SINGLE FIRED MULTIPLE PASS VERTICAL CYLINDRICAL RADIANT SECTION CONFIGURATION FOR FIRED HEATERS
FIELD OF THE DISCLOSURE
The present disclosure relates to fired heaters. Particularly, but not exclusively, the present disclosure relates to a single fired multiple pass vertical cylindrical radiant section configuration for fired heaters in low pressure drop applications.
BACKGROUND OF THE DISCLOSURE
The information in this section merely provides background information related to the present disclosure and may not constitute prior art:
Fired heaters are one of the most critical equipment in a refinery. They are capital intensive and occupy huge plot space. They are also major energy guzzlers, consuming about 50-70% of total energy in any refinery, petrochemical, or process plant. Essentially, any fired heater is a refractory lined enclosure housing metal tubes that contain the fluid to be heated. Burners are used to produce heat through the combustion of fuel oil or fuel gas. The heat transfer takes place inside a fired heater via radiation and convection modes.
Conventional fired heater primarily consists of three sections: a radiant section, a convection section, and a stack. In radiant-convective fired heaters, process fluid (primary service) is preheated in the convection section before being introduced in the radiant section. While, in all radiant heaters, process fluid is heated entirely in radiant section and convection is used only for waste heat recovery i.e. secondary service. In both these cases, the primary process fluid is heated to the desired outlet temperature in radiant section only before it exits the fired heater. Stack is used for discharging the flue gases safely in the atmosphere. The stack can either be located on the convection section or separately at grade.

In fired heaters, the radiant section may consist of a box or a cylindrical type configuration. Convection section is placed on top of the radiant section. Generally, in services where a high process side pressure drop is available, vertical cylindrical configuration is a preferred choice over box type configuration. This is because vertical cylindrical heater configuration utilizes lesser space, has better heat flux distribution and is cost-effective compared to a box-type configuration.
However, conventional vertical cylindrical configuration of fired heater becomes impractical when allowable pressure drop is low. Vertical Cylindrical configuration typically consist of serpentine coils in radiant section for which the design is limited on number of passes (<=8 passes). For some low pressure drop, applications, vertical cylindrical heaters may also be configured with helical coils. However, such configuration has a limitation with respect to the number of passes that can be wrapped helically along the wall thus limits the extent of low pressure drop achievable. For low pressure drop applications, conventionally a box type configuration is used with multiple numbers of arbor coils /U-coils/I-coils in the radiant section which helps in achieving lower pressure drops.
Several units in refineries, petrochemicals, and process plants require a fired heater to provide desired outlet temperature with low allowable pressure drop. One such unit is Catalytic Reforming unit which produces high octane gasoline. A mixture of naphtha and hydrogen rich recycle gas is heated to ~540°C and the mixture is sent to a multi-stage catalytic reactor. The reaction is endothermic, and it is essential to provide heat input after every stage for preheating to reaction temperature. In such fired heaters, high process fluid outlet temperature is required, and the allowable pressure drop is low (-2-5 psi), the process fluid is heated entirely in the radiant section. Typically, a multi-cell fired heater is used wherein the radiant section is split in 3-4 radiant cells and a common convection section is placed on the top of radiant cells.

As shown in figure 1, the radiant section of conventional configuration consists of a box type configuration. The radiant section of conventional configuration is provided with multiple numbers of arbor coils /U-coils/I-coils arrangement. Each arbor coil serves as a single pass with connecting manifold at bottom / top. The process stream in gaseous phase is heated entirely in the radiant section and can be of a single fired or double fired configuration depending on the service. The convection is used primarily for waste heat recovery i.e., heating a secondary service. However, such radiant box type configuration occupies larger plot space, has inferior heat flux distribution, and is expensive compared to a vertical cylindrical radiant section configuration.
Accordingly, there is an immense need to provide a vertical cylindrical radiant section configuration for fired heaters in low pressure drop applications, where installation space is limited, and also one or more of the other drawbacks of the existing technology can be eliminated.
SUMMARY OF THE DISCLOSURE
One or more drawbacks of conventional radiant section configuration of fired heaters in low pressure drop service as described in the prior art are overcome and additional advantages are provided through a single fired, multiple pass, vertical cylindrical radiant section configuration as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be a part of the claimed disclosure.
In a preferred embodiment of the present disclosure, a vertical cylindrical radiant section configuration for fired heaters is disclosed. The vertical cylindrical radiant section comprising of a refractory lined radiant shell, an inlet manifold, an outlet manifold, a plurality of longitudinal tubes, and a floor. The plurality of longitudinal

plurality of longitudinal tubes is positioned alongside the periphery of the vertical cylindrical radiant shell. The floor is provided at the bottom of the vertical cylindrical radiant shell. Further, the plurality of burners is placed on the floor.
In an embodiment, each tube of the plurality of longitudinal tubes comprising a first end and a second end, the first end and the second end are configured to couple the inlet manifold with the outlet manifold.
In an embodiment, each tube of the plurality of longitudinal tubes is parallel to another tube of the plurality of longitudinal tubes.
In an embodiment, each tube of the plurality of longitudinal tubes is an individual pass configured to permit the lower pressure drop.
In an embodiment, the plurality of longitudinal tubes is spaced at equidistance and spacing between the tubes is based on the ratio of effective radiant tube length and tube circle diameter.
In an embodiment, the plurality of burners is configured for development of flue gas recirculation patterns.
In an embodiment, the inlet manifold and the outlet manifold comprising circular shapes. The inlet manifold is configured to distribute the fluid in the plurality of longitudinal tubes and the outlet manifold is configured to collect the fluid from the plurality of longitudinal tubes.
In an embodiment, the inlet manifold is placed on the top of the vertical cylindrical radiant shell and, the outlet manifold is placed below the inlet manifold on the bottom of the vertical cylindrical radiant shell.

In an embodiment, the inlet manifold is placed on the bottom of the vertical cylindrical radiant shell and, the outlet manifold is placed above the inlet manifold on the top of the vertical cylindrical radiant shell.
In an embodiment, the fired heater has a vertical and cylindrical structure.
BRIEF DESCRIPTION OF FIGURES
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:
Figure 1 illustrates a conventional radiant section configuration for a single fired heater for low pressure drop application, in accordance with the prior art.
Figure 2 illustrates a schematic view of a single fired, multiple pass, vertical cylindrical radiant section configuration for fired heaters in low pressure drop applications, according to an embodiment of the present disclosure.
Figure 3 illustrates a schematic view of a fired heater in low pressure drop applications, according to an embodiment of the present disclosure.
Figure 4 illustrates a top view of a single fired, multiple pass, vertical cylindrical radiant section for a fired heater in low pressure drop applications, according to the embodiment of the present disclosure.

Skilled person in art 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.
DETAILED DESCRIPTION OF DISCLOSURE
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 forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure as defined by the appended claims.
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 single fired multiple pass vertical cylindrical radiant section configuration for fired heaters in low pressure drop application. 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 benefit of the description herein.
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.
Accordingly, it is an aim of the present disclosure to provide a single fired, multiple pass, vertical cylindrical radiant section configuration for fired heaters in low pressure drop applications.
Another aim of the present disclosure is to provide a single fired, multiple pass, vertical cylindrical radiant section configuration for fired heaters in low pressure drop applications wherein installation space is limited.
Another aim of the present disclosure is to provide a vertical cylindrical radiant section configuration for fired heater that provides uniform heat flux distribution and has a simpler burner arrangement with a superior flame view.
Yet another aim of the present disclosure is to provide a single fired, multiple pass, vertical cylindrical radiant section configuration for fired heater that is robust, economical, and reliable.
The present disclosure provides a radiant section configuration for fired heaters. Particularly, the present disclosure relates to a single fired multiple pass vertical cylindrical radiant section configuration for fired heaters in low pressure drop application.
The fired heater comprising a vertical cylindrical radiant section configured to support one or more components of the heater, a convection section mounted on the top of the vertical cylindrical radiant section and a stack is mounted on the convection section and configured to discharge the flue gases into the atmosphere. The convection section may be used for waste heat recovery. The convection section may be placed on the top radiant section and has tubes placed horizontally or in a perpendicular direction to flow of flue gas exiting the radiant section. The

heat transfer in the radiant section primarily occurs through high temperature radiation and by convection through cooled flue gases in the convection section placed atop the radiant section. The vertical cylindrical radiant section configuration comprising a refractory lined radiant shell, an inlet manifold, an outlet manifold, a plurality of longitudinal tubes and a plurality of burners. The plurality of longitudinal tubes is configured to connect the inlet manifold and the outlet manifold. The plurality of longitudinal tubes is positioned alongside the periphery of the vertical cylindrical radiant shell. The plurality of burners is disposed at the floor positioned at bottom of the vertical cylindrical radiant shell. The floor of the radiant section is termed as radiant floor. Herein, the terms "single fired multiple pass vertical cylindrical radiant section" and "radiant section" are used alternatively.
In low pressure drop applications such as a catalytic reforming unit where allowable pressure drop is -2-5 psi, the primary process fluid is heated entirely in the radiant section. Heat transfer in radiant section primarily occurs through high temperature radiation. In an embodiment of the present disclosure, the radiant section consists of a cylindrical section. In another embodiment of the present disclosure, the radiant section consists of box type section. In the radiant section, the plurality of tubes that carry the process fluid is placed vertically with respect to radiant shell. The radiant section consists of all bare tubes placed along the radiant shell. The radiant shell is refractory lined. The plurality of burners is placed at the radiant floor. The process fluid can enter the radiant section at top/bottom depending on the transfer line orientation through manifolds placed on top/bottom of the radiant section. The process fluid is distributed in the longitudinal tubes through inlet manifold. Heated process fluid is collected in the outlet manifold before being transferred further. Each longitudinal tube serves as a single pass which allows achieving low pressure drops. Process fluid outlet temperature is controlled by controlling the firing rate of burners depending on combined process fluid outlet temperature. In an embodiment of the present disclosure, the inlet and outlet manifold are circular in shape.

The figures are provided for the purpose of illustration only and should not be construed as limitations on the construction and mechanism of the present disclosure. Wherever possible, referral numerals will be used to refer to the same or like parts.
Referring to figure 3, the fired heater (100) comprising a vertical cylindrical radiant section (10) configured to support one or more components of the heater, a convection section (20) mounted on the top of the vertical cylindrical radiant section (10) and a stack (30) mounted on the convection section and configured to discharge the flue gases into the atmosphere. The convection section (20) comprising a plurality of convection inlets (22) and convection tubes (not shown), the convection section is configured to be utilized for waste heat recovery.
The stack (30) is used to discharge the flue gas safely into the atmosphere. In an embodiment, the fired heater (100) is a single fired multiple pass vertical cylindrical heater configuration for low pressure drop application specifically for limited installation space. The fired heater (100) has vertical and cylindrical structure. Thus, the fired heater (100) is also referred as single fired multiple pass vertical cylindrical heater. The fired heater is refractory lined.
Referring to figures 2 to 4, the vertical cylindrical radiant section (10) comprising a radiant shell (1), an inlet manifold (2), an outlet manifold (4), a plurality of longitudinal tubes (6) configured to connect the inlet manifold (2) and an outlet manifold (4), and a floor (9) is provided at the bottom of the vertical cylindrical radiant shell (1). The plurality of longitudinal tubes (6) is positioned alongside the periphery of the vertical cylindrical radiant shell (1). Further, a plurality of burners (8) is placed on the floor (9). The radiant shell (1) is a vertical cylindrical refractory lined shell.
The inlet manifold (2) and outlet manifold (4) are placed at top or bottom of the vertical cylindrical radiant shell (1). The inlet manifold (2) is configured to

distribute fluid in the plurality of longitudinal tubes (6) and the outlet manifold (4) is configured to collect fluid from the plurality of longitudinal tubes (6). In an embodiment, the inlet manifold (2) is placed on the top of the vertical cylindrical radiant shell (1) and, the outlet manifold (4) is placed below the inlet manifold (2) on the bottom of the vertical cylindrical radiant shell (1). In another embodiment, the inlet manifold (2) is placed on the bottom of the vertical cylindrical radiant shell
(1) and, the outlet manifold (4) is placed above the inlet manifold (2) on the top of the vertical cylindrical radiant shell (1). The plurality of longitudinal tubes (6) is provided to connect the inlet manifold (2) and outlet manifold (4). In one more embodiment, the inlet manifold (2) and outlet manifold (4) are having circular shapes. In another embodiment of the present disclosure, the inlet manifold (2) and outlet manifold (4) may have the same or different periphery. The inlet manifold
(2) and outlet manifold (4) may be made of suitable metallic material that can withstand high temperature.
The plurality of longitudinal tubes (6) comprising a first end (6a) and a second end (6b) wherein the first end (6a) and the second end (6b) are configured to couple with the inlet manifold (2) and the outlet manifold (4). Each tube of the plurality of longitudinal tubes (6) is parallel to another tube of the plurality of longitudinal tubes (6). The longitudinal tubes (6) act as individual passes configured to permit the lower pressure drop in the absence of return bends. Thus, the use of longitudinal tubes (6) eliminates the use of serpentine coils or helical wrapped coil configuration. The cylindrical configuration also saves the space required for the execution of the radiant section. The plurality of longitudinal tubes (6) is placed at equidistance. In an embodiment, the spacing between the tubes may be decided based on the resulting H/D ratio (wherein H is the effective radiant tube length and D is the tube circle diameter) limitations as per API 560. In one more embodiment, the plurality of tubes may be made of suitable metallic material that can withstand high temperature.

The plurality of burners (8) is placed at the radiant floor (9). The plurality of burners (8) is configured for development of flue gas recirculation patterns that leads to uniform radiant heat flux distribution inside the heater. The number of burners (8) is decided based on firing duty requirement and type of burner to be installed. The burner-burner and burner-tube clearances shall be controlled in accordance with the API 560 guidelines.
Example
An interheater-2 radiant section design in a multi-cell box type heater for an existing CCRUnit is considered for evaluation with single multiple pass vertical cylindrical radiant section configuration as disclosed in the present disclosure. The radiant section of this inter-heater is to be designed to heat 79,560 kg/hr of process fluid from an inlet temperature of 444.2°C to an outlet temperature of 514.7°C. The allowable coil pressure drop is 0.27 kg/cm2. The allowable average radiant heat flux is 24,500 MMkcal/hr/m2 for single fired configuration.
In the conventional box type radiant section configuration as shown in figure 1, the process fluid enters from bottom inlet manifold and splits into individual passes. Process fluid is collected in the outlet manifold placed at the bottom of the radiant section. The radiant section consists of 36 nos. of arbor coils or passes with a tube size of 3" NPS Sch. 40. Each arbor coil consists of two straight tubes of 7.0 m plus hoop with diameter of 3.7 m. The tubes are placed at a centre-centre spacing of 203.2 mm. The inside refractory lining dimensions of vertical box are 35 ft (height) x 17.38 ft (width) x 25.91 ft. (length). The calculated inside refractory lining plot area is -450 ft2. The other process and mechanical parameters are described in Annexure-I & Annexure-II for reference.

Annexure- I

Parameter Unit Conventional Design Aspects Present Disclosure Aspects
Process Duty MMkcal/hr 4.868 4.868
Flow Rate kg/hr 79,560 79,560
Inlet Temperature °C 444.2 444.2
Inlet Pressure kg/cm2(g) 4.2 4.1
Outlet Temperature °C 514.7 514.7
Outlet Pressure kg/cm2(g) 3.93 3.93
Coil Pressure Drop kg/cm2 0.27 0.17
Radiant Section
Radiant Duty MMkcal/hr 4.868 4.868
Radiant Heat Duty % 100 100
Radiant Heat Transfer Area m2 199.34 198.7
Average Rad. Section Heat Flux kcal/h.m2 24,420 24,500
Max Rad. Section Heat Flux kcal/h.m2 53,960 56,595
Fluid Mass Vel. in Rad. Sec. lb/sec-ft2 26.4 24
Bridge Wall Temperature °C 810 817
Max. Rad. Tube Metal Temperature °c 615 618
Combustion
Excess Air % 25 25
Fuel LHV Kcal/kg 9720 9720
Firing Rate MMKcal/hr 8.7 8.76
Heat Loss % 2.5 2.5
Fuel Efficiency % 55.95 55.57

Annexure- II

Parameter Conventional Design Aspects Present Disclosure Aspects
Cell height, ft (inside insulation) 35 40
Cell Width (inside insulation), ft 17.38 16.51
Box Cell Length (inside insulation), ft 25.91 -
Inside Lining Cell Plot Area, ft2 450.32 214.1
Reduction in Plot Area, % - 52.5
Number of Tubes/Passes 36 86
Coil Size 3 NPS, Sch 40 2 NPS, Sch 40
Effective Tube Length, ft 77.8* 40
*Each radiant coil/pass consists of two straight tubes of 23 ft plus hoop with diameter of 12.14 ft.
In single fired, multiple pass, vertical cylindrical heater configuration as disclosed
in the present disclosure, the process fluid enters at top inlet manifold and splits
into individual passes before entering the radiant section. Process fluid is collected
in the outlet manifold placed at the bottom of the radiant section. The radiant section
consists of 86 nos. of straight tube placed along the circumference of vertical
cylindrical shell. The tube size is 2" NPS, Sch. 40. The effective tube length is 40
ft. and tube centre-centre spacing is 177.8 mm. Burners are placed at the radiant
floor. The calculated coil pressure drop is 0.17 kg/cm2. The inside refractory lining
dimension of vertical cylindrical radiant section is 40 ft (height) x 16.51ft
(diameter). The calculated inside refractory lining plot area for this is -215 ft2.
Accordingly, it is evidently clear that the design of present disclosure results into
heater plot spacing of-50% compared to a conventional vertical box type radiant
section design.

Thus, the present disclosure provides a single fired, multiple pass, vertical cylindrical radiant section for fired heaters in low pressure drop application. The fired heater as disclosed in suitable for operation at low pressure drop. The single 5 fired, multiple pass, vertical cylindrical radiant section is simple in construction, and provides uniform heat flux distribution. The single fired, multiple pass, vertical cylindrical radiant section may save up to 50% of the plot space as compared to the conventional box heater configuration. Thus, the single fired, multiple pass, vertical cylindrical radiant section of present disclosure, overcomes the limitation of low 10 installation space. In addition, the present disclosure provides has a simple burner arrangement with a superior flame view. Further, the single fired, multiple pass, vertical cylindrical radiant section of present disclosure is robust, economical, and is easily serviceable.
EQUIVALENTS:
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the description. Descriptions of well-known components and processing techniques are omitted so
as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such
adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be

understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within 5 the spirit and scope of the embodiments as described herein.
Throughout this specification the word "comprise'", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the 10 exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the 15 disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters 20 form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions 25 or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

We Claim:
1. A vertical cylindrical radiant section configuration for a fired heater, the vertical
cylindrical radiant section (10) comprising of:
a refractory lined radiant shell (1);
an inlet manifold (2);
an outlet manifold (4);
a plurality of longitudinal tubes (6) configured to connect the inlet
manifold (2) with the outlet manifold (4), the plurality of
longitudinal tubes (6) is positioned alongside the periphery of the
vertical cylindrical radiant shell (1);
a floor (9) provided at the bottom of the vertical cylindrical radiant
section (10); and
a plurality of burners (8) placed on the floor (9).
2. The vertical cylindrical radiant section configuration (10) as claimed in claim 1, wherein each tube of the plurality of longitudinal tubes (6) comprising a first end (6a) and a second end (6b), the first end (6a) and the second end (6b) are configured to couple the inlet manifold (2) with the outlet manifold (4).
3. The vertical cylindrical radiant section configuration (10) as claimed in claim 1, wherein each tube of the plurality of longitudinal tubes (6) is parallel to another tube of the plurality of longitudinal tubes (6).
4. The vertical cylindrical radiant section configuration (10) as claimed in claim 1, wherein each tube of the plurality of longitudinal tubes (6) is an individual pass configured to permit the lower pressure drop.
5. The vertical cylindrical radiant section configuration (10) as claimed in claim 1, wherein the plurality of longitudinal tubes (6) is spaced at equidistance and spacing between the tubes is based on ratio of effective radiant tube length and tube circle diameter.

6. The vertical cylindrical radiant section configuration (10) as claimed in claim 1, wherein the plurality of burners (8) is configured for development of flue gas recirculation patterns.
7. The vertical cylindrical radiant section configuration (10) as claimed in claim 1, wherein the inlet manifold (2) and the outlet manifold (4) comprising circular shape, the inlet manifold (2) is configured to distribute fluid in the plurality of longitudinal tubes (6) and the outlet manifold (4) is configured to collect fluid from the plurality of longitudinal tubes (6).
8. The vertical cylindrical radiant section configuration (10) as claimed in claim 1, wherein the inlet manifold (2) is placed on the top of the vertical cylindrical radiant section (10) and, the outlet manifold (4) is placed below the inlet manifold (2) on the bottom of the vertical cylindrical radiant shell (1).
9. The vertical cylindrical radiant section configuration (10) as claimed in claim 8, wherein the inlet manifold (2) is placed on the bottom of the vertical cylindrical radiant shell (1) and, the outlet manifold (4) is placed above the inlet manifold (2) on the top of the vertical cylindrical radiant shell (1).
10. The vertical cylindrical radiant section configuration (10) as claimed in claim 1, wherein the fired heater has vertical and cylindrical structure.