Gas purification issues in ammonia synthesis
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Differences between cryogenic purification and methanation methods, as well as their similarities and differences! !
These two separation methods have almost no similarities; the only difference is as follows: 1. The essence of cryogenic separation is gas liquefaction technology. Mechanical methods are typically used, such as throttling expansion or adiabatic expansion, to compress and cool the gas; subsequent distillation takes advantage of the differences in the boiling points of various gases to separate them. The feature results in high purity of the product gas, but energy consumption for compression and cooling is high. 2. Methanation involves the reaction of a small amount of CO and CO2 present in the feedstock with H2, under the action of a catalyst, to produce CH4, thereby removing them
The cryogenic purification method should be a purification technique that combines low-temperature methanol washing with liquid nitrogen washing; it is capable of completely removing impurity gases such as CO, CO2, and CH4, offering a high level of purity. The purified gas consists essentially of H2 and N2, so there is no need for a hydrogen recovery system in ammonia synthesis plants； The methanation method is a purification technique in which trace amounts of CO and CO2 are reacted with H2 under the action of a catalyst to produce methane; the purified gas contains a certain amount of methane, and its purity is relatively low, which requires hydrogen recovery in ammonia synthesis systems.
This post was last edited by Chemical Gas Purification on 2010-11-14 at 11:04. The two methods are completely different; essentially, one is a physical method while the other is a chemical method. It’s really difficult to find any common points between them, as even their products differ. The only thing in common is that both methods can effectively remove and purify carbon monoxide and carbon dioxide.
Deep cryogenic purification involves using the difference in temperatures at which gases are cooled to liquid state in order to remove gases that are not needed in the production of synthetic ammonia; it’s a costly process. Methanation, on the other hand, involves using catalysts in a methanation reactor to convert carbon monoxide and carbon dioxide into inert gases that have no impact on the synthesis of synthetic ammonia
Reply to 5# Primary School Student 009: Deep-cold purification refers to processes such as low-temperature methanol washing and low-temperature liquid nitrogen washing. It is not about liquefying gases through deep cold, as you might think; rather, it is a process in which harmful gases such as carbon monoxide, carbon dioxide, methane, and hydrogen sulfide are selectively dissolved and absorbed by liquid media at low temperatures, thereby removing them. It is similar to the conventional copper washing refinement process, only with a much higher level of purity.
Deep cryogenic purification of synthetic ammonia feed gas refers to the process of removing CO, CO2, CH4, and H2S from the feed gas using low-temperature liquid nitrogen washing at around -170 degrees Celsius; the methanation method involves reacting CO, CO2, and H2 in the presence of a nickel catalyst to produce CH4, which also serves to remove CO and CO2. This method consumes hydrogen, and the CH4 produced leads to an increase in the amount of gas that must be vented during ammonia synthesis.
As a supplementary note: cryogenic purification allows for precise control of the hydrogen-to-nitrogen ratio, and the synthesized fresh gas is clean. The methane method results in a large amount of off-gas
Deep cryogenic purification requires large investment and is suitable for the purification of large-scale ammonia synthesis systems. Methanation systems are simple to operate but not suitable for situations with large fluctuations in gas volume. The former is a physical change, while the latter is a chemical change.