Investigation on self-sustained combustion and its ash properties of coal slime in different scale fluidized beds—part II: 12t/h fluidized bed boiler of coal slime

With the increasing amount of coal slime in the process of coal washing, it is of great significance to realize the clean utilization of coal slime for sustainability and environmental protection. Based on the previous experimental results in a bench-scale fluidized bed reactor, this work further verified the self-sustained combustion performance of coal slime in a 12t/h fluidized bed boiler. The properties of the ash released from the boiler were also analyzed by inductively coupled plasma atomic emission spectrometer, X-ray diffraction, X-ray fluorescence spectrometer, etc. It was found that the average particle size of dry coal slime and fly ash reached 231.9 μm and 240.3 μm both with a mass fraction of 90%, which was relatively fine and difficult to be fluidized. High combustion efficiency of about 99% and low gaseous pollutants emissions can be achieved by adjusting the structure of the fluidized bed boiler and humidification pretreatment of coal slime. In addition, the migration of heavy metal elements indicated that most heavy metals such as Cr, Zn, Sn, Ni, Be, Cd, Cu, and Pb, were very volatile and inclined to enrich in the flue gas. The ash fusibility characteristic was studied combined with different calculated parameters to quantitatively reflect the mineral transformation mechanism and the influence of different oxides on its fusibility propensity. Other than that, a co-generation system was proposed to effectively utilize the extra thermal energy generated by the boiler. Graphical abstract