A novel methodology for comparing CO2 capture options for natural gas-fired combined cycle plants

Three concepts for capturing CO2 from natural gas-fired combined gas/steam turbine power plants are evaluated and compared in this paper: (A) separation of CO2 from exhaust gas coming from a standard gas turbine power plant, using chemical absorption by amine solutions. (B) Gas turbine combined cycle (CC) using a semi-closed gas turbine with near to stoichiometric combustion using oxygen from an air separation unit as an oxidizing agent. This produces CO2 and water vapour as the combustion products. The gas turbine working fluid is mainly CO2. (C) Decarbonization, which comprises an autothermal reforming reactor with air-blown catalytic partial oxidation of gas natural gas, a water-shift reaction and a high-pressure CO2 capture process. The hydrogen-rich reformed fuel gas is combusted in a gas turbine CC, which is integrated (air, steam and heat) with the decarbonization process. A novel method is presented that compares power plant concepts including CO2. Instead of using extensive thermodynamic calculations for these concepts, reaction equations for the conservation of molecular species together with specific energy consumption numbers for the different process sections are used to characterize the concepts with respect to fuel-to-electricity conversion efficiency. With a combined gas/steam turbine power plant giving 58% total fuel-to-electricity conversion efficiencies (no CO2 capture), calculations for the concepts with CO2 capture including CO2 compression gave: (A) 49.6%; (B) 47.2%; and (C) 45.3%. The mechanisms leading to a reduced efficiency for concepts A-C are discussed and quantified and compared to combined gas/steam turbine with no capture of CO2. (C) 2002 Elsevier Science Ltd. All rights reserved.