Deposition Phenomenon And Bonding Characteristics Of High-viscosity Ash

Ash deposition has always been a primary problem that affects the operation of thedynamic boilers, and is a serious threat to the boiler’s safe and economical operation. Itis of great theoretical and practical significance for the research on the deposition andbonding characteristics of the ash within the range of high viscosity (referred to ashigh-viscosity ash hereafter). Experiments and theoretical analysis have been carried outto investigate the deposition characteristics, and the mechanism and model of bonding.Firstly, the drop tube furnace system was built, and the effect of heat exchangesurface temperature, impact velocity, deposition time, particle size and ash chemicalcompositions to the high-viscosity ash deposition was studied. The results showed thatthe high-viscosity ash particles had strong deposition tendency. Low heat exchangesurface temperature, high impact velocity and large particle sizes can effectivelyconstrain the deposition process of high-viscosity ash. The deposition process ofhigh-viscosity ash can be divided into two periods: in the initial period fouling occurs,followed by slagging in the second period. The ash particles containing relatively highercontents of alkali and alkaline earth metals have stronger deposition tendency. The ashchemical compositions and the conditions are two key factors in the deposition behaviorof the high-viscosity ash.Secondly, the research on the model and relationship between ash compositionsand sintering characteristics was carried out. The ash chemical compositions werechanged by co-firing biomass and Yanzhou bituminous coal, and the relationshipbetween the ash chemical compositions and the sintering characteristics was studied.The results showed that the sintering temperature of biomass ash was far below that ofcoal ash, and the sintering temperatures of the blended ashes decreased with the increaseof the biomass ratio in the fuel blends. The main reason is that biomass ash containsmore alkali metals than coal ash. The sintering temperature decreases with the increaseof the base-acid ratio. The calculation model of the sintering temperature based on theash chemical compositions was proposed, and the calculating results agreed well withthe experimental data. Finally, the bonding process of high-viscosity ash, which is induced by thesolid-bridge force, was studied experimentally. The experimental system which canmeasure the solid-bridge force and tensile strength of ash at high temperatures wasdeveloped. The effect of temperature, contact time and contact pressure to the necktensile strength of high-viscosity ash was obtained, and the temperature dependence ofthe neck tensile strength development showed a bimodal distribution. The neck tensilestrength of high-viscosity ash was much smaller than the material tensile strength at thesame temperature. The calculation formula of the non-dimensional neck tensile strengthof high-viscosity ash was proposed and verified, and the calculation results accords wellwith the experimental results. The calculation formula lays a foundation for thehigh-viscosity ash deposition model based on the force analysis of the ash particles.