Preheating Analysis of Semi-Coke in a Circulating Fluidized Bed and Its Kinetic Characteristics

Abstract

Semi-coke has difficulties with stable ignition and high-efficiency combustion due to its low volatile content. Preheating in a circulating fluidized bed before combustion offers a novel method for the improvement of fuel properties. During preheating, the semi-coke was converted to preheated fuel composed of coal gas and preheated char. When increasing the preheating temperature, the ratio of CO/CO2 in the coal gas significantly increased, while the ratio of CH4/CO2 remained almost unchanged. After preheating, the release ratios for different species from the semi-coke followed the order C >H > N > S. Thermogravimetric analysis was used to evaluate the kinetic characteristics. We found that the ignition and burnout temperatures of the preheated char decreased compared to those of the semi-coke, and the reaction rate constant for the preheated char increased by 20 times. Three models were used to predict the variations in the conversion ratio with time, and the modified volumetric reaction model showed good agreement with the experiment. This investigation provides support for better developing preheating combustion technology in the future.

Keywords

• semi-coke
• preheating
• circulating fluidized bed
• kinetic characteristics