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 and a reactor furnace for mild thermal cracking of the feedstock and an intermediate separator, before being subjected to higher severity thermal cracking treatment in a coker furnace and a coking drums, 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 (40) in a reactor furnace (41) to obtain a hot feed (42); (b) introducing the hot feed (42) of step (a) in a pre-cracking reactor (43) wherein it undergoes mild thermal cracking reactions at 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 (44); wherein the pre-cracking reactor is a plug flow reactor; wherein the pre-cracking reactor is operated at a temperature range of 370 to 470 C.; (c) passing the outlet product material stream (44) of step (b) an intermediate separator (45) to split the outlet product material stream (44) into top fraction (46) and heavy bottom product (47) and transferring the top fraction (46) to a main fractionator (53); wherein the intermediate separator (45) is operated in the pressure range of 0.2 to 10 Kg/cm.sup.2; (d) heating the heavy bottom product (47) of step (c) in a coker furnace (49) to obtain a hot hydrocarbon stream (50); wherein the heavy bottom product (47) is mixed with a Clarified Oil (CLO) stream (48) prior to heating in the coker furnace (49); (e) transferring the hot hydrocarbon stream (50) of step (d) to preheated coke drums (51) 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 (52); and (f) passing the product vapors (52) of step (e) to the main fractionator (53) to obtain desired product fractions (54, 55, 56, 57, 58); wherein the hydrocarbon feedstock (40) of step a) is obtained by feeding a resid feed (39) selected from vacuum residue, atmospheric residue, deasphalted pitch, shale oil, coal tar, heavy waxy distillates, foots oil, slop oil or blends thereof, into a bottom section of the main fractionator (53) and obtained as a bottom fraction from the main fractionator (53), prior to heating in the reactor furnace, wherein the resid feed (39) is introduced into the bottom section of the main fractionator (53) below a location where the top fraction (46) and the product vapors (52) enter the main fractionator (53); wherein the hydrocarbon feedstock of step a) has conradson carbon residue content of above 4 wt % and density of at least 0.95 g/cc.

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

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

DETAILED DESCRIPTION OF THE INVENTION

(5) 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.

(6) 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.

(7) 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. According to first embodiment of the present invention, a method of reducing overall coke yield comprises the steps of:

(8) (a) heating a hydrocarbon feedstock [1, 20, 40, 59] in a reactor furnace [2, 21, 41, 60] to obtain hot feed [3, 22, 42, 61];

(9) (b) introducing the hot feed [3, 22, 42, 61] of step (a) in a pre-cracking reactor [4, 23, 24, 43, 62] wherein it undergoes mild thermal cracking reactions to obtain an outlet product material stream [5, 25, 44, 63];

(10) (c) passing the outlet product material stream [5, 25, 44, 63] of step (b) either directly to a main fractionator [69] to obtain heavy bottom fraction [64] or an intermediate separator [6, 26, 45] to split outlet product material stream into top fraction [7, 27, 46] and bottom product [8, 28, 47] and transferring the top fraction [7, 27, 46] to a main fractionator [13, 33, 53];

(11) (d) heating the heavy bottom fraction [64] or the heavy bottom [8, 28, 47] of step (c) in a secondary furnace [9, 29, 49, 65] to obtain hot hydrocarbon stream [10, 30, 50, 66];

(12) (e) transferring the hot hydrocarbon stream [10, 30, 50, 66] of step (d) to preheated coke drums [11, 31, 51, 67] where it undergoes severe thermal cracking reactions to obtain product vapors [12, 32, 52, 68]; and

(13) (f) passing the product vapors [12, 32, 52, 68] of step (e) to the main fractionator [13, 33, 53, 69] to obtain desired product fractions.

(14) According to first embodiment of the present invention, in step (a) the hydrocarbon feedstock [20, 40] is a hot feed mixed with an internal recycle stream which is obtained by passing a resid feed stock [19, 39] to bottom section of the main fractionator [33, 53].

(15) According to first embodiment of the present invention, in step (a) the heavy bottom [47] is mixed with CLO stream [48] prior to heating in the secondary furnace [49].

(16) According to first embodiment of the present invention, the hot feed [22] of step (a) is distributed in multiple pre-cracking reactors [23, 24] wherein it undergoes mild thermal cracking reactions to obtain an outlet product material stream [25].

(17) According to second embodiment of the present invention, a method of reducing overall coke yield comprises the steps of:

(18) (a) heating a hydrocarbon feedstock (59) in a reactor furnace (60) to obtain hot feed (61);

(19) (b) introducing the hot feed (61) of step (a) to a pre-cracking reactor (62), where it undergoes mild thermal cracking reactions to obtain an outlet product material stream (63);

(20) (c) passing the outlet product material stream (63) of step (b) to a main fractionator (69), where it fractionated to a heavy bottom fraction (64);

(21) (d) passing the heavy bottom fraction (64) of step (c) to a secondary furnace (65) to obtain hot hydrocarbon stream (66);

(22) (e) passing the hot hydrocarbon stream (66) of step (d) to preheated coke drums (67), where it undergoes thermal cracking reactions to obtain product vapors (68); and

(23) (f) passing the product vapors (68) of step (e) to the main fractionator (69) column to obtain desired product fractions.

(24) According to first and second embodiment of the present invention, the product fraction separated from the fractionator [13, 33, 53, 69] are offgas comprising fuel gas, LPG and naphtha [14, 34, 54, 70], Kerosene [15, 35, 55, 71], LCGO [16, 36, 56, 72], HCGO [17, 37, 57, 73] and CFO [18, 38, 58, 74].

(25) According to first and second embodiment of the present invention, the pre-cracking reactor [4, 23, 24, 43, 62] is a Plug Flow Reactor (PFR).

(26) According to first and second embodiment of the present invention, the pre-cracking reactor [4, 23, 24, 43, 62] is operated at a temperature range of 370 to 470 C.

(27) According to first and second embodiment of the present invention, the pre-cracking reactor [4, 23, 24, 43, 62] is operated at a pressure range of 1 to 25 Kg/cm.sup.2.

(28) According to first and second embodiment of the present invention, residence time of the hot feed [3, 22, 42, 61] in the pre-cracking reactor [4, 23, 24, 43, 62] is in the range of 1 to 50 minutes.

(29) According to first and second embodiment of the present invention, the intermediate separator [6, 26, 45] is operated in the pressure range of 0.2 to 10 Kg/cm.sup.2.

(30) According to first and second embodiment of the present invention, the coke drums [11, 31, 51, 67] are operated at a temperature ranging from 470 to 520 C.

(31) According to first and second embodiment of the present invention, the coke drums [11, 31, 51, 67] are operated at a pressure ranging from 0.5 to 5 Kg/cm.sup.2.

(32) According to first and second embodiment of the present invention, residence time of the hot hydrocarbon stream [10, 30, 50, 66] in the coke drum [11, 31, 51, 67] is more than 10 hours.

(33) According to first and second embodiment of the present invention, the hydrocarbon feedstock [1, 20, 40, 59] 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.

(34) According to first and second embodiment of the present invention, the hydrocarbon feedstock [1, 20, 40, 59] has conradson carbon residue content of above 4 wt % and density of at least 0.95 g/cc.

(35) Feedstock

(36) The liquid hydrocarbon feedstock to be used in the process is 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 is above 4 wt % and minimum density of 0.95 g/cc.

(37) Reaction Conditions

(38) In the process of the present invention, the pre-cracking reactor may be operated in the desired operating temperature ranging from 370 C. to 470 C., preferably between 420 C. to 470 C. and desired operating pressure inside pre-cracking reactor ranging from 1 to 25 Kg/cm.sup.2 (g), preferably between 5 to 18 Kg/cm.sup.2 (g). The residence time inside the pre-cracking reactor range from 1 to 50 minutes, preferably operated in the range of 10 to 40 minutes. The intermediate separator may be operated at a pressure ranging from 0.2 to 10 Kg/cm.sup.2 (g), preferably in the range of 1 to 6 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.

(39) Process Description

(40) A schematic process flow diagram of the invented process is provided as FIG. 1. Resid feedstock (1) is heated in a reactor 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), preferably a plug flow reactor (PFR) which is operating at a temperature range of about 370 C. to 470 C. and pressure range of about 1 to 18 Kg/cm.sup.2, 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 (13). The bottom product (8) is then subjected to heating in a coker furnace (9) to the desired coking temperature. The hot hydrocarbon stream (10) exiting the furnace is then sent to the preheated coke drum (11), where it is provided with a longer residence time for thermal cracking reactions. The product vapors (12) exiting the coke drum are sent to the main fractionator column (13) for further separation into desired product fractions like offgas with LPG and naphtha (14), Kerosene (15), Light Coker Gas Oil (LCGO) (16), Heavy Coker Gas Oil (HCGO) (17) and Coker Fuel Oil (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.

(41) An embodiment of the invention is provided in FIG. 2. Resid feedstock (19) is first sent to the bottom section of the main fractionator (33) to get the hot feed (20) mixed with the internal recycle stream. The hot feed (20) is then heated in a reactor furnace (21) to get the hot feed (22) at the desired inlet temperature of the pre-cracking reactors (23) and (24). Hot feed at desired temperature and pressure is sent to multiple pre-cracking reactors (23) and (24), preferably plug flow reactors (PFR), where it undergoes mild thermal cracking reactions. The combined outlet product material stream (25) from pre-cracking reactors is then sent to the intermediate separator (26) to split the hydrocarbons into two fractions. The top fraction (27) containing lighter products including gases are sent to the main fractionator (33). The bottom product (28) is then subjected to further heating in a coker furnace (29) to the desired coking temperature. The hot hydrocarbon stream (30) exiting the furnace is then sent to the preheated coke drum (31), where it is provided with a longer residence time for delayed coking reactions. The product vapors (32) exiting the coke drum are sent to the main fractionator column (33) for further separation into desired product fractions like offgas with LPG and naphtha (34), Kerosene (35), Light Coker Gas Oil (LCGO) (36), Heavy Coker Gas Oil (HCGO) (37) and Coker Fuel Oil (CFO) (38). 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.

(42) Another embodiment of the invention is provided in FIG. 3. Resid feedstock (39) is first sent to the bottom section of the main fractionator (53) to get the hot feed (40) mixed with the internal recycle stream. The hot feed (40) is then heated in a reactor furnace (41) to get the hot feed (42) at the desired inlet temperature of the pre-cracking reactor (43). Hot feed at desired temperature and pressure is sent to pre-cracking reactor (43), preferably a plug flow reactor (PFR), where it undergoes mild thermal cracking reactions. The outlet product material stream (44) from pre-cracking reactor is then sent to the intermediate separator (45) to split the hydrocarbons into two fractions. The top fraction (46) containing lighter products including gases are sent to the main fractionator (53). The bottom product (47) is then subjected to further heating in a coker furnace (49) to the desired coking temperature. In the coker furnace a Clarified Oil (CLO) stream (48) is added to enhance the stability of the heavy hydrocarbon stream during heating. The hot hydrocarbon stream (50) exiting the coker furnace is then sent to the preheated coke drum (51), where it is provided with a longer residence time for delayed coking reactions. The product vapors (52) exiting the coke drum are sent to the main fractionator (53) column for further separation into desired product fractions like offgas with LPG and naphtha (54), Kerosene (55), Light Coker Gas Oil (LCGO) (56), Heavy Coker Gas Oil (HCGO) (57) and Coker Fuel Oil (CFO) (58). 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.

(43) Yet another embodiment of the invention is provided in FIG. 4. In the process scheme described in FIG. 4, resid feedstock (59) is heated in a reactor furnace (60) to get the hot feed (61) at the desired inlet temperature of the pre-cracking reactor (62) preferably a plug flow reactor (PFR). Hot feed at desired temperature and pressure is sent to the pre-cracking reactor (62), where it undergoes mild thermal cracking reactions. The outlet product material stream (63) is then sent to bottom section of the main fractionator (69) along with the internal recycle stream (68). Heavier bottom material (64) from the main fractionator column (69) is sent to a coker furnace (65) for heating to the desired coking temperature. The hot hydrocarbon stream (66) exiting the coker furnace is then sent to the preheated coke drum (67), where it is provided with a longer residence time for thermal cracking reactions. The product vapors (68) exiting the coke drum are sent to the main fractionator column (69) for further separation into desired product fractions like offgas with LPG and naphtha (70), Kerosene (71), Light Coker Gas Oil (LCGO) (72), Heavy Coker Gas Oil (HCGO) (73) and Coker Fuel Oil (CFO) (74). 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.

(44) The original Indian Patent Application No. 4398/MUM/2015 for which this application is an addition, describes a process in which a common furnace is employed to heat the feed going into the pre cracking reactor and the coke drums. In the said scheme, the use of a common furnace limits the variation in temperature severity that can be applied for thermal cracking reactions in pre cracking reactor and coke drums. The embodiments of the present invention offers better thermal selectivity control of both delayed coking unit and pre cracking reactor thereby enabling optimized operating severities in both pre cracking reactor and coke drums, resulting in significant reduction in overall yield of coke. Reduction in coke yield ultimately results in increased efficiency of processing of heavy petroleum residue and the refinery as a whole.

(45) Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims. Further, using a plug flow reactor as pre-cracking reactor minimizes back-mixing inside the reactor, which otherwise will affect the conversion rate as well as coke formation rate.

(46) While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein.

EXAMPLES

(47) 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.

(48) 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 % C. 0 409 10 506 30 562 50 600 70 639 80 659 90 684 95 698 Metal, ppm Fe 6 Ca 3 Cr 1 Si 1

(49) 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, 1.05 Kg/cm2 (g) 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.

(50) TABLE-US-00002 TABLE 2 Base case pilot plant experimental data with resid feedstock at delayed coker conditions. Feed characteristics Unit Value Feed rate Kg/hr 8 Run duration Hr 12 Coil Outlet Temperature C. 495 Drum pressure kg/cm.sup.2 1.05 Yield (Basis: fresh feed) Unit Value 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

(51) 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.

(52) 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. Heavy bottom material (370 C.+) generated from the pre-cracker reactor is separated in a fractionator/intermediate separator and this material is subjected to coking, in the delayed coker section. The major operating parameters for this experiment are provided in Table-3.

(53) TABLE-US-00003 TABLE 3 Pilot plant experimental conditions maintained for the scheme of current invention Process conditions Unit Value Run duration hrs 12 Feed rate Kg/hr 8 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 Coil Outlet Temperature (for heavy bottom C. 495 material from intermediate separator) Drum pressure Kg/cm.sup.2(g) 1.05

(54) From the experimental data the yields for the invented process scheme is estimated and is compared with the base case delayed coker yields, in Table-4.

(55) TABLE-US-00004 TABLE 4 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 6.62 6.82 0.20 LPG 5.81 5.66 +0.15 C.sub.5-140 C. 9.4 9.38 +0.02 140-370 C. 35.01 26.80 +8.21 370 C.+ 21.66 24.40 2.74 Coke 21.5 26.94 5.44

(56) The experimental data reported in Table-4 shows that there is improvement in diesel range product of about 8.21 wt % and reduction in coke and fuel oil yields of about 5.44 wt % and 2.74 wt % respectively for the process scheme of the present invention over the conventional delayed coking process.

(57) 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.