Hydrogen production cycle
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When our plant starts hydrogen production and switches from a two-circuit circulation to a single-circuit circulation, it is necessary to depressurize the desulfurization system first, followed by pressurizing it again from the conversion system. Once the pressure is balanced, the system is switched to single-circuit circulation. The purpose of this is to maintain a certain hydrogen concentration in the system, which facilitates feeding. It should be noted that the desulfurization system does not require pre-sulfurization; only heating through circulation is needed. However, the conversion process requires reduction, and I don’t think this approach is very reliable. First, the catalysts in the hydrogenation reactor are prone to being reduced. Second, if pressure is not released during desulfurization and the system remains in two-circuit circulation, the hydrogen concentration in the system isn’t too low either, so there shouldn’t be any problems for a system that has just started receiving feed. I’m not sure if my understanding is correct ? I’d like to ask the experts here! ! ! :)
Nitrogen is generally used to raise the temperature in the desulfurization system. If a reducing gas is used, reduction does not occur below 220°C; it also does not occur within a short period of time (usually eight hours) at temperatures above 220°C. When the system is connected, depressuring the desulfurization section is done to ensure that the hydrogen concentration in the conversion system remains above 60%
1. Our approach is to reduce the conversion catalyst together with the medium-temperature shift catalyst, using a long-cycle operation mode. 2. Once reduction is complete, before feeding the material, shorten the cycle; after feeding the material for desulfurization, direct it to the flare, and maintain a constant temperature during subsequent processes such as conversion. Wait until the desulfurization analysis shows satisfactory results before feeding the material for conversion, thereby establishing a normal production process. 3. During the reduction process, the hydrogen concentration is very low, and the temperature at the inlet is controlled at around 220 degrees; thus, even when the feedstock is heated before being fed into the hydrogenation reactor, there is no need to worry about the reduction of the hydrogenation catalyst. Furthermore, depending on the catalyst used, medium-temperature shift catalysts release trace amounts of sulfur, and we do not add sulfur specifically to pre-sulfurize the hydrogenation catalyst.