Systems based CFD modelling of package steam boilers

Abstract

Dynamic thermo-fluid models of fire-tube steam boilers can be used to optimise the design and operation of equipment, resulting in possible energy and emissions savings. This work presents the development of a dynamic boiler model of a 4-pass wetback fire-tube boiler, using the commercial 1-dimensional CFD tool Flownex®. The thermal model includes all relevant heat transfer and fluid flow phenomenon between the combustion flue gasses and the boiler water/steam. The predicted exhaust flue gas temperatures at different operating pressures are compared favourably to the performance data for a PFTA500-4 boiler, with accuracy improvements over previous modelling studies in the literature. Finally, the transient simulation capabilities of the model are demonstrated for a case of varying steam demand levels, with PID control algorithms implemented to control the feedwater control valve on the mass flowrate of fuel to the boiler. The modelled control system will be further refined in future work to include oxygen trim control over the air/fuel ratio. The completed model will be integrated into larger steam generation and distribution steam networks in Flownex, to assist industrial companies in South Africa in improving their energy efficiency.