Abstract:
The present disclosure describes a recovery boiler startup burner assembly that can mitigate the harmful effects of smelt fouling, airflow interference, and operator exposure to hot air from the furnace and win box through use of an extractable startup burner and an isolation chamber engaged to a windbox. The present disclosure also describes a method for safely extracting a startup burner from an active recovery boiler as has method for inserting an extractable startup burner into a recovery boiler during operation.

Description:
CROSS-RELATED APPLICATION 
       [0001]    This application is a Non-Provisional Application claiming the benefits of U.S. Provisional Patent Application Ser. No. 61/939,775 filed Feb. 14, 2014, the entirety of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. TECHNICAL FIELD 
         [0003]    The invention relates generally to startup burners and specifically to startup burners used in chemical recovery boilers in the pulp and paper industry. 
         [0004]    2. RELATED ART 
         [0005]    Chemical recovery boilers isolate useful compounds from manufacturing byproducts. In the pulp and paper industry, pulp mills typically use a manufacturing process in which wood chips or other lignocellulosic biomass are treated with chemical liquor comprising cooking chemicals. The wood chips or other lignocellulosic materials are then cooked in a digester at predetermined temperature and pressure to form a slurry comprising spent liquor and a rough pulp with inconsistent particle size. After cooking, equipment washes the spent chemical liquor from the rough pulp. The spent liquor is commonly known as “black liquor” and comprises organic and inorganic chemicals left over from the cooking process. The pulp is generally sent to other equipment for further refinement. The black liquor is eventually pumped to a chemical recovery boiler and processed to recover the cooking chemicals. Without recovering and reusing the cooking chemicals from the black liquor, the cost of industrial paper-making processes would be prohibitive. 
         [0006]    Chemical recovery boilers generally evaporate excess moisture from black liquor solids, burn organic liquor components, supply heat for steam generation, and recover inorganic compounds—notably sodium sulfide and sodium carbonate. Some of these compounds can be re-causticized and used elsewhere in the manufacturing process. 
         [0007]    In the recovery process, the black liquor is typically concentrated into a solution containing a solids concentration of above sixty percent by mass. Nozzles in the furnace wall then spray black liquor into a furnace. The nozzles are generally located in the bottom quarter of the furnace and may be several meters above the bottom of the furnace. The furnace is a reactor that generally dries and partially pyrolyzes the liquor droplets as they fall toward the bottom of the furnace. The furnace also evaporates, gasifies, oxidizes, and reduces, components within the black liquor to recover the cooking chemicals. 
         [0008]    The partially dried and reacted black liquor accumulates in a mound at the bottom of the furnace known as a “char bed”. Nozzles typically permit airflow into the furnace at a low, middle, and upper elevation. The air, together with the lignin, wood extracts, and other organic compounds maintain combustion in the furnace. Inorganic compounds are often reduced in the char bed into a molten smelt. The smelt may accumulate and flow out of the furnace through a smelt spout and into a collection tank. These reactions consume heat. As such, operators generally regulate and redistribute airflow and black liquor input, to promote and maintain combustion for efficient chemical recovery. 
         [0009]    In traditional recovery boilers, the furnace is internally lined with a series of densely-arranged, high-pressure coolant-filled tubes. The coolant is commonly water and a collective series of tubes is generally known as a “water wall.” To regulate temperature efficiently, the water wall tends to cover a large internal surface area. In some existing chemical recovery boilers, three inch coolant tubes are generally separated by one inch filler bars so as to form a gas-tight barrier enclosing the furnace. 
         [0010]    To operate safely and efficiently, the furnace generally operates under negative pressure. A constant inflow of air near the base of the furnace is generally required to maintain combustion and to replace air and other gases that exit the recovery boiler near the top of the furnace. Air generally enters the otherwise gas-tight furnace through openings in the furnace water walls. Such openings include air ports and throats, which are designed to inject pressurized air. Ambient air generally flows through other openings, such as those for smelt spouts, due to the negative pressure in the furnace. For most such openings, the coolant tubes generally bend around the opening in the furnace wall. 
         [0011]    Air manifolds or windboxes generally flank the throat and air port openings on the outer wall of the furnace. Large fans ducted to the windboxes can cause air to flow into the furnace through the various throats and air ports in the furnace walls. 
         [0012]    Airflow is the primary variable of operation aside from the rate of black liquor input. Large quantities of air are generally forced through the narrow throat and air port openings to maintain combustion. The flow of air through a throat and, diffuser, or swirler is desirable to maintain auxiliary combustion from active startup burners. Unfortunately, conditions within the furnace contribute to the gradual obstruction of air flow as smelt slowly accumulates over the various openings. Over time, accumulations of frozen smelt on and around the coolant tubes can grow to obstruct the openings, thereby reducing an operator&#39;s ability to regulate combustion. Recovery boilers may need to be deactivated when smelt accumulations significantly interfere operation. This extensive maintenance period results in loss of production. 
         [0013]    Temperature is another variable of operation. Startup burners help regulate internal furnace temperature. Startup burners are auxiliary burners that commonly fire natural gas, propane, and/or fuel oil, and are generally used to initiate combustion within the furnace after a period of dormancy. Once the startup burners increase furnace temperature to an established minimum, liquor firing can commence. Liquor firing is then increased until the liquor itself sustains combustion. The startup burners are then generally deactivated. Startup burns have also been used to provide supplementary heat to the furnace when liquor flow is interrupted or insufficient to meet boiler demand. 
         [0014]    When inactive, the startup burner generally rests in the windbox within a burner housing adjacent to the throat opening. Radiant heat from the furnace can damage inactive startup burners. Moreover, splashes of black liquor through the throat openings can cause smelt fouling directly on the startup burner, particularly on the firing end of the startup burner, comprising, for example, the fuel nozzles, swirler, igniter assembly, and flame detection equipment. Smelt fouling can render the startup burner ineffective, unsafe, and unreliable. 
         [0015]    There is a need to increase the intervals between recovery boiler maintenance and to reduce the amount of maintenance time while preserving or improving the operability of the recovery boiler after said maintenance. 
       SUMMARY OF THE INVENTION 
       [0016]    The problems of loss of production caused by deactivating a chemical recovery boiler for the purpose of manually dislodging accumulations of smelt, airflow interference in the chemical recovery boiler, exposing operators to hot air from the furnace and windbox, and startup burner damage due to smelt spattering and radiant heat from the furnace is mitigated by using a system of isolation chambers engaged to the outer wall of a windbox to extract startup burners from windboxes engaged to the outer wall of the furnace of the chemical recovery boiler, such that the isolation chambers are configured to partially isolate the startup burner from the windbox and furnace environment before extraction. In alternative embodiments, the isolation chambers may isolate the extractable startup burner substantially completely from the windbox and furnace environment. 
         [0017]    Some conventional startup burners may have a retraction feature whereby the burner can be manually or automatically retracted from an active position. That is, while the firing ends of the startup burners can be retracted from the furnace, the body and firing ends remain in the windbox proximate to the furnace and directly behind the wall openings in the furnace. Retracted firing ends are typically eight to sixteen inches from the furnace. By retracting an inactive conventional startup burner from the furnace, conventional burners have sought to reduce exposure to furnace temperature and smelt fouling. While conventional burners have been somewhat effective in prolonging the useful life of startup burners, conventional burners have significant drawbacks. 
         [0018]    Conventional burners preclude startup burner maintenance while the recovery boiler is operational. The potential for smelt splatter renders human intervention unsafe. Hot air in the pressurized windbox and radiant heat from the furnace complicate human intervention. Conventional startup burners generally require constant exposure to moving air to prevent overheating. This tramp air flowing from the windbox through the throats and into the furnace can also provide oxygen to maintain combustion. Operators generally consider the amount of air entering the furnace as a variable when attempting to maintain a desirable combustion rate. To this end, some conventional startup burners are placed within housings having variable position dampers. The housings are likewise placed within the windbox. The variable position dampers can allow operators to affect the amount of air flowing over the startup burner to the boiler. However, the desire to preserve the startup burner from overheating prevents operators from closing variable position dampers completely. 
         [0019]    Airflow within the windbox may become dynamic and irregular based partially on the oxygen demands of the furnace. Additionally, the startup burner obstructs the air flow in the housing, thereby facilitating an irregular and unpredictable insertion of air into the recovery boiler. 
         [0020]    With regard to retracted startup burners, smelt fouling still occurs due to residual splashing of black liquor droplets through the throats and onto the firing end. The firing end generally includes a diffuser, or swirler, which can be used to direct or shape the flame emanating from the startup burner. The swirler&#39;s large surface area relative to the throat can increase the incidence of smelt accumulation on the swirler. Additionally, radiant heat from the furnace can damage the startup burner. The presence of retracted startup burners directly behind the occluded throats can interfere with operator&#39;s ability to clear the occlusions and perform necessary maintenance of the burners while the boiler remains operational. 
         [0021]    Embodiments of the current disclosure comprise an isolation chamber located behind an extractable startup burner in a windbox. The assembly separates an operator from the pressurized hot air in the windbox and furnace thereby permitting operators to remove inactive startup burners safely while the recovery boiler is operational. Once the startup burner is removed, operators may use a rod, a cleaning brush mounted on a pole, or other suitable cleaning means to clean the throats manually. If the width of the isolation chamber is sufficiently wide, operators may clean multiple openings in the furnace wall through a single isolation chamber. Additionally, the exemplary assembly allows operators to replace or repair startup burners, as needed for optimal boiler operation, between scheduled outages. 
         [0022]    Further, use of an extractable startup burner with an isolation chamber may eliminate or reduce the need for burner-cooling air. In conventional burners, variable position dampers in burner housings remain partially opened when the startup burner is inactive. The variable position dampers allow air from the windbox to cool the inactive startup burner and to counter effects of radiant heat. Throats in the furnace wall are generally uncovered when a startup burner is not in use, so tramp air in the burner housing used to cool the inactive startup burner may also flow into the furnace uncontrollably. This undesirable influx of air into the furnace can complicate an operator&#39;s ability to control and maintain optimal combustion conditions. Additionally, the presence of a conventional retracted startup burner in the windbox can interfere with desirable airflow. 
         [0023]    Use of an extractable startup burner and isolation chamber as set forth in the present disclosure may allow operators to close fully variable position dampers in the burner housing and reduce or prevent tramp air from entering the furnace, thus improving air distribution control. Accordingly, it is an object of the present disclosure to improve air distribution control in a chemical recovery boiler—particularly in the windbox and through openings in the furnace wall. 
         [0024]    A recovery boiler startup burner assembly has been conceived comprising: a furnace having areas defining openings in a furnace wall, a windbox exteriorly engaging the furnace wall, wherein the windbox is configured to contain pressurized combustion air, an isolation chamber exteriorly engaging a windbox wall, wherein the isolation chamber is aligned with an area defining an opening in the windbox wall and an area defining an opening in the furnace wall, a startup burner disposed within the windbox, the startup burner having a firing end and a supply end, wherein the firing end is aligned with the area defining an opening in the furnace wall and the supply end is aligned with the area defining an opening in the windbox wall, wherein the startup burner is configured to be extracted through the isolation chamber, and wherein the isolation chamber is configured to isolate an extracted portion of the startup burner from the windbox. 
         [0025]    The isolation chamber may comprise a multi-door isolation chamber. In another exemplary embodiment, the isolation chamber may comprise a burner guide sleeve having a hinged door at one end and a seal plug at the other end. In still other exemplary embodiments, the isolation chamber may be configured to isolate the startup burner partially from the windbox. In yet other exemplary embodiments, the isolation chamber may be configured to isolate the startup burner from the windbox substantially completely. 
         [0026]    In still other exemplary embodiments, the assembly for a recovery boiler may further comprise a cooling carriage comprising a structural brace having a first end and a second end, the second end being mounted to an outer wall of the recovery boiler and the first end being engaged to a first end of a main support beam, a second end of the main support beam being engaged to the outer wall of the recovery boiler, the cooling carriage may further comprise a carrier assembly linkage having at least one first end and at least one second end having at least one roller rotatably mounted to the at least one second end of the carrier assembly linkage. 
         [0027]    The cooling carriage may further comprise a local temperature display. The local temperature display may be a contact-type temperature display, such as a resistance temperature detector (“RTD”) or a thermocouple detector. In other exemplary embodiments, the local temperature display may be a non-contact type display such as an infrared thermometer or a laser thermometer. 
         [0028]    A method has been conceived for extracting a startup burner comprising: deactivating a startup burner, disconnecting wires and hoses from the startup burner and an igniter assembly, withdrawing the startup burner from a throat in a furnace wall, removing the igniter assembly from the startup burner, lowering a support brace to the startup burner, withdrawing the startup burner into an inner space defined by the multi-door isolation chamber, closing at least one inner door of the multi-door isolation chamber to support the startup burner, withdrawing the startup burner through the inner space defined by the multi-door isolation chamber, opening at least one outer door of the multi-door isolation chamber, closing the inner door of the multi-door isolation chamber, and removing the startup burner from the inner space of the multi-door isolation chamber. 
         [0029]    A multi-door isolation chamber for use with a recovery boiler windbox has been conceived comprising: a multi-door isolation chamber disposed proximate to a windbox opening defined by an outer wall of a windbox, at least one inner door configured to occlude partially the windbox opening and support a startup burner, and at least one outer door configured to occlude a multi-door isolation chamber opening defined by an outer face of the multi-door isolation chamber. 
         [0030]    Another method has been conceived for extracting a startup burner from a recovery boiler comprising: shutting down a startup burner; disconnecting wires and hoses from the startup burner and an igniter assembly; withdrawing the startup burner from a throat in a furnace wall; removing the igniter assembly from the startup burner; lowering a support brace to the startup burner; closing the first inner door of the multi-door isolation chamber to support the support brace and startup burner; withdrawing the support brace with the startup burner through a first inner door of a multi-door isolation chamber into an inner space defined by the multi-door isolation chamber; closing a second inner door of the multi-door isolation chamber to substantially isolate the support brace with the startup burner in the inner space of the multi-door isolation chamber; opening at least one outer door of the multi-door isolation chamber; and removing the startup burner from the inner space of the multi-door isolation chamber. 
         [0031]    A method for cleaning smelt accumulations in a recovery boiler during operation has been conceived comprising: shutting down a startup burner, disconnecting wires and hoses from the startup burner and an igniter assembly, withdrawing the startup burner from a throat in a furnace wall, removing the igniter assembly from the startup burner, withdrawing the startup burner into an inner space defined by the multi-door isolation chamber, closing at least one inner door of the multi-door isolation chamber, withdrawing the startup burner through the at least one inner door of a multi-door isolation chamber to substantially isolate the startup burner in an inner space defined by the multi-door isolation chamber, opening at least one outer door of the isolation chamber, removing the startup burner from the isolation chamber, and extending a rod through the multi-door isolation chamber to dislodge smelt accumulations from the throat in the furnace wall. 
         [0032]    The method for cleaning smelt accumulations may further comprise extending a carrier assembly linkage of a cooling carrier into a path of the startup burner, placing the startup burner on rollers extending from the carrier assembly linkage, and allowing a hot end of the startup burner to cool on the rollers. 
         [0033]    A method has been conceived for replacing an extractable startup burner in a recovery boiler during operation comprising: aligning a support brace with an outer door of an isolation chamber; mounting a startup burner on a support brace, opening at least one outer door of the isolation chamber, inserting a startup burner into an inner space of the isolation chamber, closing the at least one outer door of the isolation chamber to support the startup burner, closing a second outer door of the isolation chamber to substantially isolate the startup burner in the inner space of the isolation chamber; extending the startup burner from the at least one inner door toward a throat in a furnace wall; and connecting wires and hoses to a startup burner and an igniter assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The foregoing will be apparent from the following more particular description of exemplary embodiments of the disclosure, as illustrated in the accompanying drawings. The drawings are not necessarily to scale, with emphasis instead being placed upon illustrating the disclosed embodiments. 
           [0035]      FIG. 1  is a side-view of an exemplary embodiment of a recovery boiler with windboxes and several multi-door isolation chambers engaged to the sides of the windboxes. 
           [0036]      FIG. 2   a  is a perspective view of an exemplary embodiment of the multi-door isolation chamber, the windbox, and the path by which the startup burner may be removed from the windbox. 
           [0037]      FIG. 2   b  is a cross-sectional view of an exemplary embodiment of the multi-door isolation chamber, the windbox, and the path by which the startup burner may be removed from the windbox. 
           [0038]      FIG. 3  is a burner end view of an exemplary embodiment of the multi-door isolation chamber, the throat, and the swirler with the outer doors of the multi-door isolation chamber engaged to the front plate of the multi-door isolation chamber via hinges. 
           [0039]      FIG. 4  is a top-down view of an exemplary embodiment of the multi-door isolation chamber mounted to the outer wall of the chemical recovery boiler and the startup burner extending through the windbox and into the furnace. 
           [0040]      FIG. 5   a  is a front view of an exemplary first inner door and second inner door of the multi-door isolation chamber configured to substantially completely isolate a startup burner in the multi-door isolation chamber. 
           [0041]      FIG. 5   b  a front view of an exemplary embodiment of the first inner door and second inner door of the multi-door isolation chamber that are slidably engaged proximate to the windbox along a track. 
           [0042]      FIG. 6   a  is a side view of an exemplary cooling carriage affixed to the outer wall of a windbox. 
           [0043]      FIG. 6   b  is a front view of an exemplary cooling carriage depicting the extended carriage&#39;s position relative to the multi-door isolation chamber. 
           [0044]      FIG. 7  is a side view of an exemplary burner guide sleeve with a plug and flapper seal. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0045]    The following detailed description of the preferred embodiments is presented only for illustrative and descriptive purposes and is not intended to be exhaustive or to limit the scope and spirit of the invention. The embodiments were selected and described to best explain the principles of the invention and its practical application. One of ordinary skill in the art will recognize that many variations can be made to the invention disclosed in this specification without departing from the scope and spirit of the invention. 
         [0046]    Although the drawings represent embodiments of various features and components according to the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate embodiments of the present disclosure, and such exemplifications are not to be construed as limiting the scope of the present disclosure. 
         [0047]    The present disclosure describes an isolation chamber that may be used with a startup burner configured to be removed or replaced while the boiler is operating. Natural gas, oil, propane, or other fuel known to those having ordinary skill in the art may fuel the startup burner. Although the startup burner may be used in boilers or process furnaces generally, subsequent exemplary uses will refer to recovery boilers used in the pulp and paper industry. 
         [0048]      FIG. 1  depicts an exemplary embodiment of the isolation chamber  106  attached to windboxes  190  of a recovery boiler  107 . The windboxes  190  generally span the sides of the furnace  199  horizontally and may contain throats ( FIG. 2 ,  240 ), housings ( FIG. 4 ,  491 ), startup burners ( FIG. 2 ,  200 ), or other instruments such as air nozzles or probes to record furnace conditions (not depicted). Recovery boilers  107  generally have a primary windbox  190   a , a secondary windbox  190   b , and tertiary windbox  190   c  spanning the sides of the furnace  199 . The primary windbox  190   a  is generally closest to the ground and the tertiary windbox  190   c  is generally furthest from the ground. In certain exemplary embodiments, exemplary isolation chambers  106  may be attached to the primary windbox  190   a  and secondary windbox  190   b . In other embodiments, at least one exemplary isolation chamber  106  may be attached to the primary windbox  190   a . In still other embodiments, exemplary isolation chambers  106  may be attached to any one of the primary windbox  190   a , secondary windbox  190   b , or tertiary windbox  190   c . In other exemplary embodiments, at least one exemplary isolation chamber  106  may be attached to each of the primary windbox  190   a , secondary windbox  190   b , and tertiary windbox  190   c.    
         [0049]      FIG. 2   a  depicts a perspective view of the exemplary multi-door isolation chamber  206  engaged to a mounting plate  218  secured to the outer wall  222  of the windbox  290 . In this exemplary embodiment, the multi-door isolation chamber  206  is generally in the shape of a rectangular prism (i.e. box-shaped); however, on other embodiments, the multi-door isolation chamber  206  may be generally cylindrical, generally in the shape of a geometric prism having greater than three edges, or generally irregularly shaped. A generally irregularly shaped isolation chamber  206  may have a sample cross sectional area at a first position (e.g. a measurement of cross sectional area measured along a first plane) that differs from a sample cross sectional area at a second position (e.g. a measurement of cross sectional area measured along a second plane parallel to the first plane). 
         [0050]    The startup burner  200  may comprise an inlet  207  through which natural gas, air, or other fuel enters the startup burner  200 . The inlet  207  is generally located at the supply end of the startup burner. The fuel generally flows along the length of the startup burner  200  and into the furnace  299 . Air enters the furnace through throat  240 , and may flow across swirler  250 . The swirler rotates thereby aiding fuel and air mixing. Operators may monitor the fuel input and amount of air entering the furnace  299  from the windbox  290  to increase furnace temperature and melt or burn away smelt accumulations. During operation, a startup burner  200  may extend through the multi-door isolation chamber  206  and traverse the windbox  290 . Water wall tubes  270  may bend to create an open area, which defines a throat  240 . In other embodiments, the throats  240  may be further defined by a reinforcing element (not depicted) disposed within the opening defined by the water wall tubes  270 . The reinforcing element may generally conform to the hole defined by the bend water wall tubes  270  and may be made from carbon steel or other material configured to withstand furnace heat. 
         [0051]    An exemplary startup burner assembly  241  may have an observation port  260  through which operators may view the inside of the windbox  290 , throat  240 , and furnace  299 . An operator may look through the observation port  260  to determine the amount of smelt accumulation around the throat  240 . If smelt has accumulated, an operator may insert a rod (not depicted) through port  251  to dislodge the smelt accumulations while the recovery boiler is operational. In an exemplary method, an operator may insert the rod through the multi-door isolation chamber  206 . 
         [0052]    In the exemplary startup burner assembly  241  of  FIG. 2   a , the multi-door isolation chamber  206  is configured isolate the startup burner  200  from the furnace  299  and windbox  290  by using outer doors  210 ,  216  and inner doors ( FIG. 2   b    220 ,  226 ). The outer door comprises a bottom outer door  210  engaging handle  230   b  and a top outer door  216  engaging handle  230   c . Handle  230   d  engages top inner door  226 , while handle  230   a  engages bottom inner door  220 . The outer doors  210 ,  216  and inner doors  220 ,  226  desirably open inwardly toward the furnace  299  and windbox  290 . In this configuration, pressure generated by the furnace  299  and windbox  290  exerts an outward force on the inner doors  220 ,  226  and outer doors  210 ,  216 . Inwardly opening doors may reduce the risk of sudden release of hot air and potential smelt splatter if the pivot mechanism  266  fails. If both inner doors  220 ,  226  and outer doors  210 ,  216  were configured to open outwardly, the pivot mechanisms  266  keeping the inner doors  220 ,  226  and outer doors  210 ,  216  closed would be more likely to experience prolonged stress due to the windbox-pressure and therefore be more likely to fail spontaneously and expose personnel and nearby equipment to hot, high-pressure air from the windbox  290 . Although the inner doors  220 ,  226  and outer doors  210 ,  216  desirably open inwardly, other exemplary embodiments may comprise one or more inner doors  220 ,  226  and outer doors  210 ,  216  opening outwardly away from the windbox  290  and furnace  299 . The bottom inner door  220  and bottom outer door  210  pivot at the bottom of the multi-door isolation chamber  206  in  FIG. 2   a . Likewise, the top inner door  226  and top outer door  216  pivot at the top of the multi-door isolation chamber  206 . In other exemplary embodiments, the outer and inner door may comprise two or more doors, one or more of which may pivot on the right side of the isolation chamber  206 , and one or more of which may pivot on the left side of the isolation chamber  206  (see  FIG. 5 ). In other exemplary configurations, an odd number of outer doors may be used. In yet other embodiments, an odd number of inner doors may be used. The bottom outer door  210  may have a cut-out portion  213  configured to support the startup burner  200 . The outer door may be a singular outer door. The inner door may be a singular inner door. Nothing in this disclosure limits the combination of aspects of one embodiment with aspects of one or more other embodiments. 
         [0053]      FIG. 2   b  is a cross sectional view of an exemplary startup burner assembly  241 . The startup burner  200  may be extracted through the windbox  290  and bottom inner door  220  of the multi-door isolation chamber  206 . Operators may then use handle  230   a  to close the bottom inner door  220  of the multi-door isolation chamber  206 . In this exemplary embodiment, the bottom inner door  220  may be a plate of carbon steel or other material suitable to withstand the heat and pressure of the windbox  290  and an occasional splatter of black liquor (not pictured) through the throats  240  of the furnace  299 . Bottom inner door  220  may be configured to provide support for the startup burner  200  as the startup burner  200  is extracted from the windbox  290 . The bottom inner door  220 , when closed, may occupy a portion of the opening  221  created in windbox mounting plate  218 . In other exemplary embodiments, the bottom inner door  220 , when closed, may be configured to occupy substantially all of the opening  221 ; in this manner, a portion of the startup burner  200  may be substantially completely isolated in the internal space  225  of the multi-door isolation chamber  206 . 
         [0054]    In still other exemplary embodiments, the bottom inner door  220 , when closed, may be configured to occupy half of the opening  221 . In yet other exemplary embodiments, the bottom inner door  220 , when closed, may be configured to occupy a portion of the opening  221 . In this manner, a portion of the startup burner  200  may be partially isolated in the internal space  225  defined by the multi-door isolation chamber  206 . 
         [0055]    Thus protected from the furnace environment and so isolated from the windbox  290 , an operator may open the outer door  210  of the multi-door isolation chamber  206  and remove the startup burner  200  from the multi-door isolation chamber  206  with reduced risk of burns due to hot air or molten smelt. In addition to being protected, the operator, by extracting the startup burner  200 , may extend the useful life of the startup burner  200  by removing the startup burner  200  from the recovery boiler completely. By having the startup burner  200  completely removed from the recovery boiler, the operator may maintain, repair, or replace the startup burner  200  while the recovery boiler is operational, while substantially eliminating the risk of injury from the recovery boiler. 
         [0056]    The outer doors  210 ,  216  and inner doors  220 ,  226  desirably open inwardly toward the windbox  290  and furnace  299 . The pressure created by the furnace  299  and moving air within the windbox  290  exerts a force against the closed inner doors  220 ,  226  and outer doors  210 ,  216 . By opening inwardly, the closed inner doors  220 ,  226  and outer doors  210 ,  216  remain locked in position, thereby reducing the risk that door failure will expose operators to immediate harm. An insulating liner  273  may be disposed within the multi-door isolation chamber  206 . 
         [0057]      FIG. 3  depicts a burner end view of an exemplary multi-door isolation chamber  306  in which the outer doors  310 ,  316  and inner doors  320 ,  326  of the multi-door isolation chamber  306  have pivot mechanisms (see  266 ), which rotate outer doors  310 ,  316  and inner doors  320 ,  326  of the multi-door isolation chamber  306 . This embodiment further comprises an observation port  360 . The swirler  350  is disposed around the fuel nozzle tip  398  and of the startup burner  300 . The fuel nozzle tip  398  is located at the firing end of the startup burner  300 . In an exemplary method, an operator may look through the observation port  360  to determine the amount of smelt accumulation around the throat  340 . If smelt has accumulated, an operator may insert a rod through the multi-door isolation chamber  306  to dislodge the smelt accumulations while the recovery boiler is operational. By inserting a rod through the exemplary multi-door isolation chamber  306 , an operator may have a more direct path to the throat  340  and may avoid damage to the swirler  350 , which may have been previously caused by poor visibility and suboptimal access due to mechanical interference. An operator may close the bottom inner door  320  to support the startup burner  300  while dislodging smelt. The closed bottom inner door  320  partially protects the operator from stray smelt splatter from the furnace  299 . An operator may desirably close either the top outer door  316  or bottom outer door  310  to provide additional protection from stray smelt splatter when cleaning the throat  340 . In other embodiments, an operator may extend the rod through a port  351  in the outer wall  322  of the windbox  290 . When operators desire to ignite the startup burner  300 , operators generally insert an igniter assembly ( FIG. 4 ,  480 ) through mounting tube  383 . 
         [0058]      FIG. 4  is a top-down view of an exemplary startup burner  400  and the swirler  450  extending through the multi-door isolation chamber  406  and the windbox  490  to engage the throat  440 . Water wall tubes  470  form the envelope of the furnace  499  and absorb furnace heat. The startup burner  400  may be removed from the windbox  490  through a housing  491  that spans the length of the windbox  490 . In some embodiments, the housing  491  may have a variable position damper  492  that may be opened and closed to allow air from the windbox  490  into the housing  491  and into the furnace  499  through the swirler  450  and throat  440 . This air maintains combustion at the fuel nozzle tip  498  of the startup burner  400  when active. When the startup burner  400  is dormant or extracted, the variable position damper  492  may be closed substantially completely to prevent air from entering the furnace  499  through the throat  440 . In other embodiments, the variable position dampener  492  may be partially open to accommodate a desired air flow. 
         [0059]    The startup burner  400  may further be removed from the windbox  490  and housing  491  by using the handle  430   a  to open the bottom inner door  220  of the multi-door isolation chamber  406  and by pulling the startup burner  400  through the internal space  425  of the multi-door isolation chamber  406 . After closing the inner doors  220 ,  226  the startup burner  400  may be partially or substantially completely isolated. Once isolated, the startup burner  400  may be removed through the outer doors  210 ,  216  of the multi-door isolation chamber  406 . 
         [0060]    An igniter assembly  480  of the startup burner  400  is depicted in this exemplary embodiment. The igniter assembly  480  may comprise an ionizing flame rod and spark rod  481  and intake ports  482 . Air and natural gas may flow through these intake ports  482 . A mounting tube  483  can position the igniter assembly  480 . This igniter assembly  480  may further comprise safety equipment used to ensure continuous ignition at the fuel nozzle tip  498  of the startup burner  400 . The swirler  450  stabilizes and shapes the main flame within the furnace  499 . In an exemplary embodiment, the mounting tube  483  of the igniter assembly  480  can engage the outer wall  422  of the windbox  490  outside insolation chamber  406 . In another exemplary embodiment, the igniter assembly  480  may be co-extensive with the startup burner  400  and access the windbox  490  through the isolation chamber  406 . In an exemplary embodiment, a flapper valve  484  may be engaged to at least one end of the mounting tube  483 . This flapper valve  484  may be used to prevent pressure loss from the windbox  490  when the igniter assembly  480  is not in place. 
         [0061]      FIG. 5   a  is an exemplary embodiment of the multi-door isolation chamber  206  comprising a first inner door  526  and a second inner door  527  that may rotate on a pivot mechanism  535  such as a hinge or slide along tracks  532  (shown in  FIG. 5   b ). It is to be understood by one skilled in the art that outer doors (see  FIG. 2 ,  210 ,  216 ) may be configured in similar manner to the inner doors  526 ,  527  as described herein. A multi-door isolation chamber  206  comprising two or more inner doors  526 ,  527  may be desirable to isolate the startup burner  500  completely in the multi-door isolation chamber  206  prior to extraction. By closing the two or more inner doors  526 ,  527 , operators substantially reduce the probability that operators will contact stray droplets of liquor flung through the throat  440  of the furnace  499  because these inner doors  526 ,  527  may be used to close the opening  221  defined by the outer walls of the windbox  290 . The first inner door  526  may have a cut-out section  523  configured to complement the perimeter  504  of the startup burner  500 . The outer doors may have a cut-out section (see  213 ) configured to support the startup burner. The first inner door  526  may be substantially closed when removing the startup burner  500  (shown in  FIG. 5   b ) such that the cut-out section  523  may be used to support the startup burner  500  as the startup burner  500  is extracted from the windbox  290  of the recovery boiler  107 . Once the startup burner  500  is inside the multi-door isolation chamber  206 , the second inner door  527  may be closed to substantially completely isolate the startup burner  500  in the multi-door isolation chamber  206 . In this embodiment, the second inner door  527  has a flange  528  configured to complement the cut-out section  523  of the first inner door  526 . In other embodiments, this flange  528  may be omitted. Although two inner doors  526 ,  527  are used, it is understood that configurations of inner and outer doors known to those having ordinary skill in the art may be used to isolate the startup burner  500  from the windbox environment and furnace environment. 
         [0062]      FIG. 5   b  depicts an exemplary multi-door isolation chamber  206 , which comprises a first inner door  526  and a second inner door  527 , each having runners  531  configured to slide along tracks  532  disposed on the windbox mounting plate  218 . In other embodiments, these tracks  532  may be engaged to the inner wall of the multi-door isolation chamber  406 . In still other embodiments, one track per first and second inner door may be utilized. The first inner door  526  may have a cut-out section  523  configured to complement the perimeter  504  of the startup burner  500 . The first inner door  526  may be substantially closed when removing the startup burner  500  such that the cut-out section  523  may be used to support the startup burner  500  as the startup burner  500  is extracted from the windbox  290  of the recovery boiler  107 . Once the startup burner  500  is inside the multi-door isolation chamber  206 , the second inner door  527  may be closed to substantially isolate the startup burner  500  in the multi-door isolation chamber  206 . In this embodiment, the second inner door  527  has a flange  528  configured to complement the cut-out section  523  of the first inner door  526 . In other embodiments, this flange  528  may be omitted. 
         [0063]      FIG. 6   a  is a side view of an exemplary cooling carriage  642  that may be used to hold the startup burner  600  and permit cooling after the startup burner  600  has been removed from the multi-door isolation chamber  606 . In this exemplary embodiment, a structural brace  644  having a first end  643  and a second end  645  may be mounted to the outer wall  622  of the windbox  690 . In another exemplary embodiment, the second end  645  may be mounted to the recovery boiler  107  such that the cooling carriage  642  remains aligned with the isolation chamber  606  as the recovery boiler expands during operations. A main support beam  648  may have a first end  647  attached to the first end of the structural brace  643  and a second end  649  perpendicularly attached to the outer wall  622  of the windbox  690 . In another exemplary embodiment, the second end  649  may be mounted to the recovery boiler  107  such that the cooling carriage  642  remains aligned with the isolation chamber  606  as the recovery boiler expands during operations. A carriage assembly linkage  655  may be rotatably mounted to the main support beam  648  such that the carriage assembly linkage  655  may be secured away from the path  602  of the startup burner  600  when not in use. Rollers  657  may be mounted on at least one end of the carriage assembly linkage  655 . These rollers  657  may extend below the path  602  of the startup burner  600  and support the startup burner  600  after the startup burner  600  has been removed from the multi-door isolation chamber  606 . Operators may remove the startup burner  600  from the cooling carriage  642  after the fuel nozzle tip  698  of the startup burner  600  has cooled. In other embodiments, at least one clamp, ring, hook, or other similar securing means (not shown) may be used singularly or in combination with other securing means to support the startup burner  600  as it cools. 
         [0064]    In an exemplary method, operators may deactivate the startup burner  600  and extract the startup burner  600  and swirler  650  through the housing  691 . Operators may then close an inner door  620  and rest the bottom of the startup burner  603  on a cut-out portion  623  of an inner door  620 . Once the inner door  620  is closed, operators may pull the startup burner  600  through the internal space  425  of the multi-door isolation chamber  606  and through the outer door of the multi-door isolation chamber  610 . Operators may then place the startup burner  600  on the rollers  657  of the carriage assembly linkage  655  and allow the startup burner  600  to cool. Once cool, the operators may remove the startup burner  600  from the cooling carriage  642  and store the cooling carriage  642  away until further needed. 
         [0065]    In another exemplary method, the inner door  620  need not be closed before the operator removes the startup burner  600  from the multi-door isolation chamber  606 . 
         [0066]      FIG. 6   b  is a front view of an exemplary cooling carriage  642 . The elements correspond to the elements described in  FIG. 6   a . In this exemplary embodiment, the rollers  657  may be contoured to support the startup burner  600  either singularly or in combination with at least one other roller. 
         [0067]      FIG. 7  depicts an alternative exemplary isolation chamber in the form of a burner guide sleeve  775 . This exemplary burner guide sleeve  775  comprises a plug  771  at an outer end  777  of the burner guide sleeve  775  and a flapper valve  784  at an inner end  778  of the burner guide sleeve  775 . The burner guide sleeve  775  generally extends into the windbox  790  and may support the startup burner  700  at least partially. The plug  771  may be used to prevent hot air flow from the windbox  790  when the startup burner  700  is in use. The plug  771  may be fixed to the startup burner  700 . In another embodiment, the plug  770  may be slidably engaged to the startup burner  700 . The plug may be made from a high-density, lightweight material configured to withstand air temperature in the windbox  790 . The plug  771  may desirably fill the inner perimeter of the guide sleeve  775  so as to form a seal. In embodiments where the plug  771  is fixed to the startup burner  700 , the length  708  of the plug may be at least the length  709  of the distance between the flapper valve  776  and the throat  740 . In embodiments where the plug  771  is not fixed to the startup burner  700  but is still configured to maintain a seal, the length  708  of the plug  771  may be less than the length  709  between the flapper valve  776  to the throat  740 . In exemplary embodiments in which the startup burner has been extracted from the windbox, the plug  771  may desirably fill the inner perimeter of the guide sleeve and extend through the windbox in substantially the same manner as the startup burner  700  such that the plug  771  may have an end corresponding to the firing end of the startup burner  700  and swirler  750  that substantially blocks the hole left by the extracted swirler  750 . The plug  771  may be made of a material generally known in the art, including a poly-amide-based plastic, or other suitable material configured to withstand the heat of the recovery boiler. 
         [0068]    The flapper valve  784  may rest on the startup burner  700  when the startup burner  700  interfaces with the throat  740  and furnace  799 . When the startup burner  700  is removed past the flapper valve  784 , the flapper valve  784  generally closes and rests on the front lip  794  of the guide sleeve  775  at an angle  9 . The burner guide sleeve  775  may extend partially through the housing  791  within the windbox  790 . 
         [0069]    It will be understood that the modifications of  FIGS. 3 through 7  could be employed in combination with one another as well as individually in the assembly of  FIG. 1  and the assembly illustrated in  FIG. 2 . 
         [0070]    While this invention has been particularly shown and described with references to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.