OCR Text |
Show industrial burner environment, much of the effect of different fuels on ignition and flame stabilization phenomena that is observed is related to the presence of fuel droplets in the flow. It should also be noted that the chemical kinetic rates that apply to the flame stabilization process in industrial burners are those for fuel-rich combustion: primary zone equivalence ratios on the order of two are not uncommon. Flame temperature and laminar flame speed are two indicators of the effects of a given fuel on the combustion process, and while they may not be directly relevant to the processes which take place in an industrial burner, they provide criteria for approximating the effects that may be encountered through the use of an alternative fuel. Flame temperature is defined (at a given fuel-air ratio) by the thermodynamics of the fuel; in fuel-rich operation the fuel type, which influences the fuel decomposition pathway, also plays a role. Flame temperatures can be relatively easily defined in simple experiments and provide a useful indicator to the burner designer. Laminar flame speed, on the other hand, is not directly relevant to the turbulent combustion process in an industrial burner. However, it does serve as an indicator of the reactivity of a fuel and is thus useful to classify fuels and identify potential problems with their use. Laminar flame speed is defined by the interaction between the chemical reaction rates involved in fuel decomposition and the gas phase transport properties, and laminar flame speed experiments can be used, with appropriate analysis, to determine chemical reaction rate information. Chemical Kinetics The analysis of those phenomena grouped together under the chemical kinetics heading is dependent on determination of the fuel composition and chemical kinetics rate data. Soot, NO , and SO emissions phenomena are particularly related to fuel composition, since sooting tendency has been linked directly to fuel type, NO to the presence of bound nitrogen in the fuel, and SO to the presence of sulfur in the A fuel. All of these processes are, in general, rate limited. Thus kinetics date are directly relevant to their assessment: equilibrium assumptions can produce misleading estimates of soot, NO , and SO emissions. There are a number of inter- 3 xx actions between the completion of combustion and emissions reactions and the other aspects of the combustion process that lead to secondary relationships with other fuel properties. For example, the adiabatic flame temperature has been linked to sooting propensity, and thermal NO production is itself strongly dependent on temperature. All chemical kinetic processes exhibit some degree of temperature 1.2.8 |