Mineral oils: processes and products – Chemical conversion of hydrocarbons – Cracking
Reexamination Certificate
1999-04-08
2001-01-09
Myers, Helane E. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Cracking
Reexamination Certificate
active
06171473
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for treating the petroleum residue from a refinery by an integrated process of thermal cracking and partial oxidation to obtain higher thermal cracking at reduced investment cost.
The residue from a refinery usually comprises the components boiling above about 500-575° C. These residues may comprise any such streams such as vacuum tower residue, visbreaker residue and deasphalting residue. There is a considerable amount of residue from a refinery to be treated. For example, a typical refinery processing 10 million metric tons annually (MTA) of Arabian Mix Crude will produce about 6,500-7,000 MT per stream day (SD) of vacuum tower residue. This residue can be blended into residual fuel oil (which has a low value), upgraded to high value transportation fuels (which is expensive) or gasified to produce power. Without further processing, gasification of this residue will provide about 1,200 MW of electrical power. This is greatly in excess of the amount of power which can be effectively used in the plant. Several processes are available to reduce the amount of the residue but the degree of conversion of the residue is low and/or the cost is high. Examples are:
Cost of
Wt % Unconverted
Upgrading Plant
Process
Residue or Coke Formed
$ MM
Visbreaking
84.5%
$ 29.7
Visbreaking &
66.5%
$ 38.6
Vacuum Flasher
Deasphalting
43.2%
$ 46.0
Delayed Coking
32.5%
$144.3
Conversions of more than 50% are desired for efficient and effective plant operation but the cost for obtaining such conversions with these prior art processes is high. With respect to visbreaking, the overall conversion to 500° C. and lighter components is limited to 35% in order to maintain the stability of the residue (500° C.+components) for fuel oil blending. Also, the visbreaking process is limited by the maximum skin temperature of the furnace tubes of about 650° C. Although higher yields are possible with visbreaking, the unstable nature of the fuel product and the coking of the tubes pose significant problems. Although the Eureka Process (steam cracking with superheated steam) has a good conversion (67%), it requires the injection of superheated steam to suppress coking which all has to be condensed in a downstream fractionator and then treated in a sour water stripping unit. This adds cost to the unit.
SUMMARY OF THE INVENTION
The present invention involves the thermal cracking of a residue from petroleum refining to convert the residue at low cost to useful cracked products at a high conversion yield and to generate fuel gas for power production without the need for supplying outside energy for the thermal cracking.
The present invention involves thermal cracking of a residue from petroleum refining by contacting the residue feed with hot synthesis gas produced by gasification of the tar/pitch residue remaining after the cracking of the feed. Only a portion of the hot synthesis gas produced via gasification is needed for thermal cracking. Waste heat is recovered in the form of steam from the remaining synthesis gas from the gasifier and a portion of the steam can be used in the gasification process. The cooled, combustible synthesis gas is combined with the combustible gases produced by the thermal cracking for power generation such as in a combined cycle power plant. The cracked liquid converted from the residue feed is similar to thermal products from delayed coking and visbreaking and is hydrotreated in the same manner as existing thermal products.
REFERENCES:
patent: 4938862 (1990-07-01), Vissor et al.
ABB Lummus Global Inc.
Alix Yale & Ristas, LLP
Myers Helane E.
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