Use of solar energy to sustain limestone calcination for ordinary Portland cement production

Cement manufacture is one of the most raw materials- and energy-intensive industrial processes; moreover, its contribution to global anthropogenic CO2 emission is estimated as high as 6%. Most of energy requirement and CO2 generation are mainly associated with limestone calcination (LC). The use of solar energy as non-carbogenic renewable source for LC was evaluated in this paper; to this end, a directly irradiated fluidised bed (FB) reactor has been employed as limestone precalciner upstream of a cement clinker production kiln. LC was carried out at 940°C in an atmosphere containing about 70% CO2. The experimental activity was devoted to assess the reactivity of calcinated lime toward the main clay components for the Portland clinker (PCl) production process, as compared to lime from ordinary calcination. Portland cements (obtained by mixing PCls with 5% natural gypsum) were hydrated for periods ranging from 2 to 28 days (water/cement mass ratio=0.5). Parameters as lime saturation factor, burnability, clinker phase composition and cement pastes hydration behaviour were assessed.