Medium Diameter Tubes

In a study by Koripelli et al. (2010), one finishing superheater tube sample, from a coal-fired unit, was received for metallurgical analysis. The tube was specified as a 1.875-in. outer diameter (OD) x 0.330-in. medium wall tubing (MWT), SA-213 T22 Cr-Mo steel. It had been in service for 23 years. Figure 3.4 illustrates the as-received tube sample and the internal diameter (ID) view. Significant wall thinning was observed on the flanks of the tube, characteristic of coal ash corrosion. Very hard scale was observed on the tube OD. On the steam side, there was a thick oxide. 

For the design presented in Figure B.10.1. the reactor was simulated with catalyst in 2-in (50.4 mm) diameter tubes, each 20 feet (6.096 m) long, and with a cocurrent flow of a heat transfer medium on the shell side of the shell-and-tube reactor. The resulting arrangement gives a 90% conversion of IPA per pass. 

The H-type cell devised by Lingane and Laitinen and shown in Fig. 16.9 will be found satisfactory for many purposes a particular feature is the built-in reference electrode. Usually a saturated calomel electrode is employed, but if the presence of chloride ion is harmful a mercury(I) sulphate electrode (Hg/Hg2 S04 in potassium sulphate solution potential ca + 0.40 volts vs S.C.E.) may be used. It is usually designed to contain 10-50 mL of the sample solution in the left-hand compartment, but it can be constructed to accommodate a smaller volume down to 1 -2 mL. To avoid polarisation of the reference electrode the latter should be made of tubing at least 20 mm in diameter, but the dimensions of the solution compartment can be varied over wide limits. The compartments are separated by a cross-member filled with a 4 per cent agar-saturated potassium chloride gel, which is held in position by a medium-porosity sintered Pyrex glass disc (diameter at least 10 mm) placed as near the solution compartment as possible in order to facilitate de-aeration of the test solution. By clamping the cell so that the cross-member is vertical, the molten... 

Elutriation differs from sedimentation in that fluid moves vertically upwards and thereby carries with it all particles whose settling velocity by gravity is less than the fluid velocity. In practice, complications are introduced by such factors as the non-uniformity of the fluid velocity across a section of an elutriating tube, the influence of the walls of the tube, and the effect of eddies in the flow. In consequence, any assumption that the separated particle size corresponds to the mean velocity of fluid flow is only approximately true it also requires an infinite time to effect complete separation. This method is predicated on the assumption that Stokes law relating the free-falling velocity of a spherical particle to its density and diameter, and to the density and viscosity of the medium is valid... 

The reaction is exothermic and so to avoid serious temperature excursions the reactor consists of a bundle of narrow tubes, each a few centimeters in diameter, surrounded by a heat transfer medium. The catalyst consists of relatively large silver particles on an inert a-Al203 support. The surface area is below 1 m g". Promoters such as potassium and chlorine help to boost the selectivity from typically 60% for the unpromoted catalysts to around 90%, at ethylene conversion levels of the order of50%. 

P 29] A set-up comprising a steel caterpillar mini mixer and four steel tubes attached was used, being dipped into a cylinder completely filled with a cooling medium (scale-up set-up) [48,108]. By means of a 5/2-way valve, it was possible to switch the reactants to either of the tubes acting as delay loops, differing in inner diameter and hence residence time. 

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