UPTAKE FIRES
- Parent Category: Technical Articles
- In: Boilers & Steam system
- 15Nov2009
- Last Updated on Tuesday, 13 September 2011 17:28
- Published Date
- By sivasankar
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Uptake Fires
On break out of an uptake fire the priority is to boundary cool to contain the fire and give cooling effect.
Modern ship
An uptake fire generally starts when the load on the boiler is reduced. This is due to the quantity of excess air being very low at high loads.
Should a fire break out then the possibility of speeding up and reducing the excess air should be considered.
The amount of feed heating should be reduced to lower the inlet feed temperature and aid with cooling parts.
Where the possibility exists of damage to the superheater, then after first relieving pressure, it should be flooded.
Older ship
Where the excess air on older boilers is high even at high loads a different plan of attack must be used.
The flames should be extinguished and the air shut off. The amount of feed heating should be reduced.
The safeties should be lifted to keep a high steam flow and hence high feed flow requirements. ( the boiler is now being fired by the uptake fire )
Lifting the safeties give the added advantage of reducing the boiler pressure and hence corresponding saturation temperature of the water aiding the cooling effect
Tackling the fire
If a direct attack should be made on hot non-pressurised parts then the nozzle should be set to solid jet and aimed at the seat of the fire.
This should not be carried out on hot pressurised parts due to the risk of a steam explosion.
Dry powder is a suitable extinguishing medium.
Disassociation
Under certain conditions an extremely destructive fire, commonly known as a hydrogen or 'rusting' fire, may occur Under high temperatures water will tend to disassociate to hydrogen and oxygen. The percentage amount increases with increased temperature These will recombust again liberating heat In a fire there is a danger that the use of superheated steam as an extinguishing agent (say sootblowers on an air heater fire) could in fact feed the fire and accelerate the growth. For example the displacement which occurs about 707oC
Heat + Hot 3Fe + 12H2O Ћ 3FeO3 + 12 H2
see Theory section for a more complete explanation
Tackling this type of fire is very hazardous and consists mainly of boundary cooling and shutting off water and air supplies as effectively as possible.Under no circumstances should steam smothering be considered.
A typical scenario for this fire is a badly cleaned uptake igniting leading to tube failure
