A low-carbon approach for lime production using self-propagating high temperature synthesis-driven limestone calcination

Limestone calcination produces calcium oxide (or lime), that forms the basis for the manufacturing of many critical engineering materials such as cement and iron-and-steel. Limestone calcination—an endothermic reaction—is regarded as one of the most energy-and-CO2 intensive industrial chemical reactions, and is facilitated by fossil fuels, since the high temperature requirement (∼900 °C) renders it less conducive to electrification through renewable energy sources. In this study, a novel, low-temperature (∼450 °C) pathway for ultrafast calcination of limestone using combustion synthesis or self-propagating high-temperature synthesis (SHS) is developed. SHS leverages exothermic heat from the combustion of lignin or biomass—as low-carbon fuels—mixed with limestone. Pelletized samples consisting of different limestone-fuel ratios are subjected to SHS reactions in a furnace maintained at 350 °C or 450 °C, and the degree of limestone-to-lime conversion is determined using thermogravimetry. The type and content of fuel and the kinetics of combustion influence the: (a) temperature evolution in the sample; (b) time to attain peak temperature and the total SHS time (<15 min); (c) expansion of the pellet; and (d) rate and extent of reactant-to-product conversion. The use of lignin alone, or an equal mix of lignin and biomass as fuel, achieves a limestone-to-lime conversion exceeding 90 %, contingent on processing conditions like pellet size and airflow rate. It is thus shown that SHS—which (i) uses less than half the energy, (ii) releases 25–30 % lower CO2 emissions, and (iii) is > 4X faster than a conventional thermal process—is a sustainable and viable approach for limestone calcination.