Distillation: apparatus – Apparatus – Systems
Reexamination Certificate
1998-12-09
2001-02-27
Knode, Marian C. (Department: 1764)
Distillation: apparatus
Apparatus
Systems
C202S120000, C220S677000
Reexamination Certificate
active
06193848
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to pressure-tight vessels for handling large volumes of a product as the product is treated through a thermal cycle with an upper temperature in excess of approximately 700 degrees Fahrenheit. In particular, the invention relates to pressure-tight vessels that could be used for delayed petroleum coking.
Delayed petroleum coking is a process in which a petroleum fraction is heated to a temperature at which it thermally decomposes to provide a solid coke product and a hydrocarbon distillate product. In general, a liquid petroleum feed stock is first distilled until the lighter ends have been recovered and a heavy residuum remains. This heavy residuum is generally preheated to a temperature of at least about 700° F. before being fed to pressure-tight vessel. In the vessel, it may be further heated to temperatures up to 1000° F. under high-pressure conditions that prevent the petroleum fraction from vaporizing until it has partially decomposed.
The decomposition process produces hydrocarbon vapors vessel and a heavy tar that continues to decompose until a porous coke is left in the vessel. The vaporization results in pores and channels in the residuum that may be filled with additional residuum.
Once the vessel is filled, the residuum is allowed to cool, forming coke. The coke may then be purged with steam to remove any remaining volatile components.
To complete the process, water is added to the vessel to quench the coke. As the level of the water progressively rises in the vessel, it quenches the coke to a temperature below 200° F.
In order to increase production speed, the quenching operation is often done as quickly as possible. Unfortunately, the faster the coke is quenched, the greater the wear and tear on the vessel. One of the primary causes of this wear and tear is that the steel plate and the weld material joining the rings of plate that form the vessel have different yield and creep strengths. At the circumferential weld sites, thermal cycling causes progressively increasing permanent strains, eventually leading to distortion and cracking in or near the welds and often bringing to an end the useful life of the vessel.
As described in U.S. Pat. No. 3,936,358, some efforts have been made to reduce the wear and tear on vessels by controlling the quench rate. Unfortunately, this can reduce production speed.
More recently, efforts has been made to adjust the composition of the weld material so that its yield strength more closely matches that of the adjacent steel plates. It is hoped that a closer match will reduce the stresses at the weld sites, extending the life of the vessel. Unfortunately, vessels using the new weld materials have not been in service long enough to know whether this solution will be successful.
There remains a need for a pressure-tight vessel that can better withstand extreme thermal cycling.
SUMMARY OF THE INVENTION
The invention relates to a pressure-tight vessel that has improved resistance to extreme temperature cycling, and thus an improved lifespan when used in operations like delayed petroleum coking.
Like many vessels designed to handle products under severe thermal cycling, the vessel has a vertically-disposed cylindrical section that contains most of the vessel's working volume. The cylindrical section is made of large metal plates, generally on the order of 10′ by 40′ plates.
Unlike prior vessels used for these purposes, the metal plates are arranged vertically, rather than horizontally. Arranging the plates in this way, so that the vertical edges of each metal plate are greater than sixteen or twenty feet in length, provides a critical section with an extensive height in which there are no horizontal seams. Most conventional plate bending equipment is not capable of bending a plates over more than a twenty-foot width. Accordingly, while it is relatively easy to bend a 10′ by 40′ plate so that the 10′ edges remain straight and the 40′ edges are curved, it is more difficult to bend plates as needed for this invention; that is, so that they have a straight edge that is more than sixteen or twenty feet in length.
It has been found that the distortion and cracking in welds that end the useful life of pressure-tight vessels used for delayed petroleum coking commonly occur at a horizontal (or circumferential) seam within or near the lowermost sixteen feet above the base of the vessel. As a result of eliminating horizontal seams at this location, the most likely point of failure can be eliminated, significantly increasing the expected lifespan of the vessel. Alternatively, if the critical section of the vessel is viewed as being at a higher location, the vertically-arranged plates can be positioned there.
REFERENCES:
patent: 2179774 (1939-11-01), Zerbe
patent: 2244064 (1941-06-01), Hodge
patent: 2337049 (1943-12-01), Jackson
patent: 2684170 (1954-12-01), Schmitz
patent: 3366263 (1968-01-01), Murdock
patent: 4147594 (1979-04-01), Cain et al.
patent: 4241843 (1980-12-01), Walker et al.
patent: 4396337 (1983-08-01), Johanning
patent: 4667731 (1987-05-01), Baumgartner et al.
patent: 5622604 (1997-04-01), Gerstenkorn et al.
ARCO coke drum in Carson, Carolina, repaired in 1991 by Nooter Corporation
Shockley Lestle R.
Stewart Coby W.
Chicago Bridge & Iron Company
Knode Marian C.
Marshall, O'Toole, Gerstein, Murray & Borun.
Varcoe, Jr. Frederick
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