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

Highlights: • Thermodynamic assessment of WHR-ORCs to recover heat from biomass IGCCs with CCS. • Zeotropic mixture ORCs have slightly superior thermodynamic and techno-economic performance. • Maximum plant efficiency improvement (2.81%) is achieved in syngas cooling scenario. • Combined integration scenario results in plant efficiency improvement by 4.61% • LCOE of syngas cooling and combined integration scenarios is 35.42 and 49.76 €/MWh_e. 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 €/MWh_e 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 €/MWh_e 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.