Control criteria for sulfur content in the production processes of synthetic ammonia and urea
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Dear colleagues, in the process we have been testing recently, the levels of hydrogen sulfide and COS are particularly low. Especially after the decarburization step, the hydrogen sulfide level in the gas resulting from decarburization purification is 0, while COS is 0.03 mg/m³. In the purified carbon dioxide gas, the hydrogen sulfide level is only 0.06 mg/m³ and COS is 0.3 mg/m³. Before the decarburization step, however, the hydrogen sulfide level was 55 mg/m³ and COS was 0.56 mg/m³. The instrument used for testing is a gas chromatograph. I’m curious to know how others in the industry manage these levels There is currently skepticism regarding the data obtained from the instruments! ! ! :handshake :handshake :handshake :handshake :handshake Last edited by chenranbaobei on 2007-11-6 09:06 ]
“In the purified carbon dioxide gas, the hydrogen sulfide concentration is only 0.06 Mg/m3, while the COS concentration is 0.3 mg/m3. This level is suitable for industrial-grade carbon dioxide, but it is completely unsuitable for food-grade carbon dioxide; a concentration of over four nines is required. “Before the decarburization process, the hydrogen sulfide level was 55 mg/m3, and the COS level was 0.56 mg/m3 – which is quite high. It is acceptable for the carbonization process, but for ammonia synthesis and urea production, this value is quite high; it is detrimental to the system and increases the costs associated with subsequent catalysts and equipment. Generally, after the transformation and removal process, keeping it at 10 milligrams per cubic meter is beneficial for subsequent steps.
What I mean is the desulfurization efficiency in the decarbonization process when using propylene carbonate – whether it can reach the levels specified
Regarding the poster’s question, propylene carbonate is used in the decarburization process. If decarburization and desulfurization are carried out simultaneously, the hydrogen sulfide content in the purified gas can reach the levels specified. Since the hydrogen sulfide concentration at the inlet for decarburization is 55 mg/m3, all of this hydrogen sulfide ends up in the carbon dioxide-rich gas stream. It is definitely not possible to use this gas without any desulfurization treatment. Carbon dioxide gas must be desulfurized (dry or wet method)
After decarburization, all of the hydrogen sulfide ends up in the carbon dioxide stream. At present, the amount of hydrogen sulfide in the carbon dioxide gas is also minimal; therefore it’s a bit confusing. The color of the propylene carbonate solution is currently a bit abnormal
It can be analyzed from two perspectives: 1. There are errors in the data analysis; issues with the instruments have led to inaccurate values for sulfur content at the inlet and outlet, or the analysis method used is not suitable, meaning that such data has no reference value. 2. The gas separation in the propylene carbonate solution is incomplete; some sulfur-containing gases and CO2 remain. Given that the color of the propylene carbonate solution is abnormal, there is likely a problem, possibly due to quality issues with the solution itself. A comprehensive analysis should be conducted to investigate this matter. It is recommended to analyze the components of the carbon propyl liquid and rule them out one by one; this will naturally help identify the root cause.
Based on what I understand, the hydrogen sulfide level in the purge gas should be relatively high; it is necessary to analyze the hydrogen sulfide levels before and after decarburization as well as in the purge gas using chemical titration methods before drawing any conclusions
If trace amounts of hydrogen sulfide are detected in the exhaust gas, it indicates that hydrogen sulfide has been completely regenerated within the carbon propylene system and converted into elemental sulfur; as a result, the color of the carbon propylene will definitely be slightly red (purplish-red). At the same time, mild corrosion may occur in the equipment, so this should be checked. It would also be advisable to examine whether there is any sulfur buildup in the heat exchangers if possible.
There is indeed a lot of elemental sulfur at the moment; that makes sense
The Kellogg process requires that the sulfur content after desulfurization be kept below 3 ppm. Because sulfur is the main poison for conversion and transformation catalysts, and it causes permanent poisoning.
Normal! Maybe too much was carried away by the flashing! Or elemental sulfur is formed during system regeneration! Also, the concentration varies depending on the pressure level!