Quench System Solvation

Abstract

Methods are provided to reduce or minimize fouling within quench systems when quenching effluents containing heavy components, such as heavy hydrocarbons and/or pyrolysis tars/coke. The methods include injecting a low density, low boiling point, high aromatic content fluid into the quench system as a quench solvent. The quench solvent also has a reduced or minimized content of fouling precursors, such as styrene, cyclopentadiene, or dicyclopentadiene.

Claims

1. A method for quenching a heavy hydrocarbon effluent, comprising: contacting a hydrocarbon effluent having an effluent temperature with quench water in a quench system to form an overhead gas and one or more additional fractions having a higher boiling range than the overhead gas, the overhead gas having an overhead gas temperature that is lower than the effluent temperature by 10 C. or more, mixing a quench solvent with the quench water prior to the contacting, during the contacting, after the contacting, or a combination thereof, at least one additional fraction of the one or more additional fractions further comprising at least a portion of the quench solvent, the quench solvent comprising i) 70 wt % or more of aromatics, ii) 0.0 wt % to 4.0 wt % of cyclopentadiene, dicyclopentadiene, or a combination thereof, iii) 0.0 wt % to 1.0 wt % of styrene, and iv) 5.0 wt % or more of combined paraffins and olefins, the quench solvent having a specific gravity at 15 C. of 0.92 or less, at least one of an initial boiling point of 62 C. or higher and a T10 distillation point of 80 C. or higher, and at least one of a final boiling point of 200 C. or lower and a T90 distillation point of 180 C. or lower; separating the at least one additional fraction to form at least a hydrocarbon-containing fraction and a quench recycle fraction.

2. The method of claim 1, wherein the hydrocarbon effluent comprises 200 C.+ components, and wherein a weight ratio of the quench solvent to the 200 C.+ components in the hydrocarbon ratio is 3.0 to 9.0.

3. The method of claim 1, wherein the effluent temperature is 90 C. to 250 C.

4. The method of claim 1, wherein the overhead gas temperature is 120 C. or less.

5. The method of claim 1, wherein the quench recycle fraction comprises 0.5 wt % or less of hydrocarbons having a boiling point of 400 C. or higher.

6. The method of claim 1, wherein the quench system comprises a quench tower, one or more quench separation stages, and one or more quench water coolers, the hydrocarbon effluent being contacted with the quench water in the quench tower, the quench recycle fraction being formed in one of the one or more quench separation stages, at least a portion of the quench recycle fraction being passed into the quench water coolers to form a cooled recycle fraction, the quench water comprising at least a portion of the cooled recycle fraction.

7. The method of claim 6, wherein the quench solvent is mixed with the quench recycle fraction, the quench recycle fraction comprising 98.0 wt % or more of water prior to mixing the quench solvent with the quench recycle fraction.

8. The method of claim 6, wherein the quench solvent is mixed with the cooled recycle fraction.

9. The method of claim 1, wherein the quench solvent has at least one of a final boiling point of 150 C. or lower, a T90 distillation point of 140 C. or lower, or a combination thereof.

10. The method of claim 1, wherein the quench solvent comprises 0.5 wt % to 4.0 wt % of cyclopentadiene, dicyclopentadiene, or a combination thereof.

11. The method of claim 1, wherein the quench solvent comprises 3.0 wt % or less of cyclopentadiene, dicylopentadiene, or a combination thereof.

12. The method of claim 1, wherein the quench solvent comprises 0.1 wt % to 0.5 wt % of styrene.

13. The method of claim 1, wherein the quench solvent comprises 80 wt % or more of aromatics.

14. The method of claim 1, wherein the hydrocarbon effluent comprises 0.05 wt % to 5.0 wt % of 400 C.+ hydrocarbons, or wherein the hydrocarbon effluent comprises 0.01 wt % to 5.0 wt % of tar heavies.

15. The method of claim 1, wherein the quench solvent is formed as a product from an aromatics reforming process, a liquids cracking process, or a combination thereof.

16. The method of claim 1, wherein the one or more additional fractions comprise a process water fraction, the method further comprising mixing a second portion of the quench solvent with the process water fraction, and passing the mixture of the process water fraction and the second portion of the quench solvent into one or more process water separation stages.

17. A quench solvent comprising 70 wt % or more of aromatics, 0.0 wt % to 4.0 wt % of cyclopentadiene, dicyclopentadiene, or a combination thereof, 0.0 wt % to 1.0 wt % of styrene, and 5.0 wt % or more of combined paraffins and olefins, the quench solvent having a specific gravity at 15 C. of 0.92 or less, at least one of an initial boiling point of 62 C. or higher and a T10 distillation point of 80 C. or higher, and at least one of a final boiling point of 200 C. or lower and a T90 distillation point of 180 C. or lower.

18. The quench solvent of claim 17, wherein the quench solvent has at least one of a final boiling point of 150 C. or lower, a T90 distillation point of 145 C. or lower, or a combination thereof.

19. The quench solvent of claim 17, wherein the quench solvent comprises 0.5 wt % to 4.0 wt % of cyclopentadiene, dicyclopentadiene, or a combination thereof.

20. The quench solvent of claim 17, wherein the quench solvent comprises 3.0 wt % or less of cyclopentadiene, dicylopentadiene, or a combination thereof.

21. The quench solvent of claim 17, wherein the quench solvent comprises 0.1 wt % to 0.5 wt % of styrene.

22. The quench solvent of claim 17, wherein the quench solvent comprises 80 wt % or more of aromatics.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 shows an example of a quench system configuration.

[0009] FIG. 2 shows results from operating a quench system with various quench solvents.

[0010] FIG. 3 shows results from operating a quench system with various quench solvents.

[0011] FIG. 4 shows an example of a system that can be used for forming a quench solvent.

DETAILED DESCRIPTION

Overview

[0012] In various aspects, methods are provided to reduce or minimize fouling within quench systems when quenching effluents containing heavy components, such as heavy hydrocarbons and/or pyrolysis tars/coke. The methods include injecting a low density, low boiling point, high aromatic content fluid into the quench system as a quench solvent. The quench solvent also has a reduced or minimized content of fouling precursors, such as styrene, cyclopentadiene, or dicyclopentadiene.

[0013] The quench solvent is added to the quench system to allow quench water to be used to cool a heated hydrocarbon product while still being able to substantially fully separate the quench water from the heated hydrocarbon product. Conventionally, selection of quench solvents for use in quench systems and process water systems has been based on a balancing of several factors. One consideration has been to provide a quench solvent where at least a portion of the quench solvent has a sufficiently high boiling point to be effective for solvation of heavy hydrocarbons that are present within the quench system environment.

[0014] Generally, heavy hydrocarbons as defined herein include compounds with a boiling point of 400 C. or more. Additionally, for some types feed(s) to a quench process, such as a feed corresponding to a pyrolysis effluent, the feed may contain tar heavies which are tar-like compounds with a boiling point of 565 C. or higher. Tar Heavies (TH) means a product of hydrocarbon pyrolysis (or another reaction), the TH having an atmospheric boiling point 565 C. and comprising 5.0 wt. % of molecules having a plurality of aromatic cores based on the weight of the product. The TH are typically solid at 25.0 C. and generally include the fraction of tar that is not soluble in a 5:1 (vol.:vol.) ratio of n-pentane:tar at 25.0 C. TH generally include asphaltenes and other high molecular weight molecules.

[0015] Another consideration is to use a quench solvent that contains a substantial portion of aromatics. A high quality quench solvent, such as A200 aromatic fluid, can have an aromatics content that is close to 100 wt %. Other quench solvents such as debutanizer bottoms, hydrogenated pyrolysis gas, or pyrolysis naphtha generally have aromatics contents of roughly 50 wt % to 60 wt % relative to the weight of the quench solvent. To compensate for this lower aromatics content, larger volumes of these quench solvents are typically used to achieve a target level of total aromatics provided by the quench solvent within the quench water system.

[0016] Unfortunately, a third consideration is that conventional quench solvents can also create new difficulties within the quench water system and/or process water system. For heavier quench solvents with high aromatic content such as A200 aromatic solvent, the density of the quench solvent is similar enough to the density of water that a substantial amount of an emulsion can form. The presence of an emulsion interferes with the ability to fully separate the hydrocarbons from the quench water, resulting in increased levels of heavy hydrocarbons exiting from the quench system into the process water system or into the circulating quench water.

[0017] Lighter solvents such as debutanizer bottoms, hydrogenated pyrolysis gas, and/or pyrolysis naphtha have a reduced or minimized tendency to form emulsions. This avoids difficulties with heavy hydrocarbons exiting from the quench drum into the process water system or circulating quench water due to insufficient separation. However, these types of lighter solvents also typically contain substantial levels of fouling precursors, such as styrene and cyclopentadiene. These fouling precursors end up being incorporated into the hydrocarbon product stream, where they can polymerize in downstream processing components such as the process gas compressor. The resulting deposits of polymer within the downstream process equipment can accumulate over time, leading to the need to perform more frequent maintenance to remove the deposits. Conventionally, the problems with cyclopentadiene can be mitigated by exposing a quench solvent to conditions for conversion of cyclopentadiene to dicyclopentadiene. But this incurs additional cost.

[0018] In various aspects, the difficulties with using a quench solvent can be reduced or minimized by performing a quench using a quench solvent with properties that are different from conventional quench solvents. It has been discovered that the quench solvents with sufficiently high concentrations of aromatics provide improved mitigation of fouling even when the boiling range of the quench solvent is relatively low. Such lower boiling range quench solvents have correspondingly lower densities, in spite of the high aromatics concentration. This can allow a lower boiling range quench solvent to be used, thus reducing or minimizing emulsion formation, while still providing improved separation of hydrocarbons and water within the quench system. The quench solvent can also have a reduced or minimized content of fouling precursors.

[0019] The quench solvent can be characterized in various ways. First, the quench solvent has an aromatics content of 70 wt % or more, or 80 wt % or more, or 90 wt % or more, such as up to being substantially composed of aromatics. While quench solvents with up to 100 wt % of aromatics can be effective, in some aspects it is preferable to use quench solvents with less than 100 wt % aromatics content, as such quench solvents can be formed using fewer processing steps and with correspondingly lower costs. For example, the aromatics content can be 70 wt % to 98 wt %, or 70 wt % to 95 wt %, or 70 wt % to 90 wt %, or 80 wt % to 98 wt %, or 80 wt % to 95 wt %, or 90 wt % to 98 wt %. In some aspects, the quench solvent also has a combined content of paraffins (including n-paraffins, isoparaffins, and cycloparaffins) and olefins of 2.0 wt % or more, or 4.0 wt % or more, or 6.0 wt % or more, or 8.0 wt % or more, such as up to 30 wt %.

[0020] The quench solvent can also contain a reduced or minimized content of styrene, cyclopentadiene, and dicyclopentadiene. It is noted that when determining the combined content of paraffins and olefins, any content of styrene, cyclopentadiene, and dicyclopentadiene is not included as part of the olefins content. Although styrene is often drawn as having an olefin side chain attached to the aromatic ring, the aromatic resonance of styrene actually includes the carbons in the side chain, so that styrene is not a true olefin. Therefore any styrene content is not included when determining the olefin content. Cyclopentadiene and dicyclopentadiene are both di-olefins, and therefore are also not included when determining the olefins content. Similarly, any styrene content is also excluded when determining the aromatics content.

[0021] In some aspects, the quench solvent has a styrene content is 1.0 wt % or less, or 0.5 wt % or less, or 0.3 wt % or less, such as down to having substantially no styrene content. Additionally or alternatively, the combined content of cyclopentadiene and dicyclopentadiene in the quench solvent can be 0 wt % (detection limit) to 4.0 wt %, or 0 wt % to 3.0 wt %, or 0.5 wt % to 4.0 wt %, or 0.5 wt % to 3.0 wt %, or 1.0 wt % to 4.0 wt %, or 1.0 wt % to 3.0 wt %.

[0022] The quench solvent also has a boiling range and density that are low relative to conventional quench solvents. In various aspects, the quench solvent has a specific gravity at 15 C. of 0.92 or less, or 0.90 or less, such as down to 0.84 or possibly still lower. With regard to boiling range, the quench solvent can have one or more of the following boiling range characteristics: an initial boiling point of 60 C. or higher, or 65 C. or higher, such as up to 78 C.; a T10 distillation point of 75 C. or higher, or 78 C. or higher, or 80 C. or higher, or 100 C. or higher, such as up to 110 C.; a final boiling point of 200 C. or less, or 180 C. or less, or 150 C. or less, or 120 C. or less, such as down to 110 C. or possibly still lower; and a T90 distillation point of 180 C. or less, or 160 C. or less, or 140 C. or less, or 120 C. or less, such as down to 100 C. or possibly still lower. In some aspects, the final boiling point can be 110 C. to 200 C., or 110 C. to 180 C., or 110 C. to 150 C., or 110 C. to 120 C., or 120 C. to 200 C., or 120 C. to 180 C., or 120 C. to 150 C., or 150 C. to 200 C., or 150 C. to 180 C., or 180 C. to 200 C. In some aspects, the T90 distillation point can be 100 C. to 180 C., or 100 C. to 160 C., or 100 C. to 140 C., or 100 C. to 120 C., or 120 C. to 180 C., or 120 C. to 160 C., or 140 C. to 180 C., or 140 C. to 160 C.

[0023] It is noted that the boiling range of a quench solvent can indicate the types of aromatics that are contained in the quench solvent. For example, when the final boiling point is 150 C. to 200 C., or 150 C. to 180 C., and/or when the T90 distillation point is 140 C. to 180 C. or less, or 140 C. to 160 C., this corresponds to a quench solvent that includes C.sub.6-C.sub.9 aromatics. When the final boiling point is 120 C. to 150 C. and/or when the T90 distillation point is 120 C. to 140 C., this corresponds to a quench solvent that includes C.sub.6-C.sub.8 aromatics. When the final boiling point is 120 C. or less, this corresponds to a quench solvent that includes C.sub.6-C.sub.7 aromatics. Benzene (C.sub.6) and toluene (C.sub.7) are the only C.sub.6-C.sub.7 hydrocarbon aromatics. C.sub.8 hydrocarbon aromatics are xylene and ethylbenzene. C.sub.9 hydrocarbon aromatics are propylbenzene, methylethylbenzene, and trimethylbenzene.

Input and Output Flows for Quench System

[0024] Quench systems are used to perform the final stage of cooling for the product effluent from a high temperature process that includes heavy hydrocarbons and/or tar-like compounds in the effluent, such as a gas pyrolysis or gas cracking process. In examples where the effluent is an effluent from gas pyrolysis or a gas cracking process, prior to passing the high temperature effluent into the quench system, the high temperature effluent is cooled using one or more heat exchangers to reduce the temperature of the product effluent to a temperature of 90 C. to 250 C., or 120 C. to 250 C., or 150 C. to 250 C.

[0025] Depending on the nature of the high temperature effluent, the high temperature effluent can have a wide variety of compositions. One feature of the high temperature effluent can be the heavy hydrocarbon content, which corresponds to hydrocarbons with a boiling point of 400 C. or more. In some aspects, the high temperature effluent can contain 0.05 wt % to 5.0 wt % of heavy hydrocarbons (400 C.+), or 0.5 wt % to 5.0 wt %, or 1.0 wt % to 5.0 wt %, or 0.05 wt % to 2.0 wt %, or 0.5 wt % to 2.0 wt %. Additionally or alternatively, the high temperature effluent can contain 0.05 wt % to 5.0 wt % of tar heavies (TH), or 0.5 wt % to 5.0 wt %, or 1.0 wt % to 5.0 wt %, or 0.01 wt % to 2.0 wt %, or 0.5 wt % to 2.0 wt %.

[0026] After entering the quench system, the high temperature effluent is mixed with the quench water to cool the effluent and allow for further processing of the hydrocarbons. This can be performed, for example, in a quench tower. This mixing results in formation of an overhead gas and one or more additional fractions that correspond to a mixture of hydrocarbons and quench water. The one or more additional fractions can have a higher boiling range than the overhead gas fraction. The overhead gas flow corresponds to a cooled or quench gas flow. In some aspects, the temperature of the overhead gas flow can be lower than the temperature of the high temperature effluent by 10 C. or more, or 30 C. or more, or 50 C. or more, such as up to 150 C. Optionally, an overhead gas flow can have a temperature of 120 C. or less as it leaves the one or more separation stages, or 100 C. or less, such as down 70 C. or possibly still lower.

[0027] The mixture(s) of hydrocarbons and quench water are then separated in one or more quench separation stages, such as one or more quench drums. The quench separation stage(s) generally result in formation of least three output flows. One type of output flow is one or more hydrocarbon output flows, at least one of which is passed back to the product recovery train for the process that generates the high temperature effluent. Another output flow is a recycled quench water flow, for returning quench water back to the quench tower. The third output flow is a process water output flow, which corresponds to water with a small amount of hydrocarbon content. This process water output flow is passed into a process water recovery train for separation of the remaining hydrocarbons from the process water. Optionally, a fourth output flow can be a separate output flow containing tar/coke, which is then sent to a tar separation stage. In some aspects, this optional fourth output flow can be intermittent, so that tar/coke are allowed to accumulate in a separation stage for a period, and then passed to the tar recovery stage.

[0028] In some aspects, the recycled quench water flow, as it exits from the quench separation stage(s), can have a water content of 98.0 wt % or more, or 99.0 wt % or more, such as up to 100 wt %. Additionally or alternatively, the recycle quench water flow, as it exits from the quench separation stage(s), can have a content of heavy hydrocarbons with a boiling point of 400 C. or higher of 0.5 wt % or less, or 0.1 wt % or less, such as down to substantially no content of hydrocarbons with a boiling point of 400 C. or higher.

[0029] The quench solvent can be added to the quench system at one or more locations. Generally, in order to have the quench solvent present within the quench tower, at least a portion of the quench solvent is added to the recycle quench water flow. This addition can occur after the recycle quench water flow exits from the separation stage, within the quench cooling stage(s), and/or after the quench cooling stages. Optionally, additional quench solvent can be added to the mixture of hydrocarbons and quench water and/or added to the quench separation stage. Optionally, an additional portion of quench solvent can be added to the process water output flow, to facilitate separation of the remaining hydrocarbons from the process water.

[0030] The amount of quench solvent added to the system can be based on the composition of the heated hydrocarbon effluent that is passed into the quench system. In some aspects, the amount of quench solvent can be selected based on the amount of 200 C.+ components that are in the heated hydrocarbon effluent. The amount of 200 C.+ components in the heated hydrocarbon effluent is defined as the weight of compounds in the effluent that have a boiling point at 1.0 atm (101 kPa-a) of 200 C. or higher. This can be determined, for example, using ASTM D2887. In such aspects, a weight ratio of the quench solvent to the amount of 200 C.+ components in the heated hydrocarbon effluent can be from 3.0 to 9.0, or 5.0 to 9.0.

[0031] Optionally, more than one type of quench solvent can be used within the quench system. In some aspects, a high aromatic content, low density quench solvent as described herein can be used as the primary quench solvent. A conventional quench solvent can then be used as a secondary quench solvent. As an example, the high aromatic content, low density quench solvent described herein can be added as the primary quench solvent by adding the primary quench solvent to the recycled quench water flow and/or the cooled recycle flow. A secondary quench solvent, such as A200 aromatic fluid, can then be added on an intermittent basis to the quench separation stage.

Configuration Example

[0032] FIG. 1 shows an example of a quench water system, such as a quench water system for use in quenching the effluent from a gas cracking process. As an example of operation, a feed 105 for quenching is passed into quench water tower 110. The feed 105 is contacted in quench tower 110 with a counter-current flow of quench water 127. One product from quench tower 110 is cooled gas product 119, which contains a majority of the hydrocarbons from feed 105. The cooled gas product 119 is then further processed, such as by passing the cooled gas product 119 to a process gas compressor (not shown). The quench process also results in formation of heated quench water 115, which contains a portion of the hydrocarbons that were originally present in feed 105.

[0033] The heated quench water 115 is passed into a quench water separation stage, such as quench water drum 130. Quench water drum 130 is used to separate heated quench water 115 into at least three portions based on settling within the quench water drum 130. One portion corresponds to recovered hydrocarbons 139. The recovered hydrocarbons can then be sent to the processing train for the hydrocarbon products. Optionally, another portion can correspond to a stream (not shown) that contains tar and/or coke. Still another portion formed by the quench water drum 130 corresponds to recycled quench water stream 133. Recycled quench water stream 133 is passed through heat exchangers to recover heat, such as quench water coolers 122. For example, quench water coolers 122 can be shell-and-tube heat exchangers, with a counter-current cooling water flow 141 that receives heat in order to cool the recycled quench water stream 133. In FIG. 1, the output flow from heat exchangers 122 corresponds to a cooled recycle stream 127. This cooled recycle stream 127 corresponds to at least a portion of the quench water that is used in quench tower 110.

[0034] Still another portion that is formed by quench water drum 130 is a mixture 135 of hydrocarbons and water that undergoes further separation. The water in mixture 135 corresponds to excess water that is removed from the system in order to maintain the water level within the system. It is noted that during processes such as pyrolysis, steam is often added to feed, resulting in additional water being present in the pyrolysis effluent. When the feed 105 corresponds to an effluent from a process that generates water and/or otherwise has water in the effluent, the mixture 135 provides an outlet flow so that the amount of water in the quench system remains substantially constant over time.

[0035] The mixture 135 of hydrocarbons and water is then passed into the process water separators. In FIG. 1, the process water separators include separators 152 and 154 that coalesce the oil from the mixture of hydrocarbons and water 135 into an oil portion and a water portion. A stripper 156 then assists with removing most of the remaining hydrocarbons 165 from the water using steam 161 as a stripping gas. This results in production of a purified water stream 155 that is substantially free of hydrocarbons. The purified water stream 155 can then be passed, for example, to a dilution steam drum 170, which produces dilution steam 175 and wastewater 177.

[0036] In various aspects, quench solvent can be added to the quench water system at one or more locations. In the example shown in FIG. 1, quench solvent can be added to the recycled quench water stream 133, such as by adding quench solvent 321 to the recycled quench water stream 133. Another option is to add quench solvent 311 to the cooled recycle stream 127 prior to the cooled recycle stream 127 entering the quench tower 110. Still another option is to add quench solvent 331 to the quench separation stage 130. Yet another option is to add quench solvent 341 to the process water output flow 135. It is noted that any of the quench solvent addition locations in FIG. 1 can be used, either alone or in combination, depending on the aspect.

Steam Cracking of Gas Feeds

[0037] An example of a high temperature effluent that undergoes a quench process is the effluent from a steam cracker process for performing gas cracking.

[0038] A steam cracking plant typically comprises a furnace facility for producing steam cracker effluent and a recovery facility for removing from the steam cracker effluent a plurality of products and by-products, e.g., light olefin and pyrolysis tar. The furnace facility generally includes a plurality of steam cracking furnaces. Steam cracking furnaces typically include two main sections: a convection section and a radiant section, the radiant section typically containing fired heaters. Flue gas from the fired heaters is conveyed out of the radiant section to the convection section. The flue gas flows through the convection section and is then conducted away, e.g., to one or more treatments for removing combustion by-products such as NO.sub.x. A hydrocarbon composition (i.e., a composition comprising hydrocarbon) is introduced into tubular coils (convection coils) located in the convection section. A steam composition (i.e., a composition comprising steam) is also introduced into the convection coils, where it combines with the hydrocarbon composition to produce a steam cracking feed.

[0039] A steam cracking feed containing vaporized hydrocarbon, e.g., a feed containing C.sub.2-C.sub.4 hydrocarbons, or a feed from vapor-liquid-separator overhead or from convection coils that received vapor-liquid separator overhead, is transferred via cross-over piping from the convection coils to one or more tubular coils (radiant coils) located in the radiant section. Indirect radiant heating of the steam cracking feed in the radiant coils results in cracking of at least a portion of the steam cracking feed's hydrocarbon composition in the presence of the steam composition. More than one steam cracking furnace can be used, and these can be operated (i) in parallel, where a portion of the steam cracking feed being transferred to each of a plurality of furnaces and/or (ii) in series, where at least a second furnace is located downstream of a first furnace, the second furnace being utilized, e.g., for cracking any unreacted steam cracking feed in the first furnace's steam cracker effluent.

[0040] Conventional hydrocarbon compositions, steam compositions, steam cracking feeds, and steam cracking processes, can be utilized, but the invention is not limited thereto. Suitable compositions, feeds, and processes are disclosed, e.g., in U.S. Pat. No. 9,777,227, which is incorporated by reference herein in its entirety. Steam cracker effluent is conducted out of the radiant section and is quenched, typically with water and/or quench oil. The quenched steam cracker effluent (quenched effluent) is conducted away from the furnace facility to the recovery facility, for separation and recovery of reacted and unreacted components of the steam cracking feed.

[0041] Besides steam cracker tar, the quenched steam cracker effluent typically comprises (i) a primarily vapor-phase component comprising, e.g., one or more of acetylene, ethylene, propylene, butenes, and (ii) primarily liquid-phase component comprising, e.g., C.sub.5+ hydrocarbon, and mixtures thereof. The recovery facility typically includes at least one separation stage, e.g., for separating from the quenched effluent one or more of light olefin, steam cracker naphtha, steam cracker gas oil, steam cracker tar, water, light saturated hydrocarbon, molecular hydrogen, etc. The liquid-phase products are generally separated from the quenched effluent or a stream derived therefrom in one or more separation stages. Conventional separation equipment can be utilized in the separation stage, e.g., one or more flash drums, fractionators, water-quench towers, indirect condensers, etc., such as those described in U.S. Pat. No. 8,083,931, which is incorporated by reference herein in its entirety.

Methods for Forming the Quench SolventCatalytic Reforming

[0042] In some aspects, a high aromatic content, low density, low boiling range quench solvent can be formed as a fraction generated by a refinery process, a chemicals production process, or another process associated with petrochemical processing. Two examples of processes that can be used for forming a high aromatic content, low density, low boiling range quench solvent are aromatics reforming, such as naphtha reforming, and liquid feed steam cracking, such as naphtha steam cracking. The ability to use a quench solvent formed as a fraction from a petrochemical process is beneficial, as this can allow the quench solvent to be formed that has an aromatics content of 70 wt % or higher without requiring the distillation steps that are needed to form a high purity fraction.

[0043] Aromatics reforming is a process where a feed stream containing a substantial portion of paraffins and/or naphthenes can be converted to a product stream that contains a substantial portion of aromatics. Some current examples of aromatics reforming processes are semi-regenerative reforming processes and continuous catalytic reforming processes.

[0044] An example of a feed stream that can be reformed in an aromatics reforming process is a naphtha feed, such as a naphtha fraction separated from a crude oil. The boiling range for such a naphtha fraction can vary, but a typical boiling range for a naphtha fraction is T10 distillation point of 30 C. (roughly corresponds to boiling point of n-pentane) and a T90 distillation point of roughly 180 C., as measured according to a technique such as ASTM D86. For some types of aromatics reforming, a heavy naphtha feed may be used, so that the T10 distillation point of the heavy naphtha is 120 C. or higher, or 140 C. or higher, or 150 C. or higher. A typical naphtha fraction (including heavy naphtha fractions) can have a relatively low aromatics content, such as roughly 20 wt % or less, with the majority of the naphtha corresponding to paraffins and naphthenes. Such a feedstream can be converted to an aromatics-rich product using an aromatics reforming process.

[0045] Generally, an aromatics reforming process involves exposing the naphtha feedstock to one or more catalysts, such as zeolitic catalysts, under conditions that facilitate ring formation and dehydrogenation of naphthene rings. The ring formation and dehydrogenation processes can occur in any convenient number of stages. As one example of a configuration, a first stage and/or first group of catalyst beds, optionally in one or more reactors, can perform dehydrogenation of naphthenes. This reduces or minimizes the naphthenes content while producing aromatics. In a second stage and/or second group of catalyst beds, either in the same reactor(s) or a different group of one or more reactors, dehydrocyclization can be performed in combination with dehydrogenation. This allows n-paraffins and isoparaffins in the feed to be converted to rings, followed by aromatics formation. It is noted that the conditions for dehydrocyclization can also tend to result in opening of non-aromatic ring structures, so that converting existing naphthenes in the feed to aromatics first can provide some benefits.

[0046] During the aromatics reforming process, paraffins and naphthenes that have a sufficient number of carbon atoms (6 or more) are converted into aromatic compounds that have similar carbon numbers. For example, paraffins containing roughly 6 to 8 carbon atoms are converted into ring structures having roughly 6 to 8 carbon atoms. Dehydrogenation can then convert these ring structures into aromatics. It is noted that some cracking tends to occur under aromatics reforming conditions, so the yield of C.sub.6 to C.sub.8 aromatics may be improved by having n-paraffins and/or isoparaffins in the naphtha feed that contain larger numbers of carbon atoms, such as a heavy naphtha. Depending on the reaction conditions, the portion of the aromatics reforming effluent that corresponds to C.sub.6+ compounds can have an aromatics content of 70 wt % or more, or 75 wt % or more, or 80 wt % or more, such as up to 98 wt % or possibly still higher.

[0047] After the reforming process, the resulting aromatic-containing product can be fractionated to generate a fraction that is suitable for use as a quench solvent. Depending on the aspect, at least one fraction can be formed that has an initial boiling point of 60 C. or higher, or 65 C. or higher, such as up to 78 C.; a T10 distillation point of 75 C. or higher, or 78 C. or higher, or 80 C. or higher, or 100 C. or higher, such as up to 110 C.; a final boiling point of 200 C. or less, or 180 C. or less, or 150 C. or less, or 120 C. or less, such as down to 110 C. or possibly still lower; and a T90 distillation point of 180 C. or less, or 160 C. or less, or 140 C. or less, or 120 C. or less, such as down to 100 C. or possibly still lower. This at least one fraction formed form the aromatics reforming effluent can have a combined content of paraffins (including n-paraffins, isoparaffins, and cycloparaffins) and olefins of 2.0 wt % or more, or 4.0 wt % or more, or 6.0 wt % or more, or 8.0 wt % or more, such as up to 30 wt %. Optionally, styrene and/or cyclopentadiene and/or dicyclopentadiene can also be present in small amounts.

[0048] An example system for performing aromatics reforming is shown in FIG. 4. In FIG. 4, a plurality of fixed catalyst beds 403, 404, 405 are stacked in a single reactor 410. It is noted that each of fixed catalyst beds 403, 404, and 405 can represent a plurality of catalyst beds. Alternatively, in some aspects, some or all of catalyst beds 403, 404, and/or 405 can be located in separate reactors. This could correspond to having catalyst bed(s) 403 in a first reactor, catalyst bed(s) 404 in a second reactor, and catalyst bed(s) 405 in a third reactor. In other aspects, any convenient organization of catalyst beds 403, 404, and 405 between one or more reactors can be used. It is further noted that while catalyst beds 403, 404, and 405 are illustrated as fixed beds in FIG. 4, any other convenient type of combination of fixed beds and/or moving beds can be used.

[0049] The catalysts in catalyst beds 403, 404, and 405 represent functionally distinctive catalysts (FDC). Each of the plurality of FDC beds is designed to perform one or more of the various reforming reactions (e.g., dehydrogenation, dehydrocyclization, isomerization). Each of the plurality of FDC beds includes a reforming catalyst selective for one or more of the various reforming reactions.

[0050] FIG. 4 illustrates a reforming unit 400 comprising a pre-treatment stage 408, a heater 402, a reactor 410, a separation stage 406, and a compressor 407. A hydrocarbon feed stream 401 may be combined with a recycled hydrogen stream 418 and conveyed to a pre-treatment stage 408 to modify the disposition of the hydrocarbon feed stream 401 for compatibility with downstream processes. For example, a pre-treatment stage 408 may modify the sulfur content, the nitrogen content, and/or remove any water from the hydrocarbon feed stream 401. A waste stream 422 (which may comprise water, ammonia, hydrogen sulfide, and the like) may be separated from the pre-treatment stage effluent 409, which may then be conveyed to a heater 402 to generate a warmed hydrocarbon feed stream 411. The warmed hydrocarbon feed stream 411 may then be conveyed through a first FDC bed 103 in the reactor 410, generating a first FDC bed effluent 412. The first FDC effluent 412 may then be conveyed back through the heater 402 generating a warmed first FDC bed effluent 413, which may then be conveyed through a second FDC bed 404, resulting in a second FDC bed effluent 414. The second FDC bed effluent 414 may then be conveyed back through the heater 402, generating a warmed second FDC bed effluent 415, which may then be conveyed through a third FDC bed 405, resulting in a third FDC bed effluent 416. The third FDC bed effluent 416, comprising a hydrocarbon product stream, may be conveyed to a separation stage 406. At the separation stage 406, a hydrogen stream 417 may be isolated from the hydrocarbon product stream and conveyed to a compressor 407 to be recycled back into the system through a recycled hydrogen stream 418. The hydrocarbon product stream may be separated into two or more components 420, 421, for example, C.sub.1-C.sub.4 hydrocarbons, LPG, a quench solvent as described herein, and one or more other fractions. The separation stage may include one or more separation processes, each of which may be, for example, extraction, distillation, membrane separation, aromatic/saturate separation, or any combination thereof.

[0051] In any embodiment, the third FDC bed 105 may be absent. In such instances, the second FDC bed effluent comprises the hydrocarbon product stream. In any embodiment, there may be more than three FDC beds. In such instances, the third FDC bed effluent comprises a third intermediate hydrocarbon stream and the hydrocarbon product stream will be present in the effluent of a final FDC bed.

[0052] FIG. 4 depicts the recycled hydrocarbon stream 418 joining the treated hydrocarbon feed stream 401, however, in any embodiment, the recycled hydrogen stream 418 may be reintroduced into the system at any location prior to the reactor 410 or fed directly into the reactor 410. Additionally, the recycled hydrogen stream 418 may not be entirely derived from hydrogen produced within the reforming unit of which it is part, but in any embodiment, the recycled hydrogen stream 418 may be supplemented with hydrogen from another source (e.g., commercially available hydrogen or hydrogen from another reforming unit).

EXAMPLES

[0053] A series of tests were performed to illustrate the impact of aromatics content on the effectiveness of a quench solvent during quenching of an effluent generated by a gas cracking process. Table 2 shows the properties of two types of solvents: a steam cracked naphtha (SCN) and a blend of steam cracked naphtha with a benzene fraction. As shown in Table 2, the SCN had an aromatics content between 50 wt % and 55 wt %. The benzene fraction corresponded to a fraction that was formed by distillation of a product that primarily contained aromatics. As shown in Table 2, the benzene fraction included roughly 75 wt % benzene, and had a total aromatics content of roughly 80 wt %.

TABLE-US-00001 TABLE 1 Solvent Properties Mogas (SCN) Benzene fraction wt % wt % C5 C5 1.7 CPD 0.1 CPD 0.2 Light NAs 1.7 MCPD 0.1 Benzene 2.9 Other C6s 9.3 Toluene 22.0 Benzene 75.2 C8A 20.7 Cyclohexane 2.4 Styrene 0.3 Toluene 4.4 DCPD 0.7 Other C7+ 6.5 C9A 9.8 Total 100.0 C10+ 0.9 Others 41.0 Total 100.0

[0054] The effectiveness of quench solvents was tested by using quench solvents in the quench system for quenching of the output flow from a steam cracking process. In a first test run, one quench solvent corresponded to using the steam cracked naphtha (aromatics content of roughly 53 wt %) as the quench solvent. Another quench solvent corresponded to a blend of the steam cracked naphtha and the benzene fraction, in order to form a blended solvent with an aromatics content of roughly 70 wt %.

[0055] FIG. 2 shows results for the performance of the two types of solvents on the heat transfer capacity in the quench coolers during the first test run. In FIG. 2, the left axis shows the relative amount of SCN and benzene fraction that was used as quench solvent. The values for the left axis are normalized so that a value of 100 corresponds to the maximum SCN usage, which occurred on day 16. The right axis shows the heat transfer capacity, or U value. For the U value, the value of 0 corresponds to the initial heat transfer capacity. As the run progresses, fouling reduces the amount of heat transfer capacity, resulting in the negative values shown in the right axis. The bottom axis shows the number of days for the test. As shown in FIG. 2, initially the blend of SCN and benzene fraction was used that corresponded to a quench solvent with an aromatics content of 70 wt %. Next, in a middle portion of the test, the quench solvent was changed to primarily correspond to using only the SCN (none of the benzene fraction) with the aromatics content of 53 wt %. (There was a brief period in the middle portion of the test where the quench solvent was changed back to the blend of SCN and benzene fraction). In the final portion of the text, the solvent was switched back to the blend of SCN and benzene fraction. During all portions of the test shown in FIG. 2, the same total volume of quench solvent was delivered to the quench tower.

[0056] As shown in FIG. 2, when the blend of SCN and benzene fraction was used as the quench solvent (aromatics content of roughly 70 wt %), the quench cooler performance showed a marked improvement in stability and recovery of the heat transfer capability. This indicated that no foulant accumulation occurred in the initial portion of the test, and some removal of such accumulated foulant occurred in the final portion of the test. In the middle portion of the test when only the SCN was used as the quench solvent (aromatics content of roughly 53 wt %), the heat transfer performance showed a substantial drop. The data in Table 2 shows the superior solvation performance of the quench solvent containing roughly 70 wt % aromatics.

[0057] It is noted that based on FIG. 2 alone, an alternative explanation for the behavior of the two quench solvents is that when using SCN as the quench solvent, the total amount of aromatics in the quench solvent is lower. In other words, because the volume of quench solvent was held constant, when only SCN is used as the quench solvent, the ratio of aromatics in the quench solvent to total heavy hydrocarbons is lower in comparison with using the blend of SCN and the benzene fraction as the quench solvent. Under this alternative explanation, improved performance might be achieved when using SCN only as the quench solvent by simply increasing the volume of SCN quench solvent used, so that the total amount of aromatics delivered as quench solvent is the same as the total amount of aromatics delivered as quench solvent for the blended quench solvent. In other words, rather than holding the volume of quench solvent constant, the amount of quench solvent used is increased when using SCN only as the quench solvent, so that the amount of aromatics is constant.

[0058] To test this alternative theory, a second test run was performed. In the second test run, two types of solvents were used as blend components for forming the quench solvent. One solvent was a different steam cracked naphtha, with an aromatics content between 50 wt % and 70 wt %. The other blend component was A100 aromatic fluid (available from ExxonMobil Corporation). A100 aromatic fluid is a naphtha boiling range aromatic fluid with an aromatics content of roughly 100%.

[0059] FIG. 3 shows results from the second test run. The left axis shows the change in U value or heat transfer efficiency, indicating the loss of heat transfer efficiency as fouling occurs. The initial heat transfer efficiency is defined as a baseline, with FIG. 3 showing the loss of heat transfer efficiency as negative U values. During periods A and C, a blend of the SCN and the A100 was used as the quench solvent. In period A, the ratio of the SCN to the A100 was 10 to 8, while in period C the ratio of the SCN to the A100 was 5 to 8. In periods B and D, only the A100 was used as the quench solvent. The amount of A100 was constant during all time periods, so the only variation was the amount of SCN added during periods A and C. During periods B and D, the aromatics concentration in the quench solvent was greater than 99 wt %. During periods A and C, the aromatics concentration was reduced to roughly 70-80 wt %, although the total amount of aromatics delivered would be greater to the addition of the SCN to the baseline amount of A100.

[0060] As shown in FIG. 3, time periods B and D (A100 only) showed less degradation in performance than time periods A and C (blend of A100 and SCN). Thus, even though a greater total amount of aromatics were delivered during time periods A and C, the reduction in concentration during time periods A and C resulted in less effective solvation. This can be seen in FIG. 3 based on the relative slopes of the lines. In time periods A and C, the slope for the loss in U value is greater, while the rate of loss is lower in time periods B and D, as shown by the slope.

Additional Embodiments

[0061] Embodiment 1. A method for quenching a heavy hydrocarbon effluent, comprising: contacting a hydrocarbon effluent having an effluent temperature with quench water in a quench system to form an overhead gas and one or more additional fractions having a higher boiling range than the overhead gas, the overhead gas having an overhead gas temperature that is lower than the effluent temperature by 10 C. or more, mixing a quench solvent with the quench water prior to the contacting, during the contacting, after the contacting, or a combination thereof, at least one additional fraction of the one or more additional fractions further comprising at least a portion of the quench solvent, the quench solvent comprising i) 70 wt % or more of aromatics, ii) 0.0 wt % to 4.0 wt % of cyclopentadiene, dicyclopentadiene, or a combination thereof, iii) 0.0 wt % to 1.0 wt % of styrene, and iv) 5.0 wt % or more of combined paraffins and olefins, the quench solvent having a specific gravity at 15 C. of 0.92 or less, at least one of an initial boiling point of 62 C. or higher and a T10 distillation point of 80 C. or higher, and at least one of a final boiling point of 200 C. or lower and a T90 distillation point of 180 C. or lower; separating the at least one additional fraction to form at least a hydrocarbon-containing fraction and a quench recycle fraction.

[0062] Embodiment 2. The method of Embodiment 1, wherein the hydrocarbon effluent comprises 200 C.+ components, and wherein a weight ratio of the quench solvent to the 200 C.+ components in the hydrocarbon ratio is 3.0 to 9.0.

[0063] Embodiment 3. The method of any of the above embodiments, wherein the effluent temperature is 90 C. to 250 C., or wherein the overhead gas temperature is 120 C. or less, or a combination thereof.

[0064] Embodiment 4. The method of any of the above embodiments, wherein the quench recycle fraction comprises 0.1 wt % or less of hydrocarbons having a boiling point of 400 C. or higher.

[0065] Embodiment 5. The method of any of the above embodiments, wherein the quench system comprises a quench tower, one or more quench separation stages, and one or more quench water coolers, the hydrocarbon effluent being contacted with the quench water in the quench tower, the quench recycle fraction being formed in one of the one or more quench separation stages, at least a portion of the quench recycle fraction being passed into the quench water coolers to form a cooled recycle fraction, the quench water comprising at least a portion of the cooled recycle fraction.

[0066] Embodiment 6. The method of Embodiment 5, a) wherein the quench solvent is mixed with the quench recycle fraction, the quench recycle fraction comprising 99.0 wt % or more of water prior to mixing the quench solvent with the quench recycle fraction; b) wherein the quench solvent is mixed with the cooled recycle fraction; or c) a combination of a) and b).

[0067] Embodiment 7. The method of any of the above embodiments, wherein the hydrocarbon effluent comprises 0.05 wt % to 5.0 wt % of 400 C.+ hydrocarbons, or wherein the hydrocarbon effluent comprises 0.01 wt % to 5.0 wt % of tar heavies.

[0068] Embodiment 8. The method of any of the above embodiments, wherein the quench solvent is formed as a product from an aromatics reforming process, a liquids cracking process, or a combination thereof.

[0069] Embodiment 9. The method of any of the above embodiments, wherein the one or more additional fractions comprise a process water fraction, the method further comprising mixing a second portion of the quench solvent with the process water fraction, and passing the mixture of the process water fraction and the second portion of the quench solvent into one or more process water separation stages.

[0070] Embodiment 10. A quench solvent comprising 70 wt % or more of aromatics, 0.0 wt % to 4.0 wt % of cyclopentadiene, dicyclopentadiene, or a combination thereof, 0.0 wt % to 1.0 wt % of styrene, and 5.0 wt % or more of combined paraffins and olefins, the quench solvent having a specific gravity at 15 C. of 0.92 or less, at least one of an initial boiling point of 62 C. or higher and a T10 distillation point of 80 C. or higher, and at least one of a final boiling point of 200 C. or lower and a T90 distillation point of 180 C. or lower.

[0071] Embodiment 11. The method of any of Embodiments 1 to 9 or the quench solvent of Embodiment 10, wherein the quench solvent has at least one of a final boiling point of 150 C. or lower, a T90 distillation point of 140 C. or lower, or a combination thereof.

[0072] Embodiment 12. The method of any of Embodiments 1 to 9 or the quench solvent of Embodiment 10 or 11, A) wherein the quench solvent comprises 0.5 wt % to 4.0 wt % of cyclopentadiene, dicyclopentadiene, or a combination thereof; B) wherein the quench solvent comprises 3.0 wt % or less of cyclopentadiene, dicylopentadiene, or a combination thereof; or C) a combination of A) and B).

[0073] Embodiment 13. The method of any of Embodiments 1 to 9 or the quench solvent of any of Embodiments 10 to 12, wherein the quench solvent comprises 0.1 wt % to 1.0 wt % of styrene, preferably 0.1 wt % to 0.5 wt % of styrene.

[0074] Embodiment 14. The method of any of Embodiments 1 to 9 or the quench solvent of any of Embodiments 10 to 13, wherein the quench solvent comprises 80 wt % or more of aromatics.

[0075] When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated. While the illustrative embodiments of the disclosure have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present disclosure, including all features which would be treated as equivalents thereof by those skilled in the art to which the disclosure pertains.

[0076] The present disclosure has been described above with reference to numerous embodiments and specific examples. Many variations will suggest themselves to those skilled in this art in light of the above detailed description. All such obvious variations are within the full intended scope of the appended claims.