Boilers Development

In tracing the history of the development and application of marine steam boilers, it’s interesting that some of the basic requirements have always applied, although from time to time the emphasis has shifted from one requirement to another. In the beginning, space and weight limitations were not considered to be as important as other factors, and yet at later stages the emphasis on those items brought about the development of new types of marine steam boilers. Generally, it has been the economic or military need for increased propulsion power that has instigated significant advances in marine steam boiler design. The earliest types of marine boilers were relatively large pressure vessels, with furnaces located underneath them, but it soon became apparent that such exterior furnaces were far from satisfactory, and they were then located inside the boilers shell. The boiler exterior had now developed into an approximate cube, Fraser boiler and, no matter how heavily stayed, its flat exterior placed very low limits on the steam pressure that could be carried and also left much to be desired from a maintenance and safety standpoint. The internal furnaces and tubes, however, were cylindrical and entirely satisfactory for the demands of their time. By 1870, marine boiler pressures had reached only 4 bar; by 1900 they had increased to about 20 bar.

Scotch fire tube steam boilers with one to four furnaces

To overcome the boiler's structural weaknesses and at the same time reduce cost of fabrication, the marine steam boiler shell was made cylindrical with provision to install one or more combustion chambers fire-tube between the two flat sides of the shell. Known as the Scotch marine boilers, this boilers as finally developed, met with wide and enthusiastic approval by marine engineers. Although minor changes have been made throughout the years, its design has remained much the same and its qualities of ruggedness, reliability, ease of maintenance, and ability to stand abuse made it -- until recently -- the most popular boilers in the marine field. Even though the Scotch marine steam boilers proved to be popular and well suited for steamships, the fact that its pressure was limited to 20 bar retarded progress.

Water tube steam boilers

There was a realization that advanced steam boiler designs with greater generating capacity, higher pressure, and increased efficiency were needed to meet the changing requirements brought about by the development of turbine propulsion machinery. Stiff commercial competition among merchant fleets as well as various naval powers made these developments most urgent. Marine engineers began to adapt various types of water-tube boilers to fit into the restricted space available for installations aboard steamships, Some adaptations proved highly advantageous with respect to heat transfer and weight, and offered a variety of designs suitable for pressures in excess of the maximum of fire-tube types. Thus, new possibilities were presented for the utilization of steam aboard steamships.
Even though the marine water tube boiler almost has replaced the marine fire tube boiler, Old steamships with Scotch marine steam boilers are still sailing in salt-water as well as lake-water, managed by enthusiastic marine boiler engineers. These boilers are often new build from the original boiler drawings.

Boilers with Controlled Circulation

At high pressure, providing a more positive means of maintaining the circulation becomes desirable and advantageous.
The Controlled Circulation Boiler design is an ideal arrangement for steamships in the high pressure range. With its features of positive circulation, compactness, light weight, suitability for high pressure and temperature, and adaptability to limited space conditions, Boilers with Controlled Circulation can offer important advantages for advanced steamships design.

Design principles for the construction of furnaces for marine boilers

A number of factors determine the configuration of a marine boiler furnace. First of all, the type of steam boiler under consideration sets some of the furnace dimensions; fire room space limitations, service requirements, and burner arrangement also influence the furnace layout. The furnace arrangement must also conform to criteria which are prerequisites for proper thermal and circulation performance. The amount of waterwall surface determines the furnace exit-gas temperature that is most significant in the design of the superheater. Practical requirements must also be considered; for instance, the firing equipment must be located where it can be easily operated. Two-drum bent tube boilers are always furnished with water-cooled furnace surfaces on the side and roof and, for the majority of designs, a rear waterwall is included; waterwalls may also be installed in the furnace's front wall.