Principles of naval engineering - Historic Naval Ships Association

Chapter 10- PROPULSION BOILERSpump in some other space to supply feed to theboiler. If the operating conditions do not allowthis solution of the problem, it will be necessaryto secure the boiler immediately in orderto prevent a low water casualty.FUEL SYSTEM CASUALTIESCasualties to any part of the fuel oil systemare serious and must be remedied at once.Common casualties include (1) oil in the fueloil heater drains, (2) water in the fuel oil, (3)loss of fuel oil suction, (4) failure of the fueloil service pump, and (5) fuel oil leaks. Itshould be noted that these casualties to the fueloil system are for ships burning NSFO. Theprocedures for ships burning other types of fuelwill differ to some extent, but not in all cases.Oil leakage from the fuel oil heaters intothe drains may cause oil contamination of thedrain lines, the reserve feed tanks, the deaeratingfeed tank, and the feed system piping andpumps. The presence of oil in any part of thefeed system is dangerous because of the possibilitythat the oil will eventually reach theboilers, where it will cause steaming difficultiesand serious damage to the boilers.Fuel oil heater drains must be inspectedhourly for the presence of oil.The presence of an appreciable amount ofwater in the fuel oil is indicated by hissing andsputtering of the fires and atomizers and byracing of the fuel oil service pump. The situationmust be remedied at once; otherwise, chokedatomizers, loss of fires, flarebacks, and refractorydamage may result.A loss of fuel oil suction usually indicatesthat the oil in the service suction tank hasdropped below the level of the fuel oil servicepump suction line. This causes a mixture ofair and oil to be pumped to the atomizers. Theatomizers begin to hiss and the fuel oil servicepump begins to race. It must be strongly emphasizedthat the loss of fuel oil suction cancause serious results. Related casualties mayinclude loss of auxiliary steam and electricpower, with the complete loss of all electricallydriven and steam-driven machinery.Failure of the fuel oil service pump cancause the same progressive series of casualtiesas those which result from loss of fuel oilsuction.Fuel oil leaks are very serious, no matterhow small they may be. Fuel oil vapors arevery explosive. Any oil spillage or leakage mustbe wiped up immediately.FLAREBACKSA flareback is likely to occur whenever thepressure in the furnace momentarily exceedsthe pressure in the boiler air casing. Flarebacksare caused by an inadequate air supplyfor the amount of oil being supplied, or by adelay in lighting the mixture of air and oil.Situations which commonly lead to flarebacksinclude: (1) attempting to light off or torelight burners from hot brickwork; (2) gunfireor bombing which creates a partial vacuum atthe blower intake, thus reducing the air pressuresupplied by the blowers; (3) forced draftblower failure; (4) accumulation of unburnedfuel oil or combustible gases in furnaces, tubebanks, uptakes, or air casings; and (5) anyevent which first extinguishes the burners andthen allows unburned fuel oil to spray out intothe hot furnace. An example of this last situationmight be a temporary interruption of thefuel supply which would cause the burners togo out; when the fuel oil supply returns tonormal, the heat of the furnace might not besufficient to relight the burners immediately.In a few seconds, however, the fuel oil sprayedinto the furnace would be vaporized, and aflareback or even an explosion might result.SUPERHEATER CASUALTIESIf the distant-reading superheater thermometerdoes not register a normal increase intemperature when the superheater is firstlighted off, the trouble may be either lack ofsteam flow or failure of the distant-readingthermometer. Lack of steam flow must be consideredas a possible cause even if the superheatersteam flow indicator (if installed) showsthat there is a flow. If the thermometer doesnot register a normal increase in temperature,secure all superheater burners.When operating with superheat, it is essentialto keep a constant check on the flow of steamthrough the superheater and on the superheateroutlet temperature. Any deviation from normalconditions must be corrected without delay.It is important to remember that a casualtyto some other part of the engineering plantmay reduce or entirely stop the flow of steamthrough the superheater, and so cause a superheatercasualty, unless appropriate action is273