Fuel Oil Heating

I haven't seen many boiler plant operations but in those that I have, the flue gas is used to provide steam/hot water and the steam is used to heat the fuel.

I have to ask,
[ul square][li]is it safe to heat fuel directly from the flue? [/li]
[li]what happens if you spring a leak and get hot oil flowing into the flue?[/li]
[li]how will you control the heating? You usually have a constant flow of oil in a ring main where temperature is controlled by varying the steam flow. How would you vary the flue gas flow?(/li][/ul]

JMW
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Hi JMW!

Regarding the safety I have to admit that I haven´t really thought about this matter in this case so far, having in mind, that for example in cracking furnaces the naphtha is always preheated in the convection section.
Well, there is some diference between fuel oil and naphtha, so I will look at it . . .
The temperature control should be done by bypassing the flue gas.

Thanks for your hints!
us1612

To us1612, from my own experience I recall a finger-size hole developed in a convection bank used to superheat exhaust LP steam from a turbine used to move a centrifugal pump in a PDA unit.

Several months passed until operators noticed the loss of about 4 ton/h steam to the atmosphere.

BTW, because of the low feed temperature, it entered first the radiant section at the bottom (!) near the floor-located vertical burners.