Patent Application
20120330076
This invention generally relates to processes, such as alkylation, utilizing one or more exchangers.
The alkylation of benzene with propene may be conducted in a multi-stage, all liquid phase reactor under conditions sufficient to limit reaction temperature rise. Often, controlling the reaction temperature may be obtained by the staged addition of propene reactant also serving as an inter-stage reactor quench with a large circulating reactor effluent recycle stream passing from the final reaction stage back to the first reaction stage. The reactor effluent recycle stream can act as a heat sink to control the exotherm in the multiple stages.
As an example, the amount of the reactor effluent recycle stream can be 3.5 to 1, by volume, based on the net reactor effluent. As such, the reactor effluent recycle stream may require the use of large-capacity recycle pumps combined with various heat exchange services that cool a portion of the recycle stream before providing the inter-bed reactor quench. As a consequence, there is a strong desire to improve the efficiency of the process by utilizing heat generated from the stages rather than merely utilizing cooling apparatuses without the benefit of recapturing the heat in other suitable processes.
One exemplary embodiment can be a process for alkylating. The process can include providing a first effluent from a first alkylation zone, and providing a second effluent from a second alkylation zone. Generally, the first and second effluents are provided to an exchanger for reboiling a fractionation zone.
Another exemplary embodiment can be an exchanger. The exchanger can include a first discrete tube bundle, a second discrete tube bundle, and a third discrete tube bundle. Typically, each tube bundle is adapted to receive a different stream for exchanging heat.
A further exemplary embodiment may be a process for alkylating benzene with one or more C3− hydrocarbons. The process can include providing a first effluent including one or more alkylated benzene compounds from a first alkylation zone, providing a second effluent including one or more alkylated benzene compounds from a second alkylation zone, providing a third effluent including one or more alkylated benzene compounds from a third alkylation zone, passing the first, second, and third effluents from the stab-in reboiler to a cooling zone including one or more air coolers, and providing the first effluent to the second alkylation zone, the second effluent to the third alkylation zone, and the third effluent to a fourth alkylation zone from the cooling zone. Usually, the first, second, and third effluents are provided to a stab-in reboiler for intermediate reboiling of a benzene fractionation column.
The embodiments disclosed herein can provide a process that utilizes a plurality of effluents, namely a first and second effluent from respective first and second alkylation zones to provide heat in another process, such as reboiling a fractionation zone. Preferably, at least three effluents from respective alkylation zones are used for reboiling a fractionation zone, such as a fractionation zone separating cumene and benzene where the exchanger can be a stab-in reboiler. Utilizing an intermediate reboiler located higher in the column where the temperature differential driving forces are favorable can decrease the use of higher value, hotter heating medium, such as heat transfer oil, high temperature steam or a fuel-fired heater at the bottom reboiler, thereby improving energy efficiency and reducing external utility costs. In addition, the embodiments disclosed herein can provide an exchanger with three discrete tube bundles, each having a separate inlet and outlet, that can receive separate process streams preferably all being at substantially the same temperature for providing additional heat duty to, e.g., a fractionation zone. Moreover, eliminating the inter-bed quench can improve mono-alkylation selectivity from a plug flow reactor configuration versus back-mixing that may occur from an inter-bed quench.
As used herein, the term “stream” can include various hydrocarbon molecules, such as straight-chain, branched, or cyclic alkanes, alkenes, alkadienes, and alkynes, and optionally other substances, such as gases, e.g., hydrogen, or impurities, such as heavy metals, and sulfur and nitrogen compounds. The stream can also include aromatic and non-aromatic hydrocarbons. Moreover, the hydrocarbon molecules may be abbreviated C1, C2, C3 . . . Cn where “n” represents the number of carbon atoms in the one or more hydrocarbon molecules.
As used herein, the term “zone” can refer to an area including one or more equipment items and/or one or more sub-zones. Equipment items can include one or more reactors or reactor vessels, heaters, exchangers, pipes, pumps, compressors, and controllers. Additionally, an equipment item, such as a reactor, dryer, or vessel, can further include one or more zones or sub-zones.
As used herein, the term “alkylation” can mean the introduction of an alkyl radical into an organic molecule. As an example, an ethene and/or a propene radical can be introduced into a benzene molecule or a methanol radical can be introduced into a toluene molecule.
As used herein, the term “exchanger” may refer to an equipment item that facilitates heat transfer between two fluids and can include a stab-in reboiler, a condenser, an evaporator, an air cooler, a kettle exchanger, a double-piped exchanger, a baffled shell-and-tube exchanger, a forced-recirculation reboiler, or a vertical or horizontal thermosiphon reboiler.
As used herein, the term “rich” can mean an amount of at least generally about 50%, and preferably about 70%, by mole, of a compound or class of compounds in a stream.
As used herein, the term “substantially” can mean an amount of at least generally about 80%, preferably about 90%, and optimally about 99%, by mole, of a compound or class of compounds in a stream.
As depicted, process flow lines in the figures can be referred to interchangeably as, e.g., lines, pipes, feeds, portions, effluents, remainders, products, or streams.
Referring to
The alkylation reactor 110 can include a first alkylation zone 120, a second alkylation zone 140, a third alkylation zone 160, and a fourth alkylation zone 180. Although four alkylation zones are disclosed, it should be understood that any suitable number of alkylation zones may be utilized such as two to eight alkylation zones. The first, second, third and fourth alkylation zones 120, 140, 160, and 180 can operate at any suitable conditions, independently, such as a temperature of about 70-about 180° C. and a pressure of about 100-about 10,000 kPa. The alkylation zone effluent 184 can be passed for further processing, such as to a fractionation zone to remove light ends, which may include a depropanizer column, and be combined with other process effluents, such as a transalkylation effluent prior to being further fractionated. These exemplary zones are disclosed in, e.g., U.S. Pat. No. 7,744,828. Additionally, if the cooling zone 500 is insufficient to remove heat from alkylation effluent, at least a portion of the alkylation zone effluent 184 may be recycled to the top of the alkylation reactor 110 by being added to the combined feed 90, as hereinafter described. Generally, it is desirable to minimize any such recycling of the alkylation zone effluent 184.
After additional processing, the alkylation zone effluent 184 can be provided whole or in part as a benzene column feed 190. Particularly, the fractionation zone 200 can include a fractionation column 210, such as a benzene column. The fractionation column 210 can include a tub 260 housing at least a portion of an exchanger 300. The exchanger 300 in this exemplary embodiment can be a stab-in reboiler to provide intermediate heat duty to the fractionation column 210.
Usually, the fractionation column 210 can provide an overhead stream 220, including benzene, and a bottom stream 240, including an alkylated benzene such as cumene. The fractionation column 210 can operate at any suitable conditions, such as an operating temperature ranging from about 30-about 220° C. and a pressure ranging from about 160-about 280 kPa. The benzene in the overhead stream 220 can be provided at a temperature of about 120-about 170° C. The overhead stream 220 can be combined with the propene remainder stream 76 to form the combined feed 90 to the alkylation reactor 110.
In operation, the combined feed 90 can be provided to the first alkylation zone 120 forming a first effluent or first alkylation effluent 124. The first effluent 124 can be provided to the exchanger 300 to remove some of its heat. Generally, liquid in the fractionation column 210 collects in the tub 260, which can be reboiled by the exchanger 300. Afterwards, the first effluent 124 can be provided to the cooling zone 500.
The cooling zone 500 can include one or more air coolers, such as a first air cooler 510, a second air cooler 520, and a third air cooler 530, although any suitable number of coolers can be utilized. Also, the cooler may utilize other fluids, such as water, in one preferred embodiment the cooler is one or more air-cooled heat exchangers. Alternatively, any suitable exchanger can be utilized. Afterwards, the first effluent 124 can pass through the cooling zone 500 particularly, the first air cooler 510 to be cooled to a suitable temperature for being provided to the second alkylation zone 140. Prior to being provided above the second alkylation zone 140, the first effluent 124 can be combined with the third propene portion 72.
Similarly, a second effluent or second alkylation effluent 144 and a third effluent or third alkylation effluent 164 can exit the respective second and third alkylation zones 140 and 160. Likewise, the second effluent 144 and the third effluent 164 may be provided to the exchanger 300. Afterwards, the second effluent 144 and the third effluent 164 can pass through the cooling zone 500, particularly the respective second air cooler 520 and third air cooler 530, to be cooled to the appropriate temperature prior to being combined with, respectively, the second propene portion 68 and the first propene portion 64. Next, the second effluent 144 and the third effluent 164 can be provided to the above-respective alkylation zones, namely the third alkylation zone 160 and the fourth alkylation zone 180. The alkylation zone effluent 184 can be obtained after the reactants pass through the fourth alkylation zone 180. The cooling zone 500 can provide a cooled recycled effluent to an alkylation zone for preventing an undesirable increase in the exothermic reaction temperature.
Typically, the effluents 124, 144, and 164 can be transferred as a liquid under system pressure at an intermediate location between the benzene column feed 190 and bottom stream 240 of the benzene column 210. Internal reactor heads can ensure full flow of the effluents 124, 144, and 164 to the exchanger 300 and back to the alkylation reactor 110. After transferring heat to the material in the benzene column 210, the cooled bed effluents 124, 144, 164 return, separately, to the reactor immediately downstream of the original take-up points after cooling and mixing with more propene-rich reactant.
Usually, the first effluent 124, the second effluent 144, and the third effluent 164 are provided to the exchanger 300 at substantially the same pressure and temperature. As such, mechanical stress on the exchanger components due to temperature and pressure differentials is minimized. The exchanger disclosed herein may only have a tube side temperature difference of about 10° C. while in service from the inlet to the outlet. Thus, the low temperature difference generally allows the use the three or more discrete tube bundles while preventing damage due to fatigue.
The exchanger 300 can include a single stab-in reboiler partitioned into discrete bundles for separate streams to pass through the exchanger 300 without co-mingling. Usually, there is a discrete tube bundle for each process stream, and in this exemplary embodiment there are three discrete tube bundles. Although a stab-in reboiler is disclosed, it should be understood that other types of exchangers could be utilized such as a kettle exchanger or a horizontal thermosiphon reboiler. The kettle exchanger and the thermosiphon reboiler may be external to the fractionation column 210. An external exchanger may be advantageous if a stab-in reboiler is not suitable for the fractionation column 210 due to mechanical constraints.
Thus, the embodiment disclosed herein can allow the transfer of a portion of the heated reacted effluents from three separate zones within the alkylation reactor 110 to a location within the alkylation apparatus 100 to effectively reduce the use of higher value, hotter heating medium, such as heat transfer oil, high temperature steam or a fuel-fired heater for the generation of recycled benzene required for the alkylation reactor 110. In one exemplary embodiment, a single three-in-one service heat exchanger utilizing three discrete bundles can obtain these results. Typically, a discrete tube bundle isolates the fluid therein from other fluids passing through the exchanger.
Referring to
Referring to
The reboiler 300A can include a first sector 310, with an inlet 312 and an outlet 314, a second sector 318 with an inlet 320 and an outlet 322, and a third sector 324 with an inlet 326 and an outlet 328. Each sector 310, 318, and 324 can be internally partitioned to segregate the inlets and outlets as indicated by the dashed lines. In this exemplary embodiment, the nozzles 304 are orientated substantially perpendicular to a tangent line passing through a point on the arc where a line passing through the point and center of the exchanger bisects an inlet pie-shape, e.g., inlet 312, or an outlet pie-shape, e.g., outlet 314, as viewed from an end. Dimensionally, each sector 310, 318, and 324 can define a portion of a circle enclosed by two radii and an arc, as viewed from an end of the reboiler 300A. Generally, each sector 310, 318, and 324 supports a discrete set of tube bundles that can receive, independently, a process stream. As an example, a process fluid can enter the inlet 312 and exit the outlet 314 of the first sector 310. In this instance, each sector 310, 318, and 324 may contain discrete tube bundles and can receive a respective alkylation effluent, namely the first alkylation effluent 124, the second alkylation effluent 144, and the third alkylation effluent 164 as depicted in
Referring to
Referring to
Referring to
Usually, each one of these reboilers 300A-D provides a partitioned exchanger having separate sectors, segments, and/or regions that allow the reception of three separate process fluids into three discrete tube bundles. Although the tubes are disclosed as being U-tubes, it should be understood that any suitable tubes can be utilized, such as straight tubes with a floating tube sheet and a suitably partitioned return head. Moreover, the placement of nozzles is merely exemplary and may be provided in any suitable position to provide support for piping and ease of access during, e.g., maintenance of the exchanger, such as a reboiler. In many instances, the inlet temperature conditions and the heat removal loads are almost identical for the process streams passing through the exchanger. As such, the partitioning of the bundle is essentially for equal surface requirements.
The tube sheet can be segmented into sections, segments, or regions of approximately equal surface area and the number of tubes. The cover of the exchanger can be similarly partitioned to match so the process streams may be kept separated during introduction and removal from a bundle. Each partitioned portion of the exchanger can have its own internal partition for internal inlet and return flow. The internal partition for each partitioned portion is depicted by dashed lines in
To minimize heat transfer surface requirements, the tubes can be modified with surface heat transfer enhancements. Such enhancements can include one or more external fins, internal ridges, and/or porous layers. Procedures for making fins, grooves and/or ridges inside and/or outside a tube are disclosed in, e.g., U.S. Pat. No. 2,181,927, U.S. Pat. No. 3,559,437, U.S. Pat. No. 3,847,212, and US 2005/0145377 A1. Moreover, the inside and/or outside of the tubes can be coated, e.g., with a porous layer, such as that disclosed in, e.g., U.S. Pat. No. 4,064,914 and U.S. Pat. No. 5,091,075, to improve heat transfer and to allow boiling at a much closer temperature approach for lower hot side inlet and/or outlet temperatures. Desirably, the bundles' overall tube sheet diameter is as small as possible to minimize the size of the stab-in bundle and bundle support system requirements to minimize capital costs and to allow the fitting of a stab-in reboiler into a fractionation column. Using tubes of smaller diameter can also improve tube side heat transfer performance. Although three discrete tube bundles are disclosed, exchangers with more than three discrete tube bundles can be utilized, such as four discrete tube bundles.
In one exemplary embodiment, a staggered arrangement of tube bundles compared to a flat arrangement of tube bundles may provide a greater utilization of space. As an example, having three separate tube bundles aligned in the same plane may take more space than having the middle tube bundle elevated at an angle up to about 60°, preferably about 30-about 60°, with respect to the level of the two outer tube bundles with the angle determined by the relative diameters of the bundles in a column.
The various nozzle arrangements as depicted in
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.
From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.
