CFD Modelling of “Clean” Coal Technologies at Operating Thermal Power Plants Aimed at Reducing Harmful Emissions

Improving the environmental performance of utility boilers fired with high-ash coal requires optimisation of combustion aerodynamics and staged air supply. This article summarises studies investigating the effects of flow swirl, burner design, partial burner shutdown, and overfire air (OFA) injection above the main combustion zone. The identified relationships are illustrated using CFD modelling of a BKZ-75 boiler firing Karaganda coal with an ash content of 35.1%. Straight-through and swirl burners with a swirl angle of 30°, the shutdown of two out of four burners, and OFA fractions ranging from 0 to 30% were investigated. At nominal load, swirl reduced the CO and NO2 concentrations at the furnace outlet by 17.6% and 22.1%, respectively. Shutting down two burners resulted in reductions of 36% for CO and 7.5% for NO2. Among the operating conditions investigated, the best results were achieved at an OFA fraction of 18%, which reduced CO by 38% and NO2 by 24.7% relative to the baseline operating condition. For the BKZ-75 boiler firing Karaganda coal, 18% was the most effective among the OFA fractions studied (0–30%); this value should not be extrapolated to other conditions without additional calculations. The deviation of the baseline simulation results from measurements taken at Shakhtinskaya Thermal Power Plant did not exceed 3%. The results highlight the need for an integrated optimisation of combustion aerodynamics and staged combustion, taking into account the characteristics of the specific boiler.