Coke drum bottom throttling valve and system

Abstract

A coke drum bottom de-heading system having an internal shroud enclosure and a shroud end cap opened by a flange to a coke bottom de-heading valve capable of accepting the end of a gate valve upon actuation. Acting in coordination with the shroud enclosure to prevent the escape of steam is a gate seal assembly having a gate seal slidably engaged against the sliding gate to prevent the passage of steam thereby.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway view of the entire valve body demonstrating the interaction between the blind orifice and the valve body in the closed position (bonnets removed for clarity);

FIG. 2 is a perspective view of the valve body and shroud;

FIG. 3 is a an exploded view of the gate seal assembly;

FIG. 4 is a cross-sectional view taken through the gate seal of FIGS. 2 and 3 demonstrating the interaction between the internal components; and

FIG. 5 is a cross-sectional view of a nose ring inside a blind.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the system, device, and method of the present invention, as represented in FIGS. 1A-4, is not intended to limit the scope of the invention, as claimed, but is merely representative of the presently preferred embodiments of the invention.

The presently preferred embodiments of the invention will be best understood by reference to the drawings wherein like parts are designated by like numerals throughout. Although reference to the drawings and a corresponding discussion follow below, it is first advantageous to provide a general background of the coking process, including the process of de-heading the coke drums at the end of a manufacturing cycle.

General Discussion on Delayed Coking and Coke De-Heading

In the typical delayed coking process, high boiling petroleum residues are fed to one or more coke drums where they are thermally cracked into light products and a solid residue—petroleum coke. The coke drums are typically large cylindrical vessels having a top head and a conical bottom portion fitted with a bottom head. The fundamental goal of coking is the thermal cracking of very high boiling point petroleum residues into lighter fuel fractions. Coke is a byproduct of the process. Delayed coking is an endothermic reaction with a furnace supplying the necessary heat to complete the coking reaction in a drum. The exact mechanism is very complex, and out of all the reactions that occur, only three distinct steps have been isolated: 1) partial vaporization and mild coking of the feed as it passes through the furnace; 2) cracking of the vapor as it passes through the coke drum; and 3) cracking and polymerization of the heavy liquid trapped in the drum until it is converted to vapor and coke. The process is extremely temperature-sensitive with the varying temperatures producing varying types of coke. For example, if the temperature is too low, the coking reaction does not proceed far enough and pitch or soft coke formation occurs. If the temperature is too high, the coke formed generally is very hard and difficult to remove from the drum with hydraulic decoking equipment. Higher temperatures also increase the risk of coking in the furnace tubes or the transfer line. As stated, delayed coking is a thermal cracking process used in petroleum refineries to upgrade and convert petroleum residuum (or resid) into liquid and gas product streams leaving behind a solid concentrated carbon material, or coke. A fired heater is used in the process to reach thermal cracking temperatures, which range upwards of 1,000° F. With short residence time in the furnace, coking of the feed material is thereby “delayed” until it reaches large coking drums downstream of the heater. In normal operations, there are two coke drums so that when one is being filled, the other may be purged of the manufactured coke. These coke drums are large structures that are approximately 25-30 meters in height and from 4 to 9 meters in diameter. They are equipped with a top blind flange closure or orifice that is typically about 1.5 meters in diameter, and a bottom blind flange orifice that is typically about 2 meters in diameter.

In a typical petroleum refinery process, several different physical structures of petroleum coke may be produced. These are namely, shot coke, sponge coke, and/or needle coke, and are each distinguished by their physical structures and chemical properties. These physical structures and chemical properties also serve to determine the end use of the material. Several uses are available for manufactured coke, some of which include fuel for burning, the ability to be calcined for use in the aluminum, chemical, or steel industries, or the ability to be gasified to produce steam, electricity, or gas feedstock for the petrochemicals industry.

To produce the coke, a delayed coker feed originates from the crude oil supplied to the refinery and travels through a series of process members and finally empties into one of the coke drums used to manufacture coke. The delayed coking process is a batch-continuous process, which means that the process is ongoing or continuous as the feed stream coming from the furnace alternates filling between the two or more coke drums. As mentioned, while one drum is on-line filling up with coke, the other is being stripped, cooled, decoked, and prepared to receive another batch. This is a timely process, with each batch in the batch-continuous process taking approximately 12-20 hours to complete. In essence, hot oil, or residue as it is commonly known, from the tube furnace is fed into one of the coke drums in the system. The oil is extremely hot (95° F.) and produces hot vapors that condense on the colder walls of the coke drum. As the drum is being filled, a large amount of liquid runs down the sides of the drum into a boiling turbulent pool at the bottom. As this process continues, the hot residue and the condensing vapors cause the coke drum walls to heat. This naturally in turn, causes the residue to produce less and less of the condensing vapors, which ultimately causes the liquid at the bottom of the coke drum to start to heat up to coking temperatures. After some time, a main channel is formed in the coke drum, and as time goes on, the liquid above the accumulated coke decreases and the liquid turns to a more viscous type tar. This tar keeps trying to run back down the main channel which can coke at the top, thus causing the channel to branch. This process progresses up through the coke drum until the drum is full, wherein the liquid pools slowly turn to solid coke. When the first coke drum is full, the hot oil feed is switched to the second coke drum, and the first coke drum is isolated, steamed to remove residual hydrocarbons, cooled by filling with water, opened, and then decoked. This cyclical process is repeated over and over again in the manufacture of coke.

The decoking process is the process used to remove the coke from the drum upon completion of the coking process. Due to the shape of the coke drum, coke accumulates in the area near and attaches to the heads during the manufacturing process. To decoke the drum, the heads must first be removed. Typically, once full, the drum's contents are stripped and water quenched down to a temperature of 200° F. or less and vented to atmospheric pressure and the top head (typically a 4-foot diameter flange) is unbolted and removed to enable placement of a hydraulic coke cutting apparatus. After the cooling water is drained from the vessel, the bottom head (typically a 6-foot-diameter blind plate quench) is unbolted and removed. This process is commonly known as “de-heading” and can be a very dangerous procedure because of the size of the heads, the high temperatures within the drum, potential falling coke, and other reasons as mentioned above. Once the heads are removed, the coke is removed from the drum by drilling a pilot hole from top to bottom of the coke bed using high pressure water jets. Following this, the main body of coke left in the coke drum is cut into fragments which fall out the bottom and into a coke receiving area, and in some cases into, a bin or a rail cart, etc. The coke is then dewatered, crushed and sent to coke storage or loading facilities.

Present Invention Coke Drum De-Heading System

Although the present invention is applicable and utilized on both the top and bottom openings of a coke drum, the following detailed description and preferred embodiments will be discussed in reference to a bottom de-heading system only. One of ordinary skill in the art will recognize that the invention as explained and described herein for a coke drum bottom de-heading system may also be designed and used as a coke drum top or side de-heading system and the following discussion pertaining to the bottom de-heading system is not meant to be limiting to such.

The present invention is used in conjunction with a device for de-heading a coke drum following the manufacture of coke therein. As the present invention is especially adapted to be used in the coking process, the following discussion will relate specifically in this manufacturing area. It is foreseeable however, that the present invention may be adapted to be an integral part of other manufacturing processes producing various elements other than coke, and such processes should thus be considered within the scope of this application.

The present invention comprises a shroud and gate seal assembly. The inventive shroud and gate seal assembly may be used in conjunction with a dual seated, linear motion, goggle blind valve or other types of de-heading gate valves. FIGS. 1A and 1B depict the environment in which a typical de-heading gate valve is employed. As can be seen in more detail in FIG. 2, a shroud 20 is shown attached to a valve body 22. The shroud has a shroud cap 24, shroud body 26 and springs 28 which bias the shroud cap 24 against shroud body 26. Upon actuation of the valve, a blind is moved from an open position as shown in FIG. 2 and as the blind travels from the open position, it contacts shroud end cap 24 and releases steam pressure built up within shroud body 26. Upon actuation of the blind in the opening direction, the blind will move away from contact with shroud cap 24 allowing spring 28 to bias cap 24 against shroud body 26 thereby sealing the shroud and preventing the escape of steam. Shroud 20 is attached to valve body 22 by a flange 30. It is important that the shroud be aligned with the valve body 22 to allow proper passage of the blind as it is actuated. The tolerances and clearances between the blind and the shroud body are important. Any residual coke that follows the blind into the shroud must either remain within the blind or must be held within the shroud so that it does not fall into the lower bonnet of the valve. Any coke particulate held within the shroud will be acted upon by the steam and much of it will be ejected from the shroud cap as it is encountered by the end of the blind as it is actuated.

Turning now to another portion of the inventive system, a gate seal assembly 32 is shown located within valve body 22 in FIG. 2. FIG. 3 depicts an exploded view of the contents of the assembly which comprises a seal cap 34, a guide cup 36, a load spring 38, and seal plate 40, and a gate seal 42. Seal cap 40 is used to hold the contents inside valve body 22. Guide cups 36 serves to guide the movement of gate seal 42 which floats freely therein and operates against the sides of the blind. Because the seal between gate seal 42 and the side of the blind is not perfect, load spring 48 provides pressure against guide seal 42 to insure a fit which will prevent the flow, or at least reduce the flow of steam there through. Since valve body 22 has internal components which are under a constant positive pressure to prevent the flow of contaminates from the drum into the valve body, actuation of the blind allows pressure to flow out of the pressurized body cavity through the up stream and downstream ports of the valve. This pressure loss can result in a negative pressure boundary flowing from the drum into the body cavity. Gate seal 42 prevents the escape of this steam or at least reduces it to the point where the escape is minimal. Thus the body cavity retains a positive pressure over that of the drum.

Turning now to FIG. 4, a cross-sectional view taken along lines AA and FIG. 2 is depicted. The interaction between gate seal 22 and gate 44 is depicted. Gate seal assembly 32 remains statically in place as gate 44 moves in a linear manner when actuating the valve. The interface between the two components is kept tight by the pressure from load spring 38 against gate seal 32. Gate seal 32 is comprised of a material such as a metal impregnated graphite composite which maintains a tight seal and also provides some limited degree of lubrication to allow gate 44 to slide thereby. Seal cap 34 allows access to these internal components for maintenance and replacement.

FIG. 5 is a cross-sectional view of a nose ring 60 inside the orifice 62 of a blind 64. When used for throttling, the area around the orifice edge is exposed to harsh conditions including heat, friction and pressure. To increase the life of the blind, a replaceable nose ring 60 is installed. Nose ring 60 must have extremely close tolerances to remain attached to blind 64. Downward pressure on the inner edge will urge the ring out of the blind. To resist the pressure from coke traveling over the ring, a ring bolt or retainer extends from the lower face of the blind to secure the ring in place. The ring should be constructed of a strong material such as grade 512 chrome nitrided 4/10 stainless steel or other wear resistant material.

Claims

1. A system for preventing the escape of steam from a coke de-heading device comprising: a deheading device comprising; a main body removable attached to a coke drum;a blind seal coupled to the main body;a blind which slidably engages the blind seal; anda shroud, removably attached to the main body, surrounding the blind and the blind seal.

2. A system as recited in claim 1, wherein the blind is configured to selectively slide between an opened position and a closed position.

3. A system as recited in claim 1, further comprising one or more shroud cap return springs which bias a shroud cap end plate to prevent the release of steam from the valve body into the shroud.

4. A system as recited in claim 1, further comprising a shroud cap end plate which selectively overcomes a biasing pressure from one or more shroud cap return springs to release steam pressure.

5. A system as recited in claim 1, wherein the system is attached to a coke drum at a position selected from a group consisting of: (i) a flange on the bottom of the coke drum;(ii) a flange on the top of the coke drum; and(iii) a flange on the side of the coke drum.

6. A system as recited in claim 1, further comprising a gate seal assembly coupled to a body of the blind gate valve, wherein the gate seal assembly is configured to float within a guide cup to reduce an amount of steam from escaping from the body when pressurized.

7. A system as recited in claim 1, wherein the deheading device is selected from a group consisting of: a dual seated deheading device, a linear motion deheading device, and a goggle blind valve deheading device.

8. In a coke drum deheading system, a method of preventing the escape of steam from a coke-deheading device comprising: coupling a main body of a coke deheading system to a coke drum, wherein said coke deheading system comprises the main body, a blind, a blind seal and a shroud;coupling said seal to said main body;surrounding a gate valve of a coke deheading system with a shroud; and slideably engaging a blind against a blind seal assembly.

9. A method as recited in claim 8, wherein the blind is configured to selectively slide between an opened position and a closed position.

10. A method as recited in claim 9, further comprising the step of allowing a shroud cap end plate of the shroud to overcome a biasing pressure from one or more shroud cap return springs to release steam pressure from the valve body.

11. A method as cited in claim 10, further comprising the step of allowing one or more shroud cap return springs to bias the shroud cap end plate to prevent the continued release of steam.

12. The method as recited in claim 8, wherein the coupling of said main body to the coke drum further comprises a step consisting of: coupling the main body to the bottom of the coke drum;coupling the main body to the top of the coke drum; andcoupling the main body to the side of the coke drum.