Practical carbonaceous fuels C. R. Shaddix

FIGURE 9.19 Hypothetical coal molecule as represented by Solomon [39]. Reprinted with permission from the American Chemical Society. 

FIGURE 9.20 Chemical structure of cellulose (a), which is a glucose polymer, and xylan (b), a typical component of hemicellulose. 

The effect of heating rate on evolution of volatiles is most clearly evidenced in the case of woody biomass, which has been shown to have a volatile yield of greater than 90% when small particles are rapidly heated to 1200°C and to have a volatile yield of only 65% when large particles are slowly heated to 500°C in the commercial charcoal-making process. 

With the importance of the devolatilization process to solid particle combustion and the complexity of the chemical and physical processes involved in devolatilization, a wide variety of models have been developed to describe this process. The simplest models use a single or multiple Arrhenius rates to describe the rate of evolution of volatiles from coal. The single Arrhenius rate model assumes that the devolatilization rate is first-order with respect to the volatile matter remaining in the char [40]  

Fits of Eq. (9.43) to the experimental data typically yield an effective activation energy of about 230kJ/mol, which is consistent with the activation energy for rupturing an ethylene bridge between aromatic rings [41], 

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