Weekly Topic in Ammonia Synthesis Production: Why is the two-high-one-low operation method used for the temperature increase and reduction of ammonia synthesis catalysts?

The main purpose of catalyst reduction in the synthesis tower is to remove the moisture present therein. 1. Using a high gas flow rate enables the moisture generated during reduction to be removed quickly by means of the flow speed of the gas； 2. A high hydrogen-to-nitrogen ratio is used to leverage hydrogen in the reaction to generate more moisture within the catalyst, and it also facilitates the synthesis reaction by producing more heat ； 3. A low water vapor ratio is also intended to introduce less moisture into the catalyst bed in the initial stage. In short, these requirements are all aimed at ensuring that as much water as possible in the catalyst is removed as quickly as possible.

This is related to the properties of the ammonia synthesis catalyst. Ammonia synthesis catalysts are metal oxides that are inactive until they are reduced to elemental metals; therefore, heating and reduction must be carried out before the catalyst is introduced. The medium for temperature-induced reduction is hydrogen and nitrogen gas; the hydrogen in this mixture is used to reduce metal oxides into elemental metals. Water is certainly generated during this process, and water can cause poisoning of the reduced catalyst; therefore, increasing the space velocity can reduce the water vapor concentration, which is beneficial for catalyst reduction ； The purpose of a high hydrogen-to-nitrogen ratio is to increase the hydrogen partial pressure that reduces its weight, thereby facilitating a rapid reduction process. As for the reason for low water vapor, it has been explained earlier, so it will not be repeated here.

For a high hydrogen-to-nitrogen ratio, I think maintaining it between 2.8 and 3.0 is sufficient; there’s no need for it to be too high.

It is all to ensure that as much water as possible in the catalyst is removed as quickly as possible, thereby preventing the catalyst from undergoing repeated oxidation and reduction reactions

I agree with what was said on the first floor: when heating and reducing the catalyst in the synthesis tower, it is crucial to remove water vapor from the catalyst as quickly as possible, in order to prevent the catalysts in the lower layers of the tower (the number of layers varies; it can be 2, 3, 4, etc.) from undergoing repeated reduction due to the presence of water vapor. This helps to extend the catalyst’s lifespan and maintain its efficiency.

A high hydrogen-to-nitrogen ratio is used to leverage hydrogen in the reaction in order to generate more moisture within the catalyst, and this high ratio facilitates the progress of the synthesis reaction by producing more heat

During the heating and reduction steps in synthesis, using 2 high and 1 low is intended to prevent excessive water vapor concentrations from repeatedly oxidizing the already reduced catalyst and thereby reducing its activity!

Are there any corresponding papers on reduction theory?

The high hydrogen content is only relative, and it increases gradually. The ultimate goal is simply to remove the moisture

Moreover, for short-term parking, the synthesis tower is protected with nitrogen; simply increasing the temperature and pressure is sufficient to meet the requirements for normal production. Initially, the new catalyst should be exposed to a nitrogen atmosphere, with the bed temperature and hydrogen content being increased gradually in order to achieve catalyst reduction. Generally, catalyst manufacturers provide a complete heating and reduction protocol, along with guidance throughout the process