On the control of hydrogen sulfide concentration in the circulating hydrogen of hydrogenation units
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Recently, I’ve heard many people from design institutes saying that it’s not necessary to control the hydrogen sulfide concentration in the high-pressure gas; only the hydrogen sulfide concentration at the reactor inlet needs to be considered. What do you think? Should the hydrogen sulfide concentration in the recycle hydrogen of a hydrogenation unit be adjusted based on the concentration at the reactor inlet or that of the high-pressure gas?
The high hydrogen sulfide concentration refers to that of hydrogen sulfide separated as a product of the reaction, while the hydrogen sulfide concentration at the inlet of the reactor is that present in the hydrogen used in the reaction. In our design, we take the hydrogen sulfide concentration in the desulfurized recycled hydrogen as the standard, that is, the hydrogen sulfide concentration at the reactor inlet!
What we are looking at here is the hydrogen sulfide content of the high-pressure circulating hydrogen before it enters the desulfurization tower.
It’s better to control the hydrogen sulfide level at the reactor inlet!
Control the hydrogen sulfide content at the reactor inlet
The circulating hydrogen is used to control the concentration of hydrogen sulfide after desulfurization (i.e., at the reactor inlet); if this concentration is too low, the catalyst may undergo a reduction reaction with hydrogen, while if it is too high, it will inhibit the desulfurization reaction. The hydrogen sulfide concentration before desulfurization must be related to the properties of the feedstock; it’s not possible to control the concentration of circulating hydrogen by adjusting the degree of reaction!
What people usually mention is that the sulfur content in the raw materials is high, requiring desulfurization of the recycled hydrogen. If the sulfur content of the raw material is low, it is necessary to add sulfur to the system. As for how much sulfur should be added, should the control focus be on the hydrogen sulfide concentration at the reactor inlet or that in the high-pressure gas? Please feel free to share your opinions!
Without a desulfurization system, it is sufficient to ensure the presence of hydrogen sulfide in the circulating hydrogen system in order to prevent excessive reduction of the catalyst. The hydrogen sulfide concentration at the outlet of the high-pressure section and at the inlet of the reactor should be the same in theory; the hydrogen gas coming from the high-pressure section enters the hydrogen circulation compressor via a liquid separation tank, and then proceeds to the reactor. Thus, the hydrogen sulfide concentration at the outlet of the high-pressure section and at the reactor inlet should be identical in theory!
You still don’t understand what I mean. It’s about adding sulfur within the system; this sulfur is added continuously, rather than removing sulfur. So, how much should be added? It was previously believed in the industry that sulfur supplementation should be carried out based on the hydrogen sulfide concentration in the high-pressure gas; now, some people from design firms say that it’s not necessary to consider the hydrogen sulfide concentration in that high-pressure gas, as long as the hydrogen sulfide concentration at the reactor inlet is maintained. What I want to know is how to determine the hydrogen sulfide concentration at the reactor inlet
How does he obtain circulating hydrogen at the reactor inlet? High-pressure samples are taken at the circulating hydrogen compressor as a standard. I think it’s okay; no sulfur has been added, so there’s basically little to no waste hydrogen being released.
Is the quality of your oil that good? There aren’t even any impurities; then where is your sulfur injection point? As long as the hydrogen sulfide level in the recycled hydrogen is around 500 ppm, it ensures that the catalyst does not get over-reduced!