Fuel fired furnace models

Listed in Table 1 are the default values used in the CFD models. For initial calculations, the diameter of granules remained between 1.19mm and 2.38mm, the average of which was assumed as the default. The default flue gas composition is representative of that in a typical oxy-fuel fired furnace. It usually contains a high content of CO2 and H2O. Due to limitations on the expected materials of constmction for a pre-heating system, the default temperature of the incoming flue gas was assumed to be 800°C. 

Very often in the literature, the physical model used to describe a PBC system is a two-step model [18,19] that is, the conversion system and the combustion system are regarded as one unit referred to as the combustion system (combustion chamber, furnace), see Figure 14. The two-step model is based on the assumption that the conversion system is ideal that is, the conversion efficiency [3] is 100%, which is not the case in real solid-fuel fired systems. However, the two-step model is a functional engineering approach. 

Figure 5-23 has been used to correlate furnace performance data for a multitude of industrial furnaces and combustors. Typical operational domains for a variety of fuel-fired industrial furnaces are summarized in Table 5-7. The WSCC approach (or speckled furnace model) is a classic contribution to furnace design methodology which was first due to Hottel [op. cit.]. The WSCC model provides a simple furnace design template which leads to a host of more complex furnace models. These models include an obvious extension to a tanks-in-series model as well as multizone models utilizing empirical cold-flow velocity patterns. For more information on practical furnace design models, reference is made to Hottel and Sarofim (op. cit., Chap. 14). Qualitative aspects of process equipment have been treated in some detail elsewhere (Baukal, C. E., ed., The JohnZink Combustion Handbook, CRC Press, Boca Raton, Fla., 2001). 

Heat balance terms such as furnace stack heat loss as a fiiaction of fired fuel heating value and furnace efficiency are not calculated, mainly since these indices of performanee are not required in an optimization system that has the plant-wide operating profit as an objective function. These indices are remnants of local equipment or design optimization approaches. T5q)ically a plant s operation should not be constrained nor its performanee judged by these indices. Models can of course be easily used to ealculate these indices, and plant built to the furnace models to perform these calculations on-line. 

Baltazar, J., Carvalho, M. G., Coelho, R, and Costa, M. "Flue Gas Recirculation in a Gas-Fired Laboratory Furnace Measurements and Modeling." Fuel 76 (1997) 919-29. 

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