Fireside behavior of black liquors containing boron

Partial autocaustization using B has become an interesting option for de-​bottlenecking the recausticizing department in the chem. recovery cycle of kraft pulp mills.  Several full-​scale trials in North America showed that the autocaustization concept using B works efficiently in recovery boilers.  However, more detailed information is needed about the influence of B on the operation of the recovery boiler.  Initial information is presented about the effects of meta-​borate addn. on the liquor burning properties, smelt bed melting behavior, and fireside deposit characteristics in superheaters.  The information is based on multiphase chem. equil. calcns. of the furnace processes and results obtained at the Abo Akademi single droplet burning test facility.  The presence of B lowers the melting temp. range of the smelt and the carry over of liquor residue particles.  Larger B addns. also changed the burning behavior of the black liquor studied.  The characteristic swelling during the devolatilization stage decreased, resulting in somewhat longer burning times.  The measured release of C and the formation of NO and SO₂ from the burning droplet were not changed significantly.