Converter axial quench

As discussed above, several different types of ammonia converters are available. These types include axial quench converters (e.g., standard Kellogg reactors), tube cooled converters (e.g., TVA and Synetix designs), axial-radii designs (e.g., Ammonia Casale retrofit) and Kellogg s horizontal design. Typical operating data for different types of ammonia converters are shown in Table 6.4204. 

Hoechst WHP Process. The Hoechst WLP process uses an electric arc-heated hydrogen plasma at 3500—4000 K it was developed to industrial scale by Farbwerke Hoechst AG (8). Naphtha, or other Hquid hydrocarbon, is injected axially into the hot plasma and 60% of the feedstock is converted to acetylene, ethylene, hydrogen, soot, and other by-products in a residence time of 2—3 milliseconds Additional ethylene may be produced by a secondary injection of naphtha (Table 7, Case A), or by means of radial injection of the naphtha feed (Case B). The oil quenching also removes soot. 

Figure 11.5 (cont d) (b) ICI quench converter with axial flow quench gas is injected and mixed by means of lozenges (Twigg 1996, p. 429 reproduced with permission from Catalyst Handbook, ed. M.V. Twigg, Manson Publishing Company, London, 1996.)... 

LEAD Process (Humphreys Glasgow, now Jacobs) [940], [1091]. The LEAD process is a highly optimized conventional approach with synthesis at 125 bar and two converter vessels, the first of which contains two catalyst beds with axial-flow quenching, while the second has a third bed with small particle size catalyst and radial flow. A consumption of 29.3 GJ/t NH2 is claimed. 

Lummus Process. For the Lummus process schemes [280], [940], [1095]-[1097] a consumption of 29.6 [941] to 33.5 GJ/t NH3 [1099] is quoted. In the synthesis section either an axial flow quench converter or a radial flow converter with indirect cooling is used. C02 removal is performed with a physical solvent, and there are no special features compared to other conventional process configurations. 

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. 

Quench cooling by injection of cold gas. The injection of quench gas can be either between adiabatic beds or into a catalyst bed at different locations. Flow in the catalyst beds can be either axial or radial in vertical converters or downwards in horizontal converters. 

Axial-flow ammonia converters should use a larger particle size of catalysts. For the multi-bed axial-flow converter with direct heat-exchange between beds (cold-quench) having a diameter of 1600-3200 mm and a production capacity of 1000 t d" or more, and the height of catalyst bed 10-12m, choose large particles with a diameter of 6.7-9.4mm and 9.4-13 mm to minimize the pressure drop. For an axial-converter with a diameter of 800-1300 mm, height of catalyst bed 7-8 m, use 4.7-6.7mm or 9.4 mm particles to keep the low pressure drop. For an axial-converter with a diameter of 500-600 mm, the height of catalyst bed is only about 5 m, 2.2-3.3 mm, 3.3-4.7mm, and smaller particles may be used to increase the ammonia production. 

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. 

This section will consider modern trends in converter design, and discuss how these relate to the design of the synthesis loop. Two general trends are apparent in modern converter design the use of a radial flow pattern instead of axial flow, and the use of heat exchange instead of quench gas between the catalyst beds. 

Fig. 6.7. Three-bed Quench Cooled Axial Flow Converter. M. W. Kellogg design, (from [491])...

An axial-radial flow converter has been introduced by Ammonia Casale [490,492, 551-553]. The special feature of this design is that gas can enter each catalyst bed both from the top (in axial direction) and from the side through perforations (in radial direction), see Fig. 6.11 (from [492]). The gas leaves the catalyst bed through perforations in the inner wall. There are no perforations in an upper part of the inner wall, and the gas entering at the top of the bed is therefore forced to flow through part of the catalyst in partially axial flow before it can leave the catalyst bed. This flow principle can be used in quench cooled... 

Fig. 6.19. Four bed Kellogg quench cooled converter after modification to Ammonia Casale s four bed quench cooled axial-radical flow concept (from [591])...

Ammonia Casale Axial-radial flow through three catalyst beds with inter-bed heat exchange or quench cooling. A second converter holding the third bed has been used. 

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