With the deteriorating quality of fuels, the sizes of waste-heat units will have to be increased. This means higher costs and increased maintenance unless more attention to initial planning and design. There are two classes of auxiliary boiler, those that supply steam on motor ships for cargo heating, pumping, and other services, and those that can power main propulsion units as "get you home" facility. Among the types of boiler discussed are the Monomall and the Aalborg water-tube boilers. The main dimensions of the Monomall can be altered to suit the particular ship and designers are now being asked for units of higher efficiency. Fitting an economiser can raise efficiency from 80 to 85%. The Aalborg is a less conventional type of water-tube boiler, more in the style of a smoke-tube or fire-tube boiler. The water is inside the tube and the gas circulates round the outside and leaves tangentially after giving up its heat. This boiler is available supplying steam from 10 to 35 t/h, and it can also work in conjunction with exhaust-gas heat exchangers.
Institute of Marine Engineers
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