Heterogeneous chemical looping combustion (CLC) reactions and conjugate transports in large oxygen carrier particles were numerically investigated with computational fluid dynamics (CFD) approaches, in which a simplified noncatalytic reaction model was implemented for reducing intraparticle modelling computation. Volumic gas-solid reactions were treated as surface reactions based on the equivalent internal surface in the particle model. In large porous particles such as fixed bed CLC reactors, the heterogeneous reactions are often limited by intraparticle diffusion. Comprehensive analyses were conducted on transports across the particle surface and their influences on reactions inside the single particles. A threshold Reynolds number of external convections was found for the enhancement of intraparticle reactions. The heterogeneous reactions, intraparticle diffusions and interstitial transports in a fixed bed CLC reactor randomly packed with 597 spheres were thoroughly analysed with the same numerical approaches. Comprehensive insights of the temporal evolution and spatial distribution of scalars in the packed bed reactor were presented.
Coke formation inside radiant coils is one of the main problems during thermal cracking of hydrocarbons. The on-line preparation of the coating for coking inhibition is a promising technology because it provides more flexibility to the operators on site. The SiO 2 /S coating was prepared on the inner surface of coils in an 8-year-served GK-VI industrial cracking furnace. The effects of the coating preparation process on the operation of TLE were studied. The coking rates of the tube with and without coating preparation were evaluated by the trend change of tube metal temperature. Simulations of the coating deposition process were further carried out using the computational fluid dynamics approach. The results showed that a significant temperature increase at the outlets of TLEs during coating preparation were due to the accumulation of SiO 2 and S in a loose form under the TLE operating conditions when the concentration of coating precursors was 7500 ppm (wt. %). In the three tests, coating precursors were mainly completely consumed in tubes and TLEs. For the coated tube, the run time was extended by 4-7 days because the catalytic coking was decreased. No significant changes in the distribution of products and molar yields of main products were observed. In the simulations, it was found that increasing the inlet flow rate led to a more uniform thickness and improved the mass content of sulfur in the coating. In the tube bend section, circumferential nonuniformities for the deposition were due to circumferential differences in the temperatures and mass fractions. The mass fraction of S in the coating was within the range of 0.02%-0.1%. The control step for the SiO 2 /S coating deposition was kinetic. Based on the simulation results, the optimized coating preparation parameters were determined, i.e., the inlet flow rate of 15t/h, the outlet temperature of 1093K and the inlet mass concentration of 3000 ppm (wt. %).
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