Fire tube boilers have a really simple design: gas is transferred from the heating source and then pushed through tubes and into a water-filled tube to create steam. This design allows for many different configurations for a fire tube boiler. When you purchase a fire tube steam boiler, you need to consider what configuration will work best for your current set-up.
#1: Firebox Boiler Design
First, there is the firebox boiler design. The firebox boiler design is a one-pass design, where the combustion only goes through the locomotive boiler one time. This is different from other fire tube boiler configurations, where multiple passes may happen. With a firebox design, the furnace is often connected directly to the boiler, allowing for the furnace to be kept cool by covering the furnace with water. Firebox boiler designs are usually ideal for space heating purposes. Firebox boiler designs are also used in operations where hot water needs to be created.
#2: Scotch Marine Boiler Design
Second, there is the scotch marine boiler design, which is also called the scotch fire tube boiler design, as it uses fire tube boilers. With a scotch marine boiler, the furnace is located inside of a diameter tube inside of the boiler. This allows both the furnace and the boiler to be surrounded by water. Most modern scotch marine boilers only contain one boiler, allowing for a one-pass system. However, a decade or two ago, scotch marine boiler systems more commonly contained multiple boilers, allowing for multi-pass configurations.
There are two common designs within the scotch marine boiler system: the wet-back and dry-back designs. With a wet-back design, the end of the boiler is designed to cool off by water. With a dry-back designed, the end of the boiler is not enclosed with water, and instead uses a different system, such as a fire brick, to keep the boiler from overheating.
#3: Vertical Fire Tube Design
Finally, there is a vertical fire tube design. A vertical fire tube boiler has a one-pass boiler configuration. One of the best features of this type of configuration is that the footprint is a lot smaller than the two designs listed above. With a vertical fire tube boiler, the location of the furnace is simple. It is located at the bottom of the overall design, instead of enclosed inside of the boiler. With a vertical fire tube design, the furnace is often enclosed with a water jacket.
There are some variations in this design as well. The top tube sheet can be located below the waterline, creating a wet-top configuration. Or the top tube sheet can be located below the waterline, creating a dry-top configuration.
When installing a new fire boiler, you need to carefully consider the configuration and design of the boiler. You want the design to work optimally with your intended needs.