Suggestions on the composition of recycle gas
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Our company produces small-scale synthetic ammonia, with an annual output of around 4.7 tons of ammonia alcohol. The proportion of recycled hydrogen is generally maintained between 53% and 60%. We had not previously measured the argon content in the recycled gas; a full analysis of the recycled hydrogen was conducted a few days ago. The composition was as follows: Ar 9.01–9.08%, N2 14.92–14.56%, CH4 17.35–17.40%, and H2 58.72–58.96%. The ratio of H2 to N2 is approaching 4. Could this have an adverse effect on power consumption? Is there any way to address this issue? I hope everyone can give me some advice.
Increase the amount of gas released. What is your current synthesis rate, or in other words, what is the net ammonia output? Regarding the composition of this gas, the catalyst may function adequately at the beginning of operation; we are particularly concerned about your ammonia net value. If hydrogen recovery is available, then increase the vent gas flow rate. Keep the content of these useless gases that do not participate in the reaction, namely the inert gases, at around 10%.
With too much hydrogen, the power consumption should not be high. The hydrogen-to-nitrogen ratio in your area is indeed not optimal, and the content of inert gases is also high; I estimate that the net ammonia yield will not be very high. In such a situation, you should increase the amount of hydrogen recovered and purge the system
Remove methane, argon, and ammonia from the recycle gas; the remaining composition, when in a ratio of 3:1, represents the optimal amount of recycle hydrogen – adjust accordingly
Under normal circumstances, the Ar content should be around 30% of the methane content; however, given that the pressures in current synthesis systems are generally low, it is not unusual for the Ar content to increase. Since Ar requires instrumental analysis, it is recommended to confirm this result. If the results are confirmed to be correct, the hydrogen content in the circulating gas should be reduced, and the progress of the synthesis reaction should be monitored. Hydrogen content targets should be set on the premise of maintaining the system pressure at its lowest level, and then those targets should be implemented. By the way, what method was used by the original poster to determine the Ar content?
The ammonia net value is around 10%, and there is no H2 recovery unit downstream; all the gas released is burned in a flare, which is a bit of a shame. We are currently keeping the system pressure at around 28 MPa; if it rises, we release some pressure.
Initially, I estimated that the AR content was around 30% of that of CH4, but the results of the subsequent analysis were **unexpected. Using gas chromatography for analysis, the results should be reliable. Our analytical capabilities are quite strong; we are responsible for formulating many industry analysis standards.
Then, is there any way to increase the emissions of methane and argon while reducing the emissions of other useful gases during venting? For example, is it more advantageous to vent from a storage tank rather than from the system?
It would be best to find out what the argon content in the circulating gas is Chromatographic analysis can be used for this. This allows for an actual analysis of all components in the entire syngas. Then check the hydrogen-to-nitrogen ratio in the gas; a value of 2.0–2.8 is considered optimal.