A modified intrinsic model for conversion rate of coal char particle in chemical looping with oxygen uncoupling conditions

Our previous particle-resolved simulation study has elucidated that the conversion of coal char particle at analogous chemical looping with oxygen uncoupling conditions (a relatively low temperature, e.g., 900 degrees C, and relatively low O-2 concentration but relatively high CO2 concentration, e.g., 1 vol% O-2+ 99 vol% CO2) is characterized by that the oxidation reaction happens peripherally while the gasification reaction happens inside the char particle; the total conversion rate of the particle can be modeled as the sum of the full oxidation conversion rate r ox and the partial gasification conversion rate phi r(gasi), i.e. r = r(ox) + phi r(gasi). In this work, based on the previous conclusions and under the framework of the Smith's model, a modified intrinsic model is proposed in order to simulate the conversion rate of char particle in typical chemical looping with oxygen uncoupling conditions more accurately. The main point of the proposed model is to determine the position of the interface between the oxidation region and the gasification region by the criterion that the local gasification rate is equal to the local oxidation rate. The accuracy of the modified intrinsic model is validated by comparing the model predictions with the particle-resolved simulation results. Using the modified intrinsic model, the conversion processes of char particles under different conditions are analyzed. The differences between the proposed model and the conventional models, which either consider the oxidation only or consider the oxidation and gasification contributions independently, are also analyzed.

Automated summary

Under analogous conditions, the conversion of coal char particles involves peripheral oxidation and internal gasification reactions. A modified intrinsic model is proposed to simulate the conversion rate more accurately, by determining the interface position between oxidation and gasification regions. The accuracy of the model is validated by comparing predictions with simulation results, allowing for analysis of char particle conversion processes under different conditions and a comparison with conventional models.