Patent Application
20070130949
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.
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.
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.
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.
In the prior art it is known to use fans, which are present in a power plant boiler'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.
In the case where cooling is accomplished by ambient air forced through a boiler using the power plant'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.
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.
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.
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.
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.
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.
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.
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.
The method further comprises steps of:
(1) turning on the oil igniter atomized water mist that provides the atomized water mist when power plant burners are turned off;
(2) turning off the oil lighter atomized water mist when repair is being made in an area where the mist interferes with repair procedures;
(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;
(4) measuring temperature that comprises measuring wet and dry bulb temperatures in the work area;
(5) using a plurality of oil lighters that produce atomized water when switched from oil to water;
(6) using an ignitor used in a coal fired boiler;
(7) using a transfer valve to switch feed fluid to a burner nozzle from oil to water;
(8) using a primary burner used in an oil fueled power plant;
(9) repairing a tube leak;
(10) using an internal or external mixing nozzle to mix air with water;
(11) spraying the mist into corners of said boiler;
(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.
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.
In
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.
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
Boilers of the type shown in
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.
In
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.
