OCR Text |
Show alternative fuel in an industrial combustor. This includes overall heat release reactions, critical to ignition and flame stabilization, combustion completion reactions, and those associated with soot formation and consumption and NO and SO v xx formation. Chemical kinetic rates pl3y a major role in the processes of ignition and flame stabilization and (along with gas phase transport properties) define the laminar gas phase flame speed. The relative importance of the other fuel properties listed in Table 1 depends on the specific combustion process being considered, and on secondary interactions which are not specifically included in the table. This can best be illustrated by reviewing each of the combustion process characteristics or indicators listed in Table 1. Liquid Fuel Combustion Fuel physical properties that affect droplet and spray formation and vaporization processes are of primary importance in the liquid fuel combustion problem; thermodynamic quantities such as the heat of combustion and vaporization also play a key role. Thus, in any combustion process that involves liquid fuels, data for these properties are important to the assessment of the use of an alternative fuel. Note that there are several aspects in addition to those listed that must also be considered in addressing alternative fuel usage in industrial combustors. An example is the role of liquid viscosity in determining mean drop size. Viscosity plays a strong role in the case of pressure atomization, but for airblast atomization there is almost no fuel viscosity effect. Similarly, volatility plays a key role when the difference between the ambient temperature and the droplet boiling temperature is small, but for large values of this temperature difference (such as would be encountered with air preheat, for example) the role of volatility is much diminished. Finally, assessment of the relative effects of the physical properties relevant to the spray formation and consumption process can be carried out using suitably defined spray formation and single-droplet burning experiments in advance of specific fuel physical property data. Gas Phase Combustion The major gas phase combustion mechanism considered in Table 1 is ignition and flame stabilization. This process is primarily dependent on gas phase properties and chemical kinetic rates, and depends also on the thermodynamic properties of the fuel. However, the dependence on gas phase physical properties is weak for an industrial burner in which turbulent mixing predominates. In fact, chemical kinetic rates only begin to affect the assessment of the use of different fuels near blowout. In an 1.2.7. |