Delayed coking process with pre-cracking reactor

Abstract

The present invention relates to delayed coking of heavy petroleum residue producing petroleum coke and lighter hydrocarbon products. The invented process utilize a pre-cracking reactor for mild thermal cracking of the feedstock and an intermediate separator, before being subjected to higher severity thermal cracking in delayed coking process, resulting in reduction in overall coke yield.

Claims

1. A method of reducing overall coke yield said method consisting of the steps of: (a) heating a hydrocarbon feedstock (74) mixed with a Clarified Oil (CLO) stream (75) in a furnace (76) to obtain hot feed (77); (b) introducing the hot feed (77) of step (a) in a pre-cracking reactor (78) wherein it undergoes mild thermal cracking reactions at a temperature in the range of 350 to 470 C., a pressure in the range of 1 to 15 kg/cm.sup.2 and a residence time in the range of 1 to 40 minutes to obtain an outlet product material stream (79); (c) passing the outlet product material stream (79) of step (b) to an intermediate separator (80) to split the outlet product material stream (79) into top fraction (81) and heavy bottom product (82) and transferring the top fraction (81) to a main fractionator (73); (d) heating the heavy bottom product (82) of step (c) in a furnace (76) to obtain hot hydrocarbon stream (83); (e) transferring the hot hydrocarbon stream (83) of step (d) to preheated coke drums (84) where it undergoes severe thermal cracking reactions at a temperature in the range of 470 to 520 C., a pressure in the range of 0.5 to 5 kg/cm.sup.2 and a residence time of more than 10 hours to obtain product vapors (85); and (f) passing the product vapors (85) of step (e) to the main fractionator (73) to obtain desired product fractions (86, 87, 88, 89, 90); wherein the hydrocarbon feedstock (74) has conradson carbon residue content of above 4 wt % and density of at least0.95 g/cc; wherein in step (a) the hydrocarbon feedstock (74) is obtained by feeding a resid feed (72) selected from vacuum residue, reduced crude oil, deasphalted pitch, shale oil, coal tar, heavy waxy distillates, foots oil, slop oil and blends thereof, into a bottom section of the main fractionator (73) and obtained as a bottom fraction (74) from the main fractionator (73), prior to heating in the furnace (76), wherein the resid feed (72) is introduced into the bottom section of the main fractionator (73) below a location where the top fraction (81) and the product vapors (85) enter the main fractionator (73); wherein in step (d) the heavy bottom product (82) of step (c) is mixed with Clarified Oil (CLO) stream prior to sending to the furnace (76) to produce the hot hydrocarbon stream (83); wherein in step (c) the intermediate separator (80) is operated in the pressure range of about 0.2 to 6 Kg/cm.sup.2.

2. The method as claimed in claim 1, wherein the product fractions are selected from LPG and naphtha, Kerosene, LCGO, HCGO and Coker Fuel Oil (CFO).

Description

(1) Various objects, features, aspects, and advantages of the present invention will become more apparent from the following drawings and detailed description of preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

(2) FIG. 1. Represents schematic flow diagram of First Scheme.

(3) FIG. 2. Represents schematic flow diagram of Second Scheme.

(4) FIG. 3. Represents schematic flow diagram of Third Scheme.

(5) FIG. 4. Represents schematic flow diagram of Fourth Scheme.

(6) FIG. 5. Represents schematic flow diagram of Fifth Scheme.

DESCRIPTION OF THE INVENTION

(7) While the invention is susceptible to various modifications and/or alternative processes and/or compositions, specific embodiment thereof has been shown by way of example in tables and will be described in detail below. It should be understood, however that it is not intended to limit the invention to the particular processes and/or compositions disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the invention as defined by the appended claims.

(8) The tables and protocols have been represented where appropriate by conventional representations, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

(9) The following description is of exemplary embodiments only and is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention.

(10) According to one embodiment of the present invention, a method of reducing overall coke yield comprising the steps of: (a) heating a hydrocarbon feedstock [1, 19, 37, 54, 74] in a furnace [2, 20, 38, 55, 76] to obtain hot feed [3, 21, 39, 56, 77]; (b) introducing the hot feed [3, 21, 39, 56, 77] of step (a) in a pre-cracking reactor [4, 22, 40, 57, 78] wherein it undergoes mild thermal cracking reactions to obtain an outlet product material stream [5, 23, 41, 58, 79]; (c) passing the outlet product material stream [5, 23, 41, 58, 79] of step (b) either directly to a main fractionator [24] to obtain heavy bottom fraction [30] or an intermediate separator [6, 42, 59, 80] to split outlet product material stream into top fraction [7, 43, 62, 81] and bottom product [8, 44, 63, 82] and transferring the top fraction [7, 43, 62, 81] to a main fractionator [12, 36, 61, 73]; (d) heating the heavy bottom fraction [30] or the heavy bottom [8, 44, 63, 82] of step (c) in a furnace [2, 20, 38, 55, 76] to obtain hot hydrocarbon stream [9, 31, 45, 64, 83]; (e) transferring the hot hydrocarbon stream [9, 31, 45, 64, 83] of step (d) to preheated coke drums [10, 32, 46, 65, 84] where it undergoes thermal cracking reactions to obtain product vapors [11, 33, 47, 66, 85]; and (f) passing the product vapors [11, 33, 47, 66, 85] of step (e) to the main fractionator [12, 24, 36, 61, 73] to obtain desired product fractions.

(11) According to another embodiment of the present invention, a method of reducing overall coke yield comprising the steps of: (a) heating a hydrocarbon feedstock (19) in a furnace (20) to obtain hot feed (21); (b) introducing the hot feed (21) of step (a) to a pre-cracking reactor (22), where it undergoes mild thermal cracking reactions to obtain an outlet product material stream (23); (c) passing the outlet product material stream (23) of step (b) to a main fractionator (24), where it fractionated to a heavy bottom fraction (30); (d) passing the heavy bottom fraction (30) of step (c) to the furnace (20) to obtain hot hydrocarbon stream (31); (e) passing the hot hydrocarbon stream (31) of step (d) to preheated coke drums (32), where it undergoes thermal cracking reactions to obtain product vapors (33); and (f) passing the product vapors (33) of step (e) to the main fractionator (24) column to obtain desired product fractions.

(12) According to another embodiment of the present invention, a method of reducing overall coke yield comprising the steps of: (a) heating a hydrocarbon feedstock (54) in a furnace (55) to get hot feed (56); (b) introducing the hot feed (56) of step (a) to a pre-cracking reactor (57), where it undergoes mild thermal cracking reactions to obtain an outlet product material stream (58); (c) passing the outlet product material stream (58) of step (b) and heavier bottom fraction (60) obtained from a main fractionator (61) to an intermediate separator (59) to split hydrocarbons into top (62) and bottom (63) fractions; (d) passing the top fraction (62) of step (c) containing lighter products to the main fractionator (61); (e) passing the bottom fraction (63) of step (c) to the furnace (55), where it undergoes heating to obtain a hot hydrocarbon stream (64); (f) passing the hot hydrocarbon stream (64) of step (e) to preheated coke drums (65), where it undergoes thermal cracking reactions to obtain product vapors (66); and (g) passing the product vapors (66) of step (f) to the main fractionator (61) column to obtain desired product fractions.

(13) According to preferred embodiment of the present invention, in step (a) the hydrocarbon feedstock [37, 74] is a hot feed mixed with an internal recycle stream which is obtained by passing a resid feed stock [35, 72] to bottom section of the main fractionator [36, 73].

(14) According to preferred embodiment of the present invention, in step (a) the hydrocarbon feedstock [74] is mixed with CLO stream [75] prior to heating in the furnace [76].

(15) According to preferred embodiment of the present invention, in step (c) the bottom fraction [82] of the intermediate separator is mixed with CLO stream [75] prior to sending to the furnace [76] to produce the hot stream [83].

(16) According to preferred embodiment of the present invention, the product fraction is offgas selected from LPG and naphtha [13, 25, 48, 67, 86], Kero [15, 27, 50, 68, 87], LCGO [16, 28, 51, 69, 88], HCGO [17, 29, 52, 70, 89] and CFO [18, 34, 53, 71, 90].

(17) According to preferred embodiment of the present invention, the pre-cracking reactor [4, 22, 40, 57, 78] is operated at a temperature range of about 350 to 470 C.

(18) According to preferred embodiment of the present invention, the pre-cracking reactor [4, 22, 40, 57, 78] is operated at a pressure range of about 1 to 15 Kg/cm.sup.2.

(19) According to preferred embodiment of the present invention, residence time of the hot feed [3, 21, 39, 56, 77] in the pre-cracking reactor [4, 22, 40, 57, 78] is in the range of 1 to 40 minutes.

(20) According to preferred embodiment of the present invention, the intermediate separator [6, 42, 59, 80] is operated in the pressure range of about 0.2 to 6 Kg/cm.sup.2.

(21) According to preferred embodiment of the present invention, the coke drums [10, 32, 46, 65, 84] are operated at a temperature ranging from about 470 to 520 C.

(22) According to preferred embodiment of the present invention, the coke drums [10, 32, 46, 65, 84] are operated at a pressure ranging from about 0.5 to 5 Kg/cm.sup.2.

(23) According to preferred embodiment of the present invention, residence time of the hot hydrocarbon stream [9, 31, 45, 64, 83] in the coke drum [10, 32, 46, 65, 84] is more than 10 hours.

(24) According to preferred embodiment of the present invention, the hydrocarbon feedstock [1, 19, 37, 54, 74] is selected from vacuum residue, atmospheric residue, deasphalted pitch, shale oil, coal tar, clarified oil, residual oils, heavy waxy distillates, foots oil, slop oil or blends of hydrocarbons.

(25) According to preferred embodiment of the present invention, the hydrocarbon feedstock [1, 19, 37, 54, 74] has conradson carbon residue content of above 4 wt % and density of at least 0.95 g/cc.

(26) Feedstock

(27) The liquid hydrocarbon feedstock to be used in the process can be selected from heavy hydrocarbon feedstocks like vacuum residue, atmospheric residue, deasphalted pitch, shale oil, coal tar, clarified oil, residual oils, heavy waxy distillates, foots oil, slop oil or blends of such hydrocarbons. The Conradson carbon residue content of the feedstock can be above 4 wt % and density can be minimum of 0.95 g/cc.

(28) Reaction Conditions

(29) In the process of the present invention, the pre-cracking reactor may be operated in the desired operating temperature ranging from 350 to 470 C., preferably between 420 C. to 470 C. and desired operating pressure inside pre-cracking reactor ranging from 1 to 15 Kg/cm.sup.2 (g) preferably between 5 to 12 Kg/cm.sup.2 (g). the residence time inside the pre-cracking reactor range from 1 to 40 minutes, preferably operated in the range of 5 to 30 minutes. The intermediate separator may be operated at a pressure ranging from 0.2 to 6 Kg/cm.sup.2(g), preferably in the range of 1 to 5 Kg/cm.sup.2(g). The second stage coke drums may be operated at a higher severity with desired operating temperature ranging from 470 to 520 C., preferably between 480 C. to 500 C. and desired operating pressure ranging from 0.5 to 5 Kg/cm.sup.2 (g) preferably between 0.6 to 3 Kg/cm.sup.2 (g). The residence time provided in coke drums is more than 10 hours.

(30) Process Description

(31) A schematic process flow diagram of the invented process is provided as FIG. 1. Resid feedstock (1) is heated in a furnace (2) to get the hot feed (3) at the desired inlet temperature of the pre-cracking reactor. Hot feed at desired temperature and pressure is sent to the pre-cracking reactor (4) which is operating at a temperature range of about 350 to 470 C. and pressure range of about 1 to 15 Kg/cm2, where it undergoes mild thermal cracking reactions. The outlet product material stream (5) is then sent to the intermediate separator (6) to split the hydrocarbons into two fractions. The top fraction (7) containing lighter products including gases are sent to the main fractionator (12). The bottom product (8) is then subjected to heating in furnace (2) to the desired coking temperature. The hot hydrocarbon stream (9) exiting the furnace is then sent to the preheated coke drum (10), where it is provided with a longer residence time for thermal cracking reactions. The product vapors exiting the coke drum (11) are sent to the main fractionator (12) column for further separation into desired product fractions like offgas with LPG and naphtha (13), Kero (15), LCGO (16), HCGO (17) and CFO (18). The entry points of products from intermediate separator and coke drum to the main fractionators may be suitably selected based on good engineering practices.

(32) An embodiment of the invention is provided in FIG. 2, with lesser hardware requirement. In the process scheme described in FIG. 2, resid feedstock (19) is heated in a furnace (20) to get the hot feed (21) at the desired inlet temperature of the pre-cracking reactor (22). Hot feed at desired temperature and pressure is sent to the pre-cracking reactor (22), where it undergoes mild thermal cracking reactions. The outlet product material stream (23) is then sent to the main fractionator column (24), where the product hydrocarbons get fractionated to different desired product streams. The heavy bottom fraction is withdrawn from the main fractionator bottom (30) and is sent to the furnace (20) for heating to the desired coking temperature. The hot hydrocarbon stream (31) exiting the furnace is then sent to the preheated coke drum (32), where it is provided with a longer residence time for delayed coking reactions. The product vapors exiting the coke drum (33) along with product stream from pre-cracking reactor are sent to the main fractionator (24) column for further separation into desired product fractions like offgas with LPG and naphtha (25), Kero (27), LCGO (28), HCGO (29), CFO (34) and heavy bottom fraction (30). The heavy bottom fraction may be subjected to vacuum flashing to remove the lighter material further. The entry points of products from pre-cracking reactor and coke drum to the main fractionator may be suitably selected based on good engineering practices.

(33) The embodiment as represented in FIG. 2 achieve following advantages by directing the whole of effluents from pre-cracker reactor to the main fractionator column:

(34) 1) Elimination of intermediate separator column.

(35) 2) Heat content of precracker effluent can be used for better separation in the main fractionator as with intermediate separator, one need to cool the precracker effluent and operate intermediate separator at a lower temperature.

(36) Another embodiment of the invention is provided in FIG. 3. Resid feedstock (35) is first sent to the bottom section of the main fractionator (36) to get the hot feed (37) mixed with the internal recycle stream. The hot feed (37) is then heated in a Furnace (38) to get the hot feed (39) at the desired inlet temperature of the pre-cracking reactor (40). Hot feed at desired temperature and pressure is sent to the pre-cracking reactor (40), where it undergoes mild thermal cracking reactions. The outlet product material stream (41) is then sent to the intermediate separator (42) to split the hydrocarbons into two fractions. The top fraction (43) containing lighter products including gases are sent to the main fractionator (36). The bottom product (44) is then subjected to further heating in furnace (38) to the desired coking temperature. The hot hydrocarbon stream (45) exiting the furnace is then sent to the preheated coke drum (46), where it is provided with a longer residence time for delayed coking reactions. The product vapors exiting the coke drum (47) are sent to the main fractionator (36) column for further separation into desired product fractions like offgas with LPG and naphtha (48), Kero (50), LCGO (51), HCGO (52) and CFO (53). The entry points of products from pre-cracking reactor and coke drum to the main fractionator may be suitably selected based on good engineering practices.

(37) Yet another embodiment of the invention is provided in FIG. 4. In the process scheme described in FIG. 4, resid feedstock (54) is heated in a furnace (55) to get the hot feed (56) at the desired inlet temperature of the pre-cracking reactor (57). Hot feed at desired temperature and pressure is sent to the pre-cracking reactor (57), where it undergoes mild thermal cracking reactions. The outlet product material stream (58) is then sent to the intermediate separator (59). Heavier bottom material (60) from the main fractionator column (61) is also put in the intermediate separator (59). Vapor products (62) separated in the intermediate separator is routed to the main fractionator column (61) for separation into desired products. The heavy bottom fraction (63) is withdrawn from the intermediate separator (59) and is sent to the furnace (55) for heating to the desired coking temperature. The hot hydrocarbon stream (64) exiting the furnace is then sent to the preheated coke drum (65), where it is provided with a longer residence time for thermal cracking reactions. The product vapors exiting the coke drum (66) are sent to the main fractionator (61) column for further separation into desired product fractions like offgas with LPG and naphtha (67), Kero (68), LCGO (69), HCGO (70) and CFO (71). The heavy bottom fraction (60) is routed to the intermediate separator (59). The entry points of products from pre-cracking reactor and coke drum to the main fractionator may be suitably selected based on good engineering practices.

(38) The embodiment as represented in FIG. 4 has a superior control over the recycle ratio of the operation of the coke drum section. By varying the quantity of the heavier bottom material (60), one can manipulate the recycle ratio to impact both coke properties and the liquid product properties. This offers a great flexibility to the refiner over product quality.

(39) Yet another embodiment of the invention is provided in FIG. 5. Resid feedstock (72) is first sent to the bottom section of the main fractionator (73) to get the hot feed (74) mixed with the internal recycle stream. The hot feed (74), along with CLO stream (75) from FCC/RFCC is then heated in a Furnace (76) to get the hot feed (77) at the desired inlet temperature of the pre-cracking reactor (78). Hot feed at desired temperature and pressure is sent to the pre-cracking reactor (78), where it undergoes mild thermal cracking reactions. The outlet product material stream (79) is then sent to the intermediate separator (80) to split the hydrocarbons into two fractions. The top fraction (81) containing lighter products including gases are sent to the main fractionator (73). The bottom product (82) is then subjected to further heating in furnace (76) to the desired coking temperature. The hot hydrocarbon stream (83) exiting the furnace is then sent to the preheated coke drum (84), where it is provided with a longer residence time for delayed coking reactions. The product vapors exiting the coke drum (85) are sent to the main fractionator (73) column for further separation into desired product fractions like offgas with LPG and naphtha (86), Kero (87), LCGO (88), HCGO (89) and CFO (90). The entry points of products from pre-cracking reactor and coke drum to the main fractionator may be suitably selected based on good engineering practices.

(40) In another embodiment, CLO stream (75) is mixed with the bottom product (82) of the intermediate separator (80) before sending to furnace (76) to produce the hot stream (83).

(41) In embodiment as represented in FIG. 5, CLO stream (75) is a predominantly aromatic stream from fluid catalytic cracking unit. Addition of this stream in the feedstock helps in improving the stability of asphaltene molecules (asphaltene molecules in the feedstock causes coke deposition inside the furnace tubes).

EXAMPLES

(42) Pilot scale experimental study is carried out for validating the merits of the invented process schemes. Experiments are carried out with a resid feedstock of characteristics provided in Table-1.

(43) TABLE-US-00001 TABLE 1 Properties of resid feedstock Feed characteristics Value Density, g/cc 1.042 CCR, wt % 23.39 Asphaltene content, wt % 7.8 Sulfur, wt % 5.73 Liquid analysis (D2887/D6352) wt % Deg C. 0 409 10 506 30 562 50 600 70 639 80 659 90 684 95 698 Metal, ppm Fe 6 Na 47 Ca 3 Cr 1 Si 1

(44) A base case experiment is carried out in the delayed coker pilot plant using the resid feedstock at delayed coking conditions. The operating conditions for all the experiments are 495 C., feed furnace outlet line temperature, 14.935 psig coke drum pressure, 1 wt % steam addition to the coker feed and a feed rate maintained at about 8 kg/h. The operation is carried out in semi batch mode. The vapors from the coking drums are recovered as liquid and gas products and no coker product is recycled to the coker drum. Major operating parameters and the corresponding discrete product yield pattern are provided in Table-2.

(45) TABLE-US-00002 TABLE 2 Base case pilot plant experimental data with resid feedstock at delayed coker conditions. Unit Value Feed characteristics Feed rate Kg/hr 8 Run duration Hr 12 COT C. 495 Drum pressure kg/cm.sup.2 1.05 Yield (Basis: fresh feed) Fuel gas wt % 6.82 LPG wt % 5.66 C.sub.5-140 C. wt % 9.38 140-370 C. wt % 26.80 370 C.+ wt % 24.40 Coke wt % 26.94

(46) The yields obtained from the base case experiment as provided in Table-2 form the conventional Delayed coker unit (DCU) process yields for the resid feedstock taken. In order to find the yields from invented process, a first experiment is carried out with the resid feedstock of Table-1 at mild thermal cracking conditions envisaged for the pre-cracker reactor. The major operating parameters and the corresponding discrete product yield pattern are provided in Table-3.

(47) TABLE-US-00003 TABLE 3 Pilot plant experimental data with resid feedstock using pre-cracker reactor. Value Process conditions COT, C. 444 Pre-cracker inlet temp, C. 436 Pre-cracker outlet temp, C. 409 Pre-cracker inlet pressure, Kg/cm.sup.2(g) 12.3 Pre-cracker outlet pressure, Kg/cm.sup.2(g) 11.9 Product yield pattern, wt % Fuel gas 1.22 LPG 1.59 C.sub.5-140 C. 3.05 140-370 C. 11.89 Pre-cracker bottom (370 C.+) 82.25

(48) Heavy bottom material (370 C.+) generated from the pre-cracker reactor is separated in a fractionator/intermediate separator and experiment is carried out using this material at the conditions of delayed coking, in the delayed coker pilot plant. The major operating parameters and the corresponding discrete product yield pattern are provided in Table-4.

(49) TABLE-US-00004 TABLE 4 Pilot plant experimental data with heavy bottom material (370 C.+) from intermediate separator at delayed coker conditions. Value Process conditions Run duration 12 hrs Feed rate, Kg/hr 8 Run duration, hr 12 COT, C. 495 Drum pressure, Kg/cm.sup.2(g) 1.05 Yield in wt % (Basis: fresh feed) Fuel gas 7.46 LPG 5.07 C.sub.5-140 C. 7.16 40-370 C. 26.40 370 C.+ 26.09 Coke 27.82

(50) From the experimental data as provided in Tables-3 & 4, the yields for the invented process scheme is estimated and is compared with the base case delayed coker yields, in Table-5.

(51) TABLE-US-00005 TABLE 5 Comparison of yields obtained in invented process and the base case DCU yields Invented Base case DCU Yield process yields yields improvement Yields Wt % Wt % Wt % Fuel gas 7.36 6.82 +0.54 LPG 5.76 5.66 +0.10 C.sub.5-140 C. 8.94 9.38 0.45 140-370 C. 33.60 26.80 +6.80 370 C.+ 21.46 24.40 2.94 Coke 22.88 26.94 4.06

(52) The experimental data reported in Table-5 shows that there is improvement in diesel range product of about 7 wt % and reduction in coke and fuel oil yields of about 4 wt % and 3 wt % respectively for the process scheme of the present invention over the conventional delayed coking process.

(53) Those of ordinary skill in the art will appreciate upon reading this specification, including the examples contained herein, that modifications and alterations to the composition and methodology for making the composition may be made within the scope of the invention and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventor is legally entitled.