ATOMIZING NOZZLE FOR A COAL-TAR AIR COMBUSTION IN AN INDURATION FURNACE AT PELLET PLANT

TECHNICAL FIELD
[0001] The present disclosure relates to an atomizing nozzle for a coal-tar air combustion in an induration furnace at pellet plant.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Coal-tar is used as a fuel in a firing zone of an induration furnace at pellet plant to heat the green pellets to a certain temperature range. In the induration furnace, a combustion chamber of a coal tar burner is designed in circular shape protected by a refractory lining. Exhaust gases coming out of the combustion chamber heat the pellets moving on a traveling grate car through a downward draft and is recirculated back into the combustion chamber through down-coming ducts. However, the exhaust gases of combustion, passing through pellet bed and grate bars, collect the fine particles of iron ore which travel through the down-coming ducts and again recirculated back into the combustion chamber. The fine particles follow the streamlines of the high volume flow rate down-coming air and get sintered when they come in contact with the turbulent oscillating coal-tar flame. After sintering, fused particles get settled/deposited on the bottom wall of a refractory port of the combustion chamber. The deposited particles then get solidified as a slag layer and this is a major operational and maintenance issue of the induration furnace at the pellet plant.
[0004] Thus, the coal-tar flame oscillations caused by a high volume flow rate and momentum of secondary air from down-coming, and thereby frequently anchoring to a bottom refractory wall causes the iron dust particles to be sintered and settle down as the slag. The coal-tar flame oscillations anchoring to the refractory also causes higher thermal stresses and failure of the refractory bricks due to cracks during long term operation of the burner. To avoid this, the furnace has to be shut down regularly for the cleaning and maintenance of the refractory or for the complete relining of the burner port which significantly affects the operational performance and productivity of the induration furnace and pellet plant. The coal-tar flame oscillations are also caused by an inherent nozzle design which produces larger droplets and wider spray cone angles while atomization of the coal-tar fuel.
[0005] Therefore, there is a requirement of a novel atomizing nozzle design to generate a straight, narrow, and long flame with reduced oscillations.

OBJECTS OF THE DISCLOSURE
[0006] In view of the foregoing limitations inherent in the state of the art, some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed hereinbelow.
[0007] It is a general object of the present disclosure to provide an atomizing nozzle for a coal-tar air combustion in an induration furnace at a pellet plant.
[0008] It is an object of the present disclosure to provide a novel atomizing nozzle design to generate a straight, narrow, and long flame with reduced oscillations.
[0009] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY
[0010] This summary is provided to introduce concepts related to an atomizing nozzle for a coal-tar air combustion in an induration furnace at a pellet plant. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0011] The present disclosure relates to an atomizing nozzle for a coal-tar air combustion in an induration furnace at a pellet plant. The atomizing nozzle includes an air injection portion having multiple radially inclined air passages; an atomizing portion to receive a high-pressure injection of atomizing air flow from an annular air tube through multiple radially inclined air passages; a central fuel supply pipe for subjecting an incoming fuel therefrom to the primary break-up into droplets in the atomizing portion by the atomizing air flow injected at high velocity through the air passages; a divergent portion fluidly connected to the atomizing portion to receive the flow of the droplets for further atomization into finer droplets; and a nozzle tip with multiple outlet passages fluidly connected to the divergent portion for emanating a high velocity of the fuel in form the finer droplets.
[0012] In an aspect, the number of inclined interior passages and the diameter of each air passage are adapted to be varied so as to increase the velocity of the atomizing air flow for the breakup of the fuel into the finer droplets.
[0013] In an aspect, the central fuel supply pipe is having a smaller diameter in comparison to the diameter of a main coal tar pipe of a coal tar burner.
[0014] In an aspect, the atomizing portion, the central fuel supply pipe, the divergent portion, and the nozzle tip are connected by internal or external threading.
[0015] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and methods that are consistent with the subject matter as claimed herein, wherein:
[0017] FIG. 1 shows an actual image of a burner refractory port with iron ore slag deposited at a bottom, in accordance with the state of the art;
[0018] FIG. 2 shows a thermal image of the refractory port with the temperature at the bottom and a flame anchoring at the bottom, in accordance with the state of the art;
[0019] FIGS. 3A-3C show an oscillating flame at different instants of time from the transient computational fluid dynamics (CFD) simulation of a furnace, in accordance with the state of the art;
[0020] FIG. 4 shows an atomizing nozzle proposed in accordance with an embodiment of the present disclosure; and
[0021] FIGS. 5A-5C show a straight and steady flame at different time instants predicted from the transient CFD simulation of the furnace with the proposed atomizing nozzle in accordance with an embodiment of the present subject matter.

DETAILED DESCRIPTION
[0022] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0023] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0024] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, “consisting” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0025] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0026] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0027] Embodiments and/or implementation of the present disclosure relates to an atomizing nozzle for a coal-tar air combustion in an induration furnace at a pellet plant. The existing atomizing nozzle has been supplied by a furnace manufacturer or Original Equipment Manufacturer (OEM). The existing atomizing nozzle of the induration furnace coal-tar burner is adapted to atomize a coal-tar fuel into droplets just at an exit of a nozzle tip in which the fuel flowing in an axial direction is split or atomized into droplets by an atomizing air jet injected at high pressure at an angle of approximately 90°. These droplets generated along with the atomizing air is sprayed into a combustion chamber through an orifice. Due to the atomizing of the liquid fuel at the nozzle tip, the existing atomizing nozzle generates a wider spray cone angle and larger size droplets. The larger droplets and wider spray cone form a wider and oscillating flame in the combustion chamber. Also, the high volume flow rate secondary air from a downcomer deflects the flame towards a bottom refractory wall. FIG. 1 shows a fusion of the iron ore particles and formation of slag deposition on the bottom refractory wall. FIG. 2 shows a thermal image of the flame and a burner port refractory temperature profile as seen from an opposite side peep hole.
[0028] FIGS. 3A-3C show flame temperature contours with the existing atomizing nozzle at different instant of time predicted from the transient three dimensional (3D) computational fluid dynamics (CFD) analysis of the induration furnace combustion chamber with the existing nozzle.
[0029] To overcome the issues related with the existing atomizing nozzle, embodiments of the present disclosure relate to an atomizing nozzle as shown in FIG. 4. The atomizing nozzle proposed herein is developed to reduce the flame oscillations, to create a narrow, and long flame that eliminates the flame anchoring to the refractory wall at the bottom. This reduces the iron ore sintering which is caused by the iron dust particles flowing through the combustion chamber from the downcomer secondary air getting fused and settling on the bottom refractory due to self-weight. The atomizing nozzle proposed herein further has a reduced inner diameter of a central fuel supply pipe 7 compared to the prior art to increase the velocity of the fuel into a nozzle atomizing/mixing chamber having a primary break up zone or an atomizing portion 4. The fuel is coal tar in the present disclosure.
[0030] In an aspect, the central fuel supply pipe 7 is having a smaller diameter in comparison to the diameter of a main coal tar pipe 1 of the coal tar burner. That is, the main coal tar pipe 1 of the coal tar burner, originating from its header side is at a higher diameter and reduces in diameter towards the central fuel supply pipe 7 near the atomizing nozzle proposed herein The atomizing air flow from an annular tube 2 at higher pressure is injected into the atomizing portion 4 of the atomizing nozzle through multiple radially inclined interior air passages 3 formed at an air injection portion.
[0031] The fuel jet from the central fuel supply pipe 7 will be subjected to primary break up into the droplets by the atomizing air at high velocity injected from the inclined air passages 3, in the atomizing portion 4. The number of the inclined air passages 3 and the diameter of each air passage 3 can be varied to increase the velocity of air jet for the breakup of the fuel into smaller droplets. The small droplets can flow into a divergent portion 8, also called a secondary break up zone, of the atomizing nozzle, for further atomization into finer droplets.
[0032] Such design of the atomizing nozzle will generate the final fuel-air mixture with finer droplet size. When the mixture exits from nozzle outlet passages 5 on a nozzle tip 6, the spray cone angle will be less than the nozzle design of the conventional atomizing nozzle where the atomizing air injecting and atomizing the fuel just at the tip of the nozzle outlet passages 5. Due to the high velocity of the jet emanating from the nozzle outlet passages 5, the flame will be long and narrow as shown in FIGS. 5A-5C.
[0033] Thus, with an embodiment of the present disclosure, an atomizing nozzle design is proposed herein to generate finer droplets due to the primary and secondary breakup of fuel oil jet. In particular, the atomizing nozzle proposed herein can be fit to the existing burner with certain modifications and generates a smaller spray cone angle and a narrow long flame with reduced oscillations. This is accomplished by having an internal mixing chamber with a diverging portion incorporated to the atomizing nozzle which helps in the secondary breakup of the fuel jet into smaller droplets.
[0034] Furthermore, those skilled in the art can appreciate that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0035] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0036] While the foregoing describes various embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof. The scope of the present disclosure is determined by the claims that follow. The present disclosure is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

We claim:

1. An atomizing nozzle for a coal-tar air combustion in an induration furnace at a pellet plant, the atomizing nozzle comprising:
an air injection portion having multiple radially inclined air passages (3);
an atomizing portion (4) to receive a high-pressure injection of atomizing air flow from an annular tube (2) through the air passages (3);
a central fuel supply pipe (7) for subjecting an incoming fuel therefrom to primary break up into droplets in the atomizing portion (4) by the atomizing air flow injected at high velocity through the air passages (3);
a divergent portion (8) fluidly connected to the atomizing portion (4) to receive the flow of the droplets for further atomization into finer droplets; and
a nozzle tip (6) with multiple outlet passages (5) fluidly connected to the divergent portion (8) for emanating a high velocity of the fuel.

2. The atomizing nozzle as claimed in claim 1, wherein the number of the air passages (3) and the diameter of each air passage (3) is to be varied so as to increase the velocity of air jet for the breakup of the fuel into the smaller droplets.

3. The atomizing nozzle as claimed in claim 1, wherein the central fuel supply pipe (7) is having a smaller diameter in comparison to the diameter of a main coal tar pipe (1) of a coal tar burner.

4. The atomizing nozzle as claimed in claim 1, wherein the atomizing portion (4), the central fuel supply pipe (7), the divergent portion (8), and the nozzle tip (6) are connected by internal or external threading.