Abstract:
A burner assembly for and method of producing ethylene having a mechanism to inject either primary fuel, staged fuel, or both by premix methods before combustion in a furnace. The burner assembly has at least one premix injection assembly for either exclusively primary fuel or exclusively staged fuel injection paired with a nozzle mix injection or injection means for primary and staged fuel both by premix methods. The primary fuel premix assembly associates with a burner tile that consists of multiple inlets and outlets connected by venturi channels to direct and combine combustion air and staged fuel coming from staged fuel orifice spuds. Primary fuel and combustion air are mixed in a premix assembly and directed inside the furnace, and above the burner tile to complete the reaction with the staged fuel and combustion air mixture in a combustion zone inside of the furnace.

Description:
1. FIELD OF THE INVENTION 
       [0001]    This invention relates generally to a burner assembly for use in a furnace. More specifically, the invention relates to a burner assembly for improved, ultra-low NO x  burner performance in ethylene cracking furnaces. 
       2. BACKGROUND AND DESCRIPTION OF THE RELATED ART 
       [0002]    Ethylene production continues to grow and has replaced acetylene for many applications. Ethylene production occurs mainly through pyrolysis which is the thermal cracking of various hydrocarbon streams in the presence of steam. The heat transfer in the radiant section of a thermal cracking furnace is critical. Cracking furnaces present both burner design and operating challenges in comparison to typical process heaters. The thermal cracking of hydrocarbons in the radiant section process tubes of a cracking furnace occurs at a higher temperature compared to most other refinery or chemical processes. In order to crack hydrocarbons in the presence of steam, the temperature of the combustion products in the radiant section of the furnace must be high to achieve the required heat transfer. 
         [0003]    Fuel gas burned at high temperatures in an excess air environment results in the production of Nitrogen Oxides (NO x ). NO x  is considered hazardous to the environment and, thus, environmental regulations have been placed on the quantity of NO x  that could be produced in the combustion process in fired heaters and furnaces. Due to various regulations, burner designs used in cracking furnaces have evolved in recent years, improving the efficiency of combustion while reducing the amount of NO x  produced. In one approach, staged combustion has been used to reduce the amount of NO x  formed in the combustion process by reducing the flame temperature and reducing the concentration of oxygen available. Staged combustion involves delaying the mixing of the fuel and air and promotes the mixing of combustion products with the fuel and air mixture to provide a reduction in flame temperature and a reduction in the partial pressure of oxygen. Combustion products are the products of combustion from the burner which fill the inside of the furnace prior to discharge at the top of the furnace. Combustion products may be comprised of components such as carbon dioxide, water vapor, nitrogen and oxygen. 
         [0004]    Historically, thermal cracking furnaces were fired with a large number of premix radiant wall burners. Premix radiant wall burners are well known for their short, compact flame, which can produce uniform heat flux throughout the radiant section of the furnace. Although premix burners are a common design in cracking furnaces there are significant cost issues associated with the use of premix burners because a large number of burners must be installed. 
         [0005]    Current low NO x  burner designs employed in cracking furnaces are typically nozzle mix “deeply” staged fuel configurations. Low NO x  cracking furnace burners discharge fuel from two distinct locations. Typically one discharge location is in the burner tile throat area. This location discharges an initial source of fuel, called primary fuel, which comprises 10%-% of the total fuel burned. The burners typically include one or more (primary fuel nozzle mix tips that are located in a burner air passage that pass through the throat of a burner tile. This primary fuel burns in an environment with high excess air, which could lead to increased NO x  formation if the fuel and air are not completely mixed. The remainder of the fuel needed for the process is injected at a secondary location which is external to the burner tile and downstream from an air passage discharge used to discharge the primary fuel. The fuel discharged at the second location is called secondary or staged fuel. Secondary fuel is normally discharged through multiple nozzle fuel tips that are located external of the burner tile. Such burner assemblies are normally referred to as “deeply” staged because they use two locations for the discharge of fuel and the majority of the fuel they utilize is staged at the secondary or staged location. For minimal NO x  emissions, “deeply” staged fuel burners mix combustion products with the staged filet prior to combustion the secondary combustion zone. In such a design, the staged tip configurations that are necessary to minimize flame length and stabilize the flame in the secondary combustion zone entrain an insufficient amount of combustion products that are mixed with the staged fuel. Subsequently, the burner does not achieve maximum reduction in NO x  emissions. These burners are either floor fired burners (hearth burners) or floor fired burners in combination with side wall or balcony burners. These burners employ a rectangular discharge opening of the burner tile that sits against the furnace wall and provides a flat flame. The low NO x  premix assembly of the present invention incorporates staged fuel combustion and combustion product recirculation to reduce the level of NO x  generated, while providing minimum flame length and maximum stability. 
         [0006]    Recently, there has been an effort to reduce the physical size of the thermal cracking furnace which consequently reduces the furnace volume white increasing the heat density. Subsequently, by decreasing the length of the furnace, the space between burners has been reduced causing flame overlap and interference. This flame overlapping tends to cause NO x  emissions to increase. Further, another effect of flame overlap is for the flame length to increase, so much so that the flames between the burners tend to protrude further into the furnace space between the furnace wall and the process tubes. Combustion product flow patterns in the radiant section of the furnace have a significant impact the burner flame pattern. Combustion products flow upwards along a hot firing wall, white a downward flow recirculates back toward the furnace floor along the surface of the lower temperature tubes. If the burner flames become too long then the combustion product flow within the furnace is able to draw the flames across the furnace to the tubes causing overheating of the tubes which may lead to tube failure. 
         [0007]    Additionally, (prior art burner designs have further complications. The nozzle mix “deeply” staged fuel burner configuration results in a low discharge velocity as the primary fuel combustion products and any excess combustion air exits the burner tile. Also the prior burner design results in a delayed mixing of combustion air with the deeply staged fuel. Therefore, with the combination of circulation patterns in the furnace, low discharge velocity, and the delayed mixing of combustion air and staged fuel, a complication called “flame rollover” commonly results. Flame rollover can occur in the upper portions of the flame resulting in flame impingement or hot gas impingement on the process tubes. 
         [0008]    Yet another complication of the “deeply” staged fuel configurations is that the delayed burning of the staged fuel creates a relatively low combustion temperature above the top of the burner the and therefore the desired radiant flux profile may not be available for appropriate heat transfer giving a lower than desired efficiency. 
         [0009]    Accordingly, it is therefore desirable to provide a cracking furnace burner assembly with a burner tile design that allows for an efficient mechanism to mix combustion products with the air and fuel within the burner the prior to combustion in the furnace thereby providing an extremely uniform high velocity mixture that reduces the flame length as well as subsequent complications such as flame rollover. 
         [0010]    It is further desirable to provide a cracking furnace burner assembly that uses premix methods for discharging either or both primary and staged fuel providing a uniform fuel, air and combustion product-mixture prior to combustion thereby minimizing NO x  emissions and flame length. 
         [0011]    It is yet further desirable to provide a burner assembly design that uses premix fuel burner tips that allow gas mixtures to exit the burner tile at an extremely high velocity to prevent flame rollover. 
         [0012]    It is yet further desirable to provide a burner assembly design that utilizes combustion products from within the furnace in order to cool the system, thereby minimizing NO x  levels. 
         [0013]    It is yet further desirable to provide a burner assembly design that allows for the complete mixing of the primary fuel and the air promoting the initial 50% of combustion to occur close to the tile discharge of the burner tile and under sub-stoichiometric conditions. 
         [0014]    It is yet further desirable to provide a burner assembly design that eliminates delayed combustion accounted for in deeply staged fuel designs. 
       SUMMARY OF THE INVENTION 
       [0015]    In general, in a first aspect, the invention relates to a low NO x  burner assembly for use in an ethylene cracking furnace or similar heating application. 
         [0016]    The burner assembly may provide for a flat flame shape or a round flame shape. The burner assembly uses premix methods of discharging fuel through a choice of discharge locations. Therefore, one embodiment of the assembly provides an improvement to discharge primary fuel while retaining the current method of discharging staged fuel, another embodiment of the assembly provides an improvement upon the method of discharging staged fuel while retaining the current means of discharging primary fuel, and yet another embodiment of the assembly provides improvement for discharging both the primary fuel and the staged fuel. 
         [0017]    In the preferred embodiments, a portion (approximately 50%) of the fuel is delivered directly to the primary mixer tips while the remaining portion of the fuel is delivered to the staged fuel spuds. The primary premix venturi and tip assemblies are designed such that most (approximately 90%) of the stoichiometric air required for combusting the primary fuel is induced into the primary combustion zone by the primary fuel. The fuel and air mixture that exits a primary venturi and tip assembly is a very uniform fuel rich mixture that burns under sub stoichiometric conditions resulting in a low generation of NO x . The uniform mixture permits the combustion of the fuel without any transition from an air rich condition to a fuel rich condition that occurs during the mixing of the two streams in a nozzle mix burner. The excess air combustion that occurs during this transition creates high NO x  emissions. 
         [0018]    The remainder of the required combustion air enters the burner tile through multiple combustion air inlets that are cast into the tile. Venturi channels are also cast into the burner tile. Multiple staged fuel spuds are located at the inlet of these venturi channels in the lower portion of the tile. The energy from the staged fuel entrains combustion products from the furnace resulting in the mixing of the combustion products and staged fuel with the combustion air before exiting the tile and entering into the burner combustion zone. The combustion of this mixture of fuel, combustion products, and combustion air generates extremely low NO x  levels. 
         [0019]    The mixture of combustion products, staged fuel and combustion air is injected at a slight angle towards the primary fuel and air mixture above the burner tile providing the additional combustion air required for complete combustion of the primary fuel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a perspective view of a prior art burner design currently used in Low NO x  cracking furnaces; 
           [0021]      FIG. 2  is a perspective view of a first preferred embodiment of a burner assembly constructed according to the present invention; 
           [0022]      FIG. 3  is a cross sectional view of a first preferred embodiment of a burner assembly constructed according to the present invention; 
           [0023]      FIG. 4  is a perspective view of a second preferred embodiment of a burner assembly constructed according to the present invention; 
           [0024]      FIG. 5  is a cross sectional view of a second preferred embodiment of a burner assembly constructed according to the present invention; 
           [0025]      FIG. 6  is a perspective view of a third preferred embodiment of a burner assembly constructed according to the present invention; 
           [0026]      FIG. 7  is a cross sectional view of a third preferred embodiment of a burner assembly constructed according to the present invention; 
           [0027]      FIG. 8  is a perspective view of a third preferred embodiment of a burner assembly associated with a furnace constructed according to the present invention; and 
           [0028]      FIG. 9  is a perspective view of a premix primary venturi and tip assembly constructed according to the present invention. 
       
    
    
       [0029]    Other advantages and features will be apparent from the following description, and from the claims. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    The devices and methods discussed herein are merely illustrative of specific manners in which to make and use this invention and are not to be interpreted as limiting in scope. 
         [0031]    While the devices and methods have been described with a certain degree of particularity, it is to be noted that many modifications may be made in the details of the construction and the arrangement of the devices and components without departing from the spirit and scope of this disclosure. It is understood that the devices and methods are not limited to the embodiments set forth herein for purposes of exemplification. 
         [0032]    As shown in the drawings and understood by those skilled in the art, the burner assembly may be associated with a furnace or other heating applications to generate heat in a petroleum refinery, petro-chemical plant, or other applications. 
         [0033]    Referring now to  FIG. 1 , a perspective view of a prior art burner design currently used in low NO x  cracking furnaces. The current state-of-the-art low NO x  cracking furnace burner designs have a primary fuel discharge and a secondary fuel discharge. As shown in  FIG. 1 , current burners in the art employ a nozzle mix tip design for both the primary fuel tips  26  and the staged fuel tips  32 . Nozzle mix tips are ordinary tips that do not provide for a method of mixing fuel with combustion air before discharge of the fuel into the combustion zone. The primary fuel discharge of a prior art burner is in the throat of the burner tile. The primary fuel tips  26  are in the combustion air flow passage. Combustion air comes from outside of the furnace through a windbox opening  44  and into the windbox  46 . Two primary fuel tips  26  are shown, however the number may vary. In such a prior art burner design, the secondary or staged fuel is discharged near the base of the burner tile. As shown, the staged fuel tips  32  of prior art designs are external to the burner tile so that the staged fuel would discharge upward along the outer surface of the burner tile. Because the prior art designs use nozzle mix tips to discharge fuel, both the primary fuel and the secondary fuel exit first into a combustion zone prior to mixing with any combustion air. 
         [0034]      FIGS. 2 and 3  show a first preferred embodiment of the present disclosure.  FIG. 2  is a perspective view of a first preferred embodiment of a burner assembly. In the first preferred embodiment of the burner assembly, the primary fuel is mixed with combustion air prior to being discharged into a combustion zone within the furnace. Then this improved primary premix fuel discharge method of this preferred embodiment can be used with the current state-of-the-art nozzle mix or raw gas tip method to inject secondary or staged fuel. 
         [0035]    The bunter assembly  10  includes a burner tile  16 . The burner tile  16  may be rectangular in shape with six sides. The burner tile  16  sits within the furnace and serves to house and associate different components of the burner assembly  10 . The burner tile  16  has a front side that is parallel and adjacent to the furnace wall  12 . The remaining five sides of the burner tile  16  are positioned so that they sit or reside within the furnace. The remaining sides include a top side, a bottom side, a back side, and two sides that sit directly opposite one another. A windbox  46  extends away from the burner tile  16  and furnace. The windbox  46  has an opening  44  for the entrance of combustion air. The burner tile  16  may include a rectangular discharge opening  20  on the top side of the burner tile which may produce a rectangular, flat flame that lies against the furnace wall (not shown) which provides uniform heat distribution along the furnace wall  12 . Although not shown in the drawings, the burner tile configuration may also be rounded per requirement by each particular burner application. 
         [0036]    As best illustrated in  FIG. 3 , a portion of fuel, referred to herein as primary fuel, enters at high pressures through at least one primary fuel riser  28  that direct primary fuel into a primary fuel orifice spud  48 . The primary fuel orifice spud  48  introduces the primary fuel into the premix venturi and tip assembly  18  which is fluidly connected to a primary fuel riser  28 . The primary fuel may be natural gas fuel or any other gaseous fuels typically used in fired industrial applications. The premix venturi and tip assembly  18  may connect to the burner tile  16  and may extend outwardly away from the burner tile  16 . The premix venturi and tip assembly  18  connects to the burner tile  16  by a connective opening so they are in fluid communication. 
         [0037]    Shown in more detail in  FIG. 9 , the premix venturi and tip assembly  18  consists of an inlet  24  which is in fluid communication with an elongated venturi mixing chamber  22 . The primary fuel riser  28  introduces the primary fuel into the premix venturi and tip assembly  18  by way of a primary fuel orifice spud  48 . The admittance of primary fuel into the venturi mixing chamber  22  induces combustion air into the venturi mixing chamber  22 . The combustion air is drawn in from outside of the furnace through a windbox opening  44 . The premix venturi and tip assembly  18  is designed such that approximately ninety percent (90%) of the stoichiometric air required for combusting the primary fuel is induced into the burner assembly by the primary fuel. The primary fuel and combustion air create a mixture within the premix venturi and tip assembly  18 . The primary fuel and combustion air mixture discharges through the primary mixer tip  38  which is in fluid communication with the premix venturi and tip assembly  18 . The primary mixer tip  38  sits within the burner tile  16  and is associated with the discharge opening  20  to discharge the pre-mixed primary fuel and combustion air mixture above the burner tile and into the combustion zone of the furnace space. The primary fuel and combustion air mixture that exits the primary mixer tip  38  is a uniform mixture that burns under sub-stoichiometric conditions resulting in low levels of NO x  generation. The uniformity of the mixture is important to ensure conditions that have little to no excess oxygen or air. The mixture of the fuel and air burns rapidly providing a well-defined, compact flame that is desirable to achieve the required heat flux to the process tubes. Further, the combustion of the uniform mixture occurs close to the discharge  20  of the burner tile  16  thereby eliminating a problem of deeply staged fuel designs and the relatively low combustion temperature above the top of the burner tile. The fuel and combustion air mixture exits the primary mixer tip  38  at an extremely high velocity. As a result, the high velocity of the primary fuel and combustion air mixture combines with the combustion products in the furnace and adheres to the hot firing wall of the furnace until the mixture reaches the top of the furnace. Inside the furnace space of the furnace, the burner flames tend to flow upward and vertically, also adhering along a hot firing wall while combustion products flow or recirculate along the opposite wall of the furnace where the process tubes are located. Due to the high velocity of the mixture relative to the current inside the furnace the flame is not pulled away from the furnace wall by the low velocity furnace currents. Therefore, the flame does not rollover and contact the tubes. Shown in  FIG. 2 , the burner tile  16  may have a passageway  40  on either side of the burner tile  16  to allow the high velocity primary fuel and combustion air mixture to circulate combustion products from inside of the furnace into the burner tile  16  in order to further reduce flame temperature and subsequently reduce the amount of NO x  generated by the combustion of the primary fuel. 
         [0038]    In this embodiment, secondary or staged fuel is injected through staged fuel risers  42  and discharges through staged fuel tips  32  by way of the nozzle mix tip method that is currently used in prior art. The staged fuel tips  32  are positioned external to the burner tile  16  similarly to that in prior art burner assemblies. After injection, the staged fuel travels upward along the outer face of the burner tile  16  and does not mix with combustion an until it reaches the combustion zone in the furnace space which is above the burner tile  16 . Combustion air enters from outside of the furnace and into windbox  46  through windbox opening  44 . The combustion air may then enter the burner tile  16  through a single secondary combustion air slot (not shown) or multiple secondary air inlets  30  that are cast into the burner tile  16  and communicate from the air inlet to the furnace space. The secondary combustion air exits the burner tile  16  through discharge outlets  36  into the burner combustion zone of the furnace where it meets with the staged fuel traveling from the exterior of the burner tile  16 . 
         [0039]      FIGS. 4 and 5  illustrate a second preferred embodiment of the burner assembly constructed according to the present invention.  FIG. 4  is a perspective view of the second preferred embodiment of the burner assembly. The burner assembly sits within a burner tile  16  similar to the burner tile  16  of the aforementioned first preferred embodiment. Primary fuel is injected by primary fuel risers  28  and discharged through primary fuel tips  26 . Secondary or staged fuel is injected by staged fuel risers  42 . The staged fuel is discharged from staged fuel orifice spuds  50 . However, in the second preferred embodiment, the primary fuel is injected by the nozzle mix tip method used in prior art, but the secondary or staged fuel is injected by the improved, premix means. 
         [0040]      FIG. 5  is a cross sectional view of the second preferred embodiment of the burner assembly  10 . Primary fuel enters primary fuel risers  28  and is discharged through primary fuel tips  26 .  FIG. 4  shows two nozzle mix primary fuel tips  26 , however, the number of tips can vary from a single tip to multiple tips. The primary fuel is injected by the nozzle mix method where combustion air and the primary fuel are only partially mixed prior to the discharge of primary fuel into the combustion zone. The primary fuel is discharged from the primary fuel tips  26  and subsequently enters into the furnace space where combustion takes place. 
         [0041]    In the second preferred embodiment, combustion air enters into windbox  46  through windbox openings  44 . The combustion air then may enter the burner tile  16  through multiple combustion air inlets  30  that are cast into the burner tile  16  and communicate from the inlet to the furnace space.  FIG. 4  shows five combustion air inlets  30 , but the assembly can vary from one inlet to multiple inlets. The secondary air inlets  30  create a passageway leading secondary combustion air to venturi channels  34  cast within the burner tile  16 . Staged fuel may be injected nearly vertically from the set of staged fuel orifice spuds  50 .  FIG. 4  shows five staged fuel spuds, but could have anywhere from one to multiple. The staged fuel may consist of natural gas fuel or any other gaseous fuel typically used in industrial applications. The staged fuel orifice spuds  50  are fluidly connected to staged fuel risers  42 . The staged fuel from the staged fuel orifice spuds  50  is received by multiple staged fuel venturi channels  34  located above each staged fuel orifice spud  50 . Each staged fuel orifice spud  50  corresponds to a staged fuel venturi channel  34 . The high velocity staged fuel discharging from the staged fuel orifice spuds  50  entrains combustion products from the furnace space. The staged fuel and entrained combustion products mix within the venturi channels  34 . Subsequently, the mixture thoroughly combines with combustion air coming from combustion air inlets  30  before exiting the burner tile  16  through discharge outlets  36  and thereafter enters the burner combustion zone of the furnace. 
         [0042]    The discharge outlets  36  are on the top side of the burner tile  16  and are cast into the burner tile  16  with a slight angle so that the mixture of combustion products, staged fuel, and combustion air is injected at a slight angle towards the primary fuel and combustion air mixture which was earlier released in the combustion zone of the furnace. This provides the additional combustion air necessary for the completion of the combustion of the primary fuel. The delayed mixing of the fuel, combustion products, and the combustion air permits more heat transfer to occur during the combustion process which provides for a cooler flame. The low temperature combustion produces low levels of NO x . 
         [0043]      FIGS. 6 and 7  illustrate a third preferred embodiment of the burner assembly constructed according to the present invention.  FIG. 6  is a perspective view of the third preferred embodiment of the burner assembly. The third preferred embodiment discharges both primary fuel and secondary or staged fuel by an improved premix method. Two premix venturi and tip assemblies  18  are shown, but there could be as few as one to as many as multiple assemblies. Primary fuel enters through a primary fuel riser  28  which connects to a primary fuel orifice spud  48  which discharges the primary fuel into the venturi and tip assembly  18 . Combustion air coming from outside of the furnace through windbox opening  44  is entrained into the venturi and tip assembly  18  by the primary fuel. Approximately 90% of the stoichiometric air is induced into the premix venturi and tip assemblies  18  and mixes with the primary fuel. A uniform mixture of primary fuel and combustion air exits the premix venturi and tip assemblies  18  through the primary mixer tip  38 . The uniform mixture along with entrained combustion products then may exit the burner tile  16  through the burner discharge  20  and may enter into the combustion zone of the furnace. The primary fuel and combustion air mixture that exits the primary mixer tip  38  is a uniform mixture that burns under sub-stoichiometric conditions resulting in low levels of NO x  generation. The fuel and combustion air mixture exits the primary mixer tip  38  at an extremely high velocity. As a result, the high velocity of the primary fuel and combustion air mixture combines with the combustion products in the furnace and adheres to a hot firing wall of the furnace until the mixture reaches the top of the furnace. Due to the high velocity of the mixture relative to the current inside the furnace, the flame is not pulled away from the furnace wall by the low velocity furnace currents. Therefore, the flame does not rollover and contact the tubes. Shown in  FIG. 6 , the burner tile  16  may have a passageway  40  on either side of the burner tile  16  to allow the high velocity primary fuel and combustion air mixture to circulate combustion products from inside of the furnace into burner tile  16  in order to further reduce flame temperature and subsequently reduce the amount of NO x  generated by the combustion of the primary fuel. 
         [0044]    Shown in  FIG. 7 , combustion air coming from outside of the furnace through windbox openings  44  may enter the burner tile  16  through multiple combustion air inlets  30  that are cast into the burner tile  16  and communicate with the furnace space. The combustion air inlets  30  lead secondary combustion air to venturi channels  34  cast within the burner tile  16 . Staged fuel may be injected nearly vertically from the set of staged fuel orifice spuds  50 . The burner assembly could have one or multiple staged fuel orifice spuds  50 . The staged fuel may consist of natural gas fuel or any other gaseous fuel typically used in industrial applications. The staged fuel orifice spuds  50  are fluidly connected to staged fuel risers  42 . The staged fuel from the staged fuel orifice spuds  50  is received by multiple staged fuel venturi channels  34  located above each staged fuel orifice spud  50 . Each staged fuel orifice spud  50  corresponds to a staged fuel venturi channel  34 . The high velocity staged fuel discharging from the staged fuel orifice spuds  50  entrains combustion products from the furnace space. The staged fuel and entrained combustion products mix within the venturi channels  34 . Subsequently, the mixture combines with the combustion air coming from combustion air inlets  30  before exiting the burner tile  16  through discharge outlets  36  and thereafter entering the burner combustion zone of the furnace. 
         [0045]    The discharge outlets  36  are cast into the burner tile  16  with a slight angle so that the mixture of combustion products, staged fuel, and combustion air is injected at a slight angle towards the primary fuel and combustion air mixture earlier released in the combustion zone of the furnace. This provides the additional combustion air necessary for the completion of the combustion of the primary fuel. The delayed mixing of the fuel, combustion products, and the combustion air permits more heat transfer to occur during the combustion process which provides for a cooler flame. The low temperature combustion produces low levels of NO x . 
         [0046]      FIG. 8  is a perspective view of an embodiment of a burner assembly where the burner assembly  10  may be adjacent with a wall  12  of a furnace  14 . The burner tile  16  of the burner assembly extends into the furnace area and is positioned inside of the furnace. Above the burner tile  16  and still within the confinement of the furnace is referred to herein as the furnace space. A combustion zone is created just above the burner tile, within the furnace space. 
         [0047]    The burner assembly  10  includes at least one primary fuel premix venturi and tip  18  and at least one secondary fuel premix venturi assembly (internal to burner tile) cast as part of a burner tile  16 . 
         [0048]      FIG. 9  is a perspective view of a primary fuel premix venturi and tip assembly  18  standing alone, unattached to the burner tile (not shown). The premix burner assembly  18  includes an inlet  24 , a primary fuel orifice spud (internal, not shown), a venturi mixer  22 , and a primary mixer tip  38 . The primary fuel orifice spud, inlet  24 , venturi mixer  22 , and primary mixer tip  38  are all in fluid communication with one another. 
         [0049]    Whereas, the devices and methods have been described in relation to the drawings and claims, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of this invention.