Experimental research on morphology and drying characteristics of coal slime dough injected into circulating fluidized bed boiler

Abstract

Co-firing coal slime in circulating fluidized bed (CFB) boilers is an effective method for utilizing coal slime, as industrial solid waste, with high water content, high viscosity, high ash content and low calorific value. In order to study the morphology and drying characteristics of coal slime dough injected into the furnace, this paper studied in detail the influence of compression degree and water content on the tensile force of coal slime dough. The results show that the degree of compression is positively correlated with the tensile force of coal slime dough, while, the water content is negatively correlated. A one-dimensional quadratic mathematical relationship between the tensile force of coal slime dough and the water content is established. At different feeding locations, i.e., at the top or middle of the boiler furnace, the breaking length of the coal slime dough was predicted. With top feeding, the length is 0.17 m, and that value for the middle feeding is about 0.15 m. Using the coupling model of the movement and drying of coal slime dough inside the furnace of the CFB boiler, the temperature change of the slime dough was calculated. The results showed that the surface temperature of coal slime dough rose rapidly during the drying process, then decreased slowly before it dived into the dense bed. When the furnace temperature is 900 °C and furnace height is about 38 m, the temperature of the slime surface can reach 200 °C at the highest.