Chapter 10- PROPULSION BOILERS 



no useful purpose in combustion and is a direct 

 source of heat loss. 



Calculations will show that approximately 

 14 pounds of air will furnish the oxygen theo- 

 retically required for the complete combustion 

 of 1 pound of fuel. In actual practice, of course, 

 the amount of air necessary to ensure complete 

 combustion must be somewhat in excess of that 

 theoretically required. About 10 to 15 percent 

 excess air is usually sufficient to ensure proper 

 combustion. Too much excess air serves no 

 useful purpose, but merely absorbs and carries 

 off heat. 



When fuel is burned in the boiler furnace, 

 the difference between the HEAT INPUT and the 

 HEAT ABSORBED represents the HEAT LOSS. 

 Heat losses may be unavoidable, avoidable, or— 

 in some cases— avoidable only to a limited ex- 

 tent. Most heat losses may be accounted for, 

 but some losses cannot normally be accounted 

 for. 



All fuel contains a small amount of mois- 

 ture which must be evaporated and superheated 

 to the furnace temperature. Since the expendi- 

 ture of heat for this purpose constitutes a heat 

 loss in terms of boiler efficiency, every pre- 

 caution should be taken to prevent contamination 

 of the fuel oil with water. 



All fuel contains some hydrogen which, when 

 combined with oxygen by the process of com- 

 bustion, forms water vapor. This water vapor 

 must be evaporated and superheated, and in both 

 processes it absorbs heat. Consequently, al- 

 though the heat of combustion of hydrogen is 

 very great, a small heat loss occurs because 

 the water vapor formed as a result of the com- 

 bustion of hydrogen must be evaporated and 

 superheated. 



Since atmospheric air is the source of the 

 oxygen utilized for combustion in the boiler 

 furnace, there is bound to be some moisture in 

 the combustion air. This moisture must be 

 evaporated and superheated, and therefore con- 

 stitutes a heat loss. 



The heat loss due to heat being carried away 

 by combustion gases is the greatest of all the 

 heat losses that occur in a boiler. Although 

 much of this heat loss is unavoidable, some 

 may be prevented by keeping all heat-transfer 

 surfaces clean and by using no more excess air 

 than is actually required for combustion. 



Another heat loss occurs because of in- 

 complete combustion of the fuel. When the carbon 

 in the fuel is burned to carbon monoxide, instead 

 of carbon dioxide, there is a tremendous heat 



loss of 10,100 Btu per pound. This should be 

 considered an avoidable loss, since the admis- 

 sion of a sufficient amount of excess air will 

 ensure complete combustion. 



Heat losses that cannot be measured or 

 that are impracticable to measure are (1) losses 

 due to unburned hydrocarbons, gaseous or solid; 

 (2) losses due to radiation; and (3) other losses 

 not normally accounted for. 



FIREROOM OPERATIONS 



Although a complete discussion of fireroom 

 operations is beyond the scope of this text, 

 some understandingof the major factors involved 

 in boiler operation may be useful. 



Basically, the fireroom force must control 

 three inputs— feed water, fuel, and combustion 

 air— in order to provide one output, steam. Under 

 steady steaming conditions, when steam demands 

 are relatively constant for long periods of time, 

 there is no great difficulty about providing a 

 uniform flow of steam to the propulsion turbines. 

 But one of the special requirements of naval 

 ships is that they must be able to maneuver and 

 to change speed quickly, and this requirement 

 imposes upon the fireroom force the responsi- 

 bility for making very rapid increases and de- 

 creases in the amount of steam furnished to the 

 engineroom. Under conditions of rapid change, 

 boiler operation is a teamwork job that requires 

 great skill and alertness and smooth coordina- 

 tion of efforts by several men. 



For manual operationof the boilers, a normal 

 fireroom watch consists of one petty officer in 

 charge of the watch; one checkman for each 

 operating boiler; one burnerman for each oper- 

 ating boiler front; one blowerman for each 

 operating boiler; and one or more men to act 

 as messengers and to check the operation of 

 the auxiliary machinery. When automatic boiler 

 controls are installed, boilers may be operated 

 with fewer men on watch when the controls are 

 being used. 



When a boiler is being operated manually, 

 the checkman controls the water level in the 

 boiler by manual operation of the feed stop and 

 check valves. The checkman stands at the upper 

 level, near the feed stop and check valves, and 

 near the boiler gage glass. The checkman admits 

 water to the boiler as necessary to maintain the 

 water at or very near the designed water level. 

 The check watch requires the utmost vigilance 

 and reliability; if any one job in the fireroom 



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