Refinery boiler flue gas evaluation on assessed Subcritical Organic Rankine Cycle (SORC) by applying R1234ze(E), R1234yf, and R134a pure and zeotropic mixtures

The Organic Rankine Cycle (ORC) has gained widespread adoption in recent decades due to its efficiency in converting medium-temperature heat sources into power. This study simulates and assesses ORC performance using AspenPlus (V10), focusing on subcritical conditions to achieve near-critical pressure to generate the highest net power output. This study examines the performance of pure and zeotropic mixtures of R1234ze(E), R1234yf (environmentally friendly hydrofluoroolefins), and R134a (a widely used hydroflurocarbon) in an ORC system. This study also addresses integrating the Subcritical Organic Rankine Cycle (SORC) system with a simulated and validated refinery boiler using actual operating data. The boiler was adjusted by modifying the combustion chamber pressure to generate medium-temperature flue gas output as a heat source in the SORC system. This integration demonstrates that the flue gas can be effectively utilized to increase the net power output of the system while simultaneously reducing the flue gas output temperature. Among the evaluated pure and binary zeotropic mixtures, the ternary mixture R1234ze(E)/R134a/R1234yf (0.7/0.2/0.1) achieved the highest network output of 1470.42 kW, surpassing all other assessed configurations. The binary mixture R1234ze(E)/R134a (0.8/0.2) followed closely, with a net power output of 1468.18 kW. The superior performance of zeotropic mixtures stems from their enhanced heat recovery capability, as evidenced by a 73.3%–76.6% reduction in flue gas outlet temperature. The zeotropic mixtures require a greater heat recovery demand due to lower flue gas output temperatures, leading to increased evaporator and condenser sizes. In turn, this raises the Specific Purchased Equipment Cost, impacting key economic indicators, such as Net Earning, Return on Investment (ROI), and Payback Period. While zeotropic mixtures significantly enhance heat recovery and net power output, they also increase capital costs. Understanding these implications is crucial for assessing ORC systems in industrial waste heat recovery applications, sustainability, and cost-effectiveness.

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