Influence of Load Changes on the Deposit Behavior during Combustion of Five Different Hard Coals

This work focuses on the influence of cyclic temperature profiles on the sintering behavior of hard coal ashes. To extract mechanisms, all ashes are fully characterized concerning chemical and mineralogical composition and thermal behavior including the characterization of the decomposition species and the ash fusion test with two different setups. Also, the characterization should ensure a broad variability of chemical and mineralogical compositions. To determine sintering effects, the sintering strength test was used in combination with mass and density change analysis. All samples were investigated at 12 different temperature profiles, whereas four include different cycling conditions, four use isothermal short-term conditions, and four use isothermal long-term conditions. In addition, the effect of the preparation load for this experiment was examined. Although all ashes contain similar amounts of the common hard coal ash main components like SiO2, Al2O3, and Fe2O3, they still differ a lot in alkaline and alkaline earth elements. Besides, every coal ash contains a prominent mineral, which could characterize the ash. The measurement results from the different temperature profiles indicate many influences of certain minerals and also an alkali threshold of nonreactivity was detected and quantified. To sum up, most cycled samples revealed results similar to those of the isothermal investigated samples at 950 °C. However, the possibility for lower and higher sintering due to cycled temperatures profiles was proofed and responsible minerals and chemical circumstances were identified