Reactor and main fractionator configuration for producing diesel

Abstract

Methods and systems. For producing diesel arc provided. The method for producing diesel can include cracking a first hydrocarbon feed in a first riser under first cracking conditions to provide a first effluent containing a first light cycle oil, a heavy cycle oil, and a first bottoms and Fractionating at least a portion of the first effluent to separate the first bottoms and the heavy cycle oil from the first light cycle oil. The method can include cracking the separated first bottoms in a second riser under second cracking conditions to produce a second effluent containing a second light cycle oil and a second bottoms. The method can also include cracking the separated heavy cycle oil in the first riser under third cracking conditions to provide a third effluent and mixing the third effluent with the first hydrocarbon feed to provide the first cracking conditions.

What is claimed is: 
     
         1 . A method for producing diesel, comprising:
 cracking a first hydrocarbon feed in a first riser tinder first cracking conditions to provide a first effluent comprising a first light cycle oil, a heavy cycle oil, and a first bottoms;   fractionating at least a portion of the first effluent to separate the first bottoms and the heavy cycle oil from the first light cycle oil;   cracking the separated first bottoms in a second riser under second cracking conditions to produce a second effluent comprising a second light cycle oil and a second bottoms;   cracking the separated heavy cycle oil in the first riser under third cracking conditions to provide a third effluent; and   mixing the third effluent with the first hydrocarbon feed to provide the first cracking conditions.   
     
     
         2 . The method of  claim 1 , wherein the first hydrocarbon feed comprises gas oil, vacuum gas oil, hydrotreated vacuum gas oil, reduced crude, atmospheric tower bottoms, vacuum tower bottoms, or any mixture thereof. 
     
     
         3 . The method of  claim 1 , further comprising:
 separating the first effluent to produce a first spent-catalyst and a first gaseous product;   separating the second effluent to produce a second spent-catalyst and a second gaseous product;   combining the first spent-catalyst and the second spent-catalyst to provide a mixed spent-catalyst;   regenerating the mixed spent-catalyst by combusting coke in a regenerator to produce regenerated catalyst; and   recycling the regenerated catalyst to the first and second risers.   
     
     
         4 . The method of  claim 1 , wherein the first cracking conditions comprise temperatures from about 450° C. to about 530° C. and pressures from about 68 kPag to about 690 kPag. 
     
     
         5 . The method of  claim 4 , wherein the first cracking conditions further comprise a residence time of less than about 4 seconds and a catalyst-to-hydrocarbon weight ratio of catalyst to the first hydrocarbon feed of about 2:1 to about 6:1. 
     
     
         6 . The method of  claim 1 , wherein the second cracking conditions comprise temperatures from about 450° C. to about 650° C., pressures from about 68 kPag to about 690 kPag, a residence time of less than about 8 seconds and a catalyst-to-hydrocarbon weight ratio of catalyst to the first bottoms of about 10:1 to about 20:1. 
     
     
         7 . The method of  claim 1 , wherein the third cracking conditions comprise temperatures from about 500° C. to about 650° C., pressures from about 68 kPag to about 690 kPag, a residence time of less than about 8 seconds and a catalyst-to-hydrocarbon weight ratio of catalyst to the first heavy cycle oil of about 10:1 to about 20:1. 
     
     
         8 . The method of  claim 1 , further comprising fractionating at least a portion of the second effluent to provide the second light cycle oil and second bottoms, wherein the fractionating of the second effluent is independent of the fractionating of the first effluent. 
     
     
         9 . The method of  claim 1 , wherein the first light cycle oil and second light cycle oil have a combined yield of about 35% to about 60%. 
     
     
         10 . A method for producing diesel, comprising:
 cracking a first hydrocarbon feed in a first riser under first cracking conditions to provide a first effluent comprising a first light cycle oil, a heavy cycle oil, and a slurry oil;   fractionating at least a portion of the first effluent to separate the slurry oil and the heavy cycle oil from the first light cycle oil;   stripping the slurry oil to provide a first bottoms;   cracking the first bottoms in a second riser under second cracking conditions to produce a second effluent comprising a second light cycle oil and a second bottoms;   fractionating at least a portion of the second effluent to separate the second bottoms from the second light cycle oil;   cracking the separated heavy cycle oil in the first riser under third cracking conditions to provide a third effluent;   mixing the third effluent with the first hydrocarbon feed to provide the first cracking conditions; and   mixing the first light cycle oil with the second light cycle oil to provide a light cycle oil product.   
     
     
         11 . The method of  claim 10 , wherein the first hydrocarbon feed comprises a C 8 + hydrocarbons concentration from about 95 wt % to about 99 wt %. 
     
     
         12 . The method of  claim 10 , further comprising:
 separating the first effluent to produce a first spent-catalyst and a first gaseous product;   separating the second effluent to produce a second spent-catalyst and a second gaseous product;   combining the first spent-catalyst and the second spent-catalyst to provide a mixed spent-catalyst;   regenerating the mixed spent-catalyst by combusting coke in a regenerator to produce regenerated catalyst; and   recycling the regenerated catalyst to the first and second risers.   
     
     
         13 . The method of  claim 10 , wherein the first cracking conditions comprise temperatures from about 450° C. to about 530° C., pressures from about 68 kPag to about 690 kPag, a residence time of less than about 4 seconds and a catalyst-to-hydrocarbon weight ratio of catalyst to the first hydrocarbon feed of about 2:1 to about 6:1. 
     
     
         14 . The method of  claim 10 , wherein the second cracking conditions comprise temperatures from about 450° C. to about 650° C., pressures from about 68 kPag to about 690 kPag, a residence time of less than about 8 seconds and a catalyst-to-hydrocarbon weight ratio of catalyst to the first bottoms of about 10:1 to about 20:1. 
     
     
         15 . The method of  claim 10 , wherein the third cracking conditions comprise temperatures from about 500° C. to about 650° C., pressures from about 68 kPag to about 690 kPag, a residence time of less than about 8 seconds and a catalyst-to-hydrocarbon weight ratio of catalyst to the heavy cycle oil of about 10:1 to about 20:1. 
     
     
         16 . The method of  claim 10 , wherein the fractionating of the second effluent is independent of the fractionating of the first effluent. 
     
     
         17 . The method of  claim 10 , wherein the first hydrocarbon feed comprises gas oil, vacuum gas oil, hydrotreated vacuum gas oil, reduced crude, atmospheric tower bottoms, vacuum tower bottoms, or any mixture thereof. 
     
     
         18 . The method of  claim 10 , wherein the light cycle oil product has a yield of about 35% to about 60%. 
     
     
         19 . A method for producing diesel, comprising:
 cracking a first hydrocarbon feed in a first riser under first cracking conditions comprising temperatures from about 450° C. to about 530° C. to provide a first effluent comprising a first light cycle oil, a heavy cycle oil, and a slurry oil; fractionating at least a portion of the first effluent to separate the slurry oil and the heavy cycle oil from the first light cycle oil;   stripping the slurry oil to provide a first bottoms;   cracking the first bottoms in a second riser under second cracking conditions comprising temperatures from about 450° C. to about 650° C. to produce a second effluent comprising a second light cycle oil and a second bottoms;   fractionating at least a portion of the second effluent to separate the second bottoms from the second light cycle oil;   cracking the heavy cycle oil in the first riser under third cracking conditions comprising temperatures from about 500° C. to about 650° C. to provide a third effluent;   mixing the third effluent with the first hydrocarbon feed to provide the first cracking conditions;   mixing the first light cycle oil with the second light cycle oil to provide a light cycle oil product;   separating the first effluent to produce a first spent-catalyst and a first gaseous product;   separating the second effluent to produce a second spent-catalyst and a second gaseous product;   combining the first spent-catalyst and the second spent-catalyst to provide a mixed spent-catalyst;   regenerating the mixed spent-catalyst by combusting coke in a regenerator to produce regenerated catalyst; and   recycling the regenerated catalyst to the first and second risers.   
     
     
         20 . The method of  claim 19 , wherein the first hydrocarbon feed comprises gas oil, vacuum gas oil, hydrotreated vacuum gas oil, reduced crude, atmospheric tower bottoms, vacuum tower bottoms, or any mixture thereof. 
     
     
         21 . A system for producing diesel, comprising:
 a first riser comprising a first reaction zone and a second reaction zone, wherein the second reaction zone is adapted to crack a first hydrocarbon feed under first cracking conditions to provide a first effluent comprising a first light cycle oil, a heavy cycle oil, and a slurry oil;   a fractionator in fluid communication with the first riser, the fractionator adapted to fractionate at least a portion of the first effluent to separate the heavy cycle oil and the bottoms from the first light cycle oil;   a stripper in fluid communication with the fractionator, the stripper adapted to separate a first bottoms from the slurry oil;   a second riser for cracking the separated first bottoms under second cracking conditions to produce a second effluent comprising a second light cycle oil and a second bottoms; and   a mixing zone located in the first riser for mixing a third effluent with the first hydrocarbon feed to provide the first cracking conditions, wherein the first reaction zone of the first riser is adapted to crack the separated heavy cycle oil to provide the third effluent.   
     
     
         22 . The system of  claim 21 , further comprising:
 a first fluid outlet of the first riser in fluid communication with a first catalyst disengagement zone;   a second fluid outlet of the second riser in fluid communication with a second catalyst disengagement zone;   a first cracked product outlet in fluid communication with the first catalyst disengagement zone;   a second cracked product outlet in fluid communication with the second catalyst disengagement zone; and   a catalyst regenerator in fluid communication with the first and second catalyst disengagement zones.   
     
     
         23 . The system of claim wherein the first and second catalyst disengagement zones each comprise one or more cyclone separators. 
     
     
         24 . The system of  claim 22 , wherein the first catalyst disengagement zone is fluidly isolated from the second catalyst disengagement zone. 
     
     
         25 . The system of  claim 24 , further comprising a second fractionator in fluid communication with the second riser, wherein the second fractionator is fluidly isolated from the first fractionator.