THERMODYNAMICS MANUAL / B-TECH MECH / LANCASHIRE BOILER

AIM: - TO STUDY OF LANCASHIRE BOILER

APPARATUS: - A MODEL OF LANCASHIRE BOILER

THEORY: -

A LANCASHIRE BOILER IS A DOUBLE FIRE TUBE BOILER, INTERNALLY FIRED, HORIZONTAL, NATURAL DRAUGHT, AND NATURAL CIRCULATION TYPE OF BOILER. THIS BOILER IS VERY POPULAR AND RELIABLE BECAUSE OF SIMPLICITY OF DESIGN AND EASE OF OPERATION. THE BOILER HAS GOOD STEAMING QUALITY, AND COAL OF INFERIOR QUALITY CAN BE USED. IT HAS LOW MAINTENANCE AND OPERATING COST. THIS BOILER IS WIDELY USED IN SUGAR MILLS AND CHEMICAL INDUSTRIES. THIS BOILER IS USED WHERE LARGE RESERVOIR OF WATER AND STEAM ARE REQUIRED.

ITS MAIN FEATURES AND BRICKWORK SETTING IS SHOWN IN THE FIGURE. SEVERAL RINGS OF STEEL PLATES WE ARE EITHER WELDED OR RIVETED TO MAKE THE CYLINDRICAL SHELL OF SUITABLE DIMENSIONS. THIS BOILER HAS TWO PARALLEL FLUE PIPES THROUGH OUT THE LENGTH OF BOILER. BOTH THE FLUE TUBES, WHICH CARRY HOT GASES, LAY BELOW THE WATER LEVEL. TO ACCOMMODATE A GRATE OF SUFFICIENT AREA AND MINIMUM LENGTH, THESE FLUE TUBES ARE LARGER IN DIAMETER AT THE FRONT OF THE SHELL. TO CONTROL THE GAS FLOW AND TO CONTROL THE AMOUNT OF AIR ENTERING THE GRATE, DAMPERS ARE USED WHICH ARE PLACED IN PATH OF FLUE GASES.

COAL IS FED TO THE GRATES THROUGH FIRE DOORS. EACH OF THE FLUE TUBES HAS ITS OWN FURNACE WITH GRATES WHERE ITS COMBUSTION TAKES PLACE AND THE FLUE GASES RISING FROM THE FURNACES PASS OVER THE FIRE BRIDGE AND TRAVERSE ALONG THE HORIZONTAL PATH. THE HOT GASES LEAVING THE GRATE PASS UP TO THE BACK END OF THE TUBES AND THEN TRAVEL BACK FROM THE BOTTOM FLUE PASSAGE TO THE FRONT OF BOILER, WHERE THE GASES BIFURCATE AND PASS INTO THE TWO SIDE FLUES. THEREAFTER, THE GASES IN THE TWO SIDE FLUES ENTER THE COMMON FLUE AND FINALLY DISCHARGED TO THE ATMOSPHERE THROUGH CHIMNEY.

THE VARIOUS MOUNTINGS ARE:-

• SAFETY VALVE: - THE FUNCTION OF SAFETY VALVE IS TO PERMIT THE STEM IN THE BOILER TO ESCAPE TO ATMOSPHERE WHEN PRESSURE IN THE STEAM SPACE EXCEEDS A CERTAIN SPECIFIED LIMIT. IT IS LOCATED ABOVE STEAM SPACE IN THE BOILER.

• WATER LEVEL INDICATOR: - THE FUNCTION OF THE WATER LEVEL INDICATOR IS TO ASCERTAIN CONSTANTLY AND EXACTLY THE LEVEL OF WATER IN THE BOILER SHELL.

• FUSIBLE PLUG: - ITS FUNCTION IS TO EXTINGUISH THE FIRE IN THE EVENT OF WATER LEVEL IN THE BOILER SHELL FALLING BELOW A CERTAIN SPECIFIED LIMIT.

• PRESSURE GAUGE: - ITS FUNCTION IS TO SHOW THE PRESSURE AT WHICH THE STEAM IS BEING GENERATED IN THE BOILER.

• BLOW OFF COCK: - THE BLOW OFF COCK SERVES TO DRAIN OUT THE WATER FROM THE BOILER AND TO DISCHARGE MUD SCALE ETC. PERIODICALLY OR TO EMPTY THE BOILER FOR INTERNAL CLEANING AND INSPECTION ETC.

• FEED CHECK VALVE: - THE FEED CHECK VALVE ALLOWS THE FEED WATER TO PASS INTO THE BOILER AND TO PREVENT THE BACK FLOW OF WATER FROM THE BOILER IN THE EVENT OF FAILURE OF FEED PUMP.

HIGH STEAM & LOW WATER SAFETY VALVE:-

THE FUNCTION OF HIGH STEAM & LOW WATER SAFETY VALVE IS TWO FOLD: ---

• IT BELOW OUT STEAM WHEN THE WATER LEVEL IN THE BOILER IS LOW.
• IT BLOWS OUT STEAM IF THE STEAM PRESSURE IS HIGHER THAN THE WORKING PRESSURE.

MAN HOLE: - THESE ARE DOORS TO ALLOW MEN TO ENTER INSIDE BOILER FOR REPAIR OR INSPECTION.

THE ACCESSORIES USED IN THIS BOILER ARE:-

• SUPER HEATER: - THE FUNCTION OF SUPER HEATER IS TO SUPERHEAT THE STEAM (USUALLY WET) GENERATED IN THE BOILER BY THE HEAT IN EXHAUST FLUE GASES.
• ECONOMIZER: - ECONOMIZER IS USED TO RECOVER SOME OF THE HEAT FROM THE HEAT CARRIED AWAY IN THE FLUE GASES UP THE CHIMNEY & UTILIZED FOR HEATING THE FEED WATER TO THE BOILER.