Reaction order, carbon combustion

Reaction Order. Studies of the reaction of oxygen with carbon at temperatures of interest for AFBC s suggest that it is near zero order in oxygen (62). Most models have been based on an assumed first order reaction but they can be readily modified to accommodate the more realistic lower reaction order (63, 64). The correction for order of reaction will be most important for the prediction of the combustion of recycled fines which are in the size range in which chemical kinetics dominate and for predicting the performance of pressurized fluidized beds. 

Carbon combustion reaction is first order and the rate of reaction is the rate controlling step. 

Equation (5.28) also incorporates the mass fraction of the combustible surface species, which is carbon wc here, and an effectiveness feictor rj, which is defined as the area of the reacting surface divided by the external (equivalent-sphere) surfece area of the particle [7] the latter is the basis for the reaction rate terms. The effectiveness factor and the carbon mass fraction determine the accessible surface of the particle, allowing the empirical adoption of a pore diffusion restriction as indicated in Equation (5.17). In the frequent case of the reaction order being unity, expression (5.28) can be simplified to... 

Figure la shows TG/DTG curves of the Ni(N03)2-impregnated caibon under 80% Arand 20% O2. As can be seen in Fig. la, mass loss of about 24% from 60 to 160°C can be attributed to the removal of surface physisorbed water and partial dehydration of the precursor. The maximum rate of mass loss occurs at 260°C due to the decomposition of Ni(N03)2 and the partial combustion of carbon template. A small peak at 330 °C may be due to the further loss of caibon template. The carbon combustion is completed at temperature higher than 400°C. It had been found that the presence of the metal nitrate can catalyze the combustion of the activated carbon [14], which results to sintering of the synthesized inorganic particles. Therefore, Ar was firstly passed over the Ni(N03)2-impregnated caibon before the oven was heated to 300°C in order to avoid severe combustion reaction, then Ar was switched to the 20% 02/Ar and heated to 500 °C for 200 min to remove caibon template completely in the preparation process. 

Exothermic reactions culminate at about 640°C. (point F), reflecting both accelerated oxidation and crystallite ordering. The down slope of the exothermic peak after 640°C. suggests that Combustible volatiles have been depleted, and reactive surface area has been reduced. The trace then tends to reflect the general endothermic character of carbonized coals. Smothers and Chiang (34) have demonstrated that this exotherm (F) is caused mainly by... 

Analogous experiments with mixtures of identical combustion temperature containing various excess amounts of carbon monoxide showed that the flame velocity is proportional to [CO ]1/2, where [CO ] is the carbon monoxide concentration in the reaction zone. From this it follows that the chemical reaction in a flame is first order in carbon monoxide. The role of water in the combustion of carbon monoxide is well known. Analysis of available data shows that the flame velocity is proportional to [H20]1//2, i.e., the reaction is first order in water vapor content. The influence on combustion of such flegmatizers as CC14 may be ascribed to the binding of hydrogen by halogen with the formation of a molecule of HC1, which is dissociable only with difficulty. However, the latest experiments by Kokochashvili in our laboratory show that the influence of the... 

The regeneration curves are often derived from CO2 generation data in closed-loop laboratory systems. It is assumed that the formal kinetics of soot combustion may be described by the oxidation of carbon with oxygen. A typical formal kinetic model comprises two parallel reactions of n-th order ... 

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