Synergy in co-combustion of oil shale semi-coke with torrefied cornstalk

- A synergistic effect did exist in the co-combustion process.
- The synergy effect was confirmed by the evaluated values of the activation energies.
- Burnout times in a CFB were predicted by AKTS-Thermokinetics Software.

Previous research has indicated that combing semi-coke with torrefied cornstalks can help to easily initiate combustion, and reduce the hazardous nature of semi-coke for disposal. Combustion experiments with oil shale semi-coke from Huadian retorts, torrefied cornstalk as well as their blends were conducted using a thermogravimetric analyzer under air atmosphere in order to assess the combustion behavior and synergy in the co-combustion process. Combustion kinetic parameters and predicted burn times in a circulating fluidized bed were then calculated using AKTS-Thermokinetics Software applying the differential isoconversional analysis of Friedman. The interaction index MR and an average activation energy values were used to analyze the synergy of the co-combustion process. The results showed that a synergistic effect was observed in the system: oil shale semi-coke and torrefied cornstalks during co-combustion. Interpretation of the MR curve indicates that the influence of the torrefied cornstalks on the combustion process is observed mainly during the second phase of the process. The shortest burnout time estimated in a circulating fluidized bed (CFB) was observed for a mixture of 70 wt% semi-coke and 30 wt% torrefied (275 °C) cornstalk.