Thermoelectric power station is often operated in partially loaded mode of which the operating condition varies in a wide range. The operation system employs advanced controls and prediction techniques incorporated with a dynamic simulator. One of the most important functions of the simulator is accurate real-time simulation of boiler system.
The dynamic characteristics of the boiler system exhibits both fast and slow dynamics simultaneously, since it is governed by combustion of fuel, various modes of heat transfer, and phase change of thermal media. In consequence, the boiler model consists of highly nonlinear and coupled partial differential equations with time-varying coefficients. Recent researches focus on the analysis of inner circulation flow rate, which is the most complicated part of the simulator and requires extremely time-consuming computation. Most simulators have either neglected or, at best, oversimplified the inner circulation part.
A rigorous momentum balance model equation is developed to describe the circulation flow rate in riser. The quasi-steady state approximation (QSSA) is applied to the model to accelerate and stabilize the numerical integration of model differential equations. It is demonstrated that the QSSA does not introduce any noticeable error in the numerical results while it reduces the computation time to a factor of 100.
