I am working on sulfuric acid production plant. I want to design a level measuring system for 98.5% sulfuric acid storage tank. Which type of level sensors are more efficient, bubbler type or non-intrusive such as radar or ultrasonic?
Hello
In my opinion the radar will work well, as it is not exposed to the fumes. The ultrasonic, if exposed to the fumes, using standard units, may mess up the lens in a very short time. Bubbler, once again – it has a lot of parts that are exposed and can you find compatible material?
You will have to make the final decision – but it seems the best materials for S/A 75 to 100% is Teflon or PVDF if you go with intrusive. You will find intrusive more cost effective for a simple application.
Another good option, probably the best, would be a standoff or flag indication. We call it an RVI, (Remote Visual Indication) this is an engineered pipe or tube that can be bolted to the side of the tank. A compatible magnetic equipped float rides inside the pipe following the fluid level. You then have one or several options. On the outside can be a device with magnetic flags. As the float moves – the flags flip visually showing the level – very safe, as you would have to smash the pipe for it to leak. You can also have a continuous readout made from a cost effective material as it is on the outside of the vessel. Or you can place individual adjustable latching reed switches for pump or alarm control.
If you can go with a point level system (1 to 6 levels can be selected) then definitely intrusive will be more cost effective and easier to install and maintain. If you are after a continuous reading – intrusive is still more cost effective. Standard continuous models can have about 3/8” +/-accuracy or a higher end model can seriously get fine measurements but probably double
We have used ultrasonic level transmitters in this application with good success. We used a stilling tube/well and ordered the transmitter in PVDF. This was placed in a 2500 gallon day tank for the plants wastewater treatment system.
One word to the wise... Use a different level sensing technology to back up the level transmitter to provide high/high or low level alarm in the event the transmitter fails.
You could use a radar instrument made out of PVDF in stilling well
but this is very high cost route. It would be more economical to utilise a standard horn type antenna radar instrument and penatrate the tank through a opaque window therfore not having direct contact with the media. This type of arrangment can be used with the likes of Vega radar.
Richard Wiseman
Systems Engineer [email protected]
With radar level prices having come down considerably, under $2K for a basic system, this technology is worthy of consideration in many
applications these days including this one. Configurations are available where no probe intrudes into the process.
The best solution I know is a radar gauge, with PTFE rod antenna. Exposed side of the flange is also coverede with a PTFE disk. Have a look at "www.us.endress.com":http://www.us.endress.com .
Accuracy can be 1 mm or 10 mm, depen dig on your budget
I have just finished an inventory control project for a chemical supplier in Canada. We installed ultrasonic with PVDF face for tanks which were 30ft deep on concentrated HCl, HNO3, NaOH, KOH and H2SO4 tanks with no problem. We had the choice of Milltronics or Burkert but the Burkert stuff was less expensive and easier to network. You could try E+H too.
i am now working in sulfuric acid plant, and from experiance, i think that the use of bubbler type is easier than other types, and the frequency of problems is a long period times.
You can use a metal alloy like Hastelloy C or better yet, 316 SS, or you can use a polymer pipe that will operate in 50% sulfuric at 60 deg. C. SS316 is rated "A" for 50% sulfuric acid. Generally speaking that polymer pipe would be PVDF or PEX. PVDF is rated "B" up to 212 deg F. or 100 deg. C, while PEX is rated "B" up to 240 deg F. As long as it is operating at very low pressure, the deration curves for PVDF or PEX should not interfere.
Depending on the length of the bubbler tube, I might be tempted to make it out of welded SS316 and forget it.
Walt
Walt Boyes
Editor in Chief
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