The influence of boron on the emission of sodium during black liquor combustion under oxidative conditions

The addition of boron to black liquor has the potential to reduce fume formation in a kraft recovery boiler. Two kraft black liquors, with and without boron, were analysed. Single 10 mg droplets were introduced into a furnace and were burned at temperatures of 900, 1000 and 1050 degrees C with oxygen concentrations of 2, 5 and 10 (vol %). Under these conditions, the addition of boron to the black liquor is found to reduce both the extent of sodium emission and the combustion time. This shows that the boron reduced the sodium loss due to the lower amount of sodium carbonate available to be decomposed by the char. The char combustion time of the liquor with boron is found to be shorter because some of the char may be consumed by the borate. The added boron reduced the sodium loss mainly during the char combustion stage.