Interaction of Potassium and Calcium in the Catalytic Gasification of Biosolids and Switchgrass

Catalytic gasification is a method of converting biosolids, the solids created during wastewater treatment, into a valuable gaseous stream. One of the challenges with this process is that the components in the ash of the biosolids can interact with the gasification catalyst(s)-in particular, calcium and potassium. In this study, the behaviors of different combinations of switchgrass (the source of potassium), biosolids, ash-free carbon black, and mixtures of each feed with added calcium and/or potassium were observed with a thermogravimetric analysis unit. The results were consistent with calcium preferentially reacting with components in the ash, preventing the deactivation Of potassium. Any additional calcium available may form bimetallic compounds with the potassium, but this interaction did not increase the rate of reaction. Modeling was performed using the random pore model and extended random pore model, with the appropriate model chosen for each mixture. The extended random pore model was better suited for the data with the highest reaction rates.