Application of an amine-based CO2 capture system in retrofitting combined gas-steam power plants

Abstract

Natural gas combined cycles (NGCCs) represent the main power generation technology in Italy, with a share of more than 40% of global thermoelectric power production. Due to their high operational flexibility, it is likely that NGCCs will continue to play a very important role in maintaining the reliability of supply in a power generation infrastructure characterized by the increasing spread of renewable energies. In this context, the integration of carbon capture technologies is regarded as an essential step to cope with the long-term climate protection target set by the European Union.This study investigates the retrofitting of three Italian NGCCs with a chemical absorption unit, capturing 90% of the CO2 from the exhaust flue gases. Two main options to meet the heat requirement for solvent regeneration are explored. The first provides for a medium-low pressure steam extraction, representing the main reason for power plant capacity derating. In the second option, steam extraction is partially replaced by external steam production from an auxiliary combined heat and power (CHP) unit that is designed to compensate for the additional power requirement of the CO2 separation and compression system equipment. Depending on the size and complexity of the NGCC, several types of auxiliary system are envisaged, basically differing in terms of the cogeneration technology and degree of integration inside the power block.Simulation results highlighted that the integration of an auxiliary cogeneration unit, besides eliminating power plant derating, has the potential to improve the energy and economic performances of the retrofitted plants to a certain extent.