Heat Transfer Model for Regenerative Beds

Regenerative catalytic oxidizers (RCO) are an economic and effective means of controlling volatile organic compounds with concentrations exceeding 1,200 mg/m3 in a gas stream. However, factors influencing the performance of RCO when treating volatile organic compounds in gas streams have seldom been addressed. Therefore, this study presents a convection-dispersion model with an effective thermal diffusivity (alpha)e as a parameter to simulate the performance of RCO. To verify the effectiveness of the proposed model, a pilot-scale RCO was constructed with two 20 × 200 cm (inside diameter × height) regenerative beds. Gravel was used as the thermal regenerative solid material. Experimental results indicated that the model with an (alpha)e of 2.0-3.8 × 10-6 m2/s can be used to describe the time variation of solids temperature with the packing height at superficial gas velocities Ug of 0.080-0.382 m/s. Values of (alpha)e for the bed are closer to those for the gravel solids ((alpha)s = 1.0 × 10-6 m2/s) than for air ((alpha)g = 54 × 10-6 m2/s). Those results further demonstrate that the conductive heat transfer in the solid material in the axial direction of the bed is a major controlling factor for the performance of the RCO and the convective one is a minor factor in the present case.