Abstract:
A process for recovering processing liquids from a feed stream which contains processing fluid, water, and at least one alkaline earth metal cation. The process includes reacting at least one alkaline earth metal cation with a suitable anion to form a substantially water-insoluble salt precipitate, the precipitate being formed in one of a fractionation column having a forced recycle loop or a flash vessel having a forced heated recycle loop.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Application No. 62/027,484 filed on Jul. 22, 2014 the disclosure of which is incorporated herein by reference for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a process for recovering a processing liquid, particularly from a feed stream containing processing liquid, water, and an alkaline earth metal cation. 
       BACKGROUND OF THE INVENTION 
       [0003]    Processing liquids such as alcohols and glycols are used in the production of natural gas from oil and gas wells. Thus, typical processing liquids include alcohols and glycols such as mono-, di-, or tri-ethylene glycols (MEG, DEG, and TEG, respectively). When used in the production of natural gas, the processing liquids quickly become contaminated with water, e.g., produced water from the formation, as well as, alkaline metal cations such as magnesium, calcium, etc. and other contaminants primarily dissolved salts such as sodium chloride. Water-insoluble salts of the alkaline earth metal cations are a common cause of fouling in heat exchangers, reboilers, transfer lines, pumps, valves, etc. which are used in systems for recovering the processing liquid for reuse. 
         [0004]    U.S. Pat. Nos. 5,152,887; 5,158,649; 5,389,208; 5,441,605; 5,993,608;and 6,508,916, all of which are incorporated herein by reference for all purposes, deal with the recovery or reclamation of processing fluids used in gas processing including the production of natural gas from oil and/or gas wells. 
         [0005]    As noted above, processing liquids such as MEG used in natural gas production become contaminated with alkaline earth metal cations, primarily calcium and magnesium. Presently, to deal with these cations which can form substantially water-insoluble salts accompanied by the attendant problems described above, it is common to attempt to remove these cations prior to any regeneration and/or reclamation by effecting precipitation of the cations using precipitants such as carbonates, bicarbonates, hydroxides, etc. This “up-front” pre-treatment to remove the alkaline metal cations prior to the processing liquid being recovered invariably involves equipment such as residence tanks, valves, pumps, piping, filters, filter presses, and other equipment commonly used for separating precipitated solids from the processing liquid prior to regeneration and/or reclamation of the latter. In short, this pretreatment to remove the alkaline earth metal cations is expensive and can involve the utilization of valuable space, e.g., if the system was on an offshore platform. 
       SUMMARY OF THE INVENTION 
       [0006]    In one aspect, the present invention provides a process for recovering a processing liquid from a feed stream containing the processing liquid and an alkaline earth metal cation. 
         [0007]    In a further aspect, the present invention provides a process for recovering a processing liquid from a stream containing the processing liquid, water, and at least one alkaline earth metal cation. 
         [0008]    In yet another aspect, the present invention provides a process for recovering a processing liquid from a feed stream containing the processing liquid, water, dissolved salts, and at least one alkaline earth metal cation. 
         [0009]    These and further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic flow sheet of one embodiment of the process of the present invention. 
           [0011]      FIG. 2  is a schematic flow sheet of another embodiment of the process of the present invention. 
           [0012]      FIG. 3  is a schematic flow sheet of yet another embodiment of the process of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0013]    While the present invention will be described with particular reference to a feed stream used in the production of oil and gas, it is not so limited. Basically, the process of the present invention can be used in any process where there is a processing stream or liquid, however used, which becomes contaminated with alkaline earth metal cations (AMC) which form substantially water-insoluble salts. As used herein, the term “substantially water-insoluble salts” refers to a salt or mixture thereof wherein the solubility of the salt(s) in water is less than about 0.5 wt % at 0° C. 
         [0014]    Basically, the process of the present invention can comprise a reclamation stage alone or in combination with a regeneration stage. With regard to the latter, it is common in oil and gas production to inject processing liquids, e.g., alcohols and glycols, into the well during production to alleviate the formation of gas hydrates or clathrates. Because these processing liquids cannot be readily disposed of and also due to their expense, it is necessary to recover them for reuse employing processes described in the above mentioned patents. The feed stream from the well, e.g., the stream containing the used processing liquids, invariably contains water from the formation, water of condensation, varying amounts of salts, e.g., sodium chloride, and other contaminants, e.g., AMC&#39;s. In general if the salt content is low, e.g., less than about 3 wt % of the feed stream, regeneration, basically a fractionation, will sometimes suffice to recover the processing liquid. In regeneration, the water is separated from the processing liquid in a fractionation column, the water being an overhead stream, the processing liquid being recovered as a bottoms stream. However, in cases where the feed stream returning from the well, in addition to the processing liquid and water, contains large amounts of salts, dissolved or suspended, then it is necessary to use a reclaiming step or a combination of regeneration and reclaiming. 
         [0015]    Referring then to  FIG. 1 , there is shown a process flow scheme for a reclaiming process with a feed stream source containing high salt content, e.g. greater than about 3.0 wt %. A feed stream comprised of, for example, processing liquid, water, dissolved and suspended salts, and at least one AMC from a source  10  is introduced via line  11  into a flash vessel  12  from which there is produced an overhead vapor stream  14  and a bottoms, residuum stream  16 . Overhead stream  14  comprises water, processing liquid, and any other volatile materials and is introduced into a product handling section  18 . Product handling section  18  can comprise a fractionation column and various other equipment used in solid-liquid, liquid-liquid, and gas-liquid separation techniques. Purified processing liquid is removed from product handling section  18  via stream  20  for reuse. Portions of product handling section  18  as well as flash vessel  12  are under reduced pressure via line  22  and a vacuum system  24 . 
         [0016]    The residuum stream removed in  16  from flash vessel  12  passes via pump  26 , line  28 , heat exchanger  30  and in-line mixer  32  as a recycle stream to flash vessel  12  via line  34 . It will be appreciated that the recycle stream can be admixed with the feed stream  11  from feed source  10  prior to being introduced into flash vessel  12 . In effect, the loop R 1  formed inter alia by streams  12 ,  16 ,  26 ,  28 ,  30 ,  32  and  34  is a forced reboiler recycle loop. 
         [0017]    There is a precipitant source  36  from which one or more precipitants can be introduced into flash vessel  12  via lines  38  and  11  to effect formation of the AMC precipitates. 
         [0018]    A portion of the residuum stream in line  16  which comprises dissolved liquids including minor amounts of processing liquid, dissolved salts, and solids including precipitates of the AMCs is removed via line  40  and introduced into a residue handling zone  42 . In residue handling zone  42 , the residuum can be separated into solids, including any solids which were originally present in the feed stream from source  10  and any solids which are formed in flash vessel  12 , and a liquid waste stream. The solids can be separated from the liquids, if desired, by any solid-liquid process or other separation techniques well known to those skilled in the art and can be discharged in one or more streams, e.g., stream  44  to a suitable waste discharge receiver  46 . 
         [0019]    The composition of the feed stream from feed source  10  can vary widely, particularly in the case of a processing liquid used in the production of oil and/or gas from wells. However, as noted invariably it will contain processing liquid, water, dissolved salts, and at least one AMC. 
         [0020]    As noted, flash vessel  12  is under reduced pressure and is generally operated at a pressure of from about 0.03 to about 0.99 Bar and a temperature of from about 40 to about 165° C., depending upon the composition of the feed stream. Whether recycled directly to flash vessel  12  or, in admixture with the feed stream in line  11 , circulation of residuum through recycle loop R 1  is generally conducted at a flow rate of about 10 ft/s or greater, preferably about 10 to about 20 ft/s. 
         [0021]    Solids, water, and any other waste materials from product handling section  18  can be removed via line  43  and introduced into residue handling zone  42  and appropriately treated for disposal. 
         [0022]    As noted above, one of the primary goals of the present invention is the removal of AMCs, and more particularly, salts of AMCs from the feed stream. To this end, and as discussed above, one or more suitable precipitants from a precipitant source  36  is introduced via line  38  into flash vessel  12  via line  11 . It will be understood however, that the precipitant(s) can be introduced into the residuum recycle loop R 1  or directly into vessel  12 , if desired. The introduction of a precipitant allows removal of AMC precipitates during this reclaiming stage as opposed to requiring any pre-treatment of the feed stream prior to introduction into the reclaiming stage. 
         [0023]    The precipitants can be any of numerous anions that will react with the one or more AMCs that are present in the feed stream from feed source  10  to form a substantially water-insoluble salt. The AMCs can be anyone of the alkaline earth metal cations, but generally will be one of barium, calcium, magnesium, or strontium, and in particular, calcium and/or magnesium. Suitable precipitants include preferably water soluble salts such as water soluble carbonates, bicarbonates, hydroxides, sulfates, certain divalent carboxylic acid salts, such as oxalates, and the like. The selection and amount of precipitant(s) added will depend upon which and how much of the particular AMCs are present. This can be readily determined by well known analyses of the feed stream from the feed source  10  but is a function of the source of the feed stream. 
         [0024]    Referring now to  FIG. 2 , there is shown a schematic flow sheet of another embodiment of the present invention wherein there is a regenerator section, as depicted by the dotted box A and a reclaimer section as depicted by the dotted box B. Referring then to  FIG. 2 , a feed stream  50  from a feed source  52  is introduced into a regenerator column  54  which is basically a fractionation column. An overhead stream is removed from column  54 , via line  56 , while a residuum/bottoms stream is removed from column  54  via line  58 . The residuum stream is split into two portions, a first portion passing through a forced recycle loop R 2  comprising line  60 , pump  62 , line  64 , heat exchanger  68 , and in-line mixer  70  R 2  to be reintroduced into column  54 . This portion of the residuum stream can alternatively be admixed with the feed in line  50  to be introduced into column  54 . 
         [0025]    An overhead stream via line  56  passes through a reflux loop comprised of a condenser  72  and line  74  back into column  54 . A fraction of the overhead stream is sent via line  75  to a residue handling section  76  which performs substantially the same function described above with respect to product handling section  18  of the embodiment of  FIG. 1 . In this regard, it should be noted that the feed from feed source  52  comprises the processing liquid, water, any dissolved salts, and at least one AMC. Accordingly, the overhead vapour in line  56  from column  54  comprises primarily water since in all embodiments of the present invention the processing liquid comprises a higher boiling material than water. 
         [0026]    A second portion of the residuum stream from line  58  is sent via line  78 , pump  80 , and line  82  into a reclaimer shown generally as  84  forming part of reclaimer section B. For all intents and purposes, reclaimer  84  operates under substantially the same conditions of temperature, pressure, recycle flow rate, etc. as in the case of reclaiming embodiment shown in  FIG. 1 . An overhead stream  86  removed from reclaimer  84  is quite similar to overhead stream  14  removed from flash vessel  12  as in the embodiment shown in  FIG. 1 . In like fashion, the overhead fraction in line  86  is introduced into a product handling section  88 . As is the case in the embodiment shown in  FIG. 1 , the reclaimer  84  in reclaimer section B is under reduced pressure via a vacuum source  90  and line  92 . As is the case of the embodiment of  FIG. 1 , via suitable separation techniques well known to those skilled in the art and discussed above with respect to the embodiment of  FIG. 1 , a purified processing liquid is removed via line  94  and sent to a product recovery section  96  for reuse. 
         [0027]    As is the case in the embodiment shown in  FIG. 1 , a bottoms or residue fraction from reclaimer  84  is removed via line  85  and sent to residue handling section  76 . 
         [0028]    Via a precipitant source  100  and line  102 , a first portion of one or more precipitants is introduced via line  104  and line  50  into column  54 . A second portion of one or more precipitants from precipitant source  100  is introduced via line  104 , valve  106 , and line  108  into the reclaimer  84  as discussed above with respect to the embodiment of  FIG. 1 . As noted, the precipitant in line  108  is admixed with the residuum stream from column  54  and introduced with that residuum stream into reclaimer  84 . Thus, one or more precipitants is introduced both into the regenerator section A and the reclaimer section B. 
         [0029]    There is also a residue fraction removed from product handling section  88  via line  110  which is sent to residue handling section  76 , residue handling section  76 , as described above with respect to the embodiment of  FIG. 1 , serving to affect solid-liquid separation for discharge through one or more discharge lines  112  into waste receiver  114 . 
         [0030]    Conditions in the flash vessel forming part of reclaimer  84  are substantially the same as those described above with respect to the embodiment of  FIG. 1 . 
         [0031]    With respect to column  54 , column  54  is substantially a fractionator wherein the lighter water fraction is taken overhead via line  56  while processing liquid, salts including salts of the AMC and other heavies are removed via line  58 . Forced recycle loop R 2  can be operated under substantially the same conditions as forced recycle loop R 1  described above with respect to the embodiment described in  FIG. 1 . In general, column  54  will operate at a pressure of from 0.9 to 2 Bar and at temperatures of from 95 to 135° C. 
         [0032]    It will be understood that the embodiment of  FIG. 2  will generally be employed when a feed stream from source  52  has a relatively high dissolved salt content greater than about 3% by weight. Under these conditions, the circulating salts in recycle loop R 2  can become highly concentrated with a reduced water content in the recycle loop R 2 . Thus, in the embodiment shown in  FIG. 2 , when the water in recycle loop R 2  reaches a predetermined level relative to the salt content, a portion of the residuum, as shown, will be introduced into the reclaiming section B. If desired, this split of the residuum stream from line  58  can be accomplished using a control valve  79 . 
         [0033]    Generally speaking, once the water content in recycle loop R 2  falls below about 80 wt % of the recycle stream, the embodiment of  FIG. 2  would be employed wherein at least a portion of the residuum stream is sent to reclaiming section B. It will be understood that because of the varying nature of the feed source  52 , the composition of salts, water, and other constituents can vary widely the water content in the recycle loop R 2  is controlled by discharge through line  75  to residue handling section  76 . Thus, it is within the skill of the art to adjust/control the amount of residuum  58  to circulate through recycle loop R 2  as opposed to the amount of residuum in line  58  which is sent via line  82  reclaimer section B. 
         [0034]    Referring now to  FIG. 3 , there is shown another embodiment of the present invention. The embodiment shown in  FIG. 3  is very similar to that shown in  FIG. 2  with the exception that in the embodiment shown in  FIG. 3  the feed stream emanating from feed source  52 A has a salt loading, primarily dissolved, also at around 3 wt %. To more strictly control the concentration of the dissolved salts returning downhole in reuse of the processing liquid, a portion of the recycle stream line  82 A from column  54  is introduced into a clarification/separation system  200  from which is removed a virtually solids free fraction comprising processing liquid, water at the requisite concentration and residual dissolved salts which is transferred via line  202  to product handling section  88 . A second fraction from section  200  comprising solids, dissolved salts, water and any other residue type materials is removed via line  204  and introduced into reclaimer  84 . In reclaimer  84 , virtually all the dissolved salts and solids are removed and introduced via line  55  to residue handling zone  76  for eventual removal via line  112  to residue discharge location  114 . Highly purified processing liquid and water are directed to the product handling zone  88  for eventual recombination with the contents of line  202  prior to delivery via line  94  to a product recovery section  96  for reuse. Conditions in the regenerator column  54  in the regenerator zone A are generally as those described above with respect to the regenerator  54  shown in the embodiment of  FIG. 2 . Likewise, conditions in reclaimer  84  of the embodiment shown in  FIG. 3  are similar to those described above with respect to reclaimer  84  shown in the embodiment of  FIG. 2 . 
         [0035]    Via a precipitant source  100 , a first portion of one or more precipitants is introduced via line  102  and line  50  into column  54 . A second portion of one or more precipitants from precipitant source  100  is introduced via line  104 , valve  106 , and line  108  into the reclaimer  84  as discussed above with respect to the embodiment of  FIG. 1 . As noted, the precipitant in line  108  is admixed with the second stream from clarification section  200  via line  204  and introduced with that residuum stream into reclaimer  84 . Thus, one or more precipitants is introduced both into the regenerator section A and the reclaimer section B. 
         [0036]    As can be seen from the above, the process of the present invention provides a simple, efficient way to separate generally water-insolube salts/precipitants of alkaline earth metal cations from processing fluids such as those used in the production of oil and gas. In particular, the utilization of a forced recirculating reboiler loop as disclosed and claimed in many of the aforementioned patents and as described herein with respect to the embodiments of  FIGS. 1, 2, and 3 , eliminates the need for pretreatment of used processing liquids to remove the AMC salts prior to their regeneration and/or reclamation. It will be understood that if desired, a regenerator section can be installed downstream of the reclaimer section, especially, for example, in the embodiment shown in  FIG. 1  or integrated in the same. 
         [0037]    With respect to the handling of the streams containing solids of either the AMC salts or otherwise, traditional solids-liquids separation processes can be used, thus settling tanks, centrifuges, filter presses, etc. can be employed. Furthermore, in some cases wherein the dissolved salt content of the feed stream is high, it may be desirable in the residue handling section to selectively remove these soluble salts from the generally water-insoluble salts via methods well known to those skilled in the art. In still other cases, the dissolved salts and precipitated solids can be removed and disposed of together. 
         [0038]    Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.