Technoeconomic Comparison of sCO2 and ORC Systems for Waste Heat Recovery

Various supercritical carbon dioxide (sCO2) power cycles are an emerging bottoming cycle technology for gas turbine waste heat recovery with potential advantages relative to Organic Rankine Cycle (ORC) systems, including improved performance, compactness, improved economics, nonhazardous working fluids, and faster ramp capabilities. This work compares a waste heat recovery system based on an integrally geared compander in a sCO2 preheat cycle configuration with split recuperator with a recuperated ORC in the literature. The integrally geared system is comprised of an 1800 rpm generator with high-pressure and low-pressure pinions splitting a two-stage compressor and expander. Cycle constraints and design drivers, and optimization of the sCO2 system are described, along with current technology readiness and full-pressure full-temperature opera ting experience of the various components including compressors, expanders, heat exchangers, and other system components. Both cycles are paired with a commercial 15 MW gas turbine, and the resulting system costs, performance, and other attributes are presented. The cycles are compared with an cold-side temperature of 35 °C, showing an ORC system output of 5066 kW and an sCO2 system output of 5660 kW, i.e. an 11.7 % performance benefit for sCO2. Additionally, cost and size requirements and costs for the sCO2 and ORC-based systems are compared, indicating comparable nominal costs for both systems and a potentially lower cost for sCO2 systems, particularly when an indirect heat transfer loop is needed.