OCR Text |
Show 5. ANALYSIS Understanding the complex combustion process of slurry fuels such as PETCOM is tantamount to predicting their behavior in a variety of combustion systems. While small-scale tests have shown excellent combustion efficiency of a high viscosity PETCOM with air atomization, lower pressure steam atomization tests indicate considerably lower combustion efficiency and carbon burnout. A detailed analysis of the test results along with proper consideration of the combustion processes of liquid and solid fuels has led to considerable insights to the nature of PETCOM and slurry fuels in general. The PETCOM combustion process proceeds through a number of stages as shown in Figure 5-1. Because of the plug flow nature of the Franklin combustion chamber used in our experiments, these dominating stages occur at various distances from the burner. Thus, the model we propose for the combustion of PETCOM occurs according to the following steps as the fuel is injected by the fuel atomizer: Atomization and fuel spray formation. Fuel oil evaporation. Secondary droplet breakup or droplet agglomeration. Particle/agglomerate ignition. Tertiary particle breakup. Diffusion-limited particle burning of large particles. Kinetic-limited particle burning of small particles. Particle extinction or burnout. As these processes take place, gas phase reactions are occuring as unreacted gases evolve from liquid/particle droplet and the isolated particle/ agglomerate. The mechanism of the burning of slurry fuel droplets is being pursued by a number of investigators. The combustion experiments and models developed for carbon slurry droplets by Faeth (Ref. 8) are very applicable to our PETCOM. As most of the petroleum coke particles burn beyond the fuel oil reaction zone, the influence of gaseous species, such as C02, CO, S02, H20 and NO on the particle combustion kinetics is of special interest to the study of PETCOM. 19-18 |