Furnace Forced Cooling

I’m confused over what type of furnace cooling should be used – if any - during emergency shutdown under low water condition.

When the water level is not visible in the gage glass, emergency shutdown of the boiler must be carried out, such as cutting off the burner, shut off feed pump, and close the main steam valve.

However, there are various opinions on types of cooling. Some said that the boiler must be forced cooling by continuing running the FD fan (or ID fan). Some said the fan must be stopped to allow natural cooling because thermal stress imposed by forced cooling could damage the boiler / alter the metallurgy.

Opinions please.


In my opinion it is best to leave the boiler to cool down by itself without any form of assistance such as leaving the FD fan operate. Otherwise, tubes that were deformed during the low water condition may set and will not restore to their original length; then you will need to replace most of the tubes.

Above is a snippet.