Do you know the maximum allowable concentration of hydrogen sulfide in the circulating hydrogen of a hydrogenation unit?
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In a diesel hydrogenation unit, the hydrogen sulfide concentration in the recycle hydrogen is maintained at 100 µL/L – is this high? What is the maximum allowable concentration of hydrogen sulfide in the recycle hydrogen of your hydrogenation unit? What kind of hydrogenation unit and catalyst are used? zhang (oneplustech@yahoo.com)
100 ppm isn’t high; we have a hydrogenation unit where the level is often 2%, but we struggle with the lack of desulfurization of recycled hydrogen.
In my personal opinion, there should actually be no limit set for the hydrogen sulfide concentration in recycled hydrogen. It varies depending on the raw materials used. If the type of oil in your device remains unchanged, and the raw materials fed into the device from upstream also remain unchanged, then it is still possible to set a specific value. But now refineries around the world cannot guarantee that their raw materials remain unchanged. So personally, I think this value can only be used as a reference, provided you understand the principle of hydrogenation. You will know when this value is larger and when it is smaller.
It needs to be determined based on the production conditions; if the products are of good quality and the equipment permits it, then a higher level can be used.
Studies have shown that when the volume fraction of hydrogen sulfide in the gas phase is above 0.3%, the sulfided structure of the catalyst can be well maintained. For the hydrogenation process using non-precious metal sulfide catalysts, a certain concentration of hydrogen sulfide must be maintained in the system; whereas in the hydrodearomatization process with catalysts based on active precious metals in their reduced state, hydrogen sulfide should be removed as much as possible. This is because only at a certain concentration of hydrogen sulfide do the active metal components of sulfide catalysts remain in their sulfide form and not get reduced by hydrogen.
It has nothing to do with the raw materials; it depends only on the properties of the catalyst. A slightly higher temperature for a short period is not a problem, as it only affects the catalyst’s performance and lifespan.
I quite agree with what was said on floor 5; at the same time, it’s also important to pay attention to whether the quality grade of the diesel fuel is Euro 3 or Euro 4.
100 ppm is a bit low; this will affect the catalyst’s activity. It is recommended to add sulfur or use crude oil with a higher sulfur content! Being too high is also not good; it affects the hydrogen partial pressure and leads to unnecessary increased compressor load!
It is reasonable to keep the hydrogen concentration in the circulating hydrogen between 1000–5000 PPm, but this also depends on the requirements of the catalyst being used.
Our unit is for diesel hydrogenation; the design pressure is 12.0 MPa. It uses Fuyan catalysts and has two reactors – the first reactor is used for refining, while the second is used for upgrading. The concentration of recycled hydrogen is around 2000. I think this concentration doesn’t need to be controlled. If the control is set too low, hydrogen loss increases, hydrogen sulfide accumulation rises, which causes severe corrosion to the equipment, especially the recycle hydrogen compressor. And it also needs to be adjusted according to the product quality.
Experts say that when H2S levels exceed 15,000 PPM, hydrogen desulfurization should be carried out; levels that are too high are not conducive to the progress of hydrogenation reactions； 2. It exacerbates equipment corrosion.