Abstract:
A combustion gas flow for an atmosphere of a melter includes a first gas flow at a first velocity introduced into the atmosphere, and a second gas flow at a second velocity less than the first velocity introduced into the atmosphere for entraining corrosive or condensable vapors in the atmosphere and shrouding and inhibiting the first gas flow from entraining condensable or corrosive vapors at a higher rate than the second gas flow.

Description:
[0001]    The embodiments relate to the entrainment of the atmosphere in a melter by jets. 
         [0002]    As the velocity of a jet is increased in an atmosphere of a furnace or a melter, the surrounding atmosphere including condensable and corrosive vapors are pulled into the jet at an increased rate. In the case where a jet issues from an opening in a wall of the furnace or melter, the entrainment of the jet in the region proximate the wall requires material be drawn into the jet stream substantially parallel, if not parallel, to the wall surface. If the jet is moving at a high velocity rate, the rate of entrainment is high and consequently the velocities of the atmosphere flowing parallel to the wall surface and containing the condensable and corrosive species will therefore also be high, thereby resulting in increased wear or chemical attack on the wall or crown surface. 
         [0003]    In order to reduce refractory wear in the melter, one could reduce overall jet velocity, but such would limit the total jet momentum in the melter, which would in turn affect flame characteristics, stability or deflection by existing currents in the furnace combustion atmosphere. Use of different refractory materials to counteract such would require increased or additional costs and could raise material compatibility issues with either the glass product, leading to defects, or with other materials of construction of the furnace wall, leading to more frequent repair of the existing melter, thereby resulting in down time of the melter and attendant production losses. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    For a more complete understanding of the present embodiments, reference may be had to the following description taking in conjunction with the drawings, of which: 
           [0005]      FIG. 1  shows a burner embodiment for use in a melter. 
           [0006]      FIG. 2  shows a table of the burner embodiment characteristics. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0007]    Referring to  FIG. 1 , embodiments of the burner are shown generally at  10 . The burner  10  generates a central higher velocity jet type flame  14  surrounded by a low velocity shroud  16 . The central higher velocity flame jet  14  comprises a combusting flow or flame formed by the combination of a natural gas stream  30  and an oxygen stream  32 . The natural gas stream  30  is delivered through a pipe  25  that terminates within a cavity  34  of the burner  10 . The oxygen stream  32  is delivered though a passage  31  formed between the pipe  25  and a wall of the cavity  34  of the burner  10 . 
         [0008]    The burner  10  introduces a low velocity shroud stream  12  of oxygen through conduit  27  to form a surrounding or outer low velocity shroud  16  around the central higher velocity flame jet  14 , wherein the high velocity flame jet  14  entrains the surrounding or outer low velocity shroud  16  near a wall  18  of a furnace or melter, while the low velocity shroud  16  entrains material  20  from the immediate surrounding atmosphere  22  at a substantially lower rate than the high velocity flame jet  14  entrains material  28  from the surrounding atmosphere  22  distant from wall  18 . The shroud  16 —traveling at a lesser velocity than the velocity flame jet  14 —is entrained into said flame jet  14 . In this manner, velocities of surrounding atmosphere currents  26  near the wall  18  in the vicinity of the jet-shroud  14 ,  16  combination are reduced. Currents  28  in the atmosphere  22  are of a higher velocity further away from the wall  18 . 
         [0009]    The burner  10  reduces chemical wear of refractories surrounding for example oxy-fuel burners—in particular silica attack in soda-lime furnaces. Reducing the velocity of the furnace atmosphere near silica walls, such as the wall  18 , of a melter will reduce the attack by chemical species contained in the furnace atmosphere, such as alkali vapors, on the walls. 
         [0010]    The embodiments reduce the velocity of the corrosive furnace atmosphere near burners in glass furnaces or other types of melters. That is, condensable vapors in the furnace atmosphere  22  which would otherwise degrade the furnace wall  18  or crown are limited in their ability to do so, as the reduced velocity shroud  16  entrains said condensable vapors contained within material  20  at a reduced rate. This reduces the rate of chemical attack of, for example, silica by sodium hydroxide or sulphate species transported to the wall surface by the furnace atmosphere currents. This will result in longer furnace life before repair. 
         [0011]    The outer shroud  16  has a composition similar to an external portion of the central flame jet  14 . With a pipe-in-pipe burner with a center natural gas stream  30  and an outer oxygen stream  32 , the outer shroud  16  is also comprised of oxygen and such would be introduced external to the cavity  34  that confines the initial flame jet  14 . 
         [0012]    Velocities of the central natural gas stream  30  and oxygen stream  32  are approximately equal (within 10% of each other). The outer shroud  16  includes approximately 10-50% of the total oxygen supplied and at an initial velocity is approximately equal to 10-50% of that of the oxygen stream  32  supplied through the central cavity  34  of the burner. 
         [0013]    Suitable fuels for combustion may be gaseous, atomized liquid or a suspended particulate solid. Suitable gaseous fuels include, but are not limited to methane, natural gas, liquefied natural gas, propane, liquefied propane gas, butane, low BTU gases, town gas, producer gas or mixtures thereof. Suitable liquid fuels include, but are not limited to heavy fuel oil, medium fuel oil, light fuel oil, kerosene, diesel or mixtures thereof. Suitable suspended particulate solid fuels include, but are not limited to coal, coke, petroleum coke, rubber, woodchips, sawdust, straw, biomass fuels or mixtures thereof suspended in a carrier gas selected from air, nitrogen, carbon dioxide or a gaseous fuel, the gaseous fuel selected from methane, natural gas, liquefied natural gas, propane, liquefied propane gas, butane, low BTU gases, town gas, producer gas or mixtures thereof. 
         [0014]    Preferred oxidants for use with the embodiments include oxygen-enriched air, containing greater than 20.9 volume percent oxygen to about 80 volume percent, preferably greater than 50 volume percent, such as produced by filtration, absorption, membrane separation, or the like; non-pure oxygen such as that produced by, for example, a vacuum swing adsorption process and containing about 80 volume percent to 95 volume percent oxygen; and “industrially” pure oxygen containing about 90 volume percent to about 100 volume percent oxygen, such as produced by a cryogenic air separation unit (ASU) or plant. 
         [0015]    In the Example below, computational fluid dynamic modeling was performed on a pipe-in-pipe burner  10 , wherein an initial flame jet  14  is formed by the interaction of a methane  30  stream issuing from the pipe  25  and a surrounding annular pure oxygen stream  32 , both contained within the cavity  34  within a refractory burner block. The pipe  25  carrying the methane is set back within the cavity  34  within a refractory burner block and a flame jet  14  is formed in the cavity  34  between the resultant co-flowing methane  30  and oxygen  32  streams. A shroud stream  12  of oxygen is introduced surrounding the central cavity  34  via an annular conduit  27  to form an oxygen shroud  16  surrounding the central flame jet  14 . The relevant dimensions for a range of shroud stream  12  flowrates and initial shroud  16  velocities were determined using the following fixed variables. 
       EXAMPLES 
       [0000]    
       
         Methane volumetric flow rate(stream  30 ): 184 Nm 3 /hr. 
         Total Oxygen volumetric flow rate (stream  32 +stream  12 ): 377.2 Nm 3 /hr. 
         Fuel velocity (stream  30 ): 30.48 m/s. 
         Central Oxygen velocity (stream  32 ): 30.48 m/s. 
         Internal diameter of pipe  25  carrying the fuel: 47.96 mm. 
         External diameter of pipe  25  carrying the fuel: 54.31 mm. 
         Distance the tip of pipe  25  is recessed from the discharge end of burner block cavity  34 : 152.4 mm. 
         Distance between cavity wall  34  and inside edge of shroud conduit  27 : 19.05 mm. 
       
     
         [0024]    Referring to  FIG. 2 , a series of examples based on the above fixed variables and the shroud parameters were examined to determine the effect of the proportion of the oxygen delivered via shroud stream  12  and the oxygen shroud  16  velocity on the entrainment of the atmosphere  22 .  FIG. 2  shows in a table  40  the volume of gases that are entrained near the wall  18 . This is determined by the volume of gases flowing across a hypothetical cylindrical boundary of radius 154.2 mm co-axial with burner  10  and extending 152.4 mm from the wall  18 . As can be seen, the design of the shroud  16  has a significant effect on the volume of gases entrained across the cylindrical boundary and drawn along the wall  18  and into the flame jet  14 . As a result, local velocities in the vicinity of the wall  18  and the burner  10  are accordingly reduced. 
         [0025]    In the Table  40  of  FIG. 2 , columns I-VIII shown generally at  42 - 56 , respectively, represent:
       I. Reference number for Examples 1-9 ( 42 ).   II. The percentage of the total oxygen flow that is delivered as outer shroud  16  via stream  12  ( 44 ).   III. The initial velocity of the outer shroud  16  expressed as a fraction of the initial central oxygen stream  32  velocity ( 46 ).   IV. The diameter of the cavity  34  through which the central flame jet  14  issues ( 48 ).   V. The inner diameter of the annular shroud passage  27  ( 50 ).   VI. The outer diameter of the annular shroud passage  27  ( 52 ).   VII. The volume of the atmospheric gas  22  that is entrained into the initial region of the shroud  16  and central flame jet  14  ( 54 ).   VIII. The percentage reduction in the volume of gas entrained (VII) from the Example 1, where there was no shroud ( 56 ).       
 
         [0034]    By way of example, Example 1 represents a base case for the burner  10  without the shroud  16  to which later Examples 2-9 are compared. Columns II and III show, for Example #1, that no oxygen is diverted to the annular shroud  16 . Column IV is the diameter, of the burner block cavity  34  into which issues the fuel stream  30  and oxygen stream  32 . This is obtained by determining the annular flow passage area  31  required between the outside of the fuel feed pipe  25  and the inside of the burner block cavity  34  so that an oxygen stream  32  velocity of 30.48 m/s is obtained. In this example, as all the oxygen flows through the annular region  31  the area is such that a burner block cavity  34  diameter of 87.5 mm is required. Columns V, VI and VIII are blank as there is no shroud  16 . Column VII shows that in this case with all of the oxygen issuing at high velocity through stream  32  that a volume of 0.123 m 3 /h is entrained into the initial region of the burner  10  near the wall  18 . 
         [0035]    Example 4 is where 30% of the total oxygen is delivered through the shroud  16  at a velocity of 0.3 times that of the central oxygen stream  32 , ie a shroud stream  12  flow rate of 113.2 Nm 3 /hr at an initial shroud  16  velocity of 0.3×30.48=9.1 m/s. Column IV represents the reduced diameter of the burner block cavity  34  to accommodate the smaller flow area required for the smaller volume of oxygen (stream  32 ) issuing into the central burner block cavity  34 . Here the flowrate of oxygen stream  32  into the central cavity  34  of the burner block has been reduced from 377.2 Nm 3 /hr to 264 Nm 3 /hr and with the constant oxygen velocity of 30.48 m/s of stream  32  the diameter of the burner block cavity  34  is accordingly reduced from 87.5 mm in Example 1 to 79.1 mm. Column V shows that the inner diameter of the annular conduit  27  is 117.2 mm, by adding the constant distance of 19.05 mm to the diameter of the burner block cavity  34 . Column VI shows the outer diameter of the annular conduit  27  as being 135.8 mm, this being determined by the area needed to flow the 4305 scfh shroud stream  12  oxygen at an initial shroud  16  velocity of 9.1 m/s. Column VII shows the result that the volume of gas entrained into the initial region of the jet is reduced to 0.078 m3/s. Column VIII shows that the volume entrained has been reduced by 37% from Example 1 where there was no shrouding. 
         [0036]    The least significant factor appears to be increasing the initial velocity of the shroud  16  (comparing Examples 2, 6 and 7 with Example 1) at a constant low shroud flow volumes (stream  12 ) of 10% of the total oxygen flowrate where an approximate 10% reduction in volume entrained is observed. 
         [0037]    A more significant effect is seen when increasing the amount of flow stream  12  to the low velocity shroud  16  (comparing Examples 2, 8 and 9 with Example 1) where up to a 50% reduction in entrained volume is achievable while maintaining a low constant initial shroud  16  velocity of 0.1×the initial central fuel and oxygen velocities (streams  30 ,  32 ). 
         [0038]    From a practical standpoint in some applications a very low velocity shroud  16  passing a significant volume of the total oxygen flow may result in excessively large dimensions for the conduit  27  (e.g. Example 9) which may be prohibitive for installation and it may be preferable to operate an intermediate velocity shroud  16  with a modest shroud stream  12  proportion to be dimensionally reasonable. It is observed that a 30% volume from stream-shroud  12 ,  16  combination flowing at 30% of the central fuel and oxygen streams  30 , 32  velocities performs well with a 37% reduction in entrained volume. 
         [0039]    A further benefit is obtained in reducing the transport of condensable species within the furnace atmosphere to the outer edge of high velocity oxy-fuel burners. By reducing the rate of entrainment of the furnace atmosphere, the rate of transport of condensable species to the oxy-fuel burner is reduced and the rates of condensation and deposition of material is reduced. Such species can condense and produce a build up of material around the burner that can deflect the flame and cause refractory damage. By reducing or eliminating the build up of material, burner maintenance needs are reduced and the risk of damage through flame deflection is reduced. 
         [0040]    It will be understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described herein. It should be understood that the embodiments described above are not only in the alternative, but may be combined.