[0001] FIELD OF THE DISCLOSURE
[0002] The present application generally relates to the field of industrial equipment. Particularly, but not exclusively, the present disclosure relates to the construction and arrangement of a coker heater. More particularly, the present disclosure discloses a decoupled twin cell arrangement for delayed coker heaters for longer run-length and improved turn-down capability.
[0003] BACKGROUND OF THE DISCLOSURE
[0004] The information in this section merely provides background information related to the present disclosure and may not constitute prior art(s).
[0005] Delayed coking is a process for thermally cracking heavy hydrocarbon molecules to produce lighter and valuable hydrocarbon products. The process cracks heavy vacuum residue into various lighter cuts such as fuel gas, gas oil, naphtha, and coke, etc. The hydrocarbon cuts are further processed in various processing units to add value to these products and to render them saleable. The coke is utilized in various industries such as petcoke power generation, cement plants, etc. Among various equipment in the delayed coking unit (DCU), a fired heater is a major component that provides the heat for cracking.
[0006] The DCU heater is critical equipment in the delayed coking process. The feedstock is heated in the DCU heater up to desired cracking temperature. The intent is to delay the feedstock cracking beyond the fired heater i.e. actual cracking should take place after the heated feedstock leaves the heater and enters the coke drum. However, cracking starts in the fired heater itself to a certain extent and hence, results in coke formation inside fired heater tubes. Coking inside fired heater tubes is an inevitable phenomenon in the DCU and efforts are made to minimize the same as much as possible. Gradual deposition of coke inside tubes enforces the heater to shut down as soon as the tube metal temperature (TMT) reaches the tube's

metallurgical limit, or the hydraulic pressure drop increases to such an extent that the charge pump is limited. Even after adopting the latest design techniques, coking inside heater tubes cannot be completely avoided.
[0007] The process of decoking the delayed coker heater is now explained. In this spalling or decoking process, moderately high-velocity steam along with some air enters the delayed coker heater either at the convection inlet or at the furnace crossover tube. The air-steam mixture is passed through the coked tubes for scrapping and burning of the coke particles. Due to this scrapping and burning action, the coke particles detach from the metal surface and are eventually routed out of the furnace into a decoking pot where the hot effluent is quenched. Individual passes are taken offline and decoking operation is undertaken to remove the coke. On completion of the steam air decoking or spalling, the tubes are returned to an appreciably clean condition which helps in enhancing the efficiency of the furnace.
[0008] The time period between the start-up of the delayed coker heater and subsequent complete shutdown of the heater for decoking of tubes is termed as run-length of the delayed coker heater. The run length of the delayed coker heater is critical in determining the overall run length of the unit. A concurrent approach for increasing heater run-length is to employ steam air decoking or spalling of coked heater passes through the passing of steam that scrapes off the coke particles from inside tube surface. With an online facility, only a part of the heater is taken out of service for cleaning and the other cells remain in service. Thus, the overall run-length of the delayed coker heater is enhanced. In large duty coker heaters, there are multiple cells (4 to 6 cells in one heater) with each cell housing a coker heater pass.
[0009] FIG. 1 shows a similar kind of configuration, in which a delayed coker heater (1) comprises a radiation section (2), a convection section (3), a stack (4), refractory-lined walls (5), and a plurality of burners (7). FIG. 1 further shows two coker heater cells (2a, 2b) which are configured to have a common convection tube

arrangement (8) that caters to both the radiant passes. The radiation coker heater cells (2a, 2b) are connected to the convection section (3) through flue gas ducts (9). For such heater configurations as shown in FIG. 1, in case one of the passes is taken up for decoking and the other pass is kept in hydrocarbon heating service, the common convection section of the passes emerges as a major bottleneck. The cell that caters to the hydrocarbon pass experiences very high-temperature flue gas in the range of 800-900°C. The high-temperature flue gas from this hydrocarbon heating cell enters the common convection section where half of the tubes are catering to hydrocarbon service whereas the other half caters to decoking service. However, the fluid flow in the decoked pass is only a fraction of the hydrocarbon pass. Thus, when the high-temperature flue gas from the hydrocarbon heating cell faces the decoking pass tubes, chances of hot spot increases in the decoking pass tubes which may ultimately lead to their mechanical failure. Thus, for heater configurations shown in FIG.l, both the radiant passes (2a, 2b) are required to be decoked simultaneously as a continuation of hydrocarbon service in one of the cells can mechanically damage the decoking pass tubes of the shared convection section. Thus, the conventional configuration approach is acceptable to an extent for large capacity coker heaters, where there are 6 or 8 passes and the unit can be operated with reduced throughput even if two coupled convection passes are taken offline. However, for small capacity coker heaters where the heater has only 2 passes, such coupled configuration leads to shutdown of the complete coker unit till the decoking or cleaning activity is completed, leading to a loss in production and profitability that can be vital.
[0010] Moreover, it is of paramount importance to maintain a minimum mass velocity in coker heater tubes to delay the onset of coking. Mass velocity is defined as the amount of fluid mass that flows inside the tube per cross-sectional area basis. This mass velocity works in two ways- a high mass velocity scrapes off the deposited coke through the shearing action as well as reduces the residence time of the high-temperature process fluid inside the heater. As usually seen for small capacity coker units, maintaining this minimum mass velocity in a 2-pass furnace

is a challenge due to tube size limitations. To enhance the mass velocity, a possible option is to go for a smaller tube size, however, going below a certain tube size poses limitations w.r.t. decoking, spalling, and coke removal procedures. In fact, very small tube sizes experience choking due to excessive coke removal rate which can derail the decoking activity and may lead to mechanical cutting/ removal of the tubes. Hence, the small capacity coker heaters are limited by certain tube size criteria which also plays an important role in dictating the turndown percentage. Thus, low turndown in small capacity coker units is not recommended to ensure that the hydrocarbon flow through the heater does not fall below the minimum recommended values. Turndown capacities of merely 90-95% are commonplace for such small capacity coker units which often turn out to be a hindrance to the refinery's operational flexibility.
[0011] Accordingly, there is a need in the art to provide an arrangement that can overcome the one or more limitations stated above or any other limitations associated with the prior art.
[0012] SUMMARY OF THE DISCLOSURE
[0013] The present disclosure overcomes one or more drawbacks of conventional arrangements as described in the prior art and provides additional advantages through an arrangement as claimed in the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.
[0014] The present disclosure achieves the above-stated objective by providing a decoupled twin cell arrangement for delayed coker heaters as described in the present disclosure. Decoupled arrangement refers to the arrangement where each radiant cell has a corresponding dedicated convection cell instead of a common convection cell which is provided in the prior art. The dedicated radiation-

convective cell arrangement shall house a single hydrocarbon pass entering the convection section at the top and flowing down to exit the heater at the radiation section outlet.
[0015] In one non-limiting embodiment of the present disclosure, a delayed coker heater with a decoupled cell arrangement is disclosed. The delayed coker heater comprises, a convection section comprising at least two convection heater cells, and a radiation section comprising at least two radiation heater cells. Further, a flue gas duct is configured for fluid communication between the radiation section and the convection section. The decoupled cell arrangement comprises a first cell arrangement comprising a first radiation heater cell and a first convection heater cell and a second cell arrangement comprising a second radiation heater cell and a second convection heater cell. A plurality of shut-off blinds being configured to decouple the first cell arrangement and the second cell arrangement.
[0016] In an embodiment of the present disclosure, the first cell arrangement and the second cell arrangement are configured for heating a coker feedstock.
[0017] In an embodiment of the present disclosure, the coker feedstock is preheated in the convection section by hot flue gases from the radiation section.
[0018] In an embodiment of the present disclosure, the radiation section comprises a plurality of heating tubes positioned centrally in the radiation heater cell.
[0019] In an embodiment of the present disclosure, the delayed coker heater comprises a support structure configured to support the plurality of heating tubes inside the radiation heater cells.
[0020] In an embodiment of the present disclosure, the delayed coker heater comprises a plurality of burners located on a radiation section floor. The plurality of burners is configured to heat the plurality of heating tubes.

[0021] In an embodiment of the present disclosure, the convection section comprises a shield section and an extended surface tube section.
[0022] In an embodiment of the present disclosure, the shield section includes a plurality of bare tubes, and the extended surface tube section includes a plurality of studded or finned tubes.
[0023] In an embodiment of the present disclosure, the delayed coker heater comprises a stack to release exhaust flue gases from the convection section into the atmosphere.
[0024] In another non-limiting embodiment, a process of heating the coker feedstock in the delayed coker heater is disclosed. The process comprises generating heat by combustion of a fuel with air in the plurality of burners and heating the coker feedstock present in the heating tubes by the surrounding flue gases. The process further includes transferring the flue gases from the radiation section to the convection section through the flue gas duct and preheating the coker feedstock by the hot flue gases coming from the radiation section through the convective mode of heat transfer. Lastly, exhausting the flue gases through the stack into the atmosphere after transferring heat in the convection section.
[0025] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
[0026] BRIEF DESCRIPTION OF DRAWINGS
[0027] The novel features and characteristics of the disclosure are set forth in the description. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to

the following description of an illustrative embodiment when read in conjunction with the accompanying drawings. One or more embodiments are now described, by way of example only, with reference to the accompanying drawings wherein like reference numerals represent like elements and in which:
[0028] FIG. 1 illustrates a schematic view of an existing 2-pass Coker Heater with common convection and separate radiation firebox for each pass, according to the prior art.
[0029] FIG. 2 depicts a schematic view of the decoupled twin cell coker heater, according to an embodiment of the present disclosure.
[0030] Skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
[0031] DETAILED DESCRIPTION
[0032] While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the figures and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and the scope of the disclosure as defined by the appended claims.
[0033] Before describing in detail embodiments, it may be observed that the novelty and inventive step that are in accordance with the present disclosure resides in a decoupled twin cell arrangement for delayed coker heaters. It is to be noted that

a person skilled in the art can be motivated from the present disclosure and modify the various constructions of the proposed invention. However, such modification should be construed within the scope and spirit of the disclosure. Accordingly, the drawings are showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
[0034] The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such setup or device. In other words, one or more elements in a system or apparatus proceeded by "comprises... a" does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.
[0035] Reference will now be made to the exemplary embodiments of the disclosure, as illustrated in the accompanying drawings. Wherever possible same numerals will be used to refer to the same or like parts.
[0036] Referring now to the drawings in detail, FIG. 2 illustrates a decoupled twin cell arrangement for a delayed coker heater (10) according to an embodiment of the present disclosure. The delayed coker heater (10) having decoupled twin cell arrangement for heating a coker feedstock (synonymously referred to as hydrocarbon fluid) is configured. The delayed coker heater (10) is comprised of two heating sections, a convection section (12) configured to provide convective heat to the coker feedstock as it enters the coker heater and a radiation section (11) which further heats such feedstock, by predominantly radiant heating means. The convection section (12) comprises at least two convection heater cells (12a, 12b). The radiation section (11) comprises at least two radiation heater cells (11a, lib) corresponding to each of the at least two convection heater cells (12a, 12b). Further, a plurality of flue gas ducts (17a, 17b), each catering to individual radiation heater

cells (11a, lib) are configured for fluid communication between each radiation heater cell (11a, 1 lb) with the corresponding convection heater cell (12a, 12b). The decoupled twin cell arrangement comprises a first cell arrangement (23) comprising a first radiation heater cell (11a) and a first convection heater cell (12a) and a second cell arrangement (24) comprising a second radiation heater cell (1 lb) and a second convection heater cell (12b). A plurality of shut-off blinds (18a, 18b) is configured to decouple the first cell arrangement (23) with the second cell arrangement (24).
[0037] The radiation section (11) is a refractory-lined enclosure where the feedstock is heated primarily by the radiant mode of heat transfer. In accordance with a preferred embodiment, the radiation section (11) comprises two coker heater cells (11a, lib). The radiation coke heater cells (11a, lib) in the delayed coker heater (10) are generally a box type. A horizontally positioned heating tubes (15) are positioned centrally in the radiation section (11) with a plurality of burners (16a, 16b) firing the tubes from both sides. In a preferred embodiment, the heating tubes (15) are double-fired tubes and are generally represented as a serpentine coil placed horizontally along the center of the radiation coke heater cells (11a, 1 lb). A support structure (not shown) is configured to support the horizontally positioned heating tubes (15) inside the radiation heater cells (11a, lib). Further, the plurality of burners (16a, 16b), each catering to individual radiation heater cells (11a, lib) is located on the corresponding radiation section floor (25a, 25b) for firing in the radiation section (11). In an embodiment, the burners (16a, 16b) are positioned on both sides of the double-fired heating tubes (15) so as to be capable of providing heat from both sides to the heating tubes (15). In an embodiment, the burners (16a, 16b) are capable of either 100% fuel oil firing or for 100% fuel gas firing or any combination of these.
[0038] The coker feedstock is routed through the heating tubes (15) and receives heat from surrounding very high-temperature flue gases. The heat is generated by the combustion of a fuel with air in the burners (16a, 16b). The burners (16a, 16b) are generally arranged in rows on both sides of the heating tubes (15) for better heat

distribution. The flue gases from the radiation section (11) are then routed to the convection section (12), which is placed on top of the radiation section (11). It is to be noted that in the proposed configuration, the first cell arrangement (23) and the second cell arrangement (24) are configured for 2-passes of the delayed coker heater (10) as shown in FIG. 2. The operation of one cell arrangement does not affect the other cell arrangement. The flue gases flow from the radiation section (11) to the convection section (12) through the flue gas ducts (17a, 17b).
[0039] The convection section (12) is configured to provide convective heat to the coker feedstock as the coker feedstock enters the delayed coker heater (10). The coker feedstock is counter-currently heated by the hot flue gases coming from the radiation section (11) through a convective mode of heat transfer. Due to the high operating temperatures in the radiation section (11), a lower part of the convection section (12) is configured to have a shield section (19). The shield section (19) includes a plurality of bare tubes (21). The shield section (19) comprising of bare tubes (21) protects the subsequent section of the convective heater cells (12a, 12b) from receiving direct radiation from the radiation section (11). In an embodiment, the bare tubes (21) are of the same material and thickness as the plurality of heating tubes (15) inside the radiation heater cells (11a, lib). After the hot flue gases are passed through the shield section (19), it arrives at an extended surface tube section (20) of the convection section (12). The extended surface tube section (20) includes a plurality of finned or studded tubes (22). The finned or studded tubes (22) are configured to increase the heat transfer rate of the convection section (12).
[0040] The coker feedstock enters the convection section (12) first at the extended surface tube section (20) and then flows to the shield section (19) in the convection section (12) which consists of bare tubes (21). The coker feedstock is then transferred to the radiation section (11) through the double-fired heating tubes (15). Finally, after heating in the double-fired tubes (15), the coker feedstock leaves the delayed coker heater (10) and is routed for further processing in downstream equipment.

[0041] In the delayed coker heater (10), a stack (13) is configured to release exhaust flue gases from the convection section (12) into the atmosphere. Therefore, after transferring heat in the convection section (12), exhaust flue gases are finally routed through the stack (13) to the atmosphere. In an embodiment, the delayed coker heater (10) in which steam generation system or superheating or air preheating or any other heat recovery sections are present, the flue gases first releases the residual heat to the steam generation system or superheating section or air preheater or any other heat recovery section and then it is routed to the stack (13) for disposal to the atmosphere. In another embodiment, if the delayed coker heater (10) configures a Carbon Capture, Usage and Storage (CCUS) technology, the exhaust flue gases are routed accordingly, instead of disposal to the atmosphere.
[0042] In general, the coker feedstock flows from top to bottom in the delayed coker heater (10). The convection section (12) contributes to approximately 30-40% of the overall absorbed duty. In an embodiment, a residual heat from flue gas exiting the convection section (12) is further recovered in an air preheater, after which it is routed to the stack (13) for safe disposal to the atmosphere. It is to be noted that in the present disclosure, the radiation section (11), the convection section (12), and the stack (13) are in fluid communication with one another. The delayed coker heater system is lined with a refractory lined wall (14) and insulation to minimize heat loss.
[0043] A process of heating the coker feedstock in the delayed coker heater (10) is now disclosed. The process comprises generating heat by combustion of a fuel with air in the plurality of burners (16a, 16b) and heating the coker feedstock present in the double-fired heating tubes (15) by the surrounding flue gases. In an embodiment, the fuel used for combustion is either a fuel gas or fuel oil. The process further includes transferring the flue gases from the radiation section (11) to the convection section (12) through the flue gas duct (17a, 17b) and preheating the coker feedstock by the hot flue gases coming from the convection section (12)

through the convective mode of heat transfer. Lastly, after transferring heat in the convection section (12), exhaust flue gases are finally exhausted through the stack (13) into the atmosphere. In an embodiment, the delayed coker heater (10) in which steam generation system or superheating or air preheating or any other heat recovery sections are present, the flue gases first releases the residual heat to the steam generation system or superheating section or air preheater or any other heat recovery section and then it is routed to the stack (13) for disposal to the atmosphere. In another embodiment, if the delayed coker heater (10) configures a Carbon Capture, Usage and Storage (CCUS) technology, the exhaust flue gases are routed accordingly, instead of disposal to the atmosphere.
[0044] The decoupled configuration as disclosed in the present disclosure allows for cell isolation and undertakes decoking of one pass while simultaneously keeping the other pass in hydrocarbon operation. The shut-off blinds (18a, 18b) are configured for cell isolation by decoupling the first cell arrangement (23) with the second cell arrangement (24). Whenever a tube metal temperature (TMT) of the decoked coker heater (10) approaches its limit or the pressure drop exceeds the allowable value the cell isolation takes place. During decoking one pass, the delayed coker heater (10) can continue to operate at 50% of its capacity till the time one pass is being decoked. Thus, the unit's availability and profitability are maximized to a large extent as the unit remains in operation, although at reduced throughput only for a limited period. Accordingly, it is an advantage over complete unit shutdown which also presents safety challenges during frequent start-ups and shutdowns. In addition, the proposed configuration facilitates 50% process flow turndown by isolating one of the cells completely from the operation. Thus, without compromising on tube mass velocity, greater flexibility in operation is realized. This adds value to the refinery's flexibility of crude processing and goes a long way in resolving an age-old chronic problem. Further, the delayed coker heater (10) having decoupled twin cell arrangement for heating the coker feedstock is configured for longer run-length and improved turn-down capability.

[0045] It is to be understood that a person of ordinary skill in the art may develop a system of similar configuration without deviating from the scope of the present disclosure. Such modifications and variations may be made without departing from the scope of the present invention. Therefore, it is intended that the present disclosure covers such modifications and variations provided they come within the ambit of the appended claims and their equivalents.
[0046] Equivalents:
[0047] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
[0048] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation, no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be

interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances, where a convention analogous to "at least one of A, B, or C, etc." is used, in general, such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B." While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
[0049] Referral Numerals:
Reference Number Description

Prior art
1 Delayed coker heater
2 Radiation Section
2a, 2b Coker heater cells
3 Convection Section
4 Stack
5 Refractory lined walls
6 Double fired tubes
7 Burners
8 Common convection tube arrangement
9 Flue gas ducts
Present Invention
10 Delayed coker heater
11 Radiation Section
11a, lib Radiation heater cells
12 Convection Section
12a, 12b Convection heater cells
13 Stack
14 Refractory lined walls
15 Double fired heating tubes
16a, 16b A plurality of burners
17a, 17b A plurality of flue gas ducts
18a, 18b A plurality of shut-off blind

19 Shield section
20 Extended surface tube section
21 Shield tubes
22 Finned or studded tubes
23 First cell arrangement
24 Second cell arrangement
25a, 25b Radiation section floor

[0050] We claim:
1. A delayed coker heater (10) with a decoupled cell arrangement, comprising:
a convection section (12) comprising at least two convection heater cells (12a, 12b);
a radiation section (11) comprising at least two radiation heater cells (11a, lib);
a plurality of flue gas ducts (17a, 17b) for fluid communication between the radiation section (11) and the convection section (12); wherein
the decoupled cell arrangement comprises:
a first cell arrangement (23) comprising a first radiation
heater cell (11a) and a first convection heater cell (12a);
a second cell arrangement (24) comprising a second
radiation heater cell (1 lb) and a second convection heater cell (12b);
and
a plurality of shut-off blinds (18a, 18b) being configured to
decouple the first cell arrangement (23) and the second cell
arrangement (24).
2. The delayed coker heater (10) as claimed in claim 1, wherein the first cell
arrangement (23) and the second cell arrangement (24) are configured for
heating a coker feedstock.
3. The delayed coker heater (10) as claimed in claim 2, wherein the coker
feedstock is preheated in the convection section (12) by hot flue gases from
the radiation section (11).
4. The delayed coker heater (10) as claimed in claim 1, wherein the radiation
section (11) comprises a plurality of heating tubes (15) positioned centrally
in the radiation heater cells (11a, 1 lb).

5. The delayed coker heater (10) as claimed in claim 4, comprising a support structure configured to support the plurality of heating tubes (15) inside the radiation heater cells (11a, 1 lb).
6. The delayed coker heater (10) as claimed in claim 1, comprising a plurality of burners (16a, 16b) located on a radiation section floor (25a, 25b), wherein the plurality of burners (16a, 16b) are configured to heat the plurality of heating tubes (15).
7. The delayed coker heater (10) as claimed in claim 1, wherein the convection section (12) comprises a shield section (19) and an extended surface tube section (20).
8. The delayed coker heater (10) as claimed in claim 7, wherein the shield section (19) includes a plurality of bare tubes (21), and the extended surface tube section (20) includes a plurality of finned or studded tubes (22).
9. The delayed coker heater (10) as claimed in claim 1, comprising a stack (13) to release exhaust flue gases from the convection section (12) into the atmosphere.
10. A process of heating the coker feedstock in the delayed coker heater (10) as claimed in claims 1 to 9, the process comprising:

- generating heat by combustion of a fuel with air in the plurality of burners (16a, 16b);
- heating the coker feedstock present in the heating tubes (15) by the surrounding flue gases;
- transferring the flue gases from the radiation section (11) to the convection section (12) through the flue gas duct (17a, 17b);
- preheating the coker feedstock by the hot flue gases coming from the radiation section (11) through the convective mode of heat transfer;

- exhausting the flue gases through the stack (13) into the atmosphere after transferring heat in the convection section (12).