Evaluation, comparison and validation of deposition criteria for numerical simulation of slagging

The objective of this study is the comparison of various sticking probabilities based on three different approaches: (1) empirical viscosity models, (2) experimental results based on ash fusion and thermo-gravimetry and (3) thermodynamic equilibrium calculations. More specifically the viscosity models of Urbain, Kalmanovitch and Watt & Fereday are compared. Sticking probabilities from ash fusion tests are based on the characteristic temperatures and the sample height. The thermo-gravimetric results combine the mineral phase change in dependence of temperature and the mass loss due to evaporation of minerals. The thermodynamic equilibrium calculations are carried out with the software FactSage and as a result the liquid fraction in the ash is obtained. The derived criteria are compared among each other and implemented in an applicable form in FLUENT in order to determine the deposition rate for the experiments in the entrained flow reactor of the Technische Universität München. The results are then compared with experimental observations for two different hard coals, El Cerrejon and Pittsburgh No. 8. An optical deposition-rate measurement technique based on a deposition probe and a CCD-camera is applied to the experiments, which makes use of a shadow image of the deposition probe. This technique is able to evaluate the time dependence of the deposit build-up.