Fluid catalytic cracking with supplemental heat

Abstract

A potentially heat-deficient fluid catalytic cracking process for effecting a bulk boiling point conversion of a high boiling point petroleum feed to lower boiling products in which the overall enthalpy balance between the endothermic cracking and exothermic regeneration is maintained by combustion of a supplemental fuel in the middle or upper region of the dense bed in the regenerator (including the region immediately above the dense phase bed). There is a direct economic benefit from operation of the cracking process in this way since the preferred supplemental fuel is methane (natural gas) which is currently a low cost fuel while liquid products are higher value. Use of natural gas as a supplemental fuel will allow re-optimization of the catalyst and operations separately from the heat balance demand.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to U.S. Provisional Application Ser. No. 62 / 172,917 filed Jun. 9, 2015, which is herein incorporated by reference in its entirety.FIELD OF THE INVENTION[0002]The present invention relates to the fluid catalytic cracking (FCC) process for converting high boiling point petroleum oils to lower boiling products.BACKGROUND OF THE INVENTION[0003]The fluid catalytic cracking (FCC) process has become the pre-eminent source for motor gasoline in the USA and also serves the petrochemical industry with light olefins as petrochemical feedstock. In the FCC process, a pre-heated high boiling point petroleum feed such as a vacuum gas oil or residual fraction is subjected to a bulk boiling range conversion by contact with a hot, acidic-function catalyst in a specialized process unit in which the feed comes into contact with the hot catalyst at the bottom of a tall vertical pipe or “riser” in which the essential cracking r...

AI Technical Summary

Benefits of technology

[0009]We have now devised an improved scheme for redressing an inadequate heat supply to the cracking reactions in the FCC unit by the substitution of methane (natural gas) (or other light fuels such as fuel gas) for this ‘discretionary coke’. The combustion of this supplementary fuel in the regenerator itself will result in increased regenerator heat release for the same amount of air / oxygen consumption while decreasing CO2 emissions. The supplementary fuel is injected into a dense bed of the catalyst in the middle or upper region of the dense bed or even or just above the bed. Operation of the regenerator in this way will maximize the oxygen concentration at the bottom of regenerator for coke burning purposes which is a slower reaction while essentially eliminating excess oxygen in the dilute phase and the flue gas resulting in a more reducing atmosphere for minimizing NOx formation. The added heat of combustion is directly added to the body of catalyst being regenerated so avoiding problems of heat transfer and catalyst hang-ups in separate combustion chambers.

[0011]The present fluid catalytic cracking process for effecting a bulk boiling point conversion of a high boiling point petroleum feed to lower boiling products contacts the feed with a hot cracking catalyst to effect endothermic cracking of the feed after which the spent catalyst is exothermically regenerated by oxidative combustion of coke deposited on the catalyst during the cracking in a dense bed of catalyst in a regeneration step; in this process, the overall enthalpy balance between the endothermic cracking and exothermic regeneration is maintained by combustion of a supplemental fuel in the middle or upper region of the regeneration dense bed (including the region immediately above the dense phase bed). There is a direct economic benefit from operation of the cracking process in this way since the preferred supplemental fuel is methane (natural gas) which is currently a low cost fuel in the USA while liquid products are higher value. Use of natural gas as a supplemental fuel (in a manner similar to torch oil in the regenerator) will allow re-optimization of the catalyst and operations separately from the heat balance demand.

Problems solved by technology

With lighter (lower boiling) feeds and hydroprocessed feeds, stable unit operation becomes problematical without operating under conditions which result in a greater amount of coke being generated during the cracking portion of the FCC cycle simply in order to supply the heat demands of the unit.

Thus, changes in catalyst, unit design and / or operations could be made to decrease the in-unit coke yield with consequent increases in liquid product yield but the heat balance then registers a deficit.

While the proposals in U.S. Pat. Nos. 8,753,502 and 8,354,065 appear in principle of maintaining the unit enthalpy balance, they fail to make the most effective use of the existing unit, requiring specialized unit modifications to provide the combustion chambers in which light hydrocarbon fuels are burned to supply the additional heat with this heat being transferred to the main body of circulating catalyst by means of a catalyst stream which is passed into or through the combustion chamber.

With combustion chambers such as those described, necessarily operating at a high temperature, there exists the potential for catalyst hold-up in the chamber, excessive erosion by fast circulating catalyst flows, as well as inefficient heat transfer by a limited stream of catalyst.

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