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Level Switches

I have a question about some Level Switches. We have an Acid Gas knock-out drum at the front of our sulfur plant. It normally runs empty. It gets a little water, and a very little amine from our sweetening unit in it (unless we puke our regen). Because it's at such a low pressure, we have a couple of small pumps off the bottom of the vessel that pump the liquid out. Presently they're run by a couple of float style Magnetrol level switches (a low and a high) in 2 external float columns (the really old ones -- mercury switch). We have these switches all over the plant, and they work great, except here. They always hang up in the column, primarily because of the crap that gets built up on them. Anyone whose worked in a sour gas facility should know the stuff I'm talking about. That black stuff. Anyway I'm wondering if anyone has ever had a similar problem and how it was solved. It would be nice to use the existing columns, just put something else inside them.

Thanks.

Curtis

Reply to
Curtis
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Curtis

sounds like your level measuring device will not work because of the crap going in to the tank. have you considered ultrasonic level measurement? This is better than a DP level measure as it is not affected by density changes or crap build up.

Ultrasonic measurement is not effected by pressure variations, but u need to consider surface material (obscured by foam/dust clouds), acoustic noise inside vessele, temperature etc..

Cheers Jack

Reply to
Jack

Actually, the DP Transmitter works great. It's the float level switches that don't work so good. I could replace the switches with a transmitter, and do the pump on and off in the DCS. My float columns are only 16" deep and 6 or so inches in diameter, so it would be pretty hard to put an ultrasonic on there. We do use quite a few Milltronics Ultrasonics in the plant, but I don't think they would work well here.

Reply to
Curtis

This may be a stupid suggestion, because my experience is controlling itty bitty clean things, not great big dirty things. So for what its worth, have you considered sensing the pressure difference between the top and bottom of your float columns, and deducing the level as head/density? It looks like you want to detect a head change of 6" or so, which is admittedly pretty small. I can see a number of other potential problems with this, but they may be easier to solve than the ones you have now, and they'll have the novelty of being _different_ problems than what you have now.

Reply to
Tim Wescott

Curtis,

That is exactly what I would do. Only I would use diaphragm seals and place them directly onto the nozzles that the float chambers are connected to. You will want a full port gate valve for isolation at each nozzle.

Walter.

Reply to
Walter Driedger

i dont think the ultrasonic sensor will work in the column. But you can install it inside the vessele. But since u have a DP, you will not need it.

so i dont understand y you need a level switch when you have a perfectly working DP transmitter. Why do u need the float in the first place? Is it to sense the low level to turn off the pumps?

what about conductive level measurement on your column?. conductive rod installed down the the column - as the height change, the resistance (R) change. So

V(24Vdc)/R = I amps. U measure I amp which directly relates to the height change in column.

Reply to
Jack

You just re-invented the DP transmitter. Definitely one of the preferred options.

Walter.

Reply to
Walter Driedger

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