Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2001-03-20
2001-10-02
Doerrler, William (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S902000, C062S903000
Reexamination Certificate
active
06295839
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to cryogenic air separation and, more particularly, to the integration of various levels of heat-transfer and mass-transfer in order to enhance thermodynamic efficiency and to reduce capital costs.
BACKGROUND OF THE INVENTION
Cryogenic air separation systems are known in the art for separating gas mixtures into heavy components and light components, typically oxygen and nitrogen, respectively. Generally, the separation process takes place in plants that cool incoming mixed gas streams through heat exchange with other streams (either directly or indirectly) before separating the different components of the mixed gas through mass transfer methods such as distillation and/or reflux condensation (dephlegmation). Once separated to achieve desired purities, the different component streams are warmed back to ambient temperature. Typically, the different warming, cooling, and separating steps take place in separate pieces of equipment, which, along with the installation and piping, adds to the manufacturing costs for the plant.
Various air separation systems have been introduced that combine some of the separate heat transfer components in order to provide an integrated device that may perform a variety of functions. In particular, systems have been proposed that partially combine different heat exchangers for warming or cooling fluid streams and separation devices for separating out heavy and light components in the streams into a single heat exchange core in order to reduce the number of pieces of equipment needed in an air separation plant. This may reduce the overall cost of the plant.
SUMMARY OF THE INVENTION
The present invention is directed to an air separation system with a unique integration design that provides a single brazed core that can combine separation networks with a host of heat exchange functions.
Increasing the total cross section of a heat transfer core provides a greater opportunity for heat transfer between streams, thus increasing efficiency. This improvement may come at an attractive cost per unit area of heat transfer.
The present invention also reduces the capital costs associated with air separation systems (particularly the cold boxes of cryogenic air separation systems) and increases overall thermodynamic efficiency by utilizing designs that optimally combine mass-transfer functions with heat-transfer functions in a single core which results in the reduction or elimination of a significant amount of interconnecting piping and independent supporting structures and cold box volume thereby reducing piping and installation costs.
Typically, the integrated core is used to (i) cool the process feed air down to a cryogenic temperature, (ii) boil the heavy component product (typically liquid oxygen), and (iii) superheat/subcool various process streams. Preferably, the integrated core is a brazed plate-fin core made of aluminum. The integrated core may include a plurality of passages arranged so as to effectively combine the various levels of heat-transfer, as well as different levels and types of mass-transfer (such as rectification and stripping).
In a preferred design of the present invention, an integrated core is provided in flow communication with a double column separation apparatus having a higher pressure column (generally termed the lower column) and a lower pressure column (generally termed the upper column). The double column separation apparatus may be of any conventional design that provides separation of heavy and light components from various vapor streams.
In a preferred design, the integrated core includes a first set of intake passages (although, it should be recognized that only one passage for each stream in the system is required to achieve the benefits of the present invention) in which an incoming feed air stream is cooled and then directed into the double column separation apparatus (typically the lower column). The cooling is preferably accomplished by positioning the first set of intake passages in a heat exchange relationship with at least one other passage in the integrated core. In variations of this embodiment, the first set of intake passages may include a section for mass transfer, in which a condensate in the passage serves as reflux to rectify the feed air stream. In this case, the first intake passages will form a condensate stream that may be directed into the upper column.
A first set of cooling passages cools a first bottom stream from the separation apparatus (typically the lower column) and feeds the cooled, first bottom stream back into the separation apparatus (typically the upper column). The first set of cooling passages may be in a heat exchange relationship with at least one other passage (or set of passages) in the integrated core.
A first set of warming passages warms a first overhead stream from the separation apparatus (preferably the upper column) and discharges the warmed first overhead stream from the integrated core. The first set of warming passages may be in a heat exchange relationship with at least one other set of passages in the integrated core.
A separating section (preferably a stripping column) in the integrated heat exchanger core separates a second bottom stream from the separation apparatus (preferably from the upper column external to the integrated heat exchanger core) to form an oxygen enriched stream and a nitrogen enriched stream. The nitrogen enriched stream may be directed back into the separation apparatus (preferably into the upper column). Preferably, the oxygen stream is separated into a vapor phase stream and a liquid phase stream by a phase separator. The vapor phase stream typically is directed back into the separating section. In preferred embodiments, the separating section is integrated within the integrated core and the separating apparatus is external to the integrated core. In addition, a pump may be provided to pump the liquid phase through the integrated core.
A set of vaporization passages vaporizes the liquid phase stream from the phase separator and discharges the vaporized liquid phase stream from the integrated core. The vaporization passages may be in heat exchange relationships with at least one other set of passages of the integrated core.
The integrated core may also include a second set of cooling passages that cools a condensed stream from the upper column and directs the cooled, condensed stream back into the separation apparatus (typically into the upper column). As with the first set of cooling passages, the second set is preferably in a heat exchange relationship with at least one other set of passages in the integrated core.
The integrated core may also include a second set of warming passages that warms a second overhead stream from the stripping apparatus (preferably from the lower pressure column) and discharges the warmed second overhead stream from the integrated core. The second set of warming passages may also be in a heat exchange relationship with at least one other set of passages in the integrated core.
A fourth set of warming passages may be provided to warm the oxygen enriched stream from the separating section and to direct the oxygen enriched stream into the phase separator. These passages may also be in heat exchange relationships with any number of other passages in the integrated core.
The integrated core may also include a second set of intake passages that cools a second incoming feed air stream and directs the cooled, second incoming feed air stream into the separation apparatus (preferably into the lower column). The second set of intake passages may be in a heat exchange relationship with at least one other set of passages in the integrated core.
The integrated core may also include a third set of intake passages that cools a third incoming feed air stream and directs the cooled, third incoming feed air stream into the separation apparatus (preferably into the lower pressure column). The third intake passages may be in heat exchange relationships with any number of other passages i
Arman Bayram
Billingham John Fredric
Bonaquist Dante Patrick
Nguyen Tu Cam
Wong Kenneth Kai
Doerrler William
Ktorides Stanley
Praxair Technology Inc.
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