The furnace, or firebox, is the large, roomlike 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

Figure 4-11.-Refactory-lined furnace.

Figure 4-12.-Combustion air and gas flow.

Figure 4-13.-Fuel-oil burner assembly.

mortar. Figure 4-11- shows a refractory-lined furnace.

The refractory lining protects the furnace steel casing and prevents the loss of heat from the furnace. The lining also retains heat for a relatively long time and helps to maintain the high furnace temperatures that are needed for complete fuel combustion.

Combustion Air

Air is forced into the furnace by a forced draft blower. The forced draft blower is a large volume fan that can be powered by an electric motor or a steam turbine. The forced draft blower blows air into the outer casing of the boiler (Fig 4-12). The air then travels between the inner casing and outer casing to the boiler front where it is forced into the furnace through the air registers. The air registers are part of the fuel-oil burner assembly that consists of four main parts: air doors, a diffuser, air foils, and the atomizer assembly. Figure 4-13 shows a side view of a fuel-oil burner assembly.

AIR REGISTERS.- The air entering the furnace through the air registers mixes with a fine fuel-oil spray through the atomizer. Figure 4-13 shows the arrangement of an air register in a fueloil burner assembly. The air doors are used to open or close the register, as necessary. They are usually kept either fully opened or fully closed. When the air doors are open, air rushes in and is given a whirling motion by the diffuser plate. The diffuser plate causes the air to mix evenly with the atomized oil in such a way that the flame will not blow away from the atomizer (atomizers are discussed in the next paragraph). The air foils guide the major quantity of air so it mixes with the larger particles of fuel oil spray beyond the diffuser.

ATOMIZERS.- Atomizers (devices for producing a fine spray) break up the fuel oil into very fine particles. In the following paragraphs we will briefly discuss the three types of atomizers. These three types are the return-flow atomizer, the steam-assist atomizer, and the vented-plunger atomizer.

Return-Flow Atomizer.- The return-flow atomizer provides a constant supply of fuel-oil pressure. Any fuel oil not needed to meet steam demand is returned to the fuel-oil service tank. This is accomplished by the return control valve installed in the piping between the boiler front and the service tank. As the return control valve is closed, more fuel oil is forced through the sprayer plate into the furnace. The return-flow atomizer is shown in figure 4-14

Figure 4-14.-Return-flow atomizer.

Figure 4-15.-TODD LVS atomizer.

Figure 4-16.---Y-Jet steam atomizer.

Steam-Assist Atomizer.- The steam-assist atomizer employs 150 psi of steam mixed with the fuel oil to help atomize the fuel oil. The two most common steam-assist atomizers in use by the Navy are the TODD LVS fig 4-15 and the Y-Jet fig 4-16. All steam-assist atomizers must have low-pressure air hookup for use as a substitute when suitable auxiliary steam is not available.

Vented-Plunger Atomizer.- The ventedplunger atomizer shown in figure 4-17 is unique in that it is the only atomizer in use in the Navy that has moving parts. The fuel oil flows down the atomizer barrel and around the atomizer cartridge. The pressure in the barrel forces the fuel oil into the cartridge through the holes drilled in the cartridge. As the fuel is forced into the cartridge, it begins to spin. This motion forces the fuel out through the orifice in a fine mist. Increasing fuel-oil pressure in the atomizer barrel and cartridge will cause the piston to overcome the spring pressure. The piston is then forced back, uncovering more holes and allowing fuel to be atomized and forced into the furnace. As pressure decreases, the opposite occurs. The spring tension recalls the piston, covering the holes and allowing less fuel oil to be atomized.

In most boilers, a torch is used to light fires. However, some boilers may have electric igniters.

Figure 4-17.-Vented-plunger atomizer.

We will describe the more common methodlighting fires with a torch.

Boiler light off is always a two-person operation. One person is needed to handle the torch, the air register, and the furnace, and the other to open the fuel-oil root valve. If fires do not light in 2 or 3 seconds, you must secure the fuel oil and investigate the reason for the failure to light. The boiler furnace must be inspected and repurged before the next attempt to light.

The basic light-off procedure involves the following steps:

1. Ensure that all fuel-oil manifold and atomizer/safety shut-off valves are shut.

2. Insert a clean atomizer with a lightingoff sprayer plate into the No. 1 burner.

3. Adjust the combustion air and fuel-oil pressures for lighting the fires.

4. Ignite the lighting-off torch.

5. Insert the lighted torch into the lightingoff port and close the port cover; visually check to ensure that the torch remains lighted. However, you should never insert a torch into a furnace until you are sure that no fuel is on the furnace deck and that the boiler has been purged of all combustible gases.

6. Open the No. 1 burner fuel-oil atomizer/ safety shut-off valve(s).

7. Open the No. 1 burner fuel-oil supply manifold valve one-half turn.

8. Observe the furnace through the No. 1 burner observation port to ensure that the ignition is successful.

9. Adjust the flame with the burner air register handle.

10. Open the No. 1 burner fuel-oil supply manifold to the fully open position.

11. Withdraw and extinguish the torch.

For specific lighting-off instructions, always refer to your ship's EOSS.

The following are a few simple suggestions to make your job easier and safer:

Do not operate any valves or start equipment until you have permission from the EOOW or EDO, and always refer to the EOSS.

Always clean up any spills or debris.

Report to your supervisor any condition that you think may be abnormal.

*Do not be afraid to ask questions!