Process for converting a vacuum tower bottoms stream

Abstract

A process for improving a recovery from a bottoms stream from a vacuum tower. The bottom stream is passed to a first cracking zone and unconverted material from the first cracking zone is passed to a second cracking zone. The first cracking zone may include a visbreaking reactor. The second cracking zone may include a slurry hydrocracking reactor.

What is claimed is: 
     
         1 . A process for increasing a recovery from a bottom stream from a vacuum tower, the process comprising:
 passing a bottoms stream from a vacuum tower to a first cracking zone to produce a converted stream and an unconverted stream; and,   passing the unconverted stream of the first cracking zone to a second cracking zone to produce a second converted stream and a pitch stream, wherein the second cracking zone is operated with a pressure that is higher than the first cracking zone.   
     
     
         2 . The process of  claim 1  wherein the first cracking zone includes a visbreaking reactor. 
     
     
         3 . The process of  claim 2  wherein the second cracking zone includes a slurry hydrocracking reactor. 
     
     
         4 . The process of  claim 1  wherein the first cracking zone is free from hydrocracking catalyst. 
     
     
         5 . The process of  claim 4  wherein the second cracking zone includes a hydrocracking catalyst. 
     
     
         6 . The process of  claim 1  wherein the converted stream from the first cracking zone includes gas oil, and the process further comprising:
 passing at least a portion of the gas oil to the second cracking zone. 
 
     
     
         7 . The process of  claim 6  wherein the second cracking zone has a combined feed ratio of at least 1.2. 
     
     
         8 . The process of  claim 1  wherein at least approximately 87% of the bottom stream from the vacuum tower is recovered converted product. 
     
     
         9 . A process for reducing a viscosity of a bottoms stream from a vacuum tower, the process comprising:
 passing a bottoms stream from a vacuum tower to a cracking zone including a visbreaking reactor, the cracking zone providing a converted stream and an unconverted stream; and,   passing the unconverted stream from the cracking zone to a hydrocracking zone, wherein the unconverted stream from the cracking zone has a lower viscosity than the bottoms stream from the vacuum tower.   
     
     
         10 . The process of  claim 9  wherein the hydrocracking zone includes a slurry hydrocracking reactor. 
     
     
         11 . The process of  claim 9  wherein the hydrocracking zone includes a catalyst. 
     
     
         12 . The process of  claim 9  further comprising:
 separating the converted stream from the cracking zone into at least a gas oil stream. 
 
     
     
         13 . The process of  claim 12  further comprising:
 passing the gas oil stream to the hydrocracking zone. 
 
     
     
         14 . The process of  claim 13  wherein the hydrocracking zone provides a second converted product stream, and the process further comprising:
 separating the second converted product stream into at least a second gas oil stream; and, 
 recycling the second gas oil stream to the hydrocracking zone. 
 
     
     
         15 . The process of  claim 14  wherein the hydrocracking zone has a combined feed ratio of at least 1.2. 
     
     
         16 . The process of  claim 15  wherein the cracking zone is operated to convert approximately 10 to 40% of material with a boiling point of 349° C. (660° F.) of higher from the bottoms stream of the vacuum tower. 
     
     
         17 . The process of  claim 15  wherein the hydrocracking zone is operated to convert at least approximately 87% of the unconverted stream from the cracking zone. 
     
     
         18 . A process for increasing a conversion of a bottoms stream from a vacuum tower, the process comprising:
 passing a bottoms stream from a vacuum tower to a visbreaking reactor, the visbreaking reactor converting approximately 25 to 55% of material with a boiling point of 521° C. (970° F.) of higher from the bottoms stream into a converted stream and the remaining portion of the bottoms stream comprising an unconverted stream; and,   passing the unconverted stream from the visbreaking reactor to a slurry hydrocracking reactor, wherein the unconverted stream from the visbreaking reactor has a lower viscosity than the bottoms stream from the vacuum tower.   
     
     
         19 . The process of  claim 18  further comprising:
 converting approximately 10 to 20% of the bottoms stream from the vacuum tower into a gas oil stream. 
 
     
     
         20 . The process of  claim 19  further comprising:
 passing a portion of the gas oil stream to the slurry hydrocracking reactor.