Chemical looping combustion for carbon capture
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Among the well-known state-of-art technologies for CO2 capture, Chemical Looping Combustion (CLC) stands out for its potential to capture with high efficiency the CO2 from a fuel power plant for electricity generation. CLC involves combustion of carbonaceous fuel such as coal-derived syngas or natural gas via a red-ox chemical reaction with a solid oxygen carrier circulating between two fluidised beds, air and fuel reactor, working at different hydrodynamic regimes. Avoided NOx emissions, high CO2 capture efficiency, low CO2 capture energy penalties and high plant thermal efficiency are the key concepts making worthy the investigation of the CLC technology. The main issue about the CLC technology might concern the cost of the solid metal oxides and therefore the impact of the total solid inventory, solid make-up and lifetime of the solid particles on the cost of the electricity generated. A natural gas fired power plant embedding a CLC unit is presented in this work. Macro scale models of fluidised beds (i.e. derived applying macroscopic equations) are developed and implemented in Aspen Plus software. Kinetic and hydrodynamic phenomena, as well as different operating conditions, are taken into account to evaluate their effect on the total solid inventory required to get full fuel conversion. Furthermore, a 2D micro scale model of the fuel reactor (i.e. derived applying partial differential equations), making use of a CFD code, is also developed. The results, in terms of the effect of the different kinetic and hydrodynamic conditions on the outlet gas conversion, are compared with the results using the macro-scale model implemented in Aspen Plus. Based on the micro scale (CFD) outcomes, the macro scale model is enhanced to capture the main physics influencing the performance of the fuel reactor. Thus, the improved macro scale model is embedded into different power plant configurations and mass and energy balances are solved simultaneously. Thermal efficiency evaluations for the different plant arrangements are carried out. A detailed economic evaluation of the CLC power plant is undertaken by varying two relevant parameters: fuel price and lifetime of the solid particles. The effect of the aforementioned parameters on the Levelised Cost Of Electricity (LCOE) is investigated and the resulting outcomes are critically discussed.