The effect of fuel composition on pyrolysis kinetics

摘要

Penn State's Earth and Mineral Sciences Energy Institute (EI) and the Foster Wheeler Development Corporation (FW) have been collaborating on advanced fuel characterization analysis for many years. EI has determined the reactivity and pyrolysis kinetics for a number of coal and biomass samples for Foster Wheeler. These studies were performed to obtain kinetic data to assist FW in burner design and furnace model development. Understanding the kinetics of fuel pyrolysis and combustion is critical in the development of technologies that can utilize fuels in the most efficient and beneficial manner. Combustion of coal involves four steps: moisture evaporation, devolatilization, volatile matter combustion, and char combustion [1]. The second step, devolatilization, usually occurs between 400 and 900°C and influences the rate of the subsequent reactions [2]. The third step, combustion of volatile matter, is the fastest step because it is a homogeneous reaction in the gas phase [3]. The combustion of char is a slower process because it is a heterogeneous reaction between gas and solid materials [3]. Pyrolysis is the process of heating a fuel in an environment of little or no oxygen thereby producing char. It is the key to fuel quality because it is the process of "thermal degradation of solid fuels [that] is present in both combustion and gasification" [4]. Fuel energy conversion is dependent on the reactivity of the char produced in pyrolysis. The pyrolysis kinetic rate constants for a variety of fuels are the focus of this study. The fuels include a variety of coals, lignite to bituminous coals, and a wide range of opportunity fuels. The reactivity of a fuel undergoing pyrolysis is dependent on temperature. As temperature increases, the reactivity of fuel increases. The goal of this study was to examine the effect that temperature, rank, oxygen content and the molar ratios between carbon, oxygen, and hydrogen have on the kinetic rate constants of fuels supplied by FW. This study looks at the basic composition of a variety of fuels to identify relationships between their composition and respective rate constants.