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(C6HWO5)„

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The adiabatic flame temperature and product composition under conditions of direct combustion was calculated over a range of conditions extending from fuel-lean to fuel-rich modes (up to 10 mol of air). Twenty major species considered in the present analysis were: C (gas), C (solid), C2, CH, CH4, CO, CO2, C2H2, C3H8, H, OH, H2, H2O (vapor), H2O (liquid), N, N2, NO, NO2, O, and O2. Additional species (a total of up to 400) could be added using the JANAF tables, but the analysis time would increase with the increase in number of species considered. Results obtained with additional species showed minor changes in the results, but the overall trends remained unchanged. In order to provide a compromise between the extensive computational time and the quality of data, it was therefore decided to limit the calculations with the above species since the overall conclusions would remain unaffected. Results shown in Figure 15.12 for the seven samples reveal the importance of plastic on the distribution of adiabatic flame temperature. Increased plastic content in the waste yields higher temperature than 100% nonplastic, and the maximum temperature is obtained when burning 100% plastic. The adiabatic flame temperature shifts to correspond with lower number of moles of air with increase in plastic content. Inclusion of plastic with nonplastic materials has a significant influence on temperature whereas exclusion of certain plastic components within the mixture has negligible influence on the peak temperature. The higher predicted flame temperature with plastic is attributed to the direct result of higher heat content of plastic material.

The product mole distribution is calculated using SOLGASMIX [36] for different moles of air and the corresponding adiabatic flame temperature. Specifically, the products formed during the combustion of seven different samples in air were examined according to the following combustion equation:

Plastic/nonplastic + a(O2 + 3.76N2)

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Figure 15.12. Combustion of plastic and nonplastic materials in air.

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Figure 15.12. Combustion of plastic and nonplastic materials in air.

where the fuel (plastic/nonplastic) represents any of the seven samples examined here. The results shown in Figures 15.13a and 15.13b and 15.14a and 15.14b are for 100% nonplastic and 100% plastic, respectively. Yields of CO2 and H2O reach a maximum at stoichiometric conditions and then decrease as the number of moles of air increases for both the 100% nonplastic and 100% plastic (note the log scale for mole fraction in the figure). Concentrations of CO and H2 decay more rapidly with 100% nonplastic than with plastic due to the variation in the reaction temperatures. Emission of NO from both the 100% nonplastic and plastic wastes first increases with the increase in moles of air (up to stoichiometric mixture) and then decreases. A similar trend was found for the NO2 except for the nonplastic waste wherein the values kept increasing well into the fuel-lean region. The amount of NO and NO2 produced from nonplastic-fueled flames was higher than plastic-fueled flames. This is attributed to some chemical interaction between the reactive chemical species produced in highly luminous plastic-fueled flames since the temperatures in nonplastic flames was determined to be lower than in plastic-fueled flames. It is also to be noted that plastic waste contained some chemically bound fuel-bound nitrogen, which should have provided higher NOX. The results therefore show the importance of reaction chemistry on the formation of NOX in flames. The exact mechanism on the formation of NO and NO2 in these flames was outside of the scope of this study, but nevertheless this requires further examination. Formation of compounds such as H2S and HCl from the combustion of plastic is due to the presence of sulfur and chlorine in different kinds of plastics (see Table 15.9).

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