Evaluation of potassium chloride emissions applying the Discrete Particle Method (DPM)

An increasing price for primary energy makes thermal conversion of biomass a very attractive alternative to produce energy. However, emissions emanating from combustion for example are of concern due to legal limits and impact components of the combustor negatively by corrosion. One of the major emission components is potassium chloride. In a vapor atmosphere it may form a very aggressive environment that will corrode boilers. Therefore, the object of this study is to evaluate the kinetic data describing the formation of potassium chloride during switchgrass combustion. Experimental data that records the combustion process and the emission formation versus time, carried out by the National Renewable Energy Institute in Colorado (US), was used to evaluate the kinetic data.The approach is based on the Discrete Particle Method (DPM) that solves the coupled differential conservation equations for mass and energy of a switchgrass particle. Processes considered were heating-up, pyrolysis, combustion of switchgrass and evaporation of potassium chloride. Thus, the conversion process of switchgrass is described sufficiently accurate in particular the evolution of temperature. The evaporation of potassium chloride is approximated by an Arrhenius-like expression including a pre-exponential factor and an activation energy. These parameters were determined by a least-square method so that the deviation between the measured data and the predictions was minimized. The kinetic data determined yielded good agreement between experimental data and predictions.