Patent Description:
Industrial burners are commonly used in process heaters, boilers, furnaces, incinerators, and other fired-heating systems to produce heat for petroleum refining, chemical production, petrochemical operations, and other large-scale industrial processes. Such a burner is known, for example, from <CIT>.

The processing units in today's refineries, chemical plants, and other facilities must be capable of operating for increasingly longer periods of time without the need to shut down for major repairs and maintenance. In fact, the maintenance cycles in many refineries and other facilities are now up to four years, or longer. Consequently, the continued, reliable operation of burners and other critical equipment for very long periods of time is also becoming increasingly important.

One of the main causes of down time for industrial burners occurs when the fuel ports of the burner tips become plugged with debris or residue. The plugging of the fuel ports can lead to reduced or completely restricted fuel gas flow.

Another issue with industrial burners is that they are increasingly required to produce lower levels of NOx and other emissions. Other conditions being equal, NOx emissions increase as the temperature of the combustion process increases. As the temperature of the burner flame increases, the stability of the covalent bond of the N<NUM> in the burner air supply decreases, causing increased production of free nitrogen and thus also increasing the production of thermal NOx emissions. Consequently, in an ongoing effort to reduce NOx emissions, various types of burner designs and theories have been developed with the objective of reducing the peak flame temperature.

Thermal NOx reduction is generally achieved by slowing the rate of combustion. Since the combustion process is a reaction between oxygen and the burner fuel, the objective of delayed combustion is typically to reduce the rate at which the fuel and oxygen mix together and burn. The faster the oxygen and the fuel mix together, the faster the rate of combustion and the higher the peak flame temperature.

One type of low NOx burner which is very effective for slowing the rate of combustion and reducing peak flame temperatures is a free-jet burner. A free-jet burner will typically comprise: (i) a burner wall, (ii) an interior passageway for delivering a flow of air or other oxygen-containing gas out of the forward end of the burner wall, and (iii) a series of outer ejectors positioned to discharge fuel streams in free-jet flow outside of the burner wall to the burner flame. The flow momentum of the free-jet streams traveling outside of the burner wall entrains a significant amount of the gaseous products of combustion (flue gas) contained in the fired heating system, thereby recirculating the flue gas back into the combustion zone to form a diluted combustion mixture which burns at a lower peak flame temperature. This NOx reduction technique is referred to as Internal Flue Gas Recirculation (IFGR).

Unfortunately, as improved free-jet burners have been developed which provide lower and lower levels of NOx emissions, the plugging resistance of these burners generally has not improved. Rather, in some cases, the plugging resistance of the burners has deteriorated to some degree. One reason is that, in many cases, greater amounts of flue gas recirculation, further reductions in NOx emissions, and greater stability have been achieved by using a greater number of outer ejectors, having very small ejection ports (typically only <NUM> (<NUM>/<NUM>th inch) in diameter), which are placed close together (i.e., less than <NUM> (<NUM> inches) apart and more preferably only <NUM> to <NUM> (<NUM> to <NUM> inches) apart). The small ejection ports are necessary for preventing interference between the adjacent fuel flow streams and facilitating flue gas entrainment.

However, the small ejection ports required by the prior free-jet burners are prone to plugging. The small fuel ejection ports can be plugged by tiny debris and/or limited buildup. Consequently, fuel strainers are generally not effective for preventing plugging, particularly in systems which have high levels of debris due to the age of the fuel pipes and/or other factors.

The use of auxiliary burner tips in free-jet burners and in other burners has also been problematic in regard to both plugging and NOx emissions. An auxiliary burner tip is a gas tip which is used to enhance the stability of the main flame of a burner, particularly during upset conditions. Examples of upset conditions which can cause the burner flame to become unstable include, but are not limited to: (a) a reduction in the air flow to the burner to a sub-stoichiometric level, (b) a loss of temperature in the fired-heating system to a level below the minimum temperature required for igniting the fuel, or (c) the occurrence of pressure excursions in the fired-heating system.

In the auxiliary burner tips currently used in the art, the speed of combustion and the peak flame temperature of the tip are typically sufficiently high that the use of one or more auxiliary tips can contribute significantly to the NOx emissions of the burner. Moreover, the auxiliary tips currently used in the art for purposes of flame stabilization are particularly susceptible to plugging. The fuel gas ports of these tips are very small, typically <NUM> (<NUM>/<NUM>th inch) in diameter (i.e., a port flow area of only <NUM><NUM> (<NUM> in<NUM>)). As a result, auxiliary tips are prone to plugging, even after filtration.

If plugging occurs in an auxiliary burner tip which is used to maintain the stability of the burner flame, the localized temperature at the stability point can be reduced until the stability of the flame can no longer be maintained and the flame is lost. When a loss of flame occurs in one or more burners of a multiple burner heating system, significant safety concerns can arise, including the risk of an explosion.

Consequently, a need exists for an improved free-jet burner which is resistant to plugging and provides a high degree of flame stability. The improved free-jet burner will preferably also produce very low levels of NOx and other emissions which are comparable to, or better than, the Ultra-Low emissions levels of the free-jet burners currently used in the art.

The present invention provides an improved free-jet burner and method of operation, and a method of revamping an existing free-jet burner, which satisfy the needs and alleviate the problems discussed above. The improved or revamped burner is highly resistant to plugging and provides a high degree of flame stability. The inventive burner and method also provide Ultra-Low NOx emission levels which are comparable to, or better than, the emissions levels produced by the free-jet burners currently used in the art, which require the use of small fuel discharge ports and are prone to plugging.

In one aspect, there is provided an improved burner for providing low NOx emissions, wherein the burner is for use in a heating system having a flue gas therein and the burner is of a type comprising (i) a burner wall having a forward end, (ii) an interior passageway of the burner wall for a flow of air or other oxygen-containing gas out of the forward end of the burner wall, and (iii) a series of ejectors positioned to deliver a fuel from the ejectors in free-jet flow streams outside of the burner wall either directly or indirectly to a main burner flame at and/or forwardly of the forward end of the burner wall. For this burner, the improvement preferably comprises: (a) using large fuel ejection ports in the ejectors having a flow area of at least <NUM><NUM> (<NUM> inch<NUM>) which provide resistance to plugging; (b) using a wide tip-to-tip spacing between the ejectors of from <NUM> to <NUM> (<NUM> to <NUM> inches) which provides enhanced recirculation of the flue gas to the main burner flame for the free-jet flow streams from the large fuel ejection ports; and (c) positioning one or more auxiliary burner tips in the internal passageway of the burner wall to stabilize the main burner flame, each said auxiliary burner tip having a large fuel discharge port with a flow area of at least <NUM><NUM> (<NUM> inch<NUM>) which provides resistance to plugging.

In another aspect, there is provided an improved method of operating a burner for low NOx emissions wherein (a) the burner comprises a burner wall having a forward end and an interior passageway through which a stream of air or other oxygen-containing gas flows out of the forward end of the burner wall, (b) the burner is operated in a heating system, and (c) the method is of a type comprising the step of ejecting a fuel from a series of ejectors in free-jet flow streams outside of the burner wall either directly or indirectly to a main burner flame at and/or forwardly of the forward end of the burner wall. For this method, the improvement preferably comprises: (i) increasing the resistance to plugging of the ejectors by using large fuel ejection ports in the ejectors having a flow area of at least <NUM><NUM> (<NUM> inch<NUM>); (ii) enhancing the recirculation of a flue gas in the heating system to the main burner flame for the free-jet flow streams from the large fuel ejection ports of the ejectors by using a wide tip-to-tip spacing between the ejectors of from <NUM> to <NUM> (<NUM> to <NUM> inches); and (iii) enhancing the stability of the main burner flame using one or more auxiliary burner tips positioned in the internal passageway of the burner wall, each said auxiliary burner tip having a large fuel discharge port with a flow area of at least <NUM><NUM> (<NUM> inch<NUM>) which provides resistance to plugging.

In another aspect, there is provided a method of increasing the plugging resistance and maintaining low NOx emissions of an existing burner having (i) a burner wall, (ii) an interior passageway of the burner wall through which a flow of air or other oxygen-containing gas is discharged from a forward end of the burner wall, and (iii) a series of a number x of original ejectors which are positioned outside of and spaced around the interior passageway of the burner wall and which deliver a fuel from the ejectors in free-jet flow streams outside of the burner wall either directly or indirectly to a main burner flame at and/or forwardly of the forward end of the burner wall. The method preferably comprises the steps of: (a) increasing a tip-to-tip spacing by removing every other one of the original ejectors so that the number of remaining ejectors will be (i) one half of the number x of the original ejectors if the number x of the original ejectors is an even number or (ii) not more than ((x-<NUM>)/<NUM>) + <NUM> if the number x of the original ejectors is an odd number; (b) replacing each of the remaining ejectors with a plugging resistant ejector having a large fuel ejection port with a flow area of at least <NUM><NUM> (<NUM> inch<NUM>); and (c) stabilizing the main burner flame by installing at least two auxiliary burner tips in the internal passageway of the burner wall, each of the auxiliary burner tips having a large fuel discharge port with a flow area of at least <NUM><NUM> (<NUM> inch<NUM>) which provides resistance to plugging, and each of the auxiliary burner tips directing an auxiliary tip flame onto a surrounding shoulder at the forward end of the burner wall or onto a ledge or other interior feature of the burner wall.

Further aspects, features, and advantages of the present invention will be apparent to those in the art upon examining the accompanying drawings and upon reading the following detailed description of the preferred embodiments.

Before explaining the present invention in detail, it is important to understand that the invention is not limited in its application to the details of the preferred embodiments and steps described herein. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein are for the purpose of description and not of limitation.

As will be understood by those skilled in the art, the term "free jet," as used herein and in the claims, refers to a flow issuing from a port of an ejector tip, a nozzle, or other ejector into a fluid which, compared to the flow, is more at rest. In the present invention, the fluid issuing from the ejector can be a gas fuel and/or a liquid fuel, but is preferably a gas fuel, and the fluid substantially at rest is the flue gas present within the heating system. For purposes of the present invention, the heating system can be a process heater, a boiler or generally any other type of heating system used in the art. The flue gas present within the system will comprise the gaseous products of the combustion process.

As noted, the fuel used in the inventive burner and method will preferably be a gas fuel but can alternatively be a liquid fuel, or can be a fuel having both gas and liquid phases. The gas fuel used in the inventive burner and method can be natural gas, a refinery fuel gas, hydrogen, or generally any other type of gas fuel or gas fuel blend employed in process heaters, boilers, or other gas-fired heating systems. The free-jet flow employed in the inventive system operates to entrain flue gas and to thoroughly mix the flue gas with each fuel stream as it travels to the main burner flame at or forwardly of the outlet end of the burner wall.

Referring now to the drawings, <FIG> depict an embodiment <NUM> of the inventive burner apparatus. Burner <NUM> comprises a housing <NUM> and a burner wall <NUM> having an outlet or forward end <NUM>, a base end <NUM>, and internal passageway or throat <NUM> which extends through and is surrounded by the burner wall <NUM>. The outlet end <NUM> of the burner wall <NUM> is in communication with the interior <NUM> of the furnace or other heating system enclosure in which combustion takes place and which therefore contains combustion product gases (i.e., flue gas). Burner <NUM> is shown as installed through the floor or other wall <NUM> of the heating system, which is typically formed of metal. Insulating material <NUM> will typically be secured to the interior of the furnace floor or wall <NUM>.

The burner wall <NUM> is preferably constructed of a high temperature refractory burner tile material. However, it will be understood that the burner wall <NUM> can alternatively be formed of, or provided by, the furnace floor or other wall, a metal band, a refractory band, or any other material or structure which is capable of (a) providing an acceptable flow passageway for air or other oxygen-containing gas into the heating system enclosure <NUM> and (b) withstanding the high temperature conditions therein.

Combustion air or other oxygen-containing gas <NUM> is received in housing <NUM> and directed by the housing <NUM> into the inlet end <NUM> of burner throat <NUM>. The air or other oxygen-containing gas <NUM> exits the burner <NUM> at the outlet end <NUM> thereof. The quantity of combustion air or other oxygen-containing gas entering the housing <NUM> is regulated by inlet damper <NUM>. The air or other oxygen-containing gas <NUM> can be provided to housing <NUM> as necessary by forced circulation, natural draft, a combination thereof, or in any other manner employed in the art.

A series of outer tips, nozzles, or other fuel ejectors <NUM> surrounds burner wall <NUM>. In embodiment <NUM> of the inventive burner, each ejector <NUM> is depicted as comprising a fuel ejection tip <NUM> secured on the end of a fuel pipe <NUM>. Each fuel pipe <NUM> is in communication with a fuel supply manifold <NUM> and can either extend through a lower skirt portion of the burner tile <NUM> or be affixed within the insulating material <NUM> attached to furnace wall <NUM>. While the fuel pipes <NUM> are illustrated as being risers connected to a fuel supply manifold <NUM>, it will be understood that any other type of fuel supply system can alternatively be used in the present invention.

Each ejector <NUM> has an ejection port <NUM> drilled or otherwise provided therein which is preferably oriented to deliver a free-jet fuel stream <NUM> either directly (as illustrated in <FIG>) or indirectly to a main burner flame <NUM> at or forwardly of the forward end <NUM> of the burner wall <NUM>. Delivering a free-jet fuel stream <NUM> "indirectly" to the main burner flame <NUM> means, e.g., that the ejection port <NUM> of one or more of the ejectors <NUM> can alternatively be oriented to direct one or more fuel streams <NUM> at more of an inward angle toward the burner wall <NUM> or at more of an outward angle away from the burner wall such that the momentum of the air or other oxygen-containing gas <NUM> as it flows out of the forward end <NUM> of the burner wall <NUM> draws the indirect fuel steam(s) <NUM> back into the main burner flame <NUM>. As each free-jet fuel stream <NUM> flows to the main burner flame <NUM>, flue gas from the furnace enclosure is entrained therein and mixes therewith.

The ejectors <NUM> are located outside of and at least partially around (preferably entirely around) the internal passageway <NUM> of the burner wall <NUM> so that the free-jet fuel streams <NUM> travel outside of the burner wall <NUM>. As depicted in the drawings, the ejectors <NUM> are preferably located in proximity to the base <NUM> of burner wall <NUM> such that they are positioned longitudinally rearward of and laterally outward from the outer or forward end <NUM> of the burner wall <NUM>.

A burner pilot <NUM> can optionally be located within the interior passageway <NUM> to initiate combustion at the outer end <NUM> of the burner <NUM>.

In accordance with the improvements provided by the burner and method of the present invention, the plugging resistance of the ejectors <NUM> of the inventive burner <NUM> is increased by using large ejection ports <NUM> in the ejectors <NUM>. The large fuel ports <NUM> will preferably be drilled ports having a circular shape, but can alternatively be square, oval, or any other shape desired. In each case, the large fuel port <NUM> of each ejector <NUM> will preferably have a flow area of at least <NUM><NUM> (<NUM> inch<NUM>) (i.e., a diameter of at least <NUM> (<NUM>/<NUM> inch) for a circular port) and will more preferably have a flow area of at least <NUM><NUM> (<NUM> inch<NUM>) (i.e., a diameter of at least <NUM> (<NUM>/<NUM>th inch) for a circular port). The flow area of each of the large fuel ports <NUM> will more preferably be in the range of from <NUM> to <NUM><NUM> (<NUM> to <NUM> inch<NUM>) and will most preferably be about <NUM><NUM> (<NUM> inch<NUM>) (i.e., a diameter of <NUM> (<NUM>/<NUM> inch) for a circular port).

Also in accordance with the improvements provided by the burner and method of the present invention, a wide spacing <NUM> between the ejectors <NUM> (referred to herein as a wide tip-to-tip spacing) is also used. The wide tip-to-tip spacing <NUM> between the ejectors <NUM> will preferably be from <NUM> to <NUM> (<NUM> to <NUM> inches) and will more preferably be from <NUM> to <NUM> (<NUM> to <NUM> inches). The tip-to-tip spacing <NUM> between the ejectors <NUM> will most preferably be about <NUM> to <NUM> (<NUM> to <NUM> inches).

These improvements, i.e., using large fuel ejection ports <NUM> and a wide tip-to-tip spacing <NUM> are counter to the conventional wisdom and the current practices in the industry for reducing NOx emissions and providing burner stability. As noted above, it is believed in the industry that NOx reductions and burner stability are best achieved by using a greater number of ejectors which have very small ejection ports of only <NUM> (<NUM>/<NUM>th inch) in diameter and are positioned very close together at a tip-to-tip spacing of less than <NUM> (<NUM> inches), and more preferably not more than <NUM> (<NUM> inches).

In the inventive burner <NUM>, all else being equal, although the use of the large fuel ports <NUM> in the ejectors <NUM> provides resistance to plugging, it also reduces the amount of flue gas which is drawn into the combustion mixture by the free-jet streams <NUM> and by the momentum of the stream of air or other oxygen-containing gas exiting the forward end <NUM> of the burner wall <NUM>. This in turn reduces the degree of dilution of the combustion mixture which undesirably accelerates the combustion process, increases the peak flame temperature, and increases the level of NOx and other emissions produced by the burner.

In the inventive burner <NUM>, the amount of flue gas which is recirculated to the combustion mixture for the main burner flame <NUM> is enhanced and restored by using the wide tip-to-tip spacing <NUM> between the ejectors <NUM>. The increased tip-to-tip spacing <NUM> creates wider flow channels between the ejectors <NUM> for the recirculation of the flue gas, which in turn enables the free-jet streams <NUM> and the momentum of the air or other oxygen-containing gas to pull an amount of flue gas into the combustion mixture which is substantially the same as or exceeds the amount of IFGR which is achieved in the prior free-jet burners. Because of the amount of IFGR achieved in the inventive burner <NUM>, the amount of NOx emissions produced by the inventive burner <NUM> will be an Ultra-Low level of less than <NUM> ppmv in a process furnace with a furnace temperature of <NUM> ° C (<NUM>,<NUM> F), ambient air temperature, <NUM>% excess air, natural gas fuel with <NUM> psig fuel gas pressure and will more preferably be in the range of from <NUM> ppmv to <NUM> ppmv for most process furnace applications.

However, although the ejectors <NUM> used in the inventive burner <NUM> provide resistance to plugging and the wide tip-to-tip spacing <NUM> of the ejectors <NUM> increases the amount of IFGR achieved in the combustion mixture, a reliable, improved means of maintaining the stability of the main burner flame <NUM>, particularly during upset conditions, was still needed. As mentioned above, a loss of stability can increase the chances of a burner flame-out if, for example, the burner experiences a significant reduction in air flow, or there is a significant loss of temperature in the heating system, or a pressure excursion occurs in the heating system. The potential for a loss of flame in one or more burners of a multiple burner heating system creates significant safety concerns, including the risk of an explosion.

Unfortunately, as also mentioned above, the auxiliary burners heretofore used by in the art for improved stability were themselves prone to plugging, which also presented a serious flame-out risk. In addition, the level of NOx emissions produce by the prior auxiliary burner tips was not satisfactory.

In accordance with the improved burner and method of the present invention, the need for ensuring the continued stability of the main burner flame <NUM> is met by using one or more auxiliary burner tips <NUM> positioned in the internal passageway <NUM>, of the burner wall <NUM>, which are resistant to plugging and therefore do not themselves present a flame-out risk. Moreover, unlike prior auxiliary burner tips <NUM> used in the art for various purposes, each auxiliary burner tip <NUM> used in the inventive burner and method preferably produces a very low level of NOx emissions which does not contribute significantly to the total emissions of the inventive burner <NUM>.

To prevent plugging, each auxiliary burner tip <NUM> used in the inventive burner <NUM> has a large fuel discharge port <NUM> which preferably has a flow area of at least <NUM><NUM> (<NUM> inch<NUM>) (i.e., a diameter of at least <NUM> (<NUM>/<NUM> inch) for a circular port) and more preferably has a flow area of at least <NUM><NUM> (<NUM> inch<NUM>) (i.e., a diameter of at least <NUM> (<NUM>/<NUM>th inch) for a circular port). The flow area of the large fuel discharge port <NUM> will more preferably be in the range of from <NUM> to <NUM><NUM> (<NUM> to <NUM> inch<NUM>) and will most preferably be about <NUM><NUM> (<NUM> inch<NUM>). Also, in order to provide low levels of NOx emissions, each auxiliary burner tip <NUM> is a sub-stoichiometric, staged air burner tip.

The number of auxiliary tips <NUM> used in the inventive burner <NUM> can be any number y suitable for maintaining the stability of the burner flame <NUM>, particularly when subjected to upset conditions of the type described above. By way of example, but not by way of limitation, for a burner <NUM> having a heat output of less than <NUM>(. ) MW (15MMBtu/hour), and assuming that the burner <NUM> includes a burner pilot <NUM> located within the interior passageway <NUM> for initiating combustion at the outer end <NUM> of the burner <NUM>, two auxiliary burner tips <NUM> will preferably be included in the interior passageway <NUM>. For any number y > <NUM> of auxiliary tips <NUM> used in the burner <NUM>, given that the size and dimensions of the inventive burner <NUM> can range from small to very large depending upon the service in which the burner <NUM> is used and the amount of heat output required, the spacing <NUM> between each adjacent pair of the auxiliary burner tips <NUM> will typically be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more and will more preferably be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches).

Each auxiliary burner tip <NUM> used in the inventive burner and method is a staged air, sub-stoichiometric burner tip as illustrated in <FIG>. The auxiliary burner tip <NUM> comprises: a tip shield housing <NUM> having a longitudinal axis <NUM>; a mixing chamber <NUM> contained within the shield housing <NUM>; a gas fuel spud <NUM> positioned to discharge a gas fuel into the rearward longitudinal end of the mixing chamber <NUM>; and a flame diverter <NUM> on the forward longitudinal end of the shield housing <NUM>.

The tip shield housing <NUM> preferably comprises a longitudinally extending outer wall <NUM> which surrounds the mixing chamber <NUM>. The outer wall <NUM> is preferably cylindrical but can alternatively have a square, oval, or other cross-sectional shape. A series of small openings <NUM> is preferably provided around and through a rearward portion of the outer wall <NUM> to serve as contingency relief openings for gas expansion in the event that combustion occurs within the shield housing <NUM> itself.

The lateral base wall <NUM> at the rearward end of the mixing chamber <NUM> has at least a central opening <NUM> provided therethrough. As the gas fuel is discharged into the rearward end of the mixing chamber <NUM> by the gas fuel spud <NUM>, the momentum of the gas fuel stream draws air or other oxygen-containing gas, from the interior passageway <NUM> of the burner <NUM>, into the mixing chamber <NUM> through the central base opening <NUM>. In addition, the momentum of the gas fuel preferably also draws air or other oxygen-containing gas into the mixing chamber <NUM> through a plurality of openings <NUM> which are formed through the base wall <NUM> of the shield housing <NUM> around the central base opening <NUM>. The surrounding openings <NUM> are preferably smaller that the central base opening <NUM>. The base openings <NUM> and <NUM> are preferably sized such that the total amount of air or other oxygen-containing gas which is drawn into the mixing chamber <NUM> is a sub-stoichiometric amount, i.e., an amount which is not sufficient for burning all of the gas fuel which is discharged into the mixing chamber <NUM> by the gas fuel spud <NUM>.

The flame stabilization ring <NUM> at the forward end of the mixing chamber <NUM> has a central discharge opening <NUM> provided therethrough which is smaller than the cross-sectional diameter or area of the mixing chamber <NUM> so that the flow of the sub-stoichiometric mixture of fuel and oxygen-containing gas from the mixing chamber <NUM> through the flame stabilization ring <NUM> creates a reduced pressure area <NUM> on or near the stabilization ring <NUM> which assists in holding and otherwise stabilizing the flame <NUM> of the auxiliary tip <NUM>.

The gas fuel spud <NUM> includes the large fuel discharge port <NUM> at the forward end thereof for discharging the gas fuel into the rearward longitudinal end of the mixing chamber <NUM>. The fuel discharge port <NUM> of the spud <NUM> is preferably positioned rearwardly of the base wall <NUM> of the shield housing <NUM> so that the spud <NUM> discharges the gas fuel forwardly through the central opening <NUM> of the base wall <NUM>. The fuel discharge port <NUM> can be formed directly in the forward end of the gas fuel spud <NUM> or can be formed in an orifice plug which is placed in the forward end of the spud <NUM>.

In addition to the use of the large discharge port <NUM>, the gas fuel spud <NUM> is preferably connected to a gas fuel supply line or riser <NUM> having an orifice union <NUM> therein which contains a flow orifice. The flow area of the flow orifice (a) is preferably at least <NUM><NUM> (<NUM> inch<NUM>) (which is equivalent to a circular orifice diameter of at least <NUM> (<NUM>/<NUM> inch)) and will more preferably be at least <NUM><NUM> (<NUM> inch<NUM>) (which is equivalent to a circular orifice diameter of at least <NUM> (<NUM>/<NUM> inch)) but (b) is also preferably less than the size of the fuel spud discharge port <NUM>. The flow area of the flow orifice will more preferably be in the range of from <NUM><NUM> (<NUM> inch<NUM>) to about <NUM><NUM> (<NUM> inch<NUM>) and will most preferably be about <NUM><NUM> (<NUM> inch<NUM>). In the event that the system contains any debris of sufficient size to plug even the large discharge port <NUM> of the gas fuel spud <NUM>, the debris will be stopped by the flow orifice in the orifice union <NUM>, which will be positioned outside of the fired-heating system and can be easily cleaned. The flow orifice can also be used to meter the rate of flow of the gas fuel to the auxiliary burner tip <NUM> from the external fuel supply manifold <NUM>.

The flame diverter <NUM> on the forward longitudinal end of the shield housing <NUM> preferably comprises: a rearward opening <NUM>; an interior flame space <NUM>; a longitudinally extending side wall <NUM> which extends partially around the interior flame space <NUM>; an end wall <NUM> at the forward longitudinal end of the side wall <NUM>; and a lateral side opening <NUM>. The end wall <NUM> is preferably a solid circular end wall which extends laterally over and covers the interior flame space <NUM>. The longitudinally extending side wall <NUM> of the flame diverter <NUM> has a semicircular lateral cross-sectional shape which extends from a first arc end point <NUM> to a second arc end point <NUM>. The semicircular cross-sectional shape of the longitudinally extending side wall <NUM> is preferably an arc in the range of from <NUM>° to <NUM>° which extends from the first arc end point <NUM> to the second arc end point <NUM> and is more preferably an arc of about <NUM>°.

The lateral side opening <NUM> of the flame diverter <NUM> preferably (a) extends from the first arc end point <NUM> to the second arc end point <NUM> of the side wall <NUM> in the lateral cross-sectional plane and (b) extends longitudinally from the lateral flame stabilization ring <NUM> to the end wall <NUM> of the flame diverter <NUM>. The lateral side opening <NUM> is preferably oriented to discharge the flame <NUM> of the auxiliary burner tip <NUM> laterally outward at an angle which is in the range of from <NUM>° to <NUM>°, more preferable about <NUM>°, with respect to the longitudinal axis <NUM> of the tip shield housing <NUM>.

In order to maintain the stability of the main burner flame <NUM>, the flame diverter <NUM> diverts and directs the auxiliary tip flame <NUM> laterally outward onto (a) the forward end <NUM> of the burner wall <NUM>, (b) an internal ledge, shoulder or other internal feature of the burner wall <NUM>, or (c) any other stability point of the burner <NUM>. Moreover, the diversion of the auxiliary tip flame <NUM> by the flame diverter <NUM> advantageously provides a staged air operating regime for the sub-stoichiometric auxiliary tip <NUM> which reduces the NOx emissions produced by the auxiliary tip <NUM>.

In the staged air operation of the auxiliary burner tip <NUM>, the sub-stoichiometric, fuel rich, mixture of gas fuel and oxygen-containing gas (preferably air) flowing out of the forward end of the mixing chamber <NUM> begins combustion in a sub-stoichiometric combustion region <NUM>, which includes the interior flame space <NUM> of the flame diverter <NUM>. Next, the auxiliary tip flame <NUM> is diverted laterally into the air or other oxygen-containing gas flowing through the interior passageway <NUM> of the inventive burner <NUM>, outside of the auxiliary burner tip <NUM>. The diversion of the auxiliary tip flame <NUM> into the flow of air, or other oxygen-containing gas, creates a fuel lean combustion region <NUM>, outside of the auxiliary tip <NUM>, in which the remaining portion of the gas fuel which was not combusted in the sub-stoichiometric combustion zone <NUM> of the auxiliary tip <NUM> is burned.

The staged air operation provided by combusting a first portion of the auxiliary tip fuel in the sub-stoichiometric flame region <NUM> followed by combustion of the remainder of the fuel in the fuel lean flame region <NUM> reduces the peak temperature of the auxiliary tip flame <NUM> in in both regions and thereby reduces the levels of NOx and other emissions produced by the auxiliary tip <NUM>.

Although the inventive burner <NUM> is illustrated in the drawings as being in a vertical orientation, it will be understood that the burner <NUM> can alternatively be oriented downwardly, horizontally, or at any other desired angle. In addition, although various elements and features of the inventive burner <NUM> are shown and may be described as having cylindrical or circular shapes, it will be understood that these elements and features can alternatively be square or oval in shape, or can be of any other shape desired.

As exemplified in other embodiments shown and described herein, the burner wall <NUM> of inventive burner <NUM> can be circular, square, rectangular, or generally any other desired shape. In addition, the series of fuel ejectors <NUM> employed in the inventive burner <NUM> need not entirely surround the burner wall <NUM>. For example, the series ejectors <NUM> may only partially surround the burner wall <NUM> in certain applications where the inventive burner <NUM> is used in a furnace sidewall location or is specially configured to provide a desired flame shape.

Also, although only a single series of ejectors <NUM> surrounding the burner wall <NUM> is shown in <FIG>, it will be understood that the burner <NUM> could have one or more additional series of ejectors spaced radially outward and/or radially inward from the series of ejectors <NUM>. The main burner flame <NUM> can also comprise either a single combustion stage or multiple combustion stages. Additional fuel tips or pre-mix tips for the main burner flame <NUM> can also be included in the interior passage <NUM> of the burner wall <NUM>. Further, other possible additions to the burner <NUM> can include a regen tile, a swirler, and/or a stabilization cone in the burner throat <NUM>, particularly in the event that a liquid fuel is ejected within or just outside of the forward end of the burner throat <NUM>.

To further facilitate the entrainment and mixing of flue gas with the fuel jet flow streams <NUM>, the inventive burner <NUM> preferably comprises one or more exterior impact structures 42a-c which can be positioned at least partially within the paths of some or all of the flow streams <NUM>. Each such impact structure 42a-c can generally be any type of obstruction which will decrease the flow momentum and/or increase the turbulence of the fuel streams <NUM> sufficiently to promote flue gas entrainment and mixing while allowing the resulting mixture to flow on to the main burner flame <NUM>.

Although other types of impact structures 42a-c can be employed, the impact structures 42a-c used in the inventive burner <NUM> will most preferably be tiered ledges or other features of a type which can be conveniently formed in a poured refractory as part of and/or along with the burner wall <NUM>. In addition, although three impact ledges 42a-c are shown in <FIG>, it will be understood that the inventive burner <NUM> can have any number from one to n of such tiered ledges <NUM> and that the number n of tiered ledges used in the inventive burner <NUM> will preferably be in the range of from <NUM> to <NUM>.

The burner wall <NUM> employed in inventive burner <NUM> provides a particularly desirable tiered exterior shape wherein the diameter of the base <NUM> of the burner wall <NUM> is broader than the forward end <NUM> thereof and the exterior of the burner wall <NUM> presents a series of concentric, spaced apart, impact ledges <NUM> a-c. The outermost impact ledge 42c is defined by the flat, radial, surrounding shoulder <NUM> at the forward end <NUM> of burner wall <NUM>. At least one, preferably at least two, additional impact ledges 42a and 42b are then positioned on the exterior of burner wall <NUM> between the ejectors <NUM> and the forward shoulder/ledge 42c. Proceeding from the outer end <NUM> to the base <NUM> of the burner wall <NUM>, each additional ledge <NUM> is preferably broader in diameter than, and is spaced longitudinally rearward of and laterally outward from, the previous ledge <NUM>.

Depending upon the characteristics and size of the heating system in which the inventive burner <NUM> is used, and the amount of heat output required, the size and dimensions of the burner <NUM> can range from small to very large. Consequently, the longitudinal height 60a-c of each of the tiered ledges 42a-c of the burner <NUM> can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more. However, for most applications the longitudinal height 60a-c of each ledge 42a-c will preferably be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches). Similarly, the radial width 62a-c of each impact ledge 42a-c can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more. However, for most applications the radial width 62a-c of each impact ledge 42a-c will preferably be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) and will more preferably be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches).

As illustrated, for example, in <FIG>, the internal passageway <NUM> extending through the burner wall <NUM> can be a tapered throat having a wider diameter at the base <NUM> than at the outer end <NUM> of the burner wall <NUM>. A tapered throat <NUM> of the type depicted in <FIG> provides a choke point for the flow of air or other oxygen-containing gas which increases the velocity of the flow and creates even more of a reduced pressure region at the outer end <NUM> of the burner <NUM>. The enhanced reduced pressure region assists in (a) holding the main burner flame <NUM> on or closely adjacent to the surrounding radial shoulder <NUM> at the forward end <NUM> of the burner wall <NUM> and (b) drawing additional flue gas into the main flame combustion mixture.

Because the entire quantity of fuel used in the inventive burner <NUM> is so well conditioned with the furnace flue gas, combustion occurs at a significantly reduced rate and lower flame temperature, thus resulting in lower NOx emissions.

An alternative embodiment <NUM> of the inventive burner is depicted in <FIG>. Burner <NUM> is substantially identical to burner <NUM> except that the exterior of the burner wall <NUM> is substantially cylindrical in shape such that the burner wall <NUM> has only a single impact ledge <NUM> provided at the outer end <NUM> thereof. The longitudinal height <NUM> of the single impact ledge <NUM> can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more and will more typically be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches). The radial width <NUM> of the surrounding shoulder <NUM> at the forward end of the burner wall <NUM> of the burner <NUM> can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more and will more typically be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches).

<FIG> shows another alternative embodiment <NUM> of the inventive burner which is substantially identical to burner <NUM> except that the burner <NUM> has a sloped impact surface <NUM> provided on the exterior of burner wall <NUM>. The sloped surface <NUM> tapers inwardly toward the outer end <NUM>. The longitudinal height <NUM> of the rearward end <NUM> of the sloped surface <NUM> can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more and will more typically be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches). The longitudinal distance <NUM> from the rearward end <NUM> of the sloped surface <NUM> to the outer end <NUM> of the burner wall <NUM> of the burner <NUM> can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more and will more typically be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches). The radial width <NUM> of the surrounding shoulder <NUM> at the forward end of the burner wall of the burner <NUM> can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more and will more typically be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches).

<FIG> depicts another alternative embodiment <NUM> of inventive burner which is identical to burner <NUM> except that burner <NUM> is rectangular rather than circular in shape. <FIG> is a top view of the rectangular burner <NUM> wherein the burner wall <NUM> possesses a plurality of tiered, exterior impact ledges <NUM>. A multiplicity of fuel ejection tips <NUM> are located outside the periphery of the burner wall <NUM> and a pair of auxiliary burners <NUM> are positioned in the interior flow passageway <NUM> as afore described. A burner pilot <NUM> can optionally be located within the interior passageway <NUM> to initiate combustion at the outer end <NUM> of the burner wall <NUM>. The spacing of the fuel ejection tips <NUM>, the size of the ejection ports, the spacing of the auxiliary tips <NUM>, the dimensions of the impact ledges, etc. are preferably all the same as described above for burner <NUM>.

<FIG> and <FIG> depict structures of a type which can desirably be used in any of the embodiments described above to enhance the reduced pressure region at the outer end of the burner wall. The structure employed in <FIG> is an internal ledge <NUM> which forms a radial shoulder just inside of the outer end <NUM> of the internal passageway <NUM> for the air or other oxygen-containing gas. The longitudinal depth <NUM> of the ledge <NUM> can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more and will more typically be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inch). The radial width <NUM> of the ledge <NUM> can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more and will more typically be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches). The radial width <NUM> of the surrounding shoulder <NUM> at the forward end <NUM> of the burner wall can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more and will more typically be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches).

The structure employed in <FIG> is a sloped (beveled), outwardly diverging surface <NUM> formed just inside of the outer end <NUM> of the internal passageway <NUM> for the air or other oxygen-containing gas. The longitudinal depth <NUM> of the beveled surface can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more and will more typically be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inch). The radial width <NUM> of the beveled surface can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more and will more typically be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches). The radial width <NUM> of the surrounding shoulder <NUM> at the forward end <NUM> of the burner wall can be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches) or more and will more typically be in the range of from <NUM> to <NUM> (<NUM> to <NUM> inches).

The structures of <FIG> and <FIG>, or structures similar to those of <FIG> and <FIG>, further enhance the reduced pressure zone at the outlet end of the air flow passageway to assist in stabilizing the main burner flame by drawing the combustion flame to and holding the flame at the outer/forward end of the burner wall. The reduced pressure region also assists in mixing the combustion air or other oxygen-containing gas with the fuel streams and flue gas.

The burner <NUM> or other burner provided by the present invention can be a new burner or can be an existing prior art free-jet burner which is revamped to be resistant to plugging while maintaining low NOx emissions. The existing prior art burner will typically comprise: (i) a burner wall, (ii) an interior passageway of the burner wall for a flow of air or other oxygen-containing gas out of a forward end of the burner wall, and (iii) a series of x original ejectors which are positioned outside of and spaced around the interior passageway of the burner wall to deliver a fuel from the ejectors in free-jet flow streams outside of the burner wall either directly or indirectly to the main burner flame at and/or forwardly of the forward end of the burner wall.

In accordance with another aspect of the method of the present invention, the existing prior art free-jet burner is preferably revamped by: (a) increasing the tip-to-tip spacing of the ejectors by removing every other one of the original ejectors so that the number of remaining ejectors will be (i) one half of the number x of the original ejectors if the number x of the original ejectors is an even number or (ii) not more than ((x-<NUM>)/<NUM>) + <NUM> if the number of the original ejectors is an odd number; (b) replacing each of the remaining ejectors with a plugging resistant ejector having a large fuel ejection port with a flow area of at least <NUM><NUM> (<NUM> inch<NUM>); and (c) stabilizing the main burner flame by installing at least two auxiliary burner tips in the internal passageway of the burner wall which each direct an auxiliary tip flame onto the surrounding shoulder at the forward end of the burner wall or onto a ledge or other interior feature of the burner wall.

Concerning the original ejectors which are removed from the existing burner, pipe plugs will preferably be used to plug the locations in the exterior fuel supply manifold where the risers for these ejectors were connected. If the remaining ejectors comprise ejector tips positioned on the ends of fuel risers, the ejection ports will preferably be replaced by removing the original tips from the risers and installing new tips having larger ejection ports on the existing risers. The larger ports of the new tips will preferably have a flow area of at least <NUM><NUM> (<NUM> inch<NUM>) as mentioned above and will more preferably have a flow area of at least <NUM><NUM> (<NUM> inch<NUM>).

The auxiliary burner tips can be any tips which are resistant to plugging and provide low NOx emissions. Each of the auxiliary burner tips will be a sub-stoichiometric staged air burner tip <NUM> as described above and shown in <FIG>. As also described above, the fuel supply line extending to the gas fuel spud <NUM> of each auxiliary burner tip <NUM> will preferably include an orifice union <NUM> with a flow orifice therein. The orifice will preferably have a flow area of at least <NUM><NUM> (<NUM> inch<NUM>), more preferably at least <NUM><NUM> (<NUM> inch<NUM>), and the flow area of the fuel port <NUM> of the gas fuel spud <NUM> will preferably be larger than the flow area of the flow orifice.

Claim 1:
A burner (<NUM>) providing reduced NOx emissions, wherein the burner is for use in a heating system having a flue gas therein and the burner comprises (i) a burner wall (<NUM>) having a forward end (<NUM>), (ii) an interior passageway (<NUM>) of the burner wall for a flow of air or other oxygen-containing gas out of the forward end of the burner wall, and (iii) a series of ejectors (<NUM>) positioned to deliver a fuel from the ejectors in free-jet flow streams outside of the burner wall either directly or indirectly to a main burner flame (<NUM>) at and/or forwardly of the forward end of the burner wall, wherein the burner comprises:
large fuel ejection ports (<NUM>) in the ejectors having a flow area of at least <NUM><NUM> (<NUM> inch<NUM>) which provide resistance to plugging;
a wide tip-to-tip spacing (<NUM>) between the ejectors of from <NUM> to <NUM> (<NUM> to <NUM> inches) which provides enhanced recirculation of the flue gas to the main burner flame for the free-jet flow streams from the large fuel ejection ports; and
one or more auxiliary burner tips (<NUM>) in the internal passageway of the burner wall to stabilize the main burner flame, each said auxiliary burner tip having a large fuel discharge port (<NUM>) with a flow area of at least <NUM><NUM> (<NUM> inch<NUM>) which provides resistance to plugging;
each of the one or more auxiliary burner tips being a sub-stoichiometric, staged air burner tip comprising:
a shield housing (<NUM>) having a mixing chamber (<NUM>) therein and a longitudinally extending outer wall (<NUM>) which surrounds the mixing chamber;
a gas fuel spud (<NUM>) which includes the large fuel discharge port, the large fuel discharge port of the gas fuel spud being positioned to discharge a gas fuel into a rearward longitudinal end of the mixing chamber;
a lateral base wall (<NUM>) of the shield housing at a rearward longitudinal end of the mixing chamber, the lateral base wall having at least a central opening (<NUM>) provided therethrough;
a lateral flame stabilization ring (<NUM>) of the shield housing at a forward longitudinal end of the mixing chamber, the flame stabilization ring having a discharge opening (<NUM>) for the mixing chamber provided therethrough; and
a flame diverter (<NUM>) on a forward longitudinal end of the shield housing configured to divert the flame laterally outward.