THERMODYNAMICS MANUAL / B- TECH MECHANICAL/ BABCOCK & WILCOX BOILER

AIM: - TO STUDY OF LOCOMOTIVE BOILER

APPARATUS:-A MODEL OF LOCOMOTIVE BOILER.

THEORY:-

A FIRE-TUBE BOILER IS A TYPE OF BOILER IN WHICH HOT GASES FROM A FIRE PASS THROUGH ONE OR MORE TUBES RUNNING THROUGH A SEALED CONTAINER OF WATER. THE HEAT ENERGY FROM THE GASES PASSES THROUGH THE SIDES OF THE TUBES BY THERMAL CONDUCTION, HEATING THE WATER AND ULTIMATELY CREATING STEAM.

THE FIRE-TUBE BOILER DEVELOPED AS THE SECOND OF THE THREE MAJOR HISTORICAL TYPES OF BOILERS: LOW-PRESSURE TANK OR "HAYSTACK" THIS TYPE OF BOILER WAS USED ON VIRTUALLY ALL STEAM LOCOMOTIVES IN THE HORIZONTAL "LOCOMOTIVE" FORM. THIS HAS A CYLINDRICAL BARREL CONTAINING THE FIRE TUBES, BUT ALSO HAS AN EXTENSION AT ONE END TO HOUSE THE "FIREBOX". THIS FIREBOX HAS AN OPEN BASE TO PROVIDE A LARGE GRATE AREA AND OFTEN EXTENDS BEYOND THE CYLINDRICAL BARREL TO FORM A RECTANGULAR OR TAPERED ENCLOSURE.

A FIRE-TUBE BOILER IS SOMETIMES CALLED A "SMOKE-TUBE BOILER" OR "SHELL BOILER" OR SOMETIMES JUST "FIRE PIPE".

A LOCOMOTIVE BOILER IS A FIRE TUBE, INTERNALLY FIXED, HORIZONTALLY, MULTI TUBULAR BOILER. IT IS MAINLY EMPLOYED IN LOCOMOTIVES THROUGH IT MAY ALSO BE USED AS A STATIONARY BOILER. THE HOT GASES WHICH ARE GENERATED DUE TO BURNING OF THE COAL ARE DEFLECTED BY AN ARCH OF A FIRE BRICKS, SO THAT WALLS OF THE FIRE BOX MAY BE HEATED PROPERLY.

IN THE LOCOMOTIVE-TYPE BOILER, FUEL IS BURNT IN A FIREBOX TO PRODUCE HOT COMBUSTION GASES. THE FIREBOX IS SURROUNDED BY A COOLING JACKET OF WATER CONNECTED TO THE LONG, CYLINDRICAL BOILER SHELL. THE HOT GASES ARE DIRECTED ALONG A SERIES OF FIRE TUBES, OR FLUES, THAT PENETRATE THE BOILER AND HEAT THE WATER THEREBY GENERATING SATURATED ("WET") STEAM.

IN THE LOCOMOTIVE BOILER, THE SATURATED STEAM IS VERY OFTEN PASSED INTO A SUPERHEATER, BACK THROUGH THE LARGER FLUES AT THE TOP OF THE BOILER, TO DRY THE STEAM AND HEAT IT TO SUPERHEATED STEAM.

DRAUGHT FOR FIRE TUBE BOILERS, PARTICULARLY IN MARINE APPLICATIONS, IS USUALLY PROVIDED BY A TALL PARTIAL VACUUM. MODERN INDUSTRIAL BOILERS USE FANS TO PROVIDE FORCED OR INDUCED DRAUGHTING OF THE BOILER.

ANOTHER MAJOR ADVANCE IN THE ROCKET WAS LARGE NUMBERS OF SMALL-DIAMETER FIRE TUBES (A MULTI-TUBULAR BOILER) INSTEAD OF A SINGLE LARGE FLUE. THIS GREATLY INCREASED THE SURFACE AREA FOR HEAT TRANSFER, ALLOWING STEAM TO BE PRODUCED AT A MUCH HIGHER RATE. WITHOUT THIS, STEAM LOCOMOTIVES COULD NEVER HAVE DEVELOPED EFFECTIVELY AS POWERFUL PRIME MOVERS.

LOCOMOTIVE-TYPE BOILERS ARE ALSO USED IN TRACTION ENGINES, STEAM ROLLERS, PORTABLE ENGINES AND SOME OTHER STEAM ROAD VEHICLES. THE INHERENT STRENGTH OF THE BOILER MEANS IT IS USED AS THE BASIS FOR THE VEHICLE: ALL THE OTHER COMPONENTS, INCLUDING THE WHEELS, ARE MOUNTED ON BRACKETS ATTACHED TO THE BOILER. IT IS RARE TO FIND SUPERHEATERS DESIGNED INTO THIS TYPE OF BOILER, AND THEY ARE GENERALLY MUCH SMALLER (AND SIMPLER) THAN RAILWAY LOCOMOTIVE TYPES.