Due to the complexity, nonlinearities and time-varying nature of the boiler system of a power plant, it is usually difficult to build a conventional mathematical model of the boiler system, especially for diagnosis purpose. Hence, in diagnosing the faults, the expert system approach is often employed based on the experts' knowledge and experience. In this thesis, a fuzzy expert system is studied for fault diagnosis of a drum-type boiler system in fossil power plants. The main objective of the fuzzy expert system is to check the states of the system including the drum level and detect faults such as the feedwater flow sensor fault, feedwater flow control valve fault, and water wall tube rupture. The fuzzy expert system diagnoses faults using process values, manipulated values, and knowledge base which is built via interviews and questionaries with the experts on the plant operations. Finally, the validity of the developed fuzzy expert system is shown via simulations.
