Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2000-04-14
2001-05-29
Doerrler, William (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S903000
Reexamination Certificate
active
06237366
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to an integrated heat exchange core that includes sections for various levels of heat transfer and mass transfer, in order to enhance thermodynamic efficiency and to reduce capital costs in cryogenic air separation systems.
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. 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 rectification, stripping, reflux condensation (dephlegmation), and reboiling. Once separated, the different component streams must then be warmed back to ambient temperature through heat transfer components. Typically, the different warming, cooling and separation steps take place in separate structures, each of which adds to the manufacturing costs.
It is generally desired in the art to improve air separation devices by increasing their efficiency and/or reducing capital costs of the systems. Various air separation systems have been introduced that combine what were traditionally separate structures in order to provide an integrated device. In particular, different heat exchangers for warming or cooling fluid streams, and separation devices for separating out heavy and light components in the streams, may be partially combined in a single heat exchange core to reduce the number of structures needed in an air separation plant.
However, none of the known systems provides a suitable design for fully integrating a number of heat transfer functions with separation systems for simultaneous heat and mass transfer.
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.
The present invention provides the opportunity to increase the core size because of the increased number of streams and operations to be carried out. This allows for improved economy because of core size. Proper distribution of flows permits optimizing the utilization of heat transfer area. Use of proper velocities for two phase flows also prevents problems such as flooding.
Generally speaking, the present invention relates to an air separation system utilizing an integrated core that provides simultaneous heat and mass transfer. 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 a number of levels of heat transfer (such as cooling a feed air stream down to cryogenic temperatures, subcooling/superheating process streams, and boiling liquid streams), as well different types of mass transfer (such as rectification and stripping).
In a preferred design of the integrated core, a set of entrance passages (although only one passage for each different function or stream of the core is necessary) receives an incoming feed air stream and cools the incoming feed air stream against exiting streams in other passages. A rectification section, including at least one passage for receiving the feed air stream, provides mass transfer of the feed air stream to produce a first liquid stream, enriched in a heavy component (typically oxygen), and a first vapor stream, enriched in a light component (typically nitrogen). A first set of exit passages, in a heat exchange relationship with the entrance passages, receives the first vapor stream and discharges the first vapor stream, while warming it, from the integrated core.
A separation section is provided and includes at least one passage in a heat exchange relationship with the passages of the rectification section. The separation section receives the first liquid stream and further separates the first liquid stream into a second liquid stream and a second vapor stream. Preferably, the separation section is a stripping column that provides mass transfer by stripping (using countercurrent flow) the first liquid stream. However, in other embodiments, other separation systems may be used. In particular, the separation section may boil the first liquid stream to separate it into liquid and gas phases.
The integrated core may also include another set of exit passages, in a heat exchange relationship with the entrance passages. The other exit passages receive the second vapor stream and discharge it from the integrated core as it is warmed. A set of vaporization passages, preferably in a heat exchange relationship with the entrance passages, receives and vaporizes the second liquid stream, and then discharges the vaporized second liquid stream from the integrated core.
Typically, the integrated core is designed so that the entrance and exit passages are at the same end of the core. In this type of design, the feed air stream enters the entrance passages in an upward direction of flow, and the passages discharging the process streams are orientated so as to discharge their streams in a downward direction of flow. In such an arrangement, the separation sections are located at the other end of the integrated core, above the openings for receiving and discharging air streams. The end including the separation systems generally is the cooler end of the integrated core. This design, however, may be reversed such that the air streams are received and discharged from a top end of the integrated core and the separation sections are located in a bottom end of the integrated core.
In another embodiment of the present invention, a double column separation device may be used in conjunction with the integrated core to provide additional separation. In such a device, the integrated core may be modified to discharge streams to and receive streams from the higher pressure column and lower pressure column of the double column separation device. The double column separation device may operate similarly to conventional double column systems, with the columns being in flow communication with each other. In the present invention, all of the feed streams for the double column system may be provided from the integrated core. Similarly, the integrated core may receive all of the waste and product streams from the double column system for further processing.
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Arman Bayram
Bonaquist Dante Patrick
Nguyen Tu Cam
Wong Kenneth Kai
Doerrler William
Ktorides Stanley
Praxair Technology Inc.
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