Abstract:
A closed loop process for recovering purified processing fluid from contaminated processing fluid. The contaminated processing fluid is subjected to a first separation step, and there is recovered a first stream comprising the bulk of the processing fluid substantially free of contaminants, and a second stream containing processing fluid with concentrated levels of contaminants. The second stream is subjected to a second separation zone to produce a third stream comprising purified processing fluid and a fourth stream comprising contaminants.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to purifying processing fluids; e.g., solvents, chemicals, etc., used in various refinery and petrochemical operations. More particularly, the present invention relates to a process to maximize the recovery of a desired processing fluid from a mixture/solution of a processing fluid and contaminants. 
     2. Description of Prior Art 
     In refining, petrochemical and other industrial applications, processing fluids are used to perform certain functions; e.g., remove acidic components from gas streams, as solvents in extractive distillation processes, etc. In addition, heavy components (contaminants) become entrained in the processing fluid. In most cases, these processing liquids are expensive and/or pose environmental disposal hazards and accordingly, must be purified or reclaimed for further use. In addition to the use of processing fluids in refinery/petrochemical operations, processing fluids can be used in other environments; e.g., the well known use of glycols to prevent gas hydrate formation in offshore oil and gas operations. 
     Typically, in purifying/reclaiming the processing fluids, by whatever method, there is a waste stream which contains entrained impurities which have been removed during the purifying/reclaiming process. As noted, many of these processing fluids are quite expensive and the goal of any purifying/reclaiming process is to ensure that, to the extent possible, all of the processing fluid has been recovered; i.e., there is essentially no or a de minimus amount present in the waste stream from the purifying/reclaiming process. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present invention provides a closed loop process or method for removing contaminants from a used processing fluid, so that the processing fluid can be recycled for further usage. 
     In another aspect, the present invention provides a two-step method to maximize recovery of a processing fluid from a processing fluid/contaminant mixture or solution. In the first step, the processing fluid/contaminant mixture is subjected to a first separation zone, generally a vacuum flash to provide a first stream comprising the bulk of the processing fluid freed of contaminants; and a second stream containing the remainder of the processing fluid and contaminants. In the second step of the process, the second stream is subjected to a second separation zone, preferably in a wiped film evaporator, to produce a third stream comprising purified processing fluid and a fourth stream comprising waste products/contaminants from the processing fluid/contaminant mixture. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The single FIGURE is a schematic flow sheet showing one embodiment of the present invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     While the present invention will be described with respect to the recovery of amines such as diethanol amines used to scrub gas streams to natural gas, to absorb components such as sulphur containing and other gases, it will be understood, as noted above, that it is not so limited. Accordingly, the process of the present invention can be used to reclaim and/or purify any number of processing liquids used in any number of processes. 
     As noted above, in addition to the absorbed components; e.g., the acidic gases, the processing fluid becomes entrained with heavy, generally non-absorbed components which, over time deleteriously affects the efficacy of the processing fluid, causes damage to equipment, etc. One of the goals of the present invention is to separate the generally non-absorbed, heavy components, hereafter referred to as contaminants, impurities or waste products from the processing fluid. 
     Referring then to the single FIGURE, a contaminated stream of an alkanol amine (processing fluid) and impurities which has been adjusted to a pH of from about 8 to 11 is fed via line  10  where it is mixed with a stream from line  13 , described more fully hereafter. The combined streams pass through and are heated in a steam heat exchanger  14 , the temperature being raised to about 250-350° F., and introduced via line  16  to a flash vessel  18 . It will be understood that flash vessel  18  can take many different forms, and is typically operated under vacuum, in this case provided by a vacuum system shown schematically as  20 . 
     As noted, the feed stream  10  is mixed with a stream from line  13 , the stream in line  13  being excess liquid from flash vessel  18 , which requires reboil. The remaining portion of the feed to vessel  18  is pumped via pump  42  and line  44  to a distillation zone; e.g., an evaporator, particularly a wiped film evaporator  46 , to distill the processing fluid and separate it from various, low vapour pressure impurities/contaminants. As noted, excess liquid and low vapour pressure impurities not sent via line  44  to evaporator  46  are recirculated as reboil to flash vessel  18 . The flash loop allows for steady and consistent feed rate to evaporator  46  which, as is known to one skilled in the art, is essential to its operation. A back pressure device (not shown) is in line  16  just prior to the stream passing through line  16  entering flash vessel  18  to eliminate any two phase flow in the circulation of the excess liquid from flash vessel  18 . 
     The high vapour pressure components that boil at preset operating temperatures and pressures in flash vessel  18  form vapours that are drawn by a vacuum system  20  via line  22  through condenser  24  to form a liquid which accumulates in receiving vessel  26 . 
     A slip stream, which constitutes typically 10 to 30%; e.g., 20%, of the total feed stream introduced into flash vessel  18 , as noted, is introduced into evaporator  46  via line  40 , pump  42 , and line  44 . Distillate from evaporator  46  is removed via line  52  and collects in receiving vessel  54 . Alternatively, the distillate from evaporator  46 , as shown, can be discharged as a product stream via line  55  or sent to receiving vessel  26 , wherein it is mixed with liquid product initially flashed from flash vessel  18 . 
     In the case of alkanol amines, the operating conditions in flash vessel  18  versus the operating condition in wiped film evaporator  46  are such that the temperature conditions in evaporator  46  are generally in the range of from 300° to 400° F. and under a vacuum of less than about 25 mm Hg preferably less than 10 mm. Hg, in order to effect proper distillations, whereas in the case of flash vessel  18 , the temperature can range from about 250° to 350° F., and the pressure from about 30 to 500 mm Hg. 
     The impurities or waste from evaporator  46  are removed via line  48  and pump  50 , and discharged as waste through line  38 . Typically, the amount of impurities in the contaminated feed stream; i.e., the stream in line  10 , are relatively small and accordingly, recycling of separated impurities back to evaporator  46  can be used. 
     As noted, purified processing fluid is collected in receiving vessel  26 , both from initial flash from flash vessel  18  and the distillate from evaporator  46  and constitutes the final product which is removed via line  28 . 
     Vacuum system  20 , as noted above, provides reduced pressure (30 to 500 mm Hg) in the flash vessel  18 , and a deeper vacuum (less than 25 mm Hg, preferably less than 10 mm. Hg) in evaporator  46 . 
     Any low boiling, high vapour pressure components that are not condensed elsewhere in the system are drawn in to vacuum system  20  and exit as a recovered component. Generally, these low boiling, high vapour pressure components are sulphur-containing gases or similar materials, which the processing fluid is designed to absorb. Thus, they are not a contaminant or waste product as are the heavier components that become entrained in the processing fluid. Accordingly, they, together with the processing fluid free of the entrained heavier components, can be further used. The recovered components are compressed in compression station  29  and are introduced into the final product stream  28  via line  30 . This final step allows recovery of all components, other than the undesirable impurities and waste from the alkanol amine. This novel approach makes the process a closed loop system (only rejecting the components considered as waste) and produces no waste vapour (emissions) stream. Water condensate from vacuum system  20  is directed to a receiving vessel  34  via line  32  and, as shown, can be recycled via pump  36  into line  38  to dilute and allow better flow of the concentrated impurities (waste) from evaporator  46 . 
     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 are 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.