| OCR Text |
Show For petroleum coke particles between 18-77 um, Young (Ref. 21) found that the burning rate was limited by pore diffusion and surface chemical reaction. Young and Smith (Refs. 22, 23) have shown that petroleum cokes exhibit higher combustion rates than anthracite, bituminous coal char and pure carbons. Using the kinetic parameters developed by Smith, burn times were calculated (shown in Figure 5-5) at various particle diameters (spheres with no porosity) and particle temperatures for an average oxygen partial pressure of 0.1 atm as being typical of the combustion environment. Since the actual praticles/agglomerates have porosity, especially with delayed cokes and ultrafine grinds, actual burn times can be expected to be less than shown in Figure 5-5. The actual gas residence time in the Franklin combustor was determined to be on the order of 1 to 2 seconds, sufficient for complete burnout of ultrafine PETCOM expected with proper atomization. Influence of Gas Environment on Combustion Rates As much of the above described kinetic data was developed for burn rate dependence on oxygen, the influence of other gases on combustion rates is especially important considering the slurry fuel burning process where most of the oil constituent has burned before coke particles have ignited. This oil produces a gaseous environment containing primarily CO, CO2, NO, SO2, SO3 and water vapor. Several important studies have been performed recently on the influence of the gaseous constituents on carbon reactivity (Refs. 25, 26, 27, 28, 29). With the exception of water vapor, all decrease the weight loss of carbon in oxygen-containing environments. Equilibrium calculations were performed to determine the effect of atomizing steam flow rates on adiabatic flame temperatures using NASA CEC 71 (Ref. 30) computer program. Shown in Figure 5-6 is the influence of steam on adiabatic flame temperature at experimental conditions (250°F saturated steam) for a PETCOM fuel-to-steam ratio is 5:1. Thus, according to calculations, flame temperature is lowered by approximately 50°F at a fuel-to- steam ratio of 5:1 versus no steam at most excess air levels. Actual experimental thermocouple readings indicated a lower temperature of approximately 100 to 150°F for steam consumption of 19-28 |
