Study On Exhaust Wetness Measurement On-line For Steam Turbine

The last few LP stages of condensing turbines for the fossil-fired power plant and the all stages of nuclear turbines operate in wet steam region. The wet steam appearing in the turbine decreases the efficiency and may erode the blade of turbine stages. The wetness measurement on line for steam turbine is very important for the security of the generating units, heat economy, and operation parameter optimization.There are many methods in steam wetness measurement. Two methods have been used to on-line monitor steam turbine exhaust wetness in industry test, optics method and thermodynamics method. The others are still at experimental stages. Yang Shanyang's double-region-heating steam wetness model have been proved valid and been tested in Huaneng Dalian Power Plant. But the test result reflects a lot of problem, such as couldn't calculate accurately the lost calorific capacity etc.Based on shortcomings of the double-region-heating probe for measuring wetness had been found in the pilot plant test, the experimental design and simulation research has been underway. First of all, this paper uses the computational fluid software FLUENT to calculate steam vaporization length in typical operation conditions of turbine. It looks the vapor phase as continuous phase , looks the liquid as the discrete phase. It used the calculation method of coupling to conclude the relationship of water diameter of steam wetness, vaporization length and heat flux. It had same basic conclusions of the wetness probe design and optimization. Secondly, it had been readjusted in hardware and software of the wetness data acquisition system. The connection between the data acquisition cards and the industrial computer has been completed. At the same time, in order to prevent electromagnetic interference and data drifting, every module was needed to ground and electromagnetic shielding. The data acquisition and communication between the DAQs has been accomplished. The data acquisition will be sent to the industrial computer in the form of table or curve. With the data flittering , the temperature,pressure and heating power will be stored in the database. The former steam flow measurement device could measure the wetness under the normal atmosphere pressure. But in the new experimental conditions, namely in vacuum condition, the advantages of former measuring devices will not exist, so a new experimental condenser has been designed. The new steam flow measurement device was set in the new design condenser. it could achieve the aim of continuous measurement through controlling the four valves orderly. Thirdly, Through the simulation software of LabVIEW, static simulation model for double heating area was in research. It changed the mathematical model of double heating area method into the diagram. The affection that different heating power influence the wetness has been discussed. In order to measure the dynamic character of the wetness system and error, the labview can accomplished.