A Study of an Oxy-coal Combustion with Wet recycle using CFD Modelling

Abstract

Coal use presents challenges for reducing emissions of air pollutants and carbon dioxide (CO2). In response to these challenges the research is focused on technologies that significantly reduce emissions of SO2, NOx, particulate matter (PM), and mercury (Hg), in order to develop toward “near zero emission” power plants. CO2 emissions are gaining significant attention. Greater reduction of CO2 emissions can be achieved by CO2 capture and geological sequestration (CCS). One of the most important technologies for CCS is the oxy-combustion, which, due to its almost N2-free flue gases, reduces the CO2 capture cost. The main aim of this work is to study, using the CFD commercial code FLUENT, the performances of pulverized coal combustion with exhaust gas recirculation, to evaluate the gas temperature and NOx emissions. Three dimensional steady-state simulations of a quarter of the IFRF no.1 furnace have been performed, for high-volatile bituminous coal. The Eddy Dissipation Model and Discrete Ordinates model have been used for turbulence-chemistry interaction and radiation respectively. The turbulence has been modeled using the standard k-ɛ model, with standard wall functions. A Lagrangian description has been used for the solid phase and empirical sub-models have been implemented for devolatilization and char burnout. Different combustion cases have been considered in several oxy-coal combustion environments, with different CO2/H2O concentrations in the gas recirculation. The effect of dry and wet recycle conditions on combustion characteristics has been considered. The results show the benefits in term of NOx emission in oxy-coal combustion. The temperature and emission profiles are influenced by the mixture of gas recycled, in fact the gas temperature and Thermal-NOx decrease when N2 is replaced by CO2. The simulations were performed with the same mass flow rate of oxygen at inlet in order to evaluate also the effect of CO2 and H2O.