Unit Load Boundary Investigation Of Coal-Fired Power Plant

The load boundary of thermal power unit usually varies with the status of auxiliary equipment, coal quality and ambient conditions. The lower output of induced fan and forced fan, the reduction of coal feeder output, the use of inferior coal and the tough ambient conditions, all of those could lead to a decrease of maximum output of a boiler of power plant. Currently, in order to minimize the cost of power generation, the major power companies usually adopt the way of choosing a variety of coal supplies, using blending coal to generate electricity, which cause characteristic of the supplied coal to vary widely. It is well known that the design of power plant is based on the characteristic of design coal. The difference between the fired coal and the design coal inevitably affects the performance of the boiler of power plant and results in a decrease of boiler’s efficiency, causing wide changes of unit power load. It would bring security risks to the stable operation of the power plant. In addition, the grid dispatching center is difficult to obtain the unit output dynamic features, which brings difficulties to the power grid scheduling.In response to these problems, in order to better grasp the load boundary characteristics when the off-design coal is used, this work presents the idea to find the load boundary of thermal power units as the fired coal is changed. The work involves the online performance monitoring of the auxiliaries of boiler system and load forecast, the maximum load prediction under the different coals, load prediction of the steam turbine based on the operation data and the unit load prediction for the grid dispatching.In this work, No.8 Unit of Xiaolongtan Power Plant in Yunnan Province is selected as the research object. Firstly, the unit operation status in real time, the operation conditions can be confirmed according to the variations of the key parameters of the auxiliaries, such as vibrations, pressures, temperatures and flow rates. The mathematical model of the coal feed system is built to determine the coal feeding load. Then, the operation conditions of the limestone conveying system and the air-flue gas system can be confirmed. Based on the operation parameters of all the systems, the coal quantity is determined under the maximum unit load. Secondly, a load calculation program is developed under Visual C++ platform. The program reads the analysis parameters of coal and limestone, the coal quantity, and boiler operation parameters from the database, and can be used to calculate the maximum load of the boiler. Finally, the steam turbine operation data is used to find the relationship between the unit load and the main steam flow. Consequently, the maximum load of the unit can be predicted according to the corresponding coal. Meanwhile, the unit minimum load is verified by minimum load value screened from historical load database. The research in this work is expected to provide load boundary of the thermal power unit for the dispatch center in time, so as to realize the safe dispatch of electric power.