Abstract:
The present invention provides a method and apparatus for the recovery of salt from a glycerine process, allowing the salt to be used in a brine solution. A salt settling tank is positioned inline between the foots from a crude still bottom and a foot still. Salt settles to the bottom of the settling tank and into a salt receiver positioned below, while clarified liquid overflows to the foot still. Salt from the salt receiver is then semi-continuously transferred into a salt extractor where the salt is removed from the mother liquor. A condensate is then circulated into the salt extractor and the salt slurry is then stored in a brine storage tank.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of separators. More specifically, the present invention relates to a system for separating salt in a glycerine refining process. 
     2. Background of the Prior Art 
     Recovery of glycerine in the typical glycerine refining process invariably involves a step wherein at least a portion of the glycerine product is distilled overhead from a salt and heavy ends bottoms product. This bottoms product known conventionally as the glycerine crude still bottom. The crude still bottom contains a large weight percentage of salt, in addition to unrecovered glycerine. The crude still bottom would be fed to the glycerine foots bottom or foots still to remove more glycerine by evaporation. The remainder of the heavy residue and salt slurry is disposed of such as in a landfill. It is becoming increasingly difficult and/or expensive to dispose of these waste streams. Methods of reducing the waste and recycling the stream are critical in the glycerine process. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for the recovery of salt from a glycerine refining process. 
     Foots from a crude still bottom are transported to a foots salt settling tank. In the foot salt settling tank, the crystallized salt is allowed to settle to the bottom of the foots salt settling tank leaving a clarified liquid fraction on the top portion. An overflow outlet is positioned in a sidewall of the foots salt settling tank allowing the clarified liquid to spill over into a foot still once the clarified liquid reaches the level of the overflow outlet. 
     A salt receiver is positioned below the foots salt settling tank. A line feeds salt from the lower portion of the foots salt settling tank to an inlet in the top portion of the salt receiver. The salt receiver has a sight glass positioned on a sidewall. When the level of salt in the salt receiver reaches the sight glass, the salt extractor is prepared for automatic transfer of the salt from the salt receiver. When this occurs, the line between the foots salt settling tank and salt receiver is closed and a vacuum is pulled within the salt extractor. 
     The line between the salt receiver and salt extractor is opened to deliver the salt and mother liquor from the outlet at the bottom portion of the salt receiver to the inlet in the top portion of the salt extractor which is positioned below the salt receiver. The salt receiver is agitated so as to capture salt crystals in a mesh, and to blow back the mother liquor into the salt receiver. Once the salt has been extracted and the mother liquor substantially removed from the extractor, the salt crystals can be prepared for use in brine making. 
     The salt is prepared for brine making by circulating a steam condensate and delivering the slurry or brine solution to a brine storage tank. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is an organizational figure illustrating the relationship of what is shown schematically in  FIGS. 1   a  and  1   b.    
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a foots salt settling tank  370  for receiving foots  40  from a crude still bottom. The settling tank  370  includes a housing  70  for receiving foots  40  from the crude still bottom therein. The foots from the crude still bottom  40  enters the settling tank  370  through an inlet  72  in a sidewall  74  of the housing  70 . The housing  70  has a conically shaped lower portion  76 . An outlet  78  is positioned at the nose  80  of the lower portion  76  to provide fluid communication between the settling tank  370  and a salt receiver  375 . An overflow outlet  82  is positioned in the sidewall  74  of the foots salt settling tank  370  to allow fluid communication between the foots salt settling tank  370  and a foot still  84 . A top outlet  86  is positioned on a top portion  88  of the foots salt settling tank  370  to allow fluid communication with a foot still condenser  90 . 
     In operation, a line  94  connecting the crude still bottom  40  to the inlet  72  allows the foots from the crude still bottom  40  to enter the foots salt settling tank  370 . The foots from the crude still bottom  40  contains a salt slurry and glycerine, among other residue components. This foots from the crude still bottom  40  is continuously discharged by a foots pump  96  which delivers the glycerine laden residue to the foots salt settling tank  370 . 
     The foots salt settling tank  370  is configured to separate the crystallized salt from the glycerine by allowing the crystallized salt to settle towards the bottom portion  76  of the foots salt settling tank  370 , forming a foots liquid fraction  98  above the salt settling portion  100 . This creates a foots liquid fraction  98  that is free of crystallized salt. The overflow outlet  82  is positioned within the foots salt settling tank  370  such that the liquid fraction  98  overflows into a foots still  84  when the level of the liquid fraction  98  reaches the overflow outlet  82 . In the foots still  84 , glycerine is distilled from the desalted liquid fraction, maximizing glycerine recovery yield. 
     A gas outlet  86  is positioned at a top portion  88  of the housing  70  for allowing gases entering and/or forming within the foots salt settling tank  370  to be removed from the foots salt settling tank  370  to a foots still condenser  90 . 
     The bottom outlet  78  in the lower portion  76  of the foots salt settling tank  370  allows crystallized salt to pass through the outlet  78  and accumulate in the salt receiver  375 . A solenoid valve  302  is positioned between the feed line  92  connecting the outlet  78  of the foots salt settling tank  370  to the inlet  102  of the salt receiver  375 . In operation the valve  302  is left open to allow salt to continuously settle into the salt receiver  375 . 
       FIG. 1  also shows the salt receiver  375 . The salt receiver  375  is positioned beneath the foots salt settling tank  370 . The salt receiver  375  includes a housing  104  defining a cavity for receiving crystallized salt and mother liquor from the foots salt settling tank  370  through a salt inlet  102  in a top portion  106  of the housing  104  of the salt receiver  375 . 
     The salt receiver  375  has a conical lower portion  108  having an outlet  110  at a nose  112  for dispensing salt into a salt extractor  380  positioned below the salt receiver  375 . A line  114  extending between the outlet  110  of the salt receiver  375  and an inlet  200  of the salt extractor  380  has one or more valves  305 ,  306  for selectively opening and closing the line  114 . 
     A sight glass  118  is positioned in a sidewall of the housing  104  of the salt receiver  375 . When the salt level in the salt receiver  375  reaches the sight glass  118 , the salt extractor  380  is prepared for transfer of the salt from the salt receiver  375  to the salt extractor  380 . A vacuum is pulled on the salt extractor  380  and the valves  305 ,  306  between the salt extractor  380  and salt receiver  375  are opened, and the valve  302  between the toots salt settling tank  370  and salt receiver  375  is closed. 
     Transfer of the salt from the salt receiver  375  to the salt extractor  380  is automatically initiated upon the salt reaching the level of the sight glass  118  in a sequence of actuated valves which pressurize the salt receiver  375  and generate a vacuum in the salt extractor  380 . Upon completion of transfer of the salt to the salt extractor  380  the valves  305 ,  306  between the salt receiver  375  and salt extractor  380  are closed to allow the salt extractor  380  to extract salt. 
       FIG. 1  shows the salt extractor  380  for extracting crystallized salt from the mother liquor in which it is entrained. The salt extractor  380  is positioned below the salt receiver  375  and connected by a line  114  therebetween. The salt extractor  380  has a housing  400  defining a cavity for receiving the salt and mother liquor via an inlet  200  in a top portion  402  of the housing  400  of the salt extractor  380 . 
     The salt extractor  380  is prepared for transfer of salt from the salt receiver  375  when the salt level in the salt receiver  375  has reached the sight glass  118 . At such time, a vacuum is pulled on the salt extractor  380  by opening the valves  304 ,  316  at the vacuum outlet  404  and at the start-up ejector  406 . 
     Salt is then discharged from the salt receiver  375  to the salt extractor  380  by opening the valves  305 ,  306  in the line  114 , wherein at such time the valve  302  between the foots salt settling tank  370  and salt receiver  375  is closed. The valves  304 ,  316  used to create a vacuum remain open during this step. 
     When the transfer of the salt and mother liquor from the salt receiver  375  to the salt extractor  380  is complete, the in-line valves  305 ,  306 , motive steam valve  316 , and vacuum valve  304  are closed. The mother liquor is pushed back by opening the agitation valves  301 ,  303 ,  308 ,  311 . The salt extractor  380  is further agitated by opening the lower outlet valve  310 . Additional agitation is created by opening the side outlet valve  309 . 
     The lower outlet valve  310  and side outlet valve  309  of the salt extractor  380  are then closed to push the remaining mother liquor into the salt receiver  375  via the agitation valves  301 ,  303 ,  308 ,  311 . The lower outlet valve  310  and side outlet valve  309  may then again be reopened to continue to return the mother liquor to the salt receiver  375 . This process may be repeated as necessary to achieve a predetermined extraction efficiency. Once the transfer of the mother liquor to the salt receiver  375  is complete, the agitation valves  303 ,  308 ,  311  are closed and a vacuum is pulled on the salt receiver  375  by leaving open the corresponding vacuum valve  301 . 
     The salt extractor  380  has a filtering mesh  408  in its interior. During extraction, the salt crystals are retained in the mesh  408  and the mother liquor is separated out and blown back to the salt receiver  375 . Then the foot salt settling vessel  370  and foots salt receiver  375  are put back in line to continue the salt settling process. 
     Once the mother liquor has been removed from the extractor  380  leaving only salt crystals, the salt crystals can be used to make brine by filling the salt extractor  380  with condensate and circulating it in the foots salt extractor  380  by opening a condensate inlet and circulation valves  304 ,  313 ,  314 ,  316  and corresponding pump  381 , while maintaining the vacuum valve  301  in salt receiver  375  open. 
     The salt in the salt extractor  380  is mixed with steam condensate and the slurry or brine solution is sent to the brine storage  410 . 
     To make brine, the salt extractor  380  is filled with condensate, which is circulated therein. The condensate enters the salt extractor  380  through a condensate inlet valve  412 . Condensate is circulated by opening a series of circulation valves  304 ,  313 ,  314  and a steam valve  316  and pumping the condensate by a pump  381 . The vacuum valve  301  in the salt receiver  375  is kept open during this process. 
     Once the condensate has circulated and filled the salt extractor  380 , the condensate inlet valve  313 , vacuum valve  301  and steam valve  316  are closed. The steam agitator valve  307  is used to vent to atmosphere, when circulating and agitating the salt extractor  380 . Agitation is stopped by closing the steam agitator valve  311  and continuing to circulate the condensate. 
     The foots salt settling tank  370  and salt receiver  375  are put back in line by opening the in-line valve  302 . Brine is emptied from the salt extractor  380  into a brine holding tank  410  by closing the upper agitation valve  314  and opening the brine holding tank inlet valve  315  allowing the previously recirculated brine to be sent to the brine storage  410  via an outlet line  420 . 
     After the extraction of salt a vacuum is pulled on the salt extractor  375 , and the pump  381  is shut off.