Ammonia/flyash interactions and their impact on flue gas treatment technologies

Ammonia/flyash interactions were investigated to assess their importance in flue gas treatment processes. Theoretical calculations are presented for the upper bound of ammonia uptake by flyash during selective catalytic reduction. Assuming diffusion-controlled uptake, significant ammonia loss to flyash is predicted; this is not supported by industrial experience. Thus, experiments were conducted to measure ammonia adsorption and reaction on flyash as a function of temperature. Based on the experimental results, ammonia/flyash interactions are not expected to interfere with either current or proposed low-temperature (110-160°C) operation. When adding ammonia as an electrostatic precipitator (ESP) conditioning agent, however, the extent of adsorption onto flyash will be very sensitive to operating conditions. This may explain the erratic performance of ammonia in ESP conditioning reported in the literature. Finally, the saturation capacity for ammonia adsorption onto flyash exceeds the maximum threshold established for flyash reuse as a cement additive and thus could limit this large-volume opportunity for mitigating flyash disposal.