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COMSOL Conference 2014 Boston October 8-10 Patrick L. Mills Dept. of Chemical & Natural Gas Engineering Texas A & M University - Kingsville Kingsville, TX 78363-8202 USA [email protected] Transport-Kinetic Interactions for SO 2 Oxidation to SO 3 in Particulate and Monolith Catalysts Anuradha Nagaraj Dept. of Environmental Engineering Texas A & M University - Kingsville Kingsville, TX 78363-8202 USA [email protected] SO 2 Oxidation Catalysts SO 2 Oxidation Convertor 9 mm Daisy 12 mm Daisy 20 mm Rings 14 mm Rings 10 mm Rings 6 mm Cylinder Transport-kinetic interactions in commercial porous catalyst shapes used for SO 2 oxidation are analyzed using the Wilke, Wilke-Bosanquet, Maxwell-Stefan, and Dusty-Gas flux models. Particle effectiveness factors derived from the various flux models can differ for otherwise identical values for kinetic and transport parameters. Development of new catalysts having higher activity, lower pressure drop, and adequate crush strength to meet the anticipated reduction in SO 2 emissions from H 2 SO 4 manufacturing plants will potentially benefit by using this more realistic approach for particle-scale shape modeling. Introduction VK-38 Rounded Step Circle Cosine Light Bulb Catalyst Particle Shapes d P = 12 mm • Review the current state-of-the art in modeling transport-kinetic interactions for catalyst particle shapes utilized in the SO 2 oxidation. • Develop a rigorous modeling framework that accounts for diffusion and non-isothermal reaction in various realistic 3-D commercial catalyst shapes using different flux models. • Employ this framework to compare the performance of these various catalyst shapes under typical multi-pass convertor operation. Objectives Transport-Kinetics Particle Model 2 3 SO 3 SO2 2 P O2 SO2 SO3 SO2 O2 1 p K p K 1 414 . 22 K p p p - 1 p p k r SO 2 Oxidation Kinetics: (Collina et al, 1971) P i i r N p rxn r ) H ( - q Species Mass Balance: Energy Balance: where i = SO 2 , O 2 , SO 3 & N 2 T = 420 to 590 o C C D - N i m ei, i Wilke Model Dusty-Gas Model D 1 D x C - D v C D N x N n i j , 1 j k ei, e ij j n i j , 1 j i k ei, * i e ij j i i where Diffusion Flux Models C D - N i eff i, i Wilke-Bosanquet Model D 1 D 1 D 1 k ei, m ei, eff i, where D x D N x C - N n i j , 1 j e ij j n i j , 1 j e ij j i i i Maxwell-Stefan Model P S S V 0 V ) T , r(C dV T) r(c, P Effectiveness Factor P 32 d - V 2 pore * Dimensionless Velocity D / x 1 D n i j , 1 j e ij j m ei, Results Wilke Wilke-Bosanquet Dusty Gas SO 2 SO 2 SO 2 SO 2 SO 3 Maxwell-Stefan T 0 = 420 o C 11% SO 2 9%O 2 1-D Catalyst SO 3 SO 3 SO 3 CONCLUSIONS The Wilke model produces results that closely approximates those for the Dusty Gas Model for a uniform macroscopic pore structure for a given shape. However, the effectiveness factor varies with shape so it should be optimized in view of other factors, i.e., P and crush strength. Detailed data on pore structure would be captured by the Dusty Gas Model. Monoliths provide another potential catalyst platform for SO 2 oxidation. Detailed models that account for transport-kinetic interactions can provide rationale approaches for comparing traditional particulate vs monolith reactor performance. Monolith H 2 SO 4 Catalysts • In 1991, Bespalov and coworkers* at Moscow Chemical Engineering Institute developed a numerical model for SO 2 oxidation in monolith catalysts. • This is the only known open literature on SO 2 oxidation modeling for a monolith. • An opportunity ALSO exists to develop advanced models for the purpose of design and analysis. Modeling of SO 2 Oxidation in Honeycomb Structures *Bespalov, A.V. et al.(1991) Zhurnal Prikladnoi Khimii, 64(10) pp 2048 - 2053 Particulate Monolith SO 2 Profile SO 2 Profile Inlet Conditions T B = 420 o C 11% SO 2 9%O 2 ID = 2 mm OD = 6 mm Washcoat Thickness = 0.625 mm Channel Length = 75 mm Channel Width = 1.5 mm Particle Concentration Profiles SO 3 O 2 SO 2 Monolith Bulk Concentration Profiles SO 3 O 2 SO 2 Particulate vs Monolith Catalysts 1-D Adiabatic Converter Profiles ɳ = 1.06 SO 3 O 2 SO 2 SO 3 O 2 SO 2 ɳ = 0.92 Wilke Dusty Gas ɳ = 1.00 SO 3 O 2 SO 2 ɳ = 0.90 SO 3 O 2 SO 2 Wilke Dusty Gas 2-D Rounded Step Shape 2-D Light Bulb Shape SO 2 Profile SO 2 Profile SO 2 Profile SO 2 Profile Commercial Multi-Pass Convertor • Maximize activity • Minimize ΔP + Monolith Catalysts d pore = 638 nm ε = 0.44 τ = 2.7 *Reference: M. E. Davis, (1982) Chem. Eng. Sci., 37(3) pp 447-452 • Brinkman Equation • Forchheimer Correction Supporting Wall Channel Block Reactive Channel Inlet Outlet Excerpt from the Proceedings of the 2014 COMSOL Conference in Boston
