OIL CONTAMINATION IN BOILERS:
MAY LEAD TO BURN DOWN BOILER |
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| Oil as a contaminator & why tubes fail |
The most dangerous contamination, is heavy fuel oil entering the condensate from the leaking tank coils or heat exchangers. This, if not observed in time, could lead to complete loss of boiler due to overheating of the furnace.
Insulation effect of oil deposits reduces heat transfer by almost 3~4 times than for e.g. by a limestone scale layer of equal thickness. Roughly, the material strength in an auxiliary boiler will be reduced to 1/3 of its original design value by an oil deposit of only 0.5mm thickness due to localized overheating. The steel material starts scaling at the fireside, when it is not cooled sufficiently and will soon lead to tube rupture.
| What needs to be done when oil suspected? |
The first action when an oil leakage into the feedwater system is suspected, is to look in the cascade or hot well tanks. If oil is found, stop blowing down the boiler from the bottom; just surface blow the boiler, else the boiler drum will be totally covered in oil. Shut down the boiler, depressurise and open the vent. Steam drum to be drained slowly until water stops flowing from the loosened, upper manhole door before opening up the manhole for inspection.
This ensures that the oil only covers the boiler up to the normal water level and can be manually removed. If drained more, the cleaning area may not accessible for cleaning. Clean the boiler.
Do not start boiler until an
oil-free feedwater supply is guaranteed!
| Prevent it before it gets late! |
The hotwell / cascade tanks have normally filters installed, filled with lofa sponges, coconut fibres etc, which effectively take up small amounts of the oil. The filter inserts have to be inspected and exchanged regularly.
Another measure and early detection is to install oil detecting device which monitors if oil is present in the condensate going to the cascade tank. By locating the sensor in the cascade tank, it can be assured that oil is detected before it enters the system. Hence no part of the feedwater is being contaminated.
Added to this, a more comprehensive system to prevent oil entering the boiler would be to transmit a signal to an air or electrically operated three-way valve switching over the condensate flow to the bilge until the oil source is pinpointed and eliminated.
Tube rupture caused by overheating
through oil contamination
Creep cracks in a boiler end plate by overheating
through oil contamination
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That is why they say oil
and water never mix!!!
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- Article written by Mr. Sanjeev Dubey, Technical Superintendent