Synthesis loop energy flows

If the makeup gas to the ammonia synthesis loop is absolutely free of catalyst poisons, such as H2O and C02, it can flow directly to the ammonia synthesis converter. This leads to the most favorable arrangement from a minimum energy point of view. This can be accomplished by allowing the gas that leaves the methanation step to pass through beds of molecular sieves to remove water and traces of C02 74... 

After final cooling, the synthesis gas is compressed (7) and sent to the synthesis loop. The loop can operate at pressures between 70 to 100 bar. The converter design does impact the loop pressure, with radial-flow designs enabling low loop pressure even at the largest plant size. Low loop pressure reduces the total energy requirements for the process. 

Synthesis loops are normally of two types, depending on whether the NHs is recovered before or after compression. The first flow sheet (Fig. 1.19) uses less energy, but both loops scrub the recirculation gases with liquid ammonia, allowing partial dissolution of the impurities and extending catalyst life. 

The previous sections mainly considered the individual process steps involved in the production of ammonia and the progress made in recent years. The way in which these process components are combined with respect to mass and energy flow has a major influence on efficiency and reliability. Apart from the feedstock, many of the differences between various commercial ammonia processes lie in the way in which the process elements are integrated. Formerly the term ammonia technology referred mostly to ammonia synthesis technology (catalyst, converters, and synthesis loop), whereas today it is interpreted as the complete series of industrial operations leading from the primary feedstock to the final product ammonia. 

In order to meet the need to process with lesser energy consumption, the Topsoe corporation designed a synthesis loop (S-250 series), which included two converters, three beds and two waste heat boilers in order to by-produce high pressme steam as much as possible as shown in Fig. 9.3. The Topsoe S-250 series is composed of a radial-flow S-200 converter (1) with two beds and a radial-flow S-50 converter, and (2) with one bed. The outlet of every converter has the waste heat boiler to... 

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