Production and Analysis of BYF Clinker Produced via the Combustion of Elemental Sulfur

Including calcium sulfoaluminate (CSA) cement associated phases in clinker can provide a useful approach to compensate for a lack of consistency in raw material compositions, such as high alumina contents in clays and shales as well as high sulfur levels in fuels. Furthermore, there are key advantages when comparing CSA clinker product with Ordinary Portland cement (OPC) clinker, such as lower clinkering temperatures and limestone requirements which lower process CO2 emissions; it seems natural to explore the production of ye’elimite containing clinkers. Here, a production technique that utilizes sulfur as both a raw material and source of fuel was used to produce CSA clinker product. Low-cost high-alumina clays were used as the primary source of aluminum oxide and supplemented with bauxite to reach the target required to stabilize ye’elimite. A series of pilot-scale production trials were performed where the rotary kiln process conditions were optimized to produce belite-calcium ye’elimite ferrite (BYF) clinkers via a gas-to-solid mass transfer of gaseous sulfur. The composition of the produced clinker varied between 35–40 wt.% ye’elimite, 40–45 wt.% belite, and up to 5 wt.% anhydrite respectively. Samples from the obtained clinker were then blended with supplementary anhydrite to study the effect of the molar ratio of calcium sulfate to ye’elimite on hydration kinetics and strength development. An improvement in the compressive strength relative to OPC was reported after 1 and 2 days, while after 7 days (and beyond) comparable values were reached. Overall, the BYF clinker produced at pilot scale exhibited promising hydration and durability performance, where a large majority of the anhydrous phases were consumed after 182 days. In brief, the developed sulfurous fuel combustion technique was demonstrated to be a feasible and promising approach for the production of BYF clinker formulations with superior performance relative to OPC.