CFD modeling of chemical looping combustion in fuel reactor with gaseous fuel

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

Chemical looping combustion (CLC) as a potential CO2 capture technology has been considered as a promising and likely alternative to traditional combustion technology to mitigate the CO2 emission due to its prosecution of CO2 sequestration at a very low cost. In CLC, solid oxygen carriers are introduced to transfer the oxygen necessary for the combustion from air through the initial oxidation in air reactor and subsequent reduction in fuel reactor. The CLC unit utilized in this study is composed of two interconnected fluidized bed including a circulating fluidized bed as the air reactor and a bubbling fluidized bed as the fuel reactor. While a number of studies on the hydrodynamic behaviour of the CLC process in fuel reactor have been documented in the open literature, there have been limited studies on the correlation between the bubble formation and the local volume fraction. The hydrodynamic behaviours and reactive characteristics of oxygen carriers are still not fully understood although a variety of experiments and simulations have been performed. This paper aims to investigate the CLC process in a fuel reactor using the CFD modelling, coupled with the heterogeneous reactions and investigating the hydrodynamics and reaction kinetics of the CLC process in the fuel reactor. A parameter correlating the occurrence of bubble and dynamic parameters is proposed. The parameter can be acted as an indicator of time-dependent bubble evolution with a potential to be adopted in the CLC for controlling the bubbling phenomena since the occurrence of the bubbles at specific positions is highly correlated with the local large eddies embedded in the flow. The static bed height variations in the fuel reactor system affecting the flow behaviour and kinetics of the CLC process are also discussed. The results obtained from the CFD simulations indicate clearly that the CFD model developed in the current study reasonably forecasts the hydrodynamic behaviour and important phenomena observed in the fuel reactor.