WIDE FLAME BURNER

Abstract

A burner comprises a refractory nozzle body enclosing a cavity and having a plurality of conduits each extending from said cavity to openings in the exterior of said nozzle body, wherein the axes of all said conduits lie in a common plane and the axes of any two of said conduits are either parallel to each other or form an angle diverging from said nozzle body, the nozzle body also having a passageway extending from said cavity to an opening in said nozzle body located on the opposite side of said cavity from said conduits; and a reactant distributor, made of metal, comprising a plurality of feeders each comprising a first tube and a second tube surrounding and coaxial with the first tube and defining an annular space between said tubes, there being one feeder in each of said conduits, wherein the distance from the ends of the first and second tubes of each feeder to the opening of the conduit in which the feeder is located is at least 1.5 times the diameter of said opening, and an inlet for oxidant and an inlet for fuel, wherein each first tube is connected in fluid communication with one of said inlets and each of said annular spaces is connected in fluid communication with said inlet for oxidant, wherein said distributor is releasably sealably engaged in said passageway with said inlets accessible outside said nozzle body, and wherein said distributor is removable out of said nozzle body through said passageway.

Description

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for combustion, and more particularly combustion with a wide flame.

BACKGROUND OF THE INVENTION

Many industrial applications require material to be heated to very high temperatures. In many of those applications, such as glass manufacture, the required heating is provided by combusting fuel with oxidant and exposing the material directly to that combustion and to the heat that is generated by that combustion. Often it is advantageous to carry out such combustion in a manner that produces a relatively wide flame. The present invention provides the capability of producing a wide flame, and provides several advantages to the operator.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present invention is a burner for injection of oxidant and fuel into a combustion zone, comprising

(A) a refractory nozzle body enclosing a cavity and having a plurality of conduits each extending from said cavity to openings in the exterior of said nozzle body, wherein the axes of all said conduits lie in a common plane and the axes of any two of said conduits are either parallel to each other or form an angle diverging from said nozzle body, the nozzle body also having a passageway extending from said cavity to an opening in said nozzle body located on the opposite side of said cavity from said conduits; and

(B) a reactant distributor, made of metal, comprising

(1) a plurality of feeders each comprising a first tube and a second tube surrounding and coaxial with the first tube and defining an annular space between said tubes, there being one feeder in each of said conduits, wherein the distance from the ends of the first and second tubes of each feeder to the opening of the conduit in which the feeder is located is at least 1.5 times the diameter of said opening, and

(2) an inlet for oxidant and an inlet for fuel, wherein each first tube is connected in fluid communication with one of said inlets, provided that at least one first tube is connected in fluid communication with said inlet for fuel, and each of said annular spaces is connected in fluid communication with said inlet for oxidant,

wherein said distributor is releasably sealably engaged in said passageway with said inlets accessible outside said nozzle body, and wherein said distributor is removable out of said nozzle body through said passageway.

Another aspect of the present invention is a burner assembly comprising the aforementioned burner removably mounted in a refractory burner block.

Yet another aspect of the present invention is a burner for injection of oxidant and fuel into a combustion zone, comprising

(A) a first refractory nozzle body enclosing a cavity and having a plurality of conduits each extending from said cavity to openings in the exterior of said first nozzle body, wherein the axes of all said conduits lie in a common plane and the axes of any two of said conduits are either parallel to each other or form an angle diverging from said first nozzle body, the first nozzle body also having a passageway extending from said cavity to an opening in said first nozzle body located on the opposite side of said cavity from said conduits;

(B) a first reactant distributor, made of metal, comprising a plurality of feeders each comprising a first tube and a second tube surrounding and coaxial with the first tube and defining an annular space between said tubes, there being one feeder in each of said conduits of said first nozzle body, wherein the distance from the ends of the first and second tubes of each feeder to the opening of the conduit in which the feeder is located is at least 1.5 times the diameter of said opening,

wherein said first reactant distributor is releasably sealably engaged in said passageway of said first nozzle body, and wherein said first reactant distributor is removable out of said first nozzle body through said passageway in said first nozzle body,

(C) a second refractory nozzle body enclosing a cavity and having a plurality of conduits each extending from said cavity to openings in the exterior of said second nozzle body, wherein the axes of all said conduits lie in a common plane and the axes of any two of said conduits are either parallel to each other or form an angle diverging from said second nozzle body, the second nozzle body also having a passageway extending from said cavity to an opening in said second nozzle body located on the opposite side of said cavity from said conduits;

(D) a second reactant distributor, made of metal, comprising a plurality of feeders each comprising a third tube and a fourth tube surrounding and coaxial with the third tube and defining an annular space between said tubes, there being one feeder in each of said conduits of said second nozzle body, wherein the distance from the ends of the third and fourth tubes of each feeder to the opening of the conduit in which the feeder is located is at least 1.5 times the diameter of said opening,

wherein said second reactant distributor is releasably sealably engaged in said passageway of said second nozzle body, and wherein said second reactant distributor is removable out of said nozzle body through said passageway, and

(E) an inlet for oxidant and an inlet for fuel, wherein each first tube and each third tube are connected in fluid communication with one of said inlets, provided that at least one first or third tube is connected in fluid communication with said inlet for fuel, and each of said annular spaces is connected in fluid communication with said inlet for oxidant, and wherein said inlets are accessible outside said first and second nozzle bodies.

A further aspect of the present invention is a burner assembly comprising a refractory burner block in which the aforementioned burner is removably mounted.

Yet a further aspect of the present invention is a combustion method comprising feeding fuel and oxidant to any of the aforementioned burners or burner assemblies, through the respective inlets therefore, wherein fuel is fed through at least one of said first tubes and oxidant is flowed through said annular spaces at a velocity less than 90 feet per second, and combusting said fuel and oxidant.

In additional aspects of the present invention, the nozzle bodies preferably have a minimum wall thickness of at least 1.4 inches. Adjacent passageways in a nozzle body preferably diverge with respect each other at an angle between 0 and 45 degrees. In embodiments containing first and second nozzle bodies, the second nozzle body is preferably located below the first nozzle body, and more preferably the first and second nozzle bodies have the same number of passageways and the opening and the axis of each passageway in a first nozzle body is vertically aligned with, and is at the same angle with, that of a passageway in the second nozzle body. Refractory material can be placed between the first and second nozzle bodies.

The oxidant contains oxygen. It can be air, but preferably has an oxygen concentration of at least 30 percent by volume. Preferably, the oxidant contains at least 99 vol. % oxygen. The fuel preferably comprises a gaseous fuel, preferred examples of which include natural gas, and other combustible gases known in the art such as hydrogen, propane and liquefied petroleum gas. The oxidant and/or the fuel may be externally preheated prior to injecting into the combustion zone.

The burners of the present invention preferably have two or more conduits from which fuel and oxygen are fed, and two or more conduits from which only oxygen is fed. Each of the aforementioned feeders includes a conduit in which fuel is fed from a central pipe and the central pipe is surrounded by an annulus through which oxidant flows at low velocity.

The burners can be comprised of more than one, or only one, nozzle body. With more than one nozzle body, it is preferred to position one nozzle body over the other with one being used to inject fuel and the other being used to inject the oxidant for the combustion. When using just one nozzle body, all fuel and oxidant are fed through the conduits of that nozzle body.

The direction of gas flow out of the conduit openings is controlled by the orientation and shape of the ends of the first and second tubes. The feeders are preferably constructed to allow complete flow development and to enable uniform velocity distribution at the openings of all conduits.

The passageway connecting to the cavity in the refractory nozzle body allows the removal of the entire metallic reactant distributor from the nozzle body, for easy maintenance and nozzle replacement. The reactant distributor can be made as a complete unit or can be made in separate sections which are then welded or threaded together. The fluid communication within the metallic reactant distributor should not permit oxidant or fuel to pass out of the distributor except out the openings at the ends of the tubes. The tubes and their openings can be replaced to allow adjustments in gas velocity depending of the required burner energy rating. The reactant distributor is made of metal that can withstand the temperatures encountered in combustion of the fuel. Examples of suitable metals include high-temperature steel.

The respective inlets for the oxidant and the fuel are connected in any suitable manner to the tubes and annular passages through which oxidant and fuel are to flow. Manifolds and piping can be used in a manner familiar to this field. Preferably, oxidant is conveyed in pipes from the inlet to the annular passages between conduits, and where desired in other pipes to the central pipes of one or more feeders. The proportion of oxidant entering the nozzle body that is fed to the annular section can be controlled by flow regulating devices (i.e. orifice disks, valves, orifice plates, orifice nozzles) installed in the piping.

In order to prolong service life, the refractory nozzle bodies should have a minimum thickness of 1.4 inches. This thickness provides resistance to thermal stresses and reduces the tendency to form cracks. The diameters of the openings at the ends of passageways in the refractory nozzle bodies will be specified based on the desired burner rating and will generally be between 1 and 2.5 inches. The metallic reactant distributor is constructed to fit as described herein within the refractory nozzle body, and it can be slid in or out when desired. As described in greater detail below, when the distributor is in place the opening in the cavity should be sealed against flows of gas into or out of the nozzle body. One way to achieve this is to provide a plate that is unitary with the distributor and which is large enough that its edges overlap the edges around the exterior of the opening, wherein the plate can be securely attached to the nozzle body.

The operation of the burner provides staged combustion which provides low NOx emissions. The burner can be adopted with oxidant supply that is not at high pressure, such as the oxygen produced by air separation units employing pressure swing adsorption and vacuum pressure swing adsorption technology.

The velocities of the streams of fuel or oxidant emerging from the respective first or third tubes can be in the range from 60-200 feet per second. The velocities through the annular spaces are always lower than 90 feet per second. Low velocity flows through the annular spaces are useful because they provide protection to the refractory material that the nozzle body is made of, in at least two ways:

Reduced Flue Gas Entrainment

• • By reducing the flue gas entrainment into the openings of the conduits of the burners and toward the nozzle body, the attack on the refractory material is lessened or prevented and subsequent corrosion minimized.

Reduced Nozzle Cooling.

• • By permitting some increase of the temperature at the conduit openings, condensation of furnace gas components onto the refractory is avoided. This in turn prevents solids accumulation in the conduit openings and enables a longer operational period without requiring maintenance.

An additional important design feature of the burners of the present invention is the fuel refractory nozzle body inner cavity pressure. The burner is designed such that it can be operated with the internal pressure within the nozzle body being lower than the furnace pressure (i.e. the pressure in the combustion zone outside the conduit openings). This effect is caused by the aspiration force exerted by the fuel jet during its trajectory out of the conduits. Operational pressure in this cavity will always be lower than 0.0 in H₂O.

As used herein, the term “combustion zone” means a volume in which fuel and oxidant mix and react to release heat.

As used herein, the term “gaseous fuel” means a fuel composed of one or more gaseous components, some of which are combustible; droplets of combustible liquid (such as fuel oil or liquid hydrocarbons) dispersed in a gaseous medium; or solid fuel particles (such as coal or coke) dispersed in a gaseous medium.

As used herein, the term “wide” in the context of wide flame means that the flame exhibits an aspect ratio greater than 2 (i.e. the width of the flame's major axis is two or more times longer than the height of the flames minor axis) at any cross-section along the axis of the flame.

As used herein, the term “refractory” means any of a series of materials which can withstand temperatures greater than 2200° F. (1205° C.) and which are comprised of oxides, nitrides and/or carbides of metallic elements. Examples are silica, fused silica, bonded alumina-zirconia-silica, alumina, mullite, silicon carbide, silicon nitride, boron nitride, and mixtures thereof. For the purpose of this invention, the preferred refractory material is an alumina-zirconia-silica refractory containing about 66% alumina, 21% zirconia and 12% silica.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of one embodiment of this invention.

FIG. 1B is a view from another side of the embodiment shown in FIG. 1A.

FIG. 2 is a top plan view of a nozzle body useful in this invention.

FIG. 3 is a top cutaway view of the embodiment of FIGS. 1A and 1B.

FIG. 4 is a side cutaway view of another embodiment of the invention.

FIG. 5 is a head-on view of the embodiment shown in FIG. 4.

FIG. 6 is a plan view from one side of the embodiment of FIGS. 1A and 1B.

FIG. 7 is a top cutaway view of the embodiment of FIGS. 1A and 1B.

FIG. 8 is a plan view of the front of the embodiment of FIGS. 1A and 1B.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1A and 1B depict one embodiment of a burner according to the present invention. Burner 1 is comprised of two nozzle bodies 3 and 5. Preferably, fuel is emitted out opening 130 and out of the other openings that are in the same horizontal plane as opening 130, and oxidant is emitted out opening 131 and out of the other openings that are in the same horizontal plane as opening 131. Alternately, fuel could be emitted from the lower nozzle body and oxidant from the higher nozzle body without detriment of burner performance. It has been demonstrated though, that lower NOx emission levels are achieved with the configuration shown in FIGS. 1A and 1B. This is caused by the vertical positioning of the oxygen and the resulting mixing rate. Oxidant jets are typically cold and denser than the fuel jets, so when injected into a furnace they usually fall down towards the bottom of the furnace. On the other hand, most gaseous fuels are less dense than the oxidant, and once they start burning become hotter than the surroundings so they tend to rise in the furnace environment. If the oxidant is placed below the fuel, the streams diverge, and the rate of mixing is reduced. The opposite happens when the oxidant is placed on top of the fuel. With two nozzle bodies, it is preferred to orient the two nozzle bodies one above the other with their respective openings vertically aligned as shown also in FIG. 8. Plate 7 integral with the metallic distributor (which is described further herein) is attached to nozzle bodies 3 and 5 using nuts threaded onto “L-shape” bolts embedded in the refractory.

Other views of this embodiment of the improved wide flame burner are shown in FIGS. 3, 5, 6 and 7 respectively. FIG. 2 shows a nozzle body without the reactant distributor. Nozzle body 110 comprises a refractory brick housing 120 with three conduits 124, 126 and 127, ending in openings 130, 132 and 134, drilled or cast in the front face 170 to allow gas to pass into a furnace from the conduits. Three metallic feeders which are also integral parts of the distributor discharge fuel and oxidant into the three conduits. Fuel and oxidant are conveyed from respective inlets therefor at the inlet end (back face) 160 of the burner into the distributor. Each feeder is formed by two concentric pipes. The central pipes 140, 142 and 144 would carry either oxidant or fuel, while the outer pipes 190, 192 and 194 would carry only oxidant, through the annular space between the respective pairs of pipes. Four slots 180, 182, 184 and 186 are cut or cast in each side of the brick housing 120 to allow mechanical fasteners to attach brick housing 120 to metal plate 7 which is preferably also integral with the reactant distributor.

The embodiment comprising two nozzle bodies includes oxidant inlet 2 and fuel inlet 4, seen for instance in FIG. 1A. Oxidant that is fed from a source thereof through oxidant inlet 2 passes into manifold 6 where the pipe leading from inlet 2 splits into pipes that are connected to the annular spaces described herein, and to any central pipes through which oxidant is also to be fed, for oxidant flow out of nozzle body 5. Side pipes 268 convey oxidant from manifold 6 to a manifold 8A attached to the nozzle body 3. Pipes within manifold 8A convey oxidant to the annular spaces described herein, and to any central pipes through which oxidant is also to be fed, for oxidant flow out of nozzle body 3.

Fuel that is fed from a source thereof through fuel inlet 4 passes into manifold 6A wherein the fuel flow is divided so as to pass to each central pipe (described herein) in nozzle bodies 3 and 5 through which fuel is to flow. In the embodiment shown in FIGS. 1A and 1B, there is no divider between manifolds 8A and 8B.

FIG. 4 shows an embodiment wherein there is a single nozzle body. In this embodiment, oxidant inlet 2 is the opening to which one end of pipe 268 would be attached if there were two nozzle bodies together as in FIGS. 1A and 1B. Within manifolds 6 and 8, the fuel and the oxidant enter in separate lines which split to feed fuel and oxidant to the respective pipes from which the fuel and oxidant exit in the respective conduits described herein.

In FIG. 5 if the horizontal length of the burner face along the three openings may be designated as “L” and the vertical length of the burner face passing through one opening may be designated as “H”, then the minimum diameter of each opening is the length of H provided H is less than L.

FIGS. 6, 7 and 8 show another embodiment of the improved wide flame burner, comprised of two nozzle bodies 3 and 5. Though two nozzle bodies are employed, for simplicity only nozzle body 3 will be described, with the understanding that nozzle body 5 has the same features and structure. Conduits corresponding to those of a single nozzle body terminate in openings 230, 232 and 234. The separated nozzle bodies facilitate adjusting the vertical spacing of the nozzle bodies.

Plate 250 integral with the reactant distributor that is situated in nozzle body 3 is mounted to the back of nozzle body 3. Plate 250 prevents cold air from leaking into the furnace around the nozzle body and hot furnace gases from leaking out. Plate 250 is secured to the refractory nozzle body 3, by nuts 280, 282, 284 and 286 which are threaded onto bolts embedded in the refractory housing. The entire metallic distributor 220, comprising outer tubes 222, 224 and 226 and central tubes 240, 242 and 244, and plate 250, manifolds 260 and 262 including fuel and oxidant inlets, can be removed from nozzle body 3 by removing the aforementioned nuts and sliding the distributor out of the nozzle body, without having to remove the nozzle body itself from the wall of the furnace. This makes maintaining and servicing the burner easier. Manifolds 260 and 262 contain piping which distributes the flows of fuel and oxidant to the central pipes and the annular spaces as desired. The pipes 222, 224 and 226 channel the flow of oxygen and fuel up to the metallic nozzles 240, 242 and 244. Oxidant is transferred from one level to the other by means of pipe 268 and between manifolds of the same level by internal channels.

One of the most significant variables in the design of this new burner is the recess distance, that is, the distance from the ends of the central and outer tubes to the opening of the conduit in which the tubes are located. Two conditions need to be satisfied to determine the recess distance:

The majority of the annular flow should be entrained within the conduit by the stream coming from the central pipe. By satisfying this condition the entrainment produced at the opening at the end of the conduit by the stream from the central pipe at the refractory nozzle port exit is minimized. The resulting velocity profile of the stream has low velocity magnitude and flat distribution near the edges of the opening. This condition is calculated using the entrainment equations for reacting flows (flows of oxidant and fuel in the same conduit) and non-reacting flows (flows of only oxidant in a conduit). The equations are:

Non-Reacting Case—Oxidant from the Central Pipe and the Annular Space

$\frac{Q_e}{Q_j}=N\frac{z}{d_o}$

where N is 0.01 to 0.4 and preferably 0.1 to 0.35, more preferably about 0.28

Reacting Case—Fuel from the Central Pipe and Oxidant from the Annular Space

$\frac{Q_e}{Q_j}=N\frac{z}{d_o}$

where N is 0.01 to 0.4 and preferably 0.01 to 0.1, more preferably about 0.049

• • where,
  • Q_e: flow rate through the annular space (in SCFH)
  • Q_f: flow rate through the central pipe (in SCFH)
  • z: recess distance
  • d_o: nozzle diameter
  • 1. The recess distance must be more than 1.5 times the diameter of the opening at the end of the conduit. According to operational experience, this value is the threshold for properly protecting of the metallic parts against excessive heat radiation.

In operation of the burner of the present invention, the preferred operating conditions are:

Velocities

• • Velocity of fuel from a central pipe: 70 to 200 feet per second (ft/s)
  • Velocity of oxidant through an annular space in a conduit where fuel is being fed from the central pipe: 5-30 ft/s
  • Velocity of oxidant from a central pipe: 70 to 350 ft/s
  • Velocity of oxidant through an annular space in a conduit where oxidant is being fed from the central pipe: 10-90 ft/s

Amounts of Oxygen to Feed, Relative to the Stoichiometric Requirements for Combustion of the Total Amount of Fuel Being Fed Through the Burner:

• • Oxygen fed through the annular space in a conduit where fuel is being fed from the central pipe: 10-20% of stoichiometric
  • Oxygen fed through a central pipe: 25-65% of stoichiometric
  • Oxygen through an annular space in a conduit where oxidant is being fed from the central pipe: 35-75% of stoichiometric

Claims

1. A nozzle assembly for injection of oxidant and fuel into a combustion zone, comprising (A) a refractory nozzle body enclosing a cavity and having a plurality of conduits each extending from said cavity to openings in the exterior of said nozzle body, wherein the axes of all said conduits lie in a common plane and the axes of any two of said conduits are either parallel to each other or form an angle diverging from said nozzle body, the nozzle body also having a passageway extending from said cavity to an opening in said nozzle body located on the opposite side of said cavity from said conduits; and(B) a reactant distributor, made of metal, comprising (1) a plurality of feeders each comprising a first tube and a second tube surrounding and coaxial with the first tube and defining an annular space between said tubes, there being one feeder in each of said conduits, wherein the distance from the ends of the first and second tubes of each feeder to the opening of the conduit in which the feeder is located is at least 1.5 times the diameter of said opening, and(2) an inlet for oxidant and an inlet for fuel, wherein each first tube is connected in fluid communication with one of said inlets and each of said annular spaces is connected in fluid communication with said inlet for oxidant,wherein said distributor is releasably sealably engaged in said passageway with said inlets accessible outside said nozzle body, and wherein said distributor is removable out of said nozzle body through said passageway.

2. A burner comprising a nozzle assembly according to claim 1 removably mounted in a refractory burner block.

3. A nozzle assembly for injection of oxidant and fuel into a combustion zone, comprising (A) a first refractory nozzle body enclosing a cavity and having a plurality of conduits each extending from said cavity to openings in the exterior of said first nozzle body, wherein the axes of all said conduits lie in a common plane and the axes of any two of said conduits are either parallel to each other or form an angle diverging from said first nozzle body, the first nozzle body also having a passageway extending from said cavity to an opening in said first nozzle body located on the opposite side of said cavity from said conduits;(B) a first reactant distributor, made of metal, comprising a plurality of feeders each comprising a first tube and a second tube surrounding and coaxial with the first tube and defining an annular space between said tubes, there being one feeder in each of said conduits of said first nozzle body, wherein the distance from the ends of the first and second tubes of each feeder to the opening of the conduit in which the feeder is located is at least 1.5 times the diameter of said opening,wherein said first reactant distributor is releasably sealably engaged in said passageway of said first nozzle body, and wherein said first reactant distributor is removable out of said first nozzle body through said passageway in said first nozzle body,(C) a second refractory nozzle body enclosing a cavity and having a plurality of conduits each extending from said cavity to openings in the exterior of said second nozzle body, wherein the axes of all said conduits lie in a common plane and the axes of any two of said conduits are either parallel to each other or form an angle diverging from said second nozzle body, the second nozzle body also having a passageway extending from said cavity to an opening in said second nozzle body located on the opposite side of said cavity from said conduits;(D) a second reactant distributor, made of metal, comprising a plurality of feeders each comprising a third tube and a fourth tube surrounding and coaxial with the third tube and defining an annular space between said tubes, there being one feeder in each of said conduits of said second nozzle body, wherein the distance from the ends of the third and fourth tubes of each feeder to the opening of the conduit in which the feeder is located is at least 1.5 times the diameter of said opening,wherein said second reactant distributor is releasably sealably engaged in said passageway of said second nozzle body, and wherein said second reactant distributor is removable out of said nozzle body through said passageway, and(E) an inlet for oxidant and an inlet for fuel, wherein each first tube and each third tube are connected in fluid communication with one of said inlets and each of said annular spaces is connected in fluid communication with said inlet for oxidant, and wherein said inlets are accessible outside said first and second nozzle bodies.

4. A burner comprising a refractory burner block in which a nozzle assembly according to claim 3 is removably mounted.

5. A combustion method comprising feeding fuel and oxidant to a nozzle body according to claim 1 through the respective inlets therefor in said nozzle body, wherein fuel is fed through at least one of said first tubes and oxidant is flowed through said annular spaces at a velocity less than 90 feet per second, and combusting said fuel and oxidant.