Process of Modification of a Feedstock in a Delayed Coking Unit

Abstract

A process is described of delayed coking optimized for greater yield of diesel oil from coke by means of modifications to the feedstock in a Delayed Coking Unit. According to the present invention in a first embodiment of the invention the feedstock includes the bottom product of the vacuum distillation tower, known in the prior art as vacuum residuum and the heavy gas oil from coke obtained in the fractionation tower and recycled to comprise the aforesaid combined feedstock. In a second embodiment of the present invention the feedstock consists of: the bottom residuum proceeding from the atmospheric distillation tower, known in the prior art as atmospheric residuum, and heavy gas oil from coke obtained in the fractionation tower and recycled to comprise the aforesaid feedstock of the unit.

1 . A process for modification of a feedstock in a delayed coking unit wherein:
 a fresh feedstock ( 1 ) is fed to a fractionation tower ( 2 ) wherefrom one or more derivatives are removed;   a bottom product ( 9 ) of the fractionation tower ( 2 ) is fed to a furnace ( 10 ) such that one or more thermal cracking reactions may be initiated;   effluent from the furnace ( 11 ) is subsequently sent to a coke drum ( 12 ) wherein the thermal cracking and coking and/or carbonisation reactions are completed, generating from the coke drum ( 13 ) coke and an effluent comprising light hydrocarbons;   the effluent from the coke drum ( 13 ) is subsequently sent to the fractionation tower ( 2 );   
       characterised in that to the bottom product ( 9 ) of the fractionation tower ( 2 ) there is added a fraction ( 8 ′) of heavy gas oil from coke ( 8 ). 
     
     
         2 . A process according to  claim 1  in which the one or more derivatives comprise one or more of fuel gas, LPG ( 3 ), light naphtha ( 4 ), heavy naphtha ( 5 ), light gas oil ( 6 ), medium gas oil ( 7 ) and heavy gas oil from coke ( 8 ). 
     
     
         3 . A process according to  claim 1  or  2 , characterised in that the percentage by volume of the fraction ( 8 ′) of heavy gas oil from coke ( 8 ) in relation to the fresh feedstock ( 1 ) is from 16% to 50%, preferably from 20% to 40%. 
     
     
         4 . A process according to  claim 1 ,  2  or  3 , characterised in that the fraction ( 8 ′) of heavy gas oil from coke ( 8 ) is added to the bottom product ( 9 ) by means of a line external to the fractionation tower ( 2 ). 
     
     
         5 . A process according to any preceding claim, characterised in that the aforesaid fraction ( 8 ′) of heavy gas oil from coke ( 8 ) is added to the bottom product ( 9 ) within the fractionation tower ( 2 ). 
     
     
         6 . A process according to any preceding claim, characterised in that the feedstock of a delayed coking unit is the bottom residuum ( 18 ) of the atmospheric distillation tower ( 15 ).