Reformer tubes Wall thickness

This means that only two of these three parameters can be selected freely. If q v is kept constant and dt increased, the number of tubes decreases, also decreasing the number of inlet and outlet hairpins. The pressure drop over the reformer also decreases, whereas the dimensions of the furnace box remain roughly constant. The catalyst volume, however, increases linearly with d (reduced SV, eq. (11)), and the total weight of the tubes increases more than proportional to dt due to the increased tube wall thickness. Thus, the total cost of the reformer tends to increase with increasing dt above a minimum diameter below which the tube wall thickness must be kept constant for odier reasons. 

Fig. 4. Configuration of a ceramic membrane reactor for partial oxidation of methane. The membrane tube, with an outside diameter of about 6.5 mm and a length of up to about 30 cm and a wall thickness of 0.25-1.20 mm, was prepared from an electronic/ionic conductor powder (Sr-Fe-Co-O) by a plastic extrusion technique. The quartz reactor supports the ceramic membrane tube through hot Pyrex seals. A Rh-containing reforming catalyst was located adjacent to the tube (57).

The reformer tubes typically operate at maximum temperatures of 1,600°F to 1,700°F and are designed for a minimum stress-to-rupture life of 100,000 operating hours. A 35/25 Ni/Cr alloy is used that is modified with niobium and microalloyed with trace elements such as titanium and zirconium. Smaller tube diameters provide better heat transfer and cooler walls. This reduces tube and fuel costs and increases tube life. But more tubes increases the pressure drop. The optimum inside tube diameter is 4 to 5 in. The wall thickness may be as low as 0.25 inch with a length of 40 to 45 ft. The lane spacing between tube rows must be enough to avoid flame impingement from the burners. Typical spacing is 6 to 8 feet. 

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