Fireside behavior of black liquors containing boron

Partial auto-​causticization using B has become an interesting option for de-​bottle-​necking the re-​causticization department in the chem. recovery cycle of kraft pulp mills.  Several full-​scale trials in North America showed that the auto-​causticization concept using B works efficiently in recovery boilers.  However, more information is needed of the detailed influence of B on the operation of the recovery boiler.  Some 1st information of the influence of the meta-​borate addn. on the liquor burning properties, smelt bed melting behavior, and fireside deposit characteristics in super-​heaters is presented.  The information is based on multi-​phase chem. equil. calcns. of the furnace processes and results obtained by using a single droplet burning test facility.  The presence of B lowers the melting temp. range of the smelt and the carry-​over liquor residue particles.  Larger B addns. also changed the burning behavior of the black liquor studied.  The characteristic swelling during the devolatilization stage decreased, which resulted 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.