A thermohydraulic model is presented to simulate the dynamic characteristics of a boiler system. The boiler system is functionally divided into submodules, whose dynamic behavior is modeled using partial differential equations with time-varying coefficients. Major heat exchangers are treated as distributed parameter system where spatial variation of state varaiables are considered. The model equations are solved for the time and the space variables without linearization. This direct approach enables the model to be applied to the large state variations such as start-up, shutdown, and rapid load change. Simulation examples are presented using these model equations for the situations such as start-up, rapid change in steam demand, and feed pump failure. The dynamic model can be used to establish proper operation procedures for large state variations and to find possible problems of dynamic response of boiler system in the design stage.
