TOWER BOTTOMS COKE CATCHING DEVICE

Abstract

A coke catching apparatus for use in hydrocarbon cracking to assist in the removal of coke and the prevention of coke build up in high coking hydrocarbon processing units. The apparatus includes a grid device for preventing large pieces of coke from entering the outlet of the process refining equipment while lowing small pieces of coke to pass through and be disposed of. The coke catching apparatus can be easily disassembled to be removed from the refining process equipment and cleaned.

Claims

1. An apparatus for use assisting in the removal of coke and prevention of coke build up in hydrocracking units having tubular furnace reactors, used in the refining of petroleum products, comprising in combination: a grid device in the shape of an upside-down basket wherein the grid is defined by bars interconnected to create openings therebetween; the grid device being positioned within the tubular furnace reactor of the hydrocracking tower; the grid device positioned to fit over the outlet of the reactor; and the grid device allowing small pieces of coke to pass through to the outlet of the reactor while preventing large pieces of coke from reaching the outlet of the reactor and restricting the flow of process d material through the outlet of the reactor.

2. The coke catching apparatus of claim 1 wherein the diameter of the grid device is at least 2 inches larger than the diameter of the outlet of the atmospheric tower.

3. The coke catching apparatus of claim 1 including a bottom plate that is solid and includes a plurality of drain holes to allow for refined product to exit the reactor.

4. The coke catching apparatus of claim 1 includes four distinct units that are engaged together and can easily be disassembled from each other: the four distinct units include a bottom plate, two sections of the grid device, and a top hat section.

5. The coke catching apparatus of claim 4 wherein the top hat is designed to prevent coke particles from settling on top of the coke catcher apparatus.

6. The coke catching apparatus of claim 5 wherein the top hat section is separated by at least 12 inches from the grid device beneath it.

7. The coke catching apparatus of claim 1 wherein the openings of the grid device are 4 inches

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a schematic depiction of a reactor unit tower having the coke catcher invention placed inside.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] The present invention is shown by schematic in FIG. 1 as having a reactor unit, such as a fractionator or atmospheric tower (10) with a bottom outlet (12) and outlet nozzle (14). The bottom (16) of the coke catcher is as solid plate designed to fit over the outlet (12) of the atmospheric tower. Preferably, the diameter of the bottom plate (16) should overlap the diameter of the outlet (12) by a minimum of two inches. The bottom plate (16) includes a plurality of drain holes that allow all of the product to exit the atmospheric to for the purpose of a shutdown such that no product is left in the unit.

[0016] The coke catcher is preferably made up of four units A, B, C and D, which can be easily disassembled to assist in removing the coke catcher from the interior of the atmospheric tower to allow for cleaning of the coke catcher. Section A of the coke catcher includes the bottom (16). Sections B and C provide a colander-like grid for screening the coke particles. Preferably, the bar spacing of the grid is a minimum of four inches to prevent coke buildup on the bars. Sections B, C and D are held together by clamp members (22) which allow for sections B, C and to be separated from one another for easy maintenance. Section D is the top hat portion of the coke catcher which prevents coke from settling on top of the coke catcher. The gap between the top hat and the top of section C is preferably, a minimum of twelve inches to avoid coke spreading and potential plugging. As the coke spalls off the walls of the atmospheric tower, it enters the coke catcher through the colander sections B and C and through the hat supports (18). The coke catcher is supported within the atmospheric tower by support bars (20).

Experimental Performance of the Coke Catcher

[0017] During the last turnaround of a Resid Hydrotreater Unit (RHU), the coke catcher of the present invention was installed in the atmospheric tower. The historic record of the atmospheric tower of this particular RHU typically had the third year of its cycle as the most challenging. For instance, as illustrated in the Base Case timeline, the third year (2016) the unit experienced serious capacity decline prior to a planned Non-Cycle ending Turnaround (NCE) 2018. During the third year of the experimental cycle, after the installation of the coke catcher, the unit did not experience the typical capacity decline but instead set record rates. The performance centered around not having issues with the outlet hydraulics of the atmospheric tower. The improved tower bottoms hydraulics enabled an originally planned Non-Cycle Ending Turnaround (NCE) to be extended an additional year. The extension eliminated one NCE turnaround prior to the future Cycle Ending (CE) turnaround. The results of the experiment reduced the unit down time by one NCE turnaround over a 7-year period. The net impact is reduced maintenance expense and increased annual production.

[0018] An additional benefit to the installation of the coke catcher is the ability to better recover from unplanned unit shutdowns from process.

[0019] One indicator of atmospheric tower bottoms fouling is the temperature difference between feed zone and bottom product temperatures. An increase in this delta temperature suggests increased coke growth in the tower and bottoms circuit. An increase in delta temperatures is indicative of increased thermal cycling in the tower. Such thermal cycling of the tower can cause coke in the vessel to spall off and be flushed out. If the coke catcher were not installed the coke would have plugged the outlet line completely. A tower NCE turnaround would have been needed before restarting the unit. The NCE turnaround was unnecessary, resulting in a more efficient and rapid startup of the unit.

[0020] The above detailed description of the present invention is given for explanatory purposes. It will be apparent to those skilled in the art that numerous changes and modifications can be made without departing from the scope of the invention. Accordingly, the whole of the foregoing description is to be construed in an illustrative and not a limitative sense, the scope of the invention being defined solely by the appended claims.