Heating fuel oil

[op9]

I am involved with converting an industrial burner from light oil to heavy oil firing. Thats not a problem.

However the fuel storage tank needs heating to about 60-70degC. Normally that would be accompished with steam (if available) or electric heating. They want to use an old bitumen tank which is fitted with a submerged U tube (immersion tube) to which is fitted a small burner firing through the tube. This type of heating is quite common for bitumen but I have never seen it done with fuel oils. The fuel concerned is a recycled oil having a flash point >60degC (typically 90degC), Boiling point >250degC, Visc 40cSt @ 40degC, SG @15degC of 0.9

One of my concerns are, is there any possibilty that the fuel around the tube where the burner flame is,(where there is the high radiant heat), will "coke" onto the steel eventually causing local high temps of the steel? This sometimes happens on bitumen tanks and we usually fire the burner through another inner concentric SS tube (in the flame area)allowing an air gap between it and the main carbon steel tube.

Would appreciate any comments.
Thanks in advance,
Rod

Rod Nissen.
Combustion & Engineering Diagnostics

 

[ccfowler]

I agree with your concern. Is there some reasonable way to convert the arrangement to using low pressure steam? That would eliminate the hot spot risks, and steam at near atmospheric pressure would be plenty hot enough.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[op9]

Hello CC,
Unfortunately there is no steam at this site. It is an Asphalt plant and they heat their bitumen by a similar means and have electrical tracing on other bitumen lines.Some asphalt plants use hot-oil (thermal fluid) but alas not at this one.

I have had a thermocouple fitted on another installation (heating biitumen), on the metal of the immersion tube and it reads 300degC. We have a cut-out at 320degC, after which they have to empty the tank and check for any coke deposits on the tube.Luckily in other installations (without T/C fitted) I have seen no major problems in the past heating bitumen. What usually happens in the event of a tube failure leaking bitumen into the tube inside, is it starts smoking profusely. Or the tube metal expands more than usual and the outer welds crack, leaking bitumen onto the ground.

With fuel oil in the tank, I think the result could be far more catastropic.

At this installation I will be recommending that he install an electric outflow heater and recirculate back to tank to keep it warm.

Thanks for your input.
Rod

Rod Nissen.
Combustion & Engineering Diagnostics