Improved numerical prediction of ash formation and deposition using a novel developed char fragmentation model

In this work, a new CFD-model has been developed to simulate the fragmentation of the char particles during coal combustion, which has been implemented directly in the commercial CFD code Fluent 13.0 using user-defined functions. With this feature it is possible to model the fragmentation processes during the combustion of the coal particles leading to an improved deposition prediction in coal fired boilers. Calculations have been carried out to model an entrained flow reactor, which will be used to validate the simulation results. Additionally, a deposition model has been integrated to investigate the effect of the particle fragmentation on the slagging behaviour of fly ash on the probe. The results of the numerical simulations show, that there is a big effect of the particle size distribution on the deposition behaviour. The maximum deposition rate and the integral deposited mass flow are around one magnitude higher if no fragmentation occurs. This finding is based on two different calculations of the reactor with and without fragmentation and their results were compared. It can be concluded that the fragmentation modelling of char particles during pulverised coal combustion accounts for an improved prediction of fly ash deposition.