System and process for producing middle distillate petroleum products from rich aromatic petrochemical streams

Abstract

The present invention relates to a system for producing middle distillate petroleum products from a rich aromatic petrochemical stream. The system comprises a feedstock handling unit configured to receive pyrolysis fuel oil (PFO) and rerun bottom streams; a gasoline fractionator and separation section for recovering light olefins, fuel gas, hydrogen-rich gas, and PFO; and a steam cracker and pyrolysis gasoline hydrotreating unit for stabilizing pyrolysis gasoline and generating rerun bottom streams. A fraction recovery unit isolates lighter PFO fractions, blended with rerun bottom (1-5 wt %) as diesel hydrotreater feed. A diesel hydrotreating unit equipped with filtration (≤25 μm), preheat exchangers, furnaces, and fixed-bed catalytic reactors hydrogenates diolefins and aromatics, producing ultra-low sulfur distillates. A fractionation unit separates stabilized products, while an integrated control and filtration system regulates feed proportion, hydrogen consumption, and filter fouling, enabling optimized conversion of low-value streams into high-value middle distillates.

Description

FIELD OF THE INVENTION

[0001] The present disclosure relates to the field of petroleum refining and petrochemical processing, more particularly to a system and process for producing middle distillate petroleum products, such as automotive diesel fuel and superior kerosene oil, from rich aromatic petrochemical streams.BACKGROUND OF THE INVENTION

[0002] In conventional refinery operations, diesel and kerosene fractions are primarily obtained through the atmospheric distillation of crude oil, with kerosene typically recovered in the 150-250° C. range and diesel between 250-370° C. as straight-run products. However, these straight-run fractions alone are insufficient to meet growing market demands, leading to the use of secondary conversion processes such as hydrocracking, FCC, visbreaking, and delayed coking to generate additional middle distillates. To comply with stringent fuel quality standards, these fractions undergo hydrotreating to remove sulfur, nitrogen, and aromatics—improving diesel cetane number and kerosene smoke and freezing points.

[0003] At a petrochemical complex, Pyrolysis Gasoline (Pygas) from the steam cracker unit is processed in the Pyrolysis Gasoline Hydrogenation Unit (PGHU) to produce value-added fractions such as C5 End, C6 End, C7-C8 Cut, C9-180° C. Cut, and 180° C+ Cut. The PGHU includes two reactors. The first reactor effluent contains high gum-forming compounds that are removed in a Rerun Tower before being sent to the second reactor for further processing. The 180 ° C.+ bottom stream (Rerun Bottom) containing gums is blended with stripped pyrolysis fuel oil (PFO) and sold as Carbon Black Feedstock (CBFS).

[0004] However, CBFS suffers from significantly lower economic value compared to premium products such as BS VI diesel (HSD) and Superior Kerosene Oil (SKO)). Moreover, blending rerun tower bottom streams causes CBFS to fall short of density specifications, creating operational and quality challenges.

[0005] In view of the foregoing discussion, it is portrayed that there is a need to have a system and process for producing middle distillate petroleum products including automotive diesel fuel and superior kerosene oil by utilizing lighter cut of rich aromatic petrochemical stream.SUMMARY OF THE INVENTION

[0006] The present disclosure seeks to provide a system and process for producing middle distillate petroleum products from rich aromatic petrochemical streams. In disclosed system, a strategic rerouting of 5-10 m3 / hr of the rerun bottom stream to the Diesel Hydrotreating (DHDT) unit has been introduced. By co-processing this stream with diesel feed, it can be converted into high-value products such as SKO, and BS VI HSD, simultaneously bringing CBFS density within specifications at PGHU. The invention specifically addresses the utilization and upgrading of low-value heavy hydrocarbon streams, including pyrolysis fuel oil (PFO) and rerun bottom fractions from petrochemical complexes, through integrated fractionation, hydrotreating, and hydrogen management techniques to produce high-quality middle distillates with ultra-low sulfur content. This invention lies at the intersection of refinery-petrochemical integration, hydrogen optimization, and feedstock valorization technologies.

[0007] In an embodiment, a system for producing middle distillate petroleum products from a rich aromatic petrochemical stream is disclosed. The system includes a feedstock handling unit, configured to receive and store at least two heavy hydrocarbon streams selected from a pyrolysis fuel oil (PFO) stream obtained from a steam cracker stripper column, and a rerun bottom stream obtained as an 180° C. plus heavy fraction from a pyrolysis gasoline hydrogenation (PGH) rerun tower, wherein the streams are characterized by distillation range, sulfur and metal content, and solid impurities, with the PFO stream exhibiting sulfur concentration above 350 ppm and high polynuclear aromatic content, and the rerun bottom stream exhibiting sulfur concentration of approximately 353 ppm with high gum content and suspended solids.

[0008] The system further includes a gasoline fractionator having an inlet configured to receive a lighter cut rich-aromatic petrochemical feed stream comprising naphtha, LPG, and light kerosene, and having a bottom outlet and at least one side outlet line for routing fractionator overheads and side cuts to downstream sections.

[0009] The system further includes separation section coupled to the gasoline fractionator and configured to receive the overhead and side-cut streams and to produce separated product streams selected from the group consisting of fuel gas, hydrogen-rich gas, C2-C3 olefins, C4 mix, and a pyrolysis fuel oil (PFO) product, the hydrogen-rich gas being suitable for integration into a downstream hydrogenation reactor.

[0010] The system further includes a steam cracker unit coupled to the separation section to receive light olefin-containing streams, and configured to return pyrolysis gasoline and / or pyrolysis gasoline-derived streams to the separation section or to a pyrolysis gasoline hydrotreating unit.

[0011] The system further includes a pyrolysis gasoline hydrotreating unit having an inlet connected to receive a pyrolysis gasoline stream from the separation section or the steam cracker, and an outlet for delivering a stabilized gasoline product and a rerun bottom stream to the feedstock handling unit.

[0012] The system further includes a fraction recovery unit connected to the feedstock handling unit and configured to recover from the PFO stream a lighter fraction having a final boiling point (FBP) not exceeding 240° C. through simulated distillation or equivalent separation means, wherein approximately 61 wt % of the PFO stream is recovered as a lighter fraction suitable for hydro-processing.

[0013] The system further includes a diesel hydrotreating unit coupled to the fraction recovery unit, the diesel hydrotreating unit comprising a feed header, configured to receive a mixed feed comprising a main diesel hydrotreater feed blended with the recovered lighter PFO fraction and a controlled portion (1-5 wt % of total feed) of the rerun bottom stream having an FBP up to 240° C., thereby enhancing hydrogen utilization efficiency and minimizing fouling tendency; a feed filter, comprising at least one high-temperature filter with a filtration rating of ≤25 μm, disposed upstream of a hydrogenation reactor train and configured to remove coke precursors, and particulate contaminants from the blended feed prior to hydrogenation; one or more feed exchangers, arranged as shell-and-tube heat exchangers and configured to preheat the blended feed using hot reactor effluent; a feed furnace, configured to heat the preheated feed to hydrotreating reaction temperature suitable for catalytic hydrogenation; a hydrogenation reactor train, comprising a single reactor bed or at least onefixed-bed catalytic reactors arranged in series with interstage hydrogen quenching and heat recovery exchangers, configured to perform hydrogenation and desulfurization of diolefins, aromatics, and unsaturated hydrocarbons under controlled temperature and hydrogen partial pressure, thereby yielding a stabilized hydrotreated effluent; and a fractionation unit, comprising a stabilizer / fractionator column configured to separate the hydrotreated effluent into kerosene and diesel fractions meeting product specification limits, each fraction having a sulfur concentration ≤10 ppm and acceptable color and particulate levels.

[0014] The system further includes a control unit, connected to the diesel hydrotreating unit and configured to direct the flow of PFO and rerun-bottom-derived streams to the diesel hydrotreating unit, and integrate hydrogen-rich gas from the separation section into the hydrogenation reactor to maintain hydrogen partial pressure, thereby regulate the fixed-rate transfer of rerun bottom stream to the feed header in accordance with production requirements.

[0015] In another embodiment, a process for producing middle distillate petroleum products from a rich aromatic petrochemical stream is disclosed. The process includes identifying heavy hydrocarbon feedstocks selected from a pyrolysis fuel oil (PFO) stream from a steam cracker stripper column, and a rerun bottom stream from a PGH rerun tower.

[0016] The process further includes characterizing the streams for distillation range, sulfur content, metal content, and solid impurities, wherein the PFO stream exhibits sulfur concentration above 350 ppm and contains polynuclear aromatics, and the rerun bottom stream exhibits sulfur concentration of approximately 353 ppm with high gum content and suspended solids.

[0017] The process further includes routing fractionator overheads and side cuts to the separation section for producing light olefins and hydrogen-rich gas while routing pyrolysis gasoline to the pyrolysis gasoline hydrotreating unit.

[0018] The process further includes blending the recovered lighter fraction of PFO with the rerun bottom stream and mixing with a main diesel hydrotreater feed in controlled proportions ranging from 1-5 wt % of total feed.

[0019] The process further includes utilizing existing hydrotreating and filtration infrastructure to achieve conversion of low-value by-products into commercial middle distillate products.

[0020] The process further includes filtering the mixed feed using a dedicated high-temperature feed filter with a cutoff size of 25 μm to remove coke precursors, and particulate contaminants prior to entry into the hydrotreating reactor train.

[0021] The process further includes hydrotreating the filtered mixed feed in a multi-bed catalytic hydrogenation reactor under user-defined temperature, pressure, and hydrogen partial pressure to desulfurize and hydrogenate unsaturated hydrocarbons, yielding a stabilized hydrotreated effluent.

[0022] The process further includes fractionating the hydrotreated effluent into a kerosene fraction and a diesel fraction meeting sulfur specification ≤10 ppm and having acceptable colour and particulate limits.

[0023] An object of the present disclosure is to provide a system and process for producing middle distillate petroleum products, such as automotive diesel fuel (BS VI HSD) and superior kerosene oil (SKO), by efficiently utilizing lighter cuts of rich aromatic petrochemical streams including pyrolysis fuel oil (PFO) and rerun bottom fractions.

[0024] Another object of the invention is to maximize refinery profitability by converting low-value rerun bottom streams into high-value products, thereby improving overall product yield and economic return.

[0025] A further object of the invention is to ensure product quality compliance by enabling CBFS to meet density specifications in the Pyrolysis Gasoline Hydrogenation Unit (PGHU) through controlled rerouting and blending strategies.

[0026] Another object of the invention is to optimize unit operations by reducing CBFS surplus, improving hydrogen utilization efficiency, and maximizing Diesel Hydrotreating Unit (DHDT) throughput through co-processing of rerun bottom streams.

[0027] A still further object of the invention is to align the refinery product slate with market demand and enhance profit margins through integrated processing of petrochemical streams into middle distillates.

[0028] Yet another object of the invention is to provide a flexible and scalable process configuration that can be seamlessly integrated into existing refinery and petrochemical infrastructure without major hardware modifications, ensuring operational reliability and sustainability.

[0029] To further clarify the advantages and features of the present disclosure, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail in the accompanying drawings.BRIEF DESCRIPTION OF FIGURES

[0030] These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read concerning the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0031] FIG. 1 illustrates a block diagram of a system for producing middle distillate petroleum products from a rich aromatic petrochemical stream in accordance with an embodiment of the present disclosure;

[0032] FIG. 2 illustrates a flow chart of a process for producing middle distillate petroleum products from a rich aromatic petrochemical stream in accordance with an embodiment of the present disclosure;

[0033] FIG. 3 illustrates a process flow of PFO product classification in accordance with an embodiment of the present disclosure;

[0034] FIG. 4 illustrates a schematic diagram of a system for producing automative diesel fuel and superior kerosene oil in accordance with an embodiment of the present disclosure;

[0035] FIG. 5 illustrates distillation (Simdist) analysis of PFO stream from steam cracker unit in accordance with an embodiment of the present disclosure;

[0036] FIG. 6 illustrates rerun bottom stream specifications in accordance with an embodiment of the present disclosure;

[0037] FIG. 7 illustrates blend study for usage of rerun bottom in HSD pool in accordance with an embodiment of the present disclosure;

[0038] FIG. 8 illustrates full product analysis of high-speed diesel in accordance with an embodiment of the present disclosure; and

[0039] FIG. 9 illustrates full product analysis of superior kerosene oil in accordance with an embodiment of the present disclosure.

[0040] Further, skilled artisans will appreciate those elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.DETAILED DESCRIPTION

[0041] To promote an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

[0042] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

[0043] Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0044] The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

[0046] Embodiments of the present disclosure will be described below in detail concerning the accompanying drawings.

[0047] Referring to FIG. 1, a block diagram of a system (100) for producing middle distillate petroleum products from a rich aromatic petrochemical stream is illustrated in accordance with an embodiment of the present disclosure. The system (100) includes a feedstock handling unit (102) configured to receive and store at least two heavy hydrocarbon streams selected from a pyrolysis fuel oil (PFO) stream obtained from a steam cracker stripper column (104), and a rerun bottom stream (106) obtained as an 180° C. plus heavy fraction from a pyrolysis gasoline hydrogenation (PGH) unit rerun tower (108). The streams are characterized by distillation range, sulfur and metal content, and solid impurities, with the PFO stream exhibiting sulfur concentration above 350 ppm and high polynuclear aromatic content, and the rerun bottom stream exhibiting sulfur concentration of approximately 353 ppm with high gum content and suspended solids.

[0048] In an embodiment, a gasoline fractionator (110) is having an inlet configured to receive a lighter cut rich-aromatic petrochemical feed stream comprising naphtha, LPG, and light kerosene, and having a bottom outlet and at least one side outlet line for routing fractionator overheads and side cuts to downstream sections.

[0049] In an embodiment, a separation section (112) is coupled to the gasoline fractionator and configured to receive the overhead and side-cut streams and to produce separated product streams selected from the group consisting of fuel gas, hydrogen-rich gas, C2-C3 olefins, C4 mix, and a pyrolysis fuel oil (PFO) product, the hydrogen-rich gas being suitable for integration into a downstream hydrogenation reactor.

[0050] In an embodiment, a steam cracker unit (124) is coupled to the separation section to receive light olefin-containing streams, and configured to return pyrolysis gasoline and / or pyrolysis gasoline-derived streams to the separation section or to a pyrolysis gasoline hydrotreating unit.

[0051] In an embodiment, a pyrolysis gasoline hydrotreating unit (114) is having an inlet connected to receive a pyrolysis gasoline stream from the separation section or the steam cracker, and an outlet for delivering a stabilized gasoline product and a rerun bottom stream to the feedstock handling unit.

[0052] In an embodiment, a fraction recovery unit (116) is connected to the feedstock handling unit and configured to recover from the PFO stream a lighter fraction having a final boiling point (FBP) not exceeding 240° C. through simulated distillation or equivalent separation means, wherein approximately 61 wt % of the PFO stream is recovered as a lighter fraction suitable for hydro-processing.

[0053] In an embodiment, a diesel hydrotreating unit (118) is coupled to the fraction recovery unit. The diesel hydrotreating unit includes a feed header (118A) configured to receive a mixed feed comprising a main diesel hydrotreater feed blended with the recovered lighter PFO fraction and a controlled portion (1-5 wt % of total feed) of the rerun bottom stream having an FBP up to 240° C., thereby enhancing hydrogen utilization efficiency and minimizing fouling tendency.

[0054] The diesel hydrotreating unit further includes a feed filter (118B) comprising at least one high-temperature filter with a filtration rating of ≤25 μm, disposed upstream of a hydrogenation reactor train and configured to remove coke precursors, and particulate contaminants from the blended feed prior to hydrogenation.

[0055] The diesel hydrotreating unit further includes one or more feed exchangers (118C) arranged as shell-and-tube heat exchangers and configured to preheat the blended feed using hot reactor effluent.

[0056] The diesel hydrotreating unit further includes a feed furnace (118D) configured to heat the preheated feed to hydrotreating reaction temperature suitable for catalytic hydrogenation.

[0057] The diesel hydrotreating unit further includes a hydrogenation reactor train (118E) comprising a single reactor bed or at least two fixed-bed catalytic reactors arranged in series with interstage hydrogen quenching and heat recovery exchangers, configured to perform hydrogenation and desulfurization of diolefins, aromatics, and unsaturated hydrocarbons under controlled temperature and hydrogen partial pressure, thereby yielding a stabilized hydrotreated effluent.

[0058] The diesel hydrotreating unit further includes a fractionation unit (118F) comprising a stabilizer / fractionator column configured to separate the hydrotreated effluent into kerosene and diesel fractions meeting product specification limits, each fraction having a sulfur concentration ≤10 ppm and acceptable color and particulate levels.

[0059] In an embodiment, a control unit (120) is connected to the diesel hydrotreating unit and configured to direct the flow of PFO and rerun-bottom-derived streams to the diesel hydrotreating unit, and integrate hydrogen-rich gas from the separation section into the hydrogenation reactor to maintain hydrogen partial pressure, thereby regulate the fixed-rate transfer of rerun bottom stream to the feed header in accordance with production requirements.

[0060] In one embodiment, the PFO stream comprising high-boiling aromatic hydrocarbons, polynuclear aromatics, and unsaturated hydrocarbons with high carbon, sulfur, and metal content, wherein the rerun bottom stream comprising heavy aromatics, unsaturated hydrocarbons, gums, and suspended solids, wherein the separation section comprises at least one demethanizer and one C2 / C3 splitter, and the demethanizer overhead is routed as fuel gas while C2-C3 overheads are routed to the steam cracker.

[0061] In some embodiments, the pyrolysis gasoline hydrotreating unit is fluidly connected to the separation section and is configured to receive an aromatic-rich C5-C9 gasoline fraction, contact the stream with a hydrogen-containing recycle from the separation section, and produce a rerun bottom stream that is combined with PFO and fractionator bottom for forwarding to the diesel hydrotreating unit.

[0062] In one of the above embodiments, the feed furnace is configured to heat the hydrotreating feed to a reaction inlet temperature between 300° C. and 420° C., wherein the stabilizer / fractionator column is configured with overhead and side-draw sections producing superior kerosene oil (SKO) and high-speed diesel (HSD) having colour and particulate specifications meeting fuel quality standards.

[0063] In a further embodiment, the centralized process control system to prevent routing of high-boiling fractionator bottoms to the steam cracker, isolate the feed furnace when hydrogen partial pressure falls outside hydrotreating limits.

[0064] The system is implemented as a physically integrated refinery installation in which each unit corresponds to a defined mechanical structure designed for handling, separation, heat transfer, reaction, and flow regulation of hydrocarbon streams. The feedstock handling unit is formed by storage vessels, agitation provisions where required, transfer pumps, and insulated pipelines enabling receipt, storage, and controlled forwarding of pyrolysis fuel oil and rerun bottom streams containing solids and high-boiling constituents. The gasoline fractionator is a vertically oriented distillation column equipped with trays or structured packing, a reboiler at the base, overhead condenser, reflux drum, and multiple side-draw nozzles, enabling physical vapor-liquid separation of naphtha, LPG, and kerosene-range components. The separation section is constituted by discrete pressure vessels including a demethanizer column and a C2 / C3 splitter, each having internal contacting elements, overhead vapor lines, bottom liquid draw systems, and compression or routing manifolds for directing fuel gas, hydrogen-rich gas, and olefin streams. The steam cracker unit includes high-temperature cracking furnaces with radiant coils, transfer line exchangers, quench systems, and downstream piping circuits configured to thermally crack hydrocarbons and physically return pyrolysis gasoline streams through dedicated conduits.

[0065] The pyrolysis gasoline hydrotreating unit is constructed from high-pressure reactor vessels containing fixed catalyst beds, hydrogen injection distributors, inlet mixing devices, and outlet separators, enabling physical contact between hydrogen gas and hydrocarbon liquid under controlled conditions to produce stabilized gasoline and a heavier rerun bottom fraction. The fraction recovery unit is implemented as a distillation or equivalent separation column with reboiler, condenser, reflux control, and draw-off arrangements, enabling precise withdrawal of a lighter fraction below a defined final boiling point. The diesel hydrotreating unit comprises multiple interconnected hardware modules including a feed header formed by piping manifolds, blending tees, and control valves for proportioning multiple feed streams; a feed filter consisting of pressure-rated housings containing duplex sintered metal filter elements with back-flush lines, isolation valves, and pressure transducers for continuous particulate removal; and shell-and-tube heat exchangers having tube bundles, baffles, and channel heads for indirect heat exchange with reactor effluent. A fired feed furnace having burners, convection banks, refractory-lined firebox, and flue gas handling system raises the feed temperature to reaction conditions.

[0066] The hydrogenation reactor train includes one or more thick-walled pressure vessels arranged in series, each loaded with catalyst beds such as hydrodemetallization and hydrodesulfurization catalysts, and equipped with internal distributors, quench gas injection lines, thermocouple grids, and interconnecting piping to enable staged reaction and temperature moderation. Inter-bed heat exchangers and quench lines are physically installed to dissipate reaction heat and maintain temperature uniformity. The fractionation unit is a stabilizer or distillation column fitted with trays or packing, reflux drum, side draw circuits, and bottom withdrawal systems to separate hydrotreated effluent into kerosene and diesel fractions. Additionally, the system incorporates a preheat exchanger network with multiple exchangers arranged in series and parallel, along with fouling monitoring provisions based on pressure drop measurement ports. The filtration arrangement further includes pressure sensing devices and automated back-flush valves that physically actuate cleaning cycles upon reaching a defined differential pressure.

[0067] The hydrogen circulation arrangement comprises compressors or circulation lines, flow control valves, hydrogen purity analyzers, and purge lines equipped with gas analyzers for hydrogen sulfide detection, enabling controlled recirculation and purging of hydrogen streams. The control unit is realized through distributed instrumentation including flow meters, pressure transmitters, temperature sensors, control valves, and interlocked shutoff devices physically mounted on pipelines and vessels, enabling regulation of feed rates, hydrogen injection, quench flow, and safety isolation of the furnace and downstream units.

[0068] In one of the above embodiments, the feed filter comprises a duplex filter housing containing sintered metal filter elements, the housing including an inlet chamber and an outlet chamber separated by the filter elements, and a back-flush line connected to the outlet chamber, the back-flush line being actuated upon detection of a pressure differential across the filter elements measured by a pressure transducer mounted across the inlet and outlet chambers, and wherein the one or more feed exchangers are arranged in series between the feed filter and the feed furnace, each exchanger including a shell side carrying reactor effluent and a tube side carrying the blended feed, wherein the blended feed is progressively heated through indirect heat exchange prior to entry into the feed furnace.

[0069] In one of the above embodiments, the feed furnace includes a convection section and a radiant section, a blended feed passing first through convection coils for preheating followed by radiant coils for final heating, and the furnace including temperature sensors positioned along the coils to measure feed temperature prior to discharge to the hydrogenation reactor train, and wherein the hydrogenation reactor train comprises at least one fixed-bed reactors connected in series, each reactor containing catalyst beds and internal distribution trays, and interconnecting piping including hydrogen quench injection lines positioned between reactors, the quench lines introducing hydrogen into the flowing stream to control temperature rise between successive catalyst beds.

[0070] In one of the above embodiments, each reactor in the hydrogenation reactor train includes multiple thermocouple elements distributed along a catalyst bed height, the thermocouple elements connected to the control unit for monitoring temperature gradients along a flow path of the hydrocarbon stream, and wherein the fractionation unit comprises a distillation column having an overhead condenser, reflux drum, and side draw lines, the side draw lines positioned at different elevations along the column to withdraw kerosene and diesel fractions based on vapor-liquid equilibrium established within the column.

[0071] In one of the above embodiments, the separation section includes a demethanizer column and a C2 / C3 splitter column connected in series, the demethanizer including an overhead vapor outlet routed as fuel gas and a bottom outlet feeding the splitter column, and the splitter column including separate overhead and bottom outlets for recovery of light olefins, and wherein the pyrolysis gasoline hydrotreating unit includes a reactor vessel receiving an aromatic-rich gasoline stream and a hydrogen-containing recycle stream from the separation section through a mixing line, the mixing line including a junction where hydrogen gas and liquid hydrocarbon are contacted prior to entry into the reactor vessel.

[0072] In one of the above embodiments, the fraction recovery unit includes a distillation column configured to withdraw a lighter fraction from the pyrolysis fuel oil stream through an intermediate draw tray positioned above a bottom section, a withdrawn fraction being routed through a transfer line to the feed header of the diesel hydrotreating unit, and wherein the control unit includes pressure transmitters connected across the feed filter, flow transmitters positioned on a rerun bottom transfer line, and control valves located upstream of the feed header, a control unit receiving signals from the transmitters and actuating the control valves to regulate the rate of rerun bottom stream introduction into the blended feed.

[0073] In one of the above embodiments, a hydrogen circulation line connects the separation section to the hydrogenation reactor train, the line including a flow control valve and a gas analyzer positioned upstream of the reactor train, the gas analyzer measuring hydrogen purity and directing a purge stream through a separate line when impurity concentration exceeds a preset threshold.

[0074] FIG. 2 illustrates a flow chart of a process (200) of operating the system for producing middle distillate petroleum products from a rich aromatic petrochemical stream in accordance with an embodiment of the present disclosure. At step (202), the process (200) includes identifying heavy hydrocarbon feedstocks selected from a pyrolysis fuel oil (PFO) stream from a steam cracker stripper column (104), and a rerun bottom stream from a PGH rerun tower.

[0075] At step (204), the process (200) includes characterizing the streams for distillation range, sulfur content, metal content, and solid impurities, wherein the PFO stream exhibits sulfur concentration above 350 ppm and contains polynuclear aromatics, and the rerun bottom stream exhibits sulfur concentration of approximately 353 ppm with high gum content and suspended solids.

[0076] At step (206), the process (200) includes recovering from the PFO stream a lighter fraction having final boiling point up to 240° C. through simulated distillation, thereby identifying approximately 61 wt % recoverable fraction suitable for hydro-processing.

[0077] At step (208), the process (200) includes routing fractionator overheads and side cuts to the separation section for producing light olefins and hydrogen-rich gas while routing pyrolysis gasoline to the pyrolysis gasoline hydrotreating unit.

[0078] At step (210), the process (200) includes blending the recovered lighter fraction of PFO with the rerun bottom stream and mixing with a main diesel hydrotreater feed in controlled proportions ranging from 1-5 wt % of total feed within the feed header of the diesel hydrotreating unit through a dedicated injection line introducing the rerun bottom stream into a flowing feed stream.

[0079] At step (212), the process (200) includes utilizing existing hydrotreating and filtration infrastructure to achieve conversion of low-value by-products into commercial middle distillate products.

[0080] At step (214), the process (200) includes filtering the mixed feed using a dedicated high-temperature feed filter with a cutoff size of 25 μm to remove coke precursors, and particulate contaminants prior to entry into the hydrotreating reactor train.

[0081] At step (216), the process (200) includes hydrotreating the filtered mixed feed in a multi-bed catalytic hydrogenation reactor under user-defined temperature, pressure, and hydrogen partial pressure including maintaining reactor temperature in a range of 320-370° C. and hydrogen pressure in a range of 30-70 bar to desulfurize and hydrogenate unsaturated hydrocarbons, yielding a stabilized hydrotreated effluent.

[0082] At step (218), the process (200) includes fractionating the hydrotreated effluent into a kerosene fraction and a diesel fraction in the fractionation unit comprising a distillation column to produce fractions having sulfur specification ≤10 ppm and having acceptable colour and particulate limits.

[0083] In another embodiment, the hydrotreating is performed at a reactor temperature of 320-370° C. and hydrogen pressure between 30-200 bar.

[0084] In a further embodiment, the rerun bottom feed introduction rate is gradually increased from 1 wt % to 5 wt % based on monitoring of reactor differential pressure, hydrogen consumption, and product quality parameters.

[0085] In some embodiments, the fractionation of the hydrotreated effluent comprises separating the hydrotreated effluent in a distillation column configured with side draws for kerosene recovery and bottom draw for diesel recovery, wherein the recovered kerosene and diesel fractions are further treated with cetane improver additives to enhance ignition quality.

[0086] In one embodiment, hydrogen-rich gas recovered from the separation section is recycled to the hydrotreating reactor train to extract optimum hydrogen.

[0087] In one embodiment, wherein the high-temperature feed filtration is carried out at a controlled inlet temperature between 150-180° C. using duplex sintered metal filters having 25 μm cutoff size and equipped with automatic back-flush capability, wherein differential pressure across the filter is continuously monitored using a pressure transducer, and wherein the back-flush cycle is triggered upon a pressure rise exceeding 0.7 bar to prevent plugging and ensure continuous feed delivery to the reactor train.

[0088] In one embodiment, the hydrotreater reactor train comprises three catalytic beds arranged in series, with the beds containing a Hydrodemetallziation catalyst, NiMo / CoMo catalyst for hydrodesulfurization, hydrodenitrogenation and hydrogenation of aromatics and olefins, wherein the inter-bed quench hydrogen flow is regulated in the range of 5 -15 wt % of total hydrogen feed to maintain the bed inlet temperatures within ±5 ° C. of target temperature and prevent thermal runaway, and wherein the hydrogen-to-oil ratio during hydrotreating is maintained between 250-400 Nm3 / m3 by means of a closed-loop hydrogen circulation control system utilizing a hydrogen purity analyzer and flow controller, wherein the purge rate is adjusted based on off-gas composition containing hydrogen sulfide concentration measured by an online electrochemical sensor to prevent hydrogen slip and catalyst poisoning.

[0089] In one embodiment, prior to entry into the hydrotreater, the filtered mixed feed is passed through a preheat exchanger network utilizing reactor effluent heat to achieve a feed temperature between 260-280° C., and wherein the heat exchanger network is equipped with fouling factor monitoring based on pressure drop analysis to schedule preemptive cleaning cycles and maintain overall heat transfer coefficient above 80% of design value, and wherein the hydrotreating reactor is provided with an advanced distributed temperature control system having multiple thermocouple grids per catalyst bed, enabling localized detection of exotherms above 15 ° C., and wherein the system automatically modulates inter-bed hydrogen quench flow and feed rate to prevent catalyst deactivation caused by localized coking or hot spots.

[0090] In one embodiment, the hydrotreated effluent fractionation column is operated under a top pressure of 0.6 to 1.3 bar and bottom temperature of 260-300° C., wherein a reflux ratio of 0.5-1.2 is maintained for optimum kerosene-diesel separation.

[0091] In an embodiment, the blending of the recovered lighter fraction of the pyrolysis fuel oil stream with the rerun bottom stream and the main diesel hydrotreater feed is carried out within the feed header of a diesel hydrotreating unit upstream of the feed filter, the blending including introducing the rerun bottom stream through a dedicated injection line into a flowing main feed stream to form a mixed stream under turbulent flow conditions prior to filtration.

[0092] In an embodiment, filtering of the mixed feed includes passing the mixed stream through filter elements positioned within the feed filter, measuring a pressure differential across the filter elements using a pressure transducer connected across an inlet and an outlet of the feed filter, and initiating a back-flush operation through a reverse flow line upon detection of a pressure rise exceeding a predefined threshold to dislodge accumulated particulate matter.

[0093] In an embodiment, the hydrotreating of the filtered mixed feed includes introducing the feed into the hydrogenation reactor train comprising multiple fixed catalyst beds arranged in series, passing the feed sequentially through the catalyst beds, injecting hydrogen between successive beds through inter-bed quench lines, and monitoring temperature within each bed using thermocouple elements positioned along the flow path of the feed.

[0094] In an embodiment, fractionating of the hydrotreated effluent includes introducing the effluent into the fractionation unit comprising a distillation column, condensing overhead vapors in a condenser to form a reflux stream, returning a portion of the reflux stream to the column, and withdrawing kerosene and diesel fractions through side draw lines located at different elevations corresponding to boiling range separation within the column.

[0095] FIG. 3 illustrates a simulation model of PFO product classification in accordance with an embodiment of the present disclosure. The simulation was carried out in Petro-SIM software Ver 7.2 by modelling the PFO product stream and the rerun bottom stream separately, followed by blending and recovering a fraction with FBP of 240° C. This methodology indicated that 61 wt % of the PFO product stream can be recovered with FBP of 240° C. and can be routed to the Diesel Hydrotreater Unit without causing operational challenges in the Reactor. The disclosed process is adopted to produce Kerosene and Diesel product by utilising heavy hydrocarbon stream (which is having a very low commercial value) from Petrochemical complex.Pyrolysis Fuel Oil (PFO) Stream From Steam Cracker Stripper Column

[0096] In petrochemical complexes, pyrolysis fuel oil is produced from Cracker Unit Gasoline Fractionator as a heavy by-product during the thermal cracking of naphtha, gas oils, or other light hydrocarbons in steam cracker units used for olefins (ethylene, propylene) production. After separation of lighter olefins, aromatics, and pygas fractions, the heaviest residue remaining is PFO. This stream is rich in polynuclear aromatics, unsaturated hydrocarbons, and has high carbon, sulphur, and metal content. It is a dark, viscous liquid with high calorific value, but due to its poor ignition quality and instability, it is unsuitable for direct blending into transportation fuels. Instead, cracker-derived PFO is mainly used as an industrial furnace and boiler fuel, or as a feedstock in carbon black manufacturing. In some refineries, it is further processed in delayed coking or hydrocracking units to extract lighter distillates and maximize fuel yields.Rerun Bottom Stream

[0097] The Pyrolysis Gasoline Hydrogenation (PGH) Unit in Petrochemical Complex is designed to hydrotreat and fractionate the Raw Pyrolysis Gasoline from the SCU & OSBL Storage; and to produce the following products.

[0098] C5 Cut—C5 Product after PGH-1st Stage to C4 / C5 THU or Cracking Heaters

[0099] C6 Cut—Light Aromatic Rich Product after PGH-1st / 2nd stage to Benzene

[0100] Extraction Unit

[0101] C7-C8 Cut—Heavy Aromatic Rich Product after PGH-1st / 2nd stage to OSBL

[0102] storage

[0103] C9-180° C. Cut—Heavy Gasoline Product after PGH-1st / 2nd stage to OSBL

[0104] storage or wash oil storage

[0105] 180° C.+ cut—Fuel Oil Product after PGH-1st Stage to OSBL PFO storage—Rerun Bottom Product.

[0106] In the PGH First Stage Reactor, raw pyrolysis gasoline is hydrogenated at low temperatures in the liquid phase. During this stage, diolefins, styrene compounds, indenes, acetylenes, and other unstable components are selectively hydrotreated. The product from the first stage consists mainly of aromatics, olefins, and paraffins. This effluent is then sent to the Depentanizer, which fractionates the partially hydrotreated pyrolysis gasoline into two streams: an overhead product of C5 hydrocarbons and a bottoms product of C6 and heavier hydrocarbons. The C5 overhead stream is pumped forward to the C4 / C5 Hydrogenation Unit feed drum, while the C6+ bottoms stream is routed to the Rerun Tower.

[0107] In the Rerun Tower, the C6+ feed is separated into two cuts: a C6-180° C. stream recovered as overhead and an 180° C. plus heavy stream from the bottoms. The overhead cut is directed to the PGH Second Stage Reactor after heat exchange and heating, where further hydrogenation of aromatics takes place. The heavy 180° C. plus stream is combined with pyrolysis fuel oil (PFO) from the Steam Cracker Unit stripper, cooled against quench water in the PFO coolers, and finally sent to the battery limits as PFO product.

[0108] Therefore, PFO product that is sold as Carbon Black Feedstock (CBFS) is the combination of two streams PFO from Stream Cracker Unit Stripper and 180° C. plus heavy stream from the Rerun Bottom.Difficulties in Handling Heavier Streams From Petrochemical ComplexPyrolysis Fuel Oil (PFO) Product

[0109] The PFO from Stripper is a heavy by-product stream composed of complex, high-boiling hydrocarbons including polynuclear aromatics and other hard-to-crack molecules (Refer FIG. 5 for details). Its physical nature—high viscosity, high density, and low volatility—makes it difficult to handle compared to lighter refinery fractions. Due to its heavy molecular structure, PFO has a strong tendency to form coke, tarry deposits, and gums during processing. This leads to operational challenges such as fouling and choking of reactor internals, exchanger bundles, and associated piping systems.Rerun Bottom Stream

[0110] The rerun bottom stream poses significant operational challenges due to its composition and physical properties. It is a heavy stream with a high content of unsaturated hydrocarbons and gums, which tend to polymerize and form deposits during storage and processing. This gum content can foul heat exchangers, filters, and downstream reactor catalyst, leading to increased differential pressure and reduced run lengths. In addition, the stream contains suspended solid particles and coke precursors that exacerbate fouling and can physically block narrow passages in exchangers, reactors, and filters. The combination of gum formation and solids not only impairs heat transfer efficiency but also raises the risk of coking and contamination of product streams (such as kerosene and diesel) when processed directly.Experimental Work for ImprovementRouting Rerun Bottom Stream Directly in Diesel Product

[0111] The objective of this evaluation was to determine the feasibility of routing the rerun bottom stream directly into the diesel product while ensuring compliance with the diesel sulphur specification of ≤10 ppm. The rerun bottom stream contains a sulphur content of 353 ppm (Table 2 as depicted in FIG. 6), whereas the diesel product averages around 6.5 ppm. A blending calculation was performed based on the average diesel draw rate of the unit to estimate the allowable proportion of rerun bottom that can be mixed without exceeding the sulphur limit. The results of the calculation indicate that approximately 1 vol% of the rerun bottom stream can be blended into the diesel pool while maintaining the product sulphur concentration below the specified limit. From the lab analysis results after blending 1 vol % of Rerun bottom stream (Table 3 as depicted in FIG. 7), it was evident that this stream can be directly blended (with slightly increased dosage of cetane improver) in HSD pool without impacting product sulfur.

[0112] Although experiment indicated that up to 1 vol % of rerun bottom stream could be blended into diesel while maintaining the sulphur specification, subsequent trials showed that the blended diesel product failed to meet the colour specification and solid particulate matter impurities were found in the product. In addition, the limited allowance of only 1 vol % did not provide significant flexibility for processing higher quantities of rerun bottom stream. Considering these limitations, the option of routing the rerun bottom stream directly into the diesel product was not found to be practical.Feasibility of Routing Pfo Product to Diesel Hydrotreater Unit

[0113] To upgrade the PFO product into Diesel and Kerosene, it was decided to evaluate the feasibility of routing it to a Diesel Hydrotreater Unit. However, due to the heavier boiling point components in the PFO product stream, routing complete stream to Diesel Hydrotreater was not possible. Instead of routing the complete stream, a fraction having FBP of 240° C. was identified through simulation, which can be directly routed to the Diesel Hydrotreater Unit. This fraction was identified on the basis that only the lighter, more processable fraction of PFO product will be introduced in the Diesel Hydrotreater Unit, minimizing the risk of fouling, gum formation, and coke precursors associated with the heavier end, in the Reactor of the Hydrotreating Unit.

[0114] However, this separation required a significant CAPEX in the form of a new distillation column, which could separate the lighter fraction from the PFO product stream.

[0115] FIG. 4 illustrates a schematic diagram of a system for producing automative diesel fuel and superior kerosene oil in accordance with an embodiment of the present disclosure.Feasibility of Routing Rerun Bottom Stream to Diesel Hydrotreater Unit

[0116] To utilize the existing facility to the maximum extent possible, Rerun Bottom stream having FBP of ~240° C. was identified, which can be directly routed to the Diesel Hydrotreater Unit. This ensured that only the lighter, more processable fraction of PFO product was introduced in the Diesel Hydrotreater Unit.Routing Rerun Bottom to the Inlet of Fractionator in Diesel Hydrotreater Unit

[0117] Since the rerun bottom stream has distillation range of Kerosene with FBP ~240° C., it was considered suitable for routing to the Diesel Hydrotreater Unit product fractionator with the objective of separating it into SKO and HSD fractions. However, this approach faced several critical challenges which led to its discontinuation:

[0118] The rerun bottom is a heavy feed containing significant impurities, which resulted in contamination of both kerosene and diesel product streams.

[0119] Solid particles were observed in the rerun bottom stream, indicating poor feed quality.

[0120] Laboratory distillation tests failed due to excessive coke formation caused by these solid particles, raising severe concerns regarding fouling, exchanger choking, and potential reliability issues in the fractionator.

[0121] In view of these findings, the strategy of routing rerun bottom stream to the DHDT fractionator was deemed unfeasible.Routing Rerun Bottom to the Feed Filter in Diesel Hydrotreater Unit

[0122] After evaluating the challenges and limitations in earlier identified options, an alternative scheme was identified to route the rerun bottom stream to the inlet of a dedicated filter in a Diesel Hydrotreater Unit, which was designed specifically for this purpose. The filter was designed to filter solids of size greater than 25 μm. In this arrangement, the rerun bottom is mixed with the main feed of the Diesel Hydrotreater Unit, and the combined stream passes through the filter before entering the hydrogenation and hydrotreating reactors. This configuration dilutes the effect of impurities in the Rerun stream and enables effective removal of solid particles, and other impurities present in the rerun bottom stream through the filter. As a result, the heavier molecules undergo hydrogenation and hydrotreating along with the main feed, thereby preventing contamination of the diesel and kerosene product pools while also mitigating operational risks such as fouling and coke formation.

[0123] To evaluate its impact on unit performance and product quality, trials were initiated by introducing the rerun bottom stream into the Diesel Unit feed at 1 wt %. During this phase, close monitoring was carried out for critical parameters such as filter differential pressure, reactor differential pressure, hydrogen consumption, product quality and other key operating variables.

[0124] Subsequently, the rerun bottom intake was gradually increased up to 5 wt % of the total feed. The trial showed that this increase did not cause any significant operational challenges to the unit. Both kerosene and diesel products remained within specification limits (Refer FIGS. 8 & 9) for all parameters, confirming that controlled routing of rerun bottom via the dedicated filter is technically feasible.

[0125] FIG. 5 depicts distillation (Simdist) analysis of PFO stream from steam cracker unit in accordance with an embodiment of the present disclosure.

[0126] FIG. 6 depicts rerun bottom stream specifications in accordance with an embodiment of the present disclosure.

[0127] FIG. 7 depicts blend study for usage of rerun bottom in HSD pool in accordance with an embodiment of the present disclosure.

[0128] FIG. 8 depicts full product analysis of high-speed diesel in accordance with an embodiment of the present disclosure.

[0129] FIG. 9 depicts full product analysis of superior kerosene oil in accordance with an embodiment of the present disclosure.

[0130] The disclosed process is adopted for processing rerun bottom stream demonstrates several innovative measures that distinguish it from conventional handling practices selected from controlled incorporation of rerun in diesel feed, optimized cut point selection, and dedicated filtration scheme.

[0131] Controlled Incorporation of Rerun in Diesel Feed: The rerun bottom stream has been successfully introduced into the diesel feed in a controlled range of 1-5 wt %, ensuring flexibility in operations while maintaining product quality within specification.

[0132] Optimized Cut Point Selection: To prevent the processing of excessively heavy molecules, the final boiling point (FBP) was restricted to 240° C. This cut point optimization ensures that only the suitable lighter fraction of rerun is processed, thereby minimizing fouling and coke formation tendencies in the downstream reactors.

[0133] Dedicated Filtration Scheme: The rerun stream is routed upstream of a 25-micron filter, enabling the effective removal of solid particles, and other impurities prior to hydrogenation and hydrotreating. This filtration step is a critical safeguard against contamination and exchanger fouling, ensuring smooth reactor operation and stable product quality.

[0134] The disclosed process is adopted for production of Middle Distillate Petroleum Products like Automative Diesel Fuel and Superior Kerosene Oil by utilizing lighter cut of Rich Aromatic Petrochemical Stream has following advantages including significant value addition to the aromatic rich stream, which is sold as cheap CBFS, to a higher value product such as Kerosene and Diesel and integration of Refinery and Petrochemical complexes, leading to higher flexibility in operation.

[0135] The essence of the present invention lies in upgrading the Rerun Tower Bottom stream, which was conventionally blended with PFO and sold as low-value Carbon Black Feedstock (CBFS), into high-value middle distillate products such as Superior Kerosene Oil (SKO), and BS VI grade High-Speed Diesel (HSD). This is achieved by strategically rerouting the Rerun Tower Bottom from the Pyrolysis Gasoline Hydrogenation Unit (PGHU) in the petrochemical complex to the Diesel Hydrotreater (DHDT) Unit in the adjacent refinery. Within the DHDT unit, the rerun bottom stream is co-processed with multiple refinery streams including LK, HK, LGO, and HGO from the CDU, LCGO from the DCU, and LCO from the FCC unit. The combined feed undergoes hydrotreating in reactors loaded with commercial Ni—Mo and Co—Mo catalysts under conditions of 50-80 kg / cm2 pressure and 300-420° C. The reactor effluent is then stripped to remove hydrogen sulfide (H2S) and fractionated to yield kerosene and BS VI diesel, thereby significantly enhancing the economic value of the rerun bottom stream while meeting product quality specifications and optimizing overall refinery-petrochemical integration.

[0136] The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

[0137] Benefits, other advantages, and solutions to problems have been described above about specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.

Claims

1. A system for producing middle distillate petroleum products from a rich aromatic petrochemical stream, the system comprising:a feedstock handling unit, configured to receive and store at least two heavy hydrocarbon streams selected from a pyrolysis fuel oil (PFO) stream obtained from a steam cracker stripper column, and a rerun bottom stream obtained as an 180° C. plus heavy fraction from a pyrolysis gasoline hydrogenation (PGH) rerun tower, wherein said streams are characterized by distillation range, sulfur and metal content, and solid impurities, with said PFO stream exhibiting sulfur concentration above 350 ppm and high polynuclear aromatic content, and said rerun bottom stream exhibiting sulfur concentration of approximately 353 ppm with high gum content and suspended solids;a gasoline fractionator having an inlet configured to receive a lighter cut rich-aromatic petrochemical feed stream comprising naphtha, LPG, and light kerosene, and having a bottom outlet and at least one side outlet line for routing fractionator overheads and side cuts to downstream sections;a separation section coupled to the gasoline fractionator and configured to receive said overhead and side-cut streams and to produce separated product streams selected from the group consisting of fuel gas, hydrogen-rich gas, C2-C3 olefins, C4 mix, and a pyrolysis fuel oil (PFO) product, said hydrogen-rich gas being suitable for integration into a downstream hydrogenation reactor;a steam cracker unit coupled to the separation section to receive light olefin-containing streams, and configured to return pyrolysis gasoline and / or pyrolysis gasoline-derived streams to the separation section or to a pyrolysis gasoline hydrotreating unit;a pyrolysis gasoline hydrotreating unit having an inlet connected to receive a pyrolysis gasoline stream from the separation section or the steam cracker, and an outlet for delivering a stabilized gasoline product and a rerun bottom stream to said feedstock handling unit;a fraction recovery unit connected to said feedstock handling unit and configured to recover from said PFO stream a lighter fraction having a final boiling point (FBP) not exceeding 240° C. through simulated distillation or equivalent separation means, wherein approximately 61 wt % of said PFO stream is recovered as a lighter fraction suitable for hydro-processing;a diesel hydrotreating unit coupled to said fraction recovery unit, said diesel hydrotreating unit comprising:a feed header, configured to receive a mixed feed comprising a main diesel hydrotreater feed blended with recovered lighter PFO fraction and a controlled portion (1-5 wt % of total feed) of said rerun bottom stream having an FBP up to 240° C., thereby enhancing hydrogen utilization efficiency and minimizing fouling tendency; a feed filter, comprising at least one high-temperature filter with a filtration rating of ≤25 μm, disposed upstream of a hydrogenation reactor train and configured to remove coke precursors, and particulate contaminants from said blended feed prior to hydrogenation;one or more feed exchangers, arranged as shell-and-tube heat exchangers and configured to preheat said blended feed using hot reactor effluent;a feed furnace, configured to heat the preheated feed to hydrotreating reaction temperature suitable for catalytic hydrogenation;a hydrogenation reactor train, comprising a single reactor bed or at least two fixed-bed catalytic reactors arranged in series with interstage hydrogen quenching and heat recovery exchangers, configured to perform hydrogenation and desulfurization of diolefins, aromatics, and unsaturated hydrocarbons under controlled temperature and hydrogen partial pressure, thereby yielding a stabilized hydrotreated effluent; and a fractionation unit, comprising a stabilizer / fractionator column configured to separate said hydrotreated effluent into kerosene and diesel fractions meeting product specification limits, each fraction having a sulfur concentration ≤10 ppm and acceptable color and particulate levels; anda control unit, connected to the diesel hydrotreating unit and configured to direct flow of PFO and rerun-bottom-derived streams to said diesel hydrotreating unit, and integrate hydrogen-rich gas from the separation section into the hydrogenation reactor to maintain hydrogen partial pressure, thereby regulate a fixed-rate transfer of rerun bottom stream to the feed header in accordance with production requirements.

2. The system of claim 1, wherein the PFO stream comprising high-boiling aromatic hydrocarbons, polynuclear aromatics, and unsaturated hydrocarbons with high carbon, sulfur, and metal content, wherein the rerun bottom stream comprising heavy aromatics, unsaturated hydrocarbons, gums, and suspended solids, wherein the separation section comprises at least one demethanizer and one C2 / C3 splitter, and a demethanizer overhead is routed as fuel gas while C2-C3 overheads are routed to the steam cracker; and wherein the pyrolysis gasoline hydrotreating unit is fluidly connected to the separation section and is configured to receive an aromatic-rich C5-C9 gasoline fraction, contact said stream with a hydrogen-containing recycle from the separation section, and produce a rerun bottom stream that is combined with PFO and fractionator bottom for forwarding to the diesel hydrotreating unit.

3. The system of claim 1, wherein the feed furnace is configured to heat the hydrotreating feed to a reaction inlet temperature between 300° C. and 420° C. , wherein the stabilizer / fractionator column is configured with overhead and side-draw sections producing superior kerosene oil (SKO) and high-speed diesel (HSD) having colour and particulate specifications meeting fuel quality standards; and wherein a centralized process control system includes interlocks to prevent routing of high-boiling fractionator bottoms to the steam cracker, isolate the feed furnace when hydrogen partial pressure falls outside hydrotreating limits.

4. The system of claim 1, wherein the feed filter comprises a duplex filter housing containing sintered metal filter elements, the housing including an inlet chamber and an outlet chamber separated by the filter elements, and a back-flush line connected to the outlet chamber, the back-flush line being actuated upon detection of a pressure differential across the filter elements measured by a pressure transducer mounted across the inlet and outlet chambers, and wherein the one or more feed exchangers are arranged in series between the feed filter and the feed furnace, each exchanger including a shell side carrying reactor effluent and a tube side carrying the blended feed, wherein the blended feed is progressively heated through indirect heat exchange prior to entry into the feed furnace.

5. The system of claim 1, wherein the feed furnace includes a convection section and a radiant section, a blended feed passing first through convection coils for preheating followed by radiant coils for final heating, and the furnace including temperature sensors positioned along the coils to measure feed temperature prior to discharge to the hydrogenation reactor train, and wherein the hydrogenation reactor train comprises at least one fixed-bed reactor connected in series, each reactor containing catalyst beds and internal distribution trays, and interconnecting piping including hydrogen quench injection lines positioned between reactors, the quench lines introducing hydrogen into the flowing stream to control temperature rise between successive catalyst beds.

6. The system of claim 1, wherein each reactor in the hydrogenation reactor train includes multiple thermocouple elements distributed along a catalyst bed height, the thermocouple elements connected to the control unit for monitoring temperature gradients along a flow path of the hydrocarbon stream, and wherein the fractionation unit comprises a distillation column having an overhead condenser, reflux drum, and side draw lines, the side draw lines positioned at different elevations along the column to withdraw kerosene and diesel fractions based on vapor-liquid equilibrium established within the column.

7. The system of claim 1, wherein the separation section includes a demethanizer column and a C2 / C3 splitter column connected in series, the demethanizer including an overhead vapor outlet routed as fuel gas and a bottom outlet feeding the splitter column, and the splitter column including separate overhead and bottom outlets for recovery of light olefins, and wherein the pyrolysis gasoline hydrotreating unit includes a reactor vessel receiving an aromatic-rich gasoline stream and a hydrogen-containing recycle stream from the separation section through a mixing line, the mixing line including a junction where hydrogen gas and liquid hydrocarbon are contacted prior to entry into the reactor vessel.

8. The system of claim 1, wherein the fraction recovery unit includes a distillation column configured to withdraw a lighter fraction from the pyrolysis fuel oil stream through an intermediate draw tray positioned above a bottom section, a withdrawn fraction being routed through a transfer line to the feed header of the diesel hydrotreating unit, and wherein the control unit includes pressure transmitters connected across the feed filter, flow transmitters positioned on a rerun bottom transfer line, and control valves located upstream of the feed header, a control unit receiving signals from the transmitters and actuating the control valves to regulate the rate of rerun bottom stream introduction into the blended feed.

9. The system of claim 1, wherein a hydrogen circulation line connects the separation section to the hydrogenation reactor train, the line including a flow control valve and a gas analyzer positioned upstream of the reactor train, the gas analyzer measuring hydrogen purity and directing a purge stream through a separate line when impurity concentration exceeds a preset threshold.

10. A process of operating the system of claim 1 for producing middle distillate petroleum products from a rich aromatic petrochemical stream, comprising:identifying heavy hydrocarbon feedstocks selected from a pyrolysis fuel oil (PFO) stream from a steam cracker stripper column, and a rerun bottom stream from a PGH rerun tower within the feedstock handling unit;characterizing said streams within the feedstock handling unit using in-line measurement for distillation range for distillation range, sulfur content, metal content, and solid impurities, wherein said PFO stream exhibits sulfur concentration above 350 ppm and contains polynuclear aromatics, and said rerun bottom stream exhibits sulfur concentration of approximately 353 ppm with high gum content and suspended solids;recovering from said PFO stream a lighter fraction having final boiling point up to 240° C. in the fraction recovery unit through distillation within a column, thereby identifying approximately 61 wt % recoverable fraction suitable for hydro-processing;routing fractionator overheads and side cuts through outlet lines of the gasoline fractionator to the separation section for producing light olefins and hydrogen-rich gas while routing pyrolysis gasoline to the pyrolysis gasoline hydrotreating unit;blending recovered lighter fraction of PFO with the rerun bottom stream and mixing with a main diesel hydrotreater feed in controlled proportions ranging from 1-5 wt % of total feed within the feed header of the diesel hydrotreating unit through a dedicated injection line introducing the rerun bottom stream into a flowing feed stream;filtering said mixed feed using a dedicated high-temperature feed filter with a cutoff size of 25 μm to remove coke precursors, and particulate contaminants prior to entry into a hydrotreating reactor train;hydrotreating the filtered mixed feed in a multi-bed catalytic hydrogenation reactor in the hydrogenation reactor train comprising multiple catalyst beds under controlled temperature, pressure, and hydrogen partial pressure including maintaining reactor temperature in a range of 320-370° C. and hydrogen pressure in a range of 30-70 bar to desulfurize and hydrogenate unsaturated hydrocarbons, yielding a stabilized hydrotreated effluent; andfractionating said hydrotreated effluent into a kerosene fraction and a diesel fraction in the fractionation unit comprising a distillation column to produce fractions having sulfur specification ≤10 ppm and acceptable colour and particulate limits.

11. The process of claim 10, wherein the hydrotreating is performed at a reactor temperature of 320-370° C. and hydrogen pressure between 30-70 bar, wherein a rerun bottom feed introduction rate is gradually increased from 1 wt % to 5 wt % based on monitoring of reactor differential pressure, hydrogen consumption, and product quality parameters.

12. The process of claim 10, wherein the fractionation of the hydrotreated effluent comprises separating the hydrotreated effluent in a distillation column configured with side draws for kerosene recovery and bottom draw for diesel recovery, wherein the recovered kerosene and diesel fractions are further treated with cetane improver additives to enhance ignition quality; and wherein hydrogen-rich gas recovered from the separation section is recycled to the hydrotreating reactor train to extract optimum hydrogen.

13. The process of claim 10, wherein a high-temperature feed filtration is carried out at a controlled inlet temperature between 150-180° C. using duplex sintered metal filters having 25 μm cutoff size and equipped with automatic back-flush capability, wherein differential pressure across the filter is continuously monitored using a pressure transducer, and wherein a back-flush cycle is triggered upon a pressure rise exceeding 0.7 bar to prevent plugging and ensure continuous feed delivery to the reactor train.

14. The process of claim 10, wherein the hydrotreater reactor train comprises three catalytic beds arranged in series, with the beds containing a Hydrodemetallziation catalyst, NiMo / CoMo catalyst for hydrodesulfurization, hydrodenitrogenation and hydrogenation of aromatics and olefins, wherein an inter-bed quench hydrogen flow is regulated in the range of 5 -15 wt % of total hydrogen feed to maintain bed inlet temperatures within ±5° C. of target temperature and prevent thermal runaway, and wherein a hydrogen-to-oil ratio during hydrotreating is maintained between 250-400 Nm3 / m3 by means of a closed-loop hydrogen circulation control system utilizing a hydrogen purity analyzer and flow controller, wherein a purge rate is adjusted based on off-gas composition containing hydrogen sulfide concentration measured by an online electrochemical sensor to prevent hydrogen slip and catalyst poisoning.

15. The process of claim 10, wherein prior to entry into the hydrotreater, a filtered mixed feed is passed through a preheat exchanger network utilizing reactor effluent heat to achieve a feed temperature between 260-280° C., and wherein a heat exchanger network is equipped with fouling factor monitoring based on pressure drop analysis to schedule preemptive cleaning cycles and maintain overall heat transfer coefficient above 80% of design value, and wherein a hydrotreating reactor is provided with an advanced distributed temperature control system having multiple thermocouple grids per catalyst bed, enabling localized detection of exotherms above 15° C., and wherein the system automatically modulates inter-bed hydrogen quench flow and feed rate to prevent catalyst deactivation caused by localized coking or hot spots.

16. The process of claim 10, wherin a hydrotreated effluent fractionation column is operated under a top pressure of 0.6 to 1.3 bar and bottom temperature of 260-300° C., wherein a reflux ratio of 0.5-1.2 is maintained for optimum kerosene-diesel separation.

17. The process of claim 10, wherein blending of the recovered lighter fraction of the pyrolysis fuel oil stream with the rerun bottom stream and the main diesel hydrotreater feed is carried out within the feed header of a diesel hydrotreating unit upstream of the feed filter, the blending including introducing the rerun bottom stream through a dedicated injection line into a flowing main feed stream to form a mixed stream under turbulent flow conditions prior to filtration.

18. The process of claim 10, wherein filtering of the mixed feed includes passing the mixed stream through filter elements positioned within the feed filter, measuring a pressure differential across the filter elements using a pressure transducer connected across an inlet and an outlet of the feed filter, and initiating a back-flush operation through a reverse flow line upon detection of a pressure rise exceeding a predefined threshold to dislodge accumulated particulate matter.

19. The process of claim 10, wherein hydrotreating of filtered mixed feed includes introducing the feed into the hydrogenation reactor train comprising multiple fixed catalyst beds arranged in series, passing the feed sequentially through the catalyst beds, injecting hydrogen between successive beds through inter-bed quench lines, and monitoring temperature within each bed using thermocouple elements positioned along a flow path of the feed.

20. The process of claim 10, wherein fractionating of the hydrotreated effluent includes introducing the effluent into the fractionation unit comprising a distillation column, condensing overhead vapors in a condenser to form a reflux stream, returning a portion of the reflux stream to the column, and withdrawing kerosene and diesel fractions through side draw lines located at different elevations corresponding to boiling range separation within the column.

Images