tank heating coil

[curve3104]

Does anyone have experience with heating fuel oil in bulk storage tanks?
I have an application where steam coils are used to heat fuel oils (#2 to #6), so they do not gel at low temperatures. I need to calculate the maximum steam temperature to which I can deliver to the heating coils such that the temperature of the coils will not scortch the oil or make it go boom. I don't want the oil to get above 250 deg. F or so. My steam available is 1246.8 Btu/lb (260 psia @ 470 deg. F). I'm sure there will be some condensate in the line acting as an insulator.
ANYONE HAVE ANY IDEAS TO ASSURE THE SAFETY OF THE SYSTEM??

Thanks

 

[Montemayor]

Curve:

All you need in order to do what you propose, is a simple temperature transmitter that sends a signal to a main steam valve feeding the steam to the steam coil. When the oil temperature in the tank reaches your set value (approx. 245 ^oF, the valve closes. When the oil cools to 240 ^oF, the valve opens. It's an on/off control because of the large capacitance in the tank.

 

[unclesyd]

Adding a little to Montemayor's post. Depending on your arrangement you could reduce you steam to a pressure that corresponds to the 250F temperature or slightly higher which will minimize the possibility of overheating.
This course this depends on the circulation around your heating. The more the circulation the higher this temperature can be especially when you need a high heat flux.

Our large fuel oil tank(9 million gallons) was controlled this way and it worked very well for many year until the dock boys pumped a barge of asphalt onto about 3+ million gals of fuel oil. I don't recall the type but it acted like asphalt by itself and had a tremendous amount of Vanadium that screwed up the boilers royally.

 

[pleckner]

One thing to watch out for is the potential for localized over heating at the coil metal surface. The bulk temperature may be fine but you still get product degradation from the localized temperature.

 

[curve3104]

Pleckner,

You have touch on just what I am looking for. Montemayor, your suggestion is exactly what I have seen in the past also, and look to do with this app. However, I have quite a distance from my three sources of steam (HP, IP, & LP) The LP steam will never make it, only 15 psia. IP steam is 260 psia @ 470 deg. F. I can reduce the pressure, but without desuperheating, the temp remains near 420 deg. F at around 50 psia or so.
Therefore, I need a warm and fuzzy that when I heat a coil with that temp. steam, I'm not going to blow something up.

Thanks

 

[MortenA]

Maybe a second temperature (switch?) on the steam return line? If the steam temperature gets too high - its an indication of too little heat being absorbed in the storage vessel (for whatever the reason)?

Best regards

Morten

 

[25362]

I've seen heat-sensitive wax tanks using bottom coils that switched from steam- to hot condensate-heating to reduce heat flux and avoid scorching of the wax.

 

[cammax]

not sure what reg But I thought NFPA limits steam pressure for F/O tanks #6 to 15 PSI max...

 

[TangoCleveland]

Have you looked at direct fired tank heaters? I had very good success using Infernotherm heaters in asphalt service. Their design provides a very low heat flux density for heating heavy oils. Check

http://www.infernotherm.com.

Larry