There are two main industrial boiler types that you can choose from for your specific application; water tube and fire tube boilers. Deciding which of these two types will work best for you is not as easy as it may seem. It is like comparing apples to oranges; you can’t simply compare prices with steam capacity, as there are significant differences to consider.
Water tube and fire tube boilers are essentially the opposite in design. In a water tube boiler, water travels through tubes which are surrounded by the by-products of combustion, or flue gas. In a fire tube boiler, the flue gas travels through the tubes, which are surrounded by hot water. Fire tube boilers are typically designed with either three or four sets of tubes (three- or four-pass boilers). Every set of tubes that the flue gas travels through is considered a “pass”. Boilers designed for three-passes have the stack at the rear, and boilers designed for four-passes have the stack at the front. A boiler with more passes has a higher heat extraction rate and is more efficient then one with less passes.
Water tube boilers are safer by design and generally can operate many years longer than fire tube boilers. Water tube boilers are available in larger capacities and recover faster than fire tube boilers. Water tube boilers can also handle higher pressures (up to 5000 psig), and have the ability to reach very high temperatures with the use of super-heaters. Fire tube boilers are not suitable for pressures above 350 psig and actual operating steam output of fire tube boilers are less than the stated nameplate. Water tube boilers are rated at actual operating conditions.
From a maintenance standpoint, fire tube boilers are typically have lower operating costs comparable to a similarly sized water tube boiler. Fire tube boilers have easy access to the boiler’s firesides and tubes can easily be replaced without additional repair of the boiler. Although fire tube boilers are smaller in design, they...