Crude Oil / Water Interface Level Gague in Desalter

This is WAY outside my field, but when reading this I thought "Why not put a water trap/bleed mechanism in the bottom of the tank and decant water away and then only have to sense oil in the discharge rather than having all the sensors inside the tank?"

I mean have the bleed mechanism always functional and maintain a very low water level in the tank.

Like I said, way outside my field, but there's no harm in dropping in the option.

This is exactly what they should have done for a lab test. However, the desalter is connected to an oil well with substantial crude/water mix discharge and throughput. So, process dynamics is such that they have to monitor the interface inside the tank in order to have enough time to take corrective actions if too much water comes is (water content vary some 15-90 % vol) or crude oil is too heavy or wax content is high enough and it takes less or more time to separate water from. Non-contact i.e. nuclear gauges are off the game, unfortunately.

Thank you for the comment.

Hi Juri,

I have designed and am currently building a heavy oil upgrader just outside Edmonton, Alberta, Canada. We have the exact same level control issues in many of our horizontal drums and vessels that you write about. The only difference is we have problems with bitumen sticking to the level controls instead of wax. I'm pretty sure our climate is about the same.

We use the magnetrol level gauge exactly for the reasons you describe. What is important is to make sure the the gauge and the bridle (the piping attaching the gauge to the vessel) has sufficient heat tracing and insulation to maintain the pipe and gauge above the solidification temperature of your wax and heavy solids that may form in your seperator. The gauge should be enclosed in a zipper-opening canvas insulating bag so it can be visually observed only when an operator makes his checks. We use high temperature mineral-insulated electric heat trace for this application. (Thermon is our preferred brand, but there are others www.thermon.com) Maintaining heat to the bridle and gauge is the key to stopping wax and bitumen plugging of the level gauge.

For high level alarms we use electric probe level gauges with ultrasonic back-up for high-high level. As you have discovered, the probes tend to be fouled with foam or wax once immersed and may be only good for one alarm and then fouled. Hence having a second non-contact alarm (but less accurate) is important.

Hope this helps.

Cheers,

Stan

Stan,

thank you for your comment. My customer is in Syberia, so climate should be the same with some -40/-50 C in winter. I've been to Calgary once for Global Petroleum Show (I think back in June 2004 ?). Not quite sure if my customer does not have bitumen sticking problem you talk about. However, impulse lines etc. electric heating is widely used nowadays, however is not always applicable to instruments itself. By the way, I received a quote from Magnetrol for a new gauge - Eclipse 705, which is loop-powered guided wave radar (with purge connections). Details can be found at http://us.magnetrol.com/products.aspx?menu=214&product=1

I found price reasonable (will depend on options though).

Hope it may help you too. Need more info - let me know( Skype nick - juriser).

Juri.