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SECTION I(b)

(13) New Reactor Design

(c) I.G. Farben Synol Reactor. (See reference I(b)/41 at end of this Section).

This oven was developed to carry out FT reactions and related synthesis. Considerable work was done by I.G. engineers to arrive at a theoretical basis before selecting a reactor for these exothermic reactions. Three possible arrangements were considered. (See report by Dr. I. Wirth of April 1942, Leuna., Reference I(b)/34 to I(b)/37 at end of this sections)/

  1. Catalyst inside the tubes.
  2. Catalyst between plates.
  3. Catalyst outside the tubes.

The following general conclusions were drawn:

  1. The catalyst in tube arrangement required the largest cooling surface and , based on total reactor-volume, contains the least amount of catalyst. But it may be arranged to give tall catalyst layers should that be required.
  2. The catalyst outside the tubes is superior to the reverse arrangement and the improvement becomes greater as the diameter of the cooling tubes decreases. Structural difficulties apparently are the main drawback.
  3. The plate reactor is also superior to the catalyst tube reactor. But for increased heats of reaction(or better for increased heat release per m3 of reactor), less control is afforded by the plate oven, as a substantial temperature gradient develops across the plate.

These conclusions may be only of theoretical interest and are of course based on arbitrary assumptions. Particularly, on the assumption that the heat transfer coefficient between surface and catalyst is the same. This is hardly the case as this coefficient varies with the direction of flow, which may be at a right angle to the tubes in the case where the catalyst is arranged outside the tube.

It was found that the plate-oven required 71%, the catalyst outside-tube oven only 60% of the surface necessary in the catalyst in tube type for the same temperature difference (∆ T) throughout the catalyst. For varying ∆T, it appears that the specific cooling surface of the catalyst outside-tube oven depends largely on the tube diameter used in the design and the larger the ∆T, the more apparent is this advantage over the catalyst in tube type.

An example may illustrate this:

An oven containing the catalyst in 20 mm. tubes is operated to give a certain ∆T max. through the catalyst. The surface required is to be 100%. A plate oven, in order to give the same ∆T would require 71% of the cooling surface (actually 77%, since the surface of the tubes traversing the plates must also be counted). An equivalent “catalyst-outside-tube-oven” using 50 mm. tubes would require 75% of the surface but if 20 mm. tubes are used only 63% of the surface is required. If however the “basic” catalyst in tube oven were using 50 mm. tubes (indicating a higher ∆T is permissible), then the surface for a plate oven would still be 77%, but the catalyst outside tube oven employing 50 mm. tubes would need only 65%, and if 20 mm. tubes were used only 52%. Thus the advantage becomes more apparent as the heatload decreases.

The design of the furnace, finally proposed for the plant, may be seen from the attached drawing M 4949-1 (Ammoniakwerk Merseburg) and a patent application. The tube bundle consists of a multitude of bayonet type tubes closed on one end. The circulation could be forced, but it was considered preferable to install the oven at a slight incline (6°) to induce natural circulation. In order to find the minimum angle required for adequate circulation, tests were carried out to establish the velocities of air bubbles in water ascending in an inclined tube as function of the angle. This report is attached. It was determined that a 6° angle gave sufficient flow. The oven otherwise resembles closely the Lurgi reactor, in regards to catalyst arrangement, pressure and general layout. The catalyst is again enclosed in a sheet iron box.

One of the major advantages in the design of this furnace is the simple filling and removal of the catalyst since no plates are used. The commercial oven was to contain 6.8 m3 of catalyst. The 18 mm. O.D. tubes were arranged in 28 mm. triangular spacing giving a total of 800 m2 cooling surface per oven. Results obtained on this type reactor are described in the section of “Synol”.

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