Contents of methane and argon in the synthetic ammonia cycle gas
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In ammonia synthesis, the hydrogen-to-nitrogen ratio of the recycle gas is a key parameter. Since argon is generally not analyzed and is included in the nitrogen amount, this leads to inaccuracies in the hydrogen-to-nitrogen ratio, and operations are mainly based on experience. Many facilities with such requirements maintain a table comparing coal types with the argon content in the recycled gas. Our company has never had argon analyzed; when we contacted the analysts, they said the conditions were not sufficient for analysis. I wonder what the methane and argon contents are in your recycled gas. The composition of our recycled gas is: CH4: 20%, H2: 53%-60%, with the remainder being nitrogen. In practice, 55% hydrogen seems to be appropriate, and the reaction performs slightly better when methane is kept at 19%. I checked the composition of the recycled gas from several manufacturers; the methane/argon ratio is around 3. I wonder if there is any pattern to it?
Generally, manufacturers do not have the facilities to analyze the argon content in the synthesis cycle gas; this content is related to the type of coal used as raw material, with different coal types resulting in varying levels of argon. Of course, the content of coal of the same type should follow a pattern; the problem is that even the types of coal available nowadays do not follow any pattern.
There is indeed no pattern in coal types; coal yards usually have more than a dozen different kinds of coal at the same time.
Argon is an inert gas brought from air separation units; its boiling point lies between that of liquid oxygen and liquid nitrogen. Due to its limited quantity, smaller air separation units do not extract argon, while larger units can extract it as a by-product. If it is not extracted, it will enter the synthesis system along with nitrogen; since the amount is small, online detection is generally not performed, and analysis can be carried out manually. The methane control for the three synthesis towers in our company varies; it depends on factors such as catalyst activity and circulation rate.