Converter types

Fig. 7. Methanol converter types (a) quench, (b) multiple adiabatic, (c) tube-cooled, and (d) steam-raising.

The synthesis loop comprises a circulator (8) and the converter operates around 200°C to 270°C, depending on the converter type. Reaction heat from the loop is recovered as steam, and is used directly as process steam for the reformer. 

Selective testing replies by refinement of the same methods and yields a small group of the better catalyst-converter systems but with little variation of converter type. Recycle and reactivation procedures are treated as carefully as the main reaction, and the mechanical strength of the catalyst becomes a vital factor. At this stage it is desirable to discover the role of pore-size distribution, even if it cannot be eliminated, to operate under conditions close to the goal [closer to equilibrium, microcatalysts in fluidized beds, etc. (3 )] and to obtain rough estimates of catalyst life. 

FIGURE 10.80 Converter types (a) buck converter, (b) boost converter, (c) buck-boost converter, (d) nonisolated Cuk converter. 

To address the above drawbacks of conventional technologies, the Gas Institute NASU has used the principle of submerged combustion to develop a compact converter-type melting furnace that provides high-production rate while using very little refractory. 

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. 

Optimization of the control of an operating converter, and optimization of the design of the converter type and size. 

Reviews of the different converter types most frequently used in industrial applications are available in the literature. ... 

Paints and coatings can be divided into two categories convertible type which need a chemical reaction, such as oxidation or polymerization, and the non-convertible type which are formed by evaporation of the solvents. The former category includes alkyds, epoxy, esters, polyesters, urethenes, silicon and other resins. 

The most common binders used are chlorinated rubber, vinyls, silicones and urethanes. They are widely used paints, successfully applied under a wide range of conditions. They also belong to the convertible type of coating. 

In addition to the convertible Type A cabinet used in the Type B mode, there are two additional versions of the Class II Type B cabinet. These units differ from the Type A and B3 units mainly in the airflow velocities and proportion of air recirculated, as well as in certain other performance specifications. Class II Type B1 cabinetry allows a little more flexibility in working with volatile, toxic, or radioactive substances, since its exhaust is connected to an exhaust duct that exhausts the cabinet air directly outside the building (Figure 9.6). Because 70 percent of the circulating air in the cabinet is exhausted to the outdoors, most nonexplosive or nonflammable chemicals may be used safely in low concentrations. Microgram quantities of toxic, carcinogenic, or radioactive compounds may be handled in the Class II Type B1 cabinet, provided that the work is performed in the direct exhaust portion (behind the smoke split) of the work surface. 

The various converter types may be characterized by the temperature profile through the catalyst bed(s) or by the temperature/concentration profile (plots of temperature vs ammonia concentration for the gas passing the converter) (see Fig. 6.6a-d below). Such profiles are often compared to maximum reaction rate profiles, see Fig. 6.5 (from [460]). It is seen from this figure that when the temperature is increased (at otherwise constant conditions, including constant ammonia concentration), then the reaction rate will increase up to a maximum value when the temperature is further increased, the rate decreases until it becomes zero at the equilibrium temperature. The temperature/concentration points where maximum rate is achieved describe a curve, the maximum rate curve, which will normally be roughly parallel to the equilibrium curve, but at 30-50 °C lower temperature. It is clear that the minimum catalyst volume would be obtained in a converter where this maximum rate curve were followed. In the early days of ammonia production, available technology limited the obtainable size of the converter pressure shell, and the physical dimensions of the converter... 

The most important converter type using internal cooling with countercurrent flow in cooling tubes is the TVA-converter. A schematic drawing of the converter and the corresponding temperature- and temperature/conversion profile is shown in Fig. 6.6a. Feed gas enters at the top and passes in the annulus between the pressure shell and the basket to the bottom of the converter. In this way the pressure vessel is cooled (the feed gas is used as shell cooling gas ) so that a lower design temperature is applicable for the expensive pressure vessel. 

Fig. 6.6. Schematic drawing, typical temperature profile, and operating curve (temperature/am-monia concentration plot) for four important converter types, (from [471]) a Internal cooling, countercurrent flow (TVA-converter) b Internal cooling, cocurrent flow (NEC-converter) c Quench cooling d Indirect cooling (heat exchange)...

Stability problems and performance optimization of TVA-converters are discussed in [480,481,484,485]. A classical account of operating problems in a synthesis unit using TVA-converters is given in [496] which also gives mechanical details on the construction of a TVA-converter. Drawings showing mechanical details of TVA-converters may also be found in [23, 385, 497, 498]. TVA type converters have been used extensively, and may are in operation today. This converter type has been suggested quite recently for installation in new, relatively small plants (up to about 300 MTPD of ammonia) by process licensors such as Tosoe [499] and ICI [500]. 

Old converter types with countercurrent flow in cooling tubes are the Mont Cenis reactor [385, 503], the original Haber-Bosch converter [504], the Claude converter [505], and the old Fauser converter [506, 507]. These early converter types were all used in relatively small plants they are not used in modern processes. 

The most important example of this converter type is the M. W. Kellogg 3- or 4-bed Quench Converter which was used in a large number of plants. The converter is described in [490, 491, 527, 528]. A simplified drawing of a 3-bed... 

This converter type has given excellent service in industry. It is, however, due to the inherent weaknesses of the quench cooling system, not very efficient, and the performance has in many cases been improved by revamping, see Sect. 6.4.3.4. 

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