Guided Wave Radar in Agitated Tank 4

[NPKresults]

Hello,

For an upcoming tank design I would like to use a guided wave radar as the level transmitter. The radar probe is to be 16mm, 108" long, and made of 316SS. I need to determine whether this will be sturdy enough to withstand turbence created by the agitator. The tank is 108" diameter, the agitator is 37" diameter, and the probe will be 12" from the wall of the tank, leaving about 22" between the tip of the agiatator blade and the probe. The agitator has 3 blades and the design speed is 84 RPM. The media will be a mixture of liquids with SG~1.3. I do not have prior experience with guided wave radars, but I would like to use one in this situation due to potential foaming in the tank. It has been a while since fluid dynamics and I haven't been able to find any reasonable equations pertaining to this problem. Thanks for your time.

Best,

Danny B.

 

[itdepends]

I can't answer the question about the probe without looking at the thickness of the ones we are running- but we do have them in those lengths.

Have you thought about using guided radar with wire ropes?- They're secured to the bottom of the tank and are a variation on the rods- bit harder to remove for cleaning though!

Cheers.

 

[JLSeagull]

Also consider a stilling well. If the mechanical aspects permit, discuss protecting the GWR sensor inside a pipe with the vendor.

 

[NPKresults]

Thank you both for your thoughts. I realized that I fibbed earlier when I told you that it was a mixture of liquids. The reason we have the agitator is to deter silica particulate from settling out. This 'stuff' is very good at forming films on just about everything, pump lining, pipes, tank lining etc. Because this radar will be going into a new plant I am unsure of the actual silica concentration (the plant has a few modes of operation) and thus the rate at which is will foul. I like both of your ideas, perhaps you could enlighten me to the 'typical' cleaning frequency for one of these set-ups. Cleaning silica fouling is an arduous task so I would likely need an extra radar to swap out during cleaning periods. The more I think about it, the more it seems like I should try a radar without a guide first, then do a retro-fit if the foaming causes trouble.

 

[pleckner]

Before you try anything, please contact one of the vendors that supply radars. Ohmart-Vega is one very good source. I've dealt with them in the past and they will be happy to talk to you about application first and sales second.

 

[HEC]

NPKresults,
Why the choice of guided radar, why not use hydrostatic pressure measurement. If density variation is an issue use a two piont measurement system where you look at a differential head over a known height, this infers the density. If the tank haas variable head pressure then a third sensor is required for compensating the tank vapour space pressure.


Mark Hutton

 

[itdepends]

Scaling rates on the rod are likely to be similar to what you see on the tank walls. You should be able to get to 5 or 10mm of scale and still be able to operate- but may need to recalibrate.

I've had a radar probe working with up to 20mm of scale on it- but the signal begins to lose energy as it passes up and down the rod and the real level becomes harder to detect.

If your looking at cleaning regularly and scale is a problem- stay away from the cable type- the coupling at the bottom will scale up and give you problems when you remove it.

Suggest you talk to the manufacturers as per above- don't forget to ask about unguided radar probes- they can punch their signal through foam as well and you will have less of scaling issue. I've used Vega and Endress and Hauser and have been happy with both.

Cheers.

 

[NPKresults]

Thanks to all for your info:

ItDepends/pleckner: I will be in contact with the E+H rep. Unfortunately I am limited to using Siemens or E+H.

HEC: Would all the sensors be on one 'probe stick' or would I have to introduce 2-3 entire instruments to the tank? Also what are your thoughts on how H/P would handle foaming?

Best,

Danny B.

 

[HEC]

NPKresults,
Is the tank sealed, does the tank contents density change appreciably? If the answer to both these is No, then only one hydrostatic pressure taping point is required. For changing density two are required (bottom and known height) for sealed (variable pressure in vapour space) and constant density two are required (bottom and head space). If both sealed tank and variable density the three pressure taping points are required. These would generally be a diaphragm seal inside a 4" flange. as the foam is not very dense it would not register as part of the tank contents. is this a problem?
Cheers

Mark Hutton

 

[MedicineEng]

I am not experienced in what you call "guided wave radar". We only use radar level where the intrument is not in contact with the product.
We have another type of radar that it's working principle is a magnetic float level. This has a flaoting device in a tube that when the level changes, there are some small metal cylinders (not in contact with the product that roll and show a different colour and you can see immediately which is the level that you are working with. In our case this level is from Krohne.

 

[NPKresults]

HEC, thank-you for elaborating. The fluid is to be scrubber effluent containing particulate. Although it will even out eventually, it will change from 1-1.25 during start-up and upset conditions. I spoke with the E+H rep and have decided to go with an un-guided wave radar. He said that the H/P method would work but because I was unsure of the frequency of density variation, and because I was not sure what the vapor pressure variations would be like he would not recommend it. Thank-you all for your help. I will try to update this post with results, start-up won't be till next year.

 

[HEC]

NPKresults, good luck with the radar on your application. I am dissapointed in the E&H rep's response/understanding of the H/P system. The three point measurement will adjust for density and vapour pressure variations. IF the density varies by between 1-1.25, and you can tollerate a moderate error (measure only to the required accuracy) vis +/-12% then use a two point measurement H/P system.

Mark Hutton