What are fire tube boilers and what are its applications on board a ship? Find answers to all these questions in the article
Firetube boilers are used for low capacity steam production applications, mainly for vessels having diesel engines as main propulsion system. On such vessels, steam is required for auxiliary machinery. Such boilers have simple operation and can run properly even with medium quality water. All these boilers have large water capacity and are often known as tank boilers. We will learn about fire tube boiler parts in the sections below
Types of Firetube boilers
Most of the fire tube boilers now come in a complete package.The main parts of the package are :
- oil burners
- fuel pump
- forced draft fan
- feed pump
- automatic control system.
- Boiler mountings
The most basic type of a package boiler is single passage three pass design. One such boiler is shown in the figure. The first pass of the water will be through the partly corrugated furnace and the cylindrical combustion chamber. The second pass starts when the water converts into steam and flow from the furnace into small bore smoke tubes located over the furnace. At the end of the pass and near the central smoke box, the flow divides into two parts. The third pass of the steam is through the smoke tubes located outside the main arrangement and which opens at the exit on the rear of the boiler.
No refractory material is used both furnace and combustion chamber. Sealing and insulation is provided only to the combustion chamber access door and primary and secondary quarl. All the automatic functions are located at the panel located on the side of the boiler.
This is one of the recent vertical type of boiler, having a fully spherical furnace. Due to its shape the boiler is also known as spheroid. The main feature of the boiler is that the furnace of the boiler is surrounded by water and therefore there is no requirement of refractory material. It is a single phase pass boiler, which means that the hot gases pass just through the horizontal tube stack before going to the exhaust. Small bore tubes along with the retarders are used to ensure better heat transfer, higher efficiency and cleaner tubes due to turbulent gas flow.
Composite boilers are provided with systems that can be run by two ways, either by conventional oil firing and burning or by using the heat from the engine' exhaust gases. All the composite boilers are based on firetube boiler designs . Even the Cochran boiler can be modified to be used as a composite boiler. The only modification that is required is to install a separate tube bank section which takes the engine exhaust gases and exits through its own dedicated exhaust duct.
Snow, W.B. (2009) Steam-Boiler Practice. Bibliobazaar Publishing