A dynamic mesh approach to the 2D CFD modelling of ash deposition in solid fuel combustion

In the foreseeable future, it is anticipated that the use of pulverized solid fuel will continue to grow. Technologies that utilized pulverized solid fuel as a co-firing fuel will prove indispensable to meet electricity demands as well as to combat the ever-increasing threat of global warming, especially in countries where fossil fuels remain the majority of energy source. However, the ash deposition formation remains a very complex process in the furnace, which involves physical and chemical processes that account for: ash-forming, transporting, sticking and consolidating. Each of which is a non-linear process that requires a careful analysis of the temperature-time history of the fuel particles.
In this thesis, the CFD methods are employed to predict the ash deposition for the EI Cerrejon coal and the recycled wood biomass air combustion in 2D mesh. The dynamic mesh model is also employed in the simulation. A new simulation method, combining with dynamic mesh, discrete phase model and mesh partition method, is developed in the parallel ANSYS FLUENT to simulate the accurate and smooth change of the deposit surface during the ash deposition processes. It is noted that the predicted deposit rate matches the experimental data. And this method has more steady simulation and takes one third of time when compared to the current mass re-distribution method. The effect of flue gas velocity and the change of the deposition shape are also investigated. The results show that the increase of the flue gas velocity leads to the increase of the ash deposition rate in the coal air combustion case. And the ash deposition rate decreases in the biomass air combustion case when increased the flue gas velocity. It is noted that due to the change of the velocity distribution around tube caused by the change of the deposition shape, the ash particles accumulate at the windward stagnation point of the tube. In addition, the ash deposition for Zhundong lignite combustion is also investigated with this simulation method. The predicted ash deposition thickness is close to the Zhundong lignite experimental data.