A low-grade heat Organic Rankine Cycle driven by hybrid solar collectors and a waste heat recovery system

Against the backdrop of the ever growing scientific and public interest in locating alternative sources of clean energy, geared toward the overarching objective of mitigating the harmful implications of greenhouse effects on the environment, this paper proposes one such alternative. In capturing the environmental benefits to be gained from waste heat recovered during a cement industrial process, this paper demonstrates how an Organic Rankine Cycle (ORC) can be a viable source of power production. This owes to its ability to expend both medium and high-grade temperature heat sources. In the process of design and experimentation, this study adopted a hybrid solution using waste heat recovery (WHR) that was combined with a solar field, to transform power in the ORC through a thermal oil loop and produce electricity. The WHR was taken from flue gases of a rotary kiln found in cement industrial processes but that also has the advantage of working across a range of temperatures. These ranged from 250 °C to 380 °C. The solar domain incorporated a Parabolic-Trough Solar Collector (PTSC), with the working fluid R245fa. The performance of each component was then analyzed and optimized. The concluding results of this study evidences that an ORC can ultimately be of significant benefit to industry both economically and environmentally, by generating up to 323 to 360 kW of electricity that is required to power a cement plant, while providing for a payback time period within the range of 3.75 years and a net saving of 280,000 $/year.