An example of simulating design calculation

The structural parameters for S-200 type radial flow ammonia synthesis reactor with two beds of indirect heat exchange between beds and capacity of 1,000 t/d are as follows For the first catalyst bed the internal diameter, outer diameter and height are, 1.17m, 2.946 m and 3.425 m, respectively with the volume of prereducted catalyst Fri of 19.6m for the second bed the corresponding values are, 0.650m, 2.946 m and 7.925 m, respectively with the volume of imreduced catalyst Vr2 of 51.4m . The particle sizes of the catalysts are 1.5mm-3.0mm. The direction of gas flow is from outer to center. 

The calculation is based on the mathematic model and fundamental data mentioned above and kinetic parameters listed in Table 2.18 and the restrictive condition is that the outlet temperature of first bed is not higher than 480°C and 500°C for ZA-5 and AllO-2 catalyst, respectively. The results obtained by simulating calculation are listed in Table 2.19. 

The considerable agreement is reached between the results of simulation design calculation and their actual operating parameters. It can be seen from Table 2.19 that under the same conditions the output of ammonia can increase up to 1,158.6 tons per day, if AllO is replaced by ZA-5 catalyst. The temperature of the whole reactor decreases, but that of outlet of the reactor rises. Thereinto, (1) the inlet temperature of the first bed decreases from 359°C to 325°C (2) temperature at the outlet of the reactor rises to 34.5°C which is still in the range of design values permitted (3) net ammonia value increases by 2.3%, and output of ammonia increases up to l,158.6t/d, or raises by 15.8%. 

The result of simulation design calculation shows that it is feasible to replace AllO by ZA-5 with high activity in the synthesis reactors used originally for AllO catalyst.However, it should be noted that ZA-5 is a new wiistite-based catalyst operating at low-temperatures. Its superiority can be better if it is used at low-temperatures. Therefore, it is not necessary to use it at high-temperatures at 

Ertl G. Catal. Rev. Sci. Eng. 21 201, 1980. In Boudart M, Djega-Mariadassou G. Kinetics of Heterogeneous Catalytic Reactions (Chinese), Translated by Gao C, Zheng S, Li C, Liu D, Shanghai Pudan University Press, 1988. 

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