Subscale Catalytic Honeycomb Combustor

The honeycomb catalytic burner tested in this work was a subscale version of the actual catalytic combustor proposed for the micro-gas-turbine-based power unit, and was embedded inside the high-pressure vessel (see Fig. 2.4). It comprised a 35 mm inner-diameter, 75 mm long (L) and 1.5 mm thick steel tube, wherein alternating flat and corrugated FeCr-alloy foils (with thickness d = 50 pm) were rolled up forming a honeycomb structure with a channel density of 400 cpsi. 

Visual inspection of the subscale unit revealed an overall good cross-section uniformity for the catalytic channels (see Fig. 2.4). The unit tested in this study differed from the proposed mesoscale catalytic combustor only in its inner diameter (all other geometric parameters were kept constant), with the former unit having a radial dimension 42% smaller than the latter. With the number of catalyst-coated channels being proportional to the honeycomb cross sectional area, the power output of the subscale unit was reduced nearly threefold compared to the mesoscale unit heat losses from the outer combustor surface were accordingly impacted due to the reduced surface area of the subscale combustor. 

The cross section of each channel was triangular with rounded corners and the equivalent hydraulic radius was — 0.507 mm. The FeCr-alloy foils were coated with a porous 5%-wt Pt/AbOa washcoat of 15 pm thickness. Details on the 

Reinke M, Mantzaras J, Bombach R, Schenker S, Inauen A (2005) Gas-phase chemistry in catalytic combustion of methane/air mixtures over platinum at pressures of 1 bar to 16 bar. Combust Flame 141 448-468 

Reinke M, Mantzaras J, Schaeren R, Bombach R, Inauen A, Schenker S (2004) High-pressure catalytic combustion of methane over platinum in situ experiments and detailed numerical predictions. Combust Flame 136 217-240 

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Fig. 2.4 High-pressure test rig fitted with the honeycomb catalytic combustor. Points A, B and C denote the thermocouple positions. Cross-section A-A presents a top-down view of the subscale catalytic combustor. All distances are in mm...

The test rig employed in this study consisted of a high-pressure cylindrical steel vessel with a length of 1.8 m and an internal diameter of 0.28 m (see Chap. 2). Visual inspection and accessibility of the reactor assembly was achieved via a 50 mm diameter quartz window at the rear flange of the vessel and two 350 mm long and 50 mm high quartz windows at the vessel sides. Experiments were performed in two different reactors. The first reactor was the optically accessible, channel-flow reactor presented in Sect. 2.1 therein, the use of in situ laser diagnostics (Sect. 2.2) allowed for the assessment of the catalytic reactivity of propane on platinum. The second reactor was a honeycomb subscale unit of the desired catalytic combustor (see Sect. 2.3), and was used for the evaluation of combustor performance characteristics. 

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