During an emergency shutdown of a natural gas water vapor conversion top-fired furnace, can the conversion tubes be left without steam purging?
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We are a natural gas reforming hydrogen production plant with a capacity of 20,000 standard cubic feet per hour of hydrogen; it features an overhead burner. The operating procedures specify that in the event of an emergency shutdown of the reformer, the conversion tubes must be purged with steam for 10–15 minutes. Recently, technical service personnel from some conversion catalyst manufacturers said that during an emergency shutdown, there is no need for steam purging; it is sufficient to simply shut off the natural gas and steam. I was wondering whether, when your company’s natural gas conversion unit is shut down, the steam is turned off directly, without concern about carbon deposition in the conversion tubes?
The operation of the equipment should be carried out in accordance with the control logic established by the process engineers and the operating manuals; during operation, the maintenance team can make optimizations within certain limits based on their experience. But what this “technical service representative from the catalyst manufacturer” said sounded more like casual opinions expressed by someone who isn’t in the right position to make such judgments. It is recommended to ask him whether he can write down that purging is not necessary, sign it, and agree to take corresponding responsibility. Personally, I think steam purging is necessary; an accident could have serious consequences.
As catalyst manufacturers, they may focus only on the catalyst itself. Indeed, after an emergency shutdown, there is still a large amount of heat in the furnace, and since the catalyst is primarily nickel-based, it can handle such high temperatures without any problems; moreover, it doesn’t require passivation. However, one must consider the temperature resistance of the converter tubes. Therefore, overall, it is necessary to circulate a medium through the tubes after an emergency shutdown.
From a safety perspective, even after an emergency shutdown, steam must be introduced before reigniting the system. Needless to say, after an emergency shutdown, it’s essential to purge the system of hydrogen and methane. There are established operating procedures for this process; they can’t be changed at will. The catalyst manufacturer presumably shares the same view as mentioned above—that their catalyst remains in good condition under such circumstances