CFD Analysis of Coal Combustion With Oxygen/CO2/H2O Mixture

Abstract

Coal combustion with oxygen is considered one of the most effective methods to improve thermal efficiency, reduce pollutant emissions such as NOX, and facilitate capture of CO2 pollutant from flue gas. This paper presents calculations of oxygen coal combustion with flue gas recirculation. The coal is burned in oxygen/CO2/H20 mixture. In addition to solving transport equations for the continuous phase (gas), a discrete second phase (spherical particles) is simulated in the Lagrangian frame of reference. Reaction is modeled by a mixture fractions/PDF approach. Discrete phase modeling is used for the prediction of discrete phase trajectory and heat and mass transfer to/from particles. Drayton coal with a lower heating value of 27.8 MJ/Kg is used in this study. Coal is burned in oxygen/CO2/H20 mixture with a composition of VC02+H20/VO2 = 0 to 4. The results obtained in this study show clearly the benefit of burning coal with oxygen/CO2/H20 mixture compared to coal combustion with air. The CO2 emissions increases which will help to reduce the cost of CO2 capture, NOX emissions will also decrease because of the replacement of nitrogen in air by CO2/H20 mixture, and better devolatization and burnout of coal particles for coal combustion with oxygen/CO2/H20 mixture. In addition to that, with a CO2/H20 to oxygen volume ratio of 0.67, the gas temperature is the same as the gas temperature for coal combustion with air. No modifications of the combustor materials is required during the retrofitting of power plant with oxygen coal combustion systems.