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Float Type Level Switch and Foaming Problem
Float type level switch causing problems because it gets stuck due to extensive foam. Application is suction gas scrubber on Frontend compression of natural gas.

Hello,

I have two floats of same type installed on a gas suction scrubber vessel. One of them actuates an electrical contact to generate LAHH SD digital output; while the other one actuates a pneumatic vent which in turn actuates a pneumatic dump valve.

The float is mounted on a nozzle which is a pipe extending 6-8 inches out of the scrubber vessel. The same pipe extends inside the scrubber vessel by 10-12 inches. So the float which is 4-5 inches in length operates within the nozzle pipe's outside length and not directly inside the vessel.

The problem is that For some reason, there is extensive foam formation inside the scrubber. This foam gets stuck in the nozzle pipe inside the vessel and eventually clogs up the float in one place thus inhibiting its operation.

My questions:

1. Is the design of the nozzle correct i.e. extending the nozzle inside the vessel? My guess is that this extension of pipe inside the vessel is causing it to become a dead end and a place for foam accumulation.

2. What would be good, cost effective level condensate sensing alternatives in this case which would also be impervious to foam formed inside?

Thanks

2 out of 2 members thought this post was helpful...

I have used the sensitivity adjustment on a Siemens CLS 200 or CLS 300 capacitive level switch to get it to distinguish between foam and liquid. It has worked fine in each case, where the intent was to detect liquid, not foam. While I was messing with it, I tested it in three cases and found that it would detect the presence of foam versus air, if that were needed.

>1. Is the design of the nozzle correct i.e. extending the
>nozzle inside the vessel? My guess is that this extension of
>pipe inside the vessel is causing it to become a dead end
>and a place for foam accumulation.

You are correct, with heavy build up, at some point the foam streangth with thicking is not being continually flushed by the process or by a separate purge.

>2. What would be good, cost effective level condensate
>sensing alternatives in this case which would also be
>impervious to foam formed inside?

remote seal d/p, although there are a number of displacer designs that will serve well.

Capacitive probes can experience build up problems too, so there may not be a perfect solution regardless of the technology.

Is the nozzle vertical?
If so it will also trap gas won't it?

I think the nozzle (stilling well) should have a hole drilled through the side near the top of the vessel so as the liquid rises to the level of the float it forces the foam out.

You say the float is mounted On the nozzle then you say the float is In the nozzle - this is a bit confusing.

Without a sketch and description of the fluids we can really only guess.

By Daniel M on 9 July, 2017 - 9:16 am

Hello

float is not the adequate principle. Capacitive: you have to calibrate it. My suggestion is a vibrating probe, which without any calibration is not sensible to foam but only liquids. If you want more details pls inform.

Hello,

I recommend to use guided wave radar for this applications. You can ask rosemount, E&H or Vega, among other, for recommendations for your specify application.

Regards