Innovative design solutions for small-scale domestic boilers: Combustion improvements using a CFD-based mathematical model

A CFD-based model has been developed for predicting performance of a domestic central heating boiler fired with solid fuels. The model does not require a priori distinction between the fixed-bed region and the free-board region and this is a unique feature. The model is used to improve both the design and operation of the boiler. Perfecting the boiler design, resulting in reduced CO and fly ash emissions, can be achieved by repositioning of the deflector, redirection of air supply, as well as reshaping the combustion chamber. An optimized boiler design has been proposed which features a circular combustion chamber, an extra annular channel and combustion air swirling. The decrease of CO emission (compared to the original design) by more than 90% is foreseen at excess air ratio of 2.0. According to the model predictions, the optimized boiler can be operated at 1.5 excess air with 80% reduced CO emissions and more than 80% reduction of solid particles discharge.