(570f) Performance Enhancement of Steam Methane Reforming in Tubular Packed-Bed Microreactors

Rajasree, R. - Presenter, National Chemical Laboratory
V, R. K., National Chemical Laboratory
Kulkarni, B., National Chemical Laboratory

The key issue regarding the widespread commercialization of fuel cells is the ability to reduce cost and reactor dimensions to acceptable levels in both stationary and transport application. The fuel processor which produces H2 rich streams from hydrocarbon based feed stock have a major impact on overall system costs. Numerous research groups [1-10 ] in the world are actively involved in fuel processing and Research and Development has to go a long way in the development of cost-effective fuel processing and its overall optimization. The above processes are traditionally carried out in fixed bed reactors packed with catalysts. The reactions taking place are highly exothermic or endothermic in nature and controlling the reactor temperature is very crucial for optimum reactor performance.

For an endothermic reaction such as steam methane reforming (SMR), temperature gradients in the packed-bed can play a significant role in the process performance. In the present work, a dynamic 2D pseudo-homogeneous model incorporating basic mechanisms and the packed-bed reactor features have been developed to quantitatively study the effect of heat transfer limitations on SMR process behavior. The study shows there is a heat transfer limitation in the bed. Simulation studies have been carried out on SMR process with the aim of reducing heat transfer limitations and thereby increasing the process performance. This is done by simulating tubular packed-bed microreactors of various diameters and by applying catalyst dilution with an adsorbent which selectively adsorbs CO2 from the adsorption enhanced reaction zone. The study implies that packed- bed microreactors reduce heat transfer limitations and thereby enhance the process performance of SMR. For a catalyst loading of 6.25 gm, a packed bed reactor of 2.8 mm diameter gives complete conversion of methane with 80% H2 purity. For a constant total weight of solids, there is an enhancement in performance due to adsorbent dilution in the adsorption enhanced reaction zone and this increase strongly with decreasing reactor diameter. This permits larger cycle time for the cyclic operation of adsorption-enhanced SMR process. This is an added advantage in terms of operating cost. Increasing the catalyst dilution by increasing the adsorbent loading has a very significant effect on SMR performance. There is an increase in methane conversion from 40% to 100 % for an increase in dilution factor from 0.67 to 0.9 in packed bed reactor of 3 mm. The findings based on this study give an insight into the performance improvement of SMR process and will help in cost reduction and process miniaturization of fuel processor for fuel cell applications. Keywords: Steam methane reforming, Packed-bed microreactor, Mathematical modeling, Fuel cell, Heat transfer limitation

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