Particulate fouling growth rate as influenced by the change in the fouling layer structure

Particulate fouling in biomass gasifiers is a majorproblem, which may lead to inefficient operation. As the fouling layer grows, its thermal resistance increases resulting in an increase in the surface temperature of the fouling layer. The increase in the fouling layer surface temperature can lead to sintering of the layer, which changes the layer structure from a fragile powder to a robust coherent structure. The influence of the change in the fouling layer structure on the growth rate of particulate fouling is studied experimentally. Impaction experiments were carried out to determine the velocities at which an incident particle sticks, bounces off or removes particles outof the fouling layer as a function of fouling layer structure. The sticking velocity of a particle hitting a clean tube is determined theoretically. The sticking velocity of a bronze particle hitting a bronze plate is 0.006 m/s, for a powdery layer is 0.3 m/s and for a sintered layer is 0.04 m/s. The change in the heat exchanger surface from solid to powdery increases the sticking velocity, which consequently speeds up the fouling process. The further change in the heat exchanger surface from powdery to sintered decreases the sticking velocity, which reduces back the fouling process. The change in the fouling layer structures affects the sticking velocity as well as the removal velocity of incident particles, which consequently affect the fouling process.