Abstract:
A method for repairing power plant boilers provides for a water mist insertion into the furnace to provide for more rapid cooling, which allows personnel to enter into the furnace to conduct repairs in a shorter time. Water mist is provided by air-water mixing atomizing sprayers that are inserted into the boiler. Existing power plant oil igniter lighters may be switched from oil to water to provide the air-water mixed atomized mist.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention is for operation and maintenance of power plant boilers that are used for generating electricity. The invention by reducing the amount of down time during a forced outage reduces cost incurred as a result of the outage.  
       BACKGROUND OF THE INVENTION  
       [0002]     When a condition in a power boiler forces an outage, it is necessary for personnel to enter the boiler to perform repair operations. A typical condition that requires repair is a tube leak that may be found in a coal, gas or oil fired boiler. Such tube leaks necessarily force outages, which must be quickly repaired.  
         [0003]     A typical power boiler may experience from four to five outages per year with each forced outage lasting approximately 72 hours. Each forced outage may cost the power utility approximately 1.3 million in net revenue. Therefore, if the outage time can be reduced, the cost per outage will also necessarily be reduced.  
         [0004]     Before inspectors and/or welders can enter a boiler to make repairs, it must be cooled from 800 to 1000° F. to a barely tolerable 105° F. The tolerance level is often specified by the standard set forth by OSHA. Such tolerance standards may require that the temperature not exceed 95° F. at a specified humidity.  
         [0005]     In the prior art it is known to use fans, which are present in a power plant boiler&#39;s air supply system to reduce the boiler temperature after turning off the boiler. The use of such fans generally takes from 12 to 24 hours to cool the power plant depending upon the outside ambient air temperature and humidity conditions.  
         [0006]     In the case where cooling is accomplished by ambient air forced through a boiler using the power plant&#39;s own large force draft fans, the force draft fans heat the ambient air by 10 to 15° F. as it is pumped into the unit. This becomes a significant problem when the ambient air outside is already greater than 90° F. and where it is necessary to cool the boiler to 105° F. or less for entry of personnel into the boiler for repair purposes.  
         [0007]     Even a five to eight percent reduction in down time results in substantial savings to a power plant operator. In the case of the San Juan Power Plant located in New Mexico, in 2003 and 2004, there were a total of 1,490,994 megawatts lost due to 44 tube leaks. Approximately 82,000 to 124,000 megawatts in output are gained if down time is reduced 5 to 8%. At a cost $41.08/mw this represents $3,368,000 to $5,093,000 over the two-year period. This is a significant savings.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     This invention utilizes a spray, which is a mixture of high-pressure air, and water, which produces a fine mist of very small droplets within the boiler. The mist has an advantage of preventing tube cracking due to sustained contact of the water directly with tubes (saturation) during a period when the tubes are at a high temperature. A phenomenon known as hydrogen embrittlement can result in subsequent tube cracking in a power plant boiler. Use of a mist avoids impinging a sustained water stream directly on the boiler water wall when the boiler water wall is at a maximum temperature condition (typically a 350 to 400° F. differential temperature between the water used and the metal temperature for SA210A1 or similar materials). Direct water impingement or “wetting” can cause a rapid quenching, which can result in cracking or hydrogen embrittlement of boiler tubes. When a mist is used, it provides for a condition inside of the boiler, which prevents droplets from impinging directly on high temperature boiler tubes for a sustained period when the misting devices are turned on.  
         [0009]     When a water mist is sprayed into the firebox, the boiler becomes a large evaporative cooler. There is an increase in the humidity of the cooling air, which allows the heat of vaporization to work in the favor of the plant operator to reduce temperature more quickly. In this invention, a fine mist is produced by air and water mixing atomizer nozzles. The fine mist can be conveniently produced by existing igniter oil lighters which are used in coal fired plants, by separate tubes which are inserted into the boiler which have at their tip, nozzles for mixing air with water or a combination of existing igniter lighter systems and additional air-water mist insertion tubes. In a-typical power plant operation., air and fuel are supplied to the igniters from a centralized source. When igniter nozzles are utilized, the igniter is inserted into the boiler and its fluid supply is switched from oil to water. This same source of compressed air can also be utilized for supplying air to the separate mist spray insertion devices, which combine air and water at the tip to produce a mist.  
         [0010]     As the mist is inserted into the boiler, the latent heat of evaporation removes large quantities of heat from the air. The fans in the boiler plant are left on, thereby forcing the high humidity and therefore high heat content air through the boiler and to its exhaust system.  
         [0011]     Although tube leaks are the most common cause of a forced outage, there may be other reasons for a forced outage, or other reasons for temporarily shutting down a power plant boiler for repair purposes. In any event, it is important as a matter of economics to perform all necessary repairs as rapidly as possible. This in turn requires rapid reduction in boiler temperatures, which will allow quicker entry into the boiler area for purposes of repair. In a typical boiler, repair may occur to tubes located directly in the burner area, tubes located in the superheat areas of the convection pass, the convection pass heat recovery area, tubes associated with the economizers, and systems located downstream from the boiler towards the gas outlet, which would include the dampers, electrostatic precipitators and regenerative air heaters.  
         [0012]     It is known in the prior art, such as U.S. Pat. No. 6,015,099 and U.S. Pat. No. 5,540,383, both to Ducey, to use sprayed pressurized water for evaporative cooling. However, the prior art devices shown in these patents do not mix air and water, and rely on high-pressure water only to cool locations where people may assemble at outdoor events. There is no suggestion in this non-analogous prior art to utilize existing water and air supplies and existing oil fired igniters in a power plant for producing a mist to accelerate cooling of the power plant during a forced shut down.  
         [0013]     A method for repairing a power plant comprises the steps of identifying a condition in a power plant that requires repair; shutting down of the power plant; switching oil lighter fluid from oil to water; turning on the oil lighter which provides an atomized water mist inside of a combustion area of the power plant; measuring temperature inside of the power plant boiler; initiating repair when the temperature is reduced to a first predetermined level which is tolerable by a human being inside of a work area of the power plant, and repairing the power plant.  
         [0014]     The method further comprises steps of:  
         [0015]     (1) turning on the oil igniter atomized water mist that provides the atomized water mist when power plant burners are turned off;  
         [0016]     (2) turning off the oil lighter atomized water mist when repair is being made in an area where the mist interferes with repair procedures;  
         [0017]     (3) turning off the oil lighter atomized water mist when it is no longer required to maintain temperature at a tolerable level in a work area;  
         [0018]     (4) measuring temperature that comprises measuring wet and dry bulb temperatures in the work area;  
         [0019]     (5) using a plurality of oil lighters that produce atomized water when switched from oil to water;  
         [0020]     (6) using an ignitor used in a coal fired boiler;  
         [0021]     (7) using a transfer valve to switch feed fluid to a burner nozzle from oil to water;  
         [0022]     (8) using a primary burner used in an oil fueled power plant;  
         [0023]     (9) repairing a tube leak;  
         [0024]     (10) using an internal or external mixing nozzle to mix air with water;  
         [0025]     (11) spraying the mist into corners of said boiler;  
         [0026]     (12) inserting into the boiler an air and water mixing nozzle, which is on the end of a pipe that is inserted into a boiler port.  
         [0027]     This apparatus for cooling a power plant boiler has a port located in a wall of the boiler, an air and water mixing mister that is inserted into the port, and an air and water supply that is connected to a mixing mister nozzle. The air and water mixing mister inserts an air water mist into the power plant boiler and cooling is provided by evaporation of the mist. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0028]      FIG. 1  shows a power plant of the type manufactured by Babcock and Wilcox, which is rapidly cooled in accordance with this invention.  
         [0029]      FIG. 2  shows a tip of an oil igniter lighter used typically in coal fired plants.  
         [0030]      FIG. 3  shows an igniter lighter having a transfer valve for switching from oil to water.  
         [0031]      FIG. 4  shows a water-injecting nozzle on the tip of an air and water-conducting pipe, which may be inserted into a boiler.  
         [0032]      FIG. 5  shows an atomizing oil burner head, mounted on concentric pipes, that is creating an atomized mist of this invention.  
         [0033]      FIG. 6  shows a second view of the atomizing mist head of  FIG. 5 .  
         [0034]      FIG. 7  shows a third view of the atomizing mist head of  FIG. 5 . 
     
    
     DETAILED DESCRIPTION  
       [0035]     In  FIG. 1  there is shown a Babcock and Wilcox radiant reheat boiler of the type used by the Power Company of New Mexico&#39;s San Juan Station located at Waterflow, New Mexico. The boiler ( 10 ) has a furnace area ( 12 ) and is fired by coal burners ( 14 ). The coal burners are provided with an air supply or an air input ( 16 ). There are a large number of coal burners, such as a group of three high and seven wide or a total of twenty-one burners on one side of the furnace ( 12 ). A boiler having burners on two sides may have  42  coal burners. Although not shown in  FIG. 1 , there is a second group of burners located to the left hand side of the furnace ( 12 ). Associated with each burner is an oil igniter ( 18 ). The oil igniter guns are supplied with oil and air, which is supplied by a central air supply within the power plant. In this invention, the oil igniter guns ( 18 ) may also be connected to a water supply for the plant. When the oil igniter guns ( 18 ) are connected to a water supply and turned on, they will inject a mist spray, which is produced by the water and air forced into the furnace ( 12 ) by the oil igniter guns. The oil igniter guns ( 18 ) are shown in  FIG. 1  in a position where they are actually inserted into the furnace. During normal furnace operation, after ignition of the coal burners ( 14 ) the oil igniter guns are retracted from the furnace to prevent damage due to heat.  
         [0036]     In addition to oil igniter guns ( 18 ) there are also provided tubes ( 20 ) that have at their tip air-water mixing nozzles ( 22 ) located at their tip. These additional tubes are fed with water and air from the power plant. The air mix nozzles produce a mist and can be located anyplace within the boiler that there is a convenient access port.  
         [0037]     Depending from the top of the boiler are shown pendent super heater walls, which may require repair in addition to tube walls located in the furnace area ( 12 ). Still further, to the right hand side of  FIG. 1  are shown reheaters and economizers ( 26 ), which may require repair. When a mist is inserted into the furnace  12  by either the oil igniter guns ( 18 ) supplied with water, or the misting nozzles ( 22 ) which are supplied by the air and water systems available in the power plant, cooling may be effected at different locations within the boiler and at rates which provide evaporative cooling in order to quickly cool areas of the boiler which may require personnel to enter and make necessary repairs.  
         [0038]     Boilers of the type shown in  FIG. 1  are generally constructed with a rectilinear cross-section, and not a circular cross-section. Since the cross-section is rectilinear, the mist produced by this invention is particularly advantageous because the mist can travel into the corners of the furnace. Also, the cool air but no mist travels to super heater areas of the convection pass or heat recovery area ( 28 ) in order to provide uniform and efficient cooling during cooling of the boiler. The cool air travels past area ( 24 ), but this air has only vapor and no water mist because if water is present it can react with ash in this area and cause damage to the convection pass.  
         [0039]      FIG. 2  shows a nozzle of the type typically used on an oil igniter gun, see ( 22 ),  FIG. 1 . The nozzle ( 30 ) has a tip ( 32 ), which is an internal mixing tip. As shown in the drawing, there are two spray ports, which mix oil and water at points ( 34 ) internally of the head. However, there may be typically five or six such internal mixing ports, which are provided by drilling the head along the drill holes shown. A first central passage way ( 36 ) supplies oil to the head and a second outer passage way ( 38 ) provides air to the head. The drill hole at an angle of 45° carries the oil to the mixing point while the drill hole at an angle of approximately  150  carries the air to the mixing point ( 34 ). An outer pipe ( 38 ) receives the mixing head ( 32 ) that is secured by a threaded connection. The internal pipe ( 40 ) is inserted into the base of the nozzle and a seal may be provided by o-rings or the like. Pipe ( 40 ) provides passage ( 36 ) for oil supplied to the head.  
         [0040]      FIG. 3  shows an igniter lighter assembly of an oil igniter gun ( 18 ) of  FIG. 1 , where the tip ( 30 ) is at the end of a pipe section ( 52 ). The tip ( 30 ) can be inserted into the furnace for igniting the coal, and withdrawn from the furnace ( 12 ) when the not in use in order to prevent damage to the igniter ( 18 ) from the coal firing. The oil igniter gun includes an assembly ( 53 ) for attaching the tubes ( 52 ) to the (boiler) plant air supply and oil supply. In this invention, water is used in place of the oil. Water is also readily available in a power plant. A transfer valve ( 56 ) is provided for switching from oil to water. The transfer valve is preferably an electrically operated valve, which can be controlled from a single location by pressing of button by an operator or by a computer, which operates the power plant. Once the oil igniter gun is switched from oil to water, it is operated in a manner typical of any other igniter with the exception that water is substituted for the oil, which is sprayed into the power plant boiler. In a large coal fired boiler it is not necessary to use all igniters to produce a cooling mist.  
         [0041]     Any number of igniters ( 18 ) may be used at any one time to supply a mist to the furnace area ( 12 ). Any number of igniters can be controlled simultaneously by electrical controls that are either manual or computer operated. The igniter ( 18 ) and igniter valves ( 56 ) can also be each operated manually.  
         [0042]     In  FIG. 4  there is shown a mist-injecting pipe ( 62 ), which is essentially the same as the pipe ( 52 ) and is connected also to a nozzle ( 30 ). In this arrangement, air is inserted into the outside pipe ( 38 ) ( FIG. 2 ), and water is inserted into the inside pipe. Manually controlled air valve and manually controlled water valve ( 66 ) provide for control of the mist ejected from nozzle ( 30 ). This assembly is made to be manually inserted through convenient ports in the furnace walls for purposes of providing cooling at selected locations.  
         [0043]      FIG. 2  shows a typical internal mixing atomizing head used for oil igniters. If separate injecting pipes ( FIG. 4 ) are used, an external mixing head of the type known in paint spraying may be used. External mixing heads combine the fluid and air at a point outside of the nozzle where the streams intersect.  
         [0044]     In the case where the igniter burners are gas fired instead of oil fired, there will, of course, be no atomizing air fuel mixing nozzles that can be connected to a water air source. However, boiler cooling during shut down can still be performed by inserting mist injecting pipes ( 62 ) into the boiler. These may be inserted at any convenient opening in the boiler, such as at doors that hold flame observation windows, other access ports, or at openings created by withdrawal of gas burners.