The cement clinker manufacturing process is characterized by the large amount of CO2 emissions produced by the calcination of limestone fed to the kiln, necessary for the production of calcium oxide for the clinkerization reactions, and those produced by the combustion of fossil fuels necessary to reach the high temperatures required in the process (1400 ° C). In total, around 800 - 900 kg CO2 are emitted per tonne of clinker, or 700 - 800 kg of CO2 per tonne of cement produced.
Although the search for alternative fuels can reduce the greenhouse gas emissions caused by the combustion process, calcination is certainly inevitable in the manufacture of conventional cement (e.g. Portland). Among the multiple solutions proposed to mitigate the impact of the cement industry, new cement formulations, such as calcium sulfoaluminate (CSA), are certainly remarkable. This type of clinker, which can be produced without changes in kiln technology, requires less thermal energy and significantly less limestone consumption, which can lead to savings of up to 35% in the carbon footprint.
However, the increased demand for aluminum oxide and calcium sulfate in CSA-type formulations has prevented their mass production, except in those locations where these raw materials are available, such as China. In this context, IMDEA Energy developed a study of the eco-efficiency of the production of CSA-type clinker, analyzing the influence of the type of fuel, the geographical origin of the raw materials and the possibility of using elemental sulfur as raw material. This component, a by-product from oil refineries, provides energy in its oxidation to SO2 and SO3, and contributes the necessary amount of sulfate to the formulation.
The results of the study, published in the Journal of Industrial Ecology*, show the need to restrict the content of ye'elemite, the main component of CSA clinker, to contents below 40% of the final formulation, due to the high demand for bauxite from CSA cements with a high content of ye'elemite. This fact reduces the potential environmental benefits and considerably increases the production cost of CSA type cements. In general, CSA production is more eco-efficient than conventional Portland cement in locations where raw materials rich in aluminum oxide are readily available.
(*) Eco‐efficiency assessment of calcium sulfoaluminate clinker production. José‐Luis Gálvez‐Martos, Antonio Valente, Mathías Martínez‐Fernández, Javier Dufour. Journal of Industrial Ecology Vol. 24 (3), 2020. https://onlinelibrary.wiley.com/doi/10.1111/jiec.12967
More information: José Luis Gálvez Martos, Senior Assistant Researcher, Systems Analysis Unit, email@example.com
Eco-efficiency chart for CSA clinker formulations as a function of bauxite origin, type of fuel and ye'elemite content of the final formulation.