LOW NOX EMISSION BURNER AND OPERATING METHOD FOR REDUCING NOX FORMATION APPLIED TO IRON ORE PELLET SINTERING AND/OR ENDURING METHOD

Abstract

A burner (12) using the oxygen present in the descending flow (18) of gases, composed by a mixture of air with combustion products that circulates through the iron ore pelletizing furnace zones. The burner set (12) includes a fuel collector ring (24) equipped with fins (26) mounted on the inner part of the collector and further counts on a plurality of openings (30) for discharge of fuel gas. Said openings (30) make up a sequence of groups (32) aligned with each fin (26). The burner set (12) is inserted through the special window (16) and installed where the descending flow (18) needs to be heated, for example, from 850 to 1350° C. The fins (26) deflect part of the descending flow (18) and create the rotating effect in the gases in the furnace downcomer. The fuel gas jets discharged from the collector ring (24) are mixed with the flow of gases and burn in the descending flow current in a swirl. The even distribution of the fuel gas around the perimeter of the descending passage together with the descending flow swirling effect allows the quick mixing of the fuel gas with the descending oxygen flow and for this reason significantly reduces the NOx formation in the combustion zone.

Description

TECHNICAL FIELD OF INVENTION

The present patent of invention relates to low NOx emission burner and operating method for reducing NOx formation applied to iron ore pellet sintering and/or enduring method, more specifically a burner of the type used in industrial combustion for reducing NOx emission through the rapid mixing of fuel gas with the descending flow of oxidant before self-ignition and flame stabilization.

Said innovative burner integrates an operating method wherein the fuel gas jets discharged from the collector ring mix firstly with the oxidant and continue, in combustion, in a rotating movement, through the descending duct flow, also known as furnace downcomer. The even distribution of the fuel gas around the perimeter of the passage section of the downcomer, allied to the rotational effect of the downcomer flow allows the rapid mixing of fuel gas with oxygen diluted in this current.

HISTORY OF THE INVENTION

The nitrogen oxide gases NO and NO₂ (NOx) are typically formed during the combustion process, particularly industrial. The highest temperatures are observed around the stoichiometric zones of the flames and can reach 1925° C./3500 F. for the combustion of natural gas mixed with ambient air. The maximum thermal NOx is formed in these zones.

The above cited nitrogen oxides when transported through air and reacting with water, form nitric acid, affecting the entire natural cycle of the environment, contaminating soils, rivers and subterranean waters, reaching food chains, corroding metallic structures, historical monuments and buildings, among other inconveniences, as well as being able to cause the phenomenom called photochemical smog which corresponds to atmospheric pollution wherein a dark and poisonous cloud is formed consisting of smoke, fog, air, polluting gases and particulate matter.

The formation of NOx in burning processes depends on several factors, such as: fuel composition, system operation mode, burner design and combustion chamber. One of the determinant parameters of this pollutant is the presence of temperature peaks which occur in certain regions of the flame, for which reason the goal of many burner manufacturers and designers of combustion systems with low NOx emission is to reduce or eliminate the occurrence of said peaks.

During research in specialized databanks there were found documents that disclose burner models and pre-heating models for circulating air flows used in the iron ore pellet sintering process. Among the documents found there are foreseen documents JP2009235507A, AU2009272126B2, CH104114681B, JP2005060762A, U.S. Pat. No. 2,676,095A, KR10166506661, JP5458860B2, U.S. Pat. No. 8,961,650B2 and JP2008185054A.

Generally, the burners used in the sintering process and/or endurance of iron ore pellets use small quantities of primary air, provided by blower or fan, and the remaining oxidant that is necessary for the combustion reaction is obtained from the circulating hot gas flow, which is usually a mixture of hot air with combustion products. The oxygen content in this hot circulating flow is usually higher than 10% (volumetric basis). The staging of the injection of fuel gas is a commonly used technique for the control of NOx emissions, since it allows the dispersion of fuel gas inside the flame envelope, and thus reduces the temperature peaks in the flame and respective NOx formation. However, this technique does not allow a significant reduction of the NOx emissions in sintering furnaces and/or endurance of NOx iron ore pellets.

Firstly, the flame of the burner used in the process is formed by consuming oxidants at extremely high temperatures, around 850 to 1050° C.

In the second place, even with the staged injection of the fuel gas, for example, using lances surrounding the primary air jet, the burner flame has a large envelope shape being relatively wide and more or less long. The combustion reaction restricts the envelope volume, as, in this case, the envelope flame or jet type flame, always tends to present average higher temperature and thus higher NOx, in comparison with the reaction which occurs spread throughout the oven or furnace volume.

In the same manner, the I-Jet type burner provided by FCT Combustion—is an example of burners used in the iron ore pellet industries. This forms jet type flame, with the chemical combustion reaction concluded in the flame envelope formed in the front of the burner. The primary air and staging of fuel gas injection, in contact and mixed with the ambient furnace gases, form the flame, which can be longer or shorter, wider, or narrower. However, it is still a jet type flame, with high temperature. Due to the staging of the fuel gas injection, the average temperature of the flame can be reduced, which can help with the NOx reduction. However, the reduction is not significant, particularly in the process of iron ore pellet sintering and/or enduring at high temperature. This is largely due to the significant contribution of the high temperature of the oxidant used in combustion.

OBJECTIVES OF THE INVENTION

It is one purpose of the invention to present a low NOx emission burner and operating method for reducing NOx formation applied in iron ore pellet sintering and/or endurance which allows overcoming the disadvantages of the prior art.

It is another purpose of the invention to present a low emission NOx burner which comprises a fuel gas distribution and injection manifold, which is inserted in the descending channel of the sintering or iron ore pellet enduring furnace. This combination of fuel gas distribution together with the descending passage of the furnace configures the burner of this invention.

It is a further objective of this invention to present a low NOx emission burner which uses the oxygen present in the downcomer flow of hot gases, consisting mostly of hot air mixed to combustion products. This flow circulates through the zones of the iron ore pellet sintering and/or enduring furnace of the moving grate type. The flow of hot gases from the downcomer is directly heated by the burner flame to a temperature of around 1300° C./1400° C., necessary for the process of endurance of iron ore pellets. Thus, the function of this innovative burner is to heat the circulating flow to the temperature levels required for the process and have the NOx emission output as low as possible.

Another objective of this invention is to present a low NOx emission burner, which set includes the fuel gas collector manufactured in the shape of a circular ring and made, for example, from stainless steel or silicon carbide. The fuel gas collector is equipped with a set of fins mounted in the inner part of the collector. The fins present innovative special profile and are fixed to the collector so as to deflect the descending gas flow from the vertical movement with the addition of horizontal movement vector. This vector, together with the cylindrical shape of the descending channel, creates a rotating movement of the gases downstream the collector ring/fins set. The collector further comprises a plurality of fuel gas discharge openings. These openings form groups aligned with each fin. Each group can comprise, for example, from four to six fuel gas discharge openings which discharge gas against the wall of each fin. The fuel gas collector ring has at least one inlet, which is connected to the fuel gas supply system.

The burner set is inserted in the vertical passage of the furnace wherein the descending flow needs to be heated, for example from 900 to 1300° C., before entering the iron ore pellet moving grate. The fins deflect part of the descending flow and create the rotational flow effect in the vertical passage of the furnace. The descending vertical passage is necessary to create this swirling effect and allows in this manner the quick mixing of the fuel gas with oxidant before the occurrence of the combustion reaction. Therefore, the definition of the insertion place of the burner in the vertical passage is essential to achieve the desired result.

The new method, according to this invention, proposes that the fuel gas jets discharged from the collector ring mix predominantly first with the oxidant and next burn in the rotating descending flow current. The uniform distribution of the fuel gas around the perimeter of the passage of the downcomer allows the rapid mixing of the fuel gas with the descending flow diluted oxygen.

Thus, the temperature peaks are reduced. The descending flow gases are comprised mainly of oxygen (O₂), nitrogen (N₂), carbon dioxide (CO₂) and water vapor. (H₂O). The presence of these inert gases (CO₂, N₂ and H₂O) significantly reduces the adiabatic temperature of the combustion reaction. All these factors together can lead to a significant reduction in the NOx formation in the combustion zone.

DESCRIPTION OF THE FIGURES

In order to complement the present description so as to obtain a better understanding of the characteristics of the present invention and in accordance with a preferred practical embodiment of same, there is accompanying the description, attached, a set of drawings wherein, in an exemplified manner, although not limitative, the operation thereof is represented:

FIG. 1 discloses a side view in schematic elevation of the sintering and/or iron ore pellet enduring furnace with innovative window for insertion of a burner in a vertical passage;

FIG. 2 represents a top view of a burner set, represented inside the furnace cylindrical descending channel;

FIG. 3 illustrates a perspective view of the burner collector ring with the fins installed on the inner circumference of the collector;

FIG. 4 shows a side view ‘A’ indicated in FIG. 2 of the inner part of the gas collector ring of the burner and demonstrating the positioning of the fins;

FIG. 5 reveals a longitudinal sectional view on a plane through the middle of the fins to illustrate the positioning of the gas injectors relative to each fin;

FIG. 6 illustrates a view ‘B’ of the profile of the fin indicated in FIG. 4;

FIG. 7 shows the fins in perspective illustrating the most intense deflection effect of the descending flow; and

FIG. 8 shows a portion of the downcomer channel, wherein the burner is installed, to illustrate the swirling pattern of the burn flow in the channel.

DESCRIPTION OF THE INVENTION

The present patent of invention relates to a “LOW NOX EMISSION BURNER AND OPERATING METHOD FOR REDUCING NOX FORMATION APPLIED TO IRON ORE PELLET SINTERING AND/OR ENDURING METHOD”, more precisely, it relates to an industrial combustion type burner (12) and process for pelletizing iron ore, and more exactly, to the iron ore pellet sintering and/or enduring furnaces.

According to the present invention, said burner (12) is installed in the descending passage (14) of the furnace (FO) by means of the window (16), located on the upper portion of the descending passage (14). Said burner (12) elevates the temperature of the descending circulating flow (18) originating from the flue gas collector (20) to the required level before entering the moving grate (22) provided with iron ore pellets (22a). The burner (12) is comprised of a circular or rectangular section fuel gas collector ring (24). The outer diameter (D) of the ring (24) is smaller than the inner diameter (D′) of the descending passage (14).

The collector ring (24) is equipped with fins (26) (see FIGS. 2, 3 and 4) on the inner circumference thereof, oblique, in (α) angulation relative to the horizontal transversal place of the collector, which allows deflecting the descending flow and introducing horizontal velocity components to the same. Said (α) angulation promotes the speed vector to obtain tangential component and so that, in the cylindrical profile of the descending channel, there is generated the swirling or rotational effect.

The (α) deflection angle of the fin (26) can be from 30° to 60° relative to the horizontal transversal plane of the fuel gas collector ring (24). If the (α) angle is greater than 60°, the deflection and, in this manner, the rotational effect, will not be sufficiently intense to achieve the desired rapid mix of fuel gas with oxidant. On the other hand, if the (α) angle is less than 30°, the resistance to the descending flow (18) increases significantly resulting in less flow running along the fins (26) and more flow in the center of the descending channel (14).

The distance (K) between the fins (26), the length (L) of each fin (26) and number of fins (26) are determined to create the necessary descending flow rotating intensity (18) without significantly increasing the pressure loss through the burner (12) installed in the descending channel.

The determination of the three parameters (K), (L) and number of fins (26) depends on the diameter (D′) and transversal area of the descending channel (14) wherein the burner (12) is installed.

The larger the diameter (D′) of the channel (14), the larger will be the diameter (D) of the ring (24) of the burner (12) and consequently greater the number of fins (26).

The fuel gas collector ring (24) of the burner (12) is equipped with at least one inlet pipe (28) positioned orthogonally to the collector ring (24), which is connected to the fuel gas supply line. The fuel gas is injected in the hot air current (18) through a plurality of openings (30) (see FIG. 5). Said openings form aligned groups (32) and have the discharge thereof pointed in the direction of the wall of each aligned fin (26). Each group (32) can be formed by two up to eight openings (30), in this case we present a model with five openings for fuel jet discharge (34) in each fin passage (26). Part of the total descending flow (18) runs along the passage of the fin (26) mixing with the five fuel jets (34) and all together are deflected to create a rotating flow downstream the burner (12).

Each fin (26) (see FIGS. 4 and 6) is constructed as an ‘L’ shaped profile, with flap (26a) forming (β) angle 90° (see FIG. 6). This varies preferably between 45° and 90°. If the (β) angle exceeds 90°, the fuel gas jets (34) can partly escape the passage of the fin (26) and reduce the efficiency of the mixture. On the other hand, if this (β) angle is less than 45°, the fuel gas jets (34) can create unnecessary pressure fluctuations and possibly vibration of the burner (12). The choice of the dimension (N) of the fin (26) depends on the diameter (D′) and area of the descending flow (14), wherein the burner (12) is installed. The ratio of the dimensions (M)/(N) of each fin (26) is preferably between 0.25 and 0.5, if less than 0.25, the fuel gas jets (34) can escape from the passage of the fin (26), if greater than 0.5 the fin (26) will be heavier without any additional benefit to the burner.

As an option for best efficiency of the mixture, the discharge end (40) of each fin (26) can be cast so as to (see FIG. 7) deflect the descending flow (18) more horizontally, and, by doing this, promote higher rotation degree inside the cylindrical descending channel downstream of the burner (12).

The cylindrical descending channel (14) must be considered as being part of the burner (12). Part of the descending flow (18) deflected by the fins (26) is pre-mixed with the fuel gas and acquires rotating movement (42) along the cylindrical surface of the descending channel (14). In this region, with length (L) equal to approximately a diameter (D′) of the channel, the current is burned. The fuel gas is evenly distributed around the circumference (46) of this channel, the mixing occurs quickly with oxygen diluted in the inert gases, and, as a result, the temperature peaks reduce significantly, and the combustion reaction produces a very low NOx emission when compared to the prior art.

All the new and exclusive elements described above of the new model and burner method (12) of the rapid mixing allows the mixing of the gas jets (34) and descending flow oxidant (18) in a much more even manner and, therefore quicker, resulting in reduction of the average adiabatic temperature of the flame. Due to all these factors, the NOx output emission is much lower and less than that obtained with the prior art techniques.

It is certain that when the present invention is put in practice modifications relating to certain construction and shape details can be introduced, without this implying a departure from the fundamental principles which are clearly substantiated in the set of claims, being therefore understood that the terminology used does not have the purpose of limitation.

Claims

1. A LOW NOX EMISSION BURNER, comprising a burner for applying to heating process in iron ore pelletizing furnaces (FO) with low NOx emission comprising a collector ring with openings for mixing fuel gas with an oxidant and formation of flames for direct heating of a circulating gaseous medium; wherein the fuel gas discharge is executed through a collector ring provided with multiple openings for mixing the fuel gas with oxidant and flame formation; the collector ring being equipped with at least one input for fuel gas supply; said ring being, additionally, equipped with fins installed on the inner part of said collector in (α) angulation relative to a horizontal plane of the collector ring deflecting part of a descending flow of circulating hot air diluted with combustion gases originating from burning the fuel gas in a vertical direction to the horizontal resulting in a speed vector obtaining a tangential component and which in the cylindrical profile of a descending channel generates a rotation or a swirling effect.

2. The LOW NOX EMISSION BURNER, according to claim 1, wherein fuel gas collector comprises a ring shape, manufactured with a circular or rectangular section, the outer diameter (D) of the collector ring being reduced relative to the inner diameter (D′) of a descending passage.

3. The LOW NOX EMISSION BURNER, according to claim 1, wherein the deflection angle (α) of the fin being between 30° to 60° relative to the horizontal transversal plane of the fuel gas collector ring.

4. The LOW NOX EMISSION BURNER, according to claim 1, wherein each fin is modelled in ‘L’ profile with a flap in 90° (β) angle.

5. The LOW NOX EMISSION BURNER, according to claim 4 wherein the angle (β) varies from about 45° to 90°.

6. The LOW NOX EMISSION BURNER, according to claim 4, wherein the dimension (N) of the fin is related to the diameter (D′) and the area of the descending channel, wherein the burner is installed.

7. The LOW NOX EMISSION BURNER, according to claim 4, wherein the relation of the dimensions (M)/(N) of each fin are between 0.25 and 0.5.

8. The LOW NOX EMISSION BURNER, according to claim 4, wherein the distance (K) between the fins, the length (L) of each fin is determined to create an intensity of a descending swirling flow without significantly increasing the loss of charge through the burner installed in the descending channel; the determination of three parameters (K), (L) and number of fins depending on the diameter (D′) and descending channel area, wherein the burner is installed; the larger the diameter (D′) of the channel, the greater the diameter (D) of the ring of the burner and greater the number of fins.

9. The LOW NOX EMISSION BURNER, according to claim 4, wherein the shape of each fin is capable of being plane, curved, tubular or any other shape suitable for a better mixture of the fuel gas with the oxidant flow.

10. The LOW NOX EMISSION BURNER, according to claim 4, wherein the discharge of the fuel gas is positioned through the plurality of openings formed in groups, aligned, and with the discharges thereof pointed in the direction of the wall of each fin; each group of openings discharges the fuel jets in the direction of a single fin; there is a group of openings for each fin; part of the total descending flow runs along the passage of the fin mixing with the five fuel jets and all together are deflected so as to create a rotational flow downstream of the burner; each group having at least one opening, depending on the diameter of the collector ring, transversal section of the ring and number of fins installed.

11. The LOW NOX EMISSION BURNER, according to claim 1, wherein the cylindrical descending channel forms part of the burner; wherein part of the descending flow, is deflected by the fins, is pre-mixed with the fuel gas and acquires rotational movement along a cylindrical surface of the descending channel; wherein this region, has a length (L) equal to approximately a diameter (D′) of the channel, the fuel is burned; and wherein the fuel gas is evenly distributed around the circumference of this channel, the mixing occurs quickly with oxygen diluted in the inert gases, and, temperature peaks are reduced.

12. An OPERATING METHOD FOR REDUCING NOX FORMATION APPLIED TO IRON ORE PELLET SINTERING AND/OR ENDURING METHOD, according to claim 1, wherein said method comprising the steps: the fuel gas jets are discharged from the plurality of openings to be mixed with an oxidant flow which can be predominantly a flow of low or high temperature gases, which circulates, in the iron ore pellet furnace (FO) for heating the pellets during the sintering or hardening process;the fuel jets mixed with oxidant form a jet or jets of flame, which are mixing and directly heating a circulating process flow; andcirculating process flow, which is the descending flow in iron ore pelletizing furnace (FO), containing nitrogen, oxygen, carbon dioxide and water vapor are heated until the temperatures required by the process, continuing through the iron ore pellet bed, transferring the required heat for the occurrence of the necessary chemical reactions and physical transformations in the pellets.

13. The OPERATING METHOD FOR REDUCING NOX FORMATION APPLIED TO IRON ORE PELLET SINTERING AND/OR ENDURING METHOD, according to claim 11, wherein part of the descending flow is deflected, and runs through and between the passages of the fins, from vertical direction to horizontal direction, creating a swirling movement along the circumference of the cylindrical descending channel downstream of the burner ring.

14. The OPERATING METHOD FOR REDUCING NOX FORMATION APPLIED TO IRON ORE PELLET SINTERING AND/OR ENDURING METHOD, according to claim 11, wherein fuel gas is discharged from the openings of the collector ring in the form of multiple jets and directed to each deflection surface of the fin.

15. The OPERATING METHOD FOR REDUCING NOX FORMATION APPLIED TO IRON ORE PELLET SINTERING AND/OR ENDURING METHOD, according to claim 11, wherein fuel gas jets mix with the descending oxidant flow on the surface of the fin.

16. The OPERATING METHOD FOR REDUCING NOX FORMATION APPLIED TO IRON ORE PELLET SINTERING AND/OR ENDURING METHOD, according to claim 11, wherein the descending flow of oxidant pre-mixed with the fuel gas on the surface of the fin is discharged to the descending furnace channel (FO); wherein the rotational current is self-inflamed from the temperature of the process and the flames with rotational components are stabilized on the inner surface of the descending channel.

17. The OPERATING METHOD FOR REDUCING NOX FORMATION APPLIED TO IRON ORE PELLET SINTERING AND/OR ENDURING METHOD, according to claim 11, wherein fuel gas evenly distributed around the circumference of the descending channel is quickly mixed with the oxygen diluted in the inert gases, and obtains a significant reduction of the temperature peaks and consequent reduction in the NOX formation in the combustion process.