Process for production of needle coke from coal tar pitch and petroleum streams

Abstract

The present invention relates to a process for needle coke production by co-processing coal tar pitch (CTP) with petroleum streams. The process utilizes a ‘multi-residence time mild thermal cracking’ of coal tar pitch with petroleum streams (CLO, PFO) followed by solvent-assisted selective separation of undesirable quinoline insoluble (QI) and solid catalyst fines from the mixed pitch and delayed coking thereafter to produce needle coke. The solvent employed for feedstock purification is a mixture prepared from an aromatic solvent which is a lighter fraction formed by mild and severe thermal cracking of mixed feedstock, an aliphatic solvent and a polar extraction solvent.

Description

[0001] This application claims priority to Indian Application No. 202421060942 dated Aug. 12, 2024. The contents of this application are hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The present invention relates to a process for production of high-quality Graphite / Needle-grade coke for the preparation of graphite electrodes for use in the steel industry or making electrodes for batteries.BACKGROUND

[0003] Adoption of electric arc furnace (EAF) technology for steel production is increasing across the world resulting in increased Needle / Graphite coke demand. Needle coke is used for the preparation of graphite electrodes for use in the steel industry. Conventionally, needle coker feedstock is desired to be highly aromatic and lower in impurities. Additionally, adoption of coke oven batteries and coal pyrolysis units are also increasing across the world, resulting availability of coal-based feedstock such as coal tar pitch (CTP) for the production of needle / graphite coke is increased. CTP contains higher levels of impurity such as quinoline insoluble (QI), if present at higher level in the feedstock, the same gets deposited in the needle coke that is produced resulting in high coefficient of thermal expansion (CTE) lower quality needle / graphite coke.

[0004] U.S. Pat. No. 4,814,063A discloses a method for the production of needle coke comprising the steps of hydrogenation of the starting material selected from the coal tar or coal tar pitch containing less than 0.1 wt % of quinoline insoluble (QI). The said coal tar or coal tar pitch is subjected to hydrogenation using hydrogenation catalyst to produce the hydrogenated oil. The said hydrogenated oil is then subjected thermal cracking under controlled operating conditions to produce Needle coke. However, the hydrogenation process used in this invention for separation of impurities from the feedstock containing coal tar or coal tar pitch is costly. Further in said technique, there is a high possibility of a reduction in aromatic content and reactivity of the feedstock which can impact in produced needle coke quality adversely.

[0005] UK U.S. Pat. No. 2,013,710A describes a process for preparing a carbonaceous starting material for producing of electrode-grade coke comprises extracting raw coke oven tar with a petrol fraction to produce an insoluble soft pitch fraction which contains undesirable non-graphitizable impurities and an extract of tar components in the solvent. The solvent is removed from the exact tar to give a tar suitable for producing electrode coke. However, only a selective and small portion of the fraction viz. 27% of tar oil components has been used to make carbonaceous raw material for producing electrode coke. Additionally, in the prior art, a petroleum stream containing decant oil is used for mixing with tar oil without pre-pre-treatment decent oil. Decent oil contains solid catalyst fines, and it is essential to remove the said catalyst fines before use, if present it has a deleterious effect on produced coke quality.

[0006] U.S. Pat. No. 3,617,515A describes a process for production of graphitizable Needle coke and carbon grade coke from a feed containing coal tar pitch, comprising separating a feed containing coal tar pitch into two fractions. First fraction containing boiling range from 600° F. to about 1,200° F. and remaining as heavier second fraction, both fractions having a high content of mixture of condensed aromatic ring compounds. The two fractions are then subject to delayed coking to produce graphitizable needle coke and carbon grade coke. However, the said prior art did not use any pre-treatment process for the removal of impurity (namely quinoline insoluble) from coal tar pitch. The said impurity when present in the hydrocarbon matrix creates disturbance during forming of mesophase which can impact the needle coke and carbon grade coke quality adversely. The impurity also cause coke lay-down inside the furnace tubes affecting the pressure drop and heat transfer efficiency.

[0007] The hydrogenation process described in prior art has the limitation of being costly and the process adversely affects the quality of produced needle coke. Therefore, there is a requirement of a process for production of high-quality graphite / needle-grade coke.OBJECTIVES

[0008] The main objective of the present invention is to provide a process for production of high-quality graphite / needle-grade coke with low coefficient of thermal expansion (CTE) and high crystallinity.

[0009] Another objective of the present invention is to provide a process that involves a “multi-residence time mild thermal cracking” to ensure the optimum residence time of the coal tar pitch and other petroleum streams fine-tuned for each of the participating reactant molecules thereby preventing over-cracking of the same.

[0010] Another objective of the present invention is to provide a process for producing of needle coke that involves ‘multi-residence time mild thermal cracking’ which ensures the stability of the products generated from this process, offering additional process control in the hands of the refiner to make tailor-made mix feed composition needed for needle coke formation.

[0011] Another objective of the present invention is to provide a process that enables a ‘multi-residence time mild thermal cracking’ which improved mixed pitch quality like aromatic content, softening point etc, resulting mixed pitch subjected to severe thermal cracking improved coke yield and quality.

[0012] Another objective of the present invention is to provide a process for needle coke production by blending of different feed sources from coal-based and petroleum-based hydrocarbons followed by solvent-assisted selective separation of undesirable Quinoline Insoluble (QI) and solid catalyst fines from the mixed pitch and delayed coking thereafter.

[0013] Another objective of the present invention is to provide a provides a solution for the purification of pitch feedstock by solvent treatment for which a component of the employed solvent mixture is generated in-situ which is a lighter fraction formed by mild and severe thermal cracking of mixed feedstock.SUMMARY

[0014] This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended to determine the scope of the invention.

[0015] The present invention provides a process for the preparation of a needle coke, wherein the process comprises:

[0016] subjecting a feed stream to a multi-residence time mild thermal cracking in the presence of petroleum streams to obtain a mixed pitch, wherein the feed stream is selected from a group of coal tar, coal tar pitch (CTP), clarified oil (CLO), pyrolysis fuel oil, gas oils, hydrotreated vacuum gas oil and a combination thereof, preferably coal tar pitch, and wherein the petroleum streams comprise clarified oil (CLO), pyrolysis fuel oil (PFO) and a combination thereof; wherein the multi-residence time mild thermal cracking comprises steps of: heating the coal tar pitch in a mild cracking furnace; sending the heated coal tar pitch of step i) to the bottom of a mild cracking reactor; introducing the petroleum streams from a middle and top section of the said mild cracking rector to carry out the multi-residence time mild thermal cracking of the heated coal tar pitch in the presence of the petroleum streams to produce a plurality of reactor effluents; sending the reactor effluents from a top section of the mild thermal cracking reactor to a fractionator for fractionation to produce different components comprising a plurality of off-gases, a light oil, a middle oil and a mixed pitch; routing the plurality of off-gases to a gas concentration section for recovery; and sending the light oil to a solvent tank for use as an aromatic solvent and middle oil to a hydrotreating unit for recovery; purifying the mixed pitch through a solvent-assisted selective separation of undesirable quinoline insoluble (QI) and solid catalyst fines from the mixed pitch to obtain a purified mixed pitch, wherein the mixed pitch is treated with a solvent in a solvent treatment vessel followed by settling of impurities in a gravity settler; a heavy pitch-solvent mixture containing impurities is withdrawn from the bottom of the gravity settler and a purified pitch-solvent mixture is withdrawn from the top of the gravity settler; the heavy pitch-solvent mixture is heated in a first heater and then routed to the first solvent recovery column and the purified pitch-solvent mixture is heated in a second heater and then routed to the second solvent recovery column for solvent recovery; the purified mixed pitch is ultimately withdrawn from the bottom of the second solvent recovery column, the solvent to the mixed pitch has a weight ratio in a range of 0.5:1 to 10:1, the solvent treatment vessel is operated at a temperature in a range of 60° C. to 350° C. and a pressure in a range of 1 to 80 Kg / cm2 (g); and

[0017] subjecting the purified mixed pitch to delayed coking to produce the needle coke and a lighter hydrocarbon component; wherein the purified mixed pitch is mixed optionally mixed with a new hydrocarbon stream before delayed coking; the lighter hydrocarbon component is fractionated to produce a plurality of gaseous products and a plurality of liquid products containing a coker kero, a light coker gas oil, a heavy coker gas oil and a coker fuel oil; and the coker kero is sent to the solvent tank for use as an aromatic solvent.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0019] FIG. 1 depicts schematic diagram of the process for the preparation of needle coke with coal tar pitch in the presence of CLO.

[0020] FIG. 2 depicts schematic diagram of the process for the preparation of needle coke with coal tar pitch in the presence of CLO and PFO.DETAILED DESCRIPTION

[0021] For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments in the specific language 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 process, 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. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The composition, methods, and examples provided herein are illustrative only and not intended to be limiting.

[0022] The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.

[0023] In an aspect the present invention provides a process for production of needle grade coke employing a novel ‘multi-residence time mild thermal cracking’ of coal tar pitch with petroleum streams like CLO and PFO followed by solvent-assisted selective separation of undesirable quinoline insoluble (QI) and solid catalyst fines from the mixed pitch and delayed coking thereafter.

[0024] The present invention provides a solution for the purification of pitch feedstock by solvent treatment. A component of the employed solvent mixture is generated in-situ which is a lighter fraction formed by mild and severe thermal cracking of mixed feedstock. The ‘multi-residence time mild thermal cracking’ employed in the process of the present invention ensures optimum residence time of the coal tar pitch. The petroleum streams are fine-tuned for each of the participating reactant molecules thereby preventing over-cracking of the same. This also helps in ensuring the stability of the products generated from ‘multi-residence time mild thermal cracking’, offering much additional process control in the hands of the refiner to make tailor-made mix feed composition needed for needle coke formation. Additionally, this helps in fine-tuning the properties of the aromatic solvent component which is employed as part of the mixed solvent used for the purification of the feedstock. An added advantage of the present invention is that the solid catalyst fines which are present in CLO provide active sites for aggregate formation and improve the impurity removal rate. An additional advantage of the present invention is that the needle coke is produced by blending different feed sources from coal-based and petroleum-based hydrocarbons. This invention enables the purification of the coal-based and petroleum-based feedstock mixture, which when subjected to further thermal treatment results in the production of high-quality graphite or needle grade coke which is used for the preparation of graphite electrodes.

[0025] The multi-residence time mild thermal cracking is employed in the present invention wherein the different feed components like CTP, CLO and PFO are introduced into the reactor at different reactor locations (namely bottom, middle and top) based on the presence of lighter components (350° C.−) in their boiling point range or other physic-chemical characteristics including aromatic content, aromaticity etc.

[0026] The multi-residence time mild thermal cracking employed in the process of the present invention ensures optimum residence time of the coal tar pitch and other petroleum streams fine-tuned for each of the participating reactant molecules thereby preventing over-cracking of the same.

[0027] The multi-residence time mild thermal cracking’ helps in ensuring the stability of the products generated from ‘multi-residence time mild thermal cracking’, offering much additional process control in the hands of the refiner to make tailor-made mix feed composition needed for needle coke formation.

[0028] The multi-residence time mild thermal cracking helps in fine-tuning the properties of the aromatic solvent component which is employed as part of the mixed solvent used for purification of the feedstock.

[0029] The multi-residence time mild thermal cracking helps in controlling the temperature of the reacting mixture inside the mild cracking reactor, which is desirable particularly when one of the feedstocks is having high coking propensity while heating in the furnace.

[0030] The multi-residence time mild thermal cracking improves mixed pitch quality like aromatic content, softening point etc, and the resulting mixed pitch subjected to severe thermal cracking improves coke yield and quality

[0031] The separation of thermally cracked mixed feedstock (containing coal tar pitch and petroleum streams) into different cuts for generation of mixed pitch (with boiling point greater than 350° C.+) and other products such as light oil (140° C. to 270° C.), middle oil (270° C. to 350° C.)

[0032] The solvent-assisted selective separation of undesirable Quinoline Insoluble (QI) and solid catalyst fines from the mixed pitch (350° C.+) to produce purified pitch

[0033] The light oil (140° C. to 270° C.) generated in the process (by mild thermal cracking and delayed coking) is used as an aromatic solvent for purification of mixed pitch whereas middle oil (270° C. to 350° C.) is routed to the hydrotreater unit for further treatment

[0034] The solvent treatment vessel, gravity settler and solvent recovery column are used in this process for solvent treatment of mixed pitch (350° C.+) followed by separation of the purified mixed pitch from impurities and recovery of solvent (for further use) from the purified mixed pitch which is used as feedstock for the preparation of needle coke.

[0035] The thermal cracking of purified mixed pitch in a delayed coker unit produces different products such as coker kero (140° C. to 270° C.), light coker gas oil (270° C. to 350° C.), heavy coker gas oil (350° C. to 480° C.+), coker fuel oil (480° C.+), and high-quality needle grade coke.

[0036] Coker kero (140-270° C.) generated in delayed coker process is used as an aromatic solvent for purification of mixed pitch (350° C.+) whereas other cuts are light coker gas oil (270-390° C.), heavy coker gas oil (390-480° C.+) and coker fuel oil (480° C.+) are withdrawn as product streams.

[0037] The present invention provides process for the preparation of a needle coke, wherein the process comprises:

[0038] a) subjecting a feed stream to a multi-residence time mild thermal cracking in the presence of petroleum streams to obtain a mixed pitch, wherein the feed stream is selected from a group of coal tar, coal tar pitch (CTP), clarified oil (CLO), pyrolysis fuel oil, gas oils, hydrotreated vacuum gas oil and a combination thereof, preferably coal tar pitch, and wherein the petroleum streams comprise clarified oil (CLO), pyrolysis fuel oil (PFO) and a combination thereof;

[0039] wherein the multi-residence time mild thermal cracking comprises steps of

[0040] i. heating the coal tar pitch in a mild cracking furnace;

[0041] ii. sending the heated coal tar pitch of step i) to the bottom of a mild cracking reactor;

[0042] iii. introducing the petroleum streams from a middle and top section of the said mild cracking rector to carry out the multi-residence time mild thermal cracking of the heated coal tar pitch in the presence of the petroleum streams to produce a plurality of reactor effluents;

[0043] iv. sending the reactor effluents from a top section of the mild thermal cracking reactor to a fractionator for fractionation to produce different components comprising a plurality of off-gases, a light oil, a middle oil and a mixed pitch;

[0044] v. routing the plurality of off-gases to a gas concentration section for recovery; and

[0045] vi. sending the light oil to a solvent tank for use as an aromatic solvent and middle oil to a hydrotreating unit for recovery;

[0046] b) purifying the mixed pitch through a solvent-assisted selective separation of undesirable quinoline insoluble (QI) and solid catalyst fines from the mixed pitch to obtain a purified mixed pitch,

[0047] wherein the mixed pitch is treated with a solvent in a solvent treatment vessel followed by settling of impurities in a gravity settler; a heavy pitch-solvent mixture containing impurities is withdrawn from the bottom of the gravity settler and a purified pitch-solvent mixture is withdrawn from the top of the gravity settler; the heavy pitch-solvent mixture is heated in a first heater and then routed to the first solvent recovery column and the purified pitch-solvent mixture is heated in a second heater and then routed to the second solvent recovery column for solvent recovery; the purified mixed pitch is ultimately withdrawn from the bottom of the second solvent recovery column, the solvent to the mixed pitch has a weight ratio in a range of 0.5:1 to 10:1, the solvent treatment vessel is operated at a temperature in a range of 60° C. to 350° C. and a pressure in a range of 1 to 80 Kg / cm2 (g); and

[0048] c) subjecting the purified mixed pitch to delayed coking to produce the needle coke and a lighter hydrocarbon component; wherein the purified mixed pitch is mixed optionally mixed with a new hydrocarbon stream before delayed coking; the lighter hydrocarbon component is fractionated to produce a plurality of gaseous products and a plurality of liquid products containing a coker kero, a light coker gas oil, a heavy coker gas oil and a coker fuel oil; and the coker kero is sent to the solvent tank for use as an aromatic solvent.

[0049] In an embodiment of the present invention, the purification of the mixed pitch through solvent-assisted selective separation comprises steps of:

[0050] i. introducing the mixed pitch to a solvent treatment vessel for solvent treatment, wherein the mixed pitch is mixed with a solvent as received from the solvent tank;

[0051] ii. withdrawing the mixed pitch after the solvent treatment from the bottom of the solvent treatment vessel and introducing the mixed pitch into a gravity settler for the settling of impurities;

[0052] iii. withdrawing a heavy residual fractions of the mixed pitch from the bottom of the gravity settler as a pitch-solvent mixture,

[0053] iv. routing the said pitch-solvent mixture to a first heater followed by a first solvent recovery column, wherein the solvent is recovered from top of the first solvent recovery column and sent to the solvent tank,

[0054] v. withdrawing the heavy hydrocarbon from the bottom of the first solvent recovery column as heavy pitch containing residual fractions of QI and catalyst fines along with heavy refractory hydrocarbon molecules;

[0055] vi. routing the purified mixed pitch-solvent mixture coming out from the top of the gravity settler to a second heater and then transferred into the second solvent recovery column to recover a solvent stream and a purified mixed pitch; and

[0056] vii. sending the solvent stream from the second solvent recovery column to the solvent tank.

[0057] In an embodiment of the present invention, the delayed coking of purified mixed pitch comprises the steps of:

[0058] i. mixing the purified mixed pitch withdrawn from the bottom of the second solvent recovery column with a new hydrocarbon stream containing hydrotreated vacuum gas oil (HDT VGO) to obtain a mixture;

[0059] ii. routing the mixture to the mixed fractionator (MF) column, wherein the mixture mixes with an internal recycle stream and is drawn out from a bottom of the mixed fractionator (MF) column as the secondary feedstock, wherein the bottom of the mixed fractionator (MF) column is operating at a temperature in a range of 260° C. to 390° C.;

[0060] iii. sending the secondary feedstock withdrawn from the mixed fractionator (MF) column bottom to a coker furnace at a predefined hydrocarbon feed rate for heating at a temperature predefined for severe thermal cracking;

[0061] iv. additionally introducing a dilution steam or a boiler feed water stream to the coker furnace to obtain a hot feedstock comprising a heavy oil which prevent coking in furnace tubes and create additional turbulent flow.

[0062] v. routing the hot feedstock from the said coker furnace into a plurality of coke drums in the feeding step of the coking cycle, wherein the heavy oil is cracked and converted to graphitizable needle coke and a lighter hydrocarbon components;

[0063] vi. sending the lighter hydrocarbon components to the mixed fractionator (MF) column for separation to obtain an overhead vapor containing the plurality of gaseous products from a top section of the mixed fractionator (MF) column; and the plurality of liquid products containing the coker kero, the light coker gas oil, the heavy coker gas oil and the coker fuel oil from the mixed fractionator (MF) column with different cut ranges of 140 to 270° C., 270° C. to 350° C., 350° C. to 480° C. and 480° C.+ respectively;

[0064] vii. routing the overhead vapor containing the plurality of gaseous products to a gas concentration section for recovery; and

[0065] viii. routing the coker kero to the solvent tank for use as an aromatic solvent.

[0066] In an embodiment of the present invention, the feed stream is coal tar pitch (CTP); the petroleum stream contains clarified oil (CLO) and pyrolysis fuel oil (PFO).Conradson carbon residue (CCR) of coal tar pitch is in the range of 10 to 47 wt %, CLO is in the range of 1.5 to 19 wt %, PFO is in the range of 1 to 15 wt % and HDT VGO is in the range of <0.1 to 10 wt %, respectively. The quinoline insoluble (QI) content of the coal tar pitch used in the present invention is in the range of 1 to 16 wt %. The Basic sediment and water (BS&W) content of CLO used in the present invention is in the range of 0.05 to 2.5 wt %.

[0067] The solvent used in the present invention is selected from an aromatic solvent, an aliphatic solvent and a polar extraction solvent with carbon numbers ranging from 3 to 15. In the presently disclosed process, a combination of an aromatic solvent, an aliphatic and a polar extraction solvent is used as a mixed solvent for the purification of the pitch. The aromatic solvent component is selected from light oil (obtained by mild thermal cracking), coker kero (obtained by delayed coking of aromatic feedstocks namely coal tar pitch, CLO, PFO etc.), coal tar oil (obtained by distilling coal tar), anthracene oil, naphthalene oil, benzene, xylene, creosote oil, quinoline, toluene etc. The aliphatic solvent component is selected from cyclohexane, kerosene, n-pentane, n-hexane, n-heptane, diesel oil, naphtha etc. The polar extraction solvent component is n-methyl-2-pyrrolidone (NMP). The solvent mixture employed in the disclosed process is selected from aromatic solvent: 10 to 80 wt %, aliphatic solvent: 10 to 80 wt %, and polar extraction solvent: 10 to 70 wt %.

[0068] The mild cracking furnace is operating at an outlet temperature of coil between 390° C. to 475° C. In a preferred embodiment, the mild cracking furnace is operating at the outlet temperature of coil between 430° C. to 460° C.

[0069] The mild cracking reactor is operating at a temperature in a range of 380° C. to 475° C. In a preferred embodiment, the mild cracking reactor is operating at the temperature in the range of 420° C. to 450° C., depending upon the furnace outlet temperature and heat losses in the transfer line.

[0070] In an embodiment, the mild thermal cracking reactor is maintained at a pressure in a range of 5 to 15 Kg / cm2 (g). In a preferred embodiment, the mild thermal cracking reactor is maintained at the pressure in the range of 7 to 12 Kg / cm2 (g).

[0071] The hydrocarbon residence time in the mild thermal cracking reactor is maintained from 1 to 30 mins. In a preferred embodiment, the hydrocarbon residence time in the mild thermal cracking reactor is maintained from 5 to 20 mins.

[0072] The fractionator for the mild cracking section is operated at a bottom temperature between 260° C. to 390° C.

[0073] The solvent to mixed pitch ratio in the solvent treatment is kept in the range of 0.5:1 to 10:1 (wt / wt).

[0074] The solvent treatment vessel is operating at a temperature in a range of 60° C. to 350° C. In a preferred embodiment, the solvent treatment vessel is operating at the temperature in the range of 70° C. to 200° C.

[0075] The solvent treatment vessel is operating at a pressure in a range of 1 to 80 Kg / cm2 (g). In a preferred embodiment, the solvent treatment vessel is operating at the pressure in a range of 1 Kg / cm2 (g) 50 to Kg / cm2 (g).

[0076] In an embodiment of the present invention, a bottom of the mixed fractionator (MF) column of the severe thermal cracking section is operating at a bottom temperature between 260° C. to 390° C.

[0077] In an embodiment of the present invention, the needle coke derived from purified mixed pitch has a crystallinity of 77.8% to 80.3%.

[0078] The coker furnace in the severe thermal cracking section is operating at an outlet temperature of coil between 450° C. to 530° C. In a preferred embodiment, the coker furnace in the severe thermal cracking section is operating at the outlet temperature of coil between 490° C. to 515° C. The dilution steam or boiler feed water is injected in the coker furnace in a range of 0.5 to 3 wt % of the hydrocarbon feed rate.

[0079] The plurality of coke drums are operating at an operating temperature in a range of 440° C. to 520° C. In a preferred embodiment, the plurality of coke drums are operating at the operating temperature in the range of 470° C. to 500° C. The feeding cycle time of the plurality of coke drums in the severe thermal cracking section varies from 12 hrs to 56 hrs.

[0080] In an embodiment, the plurality of coke drums are maintained at a pressure in a range of 1 to 10 Kg / cm2 (g). In a preferred embodiment, the plurality of coke drums are maintained at the pressure in the range of 2.5 to 7 Kg / cm2 (g).

[0081] In an embodiment of the present invention the process for the preparation of needle coke comprises the steps as described below and depicted in FIG. 1.

[0082] Coal tar pitch (1) is heated in a mild cracking furnace (2) and then sent to the bottom of the mild cracking rector (3). A petroleum stream containing clarified oil CLO (4) is introduced from the middle section of the said rector to carry out a ‘multi-residence time mild thermal cracking’ of CLO and coal tar pitch. The reactor effluents (5) containing mixed product vapors of CTP and CLO are then sent to a fractionator (6) wherein it is fractionated to different cuts namely off-gases (7) which comprises fuel gas, LPG and naphtha, light oil (8) with boiling range from 140° C. to 270° C., middle oil (9) with boiling range from 270° C. to 350° C. and heavier (350° C.+) mixed pitch (10). The off-gases (7) are routed to the gas concentration section for further recovery. The light oil (8) is sent to the solvent tank (11) for use as an aromatic solvent in the present invention and middle oil (9) is sent to the hydrotreating unit for further treatment whereas the mixed pitch (10) is used as feedstock for needle grade coke. The mixed pitch (10) contains impurities such as QI and solid catalyst fines and the said mixed pitch is introduced to a solvent treatment vessel (12) wherein it mixes with solvent, received from the solvent tank (11). A solvent stream (13) is added to the solvent tank for solvent make-up. The mixed pitch (10) after the solvent treatment is drawn out from the bottom of the solvent treatment vessel via line (14) and then introduced in a gravity settler (15) for the settling of impurities. The heavy residual fractions of the mixed pitch get separated out and withdrawn from the bottom of the gravity settler as a pitch-solvent mixture (16). The said pitch-solvent mixture (16) is routed to a first heater (17) followed by a first solvent recovery column (18). The solvent (19) is recovered from the top of the first solvent recovery column and sent to the solvent tank (11) for further use whereas, heavy hydrocarbon is withdrawn from the bottom of the first solvent recovery column as heavy pitch (20) which contains residual fractions of QI and catalyst fines along with heavy refractory hydrocarbon molecules and may be used as feedstock for fuel grade coke. The purified mixed pitch-solvent mixture (21) coming out from the top of the gravity settler is routed to a second heater (22) and then flashed into the second solvent recovery column (23) for solvent recovery. The recovered solvent stream (24) is sent to the solvent tank (11) for further use. The purified mixed pitch after solvent recovery (25) is withdrawn from the bottom of the second solvent recovery column (23) and mixed with a new hydrocarbon stream containing HDT VGO (26) and then is routed to the mixed fractionator (MF) column (27) where it mixes with the internal recycle stream and is drawn out from the MF bottom as the secondary feedstock. The secondary feedstock (28) which is withdrawn from the MF bottom is sent to a coker furnace (29) for heating to the desired severe thermal cracking temperature. In addition, steam or boiler feed water stream (30) is introduced to the coker furnace to prevent coking in furnace tubes and create additional turbulent flow. Hot feedstock (31) from the said furnace is routed to one of the coke drums (32,33) in the feeding step of the coking cycle, where heavy oil is cracked and is converted to graphitizable needle coke and lighter hydrocarbon components like off-gases comprise of fuel gas, LPG, naphtha, gas-oils etc. Product vapors (34) of the existing coke drum are sent to the MF column (27) for further separation. The overhead vapor of the MF comprised of gaseous products (35) are routed to a gas concentration section for further recovery. Liquid products such as coker kero (36), light coker gas oil (37) and heavy coker gas oil (38) and coker fuel oil (39) are withdrawn from the MF column with different cut ranges of 140° C. to 270° C., 270° C. to 350° C., 350° C. to 480° C. and 480° C.+ respectively. Coker kero (36) stream is routed via a line (40) to the solvent tank (11) for further use as an aromatic solvent whereas light coker gas oil (37), heavy coker gas oil (38) and coker fuel oil (39) are withdrawn as product streams. Needle coke which is deposited in the coke drums is removed from the bottom (41) in the maintenance cycle by using high pressure water jets.

[0083] In another embodiment of the present invention the process for the preparation of needle coke comprises the steps as described below and depicted in FIG. 2. Coal tar pitch (1) is heated in a mild cracking furnace (2) and then sent to the bottom of the mild cracking rector (3). Petroleum streams containing clarified oil (CLO) (4) and pyrolysis fuel oil (PFO) (5) are introduced from the middle and top sections of the said rector (3) to carry out a ‘multi-residence time mild thermal cracking’ of CLO, PFO and coal tar pitch. The reactor effluents (6) containing mixed product vapors of CTP, CLO and PFO are then sent to a fractionator (7) wherein it is fractionated to different cuts namely off-gases (8) which comprises fuel gas, LPG and naphtha, light oil (9) with boiling range from 140° C. to 270° C., middle oil (10) with boiling range from 270° C. to 350° C. and mixed heavy (350° C.+) pitch (11). The off-gases (8) are routed to the gas concentration section for further recovery. The light oil (9) is sent to the solvent tank (12) for use as an aromatic solvent in the present invention and middle oil (10) is sent to the hydrotreating unit for further treatment whereas the mixed pitch (11) is used as feedstock for needle grade coke. The mixed pitch (11) contains impurities such as QI and solid catalyst fines and the said mixed pitch is introduced to a solvent treatment vessel (13) wherein it mixed with solvent, received from the solvent tank (12). A solvent stream (14) is added to the solvent tank for solvent make-up. The mixed pitch (11) after the solvent treatment is drawn out from the bottom of the solvent treatment vessel via line (15) and then introduced in a gravity settler (16) for the settling of impurities. The heavy residual fractions of the mixed pitch get separated out and withdrawn from the bottom of the gravity settler as a pitch-solvent mixture (17). The said pitch-solvent mixture (17) is routed to a first heater (18) followed by a first solvent recovery column (19). The solvent (20) is recovered from the top of the first solvent recovery column and sent to the solvent tank (12) for further use whereas heavy hydrocarbon is withdrawn from the bottom of the first solvent recovery column as heavy pitch (21) which contains residual fractions of QI and catalyst fines along with heavy refractory hydrocarbon molecules and may be used as feedstock for fuel grade coke. The purified mixed pitch-solvent mixture (22) coming out from the top of the gravity settler is routed to a second heater (23) and then flashed into the second solvent recovery column (24) for solvent recovery. The recovered solvent stream (25) is sent to the solvent tank (12) for further use. The purified mixed pitch after solvent recovery (26) is withdrawn from the bottom of the second solvent recovery column (23) is routed to the mixed fractionator (MF) column (27) where it mixed with the internal recycle stream and is drawn out from the MF bottom as the secondary feedstock. The secondary feedstock (28) which is withdrawn from the MF bottom is sent to a coker furnace (29) for heating to the desired severe thermal cracking temperature. In addition, steam or boiler feed water stream (30) is introduced to the coker furnace to prevent coking in furnace tubes and create additional turbulent flow. Hot feedstock (31) from the said furnace is routed to one of the coke drums (32,33) in the feeding step of the coking cycle, where heavy oil is cracked and is converted to graphitizable Needle coke and lighter hydrocarbon components like off-gases comprise of fuel gas, LPG, naphtha, gas-oils etc. Product vapors (34) of the existing coke drum are sent to the MF column (27) for further separation. The overhead vapor of the MF comprised of gaseous products (35) are routed to a gas concentration section for further recovery. Liquid products such as coker kero (36), light coker gas oil (37) and heavy coker gas oil (38) and coker fuel oil (39) are withdrawn from the MF column with different cut ranges of 140° C. to 270° C., 270° C. to 350° C., 350° C. to 480° C. and 480° C.+ respectively. Coker kero (36) stream is routed via a line (40) to the solvent tank (11) for further use as an aromatic solvent whereas light coker gas oil (37), heavy coker gas oil (38) and coker fuel oil (39) are withdrawn as product streams. Needle coke which is deposited in the coke drums is removed from the bottom (41) in the maintenance cycle by using high pressure water jets.

[0084] In an embodiment of the present invention, the coefficient of thermal expansion (CTE) value of needle coke is in a range of 1.33×10−6 / ° C. to 1.21×10−6 / ° C.EXAMPLES

[0085] The present disclosure with reference to the accompanying examples describes the present invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. It is understood that the examples are provided for the purpose of illustrating the invention only and are not intended to limit the scope of the invention in any way.Example 1

[0086] A coal tar pitch (CTP) sample with properties as provided in Table 1 was taken and heated in a mild cracking furnace and then routed to a mild cracking reactor. A petroleum stream (CLO) with properties as provided in Table 2 was introduced into the said rector. The mixing ratio of CTP and CLO at a wt / wt ratio of 50 / 50. The mild thermal cracking operating conditions are provided in Table 3.TABLE 1Properties of CTP (unpurified)PropertyValueDensity, g / cc1.25CCR, wt %33.1Sulfur, wt %0.52Nitrogen, wt %1.5Softening Point, ° C.54QI, w %4.35Aromatics, wt %100Distillation (ASTM D2887)Cut, wt %° C.531610329203523038750441704989059295639100709TABLE 2Properties of CLOPropertyCLODensity, g / cc1.158CCR, wt %15.9Sulfur, wt %0.42Nitrogen, wt %0.1BS&W, wt %0.7Aromatics, wt %97.8Paraffins + Naphthenes, wt %2.2Distillation (ASTM D2887)Cut, wt %° C.521910320203393036050386704229047895524100632TABLE 3Operating conditions of mild thermal crackingOperating parameterValueCoil outlet temperature of mild thermal cracking furnace, ° C.450Reactor inlet temperature, ° C.440Reactor outlet temperature, ° C.428Reactor pressure, Kg / cm2 (g)7Residence time (Coal tar pitch), min20Residence time (CLO), min10The reactor effluents (generated by mild cracking of mixed feedstock containing CTP and CLO) were further fractionated and accordingly, 350° C.+ was withdrawn from the fractionator bottom as mixed pitch and the key properties of the same are provided in Table 4. As a comparative case, CTP (of Table 1) and CLO (of Table 2) were mixed a wt / wt ratio of 50 / 50 and properties of the mixed feedstock (CTP+CLO) without mild thermal cracking are provided in Table 4.TABLE 4Properties of unpurified mixed feedstockand mixed pitch (350° C.+)Mixed PitchMixed feedstock(with mildProperty(w / o mild cracking)thermal crackingDensity, g / cc1.2031.22CCR, wt %24.4527.3Sulfur, wt %0.470.48Nitrogen, wt %0.790.80Softening Point, ° C.3669Aromatics, wt %98.8100Paraffins + Naphthenes, wt %1.20QI, wt %3.323.56BS&W, wt %0.390.41Said unpurified mixed feedstock and mixed pitch of Table 4 were subjected to solvent treatment in a solvent treatment section for separation of impurities (QI and solid catalyst fines) from the mixed feedstock and mixed pitch. The operating conditions of the solvent treatment process are provided in Table 5.TABLE 5Operating conditions of solvent treatment sectionParameterValueAromatic solventLight oil(140-270° C.)Aliphatic solventkerosene(140-270° C.)Polar extraction solventNMPSolvent mixture composition -(40:40:20)Aromatic:Aliphatic:NMP (wt %)Mixed solvent:mixed pitch2.5:1Mixing time, min40Mixing temperature, ° C.100Settling time, hour, max1The top portion of the mixed feedstock-solvent mixture and the mixed pitch-solvent mixture after solvent treatment were separated and the solvent was evaporated by heating at 300° C. for 3 hrs. The purified mixed feedstock and the purified mixed pitch after solvent recovery were analyzed for key properties such as QI (as per ASTM D2318) and BS&W (as per ASTM D4007) and the results are provided in Table 6.TABLE 6Properties of purified mixed feedstock and mixed pitchMixed feedstock (w / oMixed Pitch (withPropertymild cracking)mild thermal cracking)QI, wt %<0.1<0.1BS&W, wt %00The purified mixed feedstock and the purified mixed pitch with properties as provided in Table 6 were subjected to severe thermal cracking (as per Delayed Coking operating conditions) in a batch Micro-Coker experimental set-up. The Micro-Coker reactor operating conditions and coke quality are provided in Tables 7.TABLE 7Micro-Coker reactor experimentation conditions and coke qualityOperating parameterCase ICase IIFeedstockMixed feedstockMixed Pitch (with(w / o mildmild thermalcracking)cracking)Feed loaded, gm500500Temperature,° C.490490Pressure, kg / cm2 (g)55Holding time, hrs1212Coke yield, wt %49.453.7% crystallinity72.677.8From Table 7, it can be seen that the coke yield obtained from mixed feedstock without mild cracking (case I) was 49.4 wt % whereas, the coke yields obtained from mixed Pitch with mild thermal cracking (case II) was 53.7 wt %. These coke samples were thereafter subjected to calcination to produce calcined coke samples The calcined coke samples were then analyzed in an XRD analyzer. The results showed 72.6% crystallinity for mixed feedstock without mild thermal cracking whereas 77.8% crystallinity for mixed pitch with mild thermal cracking (invented process). The results indicated that the coke yield and quality both were improved in the invented process.Example-2As a comparative case, the unpurified CTP (without solvent treatment and blending of CLO), purified CTP (without mixing of CLO), unpurified mixed pitch and purified mixed pitch were subjected to thermal cracking in a batch Micro-Coker experimental set-up. The operating conditions and coke quality of the Micro-Coker experiments are provided in Tables 8. The solvent-treatment technique used for separation of impurities from the feedstock (unpurified CTP and unpurified mixed pitch) as per procedure mentioned in Example 1.TABLE 8Micro-Coker reactor experimentation conditions and coke qualityOperating parameterExp. IExp. IIExp. IIIExp. IVFeedstockUnpurifiedCTP (Table 1CTP (ofof ExampleUnpurifiedPurifiedTable-1) w / o1) purified inmixedmixedsolventsolvent withoutpitch (ofpitch (oftreatmentmixing of CLOTable-4)Table-6)Feed loaded, gm500500500500Temperature,° C.490490490490Pressure, kg / cm25555(g)Holding time, hrs12121212CTE of graphite2.921.622.391.33artifact, ×10−6 / °C.Five numbers of runs were carried out for each experiment (Exp. I to IV) maintaining same operating conditions (as per Table 8) to generate coke samples for measurement of coefficient of thermal expansion (CTE). Coke samples from all the runs of each experiment were subjected to calcination and graphite artifacts in the shape of coke rods were prepared. Baked coke rods were used for measurement of CTE. It can be seen from Table 8, the CTE value improved from 2.92×10−6 / ° C. to 1.33×10−6 / ° C. due to blending of CLO in CTP followed by purification.Example-3

[0094] Experiments Micro-Coker unit at similar operating conditions as Table-7 (of Example 1) were carried out a combination of purified mixed pitch (Table 6 of Example 1) with 20 wt % of hydrotreated vacuum gas oil (HDT VGO). The properties of HDT VGO are tabulated in Table 9.TABLE 9Properties of HDT VGOPropertyHDT VGODensity, g / cc0.8991CCR, wt %0.05Asphaltene0.01Sulfur, wt %0.04Nitrogen, wt %0.016Aromatics, wt %19.3Paraffins + Naphthenes, wt %80.7

[0095] Five numbers of runs were carried for this experiment maintaining same operating conditions (as per Table 7 of Example 1) to generate coke samples for measurement of CTE. The CTE of coke sample was measured as per procedure mentioned in Example 2. The resultant coke quality is provided in Table 10.TABLE 10Coke propertiesPurified mixed pitch (of Table-6)Propertywith 20 wt % HDT VGO (Table 9)CTE of graphite artifact, ×10−6 / ° C.1.21

[0096] It can be seen from Table 8 (of Example 2) and Table 10, the CTE value improved from 1.33×10−6 / ° C. to 1.21×10−6 / ° C. upon blending of HDT VGO in purified mixed pitch (containing CTP and CLO).Example 4

[0097] Coal tar pitch (CTP) sample (Table 1 of Example 1) was taken and heated in a mild cracking furnace and then routed to a reactor where the petroleum streams containing CLO (Table 2 of Example 1) and PFO (with properties as provided in Table 11) were introduced into the said rector. The mixing ratio of CTP, CLO and PFO is 50:35:15 (by weight). The operating conditions of the mild cracking are provided in Table 3 (of Example 1) where residence time for PFO was maintained for 5 mins.TABLE 11Properties of PFOPropertyPFODensity, g / cc1.034CCR, wt %7.72Sulfur, wt %, max0.001Nitrogen, wt %, max0.048Aromatics, wt %100

[0098] The reactor effluents (generated by mild cracking of mixed feedstock containing CTP, CLO and PFO) were further fractionated and accordingly, mixed pitch (350° C.+) was withdrawn from the fractionator bottom as mixed pitch (350° C.+). Said mixed pitch was subjected to solvent treatment in a solvent treatment section for separation of impurities (QI and solid catalyst fines) from the mixed pitch as described in Example 1. The purified mixed pitch with properties as provided in Table 6 (of Example 1) was subjected to severe thermal cracking (as per Delayed Coking operating conditions) in a batch Micro-Coker experimental set-up. As a comparative case, purified mixed pitch of CTP and CLO (50 wt %: 50 wt %) and purified mixed pitch of CTP, CLO and PFO (50 wt %: 35 wt %: 15 wt %) were subjected to thermal cracking in a batch Micro-Coker experimental set up. The operating conditions of the Micro-Coker experiment are provided in Table 7 (of Example 1). The Coke quality of Micro-Coker reactor experimentation are tabulated in Table 12.TABLE 12Coke quality of Micro-Coker reactor experimentationFeed% crystallinityPurified mixed pitch of CTP and CLO77.8(50 wt %:50 wt %) Table 6 of Example 1Purified mixed pitch of CTP, CLO and80.3PFO (50 wt %:35 wt %:15 wt %)

[0099] Coke samples generated from the Micro-Coker experiments were subjected to calcination to produce calcined coke samples. The calcined coke samples were then analyzed in an XRD analyzer. The results showed 77.8% crystallinity for purified mixed pitch and the value was improved to 80.3% crystallinity due to blending of PFO in the mixed pitch (containing CTP and CLO).

Examples

example 1

[0086]A coal tar pitch (CTP) sample with properties as provided in Table 1 was taken and heated in a mild cracking furnace and then routed to a mild cracking reactor. A petroleum stream (CLO) with properties as provided in Table 2 was introduced into the said rector. The mixing ratio of CTP and CLO at a wt / wt ratio of 50 / 50. The mild thermal cracking operating conditions are provided in Table 3.

TABLE 1Properties of CTP (unpurified)PropertyValueDensity, g / cc1.25CCR, wt %33.1Sulfur, wt %0.52Nitrogen, wt %1.5Softening Point, ° C.54QI, w %4.35Aromatics, wt %100Distillation (ASTM D2887)Cut, wt %° C.531610329203523038750441704989059295639100709

TABLE 2Properties of CLOPropertyCLODensity, g / cc1.158CCR, wt %15.9Sulfur, wt %0.42Nitrogen, wt %0.1BS&W, wt %0.7Aromatics, wt %97.8Paraffins + Naphthenes, wt %2.2Distillation (ASTM D2887)Cut, wt %° C.521910320203393036050386704229047895524100632

TABLE 3Operating conditions of mild thermal crackingOperating parameterValueCoil outlet temperature of mil...

example-2

As a comparative case, the unpurified CTP (without solvent treatment and blending of CLO), purified CTP (without mixing of CLO), unpurified mixed pitch and purified mixed pitch were subjected to thermal cracking in a batch Micro-Coker experimental set-up. The operating conditions and coke quality of the Micro-Coker experiments are provided in Tables 8. The solvent-treatment technique used for separation of impurities from the feedstock (unpurified CTP and unpurified mixed pitch) as per procedure mentioned in Example 1.

TABLE 8Micro-Coker reactor experimentation conditions and coke qualityOperating parameterExp. IExp. IIExp. IIIExp. IVFeedstockUnpurifiedCTP (Table 1CTP (ofof ExampleUnpurifiedPurifiedTable-1) w / o1) purified inmixedmixedsolventsolvent withoutpitch (ofpitch (oftreatmentmixing of CLOTable-4)Table-6)Feed loaded, gm500500500500Temperature,° C.490490490490Pressure, kg / cm25555(g)Holding time, hrs12121212CTE of graphite2.921.622.391.33artifact, ×10−6 / °C.

Five numbers of runs we...

example-3

[0094]Experiments Micro-Coker unit at similar operating conditions as Table-7 (of Example 1) were carried out a combination of purified mixed pitch (Table 6 of Example 1) with 20 wt % of hydrotreated vacuum gas oil (HDT VGO). The properties of HDT VGO are tabulated in Table 9.

TABLE 9Properties of HDT VGOPropertyHDT VGODensity, g / cc0.8991CCR, wt %0.05Asphaltene0.01Sulfur, wt %0.04Nitrogen, wt %0.016Aromatics, wt %19.3Paraffins + Naphthenes, wt %80.7

[0095]Five numbers of runs were carried for this experiment maintaining same operating conditions (as per Table 7 of Example 1) to generate coke samples for measurement of CTE. The CTE of coke sample was measured as per procedure mentioned in Example 2. The resultant coke quality is provided in Table 10.

TABLE 10Coke propertiesPurified mixed pitch (of Table-6)Propertywith 20 wt % HDT VGO (Table 9)CTE of graphite artifact, ×10−6 / ° C.1.21

[0096]It can be seen from Table 8 (of Example 2) and Table 10, the CTE value improved from 1.33×10−6 / ° C. ...

[0001] This application claims priority to Indian Application No. 202421060942 dated Aug. 12, 2024. The contents of this application are hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The present invention relates to a process for production of high-quality Graphite / Needle-grade coke for the preparation of graphite electrodes for use in the steel industry or making electrodes for batteries.BACKGROUND

[0003] Adoption of electric arc furnace (EAF) technology for steel production is increasing across the world resulting in increased Needle / Graphite coke demand. Needle coke is used for the preparation of graphite electrodes for use in the steel industry. Conventionally, needle coker feedstock is desired to be highly aromatic and lower in impurities. Additionally, adoption of coke oven batteries and coal pyrolysis units are also increasing across the world, resulting availability of coal-based feedstock such as coal tar pitch (CTP) for the production of needle / graphite coke is increased. CTP contains higher levels of impurity such as quinoline insoluble (QI), if present at higher level in the feedstock, the same gets deposited in the needle coke that is produced resulting in high coefficient of thermal expansion (CTE) lower quality needle / graphite coke.

[0004] U.S. Pat. No. 4,814,063A discloses a method for the production of needle coke comprising the steps of hydrogenation of the starting material selected from the coal tar or coal tar pitch containing less than 0.1 wt % of quinoline insoluble (QI). The said coal tar or coal tar pitch is subjected to hydrogenation using hydrogenation catalyst to produce the hydrogenated oil. The said hydrogenated oil is then subjected thermal cracking under controlled operating conditions to produce Needle coke. However, the hydrogenation process used in this invention for separation of impurities from the feedstock containing coal tar or coal tar pitch is costly. Further in said technique, there is a high possibility of a reduction in aromatic content and reactivity of the feedstock which can impact in produced needle coke quality adversely.

[0005] UK U.S. Pat. No. 2,013,710A describes a process for preparing a carbonaceous starting material for producing of electrode-grade coke comprises extracting raw coke oven tar with a petrol fraction to produce an insoluble soft pitch fraction which contains undesirable non-graphitizable impurities and an extract of tar components in the solvent. The solvent is removed from the exact tar to give a tar suitable for producing electrode coke. However, only a selective and small portion of the fraction viz. 27% of tar oil components has been used to make carbonaceous raw material for producing electrode coke. Additionally, in the prior art, a petroleum stream containing decant oil is used for mixing with tar oil without pre-pre-treatment decent oil. Decent oil contains solid catalyst fines, and it is essential to remove the said catalyst fines before use, if present it has a deleterious effect on produced coke quality.

[0006] U.S. Pat. No. 3,617,515A describes a process for production of graphitizable Needle coke and carbon grade coke from a feed containing coal tar pitch, comprising separating a feed containing coal tar pitch into two fractions. First fraction containing boiling range from 600° F. to about 1,200° F. and remaining as heavier second fraction, both fractions having a high content of mixture of condensed aromatic ring compounds. The two fractions are then subject to delayed coking to produce graphitizable needle coke and carbon grade coke. However, the said prior art did not use any pre-treatment process for the removal of impurity (namely quinoline insoluble) from coal tar pitch. The said impurity when present in the hydrocarbon matrix creates disturbance during forming of mesophase which can impact the needle coke and carbon grade coke quality adversely. The impurity also cause coke lay-down inside the furnace tubes affecting the pressure drop and heat transfer efficiency.

[0007] The hydrogenation process described in prior art has the limitation of being costly and the process adversely affects the quality of produced needle coke. Therefore, there is a requirement of a process for production of high-quality graphite / needle-grade coke.OBJECTIVES

[0008] The main objective of the present invention is to provide a process for production of high-quality graphite / needle-grade coke with low coefficient of thermal expansion (CTE) and high crystallinity.

[0009] Another objective of the present invention is to provide a process that involves a “multi-residence time mild thermal cracking” to ensure the optimum residence time of the coal tar pitch and other petroleum streams fine-tuned for each of the participating reactant molecules thereby preventing over-cracking of the same.

[0010] Another objective of the present invention is to provide a process for producing of needle coke that involves ‘multi-residence time mild thermal cracking’ which ensures the stability of the products generated from this process, offering additional process control in the hands of the refiner to make tailor-made mix feed composition needed for needle coke formation.

[0011] Another objective of the present invention is to provide a process that enables a ‘multi-residence time mild thermal cracking’ which improved mixed pitch quality like aromatic content, softening point etc, resulting mixed pitch subjected to severe thermal cracking improved coke yield and quality.

[0012] Another objective of the present invention is to provide a process for needle coke production by blending of different feed sources from coal-based and petroleum-based hydrocarbons followed by solvent-assisted selective separation of undesirable Quinoline Insoluble (QI) and solid catalyst fines from the mixed pitch and delayed coking thereafter.

[0013] Another objective of the present invention is to provide a provides a solution for the purification of pitch feedstock by solvent treatment for which a component of the employed solvent mixture is generated in-situ which is a lighter fraction formed by mild and severe thermal cracking of mixed feedstock.SUMMARY

[0014] This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended to determine the scope of the invention.

[0015] The present invention provides a process for the preparation of a needle coke, wherein the process comprises:

[0016] subjecting a feed stream to a multi-residence time mild thermal cracking in the presence of petroleum streams to obtain a mixed pitch, wherein the feed stream is selected from a group of coal tar, coal tar pitch (CTP), clarified oil (CLO), pyrolysis fuel oil, gas oils, hydrotreated vacuum gas oil and a combination thereof, preferably coal tar pitch, and wherein the petroleum streams comprise clarified oil (CLO), pyrolysis fuel oil (PFO) and a combination thereof; wherein the multi-residence time mild thermal cracking comprises steps of: heating the coal tar pitch in a mild cracking furnace; sending the heated coal tar pitch of step i) to the bottom of a mild cracking reactor; introducing the petroleum streams from a middle and top section of the said mild cracking rector to carry out the multi-residence time mild thermal cracking of the heated coal tar pitch in the presence of the petroleum streams to produce a plurality of reactor effluents; sending the reactor effluents from a top section of the mild thermal cracking reactor to a fractionator for fractionation to produce different components comprising a plurality of off-gases, a light oil, a middle oil and a mixed pitch; routing the plurality of off-gases to a gas concentration section for recovery; and sending the light oil to a solvent tank for use as an aromatic solvent and middle oil to a hydrotreating unit for recovery; purifying the mixed pitch through a solvent-assisted selective separation of undesirable quinoline insoluble (QI) and solid catalyst fines from the mixed pitch to obtain a purified mixed pitch, wherein the mixed pitch is treated with a solvent in a solvent treatment vessel followed by settling of impurities in a gravity settler; a heavy pitch-solvent mixture containing impurities is withdrawn from the bottom of the gravity settler and a purified pitch-solvent mixture is withdrawn from the top of the gravity settler; the heavy pitch-solvent mixture is heated in a first heater and then routed to the first solvent recovery column and the purified pitch-solvent mixture is heated in a second heater and then routed to the second solvent recovery column for solvent recovery; the purified mixed pitch is ultimately withdrawn from the bottom of the second solvent recovery column, the solvent to the mixed pitch has a weight ratio in a range of 0.5:1 to 10:1, the solvent treatment vessel is operated at a temperature in a range of 60° C. to 350° C. and a pressure in a range of 1 to 80 Kg / cm2 (g); and

[0017] subjecting the purified mixed pitch to delayed coking to produce the needle coke and a lighter hydrocarbon component; wherein the purified mixed pitch is mixed optionally mixed with a new hydrocarbon stream before delayed coking; the lighter hydrocarbon component is fractionated to produce a plurality of gaseous products and a plurality of liquid products containing a coker kero, a light coker gas oil, a heavy coker gas oil and a coker fuel oil; and the coker kero is sent to the solvent tank for use as an aromatic solvent.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0019] FIG. 1 depicts schematic diagram of the process for the preparation of needle coke with coal tar pitch in the presence of CLO.

[0020] FIG. 2 depicts schematic diagram of the process for the preparation of needle coke with coal tar pitch in the presence of CLO and PFO.DETAILED DESCRIPTION

[0021] For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments in the specific language 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 process, 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. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The composition, methods, and examples provided herein are illustrative only and not intended to be limiting.

[0022] The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.

[0023] In an aspect the present invention provides a process for production of needle grade coke employing a novel ‘multi-residence time mild thermal cracking’ of coal tar pitch with petroleum streams like CLO and PFO followed by solvent-assisted selective separation of undesirable quinoline insoluble (QI) and solid catalyst fines from the mixed pitch and delayed coking thereafter.

[0024] The present invention provides a solution for the purification of pitch feedstock by solvent treatment. A component of the employed solvent mixture is generated in-situ which is a lighter fraction formed by mild and severe thermal cracking of mixed feedstock. The ‘multi-residence time mild thermal cracking’ employed in the process of the present invention ensures optimum residence time of the coal tar pitch. The petroleum streams are fine-tuned for each of the participating reactant molecules thereby preventing over-cracking of the same. This also helps in ensuring the stability of the products generated from ‘multi-residence time mild thermal cracking’, offering much additional process control in the hands of the refiner to make tailor-made mix feed composition needed for needle coke formation. Additionally, this helps in fine-tuning the properties of the aromatic solvent component which is employed as part of the mixed solvent used for the purification of the feedstock. An added advantage of the present invention is that the solid catalyst fines which are present in CLO provide active sites for aggregate formation and improve the impurity removal rate. An additional advantage of the present invention is that the needle coke is produced by blending different feed sources from coal-based and petroleum-based hydrocarbons. This invention enables the purification of the coal-based and petroleum-based feedstock mixture, which when subjected to further thermal treatment results in the production of high-quality graphite or needle grade coke which is used for the preparation of graphite electrodes.

[0025] The multi-residence time mild thermal cracking is employed in the present invention wherein the different feed components like CTP, CLO and PFO are introduced into the reactor at different reactor locations (namely bottom, middle and top) based on the presence of lighter components (350° C.−) in their boiling point range or other physic-chemical characteristics including aromatic content, aromaticity etc.

[0026] The multi-residence time mild thermal cracking employed in the process of the present invention ensures optimum residence time of the coal tar pitch and other petroleum streams fine-tuned for each of the participating reactant molecules thereby preventing over-cracking of the same.

[0027] The multi-residence time mild thermal cracking’ helps in ensuring the stability of the products generated from ‘multi-residence time mild thermal cracking’, offering much additional process control in the hands of the refiner to make tailor-made mix feed composition needed for needle coke formation.

[0028] The multi-residence time mild thermal cracking helps in fine-tuning the properties of the aromatic solvent component which is employed as part of the mixed solvent used for purification of the feedstock.

[0029] The multi-residence time mild thermal cracking helps in controlling the temperature of the reacting mixture inside the mild cracking reactor, which is desirable particularly when one of the feedstocks is having high coking propensity while heating in the furnace.

[0030] The multi-residence time mild thermal cracking improves mixed pitch quality like aromatic content, softening point etc, and the resulting mixed pitch subjected to severe thermal cracking improves coke yield and quality

[0031] The separation of thermally cracked mixed feedstock (containing coal tar pitch and petroleum streams) into different cuts for generation of mixed pitch (with boiling point greater than 350° C.+) and other products such as light oil (140° C. to 270° C.), middle oil (270° C. to 350° C.)

[0032] The solvent-assisted selective separation of undesirable Quinoline Insoluble (QI) and solid catalyst fines from the mixed pitch (350° C.+) to produce purified pitch

[0033] The light oil (140° C. to 270° C.) generated in the process (by mild thermal cracking and delayed coking) is used as an aromatic solvent for purification of mixed pitch whereas middle oil (270° C. to 350° C.) is routed to the hydrotreater unit for further treatment

[0034] The solvent treatment vessel, gravity settler and solvent recovery column are used in this process for solvent treatment of mixed pitch (350° C.+) followed by separation of the purified mixed pitch from impurities and recovery of solvent (for further use) from the purified mixed pitch which is used as feedstock for the preparation of needle coke.

[0035] The thermal cracking of purified mixed pitch in a delayed coker unit produces different products such as coker kero (140° C. to 270° C.), light coker gas oil (270° C. to 350° C.), heavy coker gas oil (350° C. to 480° C.+), coker fuel oil (480° C.+), and high-quality needle grade coke.

[0036] Coker kero (140-270° C.) generated in delayed coker process is used as an aromatic solvent for purification of mixed pitch (350° C.+) whereas other cuts are light coker gas oil (270-390° C.), heavy coker gas oil (390-480° C.+) and coker fuel oil (480° C.+) are withdrawn as product streams.

[0037] The present invention provides process for the preparation of a needle coke, wherein the process comprises:

[0038] a) subjecting a feed stream to a multi-residence time mild thermal cracking in the presence of petroleum streams to obtain a mixed pitch, wherein the feed stream is selected from a group of coal tar, coal tar pitch (CTP), clarified oil (CLO), pyrolysis fuel oil, gas oils, hydrotreated vacuum gas oil and a combination thereof, preferably coal tar pitch, and wherein the petroleum streams comprise clarified oil (CLO), pyrolysis fuel oil (PFO) and a combination thereof;

[0039] wherein the multi-residence time mild thermal cracking comprises steps of

[0040] i. heating the coal tar pitch in a mild cracking furnace;

[0041] ii. sending the heated coal tar pitch of step i) to the bottom of a mild cracking reactor;

[0042] iii. introducing the petroleum streams from a middle and top section of the said mild cracking rector to carry out the multi-residence time mild thermal cracking of the heated coal tar pitch in the presence of the petroleum streams to produce a plurality of reactor effluents;

[0043] iv. sending the reactor effluents from a top section of the mild thermal cracking reactor to a fractionator for fractionation to produce different components comprising a plurality of off-gases, a light oil, a middle oil and a mixed pitch;

[0044] v. routing the plurality of off-gases to a gas concentration section for recovery; and

[0045] vi. sending the light oil to a solvent tank for use as an aromatic solvent and middle oil to a hydrotreating unit for recovery;

[0046] b) purifying the mixed pitch through a solvent-assisted selective separation of undesirable quinoline insoluble (QI) and solid catalyst fines from the mixed pitch to obtain a purified mixed pitch,

[0047] wherein the mixed pitch is treated with a solvent in a solvent treatment vessel followed by settling of impurities in a gravity settler; a heavy pitch-solvent mixture containing impurities is withdrawn from the bottom of the gravity settler and a purified pitch-solvent mixture is withdrawn from the top of the gravity settler; the heavy pitch-solvent mixture is heated in a first heater and then routed to the first solvent recovery column and the purified pitch-solvent mixture is heated in a second heater and then routed to the second solvent recovery column for solvent recovery; the purified mixed pitch is ultimately withdrawn from the bottom of the second solvent recovery column, the solvent to the mixed pitch has a weight ratio in a range of 0.5:1 to 10:1, the solvent treatment vessel is operated at a temperature in a range of 60° C. to 350° C. and a pressure in a range of 1 to 80 Kg / cm2 (g); and

[0048] c) subjecting the purified mixed pitch to delayed coking to produce the needle coke and a lighter hydrocarbon component; wherein the purified mixed pitch is mixed optionally mixed with a new hydrocarbon stream before delayed coking; the lighter hydrocarbon component is fractionated to produce a plurality of gaseous products and a plurality of liquid products containing a coker kero, a light coker gas oil, a heavy coker gas oil and a coker fuel oil; and the coker kero is sent to the solvent tank for use as an aromatic solvent.

[0049] In an embodiment of the present invention, the purification of the mixed pitch through solvent-assisted selective separation comprises steps of:

[0050] i. introducing the mixed pitch to a solvent treatment vessel for solvent treatment, wherein the mixed pitch is mixed with a solvent as received from the solvent tank;

[0051] ii. withdrawing the mixed pitch after the solvent treatment from the bottom of the solvent treatment vessel and introducing the mixed pitch into a gravity settler for the settling of impurities;

[0052] iii. withdrawing a heavy residual fractions of the mixed pitch from the bottom of the gravity settler as a pitch-solvent mixture,

[0053] iv. routing the said pitch-solvent mixture to a first heater followed by a first solvent recovery column, wherein the solvent is recovered from top of the first solvent recovery column and sent to the solvent tank,

[0054] v. withdrawing the heavy hydrocarbon from the bottom of the first solvent recovery column as heavy pitch containing residual fractions of QI and catalyst fines along with heavy refractory hydrocarbon molecules;

[0055] vi. routing the purified mixed pitch-solvent mixture coming out from the top of the gravity settler to a second heater and then transferred into the second solvent recovery column to recover a solvent stream and a purified mixed pitch; and

[0056] vii. sending the solvent stream from the second solvent recovery column to the solvent tank.

[0057] In an embodiment of the present invention, the delayed coking of purified mixed pitch comprises the steps of:

[0058] i. mixing the purified mixed pitch withdrawn from the bottom of the second solvent recovery column with a new hydrocarbon stream containing hydrotreated vacuum gas oil (HDT VGO) to obtain a mixture;

[0059] ii. routing the mixture to the mixed fractionator (MF) column, wherein the mixture mixes with an internal recycle stream and is drawn out from a bottom of the mixed fractionator (MF) column as the secondary feedstock, wherein the bottom of the mixed fractionator (MF) column is operating at a temperature in a range of 260° C. to 390° C.;

[0060] iii. sending the secondary feedstock withdrawn from the mixed fractionator (MF) column bottom to a coker furnace at a predefined hydrocarbon feed rate for heating at a temperature predefined for severe thermal cracking;

[0061] iv. additionally introducing a dilution steam or a boiler feed water stream to the coker furnace to obtain a hot feedstock comprising a heavy oil which prevent coking in furnace tubes and create additional turbulent flow.

[0062] v. routing the hot feedstock from the said coker furnace into a plurality of coke drums in the feeding step of the coking cycle, wherein the heavy oil is cracked and converted to graphitizable needle coke and a lighter hydrocarbon components;

[0063] vi. sending the lighter hydrocarbon components to the mixed fractionator (MF) column for separation to obtain an overhead vapor containing the plurality of gaseous products from a top section of the mixed fractionator (MF) column; and the plurality of liquid products containing the coker kero, the light coker gas oil, the heavy coker gas oil and the coker fuel oil from the mixed fractionator (MF) column with different cut ranges of 140 to 270° C., 270° C. to 350° C., 350° C. to 480° C. and 480° C.+ respectively;

[0064] vii. routing the overhead vapor containing the plurality of gaseous products to a gas concentration section for recovery; and

[0065] viii. routing the coker kero to the solvent tank for use as an aromatic solvent.

[0066] In an embodiment of the present invention, the feed stream is coal tar pitch (CTP); the petroleum stream contains clarified oil (CLO) and pyrolysis fuel oil (PFO).Conradson carbon residue (CCR) of coal tar pitch is in the range of 10 to 47 wt %, CLO is in the range of 1.5 to 19 wt %, PFO is in the range of 1 to 15 wt % and HDT VGO is in the range of <0.1 to 10 wt %, respectively. The quinoline insoluble (QI) content of the coal tar pitch used in the present invention is in the range of 1 to 16 wt %. The Basic sediment and water (BS&W) content of CLO used in the present invention is in the range of 0.05 to 2.5 wt %.

[0067] The solvent used in the present invention is selected from an aromatic solvent, an aliphatic solvent and a polar extraction solvent with carbon numbers ranging from 3 to 15. In the presently disclosed process, a combination of an aromatic solvent, an aliphatic and a polar extraction solvent is used as a mixed solvent for the purification of the pitch. The aromatic solvent component is selected from light oil (obtained by mild thermal cracking), coker kero (obtained by delayed coking of aromatic feedstocks namely coal tar pitch, CLO, PFO etc.), coal tar oil (obtained by distilling coal tar), anthracene oil, naphthalene oil, benzene, xylene, creosote oil, quinoline, toluene etc. The aliphatic solvent component is selected from cyclohexane, kerosene, n-pentane, n-hexane, n-heptane, diesel oil, naphtha etc. The polar extraction solvent component is n-methyl-2-pyrrolidone (NMP). The solvent mixture employed in the disclosed process is selected from aromatic solvent: 10 to 80 wt %, aliphatic solvent: 10 to 80 wt %, and polar extraction solvent: 10 to 70 wt %.

[0068] The mild cracking furnace is operating at an outlet temperature of coil between 390° C. to 475° C. In a preferred embodiment, the mild cracking furnace is operating at the outlet temperature of coil between 430° C. to 460° C.

[0069] The mild cracking reactor is operating at a temperature in a range of 380° C. to 475° C. In a preferred embodiment, the mild cracking reactor is operating at the temperature in the range of 420° C. to 450° C., depending upon the furnace outlet temperature and heat losses in the transfer line.

[0070] In an embodiment, the mild thermal cracking reactor is maintained at a pressure in a range of 5 to 15 Kg / cm2 (g). In a preferred embodiment, the mild thermal cracking reactor is maintained at the pressure in the range of 7 to 12 Kg / cm2 (g).

[0071] The hydrocarbon residence time in the mild thermal cracking reactor is maintained from 1 to 30 mins. In a preferred embodiment, the hydrocarbon residence time in the mild thermal cracking reactor is maintained from 5 to 20 mins.

[0072] The fractionator for the mild cracking section is operated at a bottom temperature between 260° C. to 390° C.

[0073] The solvent to mixed pitch ratio in the solvent treatment is kept in the range of 0.5:1 to 10:1 (wt / wt).

[0074] The solvent treatment vessel is operating at a temperature in a range of 60° C. to 350° C. In a preferred embodiment, the solvent treatment vessel is operating at the temperature in the range of 70° C. to 200° C.

[0075] The solvent treatment vessel is operating at a pressure in a range of 1 to 80 Kg / cm2 (g). In a preferred embodiment, the solvent treatment vessel is operating at the pressure in a range of 1 Kg / cm2 (g) 50 to Kg / cm2 (g).

[0076] In an embodiment of the present invention, a bottom of the mixed fractionator (MF) column of the severe thermal cracking section is operating at a bottom temperature between 260° C. to 390° C.

[0077] In an embodiment of the present invention, the needle coke derived from purified mixed pitch has a crystallinity of 77.8% to 80.3%.

[0078] The coker furnace in the severe thermal cracking section is operating at an outlet temperature of coil between 450° C. to 530° C. In a preferred embodiment, the coker furnace in the severe thermal cracking section is operating at the outlet temperature of coil between 490° C. to 515° C. The dilution steam or boiler feed water is injected in the coker furnace in a range of 0.5 to 3 wt % of the hydrocarbon feed rate.

[0079] The plurality of coke drums are operating at an operating temperature in a range of 440° C. to 520° C. In a preferred embodiment, the plurality of coke drums are operating at the operating temperature in the range of 470° C. to 500° C. The feeding cycle time of the plurality of coke drums in the severe thermal cracking section varies from 12 hrs to 56 hrs.

[0080] In an embodiment, the plurality of coke drums are maintained at a pressure in a range of 1 to 10 Kg / cm2 (g). In a preferred embodiment, the plurality of coke drums are maintained at the pressure in the range of 2.5 to 7 Kg / cm2 (g).

[0081] In an embodiment of the present invention the process for the preparation of needle coke comprises the steps as described below and depicted in FIG. 1.

[0082] Coal tar pitch (1) is heated in a mild cracking furnace (2) and then sent to the bottom of the mild cracking rector (3). A petroleum stream containing clarified oil CLO (4) is introduced from the middle section of the said rector to carry out a ‘multi-residence time mild thermal cracking’ of CLO and coal tar pitch. The reactor effluents (5) containing mixed product vapors of CTP and CLO are then sent to a fractionator (6) wherein it is fractionated to different cuts namely off-gases (7) which comprises fuel gas, LPG and naphtha, light oil (8) with boiling range from 140° C. to 270° C., middle oil (9) with boiling range from 270° C. to 350° C. and heavier (350° C.+) mixed pitch (10). The off-gases (7) are routed to the gas concentration section for further recovery. The light oil (8) is sent to the solvent tank (11) for use as an aromatic solvent in the present invention and middle oil (9) is sent to the hydrotreating unit for further treatment whereas the mixed pitch (10) is used as feedstock for needle grade coke. The mixed pitch (10) contains impurities such as QI and solid catalyst fines and the said mixed pitch is introduced to a solvent treatment vessel (12) wherein it mixes with solvent, received from the solvent tank (11). A solvent stream (13) is added to the solvent tank for solvent make-up. The mixed pitch (10) after the solvent treatment is drawn out from the bottom of the solvent treatment vessel via line (14) and then introduced in a gravity settler (15) for the settling of impurities. The heavy residual fractions of the mixed pitch get separated out and withdrawn from the bottom of the gravity settler as a pitch-solvent mixture (16). The said pitch-solvent mixture (16) is routed to a first heater (17) followed by a first solvent recovery column (18). The solvent (19) is recovered from the top of the first solvent recovery column and sent to the solvent tank (11) for further use whereas, heavy hydrocarbon is withdrawn from the bottom of the first solvent recovery column as heavy pitch (20) which contains residual fractions of QI and catalyst fines along with heavy refractory hydrocarbon molecules and may be used as feedstock for fuel grade coke. The purified mixed pitch-solvent mixture (21) coming out from the top of the gravity settler is routed to a second heater (22) and then flashed into the second solvent recovery column (23) for solvent recovery. The recovered solvent stream (24) is sent to the solvent tank (11) for further use. The purified mixed pitch after solvent recovery (25) is withdrawn from the bottom of the second solvent recovery column (23) and mixed with a new hydrocarbon stream containing HDT VGO (26) and then is routed to the mixed fractionator (MF) column (27) where it mixes with the internal recycle stream and is drawn out from the MF bottom as the secondary feedstock. The secondary feedstock (28) which is withdrawn from the MF bottom is sent to a coker furnace (29) for heating to the desired severe thermal cracking temperature. In addition, steam or boiler feed water stream (30) is introduced to the coker furnace to prevent coking in furnace tubes and create additional turbulent flow. Hot feedstock (31) from the said furnace is routed to one of the coke drums (32,33) in the feeding step of the coking cycle, where heavy oil is cracked and is converted to graphitizable needle coke and lighter hydrocarbon components like off-gases comprise of fuel gas, LPG, naphtha, gas-oils etc. Product vapors (34) of the existing coke drum are sent to the MF column (27) for further separation. The overhead vapor of the MF comprised of gaseous products (35) are routed to a gas concentration section for further recovery. Liquid products such as coker kero (36), light coker gas oil (37) and heavy coker gas oil (38) and coker fuel oil (39) are withdrawn from the MF column with different cut ranges of 140° C. to 270° C., 270° C. to 350° C., 350° C. to 480° C. and 480° C.+ respectively. Coker kero (36) stream is routed via a line (40) to the solvent tank (11) for further use as an aromatic solvent whereas light coker gas oil (37), heavy coker gas oil (38) and coker fuel oil (39) are withdrawn as product streams. Needle coke which is deposited in the coke drums is removed from the bottom (41) in the maintenance cycle by using high pressure water jets.

[0083] In another embodiment of the present invention the process for the preparation of needle coke comprises the steps as described below and depicted in FIG. 2. Coal tar pitch (1) is heated in a mild cracking furnace (2) and then sent to the bottom of the mild cracking rector (3). Petroleum streams containing clarified oil (CLO) (4) and pyrolysis fuel oil (PFO) (5) are introduced from the middle and top sections of the said rector (3) to carry out a ‘multi-residence time mild thermal cracking’ of CLO, PFO and coal tar pitch. The reactor effluents (6) containing mixed product vapors of CTP, CLO and PFO are then sent to a fractionator (7) wherein it is fractionated to different cuts namely off-gases (8) which comprises fuel gas, LPG and naphtha, light oil (9) with boiling range from 140° C. to 270° C., middle oil (10) with boiling range from 270° C. to 350° C. and mixed heavy (350° C.+) pitch (11). The off-gases (8) are routed to the gas concentration section for further recovery. The light oil (9) is sent to the solvent tank (12) for use as an aromatic solvent in the present invention and middle oil (10) is sent to the hydrotreating unit for further treatment whereas the mixed pitch (11) is used as feedstock for needle grade coke. The mixed pitch (11) contains impurities such as QI and solid catalyst fines and the said mixed pitch is introduced to a solvent treatment vessel (13) wherein it mixed with solvent, received from the solvent tank (12). A solvent stream (14) is added to the solvent tank for solvent make-up. The mixed pitch (11) after the solvent treatment is drawn out from the bottom of the solvent treatment vessel via line (15) and then introduced in a gravity settler (16) for the settling of impurities. The heavy residual fractions of the mixed pitch get separated out and withdrawn from the bottom of the gravity settler as a pitch-solvent mixture (17). The said pitch-solvent mixture (17) is routed to a first heater (18) followed by a first solvent recovery column (19). The solvent (20) is recovered from the top of the first solvent recovery column and sent to the solvent tank (12) for further use whereas heavy hydrocarbon is withdrawn from the bottom of the first solvent recovery column as heavy pitch (21) which contains residual fractions of QI and catalyst fines along with heavy refractory hydrocarbon molecules and may be used as feedstock for fuel grade coke. The purified mixed pitch-solvent mixture (22) coming out from the top of the gravity settler is routed to a second heater (23) and then flashed into the second solvent recovery column (24) for solvent recovery. The recovered solvent stream (25) is sent to the solvent tank (12) for further use. The purified mixed pitch after solvent recovery (26) is withdrawn from the bottom of the second solvent recovery column (23) is routed to the mixed fractionator (MF) column (27) where it mixed with the internal recycle stream and is drawn out from the MF bottom as the secondary feedstock. The secondary feedstock (28) which is withdrawn from the MF bottom is sent to a coker furnace (29) for heating to the desired severe thermal cracking temperature. In addition, steam or boiler feed water stream (30) is introduced to the coker furnace to prevent coking in furnace tubes and create additional turbulent flow. Hot feedstock (31) from the said furnace is routed to one of the coke drums (32,33) in the feeding step of the coking cycle, where heavy oil is cracked and is converted to graphitizable Needle coke and lighter hydrocarbon components like off-gases comprise of fuel gas, LPG, naphtha, gas-oils etc. Product vapors (34) of the existing coke drum are sent to the MF column (27) for further separation. The overhead vapor of the MF comprised of gaseous products (35) are routed to a gas concentration section for further recovery. Liquid products such as coker kero (36), light coker gas oil (37) and heavy coker gas oil (38) and coker fuel oil (39) are withdrawn from the MF column with different cut ranges of 140° C. to 270° C., 270° C. to 350° C., 350° C. to 480° C. and 480° C.+ respectively. Coker kero (36) stream is routed via a line (40) to the solvent tank (11) for further use as an aromatic solvent whereas light coker gas oil (37), heavy coker gas oil (38) and coker fuel oil (39) are withdrawn as product streams. Needle coke which is deposited in the coke drums is removed from the bottom (41) in the maintenance cycle by using high pressure water jets.

[0084] In an embodiment of the present invention, the coefficient of thermal expansion (CTE) value of needle coke is in a range of 1.33×10−6 / ° C. to 1.21×10−6 / ° C.EXAMPLES

[0085] The present disclosure with reference to the accompanying examples describes the present invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. It is understood that the examples are provided for the purpose of illustrating the invention only and are not intended to limit the scope of the invention in any way.Example 1

[0086] A coal tar pitch (CTP) sample with properties as provided in Table 1 was taken and heated in a mild cracking furnace and then routed to a mild cracking reactor. A petroleum stream (CLO) with properties as provided in Table 2 was introduced into the said rector. The mixing ratio of CTP and CLO at a wt / wt ratio of 50 / 50. The mild thermal cracking operating conditions are provided in Table 3.TABLE 1Properties of CTP (unpurified)PropertyValueDensity, g / cc1.25CCR, wt %33.1Sulfur, wt %0.52Nitrogen, wt %1.5Softening Point, ° C.54QI, w %4.35Aromatics, wt %100Distillation (ASTM D2887)Cut, wt %° C.531610329203523038750441704989059295639100709TABLE 2Properties of CLOPropertyCLODensity, g / cc1.158CCR, wt %15.9Sulfur, wt %0.42Nitrogen, wt %0.1BS&W, wt %0.7Aromatics, wt %97.8Paraffins + Naphthenes, wt %2.2Distillation (ASTM D2887)Cut, wt %° C.521910320203393036050386704229047895524100632TABLE 3Operating conditions of mild thermal crackingOperating parameterValueCoil outlet temperature of mild thermal cracking furnace, ° C.450Reactor inlet temperature, ° C.440Reactor outlet temperature, ° C.428Reactor pressure, Kg / cm2 (g)7Residence time (Coal tar pitch), min20Residence time (CLO), min10The reactor effluents (generated by mild cracking of mixed feedstock containing CTP and CLO) were further fractionated and accordingly, 350° C.+ was withdrawn from the fractionator bottom as mixed pitch and the key properties of the same are provided in Table 4. As a comparative case, CTP (of Table 1) and CLO (of Table 2) were mixed a wt / wt ratio of 50 / 50 and properties of the mixed feedstock (CTP+CLO) without mild thermal cracking are provided in Table 4.TABLE 4Properties of unpurified mixed feedstockand mixed pitch (350° C.+)Mixed PitchMixed feedstock(with mildProperty(w / o mild cracking)thermal crackingDensity, g / cc1.2031.22CCR, wt %24.4527.3Sulfur, wt %0.470.48Nitrogen, wt %0.790.80Softening Point, ° C.3669Aromatics, wt %98.8100Paraffins + Naphthenes, wt %1.20QI, wt %3.323.56BS&W, wt %0.390.41Said unpurified mixed feedstock and mixed pitch of Table 4 were subjected to solvent treatment in a solvent treatment section for separation of impurities (QI and solid catalyst fines) from the mixed feedstock and mixed pitch. The operating conditions of the solvent treatment process are provided in Table 5.TABLE 5Operating conditions of solvent treatment sectionParameterValueAromatic solventLight oil(140-270° C.)Aliphatic solventkerosene(140-270° C.)Polar extraction solventNMPSolvent mixture composition -(40:40:20)Aromatic:Aliphatic:NMP (wt %)Mixed solvent:mixed pitch2.5:1Mixing time, min40Mixing temperature, ° C.100Settling time, hour, max1The top portion of the mixed feedstock-solvent mixture and the mixed pitch-solvent mixture after solvent treatment were separated and the solvent was evaporated by heating at 300° C. for 3 hrs. The purified mixed feedstock and the purified mixed pitch after solvent recovery were analyzed for key properties such as QI (as per ASTM D2318) and BS&W (as per ASTM D4007) and the results are provided in Table 6.TABLE 6Properties of purified mixed feedstock and mixed pitchMixed feedstock (w / oMixed Pitch (withPropertymild cracking)mild thermal cracking)QI, wt %<0.1<0.1BS&W, wt %00The purified mixed feedstock and the purified mixed pitch with properties as provided in Table 6 were subjected to severe thermal cracking (as per Delayed Coking operating conditions) in a batch Micro-Coker experimental set-up. The Micro-Coker reactor operating conditions and coke quality are provided in Tables 7.TABLE 7Micro-Coker reactor experimentation conditions and coke qualityOperating parameterCase ICase IIFeedstockMixed feedstockMixed Pitch (with(w / o mildmild thermalcracking)cracking)Feed loaded, gm500500Temperature,° C.490490Pressure, kg / cm2 (g)55Holding time, hrs1212Coke yield, wt %49.453.7% crystallinity72.677.8From Table 7, it can be seen that the coke yield obtained from mixed feedstock without mild cracking (case I) was 49.4 wt % whereas, the coke yields obtained from mixed Pitch with mild thermal cracking (case II) was 53.7 wt %. These coke samples were thereafter subjected to calcination to produce calcined coke samples The calcined coke samples were then analyzed in an XRD analyzer. The results showed 72.6% crystallinity for mixed feedstock without mild thermal cracking whereas 77.8% crystallinity for mixed pitch with mild thermal cracking (invented process). The results indicated that the coke yield and quality both were improved in the invented process.Example-2As a comparative case, the unpurified CTP (without solvent treatment and blending of CLO), purified CTP (without mixing of CLO), unpurified mixed pitch and purified mixed pitch were subjected to thermal cracking in a batch Micro-Coker experimental set-up. The operating conditions and coke quality of the Micro-Coker experiments are provided in Tables 8. The solvent-treatment technique used for separation of impurities from the feedstock (unpurified CTP and unpurified mixed pitch) as per procedure mentioned in Example 1.TABLE 8Micro-Coker reactor experimentation conditions and coke qualityOperating parameterExp. IExp. IIExp. IIIExp. IVFeedstockUnpurifiedCTP (Table 1CTP (ofof ExampleUnpurifiedPurifiedTable-1) w / o1) purified inmixedmixedsolventsolvent withoutpitch (ofpitch (oftreatmentmixing of CLOTable-4)Table-6)Feed loaded, gm500500500500Temperature,° C.490490490490Pressure, kg / cm25555(g)Holding time, hrs12121212CTE of graphite2.921.622.391.33artifact, ×10−6 / °C.Five numbers of runs were carried out for each experiment (Exp. I to IV) maintaining same operating conditions (as per Table 8) to generate coke samples for measurement of coefficient of thermal expansion (CTE). Coke samples from all the runs of each experiment were subjected to calcination and graphite artifacts in the shape of coke rods were prepared. Baked coke rods were used for measurement of CTE. It can be seen from Table 8, the CTE value improved from 2.92×10−6 / ° C. to 1.33×10−6 / ° C. due to blending of CLO in CTP followed by purification.Example-3

[0094] Experiments Micro-Coker unit at similar operating conditions as Table-7 (of Example 1) were carried out a combination of purified mixed pitch (Table 6 of Example 1) with 20 wt % of hydrotreated vacuum gas oil (HDT VGO). The properties of HDT VGO are tabulated in Table 9.TABLE 9Properties of HDT VGOPropertyHDT VGODensity, g / cc0.8991CCR, wt %0.05Asphaltene0.01Sulfur, wt %0.04Nitrogen, wt %0.016Aromatics, wt %19.3Paraffins + Naphthenes, wt %80.7

[0095] Five numbers of runs were carried for this experiment maintaining same operating conditions (as per Table 7 of Example 1) to generate coke samples for measurement of CTE. The CTE of coke sample was measured as per procedure mentioned in Example 2. The resultant coke quality is provided in Table 10.TABLE 10Coke propertiesPurified mixed pitch (of Table-6)Propertywith 20 wt % HDT VGO (Table 9)CTE of graphite artifact, ×10−6 / ° C.1.21

[0096] It can be seen from Table 8 (of Example 2) and Table 10, the CTE value improved from 1.33×10−6 / ° C. to 1.21×10−6 / ° C. upon blending of HDT VGO in purified mixed pitch (containing CTP and CLO).Example 4

[0097] Coal tar pitch (CTP) sample (Table 1 of Example 1) was taken and heated in a mild cracking furnace and then routed to a reactor where the petroleum streams containing CLO (Table 2 of Example 1) and PFO (with properties as provided in Table 11) were introduced into the said rector. The mixing ratio of CTP, CLO and PFO is 50:35:15 (by weight). The operating conditions of the mild cracking are provided in Table 3 (of Example 1) where residence time for PFO was maintained for 5 mins.TABLE 11Properties of PFOPropertyPFODensity, g / cc1.034CCR, wt %7.72Sulfur, wt %, max0.001Nitrogen, wt %, max0.048Aromatics, wt %100

[0098] The reactor effluents (generated by mild cracking of mixed feedstock containing CTP, CLO and PFO) were further fractionated and accordingly, mixed pitch (350° C.+) was withdrawn from the fractionator bottom as mixed pitch (350° C.+). Said mixed pitch was subjected to solvent treatment in a solvent treatment section for separation of impurities (QI and solid catalyst fines) from the mixed pitch as described in Example 1. The purified mixed pitch with properties as provided in Table 6 (of Example 1) was subjected to severe thermal cracking (as per Delayed Coking operating conditions) in a batch Micro-Coker experimental set-up. As a comparative case, purified mixed pitch of CTP and CLO (50 wt %: 50 wt %) and purified mixed pitch of CTP, CLO and PFO (50 wt %: 35 wt %: 15 wt %) were subjected to thermal cracking in a batch Micro-Coker experimental set up. The operating conditions of the Micro-Coker experiment are provided in Table 7 (of Example 1). The Coke quality of Micro-Coker reactor experimentation are tabulated in Table 12.TABLE 12Coke quality of Micro-Coker reactor experimentationFeed% crystallinityPurified mixed pitch of CTP and CLO77.8(50 wt %:50 wt %) Table 6 of Example 1Purified mixed pitch of CTP, CLO and80.3PFO (50 wt %:35 wt %:15 wt %)

[0099] Coke samples generated from the Micro-Coker experiments were subjected to calcination to produce calcined coke samples. The calcined coke samples were then analyzed in an XRD analyzer. The results showed 77.8% crystallinity for purified mixed pitch and the value was improved to 80.3% crystallinity due to blending of PFO in the mixed pitch (containing CTP and CLO).

Examples

example 1

[0086]A coal tar pitch (CTP) sample with properties as provided in Table 1 was taken and heated in a mild cracking furnace and then routed to a mild cracking reactor. A petroleum stream (CLO) with properties as provided in Table 2 was introduced into the said rector. The mixing ratio of CTP and CLO at a wt / wt ratio of 50 / 50. The mild thermal cracking operating conditions are provided in Table 3.

TABLE 1Properties of CTP (unpurified)PropertyValueDensity, g / cc1.25CCR, wt %33.1Sulfur, wt %0.52Nitrogen, wt %1.5Softening Point, ° C.54QI, w %4.35Aromatics, wt %100Distillation (ASTM D2887)Cut, wt %° C.531610329203523038750441704989059295639100709

TABLE 2Properties of CLOPropertyCLODensity, g / cc1.158CCR, wt %15.9Sulfur, wt %0.42Nitrogen, wt %0.1BS&W, wt %0.7Aromatics, wt %97.8Paraffins + Naphthenes, wt %2.2Distillation (ASTM D2887)Cut, wt %° C.521910320203393036050386704229047895524100632

TABLE 3Operating conditions of mild thermal crackingOperating parameterValueCoil outlet temperature of mil...

example-2

As a comparative case, the unpurified CTP (without solvent treatment and blending of CLO), purified CTP (without mixing of CLO), unpurified mixed pitch and purified mixed pitch were subjected to thermal cracking in a batch Micro-Coker experimental set-up. The operating conditions and coke quality of the Micro-Coker experiments are provided in Tables 8. The solvent-treatment technique used for separation of impurities from the feedstock (unpurified CTP and unpurified mixed pitch) as per procedure mentioned in Example 1.

TABLE 8Micro-Coker reactor experimentation conditions and coke qualityOperating parameterExp. IExp. IIExp. IIIExp. IVFeedstockUnpurifiedCTP (Table 1CTP (ofof ExampleUnpurifiedPurifiedTable-1) w / o1) purified inmixedmixedsolventsolvent withoutpitch (ofpitch (oftreatmentmixing of CLOTable-4)Table-6)Feed loaded, gm500500500500Temperature,° C.490490490490Pressure, kg / cm25555(g)Holding time, hrs12121212CTE of graphite2.921.622.391.33artifact, ×10−6 / °C.

Five numbers of runs we...

example-3

[0094]Experiments Micro-Coker unit at similar operating conditions as Table-7 (of Example 1) were carried out a combination of purified mixed pitch (Table 6 of Example 1) with 20 wt % of hydrotreated vacuum gas oil (HDT VGO). The properties of HDT VGO are tabulated in Table 9.

TABLE 9Properties of HDT VGOPropertyHDT VGODensity, g / cc0.8991CCR, wt %0.05Asphaltene0.01Sulfur, wt %0.04Nitrogen, wt %0.016Aromatics, wt %19.3Paraffins + Naphthenes, wt %80.7

[0095]Five numbers of runs were carried for this experiment maintaining same operating conditions (as per Table 7 of Example 1) to generate coke samples for measurement of CTE. The CTE of coke sample was measured as per procedure mentioned in Example 2. The resultant coke quality is provided in Table 10.

TABLE 10Coke propertiesPurified mixed pitch (of Table-6)Propertywith 20 wt % HDT VGO (Table 9)CTE of graphite artifact, ×10−6 / ° C.1.21

[0096]It can be seen from Table 8 (of Example 2) and Table 10, the CTE value improved from 1.33×10−6 / ° C. ...

Claims

1. A process for preparing a needle coke, the process comprising:subjecting a feed stream to a multi-residence time mild thermal cracking in presence of a petroleum stream to obtain a mixed pitch, wherein the feed stream comprises coal tar pitch (CTP), and wherein the petroleum stream is selected from the group consisting of clarified oil (CLO), pyrolysis fuel oil (PFO) and a combination thereof;purifying the mixed pitch through a solvent-assisted selective separation, to remove an undesirable quinoline insoluble (QI) and solid catalyst fines to obtain a purified mixed pitch, wherein the mixed pitch has a boiling point above 350° C.; andsubjecting the purified mixed pitch to delayed coking to produce the needle coke and a lighter hydrocarbon component.

2. The process as claimed in claim 1, wherein the multi-residence time mild thermal cracking comprises:heating the feed stream in a mild cracking furnace;sending the heated feed stream to a bottom of a mild cracking reactor;introducing the petroleum stream from a middle section of the mild cracking rector to carry out the multi-residence time mild thermal cracking of the heated feed stream in presence of the petroleum stream to produce a plurality of reactor effluents,wherein the reactor effluents comprise mixed product vapors of CTP, CLO, and PFO;sending the reactor effluents from a top section of the mild thermal cracking reactor to a fractionator for fractionating and to produce components comprising a plurality of off-gases, a light oil, a middle oil and the mixed pitch;routing the plurality of off-gases to a gas concentration section for recovery; andsending the light oil to a solvent tank for use as an aromatic solvent and middle oil to a hydrotreating unit for recovery.

3. The process as claimed in claim 1, wherein purifying the mixed pitch through a solvent-assisted selective separation comprises:treating the mixed pitch with a solvent in a solvent treatment vessel;settling a heavy pitch-solvent mixture comprising impurities in a gravity settler; withdrawing the heavy pitch-solvent mixture from a bottom of the gravity settler;withdrawing a purified pitch-solvent mixture from a top of the gravity settler;heating the heavy pitch-solvent mixture in a first heater and then routing to a first solvent recovery column;heating the purified pitch-solvent mixture in a second heater and then routing to a second solvent recovery column for solvent recovery;withdrawing the purified mixed pitch from a bottom of the second solvent recovery column, wherein the solvent to the mixed pitch has a weight ratio in a range of 0.5:1 to 10:1, and wherein the solvent treatment vessel is operated at a temperature in a range of 60° C. to 350° C. and at a pressure in a range of 1 to 80 Kg / cm2 (g).

4. The process as claimed in claim 2, wherein the mild cracking furnace operates at an outlet temperature of coil in a range of 390° C. to 475° C., wherein the mild cracking reactor operates at a temperature in a range of 380° C. to 475° C., and is maintained at a pressure between 5 to 15 Kg / cm2 (g), wherein the petroleum stream and the feed stream in the mild cracking rector have a hydrocarbon residence time between 1 to 30 mins, and wherein the fractionator is operated at a bottom temperature between 260° C. to 390° C.

5. The process as claimed in claim 2, wherein the mild cracking furnace operates at an outlet temperature of coil in a range of 430° C. to 460° C., wherein the mild cracking reactor operates at a temperature in a range of 420° C. to 450° C., and is maintained at a pressure between 7 to 12 Kg / cm2 (g), wherein the petroleum stream and the feed stream in the mild cracking rector have a hydrocarbon residence time between 5 to 20 mins.

6. The process as claimed in claim 2, wherein the plurality of off-gases comprises fuel gas, LPG and naphtha, wherein the light oil has a boiling point in a range from 140 to 270° C., and the middle oil has a boiling point in a range from 270° C. to 350° C.

7. The process as claimed in claim 1, wherein the coal tar pitch has a Conradson Carbon Residue (CCR) in a range of 10 to 47 wt %, and has a quinoline insoluble (QI) content in a range of 1 to 16 wt %; wherein the petroleum stream comprises CLO in a range of 1.5 to 19 wt %, and PFO in a range of 1 to 15 wt %; and the CLO has a basic sediment and water (BS&W) content in a range of 0.05 to 2.5 wt %.

8. The process as claimed in claim 1, wherein the needle coke has a coefficient of thermal expansion (CTE) in a range of 1.33×10−6 / ° C. to 1.21×10−6 / ° C.

9. The process as claimed in claim 3, wherein the solvent treatment vessel operates at a temperature in a range of 70° C. to 200° C. and at a pressure in a range of 1 to 50 Kg / cm2 (g).

10. The process as claimed in claim 3, wherein the solvent comprises an aromatic solvent, an aliphatic solvent, a polar extraction solvent with carbon numbers ranging from 3 to 15, wherein the aromatic solvent is selected from the group consisting of light oil, coker kero, coal tar oil, anthracene oil, naphthalene oil, benzene, xylene, creosote oil, quinoline, toluene, and a combination thereof, wherein the light oil is obtained by mild thermal cracking, wherein the coker kero is obtained by delayed coking of aromatic feedstocks, wherein the aromatic feedstocks comprise coal tar pitch, CLO, PFO, and wherein the coal tar oil is obtained by distilling coal tar, wherein the aliphatic solvent is selected from the group consisting of cyclohexane, kerosene, n-pentane, n-hexane, n-heptane, diesel oil, naphtha and a combination thereof; and wherein the polar extraction solvent is n-methyl-2-pyrrolidone (NMP).

11. The process as claimed in claim 10, wherein the solvent comprises 10 to 80 wt % of the aromatic solvent, 10 to 80 wt % of the aliphatic solvent, and 10 to 70 wt % of the polar extraction solvent.

12. The process as claimed in claim 3, wherein the delayed coking of the purified mixed pitch comprises:i. mixing the purified mixed pitch withdrawn from the bottom of the second solvent recovery column with a hydrocarbon stream comprising hydrotreated vacuum gas oil (HDT VGO) to obtain a mixture, wherein the hydrotreated vacuum gas oil (HDT VGO) is in a range of <0.1 to 10 wt %;ii. routing the mixture to a mixed fractionator (MF) column, wherein the mixture mixes with an internal recycle stream and is drawn out from a bottom of the mixed fractionator column as a secondary feedstock, wherein a bottom of the mixed fractionator column operates at a temperature in a range of 260° C. to 390° C.;iii. sending the secondary feedstock withdrawn from the bottom of the mixed fractionator column to a coker furnace at a predefined hydrocarbon feed rate for heating at a temperature predefined for severe thermal cracking;iv. additionally introducing a dilution steam or a boiler feed water stream to the coker furnace to obtain a hot feedstock comprising a heavy oil which prevent coking in furnace tubes and create additional turbulent flow;V. routing the hot feedstock from the coker furnace into a plurality of coke drums in the feeding step of the coking cycle, wherein the heavy oil is cracked and converted to the needle coke and the lighter hydrocarbon component;vi. sending the lighter hydrocarbon component to the mixed fractionator column for separation to obtain an overhead vapor containing the plurality of gaseous products from a top section of the mixed fractionator column; and the plurality of liquid products containing the coker kero, the light coker gas oil, the heavy coker gas oil and the coker fuel oil from the mixed fractionator column with different cut ranges of 140 to 270° C., 270° C. to 350° C., 350° C. to 480° C. and 480° C.+ respectively;vii. routing the overhead vapor containing the plurality of gaseous products to a gas concentration section for recovery; andviii. routing the coker kero stream to the solvent tank for use as an aromatic solvent.

13. The process as claimed in claim 12, wherein the coker furnace operates at an outlet temperature of coil between 450° C. to 530° C., wherein the dilution steam or the boiler feed water stream is injected in the coker furnace in a range of 0.5 to 3 wt % of the hydrocarbon feed.

14. The process as claimed in claim 12, wherein the coker furnace operates at an outlet temperature of coil between 490° C. to 515° C.

15. The process as claimed in claim 12, wherein the plurality of coke drums operates at a temperature in a range of 440° C. to 520° C., and is maintained at a pressure in a range of 1 to 10 Kg / cm2 (g), and has a feeding cycle time in a range of 12 to 56 hrs.

16. The process as claimed in claim 12, wherein the plurality of coke drums operates at a temperature in a range of 470° C. to 500° C. and is maintained at a pressure in a range of 2.5 to 7 Kg / cm2 (g).

17. The process as claimed in claim 12, further comprising removing the needle coke deposited in the plurality of coke drums in a maintenance cycle by using a high-pressure water jet.

18. The process as claimed in claim 12, wherein the lighter hydrocarbon components comprise off-gases comprising fuel gas, LPG, naphtha, gas-oils, and a combination thereof.

19. The process as claimed in claim 12, wherein the plurality of coke drums operates at a temperature in a range of 470° C. to 500° C. and at a pressure in a range of 2.5 to 7 Kg / cm2 (g).

20. The process as claimed in claim 1, wherein the needle coke derived from the purified mixed pitch has a crystallinity of 77.8% to 80.3%.

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