EA041788B1

EA041788B1 - ISOMERIZATION UNIT, METHOD FOR PRODUCING FIRST STREAM CONTAINING C6 ISOMERIZED PRODUCT STREAM AND SECOND STREAM CONTAINING HEAVY ISOMERIZED PRODUCT STREAM

Info

Publication number: EA041788B1
Application number: EA202090743
Authority: EA
Inventors: Маниш Баргава; Руми Калита; Джозеф С. ДЖЕНТРИ
Original assignee: Зульцер Мэнэджмент Аг
Priority date: 2017-09-19
Filing date: 2018-09-18
Publication date: 2022-12-02

Description

Cross-references to related applications

This application claims priority under 35 U.S.C.C. § 119(e) by virtue of U.S. Provisional Application No. 62/560569, Sept. 19, 2017, which is incorporated herein by reference in its entirety, as if has been fully described in this document.

The field of technology to which the invention belongs

The claimed invention relates generally to top baffle columns, and in particular, but not by way of limitation, to an improved isomerization plant that reduces costs and improves efficiency.

State of the art invention

Isomerization units are important for refineries to provide an easy upgrade process for traditional low octane gasoline blends. In addition, refineries are able to control the benzene content by hydrogenating the benzene fraction. The naphtha hydrotreating (NHT) and isomerization unit 100 consists of a plurality of conventional distillation columns as shown in FIG. 1. The feed stream from the NHT reactor is sent to a first stabilizer column 102. The first stabilizer column 102 removes non-condensables from the feed stream as off-gas. The stabilized bottoms stream is fed from the first stabilizer column 102 to the naphtha separator column 104. A naphtha separator column 104 separates the stabilized bottoms product into a light naphtha overhead stream and a heavy naphtha bottoms stream.

The head stream of light naphtha consists mainly of C ₅ -C ₆ components. Typically, the light naphtha overhead stream is fed to deisopentanizer column 106 which concentrates iC ₅ as deisopentanizer column overhead stream 106. The remaining C ₅ -C ₆ components are obtained as deisopentanizer column bottom stream 106 and fed to isomerization reactor 108 for increase in octane number. After isomerization, the unstable isomerate from the isomerization reactor 108 is further processed in the second stabilizer column 110. The light hydrocarbons are then removed in the overhead stream as off-gas, and the stable isomerate is sent to the depentanizer column 112 to remove the concentrated C ₅ component stream.

The C ₅ -rich stream from depentanizer column 112 is recycled back to upstream deisopentanizer column 106 to remove iC ₅ product. The bottoms product stream from the depentanizer column 112 is fed to the deisohexanizer column 114. The C6 isomerized product stream is removed from the deisohexanizer column 114 as an overhead stream, and the heavy isomerized product stream (primarily the C ₇₊ fraction) is removed from the deisohexanizer column 114 in the form of a cubic stream. The enriched nC ₆ fraction is removed as a side stream from the deisohexanizer column 114 and returned to the isomerization reactor.

The prior art system 100 in FIG. 1 has a number of disadvantages. The first and second stabilizer columns 102, 110 in the prior art system 100 operate at relatively high pressures (in this case ~100 psig and ~160 psig, respectively). excess (1.10 MPa)). Due to the incomplete condensation used in conventional stabilizers, liquid losses to the off-gas are high. Similarly, the naphtha separator column 104 also operates at high pressure (~75 psig (0.52 MPa)). Consequently, reboiler columns operate on moderately expensive medium pressure (MP) steam.

In addition, due to the number of columns involved, the inherent high operating temperatures and high operating pressures experienced at various stages of the process, a conventional isomerization unit can be costly and energy intensive to operate. With the growing demand for isomerization units in the oil refining industry, it is desirable to improve the design of the process to make it less expensive and more efficient.

The essence of the invention

Divided wall column (DWC) technology improves the efficiency and cost of traditional isomerization process schemes. An embodiment of the invention relates to a process that uses isomerization to produce high octane C ₅ and C 6 components for gasoline blending. An embodiment of the invention includes an application in which the multi-column isomerization configuration is changed to fewer distillation columns using the DWC concept. Due to the combination of lower operating pressure, columns and improved heat integration in a system, DWC configurations consume significantly less energy and reduce heating costs.

An embodiment of the invention encompasses hydrotreating reactor stabilizer columns wherein the first stabilizer column and the downstream naphtha separator column are combined in a single column with an upper baffle plate (eg, see FIGS. 2 and 3). This configuration gives a similar number of products, while the number of columns is reduced from two to one. The new hybrid column operates at the same pressure as the traditional stabilizer.

In some embodiments, the DWC includes a baffle located on top of the DWC to form two top halves, with the two top halves acting as independent columns. For example, the first stabilizer column and naphtha separator column of the prior art system of FIG. 1 are combined in a column with an upper baffle (for example, see FIGS. 2 and 3). In this particular DWC, the side of the DWC into which the stream enters functions as an absorber. The lean naphtha stream is used as the absorbent medium. This lean naphtha stream may be obtained either from the heavier bottoms of the DWC column or from another adjacent column in the same plant. The other side of the DWC works like a conventional distillation column. Thus, an embodiment of the invention covers such columns in which both distillation and absorption take place within the same column.

Similarly, the depentanizer column and deisohexanizer column of the prior art system of FIG. 1 can also be combined into an upper DWC (eg see FIGS. 2 and 4). For this DWC column, the top of the DWC behaves like two separation zones. One side acts as a depentanizer to remove the C ₅ components, while the other side acts as a deisohexanizer to recover light (mainly C ₆ isomerate) and heavy isomerate products (C7 and heavier).

In some embodiments, the isomerization stabilizer operates at a lower pressure than the prior art system of FIG. 1. For example, the pressure may be about 75 psig. (0.52 MPa) compared to a pressure of approximately 160 psig. (1.10 MPa) for the second stabilizer column of the prior art system of FIG. 1. The operating pressure is chosen in such a way that, compared to the prior art system of FIG. 1 second stabilizer column operates at a lower heating temperature (in this case low pressure steam is used). In addition, some of the reboiler heat output for the second stabilizer column is obtained by integrating heat with the effluent bottoms from the isomerization reactor.

In some embodiments, the DWC comprising the first stabilizer column and the naphtha separator column also operates at high pressure (~100 psig (0.69 MPa). This configuration compensates for the lower operating pressure of the downstream valuable C ₅ components lost in the latter system are captured in the upstream DWC column via absorption using a lean naphtha stream.In addition, due to higher temperatures, this configuration facilitates heat integration with the deisopentanizer column .

In some embodiments, a packed flash drum is used in which the off-gas from the second stabilizer is desorbed using a portion of the heavy naphtha bottom stream from the DWC column that combines the first stabilizer column and the naphtha separator column. The residual lean naphtha stream is obtained as a liquid product from the drum and is used as the absorbent medium in this configuration.

In some embodiments, the system uses a combination of low pressure (LP) steam and medium pressure (MP) steam by utilizing DWC technology in a configuration that provides a significant reduction in operating costs compared to the prior art system of FIG. 1.

In the formula, an isomerization unit is claimed, containing the first column with a dividing wall, containing the first side, made in the form of a stabilizer column; and a second side made in the form of a naphtha separator column, wherein the first side and the second side of the first column with a dividing wall are separated by an upper dividing wall, and the first column with a dividing wall is connected to a bottom reboiler configured to receive a bottom stream from the first column with a dividing wall and returning the heated part of the bottom stream back to the first column with a dividing wall;

a second column with a dividing wall, containing the first side, made in the form of a column-depentanizer; and a second side made in the form of a deisohexanizer column, wherein the first side and the second side of the second dividing wall column are separated by an upper dividing wall, the second dividing wall column being connected to the first condenser and the second condenser, the first condenser being configured to supply the condensed portion of the overhead stream from the first side of the second baffle column to the head section of the first side of the second baffle column, and the second condenser is configured to supply the condensed portion of the overhead stream from the second side of the second baffle column to the head section of the second side of the second baffle column , and wherein the second baffle column is connected to a bottoms reboiler configured to receive the bottoms stream from the second baffle column and return the heated portion of the bottoms o flow back to the second baffle column;

a deisopentanizer column connected to the first baffle column, configured to receive an overhead stream of light naphtha from a second side of the first baffle column;

an isomerization reactor connected to the deisopentanizer column and configured to receive a bottom stream from the deisopentanizer column; and a stabilizer column connected to the isomerization reactor and configured to receive a stream containing an unstable isomerizate from the isomerization reactor and feed the stable isomerate to the second column with a dividing wall.

Preferably, the first baffle column is connected to a first condenser and a second condenser, wherein the first condenser is configured to supply the condensed portion of the overhead stream from the first side of the first baffle column to the head section of the first side of the first baffle column, and the second condenser is configured to supplying the condensed portion of the top stream from the second side of the first dividing wall column to the head section of the second side of the first dividing wall column.

Preferably, the second baffle column includes a side outlet from a position near the bottom of the second baffle column that does not include a top baffle.

Preferably, the isomerization unit further comprises: a packed flash drum connected to the first baffle column and configured to receive a bottom stream from the first baffle column and an off-gas stream from the stabilizer column to form lean solvent, which is fed back to the first baffle column. dividing wall.

According to the formula, a method is also claimed for obtaining a first stream containing a C ₆ isomerized product stream and a second stream containing a heavy isomerized product stream, carried out in the above isomerization unit, including feeding a stream that comes from a naphtha hydrotreating reactor to a first separator column. partition;

treating the stream with a first baffle column to produce an off-gas stream by using absorption through the stream of heavier hydrocarbons;

treating the stream with a first baffle column to form an overhead light naphtha stream from a second side of the first baffle column;

feeding the top stream of light naphtha to the deisopentanizer column;

treating the light naphtha overhead stream with a deisopentanizer column;

feeding the bottom stream from the deisopentanizer column to the isomerization reactor to increase the octane number of the bottom stream;

feeding the unstable isomerizate stream from the isomerization reactor to the stabilizer column;

treating the unstable isomerate stream with a stabilizer column to obtain a stable isomerate stream;

feeding the stable isomerate stream to a second partition wall column; and obtaining, by means of the second partition column, a first stream containing a C ₆ isomerized product stream and a second stream containing a heavy isomerized product stream.

Brief description of the drawings

In FIG. 1 shows a prior art system of a combined naphtha hydrotreater and isomerization unit;

in fig. 2 is a flow diagram in accordance with an embodiment of the invention using DWC technology in a naphtha hydrotreater and isomerization unit;

in fig. 3 is a flow diagram in accordance with an embodiment of the invention for an overhead DWC stabilizer/naphtha splitter; and in FIG. 4 is a flow diagram in accordance with an embodiment of the invention for an overhead DWC depentanizer/deisohexanizer design.

Detailed Description of Illustrative Embodiments

Embodiments of the invention relate to an isomerization process in which individual columns are replaced and/or combined using DWC technology to achieve minimal energy consumption.

Let us now turn to FIG. 2, which shows a schematic 200 of the isomerization process. The circuit 200 includes a first dividing wall column (DWC) 210 and a second DWC 240. The first DWC 210 includes an upper dividing wall 211 that divides the top 212 of the first DWC 210 into a first side 213 and a second side 214. In an embodiment, shown in FIG. 2, the first side 213 is configured to operate as a stabilizer column,

- 3 041788 and the second side 214 is configured to work as a naphtha separator column. In some embodiments, first side 213 includes first head section 215 and second side 214 includes second head section 216. First condenser 217 is coupled to first head section 215 and configured to condense overhead stream received therefrom. The stream from the first condenser 217 may be fed back to the first head section 215. The second condenser 218 is connected to the second head section 216 and is configured to condense the overhead stream received therefrom. The stream from the second condenser 218 may be fed back to the second head section 216. The bottom reboiler 219 is connected to the first DWC 210 and configured to receive the bottom stream from the first DWC 210 and return the heated stream back to the bottom section 220 of the first DWC 210.

The second DWC 240 includes a top baffle 241 that separates the top 242 of the second DWC 240 into a first side 243 and a second side 244. In the embodiment shown in FIG. 2, first side 243 is configured to operate as a depentanizer column and second side 244 is configured to operate as a deisohexanizer column. In some embodiments, first side 243 includes first head section 245 and second side 244 includes second head section 246. First condenser 247 is connected to first head section 245 and configured to condense the overhead stream received therefrom. The stream from the first condenser 247 may be fed back to the first head section 245. The second condenser 248 is connected to the second head section 246 and is configured to condense the overhead stream received therefrom. The stream from the second condenser 248 may be fed back to the second head section 246. The bottom reboiler 249 is connected to the second DWC 240 and configured to receive the bottom stream from the second DWC 240 and return the heated stream back to the bottom section 250 of the second DWC 240.

The exemplary flow path for circuit 200 begins with flow 230 to first side 213 of first DWC 210. In the embodiment shown in FIG. 2, the first side 213 is a stabilizer and the second side 214 is a naphtha separator. In some embodiments, stream 230 is from a naphtha hydrotreating reactor. The first side 213 removes non-condensable components from the stream 230 in the form of an off-gas stream 231. The stabilized bottoms product descends from the first side 213 and enters the second side 214. The second side 214 separates the stabilized bottoms product from the first side 213 into a light naphtha overhead stream 232 and a heavy naphtha bottoms stream 233.

The head stream 232 light naphtha consists mainly of C ₅ -C ₆ components. Light naphtha overhead stream 232 is fed to deisopentanizer column 251 which concentrates iC ₅ as overhead stream 234. The remaining C ₅ -C ₆ components are obtained as bottom stream 235 of deisopentanizer column 251 and fed to isomerization reactor 252 to increase octane through isomerization reactions. . Stream 236 containing unstable isomerate from isomerization reactor 252 is further processed in stabilizer column 254. Light hydrocarbons are removed in overhead stream 237 as off-gas and stream 238 containing stable isomerate is sent to first side 243 of second DWC 240 to remove concentrated flow C ₅ components.

In the embodiment shown in FIG. 2, the first side 243 is a depentanizer and the second side 244 is a deisohexanizer. The top stream 261, which is rich in C ₅ , is recycled from the first head section 245 of the second DWC 240 to the upstream deisopentanizer column 251 to remove the iC ₅ product. The bottoms product stream descends from the first side 243 and enters the second side 244. The C6 isomerized product stream 262 is removed from the second DWC 240 as an overhead stream and the heavy isomerized product stream 263 (primarily the C ₇₊ fraction) is removed from the second DWC 240 in the form of a cubic stream. Enriched in nC ₆ stream 264 is removed as a side stream from the second DWC 240 and recycled to the reactor 252 isomerization.

In FIG. 3 is a side-by-side comparison of columns 102 and 104 of FIG. 1 with the first DWC 210 of FIG. 2. An upper baffle 211 separates the upper portion 212 of the first DWC 210 into a first side 213 and a second side 214, i. for reference, the pre-fractionation side and the product side. The flowsheet is designed to remove non-condensable components in the form of an off-gas stream 231. In addition, the circuit concentrates the medium boiling components (C ₅ -C ₇ ) as light naphtha overhead stream 232 on the other side, while the slower boiling components (heavy naphtha) are recovered at the bottom of the column as heavy naphtha bottom stream 233. On the feed side of the upper baffle 211, the lean naphtha stream reduces the loss of valuable C ₅ components to the off-gas through absorption. On the product side of the upper baffle plate 211, the medium boiling components C ₅ to C ₇ move upwards and the low boiling components move downwards. Accordingly, this scheme combines distillation and absorption in the same column. In addition, the first absorption side condenser 217 is a water-cooled partial condenser, while the second distillation side condenser 218 is a full condenser using an air-cooled heat exchanger.

- 4 041788

The DWC 212 operates at a high operating pressure of 100 psig. (0.69 MPa) and uses steam SD as a heat carrier in the bottom reboiler 219 (for example, a thermosiphon reboiler). The high column temperature allows heat to be integrated with the downstream deisopentanizer column 251, which operates at a much lower pressure.

The deisopentanizer column 251 is a conventional distillation column that removes a concentrated isopentane stream at the top (overhead stream 234). Deisopentanizer column reboiler 251 uses LP steam while another reboiler integrates heat with hot C ₅ -C ₇ overhead vapor from DWC column 212 upstream.

In FIG. 4 shows a side-by-side comparison of columns 112 and 114 of FIG. 1 with the second DWC 240 of FIG. 2. The second DWC 240 separates four product streams: the 261 C5 recycle stream, the C6 isomerate stream 262, and the 263 C ₇₊ stream along with the 264 nC ₆ recycle stream. Two full condensers 247, 248 are provided on both sides of the top baffle 241. In some embodiments, condensers 247, 248 are air-cooled heat exchangers. The bottom reboiler 249 at the bottom of the second DWC 240 runs on LP steam.

In embodiments of the invention, the column head pressure is maintained by a head vapor line pressure regulator. On the pre-fractionation side, there is a stream coming from the overhead condenser.

In the table below. 1 shows the energy and cost savings for circuit 200 compared to prior art system 100.

Table 1

Options Unit Traditional design Construction with DWC Number of columns - 6 4 energy saving % A basic level of 30% of the base level Capital expenditures % A basic level of 70% of the base level

In the table below. 2 shows the operating parameters for circuit 200 compared to prior art system 100.

table 2

Conventional design DWC design NHT stabilizer Naphtha stabilizer/separator Working pressure psi inch g (MPa) 100 (0.69) 100 (0.69) Reboiler load SD steam SD steam Naphtha separator - Working pressure psi inch g (MPa) 75 (0.52) - Reboiler Load SD Steam - Isomerization Stabilizer Isomerization Stabilizer Working Pressure psi inch g (MPa) 150 (1.03) 75 (0.52) Reboiler load LP steam LP steam/Heat integration with reactor effluent Depentanizer Depentanizer/Deisohexanizer Working pressure psi inch g (MPa) 20 (0.14) 20 (0.14) Reboiler Load ParND ParND Deisohexanizer - Operating pressure psi inch g (MPa) 7 (0.05) - Reboiler load ParND -

Claims

CLAIM

1. Installation of isomerization, containing the first column with a dividing wall, containing the first side, made in the form of a stabilizer column; and a second side made in the form of a naphtha separator column, wherein the first side and the second side of the first column with a dividing wall are separated by an upper dividing wall, and the first column with a dividing wall is connected to a bottom reboiler configured to receive a bottom stream from the first column with a dividing wall and returning the heated part of the bottom stream back to the first column with a dividing wall;

2. An isomerization plant according to claim 1, wherein the first baffle column is connected to the first condenser and the second condenser, the first condenser being configured to supply the condensed portion of the overhead stream from the first side of the first baffle column to the head section of the first side of the first column with a dividing wall, and the second condenser is configured to supply the condensed part of the head stream from the second side of the first column with a dividing wall to the head section of the second side of the first column with a dividing wall.

3. The isomerization plant of claim 1, wherein the second baffle column includes a side vent from a position near the bottom of the second baffle column that does not include an upper baffle column.

4. The isomerization plant of claim 1, further comprising a packed flash drum connected to the first baffle column and configured to receive a bottom stream from the first baffle column and an off-gas stream from the stabilizer column to form a lean solvent that is fed back to the first column with a dividing wall.

5. The method of obtaining a first stream containing a stream of isomerized product C ₆ and a second stream containing a stream of heavy isomerized product, performed in the isomerization unit according to any one of paragraphs. 1-4, including feeding the stream that comes from the naphtha hydrotreating reactor to the first baffle column;

treating the stream with a first baffle column to produce an off-gas stream by utilizing absorption through the stream of heavier hydrocarbons;

treating the stream with the first baffle column to form an overhead stream of light naphtha from a second side of the first baffle column;

feeding the head stream of light naphtha to the deisopentanizer column;

processing the light naphtha overhead stream with a deisopentanizer column;

under the discharge of the bottom stream from the deisopentanizer column to the isomerization reactor to increase the octane number of the bottom stream;

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