The release of critical ash-forming elements during the pyrolysis and combustion of corn stover has been investigated through controlled lab-scale experiments supported by multicomponent and multiphase thermodynamic equilibrium calculations. Fuel samples were treated under isothermal conditions ranging from 500 to 1150 °C, under both pyrolysis and combustion atmospheres. The volatilized material was quantified by means of mass balances based on char and ash elemental analysis, compared to a corresponding feedstock fuel analysis. Close relations between the observed K and Cl release are found, suggesting that Cl is the main facilitator for K release through sublimation of KCl, determined to begin as the reaction temperature approaches 700–800 °C. K is present in abundance relative to Cl, and the K release is found to cease as the fuel reaches complete dechlorination. In addition, around 50 wt % of the Cl is released at temperatures below 500 °C, presumably as HCl formed through ion-exchange reactions with ...