29-05-2013, 03:19 PM
Introduction on Boilers
Boilers.ppt (Size: 1.49 MB / Downloads: 124)
Boiler is an apparatus to produce steam. Thermal energy released by combustion of fuel is used to make steam at the desired temperature and pressure.The steam produced is used for:
(i) Producing mechanical work by expanding it in steam engine or steam turbine.
(ii) Heating the residential and industrial buildings
(iii) Performing certain processes in the sugar mills, chemical and textile industries.
Boiler properties:
(i) Safety. The boiler should be safe under operating conditions.
(ii) Accessibility. The various parts of the boiler should be accessible for repair and maintenance.
(iii) Capacity. Should be capable of supplying steam according to the requirements.
MERITS OF WATER TUBE BOILERS OVERFIRE TUBE BOILERS
1. Generation of steam is much quicker due to small ratio of water content to steam content. This also helps in reaching the steaming temperature in short time.
2. Its evaporative capacity is considerably larger and the steam pressure range is also high-200 bar.
3. Heating surfaces are more effective as the hot gases travel at right angles to the direction of water flow.
Demerits :
1. It is less suitable for impure and sedimentary water, as a small deposit of scale may cause the overheating and bursting of tube. Therefore, use of pure feed water is essential.
2. They require careful attention. The maintenance costs are higher.
3. Failure in feed water supply even for short period is liable to make the boiler over-heated.
Features
1. The evaporative capacity of this boilers is high compared with other boilers (20,000 to 40,000kg/hr). The operating pressure lies between 11.5 to 17.5 bar.
2. The draught loss is minimum compared with other boilers.
3. The defective tubes can be replaced easily.
4. The entire boiler rests over an iron structure, independent of brick work, so that the boiler may expand or contract freely. The brick walls which form the surroundings of the boiler are only to enclose the furnace and the hot gases.