Coal oxy-fuel combustion requires CO2 dilution (recycling) to reduce the furnace temperature for material protection. This enhanced CO2 concentration reduces the O2 reaction rate while CO2 gasification contributes to the char reactivity. These conflicting influences together with a competitive behavior between O2 and CO2 complicate char O2/CO2 combustion behavior. Individually quantifying the influences accompanying the replacement of N2 with CO2 and clarifying the competitive behavior are essential for predicting the char O2/CO2 combustion rate, but this is difficult to obtain via experimental approaches. Here, a simplistic atomistic simulation investigated the char oxy-fuel combustion behavior. In simulations, the reactants (O2 and CO2) were either permitted to both react with char or permitted to have only one reactive gas with the other being a passive (nonreactive) gas to explore reactivity for individual gases in a O2/CO2 atmosphere. Thus, gasification contribution to char reactivity was isolated and quantified, and the synergy between O2 and CO2 reactions was evaluated. Individually quantifying the CO2 influence on O2 diffusion was also achieved by comparing the simulation of reactive O2 in passive CO2 and N2. The variation trend in char size and apparent density is similar to the experimental observation and other modeling work in zone II. Replacing N2 with CO2 decreased the char oxidation rate by 8%, being attributed to the reduction of O2 external diffusion. Competitive behavior between O2 and CO2 was observed, where the O2 and CO2 reaction rate was respectively reduced by 10% and 45% from the reactions alone (the other gas being passive). The overall char reactivity for O2/CO2 is only 78% that the sum of individual gases but is 8% higher than O2/N2 under 21 vol % O2. Simulation under a higher O2 fraction (50 vol %) and lower gas pressure (20% of the gas molecules) were also conducted. These simulations are consistent with the emerging rationalization of contributing factors to char O2/CO2 combustion.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology