The relationship between desulfurization and conversion
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Gentlemen, our plant uses the tannin method for desulfurization, and the shift reaction is carried out using the medium-high-low process, with subsequent desulfurization also employing the tannin method. There is a problem here: according to the synthetic ammonia production process, the lower the hydrogen sulfide level after desulfurization, the better. However, for the low-temperature shift process, a certain level of hydrogen sulfide is required; otherwise, re-sulfurization occurs. Based on experience, it is acceptable to keep the hydrogen sulfide content below 50. Is it possible to carry out such an operation to increase the hydrogen sulfide level after desulfurization by about 30? Will this have any impact on low-temperature and medium-temperature catalysts? Given the different hydrogen sulfide levels required for desulfurization and conversion, are there any better control methods?
The key to increasing hydrogen sulfide is not conversion but desorption. Appropriately increasing the hydrogen sulfide content in semi-water gas is beneficial only for low-temperature shift; it has no significant effect on medium-temperature shift, but it has a considerable impact on high-temperature shift, potentially leading to deterioration in the high-temperature shift operation, excessive hydrogen sulfide levels in the outlet gas, or excessive hydrogen sulfide levels in the CO2 in the regenerated gas.
Would it be better to use membrane technology to improve the process? (I’m a beginner)
The medium-string low-flow process does not have very strict requirements regarding hydrogen sulfide levels entering the conversion system; generally, there is no special control over the hydrogen sulfide content in semi-water gas during desulfurization. We maintain this level at 0.03–0.07 g/m3, which ensures the proper operation of the medium-string low-flow system； Appropriately increasing the hydrogen sulfide concentration has no effect on medium-temperature shift catalysts ； The key to controlling hydrogen sulfide is stability; fluctuations in its level are factors that lead to desulfurization and should be avoided.
I agree with the view expressed on the second floor: increasing the impact of hydrogen sulfide on the conversion process slightly does not pose a major problem. However, it increases the desulfurization load for the shift conversion process. If this process fails, the hydrogen sulfide level after conversion will exceed the allowable limits. In our plant, carbon removal is carried out using an NHD solution, and the desulfurization efficiency of this solution is many times greater than its carbon removal (CO2) efficiency. If excessive hydrogen sulfide is removed during the carbon removal stage and sulfur is oxidized and precipitated in the solution, it can cause damage to pipelines and equipment.
As a supplementary note, when our plant operates with five units in production, the hydrogen sulfide level is between 60–90 before the conversion process (that is, after one desulfurization step); whereas with four units in operation, the hydrogen sulfide level is between 100–120
The points mentioned on floors 2, 3, 4, and 5 are correct; the key lies in your ability to adjust the level of exposure. If you can do so, it’s fine to increase it slightly.
I am transformable; strictly speaking, the quality level is medium, low, low, low. Normally, we are most afraid of high oxygen levels and excessive hydrogen sulfide levels. Although high sulfur is relatively favorable for low-temperature shift catalysts, it provides a wide reaction temperature range. However, both the sulfur tolerance of medium-temperature catalysts and the corrosion resistance of the equipment have their limits. At high hydrogen sulfide levels, the phase transformation stress that occurs when Fe3O4 converts to FeS can cause the medium-temperature catalysts to crack and break down. Meanwhile, in order to ensure that the CO output meets the required standards, the steam-to-gas ratio is increased; this higher steam-to-gas ratio further increases the load on the heat exchange vessels, disrupting the thermal balance of the system and leading to deteriorated operation conditions! Due to my limited skills, there may be biases in this work; I earnestly ask for the understanding and guidance of all experts!