Quench cooling ammonia synthesis

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).

In the converter, only one of the three cooling methods mentioned above can be used, also two of them can be combined for application. For example, the cold-quench type is used between the first and the second bed, and the indirect heat exchange type is used between the second and the third bed. Some interchangers between beds are placed outside the converter such as Brown converter (Fig. 9.22). It is worth noting that because the ammonia synthesis reaction on the Fe catalyst needs high temperature (400-550°C) and high pressure (over 10 MPa), the... 

A direct water quench cools the hot gasifier exit gases and scrubs out solids. The catalytic shift reaction converts most of the CO to H2 (H2O -1- CO = H2 + CO2). The acid gases (H2S, COS, and CO2) are removed, and sulfor is recovered. The plant hydrogenates residual small amounts of CO to CH4, and compresses the gas into the ammonia synthesis system. Nitrogen for the ammonia synthesis comes from the air separation plant that provides oxygen to the gasifiers. 

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 converters with radial flow the above mentioned disadvantages do not exist. Radial flow converters can be designed for very large capacities without excessive reactor diameter, and a low pressure drop can be maintained even with very small catalyst particles. The advantages of radial flow reactors for ammonia synthesis is discussed in [459, 502, 541, 542]. The pressure drop as function of catalyst particle size is discussed in [488]. Radial flow has been used in converters with cooling tubes [520], in quench cooled converters (see below) and in converters with indirect cooling (see Sect. 6.4.3.3.2). 

Synthesis at about 125 kg/cm g in a dry synthesis loop using two converters, the first a two-bed quench-cooled converter, the second a one-bed converter. Absorption refrigeration for ammonia recovery. Cryogenic pure gas recovery. 

In an ammonia plant (Figure 4.2), the synthesis gas from the reformer furnace is fed into a secondary reformer vessel, where air is added through a burner to create outlet vessel temperatures of -1,800° F (980° C). The outlet of the secondary reformer vessel is cooled in a quench steam generator and sent to a shift converter this is followed by a carbon dioxide removal system such as the one in a hydrogen plant. The purified nitrogen from the air added in the secondary reformer vessel and hydrogen synthesis gas is fed to a methanator to convert residual oxides of carbon back to methane (which is inert in the ammonia conversion) the gas is then compressed to -3,000 psia (2,070 kPa). The compressed synthesis gas is fed to an ammonia converter vessel. As the synthesis gas passes over catalyst beds, ammonia is formed. The ammonia product is then cooled and refrigerated to separate out impurities. 

The exothermic SO3- and NHs-synthesis are carried out in reactors of the type illustrated in Fig. 11.3-2 and Fig. 11.3-3, respectively. In ammonia- or SO3-synthesis the intermediate cooling may be achieved by means of heat exchangers or by injection of cold feed. With SO3 synthesis the heat exchangers are generally located outside the reactor. Special care has to be taken to provide homogeneous distribution over the bed underneath of the quench or the flow coming from an intermediate heat exchanger. 

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