Research On The Effect Of Additives On The Sintering Behavior Of Coal Rich In Sodium Under An Oxy-fuel Combustion Atmosphere

The oxy-fuel combustion technology has been recognized as one of the most promising technologies for reducing CO2 emission in coal-fired boiler. Meanwhile, oxy-fuel combustion can contribute to an easier recovery of CO2 and a lower cost of CO2 capturing than conventional air firing combustion. However, this brings about a significantly high concentration of NOx, SO2 and alkali in flue gas under the oxy-fuel conditions, especially for the low-rank coals. These low-rank coals contain relatively higher ash, sulfur, and alkali species. Consequently, they are easy to cause ash related problems such as fouling, slagging, and erosion. Furthermore, these fouling and slagging problems strongly reduce the reliability and safety of boiler as well as the boiler efficiency. In addition, the sintering and melting behavior directly affects the slagging process, which is the significant characteristic of ash deposition. Because additives can change the sintering and melting behavior of ash, additive technology has become one of the most important methods to solve the ash related problems. In order to investigate effects of different additives on the sintering behavior of coal ash rich in sodium under oxy-fuel combustion atmosphere, a horizontal sintering furnace system with atmosphere variable is developed. The system contains the horizontal sintering furnace, a CCD monitor system, automatic driving and reversing device, and sintering probe system. The main research work is as follows:Firstly, coal ash with additive was made by mixing the pure oxide powders into the ash samples homogeneously. Then, the ash sample pressed into cubical ash blocks was placed on the sintering probe for one hour experiment in the horizontal sintering furnace with oxy-firing atmosphere. During the experiment, the shape-shifting of ash sample was monitored by the CCD camera system.Secondly, Matlab digital image processing technology with binaryzation theory was used to develop a GUI software for studying the shape-shifting of ash sample. Then, the image processing system was used for analyzing the photos captured by the CCD to obtain the shrinkage of area and height of sintered samples.Finally, the microstructure of the sintered samples was observed by a scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectrometry (EDX), which can analyze the chemical compositions. Meanwhile, the distribution of mineral phases in the sintered samples was identified by X-ray diffraction (XRD). Moreover, in order to have a better understanding of coal ash melting characteristics with additives, chemical equilibrium calculations were conducted by using the FactSage equilibrium module software and the coal ash compositions were further applied in the isothermal phase diagrams of ternary system at 1350℃ by FactSage to evaluate the solid-liquid phase equilibrium of the sample.