Fluidized bed coking with fuel gas production

Abstract

A Flexicoking™ unit which retains the capability of converting heavy oil feeds to lower boiling liquid hydrocarbon products while making a fuel gas from rejected coke to provide only a minimal coke yield. The heater section of the conventional three section unit (reactor, heater, gasifier) is eliminated and all or a portion of the cold coke from the reactor is passed directly to the gasifier which is modified by the installation of separators to remove coke particles from the product gas which is taken out of the gasifier for ultization. In one embodiment, a portion of cold coke is transferred directly from the reactor to the gasifier, and another portion of cold coke is combined with hot, partly gasified coke particles transferred directly from the gasifier to the reactor. The hot coke from the gasifier is passed directly to the coking zone of the reactor to supply heat to support the endothermic cracking reactions and supply seed nuclei for the formation of coke in the reactor. Coke is withdrawn from the gasifier to remove excess coke and to purge the system of metals and ash.

1 . A coking process for converting a heavy hydrocarbon feedstock to lower boiling products in a fluid coking process unit comprised of a fluid coking reactor and a gasifier, comprising:
 (i) introducing the heavy hydrocarbon feedstock into the coking zone of a fluid coking reactor containing a fluidized bed of solid particles maintained at coking temperatures to produce a vapor phase product including normally liquid hydrocarbons, while coke is deposited on the solid particles forming cold coke to be transferred;   (ii) transferring the cold coke by passing a first portion of the cold coke directly to the gasifier,   (iii) contacting the cold coke in the gasifier with steam and an oxygen-containing gas in an oxygen limited atmosphere at an elevated temperature of about 850 to 1000° C. and at a pressure of from about 0 to 1000 kPag to heat the cold coke into hot coke and form a fuel gas product comprising carbon monoxide and hydrogen, wherein the gasifier comprises a gasification vessel having an internal cyclone and/or an internal sintered porous metal or ceramic solids/gas filter, to separate hot coke in the gasifier from the fuel gas product,   (iv) recycling the hot coke directly from the gasifier to the coking zone, with no intervening reaction vessel, to supply heat to the coking zone, and   (v) combining a second portion of the cold coke formed in step (i) with the hot coke formed in step (iii) prior to being recycled to the coking zone.   
     
     
         2 . A process according to  claim 1  in which the oxygen-containing gas comprises air or oxygen-enriched air. 
     
     
         3 . A process according to  claim 1 , wherein the portion of cold coke in step (ii) is passed from one end of a tubular transfer line connected to a coke outlet of the fluid coking reactor and the other end connected to a coke inlet of the gasifier with no intervening reaction vessel. 
     
     
         4 . A process according to  claim 1 , wherein the gasification vessel has an internal cyclone. 
     
     
         5 . A process according to  claim 1 , wherein the elevated temperature of step (iii) is from about 900 to 980° C. 
     
     
         6 . A process according to  claim 1 , wherein the pressure of step (iii) is from about 200 to 400 kPag. 
     
     
         7 . A process according to  claim 1 , wherein the mass flow-rate of the second portion of cold coke is about 5% to 50% of the total mass flow rate of the total cold coke being transferred from (i). 
     
     
         8 . A process according to  claim 1 , further comprising a third portion of cold coke to be combined with the hot coke formed in step (iii) prior to being recycled to the coking zone. 
     
     
         9 . A fluid coking unit for converting a heavy hydrocarbon feedstock to lower boiling products and for producing a fuel gas product in a fluid coking process unit comprised of a fluid coking reactor section and a gasifier section, comprising:
 (i) a fluid coking reactor section with an inlet for a heavy hydrocarbon feedstock, an outlet for cracked hydrocarbon vapors at the top of the reactor, an inlet at the bottom of the reactor for a fluidizing gas, an inlet for heated solid particles and a solid particle outlet at the bottom of the reactor for solid particles with coke deposited on them forming cold coke,   (ii) a gasifier section with an inlet for steam and oxygen-containing gas at its bottom, a solid particle inlet for the cold coke, an outlet for fuel gas at its top and a solid particle outlet for solid particles heated in the gasifier forming hot coke,   (iii) a transfer line for passing the hot coke from the solid particle outlet of the gasifier section to the solid particle inlet of the reactor section for recycling the hot coke from the gasifier section to the reactor section to supply heat to the coking zone of the reactor, and   (iv) a transfer line for passing (a) a first portion of the cold coke from the reactor solid particle outlet directly to the solid particle inlet of the gasifier section, and (b) a second portion of the cold coke from the reactor solid particle outlet to be combined with the hot coke in the transfer line for passing the hot coke to the solid particle inlet of the reactor section.   
     
     
         10 . A fluid coking unit according to  claim 9  comprising (a) one transfer line for passing a portion of the cold coke from the reactor solid particle outlet directly to the solid particle inlet of the gasifier section, and (b) a separate transfer line for passing a portion of the cold coke from the reactor solid particle outlet to be combined with the hot coke in the transfer line for passing the hot coke to the solid particle inlet of the reactor section. 
     
     
         11 . A fluid coking unit according to  claim 9  in which the gasifier section includes a gasifier vessel having an internal cyclone to separate the hot coke from the fuel gas. 
     
     
         12 . A fluid coking unit according to  claim 9  in which the gasifier section includes a gasifier vessel in which the cold coke is contacted with the steam and oxygen-containing gas and an internal cyclone for separating the hot coke from fuel gas. 
     
     
         13 . A fluid coking unit according to  claim 9  in which the gasifier section includes a main gasifier vessel in which the cold coke is contacted with the steam and oxygen-containing gas to form fuel gas and a separator vessel having (i) a gas inlet connected to the main gasifier vessel, (ii) a cyclone for separating the hot coke from the fuel gas and (iii) a solid particle return line connecting the separator vessel to the main gasifier vessel for returning separated hot coke to the main gasifier vessel.