Modelling the Capture of Potassium by Solid Al-Si Particles at Pulverised Fuel Conditions

The capture kinetics of different potassium species on two different additives (kaolin and coal fly ash) were determined using experimental drop tube data, a numerical model and computational fluid dynamics (CFD) simulations of the experimental setup. Our model includes an equilibrium limit based on thermodynamic principles, surface degradation due to particle sintering, and can predict the simultaneous capture of KOH, KCl and K₂SO₄. Due to its design, the model is suitable for use in CFD codes with little computational overhead. The resulting kinetics shows very good agreement with experimental data over all investigated species and additives. We show that the capture of KCl and K₂SO₄ on coal fly ash can be predicted by solely modelling the capture of KOH while considering gas phase reactions. Possible reasons for this phenomenon are discussed. In conjunction with a suitable CFD setup, this model can be used to optimise the use of additives in biomass and waste-to-energy power plants.