Principles of naval engineering - Historic Naval Ships Association

Chapter 10- PROPULSION BOILERSTOSTACKFEED WATERECONOMIZERFEED WATERCOMBUSTION AIRADDITIONALSOURCE OFPOWER FORAIR COMPRESSOR-TURBINECOMPRESSORBURNERSPRESSURE-TIGHTBOILER FURNACECOMBUSTION GASESGENERATINGELEMENTSTODE5UPERHEATERIN BOILER DRUMSUPERHEATED STEAM TO ENGINESSUPERHEATERELEMENTSFigure 10-25.— Schematic view of pressurized-furnace boiler.147.86kind of energy transformation that occurs in asteam turbine; the difference is that hot combustiongases, rather than steam, carry theenergy to the gas turbine. After the combustiongases leave the gas turbine, some of the remainingheat may be used to heat feed ^water as itflows through an economizer.There are no forced draft blowers in pressurized-furnaceboiler installations. The superchargertakes the place of the forced draftblowers, thus greatly increasing plant efficiency.The steam saved by the use of a superchargerinstead of forced draft blowers may amount to asmuch as 8 or 10 percent of boiler capacity.Altogether, a pressurized-furnace boiler isnot much more than half the size and half theweight of a conventional boiler of equal steamcapacity. A large part of this saving of space andweight occurs because the increased pressure^on the combustion gas side causes a very greatincrease in the rate of heat transfer to the waterin the tubes. Thus a smaller generating surfaceis required to generate the same amount ofsteam. Another cause of space and weight savingis that the general design of the pressurizedfurnaceboiler eliminates the need for much ofthe refractory material that is required in otherForced draft blowers for conventional boiler installationsfurnish air pressures ranging from to 10pslg. In a pressurized-furnace boiler, the air compressorsupplies combustion air at pressures rangingfrom 30 to 90 psig.259