NO emission from cement calciners firing coal and petcoke: A CPFD study

NO emission from two in–line cement calciners operating with petcoke and coal, respectively, is predicted through computational particle fluid dynamics (CPFD) simulations using the commercial software Barracuda Virtual ReactorⓇ 17.4.1. In the Eulerian–Lagrangian approach used in this solver, the solid phase is modeled using the Multi–Phase Particle–In–Cell (MP–PIC) method. The chemistry of gas phase combustion and NO formation/reduction is modeled using a global reaction kinetic set. Comparison of the predicted gas temperature and species concentrations against extensive full–scale measurements along calciner height, exhibits acceptable accuracy of the CPFD model. The conversion of solid fuel is underpredicted in the lower and upper calciner vessels for both calciners, while at the calciner exit, it is well–predicted. Further evaluation of the simulation results reveals dominant contributions of NO formation by char–N and NO reduction by char–C. As a result of higher volatile content of coal in coal–fired calciner, the contributions of NO formation/reduction by CHi radicals and HCN become more noticeable, compared to the petcoke–fired calciner. For both calciners, the overall predicted NO formation is greater than NO reduction, leading to a positive net NO generation. The net NO generation in the coal–fired calciner is almost half of that of the petcoke–fired calciner.