Influence of droplet size on the release of atomic sodium from a burning black liquor droplet in a flat flame

The influence of initial droplet size on the release of atomic sodium from black liquor solids (BLS) during each stage of black liquor combustion has been assessed using a planar laser-induced fluorescence (PLIF) technique. Three different initial diameters of black liquor droplets, 1.3, 1.7 and 2.2 mm were burned in a flat flame at equivalence ratios of 0.8, 0.9 and 1.25. The temporal release of the atomic sodium under fuel rich conditions was found to be different from that under fuel-lean conditions, especially during the smelt coalescence stage. For each stage of black liquor combustion, the measured release rate of atomic sodium increases with decreasing di. This implies that significant release of atomic sodium could occur during the in-flight combustion of small droplets, which are known to be generated in recovery boilers from either the carryover or the ejecta.