Suitable instrument to protect overfilling Ammonium Nitrate solution road tanker

Hi learned guys, I do not like to re-invent the wheel and hence would appreciate if someone can point me in the right direction:
A road tanker (B Double or it could be an Isotainer) is being filled with hot Ammonium Nitrate solution (Temp: 130 to 135 deg C, has to be less than 140 deg C to comply with ADG code). We wish to install a suitable instrument (preferably non-contact type and attached to the filling arm) that will detect and close the filling valve if the level in the road tanker rises above safe fill level.
Is there any other alternative solution available to prevent overfill and subsequent cleaning up of AN solution spills? One technology that comes to my mind is having a weigh bridge under the loading station so that the road tanker can be Tared and filled at the same location.
Kindly be aware that AN solution will start to solidify almost immediately if the temperature is decreased (less than tanker fill temperature). Thanks in advance for all suggestions and pointers. Regards, Raj Sreenevasan
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Unless you need to weigh what you are filling that sounds expensive complicated and prone to operator error.
If the filling nozzle enters the tank then add another small bore pipe and pump some air down it. Detect the increasing back pressure as that pipe becomes submerged (or nearly so).
The most likely problem is the pipe getting bunged up with product, but, at least it is a safe failure.
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Raj, I know there are small radar gauges around that will do this (maybe talk to Emerson?) but how about using a high-tempreature version of Liquip's optical high level probe that is currently used in fuel tankers all over the country?
I can't remember where you moved to now, but have a chat to one of the tech guys at Liquip: http://www.liquip.com/locations_australia.html They should be able to point you in the right direction.
I hope this helps.
Cameron:-)
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Cameron, I am now based in Perth. I thought about the optical level switch. But as I pointed out if the tank surface starts to cool, then AN emulsion will solidify and may obstruct the optical path.
Secondly it will take quite a bit of money to retrofit the tankers to accommodate the optical switches. Currently our client is trialling a temperature probe inserted into the tanker at the filling point (man-hole) to shut off the filling valve. Since it requires the operator intervention, I am trying to eliminate the potential personal safety hazard. Regards, Raj

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Radar or ultrasound come to mind. Neither are all that expensive.
If you use a long spout on the filling hose, so it goes to the bottom of the tank, then measuring the back pressure would do a pretty decent job of telling you how much you have filled the tanker. Meter the flow at constant pressure. When the flow rate drops below some value, stop pumping.
Michael
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Michael, One of the problems with both Ultrasonic and High Frequence Radar is that they are affected by varying density and / or absorbed by Ammonia vapour that is often found in the vapour space inside the tanker. That is why for liquid ammonia storage tanks we use the wire-guided radar (rather than the non-contact variety) and ultrasonic instruments are a bad choice for the liquid ammonia application.
The old and tested bubbler solution (used in molten sulphur applications) is rather appealing. I will investigate it further. Regards, Raj
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