| Description |
Oxy-coal combustion technology has been suggested as the most promising strategy for retrofitting conventional coal power plants to generate electric power while capturing carbon dioxide. The current research addresses three issues in oxy-coal combustion, namely: 1- What is the effect of coal composition on the stability of co-axial turbulent diffusion oxy-flames? 2- What are the stability criteria for turbulent diffusion oxy-coal flames in an advanced triple concentric co-axial burner allowing directed streams of pure oxygen to be introduced into the combustion mix? 3- How does minimization of CO2 diluent affect radiant heat flux in the combustion chamber? It is hoped that data produced in this investigation can be used for validation of advanced simulations of the appropriate configurations considered. In order to address Issue #1 listed above, the consequences of differences in coal composition on flame stability for two types of coal in oxy-combustion were explored: Utah Skyline Bituminous and Illinois #6 Bituminous. Differences in flame stand-off distances at equivalent experimental input conditions were interpreted through differences in the structure of the two coals as well as differences in their pyrolysis behavior, as determined by fundamental solid state 13C NMR and Thermal Gravimetric Analysis (TGA), respectively. In addressing Issue #2, the consequences of segregating all the input oxygen into one stream composed of 100% oxygen were determined using the co-axial burners with different oxygen stream configurations. Flame stability, heat flux, and NOx formation measurements were taken to evaluate the differences. Flame stability was quantified through flame probability density functions (PDF) of the stand-off distance (determined using photo-imaging techniques). The PDFs obtained from these simplified prototype configurations led to physical insight into coal flame attachment mechanisms and the significant effects of fine coal particles and their radial transportation by large eddies on flame stability. Finally, in addressing Issue #3, impacts of reducing the amount of injected diluent CO2 (mimicking the minimization of the recycle ratio) on the radiation heat flux were explored. Radiant heat flux, gas temperature, and wall temperature measurements were taken, and a simple radiation model was developed to correlate the average gas temperature and radian heat flux. This study provided a better understanding of the radiation mechanism and the significant effects of soot radiation on the total heat transfer in the next generation of oxy-coal combustion. |
