Abstract:
An oxygen-fuel combustion system combines oxygen and fuel to produce a flame. The system distributes oxygen to a stream of fluidized, pulverized, solid fuel at various sites before and after ignition. The system is operable to vary the concentration of oxygen in an oxygen-fuel mixture extant at those sites.

Description:
BACKGROUND AND SUMMARY  
         [0001]    The present disclosure relates to burner assemblies, and particularly to oxygen-fuel burner assemblies configured to burn pulverized solid fuels. More particularly, the present disclosure relates to apparatus for mixing oxygen and fuel for use in a burner.  
           [0002]    Many types of coal and other solid fuels can be burned successfully in pulverized form. Coal is pulverized and delivered to fuel-burning equipment and then combusted in a furnace to produce heat for various industrial purposes.  
           [0003]    A burner is used to “fire” pulverized coal and other solid fuels. In a direct-firing system, the coal is delivered to the burner in suspension in a stream of primary air, and this mixture must be mixed with a stream of secondary air at the burner.  
           [0004]    One challenge facing the burner industry is to design an improved burner that produces lower nitrogen oxide emissions during operation than conventional burners. Typically, an industrial burner discharges a mixture of fuel and either air or oxygen. A proper ratio of fuel and air is established to produce a combustible fuel and air mixture. Once ignited, this combustible mixture burns to produce a flame that can be used to heat various products in a wide variety of industrial applications. Combustion of fuels such as natural gas, oil, liquid propane gas, low BTU gases, and pulverized coals often produce several unwanted emissions such as nitrogen oxides (NO x ), carbon monoxide (CO), and unburned hydrocarbons (UHC).  
           [0005]    According to the present disclosure, an apparatus is provided for combining oxygen and fuel to produce a mixture to be burned in a burner. The apparatus includes a fuel supply tube configured to communicate a stream of fluidized, pulverized, solid fuel to a “fuel-ignition zone” provided, for example, by a flame chamber formed in a refractory shape coupled to a downstream portion of the fuel supply tube. The apparatus further includes an oxygen supply housing coupled to an upstream portion of the fuel supply tube, an oxygen manifold coupled to the downstream portion of the fuel supply tube, and an oxygen distribution system for varying the amount of oxygen conducted to the oxygen supply housing and to the oxygen manifold.  
           [0006]    In the illustrated embodiment, the oxygen supply housing cooperates with the upstream portion of the fuel supply tube to establish an oxygen-fuel mixer defining an upstream oxygen chamber adapted to receive oxygen provided by the oxygen distribution system. The upstream portion of the fuel supply tube is formed to include an upstream set of oxygen-injection holes opening into a fuel transport passageway located in the upstream portion of the fuel supply tube. Oxygen flows through those holes to mix with a fluidized, pulverized, solid fuel flowing through the passageway to produce an oxygen-enriched (yet not spontaneously combustible) oxygen-fuel transport mixture flowing toward the fuel-ignition zone in the flame chamber.  
           [0007]    Also in the illustrated embodiment, the oxygen manifold is configured to communicate oxygen from the oxygen distribution system to the downstream portion of the fuel supply tube to produce a combustible oxygen-fuel mixture exiting the passageway to be ignited in the fuel-ignition zone to produce a flame. The oxygen manifold also is configured to communicate oxygen from the oxygen distribution system through one or more staged-oxygen bypass conduits to a portion of the flame outside the flame-ignition zone. Such “diversion” of combustion oxygen flow through the staged-oxygen bypass conduits to a region of the flame away from the root of the flame contributes to lowered nitrogen oxide emissions.  
           [0008]    A control system associated with the oxygen distribution system is used to operate a first valve located to regulate oxygen flow to the upstream oxygen chamber and to operate a second valve located to regulate oxygen flow to the oxygen manifold. The control system provides means for operating the first and second valves to establish: (1) how much of the oxygen obtained from an oxygen supply is routed to the upstream oxygen chamber through the upstream set of oxygen-injection holes to mix with the fluidized, pulverized, solid fuel stream in the oxygen-fuel mixer and (2) how much of that oxygen is routed to the oxygen manifold for discharge through the downstream portion of the fuel supply tube and the flame chamber inlet to the “root” of the flame and for discharge through the staged-oxygen bypass conduit to the “tip” of the flame.  
           [0009]    In one illustrated embodiment, an oxygen sensor is arranged to detect the amount of oxygen extant in the fluidizing gas to be mixed with the pulverized solid fuel. The control system is linked to the oxygen sensor provided and cooperates with the oxygen sensor to provide means for varying the amount of oxygen conducted through the oxygen distribution system to the oxygen-fuel mixer after determining an approximate concentration of oxygen in the stream of fluidized, pulverized, solid fuel. Such means can be used to maintain the concentration of oxygen in the oxygen-enriched (yet not spontaneously combustible) oxygen-fuel transport mixture produced by the oxygen-fuel mixer in the upstream portion of the fuel supply tube at a not spontaneously combustible level.  
           [0010]    Additional features of the present disclosure will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the disclosure as presently perceived. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The detailed description particularly refers to the accompanying figures in which:  
         [0012]    [0012]FIG. 1 is a schematic diagram showing a system for pulverizing and fluidizing a solid fuel to be fired in a staged-oxygen burner unit and showing an oxygen distribution system in accordance with the present disclosure for discharging some of the oxygen provided by an oxygen supply to an “upstream” oxygen-fuel mixer to mix with a stream of fluidized, pulverized solid fuel flowing therethrough toward a burner and discharging some of the oxygen provided by the oxygen supply to a “downstream” staged-oxygen manifold associated with the burner;  
         [0013]    [0013]FIG. 2 is a sectional view of a portion of the fuel supply tube, an oxygen-fuel mixer (on the left side of FIG. 2) defined in part by an upstream portion of the fuel supply tube and adapted to receive oxygen from the oxygen distribution system, a refractory shape provided by a burner block (on the right side of FIG. 2) formed to include a flame chamber and at least two staged-oxygen bypass conduits, and an oxygen manifold associated with a downstream portion of the fuel supply tube and configured to conduct oxygen from the oxygen distribution system to the staged-oxygen bypass conduits and to the downstream portion of the fuel supply tube at a point near an inlet into the flame chamber of the burner block, and showing an igniter arranged to ignite a combustible oxygen-fuel mixture extant in the flame chamber;  
         [0014]    [0014]FIG. 3 is a schematic view similar to FIG. 1 showing a first embodiment of the oxygen distribution system comprising a primary oxygen-fuel “ratio controller” valve for varying the flow of “primary” oxygen from the oxygen supply to the oxygen-fuel mixer to control the ratio of oxygen and fuel in the fuel supply tube downstream of the oxygen-fuel mixer and a secondary oxygen-fuel ratio controller valve for varying the flow of “secondary” oxygen from the oxygen supply to the oxygen manifold to control the ratio of oxygen and fuel in the flame chamber and in the vicinity of the flame chamber outlet; and  
         [0015]    [0015]FIG. 4 is a sectional view similar to FIG. 2 of a second embodiment of an oxygen burner unit according to the present disclosure wherein a solid-fuel nozzle module associated with the downstream portion of the fuel supply tube is mounted in the oxygen manifold to extend into an inlet passageway formed in the burner block to communicate with the flame chamber. 
     
    
     DETAILED DESCRIPTION  
       [0016]    An oxygen-fuel combustion system  10  for burning a mixture of oxygen and a fluidized, pulverized, solid fuel to produce a flame  12  is shown schematically in FIG. 1. A fuel supply tube  14  conducts fuel provided by fuel delivery system  16  and oxygen provided by oxygen delivery system  18  to a flame chamber  20  provided in burner unit  21 . An igniter  22  ignites the combustible oxygen-fuel mixture extant in a fuel-ignition zone provided by flame chamber  20  to produce flame  12 . As used herein, “oxygen” means pure oxygen and any oxidant or oxygen-enriched mixture having an oxygen concentration of about 30% or more.  
         [0017]    An oxygen-fuel mixer  24  is configured to mix oxygen supplied by oxygen delivery system  18  with a stream of pulverized, solid fuel supplied by fuel delivery system  16  and fluidized by fluidizing gas  26  discharged into fuel supply tube  14  using a blower  28  (or other suitable gas conveyance means). The oxygen-fuel transport mixture produced by mixer  24  is “designed” to be not spontaneously combustible.  
         [0018]    An oxygen manifold  30  is configured to mix oxygen supplied by oxygen delivery system  18  with the not spontaneously combustible oxygen-fuel transport mixture discharged from oxygen-fuel mixer  24  to produce an oxygen-fuel mixture that is ignited in flame chamber  20  to produce a flame  12 . Oxygen manifold  30  is also configured to discharge oxygen into one or more staged-oxygen bypass conduits  32  so that additional oxygen can be diverted to a region of flame  12  away from the root of flame  12  to help complete combustion of the oxygen-fuel mixture ignited by igniter  22 . Oxygen delivery system  18  is configured to enable a user of oxygen-fuel combustion system to monitor and control the oxygen-fuel ratio of oxygen-fuel transport mixtures established by the oxygen-fuel mixer  24 , at the inlet opening into the flame chamber  20 , and at the outlet opening(s) of the staged-oxygen bypass conduit(s)  32  so as to manage the concentration of oxygen in the fuel conducted through oxygen-fuel combustion system  10  at various stages prior to and during combustion.  
         [0019]    As suggested in FIG. 1, fuel delivery system  16  includes a solid fuel supply  34  and a pulverizer  36 . Oxygen-fuel combustion system  10  is configured to allow the burning of any solid fuel, or waste fuel, that can be pulverized or ground and conveyed by air or gas. Just as pulverized coal can be conveyed by air or carbon dioxide, solid fuels such as lignite, sawdust, agricultural wastes, ground shells, etc. could be burned in oxygen-fuel combustion system  10  to produce a flame  12  and to satisfy many industrial heating or other needs.  
         [0020]    Fuel supply tube  14  is formed to include a fuel transport passageway  38  for conveying pulverized solid fuel discharged from pulverizer  36  to flame chamber  20  in burner unit  21 . Blower  28  is used to discharge fluidizing gas  26  into an upstream portion  40  of fuel supply tube  14  to fluidize the pulverized solid fuel that is admitted into fuel transport passageway  38  at inlet port  41 . Fluidizing gas  26  is used to fluidize and convey the pulverized solid fuel through oxygen-fuel mixer  24  and oxygen manifold  30  and into flame chamber  20 .  
         [0021]    Many gases are suitable for use in fluidizing pulverized solid fuel discharged into fuel transport passageway  38 . In one illustrative embodiment, a carbon dioxide (CO 2 ) capture and sequestration system  42  is used to capture carbon dioxide generated during combustion in burner unit  21  so that the captured carbon dioxide is used as the fluidizing gas  26 . In another illustrative embodiment, treated products of combustion  44  generated during combustion in burner unit  21  provide fluidizing gas. In yet another embodiment, air  46  from any suitable source is used as the fluidizing gas  26 .  
         [0022]    As suggested in FIG. 1, oxygen delivery system  18  includes an oxygen supply  50 , an oxygen distribution system  52 , a control system  54 , and an oxygen sensor  56 . It is within the scope of this disclosure to place the oxygen sensor in any suitable location to sense the concentration of oxygen in fluidizing gas  26  communicated to fuel supply tube  14 . The oxygen concentration level sensed by oxygen sensor  56  is communicated to control system  54  as suggested diagrammatically in FIG. 1.  
         [0023]    Control system  54  is configured to provide means for operating oxygen distribution system  52  to vary or otherwise regulate the amount of oxygen supplied to oxygen-fuel mixer  24  and to oxygen manifold  30 . Using control system  54 , a system operator can cause an oxygen-enriched (yet not spontaneously combustible) oxygen-fuel transport mixture to be discharged from oxygen-fuel mixer  24  into a downstream portion  43  of fuel supply tube  14  arranged to communicate with flame chamber  20  formed in burner unit  21 . Also using control system  54 , a system operator can cause sufficient oxygen to pass through oxygen manifold  30  to raise the oxygen concentration in the oxygen-fuel mixture discharged from fuel supply tube  14  into flame chamber  20  at or very near an outlet end of downstream portion  43  of fuel supply tube  14 . System operator can also regulate the amount of oxygen allowed to flow from oxygen manifold  30  into staged-oxygen bypass conduits  32  using control system  54 .  
         [0024]    Control system  54  is used to allow an operator to adjust oxygen-fuel combustion system  10  in the field to provide optimum emission without compromising flame stability. It could also be used to allow adjustments as a plant begins operation and uses air as fluidizing gas  26 . As the plant start-up progresses, recirculated flue gas (CO 2 ) becomes available and the level of oxygen enrichment established by oxygen-fuel mixer  24  would, or could, increase. Control system  54  is also used to allow an operator to establish and vary the ratio of oxygen extant in the oxygen-fuel mixture discharged into the flame chamber  20  through fuel supply tube  14  to “feed” the root of flame  12  versus the oxygen discharged through the staged-oxygen bypass conduits  32  to feed the tip of flame  12 .  
         [0025]    Various components included in oxygen-fuel combustion system  10  are shown in greater detail in FIG. 2. Fuel supply tube  14  includes a solid-fuel conduit  60  and an oxygen-fuel nozzle  62  coupled to a downstream end  64  of solid-fuel conduit  60  as shown in FIG. 2. Reference is made to U.S. application No. Ser. 10/407,489, entitled “Apparatus for Burning Pulverized Solid Fuels with Oxygen,” filed Apr. 4, 2003, which disclosure is hereby incorporated by reference herein, for a description of a suitable solid-fuel conduit, oxygen-fuel nozzle, and staged-oxygen system.  
         [0026]    Oxygen supply housing  66  is coupled to upstream portion  40  of solid-fuel conduit  60  of fuel-supply tube  14  to define an upstream oxygen chamber  68  therebetween as suggested, for example, in FIG. 2. Oxygen supply housing  66  is formed to include an oxygen inlet  69  adapted to admit oxygen into upstream oxygen chamber  68 . Upstream portion  40  of solid-fuel conduit  60  is formed to include an upstream set of oxygen-injection holes  70  opening into fuel transport passageway  38  as shown in FIG. 2 to establish oxygen-fuel mixer  24 .  
         [0027]    As suggested in FIG. 2, oxygen  72  from oxygen supply  50  flows first through oxygen distribution system  52  into upstream oxygen chamber  68  provided in oxygen-fuel mixer  24  and then into fuel transport passageway  38  through oxygen-injection holes  70 . The oxygen  72  mixes with fluidized, pulverized, solid fuel  74  (represented by particles in FIG. 2) flowing through fuel transport passageway  38  in downstream direction  75 . The amount of oxygen  72  discharged into upstream oxygen chamber  68  is regulated using oxygen distribution system  52  and control system  54  to cause oxygen  72  to mix with fluidized, pulverized, solid fuel  74  in oxygen-fuel mixer  24  to produce an oxygen-enriched (yet not spontaneously combustible) oxygen-fuel transport mixture  76  (represented by dashed lines in FIG. 2). This not spontaneously combustible transport mixture  76  flows in direction  75  through passageway  38  in solid-fuel conduit  60  and exits conduit  60  at downstream end  64  and enters oxygen-fuel nozzle  62  as shown in FIG. 2.  
         [0028]    Oxygen supply housing  66  includes a sleeve  100  having an annular inner surface  101  as shown in FIG. 2. In the illustrated embodiment, sleeve  100  is a cylinder-shaped side wall. Upstream portion  40  of solid-fuel conduit  60  of fuel supply tube  14  passes through a channel defined by annular inner surface  101  of sleeve  100 . An annular exterior surface  102  of the upstream portion  40  of solid-fuel conduit  60  cooperates with annular inner surface  101  of sleeve  100  to define upstream oxygen chamber  68  therebetween as shown in FIG. 2.  
         [0029]    Oxygen supply housing  66  further includes a first end wall  103  coupled to a first end of sleeve  100  and formed to include a first opening  104  receiving upstream portion  40  of solid-fuel conduit  60  therein. Housing  66  also includes a second end wall  105  coupled to a second end of sleeve  100  and formed to include a second opening  106  receiving upstream portion  40  therein. Annular exterior surface  102  of the upstream portion  40 , annular inner surface  101  of the sleeve  100 , and inner surfaces of first and second end walls  103 ,  105  cooperate to define a boundary of the upstream oxygen chamber  68 . Sleeve  100  is formed to include oxygen inlet  69  and sleeve  66  is positioned to lie in spaced-apart relation to outer tube  80  (described below) as shown in FIG. 2. A tube  107  is coupled to sleeve  100  at oxygen inlet to  69  to deliver oxygen into upstream oxygen chamber  68 . Sleeve  100  and tube  107  cooperate to define a T-shaped member mating with upstream portion  40  of solid-fuel conduit  60  as shown, for example, in FIG. 2.  
         [0030]    An outer tube  80  is located in a fixed position relative to a downstream portion of solid-fuel conduit  60  to define an annular oxygen flow passage  82  therebetween as suggested in FIG. 2. Outer tube  80  is formed to include an oxygen inlet defined by a second set of oxygen-injection holes  81  opening into oxygen flow passage  82  to communicate oxygen  73  into oxygen flow passage  82 . A sealed closure  93  mates with a first end  94  of outer tube  80  to block flow of oxygen  73  through first end  94  so that oxygen  73  admitted into oxygen flow passage  82  through the oxygen inlet established by holes  81 . Suitable anchors  95  and anchor-engaging fasteners  96  are configured to retain sealed closure  93  in a fixed position on outer tube  80  as suggested in FIG. 2.  
         [0031]    Oxygen-fuel nozzle  62  is formed to include a downstream set of oxygen-injection holes  84  opening into the portion of fuel transport passageway  38  formed in nozzle  62 . Nozzle  62  is also formed to include oxygen-discharge passages  86  arranged to conduct oxygen  73  from oxygen flow passage  82  through openings  88  formed in outlet end face  90  of nozzle  62  to mix outside of nozzle  62  with the oxygen-fuel mixture  92  generated in nozzle  62  and discharged into flame chamber  20 . Reference is made to U.S. application No. Ser. 10/407,489, entitled “Apparatus for Burning Pulverized Solid Fuels with Oxygen,” filed Apr. 4, 2003, for descriptions of suitable oxygen-fuel nozzles.  
         [0032]    A second oxygen-supply housing  110  is arranged to cooperate with outer tube  80  as shown, for example, in FIG. 2 to define a second oxygen chamber  112  adapted to receive oxygen  73  from oxygen distribution system  52 . Second oxygen-supply housing  110  is formed to include an oxygen inlet  114  adapted to admit oxygen  73  into second oxygen chamber  112  and an oxygen outlet arranged to discharge oxygen  73  extant in second oxygen chamber  112  in staged-oxygen bypass conduits  32 .  
         [0033]    In use, oxygen deliver system  18  conducts a first stream of oxygen  72  through the upstream set of oxygen-injection holes  70  to mix with fluidized, pulverized, solid fuel  74  conducted through passageway  38  in upstream portion  40  of fuel supply tube  14  to produce an oxygen-enriched (yet not spontaneously combustible) oxygen-fuel transport mixture  76 . Oxygen delivery system  18  also conducts a second stream of oxygen  73  through oxygen inlet  81  formed in outer tube  80  and into oxygen flow passage  82  to pass through the downstream set of oxygen-injection holes  84  to mix with the oxygen-enriched (yet not spontaneously combustible) oxygen-fuel transport mixture  76  conducted through passageway  38  in the downstream portion  64  of the fuel supply tube  14  to produce an oxygen-fuel mixture  92  exiting passageway  38  through an outlet  108  of fuel supply tube  14  to be ignited by igniter  22  outside passageway  38  to produce a flame  12 .  
         [0034]    Oxygen delivery system  18  further includes means for approximating the concentration of oxygen in the stream of fluidized, pulverized, solid fuel  74  and varying the amount of oxygen  72  conducted through the upstream set of oxygen-injection holes  70  to maintain the concentration of oxygen in the oxygen-enriched (yet not spontaneously combustible) oxygen-fuel transport mixture  76  produced in upstream portion  40  of the fuel supply tube  14  at a not spontaneously combustible level. In one embodiment, an oxygen sensor  56  is located to sense the concentration of oxygen in fluidizing gas  26 .  
         [0035]    Oxygen delivery system  18  further includes distribution means  52  for varying an amount of oxygen  72  supplied to passageway  38  located in upstream portion  40  of fuel supply tube  14  and an amount of oxygen  73  supplied to the passageway  38  located in downstream portion  64  of fuel supply tube  14 . Distribution means  52  operates to vary an amount of primary oxygen  72  supplied to the passageway  38  in upstream portion  40  of fuel supply tube  14  and an amount of secondary oxygen  73  supplied by (1) to the passageway  38  in downstream portion  64  of fuel supply tube  14  and (2) to staged-oxygen bypass conduit(s)  32  to regulate the relative concentration of the oxygen-enriched (yet not spontaneously combustible) oxygen-fuel transport mixture  76  and the combustible oxygen-fuel mixture  92  so that a selected ratio of primary and secondary oxygen  72 ,  73  is achieved to optimize emissions generated by burning the oxygen-fuel mixture  92  in the flame chamber  20  and adjust for variations in physical properties of pulverized solid fuel entrained in a stream of fluidizing gas  26  to produce the fluidized, pulverized, solid fuel  74 .  
         [0036]    As shown diagrammatically in FIG. 3, oxygen distribution system  52  includes a first oxygen supply tube  120  arranged to conduct oxygen from the oxygen supply  50  to a first oxygen conductor  122  coupled to oxygen fuel mixer  24 , a primary oxygen-fuel ratio controller valve  124  associated with first oxygen supply tube  120  to regulate flow of oxygen from oxygen supply  50  to a first oxygen conductor  122 . Oxygen distribution system  52  also includes a second oxygen supply tube  126  arranged to conduct oxygen from oxygen supply  50  to a second oxygen conductor  128  coupled to oxygen manifold  30 , a staged oxygen-fuel ratio controller valve  130  associated with second oxygen supply tube  126  to regulate flow of oxygen from oxygen supply  50  to the second oxygen conductor  128 . Control system  54  provides means for opening and closing the primary and staged oxygen-fuel ratio controller valves  124 ,  130  to establish the selected ratio of primary and staged oxygen  72 ,  73  used in oxygen-fuel combustion system  10 . In use, control system  54  operates the primary and secondary oxygen-fuel ratio controller valves  124 ,  130  to regulate the relative concentration of oxygen (1) in an oxygen-enriched (yet not spontaneously combustible) oxygen-fuel transport mixture established in passageway  38  formed in fuel supply tube  14  when primary oxygen  72  from first oxygen chamber  68  flows through the first set of oxygen-injection holes  70  formed in fuel supply tube  14  to mix with fluidized, pulverized, solid fuel  74  passing therethrough and (2) in an oxygen-fuel mixture established by mixing an oxygen-fuel mixture  92  discharged into the flame chamber  20  with secondary oxygen  73  discharged from staged-oxygen bypass conduit(s)  32  so that a selected ratio of primary and secondary oxygen  72 ,  73  is achieved to optimize emissions generated by burning the oxygen-fuel mixture  92  extant in the flame chamber  20  and adjust for variations in physical properties of pulverized solid fuel included in the fluidized, pulverized solid fuel  74 .  
         [0037]    Control system  54  is used to control the oxygen concentration of the oxygen-fuel mixture extant in oxygen-fuel mixer  24  to minimize opportunity for premature ignition of that oxygen-fuel mixture in fuel supply tube  14 . The oxygen concentration is maintained at an optimal percentage to enhance emissions performance of system  10 , while at the same time monitoring and maintaining the oxygen concentration below a threshold level in fuel supply tube  14 . Overall control of excess oxygen inside the boiler or process (after combustion), is the result of oxygen sensors on the stack feeding information to control system  54 . Valves  124 ,  130  shown in FIG. 3 are individually controlled and used to feed a calculated (and measured by flowmeters) amount of oxygen into each zone (primary and staged). Such an arrangement allows for adjustment and tuning of the primary versus staged oxygen flow ratios to optimize emissions and adjust for differences in the physical properties of coal or other solid fuel.