Plant and method for vacuum distillation of hydrocarbon liquids

Abstract

A vacuum distillation system and method utilizing an auxiliary, low capacity vacuum producing ejector operated in parallel with a primary ejector during the winter months enables significant reduction in the absolute pressure of a vacuum distillation column. Operation of a vacuum distillation tower at lower absolute pressures results in increased yield of desirable vacuum distillation products.

1 . A method for vacuum distillation of a hydrocarbon liquid during cool season months comprising the steps of: 
 a. feeding the hydrocarbon liquid to a vacuum distillation column;    b. evacuating a first hydrocarbon-vapor product from the distillation column by a primary vacuum producing ejector and at least one auxiliary vacuum producing ejector, wherein the primary vacuum producing ejector and the at least one auxiliary vacuum producing ejector are connected in parallel to a source of motive stem;    c. circulating a cooling water stream through a first condenser and at least one second condenser;    d. at least partially condensing the first hydrocarbon-vapor product in the first condenser to form a first condensate and second hydrocarbon vapor product;    e. discharging the first condensate to a condensate collection vessel;    f. evacuating the second hydrocarbon vapor product by at least one second stage vacuum producing ejector to the at least one second condenser to form a second condensate;    g. discharging the second condensate to the condensate collection vessel.    
   
   
       2 . The method of  claim 1  wherein the auxiliary vacuum producing ejector of step b is connected to a source of motive steam in parallel with the primary vacuum producing ejector, a first valve is connected between the vacuum distillation column and the at least one auxiliary vacuum producing ejector, a second valve is connected between the at least one auxiliary ejector and the first condenser and a third valve is connected between the at least one auxiliary ejector and the source of motive steam.  
   
   
       3 . The method of  claim 1  or  2  wherein the auxiliary vacuum producing ejector has a suction load capacity about 2 percent to 20 percent of the suction load capacity of the primary vacuum producing ejector.  
   
   
       4 . The method of  claim 1  or  2  wherein the auxiliary vacuum producing ejector has a suction load capacity about 5 percent to 15 percent of the suction load capacity of the primary vacuum producing ejector.  
   
   
       5 . The method of  claim 1  or  2  wherein the auxiliary vacuum producing ejector has a suction load capacity about 10 percent of the suction load capacity of the primary vacuum producing ejector.  
   
   
       6 . The method of  claim 1  or  2  wherein the auxiliary vacuum producing ejector is operated when the cooling water stream temperature during the cool season is at least 10° F. lower than the cooling water stream temperature during the warm season.  
   
   
       7 . The method of  claim 1  or  2  wherein the first condenser pressure during the cool season is between about 55 percent and 90 percent of the first condenser pressure during the warm season.  
   
   
       8 . The method of  claim 1  or  2  wherein the first condenser pressure average during the cool season is about 65 to 75 percent of the first condenser pressure average during the warm season.  
   
   
       9 . The method of  claim 1  or  2  wherein the auxiliary vacuum producing ejector is operated in parallel with the primary ejector.