Understanding the ash deposition formation in Zhundong lignite combustion through dynamic CFD modelling analysis

A dynamic CFD model, which is based on the inertia impaction, the thermophoresis and the direct alkali vapour condensation incorporating the influence of the heat transfer to the tube, has been developed for predicting the ash deposition formation in Zhundong lignite combustion in a pilot-scale furnace. The results show that particle deposition from the inertia impaction and the thermophoresis dictates the ash deposition formation under high furnace temperatures. The deposition caused by the direct alkali vapour condensation is less significant. As deposition time increases, particle impaction efficiency decreases and sticking efficiency increases due to the thermophoresis and the local temperature conditions, which result in the time-dependent behaviour of the deposition growth. In addition, the ash deposition characteristics are influenced under different furnace temperatures, due to the change in the particle impaction and sticking behaviours. Qualitative agreement is obtained between the predicted results and the measurements for the heat flux to the tube and the ash deposition growth.