An Experimental Study of Sulfur and Chlorine Stripping from Cement Hot Meal

This work explores the feasibility of developing a new process, as an alternative to the current bypass system, for stripping S, Cl and K from cement hot meal. Laboratory scale stripping experiments have been conducted in a horizontal tube reactor. The effect of the process conditions (gaseous atmosphere, temperature, time) on the removal of S, Cl and K from a cement hot meal collected from a full-scale plant has been investigated. It was hypothesized that sulfur removal can be enhanced in reducing conditions, by converting CaSO₄(s) to SO₂(g), while Cl (and K) removal is mainly due to evaporation of KCl. Experiments were carried out in the temperature range of 800 – 1100 °C and at residence times 10 – 60 minutes. The gaseous atmosphere used was either air, or 1 – 1.8% CH₄ (with N₂ for balance). During the experiments, a gas analyzer was used to monitor the release of SO₂ during the sample conversion. After the experiments, the solid residues were collected and analyzed by, e.g., ICP-OES / IC for elemental composition, and XRD for determination of crystal phases. The experimental results revealed that a reducing atmosphere promotes the release of S from the hot meal. Substantial release of S (~40%), Cl (~40%) and K (~20%) from the hot meal was obtained at 900 °C, 30 minutes and 1% CH₄ conditions. At higher temperatures, deviation of S release calculated from integration of SO2 and ICP-OES, respectively, indicated that other forms of sulfur (e.g. SO₃ or H₂S) released. Increasing the CH4 concentration from 1% to 1.8% slightly decreased S release from the hot meal at 900-1100 °C, probably due to over-reduction forming solid phase CaS(s).