Converter types Radial flow

Retrofitting features of the more efficient reactor types have been the principal thmst of older methanol plant modernization (17). Conversion of quench converters to radial flow improves mixing and distribution, while reducing pressure drop. Installing an additional converter on the synthesis loop purge or before the final stage of the synthesis gas compressor has been proposed as a debotdenecking measure. 

Fig. 26. Experimental simultaneous converter inlet and outlet and predicted outlet CO. Vehicle Galaxie, 289 cu. in. engine with thermactor. Converter 392 cu. in. radial flow. Catalyst aged type F (12,500 miles vehicle). FTP inlet = 0.91%. FTP outlet (exp.) = 0.29%. FTP outlet (pred.) = 0.25%.

Figure 6 Schematic illustration of the flow pattern in a radial-flow autocatalyst converter of the type designed by Bosal.

Figure 17.21. Some recent designs of ammonia synthesis converters, (a) Principle of the autothermal ammonia synthesis reactor. Flow is downwards along the wall to keep it cool, up through tubes imbedded in the catalyst, down through the catalyst, through the effluent-influent exchanger and out. (b) Radial flow converter with capacities to l tons/day Haldor Topsoe Co., Hellerup, Denmark), (c) Horizontal three-bed converter and detail of the catalyst cartridge. Without the exchanger the dimensions are 8 x 85 ft, pressure 170 atm, capacity to 2000 tons/day (Pullman Kellogg), (d) Vessel sketch, typical temperature profile and typical data of the ICI quench-type converter. The process gas follows a path like that of part (a) of this figure. Quench is supplied at two points (Imperial Chemical Industries).

Kubec el al. (1974) developed a model for a radial flow quench type converter. Kjaer (1985) and Michael and Filippo (1982) formulated model equations accounting for radial as well as axial variation of temperature and concentration. They found that radial variations have insignificant influence on the model predictions. 

A new concept is proposed here which enables to eliminate these two constraints. This approach uses a new type of flow dynamical layout and constructional principles for the converter substrate. It will be shown that such substrate layouts, using a radial flow arrangement, permit the use of very high cell densities without any increase of back-pressure. In fact, the concept often allows back-pressure decrease and it also assures a very even flow distribution over the total substrate volume. 

Let us take the reduction program of ZA-5 catalyst at Topspe S-200-type converter with capacity of 1,000 t/d as example. The converter is a radial-flow reactor divided into two catalyst-bed and the indirect heat exchange between the beds. The structural parameters of the catalyst bed is as follows The inner diameter of first bed is 1.170m, outer diameter of 2.866m, height of 3.400m, filled with 18.8m ... 

In Haldor Tops0e s ammonia and methanol synthesis processes a series of adiabatic beds with indirect cooling between the beds is normally used, at least in large plants. In smaller plants internally cooled reactors are considered. In ammonia synthesis, the Tops0e solution is today the so-called S-200 converter (Fig. 7) and L6j. This converter type, which is a further development of the S-100 quench-type converter, was developed in the mid seventies the first industrial unit was started up in 1978, and today about 20 are in operation or on order. Both the S-100 and the S-200 reactors are radial flow reactors. The radial flow principle offers some very specific advantages compared to the more normal axial flow. It does, however, also require special catalyst properties. The advantages of the radial flow principle and the special requirements to the catalyst are summarized in Table 5. 

In methanol synthesis, the case for radial flow converters is less obvious. Tops0e has earlier proposed, the use of one-bed radial flow converters in large methanol plants. Later analyses, partly based on a change of catalyst type, have, however, led to the conclusion that axial flow should be preferred even in very large methanol synthesis converters. The reasons for this difference in reactor concept between ammonia synthesis and methanol synthesis are in the differences between the properties of the catalysts. As mentioned above, the ammonia synthesis catalyst is ideally suited for the radial flow principle. This is not true for the methanol synthesis catalyst. The reasons for not using the radial flow principle in methanol synthesis are the following ... 

Stea.m-Ra.ising Converter. There are a variety of tubular steam-raising converters (Fig. 7d) available, which feature radial or axial flow, with the catalyst on either shell or tube side. The near-isothermal operation of this reactor type is the most thermodynamically efficient of the types used, requiring the least catalyst volume. Lower catalyst peak temperatures also result in reduced by-product formation and longer catalyst life. 

One of the special rotary atomizers worth mentioning is the windmill type atomizer. In this atomizer, radial cuts are made at the periphery of a disk and the tips of segments are twisted, so that the disk is actually converted into a windmill that can rotate rapidly when exposed to an air flow at aircraft flight speed. The windmill type atomizer has been demonstrated 1171 to be an ideal rotary atomizer for generating a narrow spectrum of droplet sizes in the range most suitable for aerial applications of pesticides at relatively high liquid flow rates. 

---