Patent Application
20130096356
This document generally relates to methods and apparatuses for the isomerization and deisohexanizing of hydrocarbon feeds, and more particularly relates to such methods and apparatuses that provide enhanced heat recovery.
Isomerization and deisohexanizing processing of hydrocarbons is well developed and widely practiced in the petrochemical and petroleum refining industries. One constant concern for petrochemical and petroleum refiners is the utility consumption of isomerization and deisohexanizing processing units. One method of reducing utility consumption in isomerization processing is to use a heat exchange between hot streams with excess heat and cooler streams in need of energy. For instance, the standard process flow in a typical isomerization process is to heat the feed stream by indirect heat exchange against the effluent of the isomerization zone.
While current methods are able to utilize heat energy from effluent isomerization streams to preheat feedstock, the methods typically still require large amounts of utility consumption. For instance, current methods typically utilize additional heating of feedstock by passing the feedstock stream through a steam heater or a similar available source of high temperature heat. Due to the large scale of the processing, a nominal improvement in energy efficiency can significantly reduce utility consumption.
Accordingly, it is desirable to provide methods and apparatuses for the isomerization and deisohexanizing of hydrocarbon feeds that provide enhanced heat recovery. In addition, it is desirable to provide methods and apparatuses for the isomerization and deisohexanizing of hydrocarbon feeds that exchange heat between the feed and a sidecut from the deisohexanizer unit. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.
Methods and apparatuses for the isomerization and deisohexanizing of hydrocarbon feeds are provided. In accordance with an exemplary embodiment, a method for the isomerization of a feed in an isomerization zone to form an isomerized stream and the deisohexanizing of the isomerized stream in a deisohexanizer zone includes exchanging heat between the isomerization zone and the deisohexanizer zone to raise the temperature of the feed.
In accordance with another exemplary embodiment, a method for isomerization and deisohexanizing of a hydrocarbon feed includes isomerizing the hydrocarbon feed in a lead isomerization reactor to form a first isomerized stream. The first isomerized stream is isomerized in a lag isomerization reactor to form a second isomerized stream. The second isomerized stream is deisohexanized in a deisohexanizer. The method provides for drawing a sidecut stream from the deisohexanizer. Heat is exchanged between the hydrocarbon feed and the sidecut stream from the deisohexanizer to raise the temperature of the hydrocarbon feed. Further, heat is exchanged between the hydrocarbon feed and the second isomerized stream after heat is exchanged between the hydrocarbon feed and the sidecut stream. Also, heat is exchanged between the hydrocarbon feed and the first isomerized stream after heat is exchanged between the hydrocarbon feed and the second isomerized stream.
Another exemplary embodiment provides an apparatus for the isomerization and deisohexanizing of a hydrocarbon feed. The apparatus includes an isomerization zone including an isomerization unit configured to isomerize the hydrocarbon feed to form an isomerized stream. Further, the apparatus includes a deisohexanizer zone located downstream of the isomerization zone and configured to deisohexanize the isomerized stream. Also, the apparatus includes a heat exchanger coupled between the isomerization zone and deisohexanizer zone and configured to transfer heat to the feed upstream of the isomerization unit.
Exemplary embodiments will hereinafter be described in conjunction with the following drawing figure, wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the isomerization and deisohexanizing methods and apparatuses described. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. Also, additional components, loops, and processes may be included in the apparatus but are not described herein for purposes of clarity. Stream compositions presented herein are merely illustrative of an embodiment and are not intended to limit the methods and apparatuses in any way.
The UOP Penex™ process is a continuous catalytic process used in the refining of crude oil. The process isomerizes hydrocarbon feeds into higher octane, branched molecules. For example, a hydrocarbon feed such as light naphtha, which typically comprises C4-C7 paraffins and C5-C7 cyclic hydrocarbons, and often primarily comprises C5 and C6 paraffins, may be isomerized into higher-octane, branched C5/C6 molecules. The process typically uses reactors with high activity chlorinated alumina-type platinum catalysts. A single pass of feedstock with an octane rating of 50-60 through such a reactor typically produces an end product rated at 82-86. To obtain a higher octane rating, the feedstock may be subsequently passed through a deisohexanizer (DIH) unit. After deisohexanizing, the end product typically has an octane rating of 87-90.5.
Methods and apparatuses for isomerization and deisohexanizing of hydrocarbon feeds are contemplated herein. The methods and apparatuses achieve enhanced heat recovery through heat exchange between deisohexanizer and isomerization stages. To that end, heat is exchanged between a sidecut from the deisohexanizer zone and the feed into the isomerization unit. As a result, heat energy is efficiently transferred between the deisohexanizer zone and the isomerization zone within the apparatus, and the need for additional heat input from outside the apparatus is reduced.
As shown in
As shown, the isomerization zone 20 includes an isomerization unit comprised of a lead isomerization reactor 46 and a lag isomerization reactor 48. While two reactors are shown, in certain embodiments there may be either one or three or more isomerization reactors. Reactors 46 and 48 may be substantially identical, with “lead” and “lag” only referring to their positioning in relation to fluid flow in the apparatus 10. In certain embodiments, the catalyst used in the isomerization zone 20 is distributed equally between the reactors 46 and 48. In other embodiments, there may be differing catalyst distributions. The use of multiple reactors 46 and 48 facilitates a variation in the operating conditions between the two reaction zones to enhance isoparaffin production and improve cyclic hydrocarbon conversion. In this manner, the lead reactor 46 can operate at higher temperature conditions that favor ring opening but performs only a portion of the normal to isoparaffin conversion. The heat exchangers upstream of the lead isomerization reactor 46, facilitate the use of higher temperatures in the lead isomerization reactor 46. Once cyclic hydrocarbon rings have been opened by initial contact with the catalyst, the lag reactor 48 may operate at temperature conditions that are more favorable for isoparaffin equilibrium.
In
After passing through the second indirect heat exchanger 32, isomerized stream 54 exits the isomerization zone 20 and enters a fractionating column or stabilizer 56. Stabilizer 56 separates an overhead offgas product 58 typically containing HCL, hydrogen, and light hydrocarbons such as byproduct methane, ethane, propane and butane gases. Offgas 58 is scrubbed to remove HCL and then may be routed to a central gas processing plant for removal and recovery of hydrogen, propane and butane. The residual gas after such processing may become part of the refinery's fuel gas system. In
In the deisohexanizer zone 62, a deisohexanizer unit 64 deisohexanizes the bottoms product 60 and creates high octane isomerate 14 and a bottoms product 66. As shown, the deisohexanizer unit 64 includes an outlet 68 for a sidecut stream 70. In an exemplary embodiment, the sidecut stream 70 is comprised primarily of normal hexane and monomethylpentanes, particularly normal hexane, 2-methylpentane and 3-methylpentane. The exemplary sidecut stream 70 may also contain cyclohexane, some dimethylbutanes, and some heavies. Sidecut streams 70 having other compositions are contemplated herein, and are envisioned as a result of differing feedstocks and differing processing. In
In an exemplary embodiment of the apparatus 10, the temperature of the sidecut stream 70 is about 110° C. when exiting the deisohexanizer unit 64. After heat exchange at the first indirect heat exchanger 28, the temperature of the sidecut stream 70 is about 66° C.-68° C. At the first indirect heat exchanger 28, the temperature of the combined feed from line 26 is raised from about 43° C. to about 64° C.
At the second indirect heat exchanger 32, the fluid in line 30 is heated from about 64° C. to about 115° C., while the isomerized stream 54 is cooled from about 174° C. to about 135° C. At the third indirect heat exchanger 36, the fluid from line 34 is heated from about 115° C. to about 175° C., while the isomerized stream 52 is cooled from about 204° C. to about 146° C. As a result of the increased temperature of the output from the third indirect heat exchanger 36 in line 42, less energy is needed from the charge heater 44 before the isomerization reaction.
Accordingly, apparatuses and methods for the isomerization and deisohexanizing of hydrocarbon feeds have been provided. While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the isomerization and deisohexanizer apparatuses or methods in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.
