(359d) Co-Firing Characteristics of Coal and Ammonia in a Circulating Fluidized Bed Combustion Test-Rig with Ammonia Fuel Staging Under an Air-Staging System

Ammonia (NH₃) has recently garnered attention as a promising carbon-free fuel for co-firing in existing coal-fired power generation systems. In this study, a pilot-scale circulating fluidized bed combustor (CFBC) test-rig was utilized to investigate pollutant emission characteristics during NH₃ co-firing under an air-staging combustion strategy employing tertiary air. The experiments were conducted at a fixed NH₃ co-firing ratio of 21.2%, focusing on the effect of NH₃ injection position on combustion performance and emissions.

A fuel-staging strategy was applied by splitting the NH₃ supply between the windbox (WB) and the lower secondary air (LSA) line, and combustion characteristics were evaluated across various WB:LSA injection ratios. The results showed that when the NH₃ injection ratio exceeded WB:LSA = 70%:30%, CO and N₂O concentrations increased, while NO concentrations decreased. This behavior is attributed to the partial inhibition of coal combustion by excess NH₃, leading to incomplete combustion and unburned NH₃ promoting selective non-catalytic reduction (SNCR) reactions. In contrast, under the same overall co-firing conditions, full injection of NH₃ through the WB resulted in lower CO and higher NO concentrations, indicating more complete combustion of NH₃. These findings suggest that the NH₃ injection position is a critical parameter for combustion optimization and provide strategic insights for the effective utilization of NH₃ in retrofitted coal-fired power infrastructure.