Reactor shell

In many cases, cold spots on the reactor shell will result in condensation and high corrosion rates. Sufficient insulation to maintain the shell and appurtenances above the dew point of the reaction gases is necessary. Hot spots can occur where refractory cracks allow heat to permeate to the shell. These can sometimes be repaired by pumping castable refractoiy into the hot area from the outside. 

The violent motion of a fluidized bed requires ample foundations and sturdy supporting struc ture for the reactor. Even a relatively small differential movement of the reactor shell with the lining will materially shorten refractoiy life. The lining and shell must be designed as a unit. Struc tural steel should not be supported from a vessel that is sub-jec t to severe vibration. 

Erroneous use of aluminium instead of alumina pellets in a hydrogen chloride purification reactor caused a vigorous exothermic reaction which distorted the steel reactor shell. 

Thermal oxidizers must be built to provide the residence time and temperatures to achieve the desired destruction efficiency (DE). As such, thermal oxidizers are comparatively larger than catalytic oxidizers, since their residence time is two to four times greater. Historical designs of thermal oxidizers were comprised of carbon steel for the outer shell and castable refractory or brick as the thermal liner (a refractory is like a cement, which is put on the inside of the reactor shell to act as a thermal insulation barrier). Modem units are designed and built using ceramic fiber insulation on the inside, which is a lightweight material and has a relatively long life. Old refractory would tend to fail over a period of years by attrition of expansion and contraction. 

A- CONTACTOR REACTOR SHELL B- TUBE BUNDLE ASSEMBLY C- HYDRAULIC HEAD D- MOTOR E- IMPELLER F- CIRCULATION TUBE... 

Dehydrogenation of ethylbenzene to styrene. Lio.5Fe2.4Cro.1O4 with 12wt.% K2O and 3wt.% V2O3 catalytic pellets packed on reactor shell side. 

The reaction is exothermic, and the heat transfers to the water, creating steam. A backpressure control regulates how much steam is released from the reactor shell. The faster or slower the reaction, the more or less heat transfers, and the more or less steam gets generated. The controls also let in more or less fresh water, all this controlling the reaction temperature and rate ... 

There are other advantages of employing magnetic ball mills besides the control of mechanical milling modes. Since the centrifugal force becomes a secondary factor in milling, and the reactor shell rotates at low RPM, contamination from balls and shell wear is lower than in a vibrational or a planetary mill there is less ball wear involved and contaminations with Fe from steel become less of the problem. Also lower rotations and uniaxial movement of reactors paced on horizontal axle allow... 

A further improvement was the development of the reactor type unit using multiple tube-and-shell reactors for better temperature control (25). This type of reactor proved useful in larger installations and for selective polymerization of either C3 or C4 olefins only. The larger reactor type units are so arranged that the steam produced in the reactor shell by the exothermic reaction is used to preheat the feed to the proper inlet temperature. The tubes usually are from 2 to 6 inches in diameter. 

However, these processes have been found to be dangerous in that expins have occurred for one reason or another. Attempts to eliminate traces of hydrogen in the gas stream (one cause of expins) have led to the use of a Pd catalyst (Ref 28). Other attempts to keep the gaseous mixt below the use of a gas-absorbing solvent (Ref 40). Standard precautions now include sufficient maintenance procedures to eliminate plugged weep holes and corroded piping and reactor shells (Ref 41)... 

Several problems are associated with the reactor shell. Few workshops have annealing furnaces suitable for large reactors. Thus, to avoid annealing after welding and to keep the weight for transportation... 

If the inside surface of a large reactor is stainless steel, clad steel plate is the material of construction for the reactor shell. The extra cost for stainless steel cladding is relatively low. Highly polished surfaces in such reactors can best be obtained by electric polishing, which we effect by a special method. At present it is not possible to construct 100-m3 or 200-m3 reactors with enamelled inside walls. If sufficient protection could be provided against damage to enamel, which on large... 

A difficult problem is the transportation of the reactor shell from the workshop to site. Road transportation of the shell, about 6 m in diameter, is possible only if there are no obstacles such as bridges, tunnels, or bottlenecks. Transportation by rail is prohibited because clearance requirements are not satisfied. On the other hand, transportation by ship—also by river barge—can be done without difficulty. 

The particulate activity trapped on the membrane filters in the sampling packs increased during the first hour (Fig. 3.2). The concentration of condensation nuclei in air in the reactor shell was 1.2 x 1010 m-3. Megaw May showed that an accommodation coefficient of 5 x 10-3 (compare Section 1.12) would explain the observed rate of increase in particulate iodine due to adsorption on the nuclei. The subsequent decline in particulate activity was due to deposition of nuclei on surfaces. Surprisingly, in this and other experiments, release of stable iodine vapour into the containment shell 4 h after the start of the experiment made little difference to the concentration of particulate 132I. Subsequently, Clough et al. (1965) showed that the amount of... 

Fig. 3.2. Activity of radioiodine in air of reactor shell. O, First charcoal paper A, second charcoal paper x, membrane filter , charcoal pack.

From the contours of the stream function and a closeup of the flow field near the shroud and top cover plate, we note that the shroud causes significant recirculation at the top end of the catalyst bed. Also, the downward velocity field in the annular region between catalyst bed and reactor shell is found not to be uniform. The comparative... 

The high resistance offered by the support screens of Zone C leads to very low flow through that zone, and also leads to a recirculating zone in the annular space between the catalyst bed and the reactor shell. The non-uniform flow through the catalyst bed also brings about significant recirculation in the central pipe. In short, the model tells us that the mere removal of shroud and filling the catalyst in Zones B and C may not lead to capacity enhancements, due to the associated problems of maldistribution. 

Recirculation in the annular space between the catalyst bed and reactor shell is eliminated. 

Fig. 19. Vertical cross-section of the wiper-blade reactor. A, Sealing arrangement B, gas phase C, rotor D, sealing E, bearing F, excess gas flow G, gas collected from the liquid exit H, overflow vessel I, liquid exit J, rotor blades K, gas feed L, adjustable shaft M, baffles N, reactor shell O, cooling jacket P, cooling water feed and exit Q, sampling port R, grooves S, liquid phase T, gas-liquid interface U, top and bottom plates and V, liquid feed. (After Manor and Schmitz, 1984 also from Chaudhari et al., 1986, by courtesy of Marcel Dekker, Inc.).

Figures 1.6 and 1.7 offer a schematic representation of units of the Texaco and Shell type, whose special feature is to recover the carbon formed by washing with tvater, and then to extract the sludge obtained with naphtha. The extract can then be homogenized with the feed and thus sent directly to the partial oxidation reactor (Shell version), or previously treated by stripping by reboiling in the presence ofheavier hydrocarbons, such as fiiel oil or crude oil, in order to separate and recycle the naphtha (Texaco version).

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