Numerical modeling of stagnation flows over porous catalytic surfaces
Başlık çevirisi mevcut değil.
- Tez No: 403327
- Danışmanlar: Prof. Dr. OLAF DEUTSCHMANN
- Tez Türü: Doktora
- Konular: Kimya Mühendisliği, Chemical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2015
- Dil: İngilizce
- Üniversite: Karlsruher Institut für Technologie
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 228
Özet
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Özet (Çeviri)
A one-dimensional stagnation-flow reactor model is developed for simulating stagnation flows on a catalytic porous plate. The flow field is coupled with the porous catalyst in its one-dimensional form. Mass transfer in the washcoat is considered for two different conditions, i.e. instantaneous diffusion (infinitely fast mass transport) and finite diffusion within the porous layer. Finite diffusion inside the washcoat is accounted by three different approaches: effectiveness factor approach, reaction-diffusion equations and dusty-gas model. Energy balance equations in the washcoat are included to investigate heat transport inside the washcoat. A new computer code, DETCHEMSTAG, is developed to execute the numerical model. The model and computer code have the advantage (over the alternatives; CHEMKIN SPIN and DIFRUN) of incorporating different models for internal diffusion in the porous catalyst layer and coupling the diffusion model with multi-step heterogeneous reaction mechanisms. The computer code also calculates the Damköhler num-ber in stagnation flows for investigating the effect of external mass transfer limitations. Direct oxidation of carbon monoxide over a porous Rh/Al2O3 catalyst is chosen at first as an example to apply the developed models and computational tool DETCHEMSTAG. A recently established stagnation-flow reactor is used to provide the experimental data and all necessary information to quantify the characteristics of the catalyst. The effect of internal mass transfer limitations due to a thick porous layer are discussed in detail for CO oxidation. Subsequently, external and internal mass transfer limitations in water-gasshift and reverse-water-gas-shift reactions over the porous Rh/Al2O3 catalyst are studied in detail. Dusty-gas model simulations are used to discuss the influence of convective flow on species transport inside the washcoat. It is discussed how the catalyst properties such as its thickness, mean pore diameter, porosity and tortuosity affect internal mass transfer limitations. The effect of pressure, flow rates, and washcoat thickness on CO consumption and internal and external mass transfer limitations is investigated. In addition, optimum working conditions for a commercial WGS catalyst are investigated. Finally, stagnation-flow reactor model is used to study the partial oxidation and steam reforming of methane over a porous Rh/Al2O3 catalyst. The effect of internal mass transfer limitations and convective flow on species transport in the washcoat in partial oxidation and steam reforming cases is investigated. The possible reaction routes (total oxidation, steam reforming, and dry reforming) inside the catalyst are discussed in detail. The influence of pressure and flow rates on syngas production is considered as well. The influence of heat transport limitations due to a thick porous layer is also discussed.
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