Abstract:
A method is provided to facilitate combustion in a furnace having at least one burner, an inlet, an outlet, and sidewalls and a crown defining a combustion chamber for the furnace, the method consisting of identifying a region of the combustion chamber where a furnace atmosphere therein requires an increase in oxygen for combustion in the furnace atmosphere, and providing fresh oxygen to the region at a controlled flow rate for the combustion, wherein the fresh oxygen provided causes circulation of the furnace atmosphere for combining existing gases and existing oxygen of the furnace atmosphere with the fresh oxygen provided to the region for combustion.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to injection of oxygen in furnaces. 
         [0002]    Furnaces, such as glass melting furnaces, which require additional tonnage/quality or are operating at reduced tonnage due to damage or degradation of heat recovery devices in the form or regenerators or recuperators, have used oxygen and oxygen burners, and fuel burners to gain additional tonnage/quality or recover lost production. 
         [0003]    Oxygen enrichment is typically achieved by introducing oxygen into the combustion air downstream of the forced combustion air fan or blower for the furnace. The required equipment is minimal and therefore is a low cost installation. The oxygen is injected at a location that ensures the oxygen is well blended with the combustion air. Injecting pure 100% oxygen into an air stream means that approximately five times the volume of air can be removed to provide the same amount of oxygen. The actual percentage of oxygen that is possible is determined by local/CGA (Compressed Gas Association) codes and HAZOPs (Hazardous Operation Procedures), but is always less than 29% on a volumetric basis and more typically less than 25%. It should be noted that with respect to enrichment, the point of combustion is indiscriminate. For example, if a first port of a four port cross-fired regenerative furnace is partially blocked, the location at which the oxygen is really required is in the first port area. Since the remaining ports offer a path of lower resistance, there is proportionally more oxygen that goes where it is not required/desired. General enrichment may be the least expensive as far as cost of installation, but it is the least efficient method of using oxygen where it is needed in furnaces. 
         [0004]    Oxygen lancing overcomes many of the disadvantages of enrichment by injecting oxygen at the location where it is needed most. Lancing is accomplished by underport, through-port, over-port, side-of-port or from the regenerator target wall. For example, if the first port of a four port cross-fired regenerative furnace is partially blocked, the location at which the oxygen is required is in the first port area and therefore, it is in this area that the majority of the oxygen is injected. A regenerative furnace has a reversal system and therefore, it is necessary in such a furnace to have a relatively complex and expensive control system to feed a correct amount of oxygen to the correct port. Typically, if a lancing system is installed with the furnace it will feed oxygen to at least a plurality of ports. Since the oxygen requirements may vary from one side to the other, there is a requirement for flow control on each side of the furnace. A reversing three-port lancing panel would therefore require six zones of control. There is also a limit to the amount of oxygen that can be injected in the port area. Higher levels of oxygen in the port can cause too much heat release in the port area, thereby causing structural damage. In under-port applications, the flames can become too short and create an imbalance in heat distribution which can cause glass defects. 
         [0005]    Oxygen enrichment and lancing have been used to recover up to 10% of lost furnace melt capacity. 
         [0006]    When additional capacity is required, there is typically a need for fuel flows beyond the capacity of the installed air fuel system for the furnace. Oxy-fuel boosting involves the placement of at least one and sometimes a plurality of oxy-fuel burners in the zero port (area between charging wall and the first port) or in the hot spot (point of upwell melt area in furnace) of the furnace. Conventional oxy-fuel burners can either recover lost production from a furnace or increase capacity by at least 10%, and occasionally as high as 15%. The furnace design usually determines the capacity that can be obtained and where, if possible, burners can be positioned and installed. Installation is costly, since a dedicated oxygen and fuel control skid is typically required. The overall system capacity is determined by the exhaust capacity of the furnace. 
         [0007]    When there are space constraints in the furnace, or capacity in excess of 15% is required, it is possible to install oxy-fuel burners in the crown or roof of the furnace. A significant amount of energy can be injected into the furnace using roof mounted burners. It is possible to block-off existing air-fuel ports and replace the air-fuel ports with oxy-fuel. In extreme cases it is possible to create a 100% oxy-fuel furnace or in a transition phase for the furnace convert to a hybrid furnace with oxy-fuel for melting and air fuel for refining/conditioning. 
         [0008]    One of the major disadvantages of oxy-fuel boosting, especially when used with cross-fired regenerative furnaces, is the turndown (reduction in firing capacity) of the burners. This is common to both conventional or crown mounted burners. In order to avoid flame distortion or interaction, there is a minimum flowrate that is required. At certain times due to production or product mix, it is necessary to use more oxygen than is really required. 
         [0009]    Mathematical modeling shows that when converting a zero port conventional oxy-fuel boost to roof mounted burners firing with the same amount of oxygen and fuel, there has been a change in distribution of the excess oxygen in the exhaust ports. While providing fuel and oxygen through a burner in the crown provides more oxygen in the first and second ports than with conventional horizontal style burners, there is still the deficiency in known systems of not having enough oxygen to combust as necessary in certain areas of the furnace and for particular melt operations. 
         [0010]    Since air is 20.9% oxygen, with the balance being nitrogen and noble gases, replacing air with oxygen provides a reduction in volume of 79.1%. If furnace pressure is a limitation on combustion and flowrate, then replacing air with oxygen, even partially, can solve the problem as discussed below. 
       SUMMARY OF THE INVENTION 
       [0011]    There is provided injection of oxygen through a crown of a furnace, such as a glass furnace, into a selected region of the furnace to enhance the furnace atmosphere convection flow patterns, thereby providing furnace gases with higher concentrations of oxygen. There is provided more efficient combustion in a furnace to recover or provide additional capacity by positioning the oxygen at the point of greatest combustion need; and flexibility to safely inject oxygen into and at increased amounts to specific areas or zones of the furnace. 
         [0012]    There is also provided a system, whereby at least one or a plurality of oxygen jets or oxygen injectors are disposed in the roof or crown of the furnace at select positions with respect to the ports of the furnace for injecting oxygen into the combustion atmosphere of the furnace to facilitate a venturi effect of said atmosphere and induce entrained oxygen in the existing furnace atmosphere to areas desired for combustion. 
         [0013]    The system of the present invention also reduces NOX (nitrous oxides). 
         [0014]    The oxygen (O 2 ) injection and selected flow of oxygen increases the temperature of the furnace and facilitates combustion in the furnace. This is useful for existing furnaces where there is insufficient space for installing additional burners. 
         [0015]    There is provided by the present invention a selected region identified in the furnace where the oxygen is needed and therefore injected into the furnace atmosphere near an inlet of the furnace and before a first port or burner of the furnace; the first port being the port closest to the inlet of the furnace. Injection of the O 2  may be in registration with, but not be limited to, the longitudinal centerline of the furnace. 
         [0016]    A method is provided to facilitate combustion in a furnace having at least one burner, an inlet, an outlet, and sidewalls and a crown defining a combustion chamber for the furnace, the method consisting of identifying a region of the combustion chamber where a furnace atmosphere therein requires an increase in oxygen for combustion in the furnace atmosphere, and providing fresh oxygen to the region at a controlled flow rate for the combustion, wherein the fresh oxygen provided causes circulation of the furnace atmosphere for combining existing gases and existing oxygen of the furnace atmosphere with the fresh oxygen provided to the region for combustion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows a longitudinal cross-section of a cross-fired regenerative furnace having an oxygen injector of the invention for facilitating gas flow along an interior of the furnace proximate the crown and toward combustion zones of the furnace. 
           [0018]      FIG. 2  shows a lateral cross-section of the furnace of  FIG. 1 , having a plurality of the oxygen injectors across the furnace width. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Referring to  FIGS. 1 and 2 , there is shown a furnace  10 , such as a glass melting furnace, which includes a roof or crown  12 . A regenerator  14  or plurality of regenerators are disposed for communication and operational use with the furnace  10 . The regenerators  14  are in communication with a furnace atmosphere “A” of the furnace  10 . The regenerators  14  each include checkers  15 . A batch charging system  16  is in communication with the furnace  10  at an inlet  18  of the furnace for providing batch  20 , as in this case glass seed, to the furnace for the melt. A glass bath is shown generally at  22 . Exhaust flow from the furnace  10  is shown generally at  24 , moving from the furnace  10  combustion atmosphere A to the regenerator  14 . 
         [0020]    One or a plurality of ports  26  (numbered  1 - 7 ) are disposed along opposed sides of the furnace  10 . One or a plurality of oxygen injectors  28  are disposed in the crown  12  of the furnace  10 . Each one of the oxygen injectors  28  may be formed as a tube constructed from, for example, metal or ceramics. The oxygen injector  28  may be positioned anywhere along the crown  12  of the furnace  10 . That is, each oxygen injector  28  can be positioned to be in registration with a corresponding one of the ports  26  or arranged to be positioned between the ports  26 . In addition, an oxygen injector  28  can be positioned as shown in  FIG. 1 , i.e. between the inlet  18  or the batch charging system  16  and the port  26  (# 1 ) of the furnace  10 . Similarly, the oxygen injector  28  can be positioned proximate to an outlet  30  (glass discharge section or throat) of the furnace  10 , at any location along the crown  12  such as also at a longitudinal centerline “C” of the furnace  10 . 
         [0021]    The oxygen injector  28  may comprise a pipe or tube having the necessary sealing member or component where the pipe is introduced through the crown  12  of the furnace  10 . One end of the oxygen injector  28  is connected to an oxygen source (not shown) while an opposed end of the injector  28  terminates in the furnace atmosphere A as shown in  FIGS. 1 and 2 . Each injector  28  has its own controllable flow rate to provide its respective oxygen profile  29 . A plurality of injectors  28  may have their flow rates adjusted to provide a combined oxygen and burn profile selected for the particular glass bath  22  or melt. 
         [0022]    The oxygen injectors  28  may be disposed in the crown  12  of the furnace  10  at a position whereby the oxygen jet is introduced into the furnace vertically (at 90° to the bath  22 ) and up to an angle  32  as much as 45° with respect to the vertical as shown in  FIG. 1 . Some furnaces have a throat which is located at an outlet of the furnace below the glass line. The oxygen injectors  28  may be used with existing burners being used in the furnace  10 . 
         [0023]    Injection of a gaseous oxygen stream through the crown  12  of the furnace  10  generates a venturi (suction) effect in the furnace to draw gases from other parts of the furnace in the form of a circulatory current toward the injected stream for combustion. Such a circulatory current flow is shown generally by arrow  34 . Depending on the point of oxygen injection, such will determine what gases are drawn into the oxygen stream. For example, in most cross-fired furnaces there is more oxygen in the downstream ports  26  (such as port #s  5 - 7 ) than the upstream ports  26  (port #s  1 - 4 ). However, it is desirable to have a sufficient amount of oxygen in the upstream ports  26 . Therefore, injecting a gaseous stream in the upstream zone of the furnace draws furnace gas of higher oxygen concentration from the downstream ports  26  (port #s  5 - 7 ) toward the upstream ports  26  (for example, port #s  1 - 4 ). 
         [0024]    In the invention, the injected gaseous stream contains oxygen from 20.9% to 100%. However, due to the entrainment of additional oxygen molecules from an area in the furnace  10  with higher localized oxygen concentration, the total oxygen conveyed to the flame as a result of the venturi effect can be greater than the amount of oxygen injected by the injectors  28 , with the combustion air supply shown generally at  36 . This is the total of oxygen injected with the oxygen injectors  28  plus the entrained oxygen stream. The entrained stream will comprise compounds of oxygen, nitrogen, carbon monoxide, carbon dioxide, water, noble gases, gases of evolution from the glass, and combinations thereof. 
         [0025]    As shown in  FIG. 2 , having a plurality of gaseous injectors  28  disposed across the crown  12  results in a port fire flame for the furnace being provided with the additional oxygen introduced from the oxygen injector  28  and the flow stream  34  as it crosses the surface of the glass melt  22 . This flame injection of furnace gases will reduce overall nitrous oxide (NOx) formation by the increased efficient combustion. 
         [0026]    The gaseous oxidant stream flow  34  facilitated by the venturi effect of the injected oxygen resembling the circulatory current will contact the glass batch surface  38  and provide a localized high concentration of oxygen under the flame created by the combustion air supply  36  and burner being used in the furnace  10 . This flow  34  will combust the flame and ensure complete combustion prior to exiting through exhaust  24  of the furnace  10 . The resulting flame temperature in the furnace  10  will be increased and in turn will increase the localized heat transfer to the glass bath  22 . 
         [0027]    Utilizing a portable gas analyzer during commissioning and process optimization of the furnace  10  will enable the desired furnace fuel profile and heat release to be achieved with the minimum amount of oxygen to be injected and used. 
         [0028]    An important aspect of this invention is to recover unused oxygen in the furnace atmosphere and to reduce NOX (nitrous oxide) of the furnace. To do this, the oxygen stream may be directed down from the lateral centerline of the furnace  10  at an angle so as to sweep under the port  26  (# 1 ). To reduce NOX, the amount of oxygen injected under combustion fire will stoichiometrically complete the combustion of the fuel or exceed the stoichiometric amount of oxygen to complete the combustion of the fuel. Injecting the oxygen toward or at the centerline C of the furnace has the benefits of not overheating the wall of the furnace through which the incoming fuel is passing and avoiding wasting the oxygen by combusting the oxygen with the fuel-gas over the batch rather than at or in the exhaust flow  24  or in the regenerator  14 . When the stream of oxygen passes under the path of the fuel-gas, it will pull the fuel-gas down over the batch as it is combusted and reduce the amount of energy that will heat the superstructure of the furnace or the regenerators. This equates to a more efficient process of transferring energy into the bath  22  and accelerating the melting of the batch. 
         [0029]    The oxygen injector  28  does not have to provide 100% oxygen. For example, oxygen content injected could be in a range of 70% oxygen and 30% gas. There are advantages to operating the injector  28  with some fuel rather than being 100% oxygen. One advantage is that it would provide thrust to the injected oxygen stream to ensure same will pass under the first port  26  fires. This thrust would be affected by different variables in the furnace operation, such as for example the distance of the crown to the bath  22 , the speed of the circulatory flow  34  across the furnace, the amount of the gas in the first port. 
         [0030]    In order to have a port firing on the reducing side of stoichiometry, one has to either partially or completely block off that port to limit the amount of combustion air that would pass through that port or add additional fuel through that port that exceeds the stoichiometric amount of oxygen that would be in the combustion air passing through this port. In this case, the amount of air that passes though a port is proportioned by the area of that port relative to the total area of all the incoming ports. This occurs in the regenerator  14  in which all the incoming combustion air passes through a common manifold above the checkers  15  before entering the ports. 
         [0031]    The oxygen injectors  28  can be used on the furnace  10  regardless of whether the furnace is providing float, container, lighting, display or specialty glass. 
         [0032]    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 and claimed herein. It should be understood that embodiments described above are not only in the alternative, but may also be combined.