Hide/Show Apps

An experimental and numerical study on the combustion of lignites from different geographic origins

2020-10-15
Özer, Burak
Debiagi, Paulo Eduardo Amaral
Hasse, Christian
Faravelli, Tiziano
Kazanç Özerinç, Feyza
Coal combustion involves multi-scale, multi-phase and multi-component aspects, in a process where both transport phenomena and reaction kinetics must be considered. The aim of the work is to investigate the differences between the combustion characteristics of Turkish (Soma lignite, Tuncbilek lignite, Afsin-Elbistan lignite) and German (Rhenish lignite) lignites. Combustion characteristics of these lignites were investigated experimentally and numerically. Experiments were conducted using a high temperature (1000 degrees C) and high heating rate (similar to 104 degrees C/s) drop tube furnace (DTF), along with a thermogravimetric analyzer (TGA) at non-isothermal conditions (5, 10, 15, 20 degrees C/min). Both experimental trials were done in a dry air environment and atmospheric pressure. Additionally, DTF and TGA are the experimental setups used to validate the numerical model used in this work. The numerical part of the study includes the computational fluid dynamic analysis of DTF and the predictive multi-step kinetic model analysis of the fuel particle. TGA experiments showed that fuel ratio has an effect on the ignition times. Moreover, maximum reaction rates obtained by TGA experiments were inversely proportional to the ash contents of the fuels used. High heating rate DTF experiments showed similar combustion behaviours with TGA experiments. According to DTF experiments, RL has the highest reactivity (RL: 7.8 s(-1)) among all fuels (AEL: 5.3, SL: 4.7, TL: 2.9 s(-1)). In comparison to experimental data, PoliMi model predictions on high-temperature volatile yields are satisfactory with 5-7% errors. PoliMi model overpredicted the devolatilization rates whereas char oxidation rate predictions seem to be lower than the experimental results.