(342a) Large Eddy Simulation of Soot Formation in Oxy-Coal Combustion

Lignell, D. O., Brigham Young University
Josephson, A. J., Brigham Young University
Isaac, B., University of Utah, Institute for Clean and Secure Energy
Brinkerhoff, K., Brigham Young University
Oxy-Coal combustion is a promising clean coal technology. Typical combustion burns coal in air, resulting in a product mixture of water, nitrogen, and carbon dioxide. Separating carbon dioxide from nitrogen is costly. In oxy-fired combustion, nitrogen is first separated from air and a mixture of coal, oxygen, and (optionally) recirculated flue gases is burned. The resultant products are water and carbon dioxide, which are easily separated for subsequent sequestration. Oxy-fired combustion often occurs at high temperatures and under flow and thermal conditions that differ somewhat from combustion in air. Radiative heat transfer is a key process in such combustion as it is a primary source of heat transfer in steam generation applications. Radiation is present from gaseous species, ash, coal char, and soot, with soot being a significant contributor. Unfortunately, soot formation is a complex process. While much research has been done on soot formation in general, relatively little research has been published on soot formation in coal combustion. In oxy-fire systems with high water and carbon dioxide concentrations, and at high temperature, soot consumption via gasification may be significant. (Normally so consumption is dominated by oxidation reactions.)

We present a series of large eddy simulations in an oxy-coal combustor in which sensitivity to the soot formation mechanism is presented. Differences is flow, temperature, and radiative heat transfer are shown. We compare results using a previously published coal soot model, as well as extensions that include optimized gasification and oxidation rates. An advanced physics-based soot formation from coal tar mechanism is presented.