The present invention relates to a method of detecting and monitoring an abnormality of a pressurized fluidized bed combined cycle power plant and an apparatus therefor and, more particularly, to a method and apparatus suitable for detecting and monitoring an abnormality of a pressurized fluidized bed boiler.
In a pressurized fluidized bed combined cycle power plant, limestone which is a desulfurizing agent is fluidized at a pressure of 10 to 15 atm at a temperature of about 860.degree. C., and fuel such as coal and air are supplied there to effect fluidized bed combustion of the coal. The heat of combustion is recovered by a heat exchanger tube, steam generated at that time drives a steam turbine, and combustion exhaust gas drives a gas turbine.
The part that coal is subjected to fluidized bed combustion and steam of high temperature and high pressure is generated is called a pressurized fluidized bed boiler. The pressurized fluidized bed boiler is accommodated within a pressure vessel, so that it is difficult to find an abnormality when it happens as compared with a conventional pulverized coal burning boiler. Further, in the pressurized fluidized bed boiler, heat exchanger tubes are installed, and it is feared that the tubes may be worn and torn to form an opening or through hole with limestone particles of several mm diameter which are fluidized violently. Strength reduction and through hole forming due to partial temperature elevation at a high temperature piping (there are two types one of which is a single tube type wherein an inside is fire insulating construction and the other is a double tube type wherein air is flowed in a space between inner and outer tubes to cool.) for introducing combustion exhaust gas from the pressurized fluidized bed boiler to the gas turbine become a problem.
The following is known as prior art: For the through hole formation, a method of detecting propagation of steam leak sound through a heat exchanger tube by an acoustic emission sensor (AE sensor) is proposed; In high temperature gas piping, development and putting into practice of a method of observing surface temperature of the tube by an optical fiber abnormally high temperature detection sensor and detecting an abnormality is being studied ([No.930-63] Japan Machinery Society the 71 Period National Ground Meeting Lecture Papers(Vol. D) (1993-10.2.4. Hiroshima)).
Although these prior arts are useful for detection of an abnormality, they have a weak point in abnormality detection under the following operation conditions:
For the AE sensor, in case a heat exchanger tube is in a fluidized bed, the steam leaked from the tube blows out fluid particles around the heat exchanger tube, and the particle impinges on the heat exchanger tube, whereby a signal level changes greatly more than in time of a normal operation. However, in case fluid particles do not exist around the heat exchanger tube, impingement of the particles does not occur, so that a signal level of the AE sensor is almost never different from a signal level at a time of normal operation and it is difficult to detect leakage of steam. In the pressurized fluidized bed boiler, load change is effected several times a day. Since the load change rises and lowers the height of the fluidized bed, fluid particles exist around all the heat conductive tube in an operation at 100% load and at a time of partial load operation a part of the heat conductive tube is out of the fluidized bed and particles do not exist around that part of the heat conductive tube. Therefore, the detection is difficult in such a case that steam leaks from the heat conductive tube outside the fluidized bed. Further, although in a high temperature gas piping, an optical fiber abnormally high temperature detection sensor is useful, it is necessary to provide an optical fiber, a laser apparatus.
Further, hitherto, means for detecting an abnormality such as bursting, damage, etc. of a pressurized fluidized bed boiler itself was not provided. In the pressurized fluidized bed boiler, also, the inner surface of the fluidized bed boiler is worn damaged by fluidized bed combustion of limestone, etc. In case destruction occurs in the fluidized bed boiler, the above-mentioned fluid particles are jetted out from the bursting and the particles accumulate on a lower portion of the pressure vessel.
By the way, the pressure vessel is designed so as to withstand a temperature of about 350.degree. C. of compressed air which is burning air for the fluidized bed boiler and pressure of about 9.8 atm of the compressed air. When fluid particles of about 860.degree. C. accumulate on the pressure vessel, the temperature of the pressure vessel exceeds the temperature limit that the pressure vessel can withstand, and the pressure vessel melts and can not withstand 9.8 atm. Therefore, there may occur such danger as an accident such as explosion of the pressure vessel and the fluidized bed boiler.