What are the benefits of using molecular sieves in the ammonia synthesis process?
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What are the benefits of using molecular sieves in the ammonia synthesis process? All experts are welcome to participate in the discussion.
1. Absorb moisture; 2. Absorb carbon dioxide – the material commonly used for this purpose is 13X molecular sieve. This plays a significant role in protecting the synthesized catalyst.
Our process backend includes a cryogenic box process, and the most important role of molecular sieves is to remove most of the water from the process gas, thereby preventing freezing in the cryogenic box and avoiding blockages in the pipes and heat exchangers.
Small nitrogen fertilizers may not require such equipment. They just need to adjust the 3:1 ratio for the syngas compressor in the upstream section. However, in large-scale ammonia synthesis, the hydrogen-to-nitrogen ratio fed into the system is 2:1. There is a large amount of air.
In fact, the function of molecular sieves is to purify the syngas entering the synthesis tower and prevent catalyst poisoning in the tower. I wonder if it has a buffering effect? Seeking advice from experts
I’m not sure if the molecular sieve mentioned by the poster is the adsorption device used before washing with liquid nitrogen If it is mainly to prevent trace amounts of methanol and CO2 in the purified gas from the adsorption pre-process (low-temperature methanol washing) from freezing at low temperatures and blocking equipment and pipelines.
Apart from trace amounts of gases such as H2O, CO2, CO, and CH4, increasing the content of effective gases in the recycle gas boosts catalyst yield, reduces the amount of gas that needs to be vented, and increases ammonia production. The location where makeup gas is introduced can be moved to before the tower, which saves cooling energy, increases the ammonia content, and reduces the ammonia concentration within the tower; this in turn leads to higher yields and lower synthesis pressure.
We did not use molecular sieves; through pressure and temperature changes as well as methanation, the raw gas already met the required standards.
Reply to 5# zhya113: I think the statement regarding the purification of syngas is not accurate. In different process flows, the size and purpose of molecular sieves vary, but their primary function is to remove water; they also remove some carbon dioxide as well.
Adsorbs water, carbon monoxide, and carbon dioxide from process gas. 1. It can reduce the impact of oxides on ammonia synthesis catalysts. 2. It can prevent crystallization of syngas compressor blades (ammonium carbamate).
In addition to absorbing water and carbon monoxide and carbon dioxide, it can also determine whether there are any abnormalities in the upstream and downstream sections by means of absorption and regeneration temperatures, thereby providing better protection for the synthesis tower or cold box.