Can someone recommend the type of level measurement device to use to measure the level in a sump tank. The sump tank is used to collect hydraulic oil, chemicals and other liquid disposal from an offshore oil & gas platform. The tank is a open tank (not pressurized tank). The type of existing level measurement now in use is bubbler type and it is not working properly. Please advise.

 

Well, because you have a variable dielectric coefficient, you may not be able to use radar. You probably can use an ultrasonic sensor. You probably can use a submersible differential pressure transducer, too, unless the tank has a sludge filled bottom. You probably can't use rf admittance or capacitance level either, but I'd ask an expert on that technology.

Do you need continuous level measurement, or can you live with point level?

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Look at ultrasonic first. Either ultrasonic or radar are non-contact so they aren't affected by the yucky contents of the sump, but radar is affected by the dielectric constant of the medium it reflects from. Hydrocarbons with their low dielectrics can be on the edge of reliable performance.

Either comes in models that have I/S or EXP ratings for hazardous areas.

If your bubbler has a conventional, loop powered DP transmitter on it to provide the level signal, then either technology has loop powered transmitters that will 'replace' the DP without extensive rewiring.

Neither technology is suited if the liquid level is covered with foam, because neither reliably shoots through foam.

I use Siemens. For short, <12m shots, the Probe LU is compact, convenient 2 wire continuous level transmitter.

http://www.lesman.com/unleashd/catalog/sensors/SITRANS_ProbeLU_Specs.pdf

David

 

Hello Peter;
Consider using a submersible type of hydrostatic device. They are a very simple, tried and true instrument when installed carefully. It may be
necessary to install in a still well or away from turbulence of pumps and flow.

Regards,
Mark

 

Ultrasonic would be an option as well as air radar. Tuning fork and ultrasonic gap sensors would be options for hi/lo alarms if that is needed.

L.Kolbert

 

Dear Peter,

Can you tell us what is the problem with the bubbler system (wrong indication, plugging)? For me the bubbler level system for this case should be working good. We have a bubbler system measuring the sulfur liquid level and is working very good. Is your bubbler system adjusted correctly (flow, transmitter range, Low side vent to the atmosphere)?

PD: Maybe you have a problem with the liquids inside the sump tanks (several
specific gravity), the design of the system was for which type of liquids (only hydraulic oil, interface or what)?

Regards
J.Pinzon
Instruments Technician

 

There are different specific gravity of the liquid contents and cause plugging and errors.

Can dP tx be used, but how to install as the only connection is on top of the tank?

 

Dear Peter,
I think that you can resolve the problem easily....I dont understand you when you said the only connection is on top of the tank. You can use the same conection, just remove the older bubbler system and install the DP Tx
and design a system to introduce a lot of flow of nitrogen or air depends of the case for clean the tubing each time that as you needed. If the level loop is only indication you will not have a problem with the cleaning system but if it is a control loop you must evaluate the situation.

I know that the several specific gravity cause a lot of error in the indication, but what is more important the accuracy or the indication?

Regards
J.Pinzon

 

First, any differential pressure device (which the bubbler is) used for level will be subject to problems with varying specific gravity. The question is whether exact level is necessary or can you calibrate the transmitter based on the worst case level (high and/or low) based on the range of specific gravity possible in the tank and satisfy your application. Also, as indicated in a previous post, proper design and care and feeding of the bubbler are also necessary for a successful measurement of level. A discussion of differential pressure level measurement including the bubbler can be found at:

http://www.omega.com/literature/transactions/volume4/T9904-12-PRESS.html<http://www.omega.com/literature/transactions/volume4/T9904-12-PRESS.html>

Some potential alternatives are guided wave radar, through the air radar, sonar, and laser which do not depend on specific gravity. Some of the manufacturers are Magnetrol, K-Tek, Siemens, Emerson, Vega, and AMETEK Drexelbrook.

William (Bill) L. Mostia, Jr.
Principle Engineer
WLM Engineering Co.

This information is provided on the basis of Cravat Emptor.

 

In my opinion, ultrasonic will be the best choice if you have enough clearance for the ultrasonic path inside the tank.

Another good choice is top mounted magnetostrictive level transmitter (if range is not too big). Since it works on float, it will not be affected by varying dielectric constant or specific gravity.

If you would have a side tapping, best could be diaphragm seal level transmitter. In sump tank exact level measurement and high accuracy is not important.

Regards,
Ashok Hait

 

Guided wave radar could be a good option if the liquid does not stick to the probe.

Regards,

Tomy Zacharia

 

Hi there! I would like to know what is the clearance required for 5 Deg. Ultrasonic level transmitter. Is there any data available relating the height, beam angle and clearance (Min distance from the wall of tank)?

Thanks.

Drex

 

hello for open type tank its better to use pressure type transmitter and given the reading to plc or dcs and set high and low alarm there. it is so simple to install and commission.

 

Use Ultrasonic type LT with rod or co-axial Antenna.