Why does the temperature in the synthesis tower drop when the hydrogen-to-nitrogen ratio is high?

Either a high or low hydrogen-to-nitrogen ratio can result in poor synthesis reactions; when the reactions are not efficient, less reaction heat is released, and as a result, the temperature of the catalyst bed drops!

Reply to 2# 654262293: But we feel that the reaction seems to work better when the hydrogen-to-nitrogen ratio is 3.2 – both the temperature and the yield are better. Why is that? ?

Reply to 3# Kuju Kaiso: Don’t you use liquid nitrogen elution to remove trace amounts? So, the substances that go into the synthesis process are essentially hydrogen and nitrogen. Theoretically, these two gases react in a ratio of 3:1; in practice, the hydrogen-to-nitrogen ratio is kept slightly above 3:1, which increases the concentration of hydrogen as a reactant and thus facilitates the ammonia synthesis reaction. However, if this ratio is too high, it will have the opposite effect.

Theoretically, the reaction ratio should be 3:1. However, since the first step in the hydrogen-nitrogen reaction is the adsorption of nitrogen molecules on the catalyst, it is necessary to have a relatively higher amount of nitrogen; therefore, the reaction ratio is generally kept between 2.2 and 2.8 (I’m not sure exactly what the optimal value is). If the hydrogen content is too high, the reaction cannot proceed quickly enough, heat generation decreases, and the temperature of the catalyst drops

The hydrogen-to-nitrogen ratio is high because there is no ammonia synthesis reaction taking place in the synthesis tower, or very little of such a reaction; as a result, the heat generated is low. Meanwhile, the circulator continues to operate at the same space velocity, carrying away all the heat, which naturally leads to a drop in temperature.

Either a high or low hydrogen-to-nitrogen ratio can result in poor synthesis reactions; when the reactions are not efficient, less reaction heat is released, and as a result, the temperature of the catalyst bed drops! Theoretically, it is 3:1, but the actual value is slightly lower; generally, 2.5–2.8 is a good range, as an appropriate increase in nitrogen content facilitates the ammonia synthesis reaction, and nitrogen adsorption is the controlling step.

We keep it around 2.6 here

Regardless of whether the hydrogen-to-nitrogen ratio is high or low, the reaction does not proceed well; less heat is generated during the reaction, and with the amount of gas fed in remaining unchanged, the bed temperature cannot be maintained

You need to thoroughly understand the factors that affect synthetic reactions: pressure, temperature, catalyst activity, and gas composition. It is an exothermic reaction with volume reduction during synthesis; therefore, when catalyst activity remains constant and the gas composition is ideal, higher pressure and lower temperature are more favorable for synthesis. Of course, it is necessary to reach the catalyst’s optimal operating temperature, and the ideal gas composition is a ratio of 3:1 of hydrogen to nitrogen, without any inert gases. This ensures that the ammonia produced can be completely separated, and the hydrogen and nitrogen dissolved in the ammonia do not affect the hydrogen-to-nitrogen ratio in the recycle gas. In reality, things are not quite like this: one reason is as mentioned earlier, namely that the adsorption of nitrogen atoms on the catalyst surface is the controlling factor, with nitrogen atoms being adsorbed first followed by hydrogen atoms. Another reason is that the proportion of nitrogen dissolved in ammonia is higher than that of hydrogen; hence, it is best to maintain a hydrogen-to-nitrogen ratio of 2.8 during production. Depending on the setup and power capabilities of each factory, slight adjustments may be necessary. Excessive deviations can lead to inefficient production processes, either resulting in unstable output or high waste emissions and increased consumption. As for the drop in temperature, adjustments are necessary; the circulation rate is used as the main method, with auxiliary measures from secondary circuits, and in cases where the gas composition is severely inadequate, rapid replacement is the preferred approach