On the intermediate-temperature shift reactor in natural gas-based hydrogen production plants
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During the shutdown, the system is not purged, and the hydrogen concentration remains around 80 percent. The bed temperature in the medium-temperature shift reactor is 320 degrees; will the removal of steam supply lead to excessive reduction of the medium-shift catalyst?
It seems there’s no impact. Every time other hydrogen-using facilities shut down, hydrogen production also goes into a large-scale cycle
At 600°C, the hydrogen supply to the furnace outlet is stopped, and nitrogen is introduced to displace it; after thorough displacement, the temperature is reduced and the steam supply is halted
Shutdown of the natural gas-based hydrogen production unit: reduce load, increase the water-to-gas ratio, and lower the temperature; natural gas supply is stopped when the temperature at the outlet of the conversion furnace tubes drops to 550–600°C. Steam is used to continue cooling during the conversion and intermediate conversion stages, while nitrogen is used for cooling during desulfurization. When the inlet temperature of the medium converter drops to 250°C, the medium converter is shut down, and the conversion furnace continues to use steam for cooling. The medium converter is cooled and purged using nitrogen supplied through the pipeline connecting it to the desulfurization unit. When the outlet temperature of the converter drops to around 350°C, the steam supply is stopped, and desulfurized nitrogen is used to continue cooling the converter. Therefore, during normal shutdown, there is no situation in which hydrogen remains in the medium-frequency furnace. In the case of an emergency shutdown, the converter is shut down immediately, and the natural gas used as feedstock is stopped; steam is then used to cool the converter and the medium shift reactor. There is also no risk of hydrogen remaining inside the equipment of the medium shift reactor during shutdown. After the unit is shut down, the conversion system needs to be completely purged with nitrogen to prevent the presence of hydrogen or natural gas in the system when it is restarted. If natural gas is present, carbon deposition will occur on the catalysts in the conversion furnace during the nitrogen circulation and heating process. Additionally, during this nitrogen circulation and heating phase, the raw material natural gas pipeline at the compressor inlet must be isolated using a blind flange. Remember! !
The medium-temperature catalyst should be iron oxide, right? After reduction, it becomes iron tetroxide; excessive reduction should be fine
There’s no fear of excessive reduction; the concern is spontaneous combustion and heat generation upon contact with air.