Catalyst Bed Thickness and Diameter

Bed 2 is thicker than bed 1 to provide a longer gas residence time, Fig. 8.5. This is necessary because bed 2 input gas contains  

First (feed gas) catalyst bed Second catalyst bed Third catalyst bed 

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Fig. 8.5. Industrial 1st, 2nd and 3rd catalyst bed gas nominal residence times. They increase with increasing bed number. This is due to the increase in bed thickness with increasing bed number, Fig. 8.3. The points have been calculated from Table 7.2 s industrial catalyst bed thicknesses, converter diameters and converter input gas flowrates.

Nominal residence times of gas in a converter s catalyst beds are calculated from measured bed thickness, converter diameter and converter gas input rate. The equation is ... 

Fig. 1.2. Catalyst pieces in a catalytic S02 oxidation converter. Converters are 15 m high and 12 m in diameter. They typically contain four, Va-l m thick catalyst beds. SOj-bearing gas descends the bed at -3000 Nm3 per minute. Individual pieces of catalyst are shown in Fig. 8.1. They are -0.01 m in diameter and length.

Catalytic butane dehydrogenation can be successfully carried out in a laboratory scale fluidized bed reactor operating at 310 °C and at atmospheric pressure. The catalytic particles have diameter 310 pm and density 2060 kg/m. Such a reactor is 150 mm in diameter and has a fixed 500 mm long catalytic bed. When the catalyst bed is fluidized with butane blown at a velocity of 0.1 m/s, it becomes 750 mm thick. 

A bed of catalyst consisting of 200 g spherical egg-shell catalysts was employed in the fixed bed reactor. The catalyst bed was diluted by shattered steatite particles (0.9 mm < d < 1.6 mm) in a mass ratio 1 1 to obtain a plug flow system. The catalyst used throughout the study was prepared by coating spherical steatite particles of 4-5 mm diameter with a porous oxidic layer. The egg-shell catalyst contained 20 weight % active component, the thickness of the shell being 215 xm. The oxidic catalyst consisted mainly of Mo, V and Cu, its preparation has been described elsewhere [10]. 

Reactors. Catalyst type and size, bed diameter and thickness, heat-interchange facilities, cycle and regeneration arrangements, materials of construction, etc., must be specified. 

Figure 12 shows some results of pressure drop measurements over a 1-m-long internally finned round tube (4-mm internal diameter, six fins, fm height 1 mm, fin thickness 0.5 mm) with a cutoff angle at the bottom end of 60 . With n-decane as the liquid and air at ambient temperature and pressure as the gas, the pressure drop increases steadily with increasing gas velocity until a certain critical gas velocity is reached. Below this critical velocity, the pressure drop is low, viz., orders of magnitude lower than in a fixed bed of catalyst under comparable conditions. It can also be seen that under these conditions the superficial velocity of the liquid in the internally finned tube has little effect on the pressure drop. 

In principle, the LFR is a fixed-bed reactor with a very low aspect ratio, i,e the ratio of bed height to bed diameter. Typically, the thickness of the catalyst layers is in the range of 15-75 mm. Hence, the reactor can be considered as a pancake reactor, in which the pancake has been folded for convenient accommodation in the reactor space. Because of the shallowness of the bed and its very large cross section, the pressure drop is much lower than in the case of a fixed bed of more conventional dimensions. 

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