Why are water tube boilers considered less dangerous than fire-tube boilers?

Advantages of fire tube boilers: - More residual heat in the water to allow for load swings - Simpler control systems due to larger volumes of water in shell - Water quality doesn't change as quickly due to larger volume of water

Disadvantages of fire tube boilers - Maximum Allowable Working Pressure is limited due to larger surfaces exposed to pressure, to about 250 psi - Danger of a pressure part explosion due to failure of the shell and resulting rapid expansion of the large volume of water in the shell - Longer warm-up times due to the large amount of water in the shell. - Larger footprint than a water tube boiler of the same rating. - Less efficient per sq. ft. of heating surface since less of the water is in contact with heating surface due to a larger volume of water in the shell.

Advantages of Water Tube Boilers - Rapid warming due to a much larger heating surface per pound of water in the boiler. - Easier to have a superheater if necessary - Virtually unlimited Maximum Allowable Working Pressure (within reason) - Smaller footprint than a fire-tube boiler of the same rating - Less working volume of water contained in the pressure parts - More water volume exposed to the heating surface than a fire tube boiler (more efficient) - Faster load change response due to less water - Less chance of a pressure part explosion due to less volume of water exposed to a rupture situation, plus, the rupture is usually into the furnace area which is safer.

Disadvantages of a Water Tube Boiler - Must be more careful of feed-water quality - More complex control systems for drum level necessary due to smaller water spaces, (although I have worked in plants with old marine three drum boilers with huge steam drums which only had thermo-hydraulic regulators for drum level) - Operators must be quicker on the draw when there is an upset because everything happens faster with a water tube boiler

Rahul Menon

Twitter- @menenrahul