Lowering the carbon footprint and energy consumption of cement production: A novel Calcium SulfoAluminate cement production process

The development of novel clinker compositions or alterations to kiln process conditions is usually a slow and incremental process. The uncertainty in the effects of any change has led to the cautious development and optimization of clinker production. This work demonstrates that the pace of change can be greatly accelerated by combining the theoretical predictions of computational thermodynamics with focused experimental research. The production of Calcium SulfoAluminate (C$A) cement via a novel process substituting traditional carbon-based fuels by elemental sulfur and/or sulfur-rich fuels is used as an example. The combustion of sulfur in the kiln is attractive as it sequesters unwanted sulfur byproducts inside a valuable and stable product (the clinker). The thermal energy of the sulfur combustion also lowers the fuel requirements and thus the CO2 emitted by the process. The chemical feasibility, benefits, and process economics of direct combustion of these “alternative” sulfur fuels for both energy and as the sulfur trioxide source in C$A cement clinker are presented. Due to the reduced calcium content of C$A, CO2 emissions of calcination are reduced by up to 35% using this technology. Sulfur-rich hydrocarbon fuels contain a variety of forms of sulfur. Using elemental sulfur as a surrogate demonstrates significant reductions in theoretical heat of clinkerization. If the sulfur is in a form equivalent to H2S and the kiln process is integrated with a wet-limestone scrubber, the theoretical heat of the C$A clinkering process can even become negative implying that the energy of the carbon content of the fuels would only be required to partially offset heat losses within the production process. Pilot plant trials using elemental sulfur are shown to conform to predictions and illuminate some of the kinetic aspects which cannot be captured by equilibrium models. This demonstrates that producing C$A cement via sulfur combustion is an attractive and feasible technology with significant environmental benefits.