Fluid coking unit stripper

Abstract

An improved, fouling-resistant configuration for the stripper sheds of fluid coking units comprises an inverted, open-bottomed channel with apertures spaced along the length of the channel and spaced from the apex of the channel. Preferably, the channels are of an inverted-V configuration with a downwardly extending lip provided on each side of the channel, extending from the bottom edge of each side of the channel. The stripper sheds may be positioned parallel to one another in the stripper section of the reactor vessel or, alternatively, the sheds in different tiers in the stripper section may be disposed so that the longitudinal axes of the sheds are rotated angularly relative to the sheds in other rows.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application relates and claims priority to U.S. Provisional Patent Application Ser. No. 61 / 300,372, filed on Feb. 1, 2010 and U.S. Provisional Patent Application Ser. No. 61 / 280,625, filed on Nov. 6, 2009.FIELD OF THE INVENTION[0002]This invention relates to an improved stripper section for mitigating fouling and hydrocarbon carryunder in fluidized bed coking units.BACKGROUND OF THE INVENTION[0003]Fluidized bed coking (fluid coking) is a petroleum refining process in which heavy petroleum feeds, typically the non-distillable residue (resid) from fractionation, are converted to lighter, more useful products by thermal decomposition (coking) at elevated reaction temperatures, typically about 480 to 590° C., (about 900 to 1100° F.). The process is carried out in a unit with a large reactor vessel containing hot coke particles which are maintained in the fluidized condition at the required reaction temperature with steam injected at the ...

AI Technical Summary

Benefits of technology

[0011]We have now devised an improved configuration for the stripper sheds of fluid coking units. According to the present invention, the improved stripper shed comprises an inverted, open-bottomed channel that has apertures spaced along the length of the channel and spaced from the apex of the channel. Preferably, the channels are of an inverted-V configuration with an included angle between the sloping sides from 60 to 120°, preferably from 80 to 100° with optimal results believed achievable at a 90° angle. An additional feature is that the channel terminates at or near the outer edge in a vertically downwards direction to increase the driving force of the gas flow through the apertures in the shed. With the preferred, inverted-V channels, a downwardly projecting lip is provided on each side of the channel at or near the outer edge of the channel, extending from the bottom edge of the channel to promote the desired gas flow through the apertures to inhibit fouling.

Problems solved by technology

During the contacting of the feed with the fluidized bed, some coke particles may become unevenly or too heavily coated with feed and during collision with other coke particles may stick together.

These heavier coke particles may not be efficiently fluidized by the steam injected into the bottom of stripper section so that they subsequently pass downwards from the reactor section into the stripper section where they may adhere to and build up on the sheds in the stripper section, mainly on the uppermost rows of sheds.

Accumulation of deposits on the stripper sheds can become so severe due to growth of the deposits into the open area between the sheds on the row above as to restrict fluidization of the coke in the reactor section and eventually shut the unit down.

As this material progresses through the stripper, additional cracking reactions occur.

With basic fluid cokers, unlike Flexicokers, this phenomenon is not greatly disadvantageous as the quantities are small but in the case of Flexicokers, this material is sent to the heater, where it is exposed to a high temperature, oxygen poor environment.

Unreacted material that enters the heater can crack to form a full range of vapor phase products.

These products are then carried up into the heater overhead where they can condense onto surfaces resulting in capacity and / or run length limitations.

As the steam moves up the stripper it becomes it is redistributed Severe fouling of the stripper sheds can occur in both fluid and Flexicoking units, resulting in the formation of large coke deposits on the shed tops that can restrict flow and eventually lead to unplanned capacity loss.

Over time, hydrocarbon species from the vapor phase condense in the interstices between the particles, creating a very hard and difficult to remove deposit.

The reduction in flow area caused by these deposits makes the stripper vulnerable and reduced clearances can trap rubble spalled during a thermal cycle.

Poor stripper hydrodynamics in the unit may reduce unit capacity and eventually lead to a shutdown of the reactor.

It has been found, however, that such shed holes may become fouled, possibly as a result of poor steam distribution.

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