An Experimental Study of the Mechanisms of Fine Particle Deposition in Kraft Recovery Boilers

摘要

Experiments on the deposition of fume (submicron) and particles produced during black liquor combustion indicate that deposit mass accumulation increases linearly with time and is independent of temperature gradient - results that are inconsistent with the classical explanation of thermophoresis as a driving force. Temperature-controlled, cylindrical probes in cross flow collected particles for periods up to ten hours and at Reynolds and Stokes numbers comparable to those in commercial boilers. Fume deposits appear dense and smooth to the unaided eye but under microscopic examination prove to have filamentary structures, with individual filaments radiating from the probe center and consisting of strings of primary (submicron) particles with relatively thick necks. Fume particle collection efficiency averaged around 2%, much higher than is theoretically predicted based on a thermophoretic driving force.