SO2, CO and NOx analysis of a SL calciner using a MI-CFD model

Combustion, calcination and emission (CO, NOx, SO₂) optimization results are presented from a separate line (SL) calciner, and are compared, where possible, with another SL calciner. Over 60% of the total fuel is fired in the calciner achieving 95% calcination levels in relatively short residence times (2.5 seconds). The use of petcoke and alternative fuels (AFR´s) saves fuel costs, but their thermal substitution rate is limited by emissions and operational difficulties. In addition to the problems of complying with emission limits (i.e., CO, NOx, VOC´s), kiln instabilities may result due to the higher sulfur and chloride contents of AFR´ s, or petcoke. The problem is exacerbated if the meal injected in the calciner drops through - at the kiln inlet/tertiary air inlet due to the formation of meal-slugs or presence of lower velocities regions. A detailed study of a Canadian cement plant´s separate line calciner is presented using a 3-D mineral interactive computational fluid dynamics (MI-CFD) model and results related to flow aerodynamics, calcination, combustion of conventional and alternative fuels and emissions (CO, SOx, and NOx) are compared with other separate line calciners. In addition, the effect of fuel-mix on emissions is analyzed and recommendations are made with regard to the burners, burner locations, meal inlets, specific to calciner geometrical characteristics. The computed results are compared with the plant data and additional MI-CFD model predictions are carried out for alternative fuels to be fired in the next project-phase. As a result, of the on-going calciner measurement and MI-CFD campaigns, the plant can easily achieve the legislative limits of NOx, CO and SO₂ for coal, low to higher sulfur petcoke blends as well as for 50% thermal substitution levels of AFR. The plant is ´AFR-ready´ pending its permitting process, which is in its final stages.