Effect of the Characteristic Dimension of Catalytic Wall Microchannels and Microslits on the Performance of Microreactors Coupling the Methane Steam Reforming and Combustion Reactions: A CFD Simulation Study

G. Arzamendi¹,

I. Uriz¹, P.M. Diéguez¹, M. Montes², M.A. Centeno², J.A. Odriozola³, and L.M. Gandía^1,*

¹Departamento de Química Aplicada. Universidad Pública de Navarra, Campus de Arrosadía s/n, E-31006 Pamplona. Spain

²Grupo de Ingeniería Química, Departamento de Química Aplicada, Facultad de Ciencias Químicas de San Sebastián, UPV/EHU, Paseo Manuel de Lardizábal 3, 20018 San Sebastián, Spain

³Instituto de Ciencia de Materiales de Sevilla, Centro Mixto CSIC-Universidad de Sevilla, Avda. Américo Vespucio 49, 41092 Sevilla, Spain

^* Corresponding author. E-mail address: lgandia@unavarra.es (L.M. Gandía)

Both H₂ and syngas (synthesis gas, a mixture of H₂ and CO) are expected to play an increasingly important role in our energetic system. H₂/syngas production technologies can be integrated in Natural Gas Combined Cycle plants for precombustion CO₂ capture, in advanced systems as the Integrated Gasification Combined Cycle with or without capture of CO₂ for future coal-based power plants and, of course, for synthetic liquid fuels production through the gas-to-liquids (GTL) and coal/biomass-to-liquids (CTL/BTL) processes [1]. Syngas can be used also as fuel for high-temperature solid oxide and molten carbonate fuel cells [2].

Steam reforming of natural gas in conventional packed-bed reactors is the preferred technology for commercial large-scale H₂ and syngas manufacture. However, for small-scale stationary or mobile/portable applications as well as production offshore or in remote areas, microreaction technology offers a convenient solution [3-5].

In this work, a Computational Fluid Dynamics (CFD) simulation study on the thermal integration of the endothermic steam reforming of methane (SRM) and exothermic methane combustion reactions in microstructured devices is presented. In a previous study on this system, the effects on the performance of catalytic wall microchannels of the gas streams space velocities, SRM catalyst loading and steam-to-carbon (S/C) ratio were investigated [6]. In this work, the effect of the characteristic dimension (d = 0.35, 0.70, 1.40 and 2.80 mm whereas their length has been kept at 0.35 mm yielded 93% methane conversion while those with d = <st1:metricconverter w:st="&'on&'" productid="&'2.80" mm&'="">2.80 mm gave 87%. An analysis of the results has shown that mass transport limitations became an issue for the largest characteristic size as evidenced by concentration profiles as the ones that can be seen in Figure 1. Therefore, decreasing the characteristic dimension has the advantages of a higher surface-to-volume ratio and a lower influence of transport limitations.

When comparing the two geometries considered in this work it is found that the performance of the microchannels is better than that of the microslides; however, the differences are small, of the order of 3-6 percent units of methane conversion at the reactor exit. This is due to the improved heat transfer characteristics and surface-to-volume ratio of microchannels compared with the microslides. Nevertheless, the microslides can be manufactured more easily and at lower cost so they are an interesting option to develop steam methane microreformers.

Literature cited

1. Wei W, Kulkarni, P, Liu K. in: Hydrogen and Syngas Production and Purification Technologies (Eds.: Liu K, Song C, Subramani V). AIChE ? John Wiley & Sons Inc., Hoboken, NJ. 2010, p. 451-485.

2. Song C. in: Hydrogen and Syngas Production and Purification Technologies (Eds.: Liu K, Song C, Subramani V). AIChE ? John Wiley & Sons Inc., Hoboken, NJ. 2010, p. 1-13.

3. Tonkovich AY, Perry S, Wang Y, Qiu D, LaPlante T, Rogers WA. Microchannel process technology for compact methane steam reforming. Chem. Eng. Sci. 2004;59:4819-4824.

4. Tonkovich ALY, Yang B, Perry ST, Fitzgerald SP, Wang Y. From seconds to milliseconds to microseconds through tailored microchannel reactor design of a steam methane reformer. Catal. Today 2007;120:21-29.

5. Subramani V, Sharma P, Zhang L, Liu K. in: Hydrogen and Syngas Production and Purification Technologies (Eds.: Liu K, Song C, Subramani V). AIChE ? John Wiley & Sons Inc., Hoboken, NJ. 2010, p. 14-126.

6. Arzamendi G, Diéguez PM, Montes M, Odriozola JA, Falabella Sousa-Aguiar E, Gandía LM. Methane steam reforming in a microchannel reactor for GTL intensification: A computational fluid dynamics simulation study. Chem. Eng. J. 2010;154:168-173.