Bench-scale study of interactions between flue gas and cofired ash in an SCR

Samples of ash collected from a full-scale utility boiler cofiring 80% wood waste with 20% Powder River Basin (PRB) coal were mixed with ground selective catalytic reduction (SCR) catalyst and exposed to simulated flue gas. Changes in mass were recorded with time, and mass gains were found to be highest without SCR catalyst present. Ash samples were analyzed before and after testing to determine what mechanisms had led to mass gain. The ash had reacted with gas-phase SO2 to form solid sulfates. Mass gain by sulfation would likely cause ash particles to grow and cover catalyst pores in the field, leading to catalyst deactivation and reduced NOx control.