Non-Linear Engineering Simulator of Coal Fired Steam Boiler Applied to Fault Detection of Optimum Combustion Control

Abstract

This paper describes an application of a steam boiler engineering simulator for detecting a faulty function of the O2 probe measuring the oxygen contents in flue gases in the control loop for air supply into the combustion chamber. A non-linear model based on a simplified form of Hammerstein's idea of separating the non-linear part from the linear part is used for developing the engineering simulator in the standard MATLAB-SIMULINK simulation package. This simulator is proposed for testing conventional PID control of air excess in order to find how strongly its performance is influenced by a small malfunction of the oxygen concentration probe, and whether we can detect this faulty function by means of the available non-linear steady state model.Minimization of gaseous emissions, above all CO and NOx, has recently been emphasized as a new objective of efficient steam boiler control. The O2-probe measuring oxygen concentration in flue gases is utilized for accurate control of the burning air. A malfunction of the probe resulting in the delivery of false data, is a quite frequent event, in particular in coal fired boilers. In such cases, emissions increase above the theoretically achievable minimum level. To improve steam boiler control a new method of O2-probe signal verification based on measuring the burning air flow-rate and mediating the other quantities has been established and tested.