426662 Thermo-Economic Investigation of a

Thursday, November 12, 2015: 4:50 PM
254C (Salt Palace Convention Center)
R. Porrazzo, G. White and R. Ocone, Chemical Engineering, Heriot-Watt University, Edinburgh, United Kingdom

Chemical Looping Combustion (CLC) is a technology able to convert energy whilst managing CO2 emissions. CLC involves combustion of carbonaceous fuel such as coal-derived syngas or natural gas via the heterogeneous chemical reaction with a solid oxygen carrier exchanged between two fluidised beds. The two fluidised beds usually operate in different hydrodynamic regimes: the so called “riser” works in fast fluidisation regime whereas the so called “fuel reactor” works in bubbling bed regime. In this work, a CLC power plant, which uses methane as fuel gas and NiO supported by Al2O3 as oxygen carrier, is implemented in a software widely used in industry, Aspen Plus, to evaluate the minimum solid inventory required to achieve full gas conversion and competitive thermal and CO2 capture efficiency. The modelling of the two fluidised beds takes into account both kinetic and hydrodynamic phenomena. We develop and simulate different hydrodynamic models for each fluidised bed able to incorporate into the commercial software the mass transfer, the variation of solid void fraction and the limiting conditions affecting the conversion. Taking into account mass and energy balances involved in the interconnected reaction system, the main variables affecting its performances are investigated: circulating solid flow-rates, the difference in solid conversion between the two reactors, the air/fuel molar ratio, the temperature and the pressure. Three different plant configurations are analysed and for each one of those the optimal operating conditions are applied in order to minimise the amount of solid loading needed to achieve nearly full gas conversion. The plant thermal efficiencies, as well as the CO2 capture efficiencies, are evaluated and the results are discussed in relation to the conditions needed to increase the thermal efficiency of the process. Furthermore, a detailed economic evaluation of the most efficient power plant configuration is undertaken by varying two relevant parameters: fuel price and lifetime of the solid particles. The effects of the aforementioned parameters on the Levelised Cost Of Electricity (LCOE) are investigated and the resulting outcomes are critically discussed.

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