Determination of alkali release during oxyfuel co-combustion of biomass and coal using laser-induced breakdown spectroscopy

Abstract

The impetus for clean energy utilization has increased acceptance of biomass as a co-fired fuel with coal, since it reduces carbon emissions. This work utilized time-resolved online LIBS measurement to investigate the release of potassium from oxyfuel co-combustion of fuels. A coal-biomass blended particle consisting of 20% biomass (energy basis) is set as a reference fuel, and its results are compared with native biomass and coal particles. As expected, the potassium release rate was highest with 100% biomass and decreased with reducing biomass content in the blend. Therefore, there are trade-offs associated with potassium-related deposition, fouling and corrosion of a boiler’s heat transfer surfaces when biomass and coal are co-fired compared with biomass alone. Analyses of particle size and surface temperature changes suggest that the evolution of potassium in the gas phase can be characterized by temperature evolution. The online measurement for a 20% blend indicates that about 80% of the releasable potassium is volatilized, mainly during the char combustion stage. The release kinetics model developed obeys an Arrhenius expression. The activation energy reported for a 20% fuel blend was 161.9 kJmol−1 K, and was much lower than that of 100% biomass, but higher than that of 100% coal.