Thermodynamic and techno-economic assessment of pure and zeotropic fluid ORCs for waste heat recovery in a biomass IGCC plant

Abstract

The present study includes a thermodynamic and techno-economic assessment of Organic Rankine Cycle (ORC) for waste heat recovery (WHR) from three types of waste heat sources in biomass-fuelled integrated gasification combined cycle (BIGCC) plants equipped with carbon capture and storage (CCS). These include (1) the air separation unit (ASU) air compression intercoolers, (2) the CCS CO2 compression intercoolers and (3) syngas cooler at the water gas shift reactor outlet. The use of ORCs operating with pure working fluids and zeotropic mixtures is investigated. In each scenario, the optimal cycles that maximize plant efficiency improvement are determined and are subsequently economically evaluated. Among the three, the syngas cooling integration scenario leads to the highest plant efficiency improvement (2.81%) and best economic performance, showing a levelized cost of electricity (LCOE) and discounted payback period (DPP) of 35.42–35.67 €/MWhe and 5.7–5.8 years. Meanwhile, if all three heat sources are utilized, an efficiency improvement of 4.61% is achieved, while the corresponding LCOE and DPP are about 49.76–51.08 €/MWhe and 9.3–9.7 years. In all scenarios, the best thermodynamic and economic results are obtained by ORCs operating with mixtures. Despite their thermodynamic superiority, however, zeotropic ORCs have a relatively small economic advantage over pure fluid cycles.