Evaluation and comparison of saltation velocity correlations in the context of pulverised fuel transportation

The reduction of harmful emissions is an important issue to be dealt with in coal-fired power stations. There are several technologies that have been successfully applied to modern power stations to reduce the emissions of oxides of sulphur and nitrogen. One such technology is low NOx burners, which employ directed fuel and air staging to create a NOx reduction zone. A requirement for effective operation is to supply these burners with a uniform stream of pulverised fuel (PF). A corequisite is to maintain a homogeneous flow through the pneumatic conveying system without particle settling. PF systems can be analysed and designed using semi-empirical correlations. Some correlations used in predicting settling were developed by Rizk [1], Matsumoto [2][3], Mewing [4], Rose and Duckworth [5], and Thomas [6]. These, however, were based on lab experimentations with pipe diameters and conveying mass flow rates much less than PF transport conditions and predictions show significant variability when the correlations are compared. This work compared the settling velocities predicted by various correlations in literature to an experimental study by Herbreteau and Bouard [7]. Correlations for saltation velocities by Rizk, Thomas and Matsumoto were noted as the more reliable of the correlations evaluated.