Effect of MgO addition to upgraded brown coal on ash-deposition behavior during combustion

► Effect of MgO addition to upgraded brown coal on the ash deposition is evaluated. ► MgO addition played a role in decreasing in molten slag fraction. ► Mg formed solid composites with Si, Fe, Al, Ca, and Mn. ► MgO addition contributed to the decreasing rate of ash deposition for the UBC.