Combustion and heat transfer characteristics in boilers with asymmetrical reversed flow flame tube

Abstract

An experimental study of the combustion characteristics in an industrial three-pass asymmetrical reversed flow flame tube boiler is presented, based on measurements of mean gas temperature, gas velocity, species concentration (CO, CO 2, O 2, SO 2 and NO x ) and soot fraction. The experiments, which were carried out at different firing rates and furnace lengths, included analysis of the influence of simultaneous use of three stabilization techniques on the combustion process inside the furnace. The three stabilization techniques used, are namely asymmetrical jet stabilization, vane type swirler stabilization and reversed flow stabilization by using reversed flow combustion chamber. Also experimental and predictive studies of heat transfer characteristics in the three-pass asymmetrical reversed flow flame tube boiler have been carried out. The experimental investigation is achieved by measuring the boiler heat transfer and its portion in the third pass pipes. The optimal furnace length and pitch of swirl generator, used in the third pass pipes, have been determined. The prediction study presents models to estimate the first–second and third pass heat transfer rates depending on the basic heat transfer equations and some of the experimental results. The predictions were compared with experimental data and found to be in a good agreement. Analysis of the results is aimed at improving the understanding of combustion and heat transfer processes in this type of flame tube boilers.