Process and apparatus for upgrading FCC product with additional reactor with thorough mixing

#This invention relates generally to processes for the fluidized catalytic cracking (FCC) of heavy hydrocarbon streams. More specifically, this invention relates to processes for upgrading catalytically cracked hydrocarbon feeds in a discrete reactor vessel.

#The FCC process is carried out by contacting the starting material whether it be vacuum gas oil, reduced crude, or another source of relatively high boiling hydrocarbons with a catalyst made up of finely divided or particulate solid material. The catalyst is transported in a fluid-like manner by passing gas or vapor through it at sufficient velocity to produce a desired regime of fluid transport. Contact of the oil with the fluidized material catalyzes the cracking reaction. The cracking reaction deposits coke on the catalyst. Catalyst exiting the reaction zone is spoken of as being “spent”, i.e., partially deactivated by the deposition of coke upon the catalyst. Coke is comprised of hydrogen and carbon and can include other materials in trace quantities such as sulfur and metals that enter the process with the starting material. Coke interferes with the catalytic activity of the spent catalyst by blocking acid sites on the catalyst surface where the cracking reactions take place. Spent catalyst is traditionally transferred to a stripper that removes adsorbed hydrocarbons and gases from catalyst and then to a regenerator for purposes of removing the coke by oxidation with an oxygen-containing gas. An inventory of catalyst having a reduced coke content, relative to the spent catalyst in the stripper, hereinafter referred to as regenerated catalyst, is collected for return to the reaction zone. Oxidizing the coke from the catalyst surface releases a large amount of heat, a portion of which escapes the regenerator with gaseous products of coke oxidation generally referred to as flue gas. The balance of the heat leaves the regenerator with the regenerated catalyst. The fluidized catalyst is continuously circulated between the reaction zone and the regeneration zone. The fluidized catalyst, as well as providing a catalytic function, acts as a vehicle for the transfer of heat from zone to zone. The FCC processes, as well as separation devices used therein are fully described in U.S. Pat. No. 5,584,985 B1 and U.S. Pat. No. 4,792,437 B1, the contents of which are hereby incorporated by reference. Specific details of the various contact zones, regeneration zones, and stripping zones along with arrangements for conveying the catalyst between the various zones are well known to those skilled in the art.

#The FCC reactor cracks gas oil or heavier feeds into a broad range of products. Cracked vapors from the FCC unit enter a separation zone, typically in the form of a main column, that provides a gas stream, a gasoline cut, light cycle oil (LCO) and clarified oil (CO) which includes heavy cycle oil (HCO) components. The gas stream may include dry gas, i.e., hydrogen and C1 and C2 hydrocarbons, and liquefied petroleum gas (“LPG”), i.e., C3 and C4 hydrocarbons. LPG and dry gas are not as valuable as naphtha in many regions However, LPG is more valuable than naphtha in some regions. The gasoline cut may include light, medium and heavy gasoline components. A major component of the heavy gasoline fraction comprises condensed single ring aromatics. A major component of LCO is condensed bicyclic ring aromatics.

#FIG. 1 is a sectional, elevational, schematical view of an FCC reactor incorporating a secondary reactor in accordance with the present invention.

#FIG. 2 is a sectional, plan view taken along segment 2-2 in FIG. 1.

#We have found that when reacting hydrocarbons produced by an FCC process in a secondary reactor they can potentially crack down to dry gas and LPG which are less valuable than naphtha in many regions. Reduced catalyst temperature will suppress thermal cracking of the naphtha olefins to dry gas and LPG which allows for higher overall naphtha yields. In one embodiment, the present invention recycles spent catalyst to the secondary reactor to be recontacted with feed. The recycled spent catalyst mixes with regenerated catalyst from a regenerator to lower the overall mixed catalyst temperature.

#Mixing the recycled spent catalyst with regenerated catalyst is a preferred method of cooling catalyst compared to use of an indirect heat exchange catalyst cooler, which operates to withdraw heat from the system that must be replaced by the generation and burning of more coke. Even if heat is conserved by heating feed to a reactor by indirect heat exchange with hot spent catalyst in the catalyst cooler, this means of heating would still be less efficient and prone to cause coking.

#The use of recycled, coke-bearing, spent catalyst also benefits operation by tempering catalyst activity. The strong acid sites of the FCC catalyst are suppressed through formation of coke. Consequently, the gasoline reformulation activity relative to the cracking activity is increased. Moderating the catalyst activity permits higher naphtha yields to be reached at the expense of production of dry gas and LPG.