FURNACE

Figure 4-10.—Side view of an economizer. It is important that all internal fittings are properly installed and in good working condition. If excessive moisture is carried over into the superheater, serious damage will result in the superheater tubes, piping, and turbines. The economizer (fig. 4-10) is an arrangement of tubes installed in the uptake space from the furnace. The economizer tubes have metal projections from the outer tube surfaces. These projections are called by various names, including FINS, STUDS, RINGS, or GILL RINGS. They are made of aluminum, steel, or other metals, in a variety of shapes. These projections serve to extend the heat transfer surface of the tubes on which they are installed. Before entering the steam drum, all feedwater flows through the economizer tubes. The economizer tubes are heated by the rising gases of combustion. The feedwater is warmed or preheated by the combustion gases that would otherwise be wasted as they pass up the stack. In figure 4-1 you can see that the economizer is positioned on top of the boiler. There it acts as a preheater. So far, you have learned how the water gets to the boiler and what happens while it’s there. Next, let’s find out how the water is heated, where the heat comes from, and what boiler components are necessary for generating this heat. FURNACE The furnace, or firebox, is the large, room- like space where air and fuel are mixed for the combustion (fire) that heats the water in the drums, tubes, and headers. The furnace is more or less a rectangular steel casing that is lined on the floor and walls with refractory (heat-resisting) material. Refractory materials used in naval boilers include firebrick, insulating brick, insulating block, and air-setting 4-11