Numerical simulation of ammonia combustion with coal in a 135 MW tangentially fired boiler

Abstract

This study conducted a simulation of coal and ammonia co-combustion in a 135 MW tangentially fired utility boiler using Fluent. The combustion process was modeled using a gas-phase non-premixed approach based on finite-rate/turbulent dissipation. Additionally, NO generation and conversion were simulated through multi-step chemical reactions. Upon verifying the accuracy of the proposed model, the effects of ammonia co-firing ratios and injection modes on boiler combustion characteristics and NO emissions were investigated. The results indicate that as the co-combustion ratio increases, the boiler temperature decreases. Concurrently, NO emissions from the furnace exhibit a trend of initial decrease followed by an increase, reaching a minimum of 136.21 ppm at a mixing ratio of 15 %. With a co-firing ratio of 30 %, a significant reduction in NO emissions can be achieved by decreasing the proportion of primary and secondary air. As the excess air factor of ammonia decreases from 0.3 to 0.1, NO emissions initially decrease, followed by a subsequent increase. Overall, optimizing the ammonia injection mode and air distribution ratio can reduce NO emissions to below 220 ppm when the ammonia co-combustion ratio is below 30 %. This study serves as a valuable reference for retrofitting utility boilers for coal-ammonia co-combustion.