Coal Combustion Technology in Wide Load Range Burners

To develop and design new burners used in wide load range coal firing boilers, the following two fundamental studies were carried out. (1) Theoretical studies on ignition of coal particles and the flame propagation velocity in relation to solid concentration. The theory revealed that the thermal diffusion in a turbulent flow affected greatly to enlarge the flame propagation velocity and that a suitable primary air velocity to sustain the stable ignition of coal existed in terms of the coal concentration. (2) Cold model tests on condensation of coal-airstream near the burner outlet. Coal and air mixture was divided into two flows with dense and lean concentrations of coal by a condensation module mounted inside the burner. Through the cold flow test, we found that the two separated flows met immediately at the burner outlet and were mixed causing the unstable ignition of coal particles. This mixing was enhanced by a large velocity gap between the two flows. Therefore the position of the condensation module inside the burner were examined to minimize the mixing at the burner outlet. Based upon the results of these studies, we devised the burner configuration and arrangement in which the flow and the coal concentration near the burner outlet were optimum for the stable ignition. Two new designed burners (coal:50 kg/h, 3600 kg/h) were succeeded in a range of practical operations without backup fuel.