Modeling Alkali Salt Deposition in Kraft Recovery Boiler Heat Exchanges in the Superheater Section, 1998 International Chemical Recovery Conference Proceedings

The aim of this paper is to describe the improved fume chemistry and deposition models that have been implemented into the previously developed computer model ABC. With the improved model, we are able to clearly identity the importance of different deposition mechanisms for vapours as well as for particles of different sizes. In the improved model Raoult’s law is used to approximate vapour pressures of condensing species on the surface of molten salt particles. Based on the sample calculation made for an Asian kraft recovery boiler, significant vapour deposition seems to occur only if the superheater inlet gas temperature exceeds 800°C. On the other hand, deposition of carry-over particles on superheater section seem to cause major part of the deposited mass. This is the case with cross flow at the entrance of superheater platens as well as with flow parallel to superheater platens. Sample calculation also indicates that increased chlorine content in the deposit layers of colder superheater platens seems to be a consequence of fume particle deposition.