FIELD OF THE DISCLOSURE

The present application generally relates to the field of industrial processes. Particularly, but not exclusively, the present disclosure relates to the construction and arrangement of air preheat ducting of fired heater systems. More particularly, the present disclosure relates to an air distribution duct system for fired heater systems.
BACKGROUND OF THE DISCLOSURE
The information in this section merely provides background information related to the present disclosure and may not constitute prior art(s).
Fired heaters play a crucial role in heating process fluids in most industrial applications. Out of the various kinds offered heaters available, VC (vertical cylindrical) type heaters are the most preferred for absorbed duty less than 35-40 MM kcal/hr and depending on other factors such as the severity of service / type of service.
To improve the fuel efficiency, APH (Air Preheat) systems may be used wherein cold air is preheated by the flue gas exiting the fired heater and the resulting hot air is supplied through hot air ducts to the fired heater burners. Burners in a vertical cylindrical heater are mounted on the heater floor in a circle, nearer to the heater center to avoid flame impingement on the heater tubes located along the cylindrical wall. The burner air distribution duct distributes the hot air uniformly to the multiple burners. In alternate arrangements, the burner air distribution duct for the Vertical Cylindrical Fired heater is horseshoe type with a reducing cross section after each burner as shown in Fig. 1. As shown in Fig. 1, the burner finger duct connects the burner to the burner air distribution duct. Due to the high temperature at the burner air distribution duct, expansion of the ducts takes place. If these expansions are restricted, the resulting thermal stresses can deform the duct and cause thermal load

on the connected burner which is highly undesirable and can even affect the burner performance and in extreme case led to heater failure.
To avoid this problem, expansion joints are provided in the burner finger ducts to isolate burners from the thermal expansion of the ducts, as the pull from the duct system can tilt the burners leading to serious consequences like flame impingement on the heater tubes.
As shown in Fig. 2, generally, alternate burner air distribution duct system comprises at least one expansion joint (11) in each burner finger duct. The burner air distribution duct has a generally horseshoe shaped (12) configuration with reducing cross sectional area after each burner. In the alternate system, the expansion joints (13) are provided before the air entry into the Air Delivery Duct of burner air distribution duct as well as in the burner finger ducts.
Although these expansion joints are successful in absorbing the thermal expansions, there are some inherent disadvantages associated with these expansion joints. The expansion joints are a potential source of leakage. The expansion joints are also expensive and add to the cost of the construction. In addition, expansion joints are long lead items and put on hold the duct fabrication process causing a waste of time and resources.
Further, in conventional arrangements (horse-shoe type), to make near uniform distribution of flow of air to each burner generally Baffle plate, Guide vanes, Deflector plates, Orifice plates or similar arrangement (14) are required to be provided based on numerical analysis which results in complex and expensive duct system.
Therefore, there is a need in the art to provide air distribution duct system for fired heater systems that is devoid of limitations associated with the existing burner air

distribution arrangements. The present disclosure is directed to overcome one or more limitations stated above or any other limitations associated with the prior art.
SUMMARY OF THE DISCLOSURE
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.
In one non-limiting embodiment of the present disclosure, an air distribution duct system for a fired heater system. The fired heater system comprises an air supply means, and a plurality of burners disposed in the heater. The air distribution duct system comprising an air delivery duct in fluid communication with the air supply means at one end for receiving the air, comprising a plurality of openings disposed at spaced points along the periphery of the air delivery duct; and a plurality of distribution ducts comprising a receiving end and a delivering end, the receiving ends of plurality of distribution ducts are placed at the openings of the air delivery duct and configured to supply the air from the air delivery duct to the plurality of burners via delivery end of the distribution ducts.
In an embodiment of the present disclosure, the air distribution duct system comprising at least one sliding support to allow thermal expansion of the air distribution duct system.
In an embodiment of the present disclosure, openings are provided at inner wall of the air delivery duct and, said opening are disposed equidistantly or symmetrically spaced along the periphery of the air delivery duct.

In an embodiment of the present disclosure, the air distribution duct system comprising at least one fixed support provided at the delivery end of the plurality of distribution ducts to prevent thermal load on the plurality of burners.
In an embodiment of the present disclosure, the sliding supports are provided at regular intervals to allow outward thermal expansion of the air distribution duct system.
In an embodiment of the present disclosure, the sliding support having first end of sliding support which is provided at air delivery and/or distribution duct and second end is configured to engage with plurality of mountings provided at the structure of the fired heater system.
In an embodiment of the present disclosure, second end of sliding support is configured to engage with a mounting provided at air delivery and/or distribution duct, whereby mounting comprising a slotted hole /or by any other means extended along the length of the distribution duct, the length of the hole is based on the allowed thermal expansion of the duct system.
In an embodiment of the present disclosure, the distributions duct comprising a flexible joint detail for accommodating thermal expansion between the air delivery duct and each of the distribution duct.
In an embodiment of the present disclosure, the flexible joint detail can be selected from a tapered section, Lesser thick Stainless-steel panel, lesser thick Stainless Steel Bend Plate, and combination thereof.
In an embodiment of the present disclosure, the air distribution duct system comprising an expansion joint disposed before an inlet of the air delivery duct.

In an embodiment of the present disclosure, the structure of the air distribution duct system is a wagon wheel structure.
In an embodiment of the present disclosure, the air delivery duct having a uniform cross section.
In an embodiment of the present disclosure, wherein the fired heater system is vertical cylindrical heater.
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.
BRIEF DESCRIPTION OF DRAWINGS
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:
FIG. 1 illustrates a schematic view of the burner air distribution duct system existing in the prior-art.
FIG. 2 illustrates a sectional view of the burner air distribution duct system existing in the prior-art.

FIG. 3(a) & (b)illustrates a schematic view of the air distribution duct system in accordance with an embodiment of the present disclosure.
FIG. 4 illustrates a sectional view of the air distribution duct system in accordance with an embodiment of the present disclosure.
FIG. 5(a), (b) & (c) illustrates schematic views of flexible joint details of the air delivery ducts and distribution ducts of air distribution duct system in accordance with another embodiment of the present disclosure.
FIG. 6 illustrates schematic and sectional views of fixed support of the air distribution duct system in accordance with an embodiment of the present disclosure.
FIG. 7 illustrates schematic and sectional views of sliding support of the air distribution duct system in accordance with an embodiment of the present disclosure.
FIG.8 illustrates details of sliding support in accordance with an embodiment of the present disclosure.
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.
DETAILED DESCRIPTION
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.
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 an air distribution duct system of a fired heater system. It is to be noted that a person skilled in 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.
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 an air distribution duct system of a fired heater system.
Another aim of the present disclosure is to provide an air distribution duct system that eliminates the limitation of using expansion joints.

Yet, another aim of the present disclosure is to provide an air distribution duct system featuring unique capability to self-absorb thermal expansion without use of expansion joints and near uniform air distribution to burners for enhancing heater performance.
Yet, another aim of the present disclosure is to provide an air distribution duct system that has a simple construct, is easy to maintain and has an increased life.
Accordingly, the present disclosure provides an air distribution duct system for a fired heater system. The fired heater system comprising a radiant section, a convection section, an air supply means, a plurality of burners and a stack configured to discharge the flue gases into the atmosphere. In another embodiment of the present disclosure, the fired heater has vertical and cylindrical structure. In yet another embodiment of the present disclosure, the fired heater is refractory lined. The plurality of burners is disposed inside the heater and configured to mix the proper ratio of air and fuel to provide stable combustion with appropriately directed flames. The plurality of burners may be disposed at the floor positioned at bottom of the vertical cylindrical radiant section.
The fired heater comprises an air Preheater (APH). In an embodiment of the present disclosure, the air Preheater is fin tube heat exchanger and used for preheating the air which is fed to the fired heater systems for combustion of fuels.
The air supply means may be a forced draft fan which is configured to receive cold air from atmosphere and transmit the same to air preheater in which the heat exchange of cold air with waste flue gases takes place. Subsequently the draft fan sends the hot air towards air distribution system through a ducting arrangement.
The air distribution duct system comprising an air delivery duct in fluid communication with the air supply means at one end for receiving the air. The duct system further comprising a plurality of openings disposed at spaced points along

the periphery of the air delivery duct and a plurality of distribution ducts comprising a receiving end and a delivering end. The receiving ends of plurality of distribution ducts are placed at the openings of the air delivery duct and configured to supply the air from the air delivery duct to the plurality of burners via delivery end of the distribution ducts. The openings are provided at inner wall of the air delivery duct and, said opening are disposed equidistantly or symmetrically spaced along the periphery of the air delivery duct.
The air distribution duct system comprising at least one sliding support to allow thermal expansion of the air distribution duct system and at least one fixed support provided at the delivery end of the plurality of distribution ducts to prevent thermal load on the plurality of burners.
The air distribution duct system further comprising a flexible joint detail for accommodating thermal expansion between the air delivery duct and each of the distribution duct.
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.
According to an embodiment of the present disclosure, as shown in Figs. 3-7, an air distribution duct system (100) is provided for fired heater systems. The fired heater system comprising a radiant section, a convection section, an air supply means, a plurality of burners (110) and a stack.
Referring to figure 3 (a) and (b), the air distribution duct system (100) comprising an air delivery duct (101) and a plurality of distribution ducts (105). The air delivery duct (101) is in fluid communication with the air supply means at one end for receiving the air. In an embodiment of the present disclosure, the one end of air delivery duct (101) defines an inlet for receiving the air from the air preheater through the ducting arrangement.

The air delivery duct (101) further comprising a plurality of openings (103) disposed at spaced points along the periphery of the air delivery duct (101). In an embodiment of the present disclosure, the plurality of openings (103) defines outlet for delivering the air. In an embodiment of the present disclosure, the air delivery duct (101) having a uniform cross section. In another embodiment of the present disclosure, the cross section of air delivery duct (101) is circular or rectangular.
The plurality of distribution ducts (105) comprising a receiving end (107) and a delivering end (109). The receiving ends (109) of plurality of distribution ducts (105) are placed at the openings (103) of the air delivery duct (101) and configured to supply the air from the air delivery duct (101) to the plurality of burners (110) via delivery end (109) of the distribution ducts. In an embodiment of the present disclosure, the openings (103) are provided at inner wall of the air delivery duct (101). In another embodiment of the present disclosure, the openings (103) are disposed equidistantly or symmetrically spaced along the periphery of the air delivery duct (101). In yet another embodiment of the present disclosure, the openings (103) are disposed within the available 360-degree angle of the air delivery duct (101).
Referring to figure 5 (a), (b) and (c), the distributions duct (105) comprising a flexible joint detail for accommodating thermal expansion between the air delivery duct (101) and each of the distribution duct (105). In an embodiment of the present disclosure, the flexible joint detail can be selected from a tapered section (121), Lesser thick Stainless-steel panel (123), lesser thick Stainless Steel Bend Plate (125) and combination thereof. The flexible joint detail is provided to reduce the stress due to the relative thermal displacement between the air delivery duct (101) and the distribution duct (105).
Referring to figure 6, the air distribution duct system comprising at least one fixed support (111) provided at the delivery end (109) of the plurality of distribution ducts

(105) to prevent thermal load on the plurality of burners. In an embodiment of the present disclosure, the fixed support (111) is disposed near to the delivery end (109) of the plurality of distribution ducts (105). The fixed support (111) ensures no movement or any thermal loads on the burners.
Referring to figures 2 and 7, the air distribution system (100) comprising at least one sliding support (113) to allow thermal expansion of the air distribution duct system (100). In an embodiment of the present disclosure, the sliding supports (113) are provided at regular intervals to allow radial outward thermal expansion of the air distribution duct system (100).
In an embodiment of the present disclosure, the sliding support (113) is a hanging type sliding support. The one end of sliding support (113) is provided at air delivery duct (101) and/or distribution duct (105) and another end is configured with the structure of the fired heater system. In an embodiment of the present disclosure, the mounting (115)or the heater structure comprising a slotted hole (117) extended along the length of the air delivery duct (101) and/or distribution duct (105). The length of the slotted hole (117) is based on the allowed thermal expansion of the air distribution duct system (100).
The system (100) is devoid of expansion joints in either of the air delivery duct (101) and the distribution ducts (105) and the shape of the air distribution duct system (100) is like a wagon wheel. Due to its shape no additional element such as baffle plate or similar arrangement is required to make the equal air flow per burner, as the system behaves like a self-correcting arrangement with no requirement of numerical analysis as done in alternate arrangements described earlier.
Referring to figure 4, the air distribution system (100) comprising an expansion joint (102) disposed before the inlet of the air delivery duct (101). The expansion joint (102) is provided to isolate the air distribution duct system from the ducting

arrangement of the system, so that the expansion ducting arrangement of the system is not transferred to the air delivery duct (101).
The system (100) forces it to expand radially outwards like a wagon wheel and the expansion of the duct system becomes predictable. The fixed support (111) near the burner inlet prevents any thermal loads on the burner. As the expansion is not restricted, no major thermal stress is generated in the system.
Example
The air distribution duct system (100) for the fired heater system is described below in detail after considering an example for the present embodiment in which the parameters of the duct system (100) in the fired heater system are studied.
GEOMETRICAL PARAMETERS:
Following geometrical parameters has been used for demonstration of the sample case are as tabulated:
MECHANICAL PARAMETERS:

Number of Burner in the system 8
Flow Area of the air delivery duct 0.932m2
Height x Width of the air delivery duct (I/S Plate) 0.990m X 0.940m
Flow Area of the distribution Duct 0.134m2
Height x Width of the distribution Duct (I/S Plate) 0.406m X 0.330m
Distance of air delivery center from the Wagon wheel system Center 4.815m
Table 1
PROCESS PARAMETERS:

Parameter Unit Design case Turn
Down
Case
Air Flow rate Kg/h 33500 14500
Temperature oC 260 12
Burner Pressure Drop mmwc 75 10
Density Of Air Kg/m3 0.66 1.24
The wagon wheel arrangement provides nearly uniform distribution of combustion air to the burner which is an important requirement to ensure uniform heat distribution within the heater firebox.
Accordingly, the system (100) is cost effective and the potential leakage points are reduced due to the elimination of multiple expansion joints. Another advantage associated with the present invention is that the burner is isolated from the duct expansion loads due to fixed supports very near to its inlet and there is no hold in the fabrication of the air distribution duct system (100) due to the long lead time of expansion joint procurement. Yet another advantage associated with the system is that it has a simple construct, is easy to maintain (because the expansion joints, if provided, need to be regularly inspected for leakage which is a difficult task as the external thermal insulation & cladding needs to be removed and replaced each time) and has an increased life.
The disclosure has been described herein, with reference to certain embodiments, in order to enable the reader to practice the disclosure without undue experimentation. However, a person having ordinary skill in the art will readily recognize that many of the components and parameters may be varied or modified

to a certain extent or substituted for known equivalents without departing from the scope of the disclosure. It should be appreciated that such modifications and equivalents are herein incorporated as if individually set forth. In addition, titles, headings, or the like are provided to enhance the reader's comprehension of this document and should not be read as limiting the scope of the present disclosure. 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.
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 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 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 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 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 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.

LIST OF REFERENCE NUMERALS

Expansion joint in each burner finger duct in prior art (11)
Burner air distribution duct in prior art (12)
Expansion joints in prior art (13)
An air distribution duct system (100)
Air delivery duct (101)
Expansion joint (102)
Openings (103)
Distribution Ducts (105)
Receiving end (107)
Delivering end (109)
Plurality of burners (110)
One fixed support (HI)
One sliding support (113)
Mounting (115)
Slotted hole (117)
Tapered section (121)
Stainless-steel panel (123)
Stainless Steel Bend Plate (125)

We Claim:

1. An air distribution duct system (100) for a fired heater system, wherein the
fired heater system comprising of an air supply means, and a plurality of burners
(110) disposed in the heater system; the air distribution duct system (100)
comprising:
an air delivery duct (101) in fluid communication with the air supply means at one end for receiving the air, comprising a plurality of openings (103) disposed at spaced points along the periphery of the air delivery duct (101); and
a plurality of distribution ducts (105) comprising a receiving end (107) and a delivering end (109), the receiving ends of plurality of distribution ducts (105) are placed at the openings (103) of the air delivery duct (101) and configured to supply the air from the air delivery duct (101) to the plurality of burners (110) via delivery end (109) of the distribution ducts.
2. The air distribution duct system (100) as claimed in claim 1, comprising at least one sliding support (113) to allow thermal expansion of the air distribution duct system (100).
3. The air distribution duct system (100) as claimed in claim 1, wherein openings (103) are provided at inner wall of the air delivery duct (101) and, said openings (103) are disposed equidistantly or symmetrically spaced along inner wall of the air delivery duct (101).
4. The air distribution duct system (100) as claimed in claim 1, comprising at least one fixed support (111) provided at the delivery end (109) of the plurality of distribution ducts (105) to prevent thermal load on the plurality of burners (110).
5. The air distribution duct system (100) as claimed in claim 2, wherein the sliding supports (113) are provided at regular intervals to allow outward thermal expansion of the air distribution duct system (100).

6. The air distribution duct system (100) as claimed in claims 2 and 5, wherein the sliding support (113) having a first end of sliding support which is provided at air delivery duct (101) and/or distribution duct (105) and second end is configured to engage with plurality of mountings provided at the structure of the fired heater system.
7. The air distribution duct system (100) as claimed in claim 6, wherein second end of sliding support (113) is configured to engage with a mounting provided at air delivery duct (101) and/or distribution duct (105), whereby mounting (115) comprising a slotted hole /or by any other means extended along the length of the air delivery duct (101) and/or distribution duct (105), the length of the hole is based on the allowed thermal expansion of the air distribution duct system (100) (100).
8. The air distribution duct system (100) as claimed in claim 1, wherein the distribution ducts (105) comprising a flexible joint detail for accommodating thermal expansion between the air delivery duct (101) and each of the distribution duct (105).
9. The air distribution duct system (100) as claimed in claim 8, wherein the flexible joint detail can be selected from a tapered section (121), a lesser thick Stainless-steel panel (123), a lesser thick Stainless Steel Bend Plate (125) and combination thereof.
10. The air distribution duct system (100) as claimed in claim 1, comprising an expansion joint (102) disposed before an inlet of the air delivery duct (101).
11. The air distribution duct system (100) as claimed in claim 1, wherein the structure of the air distribution duct system (100) is a wagon wheel structure.

12. The air distribution duct system (100) as claimed in claim 1, wherein the air delivery duct (101) having a uniform cross section.
13. The air distribution duct system (100) as claimed in claim 1, wherein the fired heater system is vertical cylindrical heater.