A heat transfer model for on-load monitoring and simulation of a utility boiler burning natural gas and fuel oil

Abstract

This work presents a model for on-load monitoring and simulation of a boiler burning alternatively two different fuels, natural gas and fuel oil. The boiler is modeled considering various components in two different sections: the furnace, where the heat transfer process by radiation dominates; and the convective section. The radiation heat transfer in the furnace is modeled using three zones, which include the furnace walls and the superheater panels. The convective section has two parallel passages of the combustion gases and is modeled considering nine heat exchanger sections corresponding to the tube bundles. The heat transfer calculations in this section are based on the solution of a non-linear system of equations using the Newton-Raphson method. The model also includes a numerical procedure that allows the estimative of the fouling resistance in the tube bundles for on-load monitoring of the boiler. These estimated values are used for simulation of the boiler for different operation conditions. Monitoring results of a boiler of the Carregado power plant (CPPE-EDP, Portugal) are presented for natural gas and fuel oil operation. The paper also presents the simulation for variations of the boiler load and of the oxygen concentration in the gases. The simulation values are compared with experimental values for the same type of variations.