Release of potassium and chlorine during straw pyrolysis

A laboratory batch reactor was used to study the release of K and Cl as a function of temperature at a heating rate of approximately 50 degrees C/s. To facilitate the interpretation of the batch reactor results thermodynamic equilibrium calculations at reducing condition were conducted and SEM (scanning electron microscopy) pictures and EDX (energy dispersive X-ray) analyses were carried out on straw and char samples. The experiments showed that chlorine was released in two steps. About 60% was released when the temperature increased from 200 to 400 degrees C and most of the residual chlorine was released between 600 and 900 degrees C. Below 700 degrees C no significant potassium release was observed, but above that temperature potassium release increased progressively. The investigation indicated that during the initial pyrolysis at 200 to 400 degrees C potassium was released from the original binding sites and redeposited as discrete particles (KCl and K2CO3) or intercalated into the organic char matrix. The initial potassium release to gas phase at approximately 700 degrees C is caused by evaporation of deposited KCl particles.