A Study Of Composition Of Kraft Recovery Boiler Carryover Particles Using An Entrained Flow Reactor PDF Download

The accumulation of fireside deposits on tube surfaces in the superheater region of kraft recovery boilers is due mainly to the inertial impaction of carryover, the molten or partially molten smelt particles, and/or partially burned black liquor particles that are entrained in the flue gas. Understanding carryover deposition and parameters affecting it is important for optimizing recovery boiler performance. This work is the first to systematically examine the dynamics of deposition of carryover particles. Due to the complexity of conditions in the boiler, it is difficult to isolate the individual effect of the interacting parameters. An Entrained Flow Reactor (EFR) was therefore built to simulate the conditions that carryover particles experience during their passage through a recovery boiler and to obtain controlled deposit samples and fundamental data on carryover deposition. Experiments using the EFR were carried out to investigate the deposition of synthetic carryover particles of different size ranges. The results show that the deposition rate is strongly affected by the chloride content, temperature, and size of the particle. Deposition occurred only when the particle chloride content exceeded a critical level. The deposition increased with an increase in chloride content up to a maximum, and then it remained constant or slightly decreased with further increase in chloride content. The chloride content required for the onset of particle deposition decreased with increasing EFR temperature, but increased with increasing particle size. Particle deposition was found to increase significantly with particle size. A heat transfer numerical model was developed to predict the velocity, temperature, and liquid content of synthetic carryover particles as they pass through the EFR. The simulation results suggest that a minimum liquid content was necessary for particles to deposit. This minimum liquid content increased with an increase in particle size. The results also suggest that deposition process follows four different stages depending on the particle liquid content. Each of the deposition stages has been linked to a type of particle rebound.