One thermodynamic parameter that is crucial to heat transport within the fluidized bed inside the rotary kiln, during clinker production, is the specific heat capacity. The particular parameter is often considered constant in the open literature, while, in reality, it strongly depends on the fluidized bed’s temperature and composition, considering that the temperature inside the kiln ranges from approx. 800 K up to 2000 K. For the current study, a mixing rule reported in the literature was applied in order to calculate the C_p of the fluidized bed, utilizing temperature and composition profiles available in the literature. An in-house code was developed for the comparison of the literature-reported C_ps and those resulting from the mixing rule. It was discovered that the C_p of the fluidized bed had a proportional increase with the increase in the temperature along the length of the kiln. The deviation between the two values (calculated and literature) is relatively small in some cases, whereas, in others, it is quite significant, ranging from 1.56% to 52.49%, thus making the adoption of the temperature-dependence of C_p necessary. Establishing a more accurate relation for the specific heat capacity leads to a better energy balance inside the kiln, which, along with other improvements, can lead to a decrease in the energy consumed and a significant reduction in greenhouse gas emissions.

The transition toward low-carbon cement production requires alternative fuels with improved environmental performance and resource efficiency. Refuse-Derived Fuel (RDF), produced from pre-treated non-recyclable waste streams, represents a promising alternative fuel; however, its heterogeneous and varying composition presents challenges for stable combustion and process optimization. In this study, a comprehensive physicochemical characterization of RDF was performed and compared with pet coke, a conventional, fossil cement kiln fuel. The analysis included manual sorting, particle size distribution, elemental characterization, Scanning Electron Microscopy coupled with Energy dispersive X-ray spectroscopy (SEM/EDS), X-ray Diffraction (XRD), thermogravimetric and differential scanning calorimetry (TGA/DSC), and Higher Heating Value (HHV) determination. The RDF sample exhibited a heterogeneous polymeric-mineral composition dominated by plastics, paper, textiles, and inorganic fractions. TGA revealed a broad multi-stage thermal degradation profile, while calorimetry indicated HHV of 19.2 ± 0.3 MJ/kg and ash content of 11.6 wt.%, compared with 34.57 ± 0.11 MJ/kg and 1.97 wt.% for pet coke, respectively. SEM/EDS and XRD analyses confirmed the coexistence of polymeric and mineral phases in RDF, whereas pet coke exhibited a predominantly carbonaceous and homogeneous composition. The generated dataset supports computational fluid dynamics (CFD)-based cement kiln combustion models and RDF utilization for fossil fuel substitution in the cement industry.