meet acid gas specifications and semi-lean amine from the separator liquid output line  124  is sent to the solvent regenerator unit  130  through a semi-lean amine input opening  404 . 
         [0029]    Referring now to  FIG. 5 , a schematic diagram illustrates another embodiment of a co-current contact system that may be used in place of the co-current contact system illustrated in  FIGS. 1-4 . The co-current contact system includes another static mixer  504  and another separator  512 . The another static mixer  504  has another static mixer input opening  506  in fluid communication with the separator vapor output line  126  for carrying treated gas, a lean amine input opening  508  in fluid communication with the lean amine output line  134 , and another static mixer output line  510 . The another separator  512  has another separator input opening  514  in fluid communication with the another static mixer output line  510 , another separator liquid output line  516  for carrying semi-lean amine, and another separator vapor output line  518  for carrying twice treated gas. In this embodiment, feed gas from the treated gas input opening  114  is mixed in the static mixer  112  with lean amine from the static mixer input opening  116 . Treated gas from the separator  120  is further mixed in the another static mixer  504  with lean amine from the lean amine input opening  508 . The treated gas from the another static mixer  504  will meet acid gas specifications and the semi-lean amine from the another separator liquid output line  516  and the separator liquid output line  124  is sent to the absorber  106 . 
         [0030]    Referring now to  FIG. 6 , a schematic diagram illustrates yet another embodiment of a co-current contact system that may be used in place of the co-current contact system illustrated in  FIGS. 1-4 . The co-current contact system includes another static mixer  504  and another separator  512 . The another static mixer  504  has another static mixer input opening  506  in fluid communication with the separator vapor output line  126  for carrying treated gas, a lean amine input opening  508  in fluid communication with the lean amine output line  134 , and another static mixer output line  510 . The another separator  512  has another separator input opening  514  in fluid communication with the another static mixer output line  510 , another separator liquid output line  516  for carrying semi-lean amine, and another separator vapor output line  518  for carrying twice treated gas. In this embodiment, feed gas from the treated gas input opening  114  is mixed in the static mixer  112  with semi-lean amine from the another separator output line  516 . Treated gas from the separator  120  is further mixed in the another static mixer  504  with lean amine from the lean amine input opening  508 . The treated gas from the another static mixer  504  will meet acid gas specifications and the semi-lean amine from the another separator liquid output line  516  is sent to the first static mixer  112 . The semi-lean amine from the separator  120  is more enriched with CO 2  than the semi-lean amine from the another separator  512 . In this manner, the total required lean amine flow rate is reduced compared to the embodiment described in reference to  FIG. 5 . 
         [0031]    Referring now to  FIG. 7 , is a schematic diagram illustrates another embodiment of a co-current contact system for use with a distillation column. The co-current contact system includes a static mixer  706 , a condenser  714 , a reflux drum  720 , and a reflux pump  730 . The distillation column  704  has a distillation column output line  705  and a distillation column input opening  734 . The static mixer  706  has a first static mixer input opening  708  in fluid communication with a reflux pump liquid output line  732 , a second static mixer input opening  710  in fluid communication with the distillation column output line  705  and a static mixer output line  712  in fluid communication with a condenser input opening  716 . The reflux drum  720  has a reflux drum input opening  722  in fluid communication with a condenser output line  718 , a first reflux drum output line  724  in fluid communication with a reflux pump input opening  728  on the reflux pump  730 , and a second reflux drum output vapor line  726 . The reflux pump liquid output line  732  is in fluid communication with the distillation column input opening  734  and the static mixer input opening  708 . In this embodiment, a portion of the reflux in the reflux pump liquid output line  732  is split and mixed with vapor from the distillation column output line  705  in the static mixer  706 . In this manner, the overall separation is enhanced and multiple stages of such mixing, as illustrated in  FIGS. 5-6 , may be added. 
         [0032]    Any of the foregoing co-current contact systems may be further modified as illustrated in  FIGS. 5 and 6 . And, the various embodiments of the co-current contact system illustrated in  FIGS. 1-7  may be applied in a new system or may be used in preexisting systems with conventional absorption and/or distillation columns. 
         [0033]    While the present disclosure has been described in connection with presently preferred embodiments, it will be understood by those skilled in the art that it is not intended to limit the disclosure to those embodiments. It is therefore, contemplated that various alternative embodiments and modifications may be made to the disclosed embodiments without departing from the spirit and scope of the disclosure defined by the appended claims and equivalents thereof.