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HF Alkylation "scale" desposits in way of valve internals...

HF Alkylation "scale" desposits in way of valve internals...

HF Alkylation "scale" desposits in way of valve internals...

(OP)
Greetings to all:

The refinery where I am employed utilizes an HF Alkylation process; one over-pressurization scenario of the columns located in this process area can result in HF vapours being directed through relief valves and into a flare header.

The subject relief system has gate type valves installed immediately downstream of each relief valve discharge, and, upstream of the discharge connection to the flare header. During the valve installation, the hand-wheel of each valve was installed at the 12:00 position and was subsequently not possible to be reached for operating from the existing grating level - of course, these valves normally remain in the fully "open" position.

I had made a suggestion to rotate the valves approximately 135-degrees, such that the valve hadn-wheels could be easily accessed from the grating level; however, I was later informed of my poor decision, and was critisized for my lack of knowlege in way of the potential of HF scale deposition that could occur in way of each of the gate valve internals. I was subequently required to design platforms for Unit Operator access in way of each valve hand-wheel, which was not terribly diffcult to do.

I had one (1) "argument" in this case, where my stated position was that the system relief valves are not intended to open under any circumstances other than during a unit upset / column over-pressurization. My thinking was that if there was typically no HF vapor flow across the valve, how could any siginificant HF scale deposits develop? Well, right-or-wrong, I was ultimately "over-ruled".

I have tried my level best to research how one goes about determining the amount of HF scale that can build up inside of a valve, and, to what level of scale fouling of the valve internals can be tolerated before the valve becomes "difficult" to operate (I suppose that this is also contingent upon process chemistry, valve type, valve operating frequency, and the like...right?).

Virtually everyone who uses this forum has more knowlege about this type of matter than I do, so any and all comments (especially those with kind overtones) will be most greatly appreaciated.  

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