Allam cycle technical and cost readiness levels: A review of the current technology status

The Allam Cycle emerged as a near-zero CO₂ emission power generation technology that promised higher efficiency and comparable specific costs to conventional gas-fired power plants with post-combustion CO₂ capture. Yet its commercial deployment has been hindered by uncertainties in technical maturity, flexibility, and cost accuracy. This review provided a systematic assessment of the Allam Cycle using a combined technology readiness level (TRL), flexibility, and cost readiness level (CRL) framework that linked component-level maturity, operational flexibility requirements, and the quality of cost estimates. A structured matrix was developed to evaluate critical components, including plant control system, oxy-combustor, sCO₂ turbine, recuperator, and oxygen storage, against TRL, flexibility (startup, shutdown, load, and fuel variation), and cost class, using criteria adapted from established guidelines and recent sCO₂ literature. The analysis showed that, despite the common perception that the Allam Cycle approaches TRL 7 at the system level, most critical components remained in the TRL 3–6 range for a utility-scale plant, with the turbine and recuperator constrained by operating at up to 300 bar and turbine inlet temperatures above 1000 °C, which further hinders the commercial deployment. Existing performance assessments reported net electrical efficiencies up to about 54–55 % (LHV) for natural gas-fired Allam Cycles and 37–43 % (HHV) for coal-based configurations, but these figures were largely based on steady-state models with simplified treatment of ASU integration and limited part-load analysis. From a cost perspective, most evaluations relied on specific capital costs of roughly 1300–1850 $/kW and Class 4–5 estimates, corresponding to CRL 3–4 with wide cost tolerances and limited project-specific detail. The review identified the need for further experimental validation of oxy-combustors and sCO₂ turbines under relevant operating conditions, development of advanced recuperators, integrated dynamic control strategies with ASU and oxygen storage, and higher-fidelity, location-specific cost assessments. The proposed TRL–flexibility–CRL matrix provided a practical roadmap to align experimental programs, component development, and techno-economic studies with the TRL ≥ 7–8 thresholds required for large-scale power-sector investments. It also highlighted priorities for maturing the Allam Cycle into a commercially robust decarbonized power option.