Exploring the Potential of Silicon Tetrachloride as an Additive in CO2-Based Binary Mixtures in Transcritical Organic Rankine Cycle-A Comparative Study with Traditional Hydrocarbons

Carbon dioxide (CO2) has been recognized as one of the potential working fluids to operate power generation cycles, either in supercritical or transcritical configuration. However, a small concentration of some of the additives to CO2 have shown promising improvements in the overall performance of the cycle. The current study is motivated by the newly proposed additive silicon tetrachloride (SiCl4), and so we perform a detailed investigation of SiCl4 along with a few well-known additives to CO2-based binary mixtures as a working fluid in transcritical organic Rankine cycle setup with internal heat regeneration. The additives selected for the study are pentane, cyclopentane, cyclohexane, and silicon tetrachloride (SiCl4). A comprehensive study on the energy and exergy performance of the cycle for warm regions is conducted at a turbine inlet temperature of 250 degrees C. The performance of the heat recovery unit is also assessed to highlight its importance in comparison to a simple configuration of the cycle. This study shows that the cycle operating with binary mixtures performs significantly better than with pure CO2, which is mainly due to its better heat recovery in the heat recovery unit. The results show that the optimal molar concentration of the additives is in between 20% and 25%. Besides having better thermal stability, SiCl4 shows an improvement in the cycle thermal efficiency by 6% points which is comparable to cyclopentane (7.3% points) and cyclohexane (7.8% points). The optimal cycle pressure ratio for SiCl4 is also relatively lower than for other additives. The energy efficiency of the cycle with pure CO2 is around 45% which is also increased to 58%, 63%, 64%, 60% with pentane, cyclopentane, cyclohexane, and SiCl4, respectively. These results suggest that additives like SiCl4 could make CO2-based cycles more viable for power generation in warm regions.