Research on formation mechanism of typical low-temperature fouling layers in coal-fired boilers

Comparative field experiments of typical low-temperature fouling layers are carried out in pulverized coal furnace (PCF) and circulating fluidized bed boiler (CFB). The reduction of heat transfer characteristics of test pipe is determined by the transformation of fouling layer, caused by the quantity of condensed acid solution exceeding the adsorption capacity of deposited ash particles. Based on the heat transfer performance of fouling layer covering the test pipe, as well as the appearance characteristics and degree of adhesion to the heating surface, three typical fouling layers are collected, i.e. dry loose ash deposits (85 degrees C), adhering ash deposits (65 degrees C) and viscous ash deposits (45 degrees C). Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) are used to analyze the formation mechanisms of three typical fouling layers. The characteristic fouling layer is determined by the reaction degree of condensed acid solution and ash particles deposited on the heating surface. Furthermore, the formation mechanisms of unsaturated acid-ash action fouling layer, supersaturated acid-ash action fouling layer and mixed acid-ash action fouling layer are proposed, providing useful guidance for the safe and efficient operation of heat exchange equipment in coal-fired boilers.