KINETIC STUDY OF COAL AND BIOMASS CO-PYROLYSIS USING THERMOGRAVIMETRY

摘要

The major driving force for adding biomass in coal utilization is to utilize renewable energy resources and reduce net coal CO2 emission. Co-firing (blend of biomass with coal combusted in air) as a co-utilization technology has been successfully demonstrated in numerous power plants and has shown reduction of CO2 emission1. A life cycle (LC) analysis concluded that co-firing of Illinois No. 6 coal and forest residue (10% heat) reduces the LC greenhouse gas (GHG) emission by 6.6%2. Simulation tools that can be used to predict behaviors of coal and biomass blends in co-utilization and to optimize system designs and operation are a potentially cost effective way to assist further technology development. Kinetic models are needed for blends of coal and biomass for devolatilization/pyrolysis, gasification and combustion processes. Thermogravimetry (TGA) has been widely used to obtain kinetics parameters of solid fuel thermal processes using non-isothermal methods at one or multiple heating rates3. Biomass mainly consists of hemicelluloses, cellulose, and lignin and it has different composition with coal. Biomass pyrolysis kinetic models are mainly developed based on the mechanism of three independent parallel first order reactions of three pseudo-components4. Iso-conversional and multi-heating rate methods are widely used in solid thermal decomposition kinetics study3. Using the methods on the co-pyrolysis is challenging due to inherent heterogeneity of both biomass and coal, and to the complexity of co-pyrolysis of these blends. The objectives of this study are to investigate thermal behavior of coal and biomass blends in inert gas environment at low heating rates and to develop a simplified kinetic model using model fitting techniques based on TGA experimental data.