Exergy-based resource consumption analysis of cement clinker production using natural mineral and using calcium carbide sludge (CCS) as raw material in China

The purposes of this study were to quantify the resource consumption intensity of cement clinker production using natural mineral in China and to determine the influence of the utilization of calcium carbide sludge (CCS) for cement clinker production on the resource-accounting result.

Exergy-based resource accounting method was adopted by this study. Cumulative exergy demand (CExD) was used to characterize the resource consumption intensity of cement clinker production using natural mineral in China. Exergy-based characterization factors of land resource and CO₂ emission were employed to determine the resource benefit brought by the substitution of CCS for natural limestone (land saving and CO₂ reduction).

The CExD value of cement clinker production using natural mineral as raw material in China is 5005 MJ/t, and the consumption of raw coal is the largest contributor to this result, accounting for approximately 81% of the CExD value. The phenomenon that coal consumption dominates the CExD result may be because, through combustion reactions, the chemical state of carbon contained in coal almost reaches equilibrium with its chemical dead state in terms of exergy and is deeply dissipated; in comparison, the major chemical compound contained in limestone, i.e., calcium oxide, is mostly transformed into cement clinker by the reactions occurred in the production system, instead of being consumed in a deeply dissipated way and emitted to the environment. The major disadvantage of using CCS for cement clinker production is the increase of coal consumption, i.e., 515 MJ/t cement clinker, and the major advantage of using CCS for cement clinker production is the resource benefit brought by CO₂ reduction (the avoided biotic resource damage in ecosystem), i.e., 1160 MJ/t cement clinker.

From the analysis on the influence of the substitution of CCS for limestone on the resource consumption intensity, we found that the resource consumption intensity of the production system using CCS is approximately 15.5% lower than that of the production system using natural mineral; however, if this resource benefit is neglected, the resource consumption intensity of the production system using CCS is approximately 7.6% higher than that of the production system using natural mineral. We suggest that establishing a theoretical bridge between the characterization models of biotic resource and abiotic resource will still be a significant research direction in the future, which is fundamental in objectively understanding and unifying the issues of emission reduction and resource saving.