Process for Production of Graphite Coke from an Admixture of Coal and Petroleum Based Hydrocarbons

Abstract

The present invention provides a process for production of graphite coke from an admixture of coal and petroleum-based hydrocarbons. This particularly describes a process wherein a mixture of coal tar pitch and hydrocarbon feedstock such as CLO is purified in a solvent treatment step and the purified mixed feedstock is subjected to thermal cracking to produce high quality graphite / needle coke. This process also provides a synergy in improved coke quality coke formation while using an admixture of coal tar pitch and CLO while subjected to common purification and coking steps.

Claims

A process for production of graphite grade coke comprising:(a)    mixing coal tar pitch and clarified oil (CLO) streams to obtain a mixed feedstock and routing the mixed feedstock to a solvent treatment vessel where it mixes with a solvent, wherein the coal tar pitch and the CLO are blended in a weight ratio ranging from 90:10 to 40:60;(b)    separating the mixed feedstock into a heavy residual fraction containing impurities and a first purified mixed feedstock without impurities, and removing the heavy residual fraction as pitch from bottom of the solvent treatment vessel, wherein the impurities are quinoline insoluble substances along with solid catalyst fines;(c)     passing the heavy residual fraction(pitch) to a first heater to obtain a heated pitch and flashing the heated pitch into a first solvent recovery column;(d)    withdrawing a heavy pitch stream from bottom of the first solvent recovery column and routing overhead of the first solvent recovery column containing recovered solvent stream back to the solvent treatment vessel;(e)    routing the first purified mixed feedstock from the solvent treatment vessel to a second heater to obtain a heated first purified mixed feedstock and flashing the heated first purified mixed feedstock into a second solvent recovery column;(f)      routing overhead from the second solvent recovery column containing recovered solvent stream back to the solvent treatment vessel and routing bottom from the second solvent recovery column to a bottom section of a fractionator column, wherein the bottom from the second solvent recovery column contains a second purified mixed feedstock without solvent;(g)    mixing the second purified mixed feedstock obtained in step (f) with an internal recycle stream in the bottom section of the fractionator column to obtain a secondary feedstock and drawing out the secondary feed stock from bottom of the fractionator column, wherein the internal recycle stream is obtained after separation of gaseous products and liquid products from lighter hydrocarbon products that are routed to the fractionator column from a coke drum;(h)    heating the secondary feed stock in a coker heater to a thermal cracking temperature to obtain a hot secondary feedstock;(i)      routing the hot secondary feedstock to a coke drum for cracking the feedstock to lighter hydrocarbon products and a graphite grade coke; wherein the graphite grade coke is a graphitizable needle coke and is deposited in the coke drum;(j)      routing the lighter hydrocarbon products from the coke drum to the fractionator column for separation into gaseous products and liquid products; and(k)     routing overhead vapour from the fractionator column comprising the gaseous products to a gas concentration section and withdrawing the liquid products from the fractionator column.The process as claimed in claim 1, wherein the coal tar pitch and the clarified oil stream are mixed in a mixing tank to obtain the mixed feedstock.The process as claimed in claim 1, wherein the coal tar pitch and the CLO stream are mixed with a hydrotreated VGO (vacuum gas oil) in a mixing tank to obtain the mixed feedstock; wherein the hydrotreated VGO is mixed in the range of 5 to 30 wt%.The process as claimed in claim 1, wherein a solvent stream from a solvent tank is introduced into the mixing tank for solvent treatment of the mixed feed.The process as claimed in claim 1, wherein the mixed feedstock containing the solvent is routed from the mixing tank to a separator vessel for separating the mixed feedstock into a heavy residual fraction containing impurities and a first purified mixed feedstock without impurities, and removing the heavy residual fraction as pitch from bottom of the separator vessel and the first purified mixed feedstock from top side of the separator vessel, wherein the impurities are quinoline insoluble substances along with solid catalyst fines.The process as claimed in claim 1, wherein the recovered solvent streams from the first solvent recovery column and the second recovery column are routed to the solvent tank.The process as claimed in claim 1, wherein the solvent for treatment of the mixed feedstock in the solvent treatment vessel is selected from a polar extraction solvent, an aliphatic solvent, an aromatic solvent, or a combination thereof;wherein the polar extraction solvent is n-methyl -2- pyrrolidone (NMP);wherein the aliphatic solvent is selected from cyclohexane, kerosene, diesel oil, and n-heptane;wherein the aromatic solvent is selected from toluene, wash oil, anthracene oil, naphthalene oil, and benzene.The process as claimed in claim 1, wherein the solvent in the solvent treatment vessel is mixed with a mixed feedstock in a ratio of solvent and mixed feedstock ranging from 2:1 to 50:1, and the solvent treatment vessel is operated at a temperature ranging from 55 to 300ºC and a pressure ranging from 1 to 60 Kg / cm2 (g).The process as claimed in claim 1, wherein the fractionator column is operated at a temperature ranging from 250ºC to 390ºC. The process as claimed in claim 1, wherein the thermal cracking temperature in the coker heater in step (h) ranges from 480ºC to 530ºC.The process as claimed in claim 1, wherein in the process step (h), steam is introduced to the coker heater to prevent coking in heater tubes and create additional turbulent flow.The process as claimed in claim 1, wherein the coke drum is operated at a temperature ranging from 475ºC to 520ºC and a top pressure is maintained between 1 to 6.5 Kg / cm2 (g); wherein a feeding cycle tome in the coke drum ranges from 16 hours to 48 hours.The process as claimed in claim 1, wherein the process for production of graphite grade coke comprises:(a)    mixing coal tar pitch and clarified oil streams in a mixing tank to obtain a mixed feedstock, wherein the coal tar pitch and the clarified oil are blended in a weight ratio ranging from 90:10 to 40:60;(b)    routing a solvent stream from a solvent tank to the mixing tank for solvent treatment of the mixed feedstock,(c)     routing outlet from the mixing tank to a separator vessel for separating the mixed feedstock into a heavy residual fraction containing impurities and a first purified mixed feedstock without impurities, and removing the heavy residual fraction as pitch from bottom of the separator vessel, wherein the impurities are quinoline insoluble substances along with solid catalyst fines;(d)    passing the pitch to a first heater to obtain a heated pitch and flashing the heated pitch into a first solvent recovery column;(e)    withdrawing a heavy pitch stream from bottom of the first solvent recovery column and routing overhead of the first solvent recovery column containing recovered solvent stream back to the solvent tank;(f)      routing the first purified mixed feedstock from top side of the separator vessel to a second heater to obtain a heated first purified mixed feedstock and flashing the heated first purified mixed feedstock into a second solvent recovery column;(g)    routing overhead from the second solvent recovery column containing recovered solvent stream back to the solvent tank and routing bottom from the second solvent recovery column to a bottom section of a fractionator column, wherein the bottom from the second solvent recovery column contains a second purified mixed feedstock without solvent;(h)    mixing the second purified mixed feedstock obtained in step (f)with an internal recycle stream in the bottom section of the fractionator column to obtain a secondary feedstock and drawing out the secondary feed stock from bottom of the fractionator column, wherein the internal recycle stream is obtained after separation of gaseous products and liquid products from lighter hydrocarbon products that are routed to the fractionator column from a coke drum;(i)      heating the secondary feed stock in a coker heater to a thermal cracking temperature to obtain a hot secondary feedstock;(j)      routing the hot secondary feedstock to a coke drum for cracking the feedstock to lighter hydrocarbon products and a graphite grade coke; wherein the graphite grade coke is graphitizable needle coke and is deposited in the coke drum;(k)     routing the lighter hydrocarbon products from the coke drum to the fractionator column for separation into gaseous products and liquid products; and(l)      routing overhead vapour from the fractionator column comprising the gaseous products to a gas concentration section and withdrawing the liquid products from the fractionator column.A system for production of graphite grade coke comprising:(a) a solvent treatment vessel (3) for receiving a mixed feedstock (1,2) and a solvent (4), and for separating the mixed feedstock into a heavy residual fraction containing impurities and a first purified mixed feedstock without impurities, wherein the impurities are quinoline insoluble substances along with solid catalyst fines;(b) a first heater (6) for receiving the heavy residual fractions as pitch (5) from bottom of the solvent treatment vessel (3);(c) a first solvent recovery column (7) for receiving a heated pitch from the first heater (6) to obtain are covered solvent stream (9) and a heavy pitch stream (8);(d) a second heater (11) for receiving the first purified mixed feedstock (10) from the solvent treatment vessel (3);(e) a second solvent recovery column (12) for receiving a heated first purified mixed feedstock from the second heater (11) to obtain a recovered solvent stream (13) and a second purified mixed feedstock without solvent (14);(f) a fractionator column (15) for receiving the second purified mixed feedstock without solvent (14) and mixing with an internal recycle stream to obtain a secondary feedstock (16), wherein the fractionator column further receives lighter hydrocarbon products (22) from the coke drum to obtain gaseous products (23) and liquid products (24,25, 26), wherein the liquid products are kerosene, light coker gas oil (LCGO), and heavy coker gas oil (HCGO);(g) a coker heater (17) for heating the secondary feedstock (16) from bottom of the fractionator column (15) at a thermal cracking temperature to obtain a hot secondary feedstock (19); and(h) coke drums (20, 21) for receiving the hot secondary feedstock (19) for cracking the feedstock to lighter hydrocarbon products (22) and a graphite grade coke, wherein the graphite grade coke is a graphitizable needle coke and is deposited in the coke drum.The system as claimed in claim 14, wherein the system comprises a mixing tank (29) for mixing the coal tar pitch and the clarified oil stream to obtain a mixed feedstock.The system as claimed in claim 14, wherein the system comprises a solvent tank (30) for receiving the recovered solvent streams from the first solvent recovery column and the second recovery column.

Images