Steam cycle options for capture-ready power plants, retrofits and flexible operation with post-combustion CO2 capture

The energy penalty for post?combustion carbon dioxide capture from fossil?fired power plants canbe greatly reduced ? independently of the intrinsic heat of regeneration of the solvent used ? byeffective thermodynamic integration with the power cycle. Yet expected changes in electricitygeneration mix and the current immaturity of post?combustion capture technology are likely tomake effective thermodynamic integration throughout the operating life of such plants a challengingobjective to achieve because of a requirement for extensive part?load operation and also formatching to future technology improvements. Most previous published studies have, however,focused on base?load operation of the power cycle and the carbon dioxide capture plant and withthe assumption of a fixed technology. For carbon dioxide capture?ready plants the characteristics of the capture plant are also not knownwhen the plant is designed. The plant must operate initially without capture at a similar efficiency to?standard? plants to be competitive. Capture?ready plants then also need to be able to be retrofittedwith unknown improved solvents and to be capable of integration with a range of future solvents. This study shows that future upgradability for post?combustion capture systems can be facilitated byappropriate steam turbine and steam cycle designs. In addition fossil?fired power plants with postcombustioncapture may need to be able to operate throughout their load range with the captureunit by?passed, or with intermediate solvent storage to avoid the additional emissions occurringwhen the absorption column is by?passed. Steam cycles with flexible steam turbines can beadequately designed to accommodate for part?load operation with these novel operating conditionsand with rapid ramp rates. Several approaches for effective capture?ready pulverised coal and natural gas plants are alsodescribed. These achieve identical performance before retrofit to a conventional plant with thesame steam conditions, but have the potential to perform well after capture retrofit with a widerange of solvents, at the expense of only a small efficiency penalty compared to hypothetical plantsbuilt with perfect foreknowledge of the solvent energy requirements. For existing plants that werenot made capture?ready, and provided sufficient space is available and other physical limits are nottoo constraining, ways to achieve effective thermodynamic integration are also discussed