Kinetic investigations on catalytic properties of mineral matter in oxy-fuel combustion
The subproject A5 of the joint research project Oxyflame investigates the catalytic influence of mineral matter in coal on pyrolysis and char burnout. It is well known that Na, K, Mg, Ca, Al and Fe effect coal gasification and promote setting the Boudouard equilibrium. The enlargement of the volume flow due to the enhanced reaction rate by the catalytically active minerals will influence the flow field of flames and has to be taken into account.
Besides the investigations of natural coal, an artificial fuel is prepared by hydrothermal carbonization of cellulose enabling the synthesis of a mineral-free, lignite-like fuel as well as model fuels selectively doped with minerals. Binary and ternary doped synthetic fuels are planned to approach the complex ash composition of natural coals. The catalytic effect will be investigated using thermogravimetric analysis in temperature-programmed and isothermal mode.
Under oxyfuel conditions coal is burnt in flue gas, whereby the presence of stream and CO2 potentially causes an increase in coal gasification rate. Therefore, the reactivity of the doped chars, prepared by thermal treatment of the synthetic coals, will be analyzed in a thermobalance and a fixed-bed reactor in O2 as well as H2O and CO2 containing reaction atmosphere. Kinetic parameters as a function of doped mineral(s) are aimed by kinetic modeling of the obtained char conversion curves.
The formed products during pyrolysis will be analyzed in detail with a pyrolysis GC/MS-GC/WLD system equipped with a pyrolyzer enabling the pyrolysis of solid fuels with high heating rates. Simultaneous detection and partially quantification of desorption and decomposition products formed during pyrolysis, namely pyrolysis gases and tars, are performed by an advanced GC/MS-GC/WLD analysis system. Considering oxyfuel combustion, CO2 and H2O will be added to the gas atmosphere.