Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By plural serial diverse separations
Reexamination Certificate
1999-12-23
2001-12-25
Griffin, Walter D. (Department: 3744)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By plural serial diverse separations
C585S800000, C585S802000, C585S655000, C062S600000, C062S611000, C062S613000, C062S617000, C062S618000, C062S619000, C062S932000, C208S102000, C208S103000
Reexamination Certificate
active
06333445
ABSTRACT:
BACKGROUND OF THE INVENTION
The function of a dehydrogenation process, when utilized in hydrocarbon processing, is to convert paraffinic hydrocarbons to their corresponding olefins.
Thus, propane is converted to propylene:
C
3
H
8
=C
3
H
6
+H
2
or isobutane is converted to isobutylene:
iC
4
=iC
4
H
8
+H
2
These are two examples of the use of the process.
The reactor effluent stream from such dehydrogenation processes contains these components in the vapor phase. A cryogenic process is employed to condense the C
3
or C
4
components as a liquid phase product. The residual vapor stream is required free of the C
3
or C
4
components to minimize their losses.
A method and apparatus for the separation of C
4
hydrocarbons from a gaseous mixture containing the same are described in U.S. Pat. Nos. 5,414,188, issued May 9, 1995, and 5,505,048, issued Apr. 9, 1996, hereby incorporated by reference.
These patents are directed to the separation of the C
4
hydrocarbons in a series of cooling for condensation, phase separation, and expansion process steps with refrigeration by indirect heat exchange between expansion products to save energy and power consumption.
It is desirable to provide a new and improved cryogenic separation process and apparatus system for the
It is desirable to provide a new and improved cryogenic separation process and apparatus system for the separation of C
3
or C
4
gaseous mixtures with hydrogen, such as produced in dehydrogenation processes to permit the use of lower Cost and more economical materials of construction in the process, to increase the extraction of energy in the process, to reduce the size of heat exchangers employed in the process and apparatus, and to otherwise improve the efficiency and economy of the separation process and apparatus system.
SUMMARY OF THE INVENTION
The invention relates to a cryogenic separation process and system for gaseous, lower hydrocarbon and hydrogen mixtures. In particular, the invention concerns an improved cryogenic separation process and system for the gaseous catalytic reactor effluent of a dehydrogenation process, more particularly, the OLEFLEX™ process (OLEFLEX is a trademark of UOP, Inc. of Des Plaines, Ill., for a dehydrogenation process).
The invention relates to an improved system and process for the separation of C
3
or C
4
hydrocarbons and hydrogen gaseous mixtures; particularly, those gaseous mixtures which comprise the effluent vapor stream from a catalytic reactor of a dehydrogenation system and process.
The invention comprises a process for the separation of olefinic hydrocarbon in an effluent vapor stream from a paraffinic feed, dehydrogenation reactor and compressed by a compressor, which process comprises partially condensing the olefinic hydrocarbon in the a first warm heat exchanger having a warm end and a cold end; separating the partially condensed olefinic hydrocarbon in a first primary separator to provide a primary vapor product and a first liquid olefinic product; then partially condensing the olefinic hydrocarbon, the primary vapor product in a second cold heat exchanger having a warm end and a cold end to provide a second liquid; then separating the second liquid olefinic hydrocarbon in a second separator to provide a secondary vapor product and a second liquid olefinic product; and isentropically expanding the primary vapor product in a high pressure expander to provide a third liquid olefin stream and a third vapor product. Next, separating the third liquid olefin stream and the third vapor product in a third separator; then reheating the third vapor product in the second cold heat exchanger; dividing the reheated third vapor product into a first portion and a second portion; reheating the first portion in the first warm heat exchanger and withdrawing as the process vapor product essentially hydrogen; isentropically expanding the second fraction in a low pressure expander; reheating the expanded second fraction in the second cold heat exchanger; subcooling a liquid paraffinic feed for use in the reactor in the first warm heat exchanger; combining the subcooled liquid paraffinic feed with the expanded reheated second fraction to provide a combined stream; and totally revaporizing the combined stream in the first warm heat exchanger; then withdrawing the revaporized combined stream and employing the revaporized combined stream as a feed stream to the dehydrogenation reactor.
The process comprises next, combining the first, second, and third liquid olefinic streams to provide a liquid combined stream; rewarming the liquid combined stream to an intermediate temperature between a warm end temperature and a cold end temperature in the first warm heat exchanger; flashing the rewarmed liquid combined stream in a liquid product drum to provide a flashed vapor stream and recycling this vapor stream to a feed compressor; pumping the flashed, rewarmed, liquid combined stream in a pump to a high pressure; reheating the pumped, high pressure, liquid combined stream in the first warm heat exchanger; and withdrawing the reheated, pumped, liquid combined stream from the first warm heat exchanger into a liquid olefin product storage system.
Next, operating the liquid product drum and the pump at a temperature such that the drum, pump, or both may be composed of carbon steel material and operating the expanding of the second fraction in the low pressure expander at a temperature to increase the power output of the expander; and governing the temperature of the cold end of the second cold heat exchanger by the high pressure expander, and the temperature of the warm end of the second cold heat exchanger by the low pressure expander to permit optimatization of the size of the first and second heat exchangers.
In a further improvement and embodiment, the process and system comprises an improved cold box for the vapor phase reactor effluent stream, which includes compressing a portion of the compressed effluent vapor stream from the discharge of reactor effluent compressors; cooling the compressed portion of the effluent vapor stream in an aftercooler; separating any condensed liquid from the cooled, compressed, effluent vapor stream and introducing the separated cooled liquid into the product storage drum; partially condensing the remaining compressed effluent vapor stream, which vapor steam is at a higher pressure than the effluent vapor stream in the first warm heat exchanger; and depressurizing the partially condensed, recovering effluent vapor stream and introducing said depressurized, partially condensed, effluent vapor stream into the first primary separator for separation.
The system and process comprises an improved, economical, efficient, cryogenic separation system and a further optional, expander-driven compressor system and process.
The cryogenic separation system and process may be utilized by both propane and isobutune dehydrogenation plants and effluent vapor streams or similar hydrocarbon-hydrogen process streams. The process conditions employed, such as temperature, pressure, and stream compositions are different for propane and isobutane; however, the basic cryogenic separation process and system and their advantages in operation are the same.
The invention will be described for the purposes of illustration only in connection with the preferred embodiment; however, it is recognized that certain changes, modifications and additions may be made to the preferred embodiment, by those skilled in the art, without departing from the spirit and scope of the invention.
REFERENCES:
patent: 4921514 (1990-05-01), Rowles et al.
patent: 5026952 (1991-06-01), Bauer
patent: 5329774 (1994-07-01), Tanguay et al.
patent: 5414188 (1995-05-01), Ha et al.
patent: 5505048 (1996-04-01), Ha et al.
Calfee Halter & Griswold LLP
Chart Inc.
Griffin Walter D.
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