Boilers

UNIT 2 Boilers

Dr S MuraliDr. S. Murali

Professor & Head

Department of Mechanical Engineering

Boiler

is an apparatus to produce steam.

– Thermal energy released by combustion of fuel is d k h d i dused to make steam at the desired temperature

and pressure.

Simple Boiler

Applications

• The steam produced is used for:– Producing mechanical work by expanding it in steam engine or steam turbine.H i h id i l d i d i l b ildi– Heating the residential and industrial buildings

– Performing certain processes in the sugar mills, h i l d t til i d t ichemical and textile industries.

Boiler Requirements

• Safety. Th b il h ld b f d ti– The boiler should be safe under operating conditions.

A ibilit• Accessibility. – The various parts of the boiler should be accessible f i d i tfor repair and maintenance.

• Capacity. – Should be capable of supplying steam according to the requirements.

Boiler Requirements

• Efficiency. Sh ld b bl t b b i t f– Should be able to absorb a maximum amount of heat produced due to burning of fuel in the furnacefurnace.

• Constructioni l i t ti– simple in construction .

• Cost – Its initial cost and maintenance cost should be low.

Boiler Requirements

• Joints.Th b il h ld h j i t d t– The boiler should have no joints exposed to flames.

E f t ti• Ease of starting.– Should be capable of quick starting and loading.

Boiler Classification

1. According to the flow of water and hot gases Fi t b ( k t b )a. Fire tube (or smoke tube) Eg: Cochran, Lancashire and Locomotive boilers

b Water tube boilersb. Water tube boilersEg: babcock & Wilcox boiler, Sterling boiler .

2 A di t th i f th h ll2. According to the axis of the shell a. Vertical boilersb. horizontal boilersc. Inclined


3. According to location or position of the furnacefurnace. a. Externally fired boilers.

ti l t b l l ti d th t h i b ilvertical tubular, locomotive and the scotch marine boilers

b. internally fired boilersCochran lancashireCochran, lancashire

4. According to the application ia. stationery

b. mobile boilers.


5. According to steam pressure L (15 20b )a. Low (15 – 20bar)

b. medium and (20 – 80bar)h h b l ( h b )c. high pressure boilers(more than 80 bar)a. Subcritical(less than 221 bar)b S iti l( th 221b )b. Supercritical(more than 221bar)

6. According to water circulation arrangementa. Natural Circulation

Lancashire, babcock and wilcox boiler

b d i l ib. Forced circulationVelox, lamont, benson boiler

Fire Tube boiler

advantages of fire tube boilers

• Low costFl i f d d b• Fluctuations of steam demand can be met easily

• It is compact in size.

Simple Vertical boilerCapacity‐2500 kg/hrPressure 7‐10 barPressure 7 10 bar

Cochran BoilerSalient features• The dome shape of the furnace

causes the hot gases to deflectcauses the hot gases to deflect back and pass through the flue. The un‐burnt fuel if any will also be deflected backbe deflected back.

• Spherical shape of the top of the shell and the fire box gives higher area by volume ratioarea by volume ratio.

• It occupies comparatively less floor area and is very compact.

• It is well suited for small capacity• It is well suited for small capacity requirements.

Cochran Boiler- features

• very compact and requires minimum floor areaarea

• Any type of fuel can be used with this boiler• Well suited for small capacity requirements• gives about 70% thermal efficiency with coal g yfiring and about 75% with oil firing

Cochran Boiler- features

• Pressure GaugeW L l I di• Water Level Indicator

• Safety Valve• Fusible Plug• Blow‐off CockBlow off Cock • Steam Stop Valve F d Ch k V l• Feed Check Valve

Cornish Boiler

No. of Flue tubes one

Diameter of Shell 1.25 to 1.75 m

Length of shell 4 to 7m

Max. Working Pressure 10.5 bar

Steam Capacity 6500 kg/hr

Lancashire Boiler

Di f Sh ll 2 3Diameter of Shell 2 to 3 m

Length of shell 7to 9m

Max. Working Pressure 16 bar


Efficiency 50 to 60 %

Lancashire boiler• It is stationary fire tube, internally fired, horizontal, natural circulation boiler. hi i id l d b il b f i d i• This is a widely used boiler because of its good steaming quality and its ability to burn coal of inferior quality.

• These boilers have a cylindrical shell 2 m in diameters and l h fits length varies from 8 m to 10 m.

• It has two large internal flue tubes having diameter between 80 cm to 100 cm in which the grate is situated.

• This boiler is set in brickwork forming external flue so that the external part of the shell forms part of the heating surface.

AdvantagesAdvantages• The feed pipe projecting into the boiler is perforated to ensure uniform water distribution.

• Its heating surface area per unit volume at the boiler is considerably large.

• Its maintenance is easy.Its maintenance is easy.• It is suitable where a large reserve of hot water is needed. This boiler due to the large reserve capacity can easily meet load fluctuationscan easily meet load fluctuations.

• Super‐heater and economizer can be easily incorporated into the system, therefore; overall ffi i f h b il b id bl i defficiency of the boiler can be considerably increased (80‐85%).

LOCOMOTIVE BOILERLOCOMOTIVE BOILER

Locomotive boiler


Muhammad Fadhli Mustaffa & Ahmad Lutfi Mohayiddinff f y


• horizontal fire tube type mobile boiler. • produce steam at a very high rate Therefore• produce steam at a very high rate. Therefore, this boiler requires a large amount of heating surface and large grate area to burn coal at asurface and large grate area to burn coal at a rapid rate. In order to provide the large heating surface area, a large number of fire g , gtubes are setup

• heat transfer rate is increased by creating y gstrong draught by means of steam jet.

AdvantagesAdvantages

• Large rate of steam generation per square metre of heating surface To some extent thismetre of heating surface. To some extent this is due to the vibration caused by the motion.I i f f b i k k i l f d i• It is free from brickwork, special foundation and chimney. This reduces the cost of i ll iinstallation.

• It is very compact.• The pressure of the steam is limited to about 20 bar.

Scotch BoilerMax. Working Pressure 17 barg


Water Tube Boiler

Merits Of Water Tube BoilersMerits Of Water Tube Boilers1. 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 larger2. 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 flowwater flow.

Merits Of Water Tube BoilersMerits Of Water Tube Boilers4. The combustion efficiency is higher because complete combustion of fuel is possible as the p pcombustion space is much larger.

5 Th h l i h b il5. The thermal stresses in the boiler parts are less as different parts of the boiler remain at uniform temperature due to quick circulationuniform temperature due to quick circulation of water.

6. The boiler can be easily transported and erected as its different parts can be separated.

Merits Of Water Tube BoilersMerits Of Water Tube Boilers7. Damage due to the bursting of water tube is less serious. Therefore, water tube boilers are sometimes called safety boilers.

8 All f h b b il il8. All parts of the water tube boilers are easily accessible for cleaning, inspecting and repairing.repairing.

9. The water tube boiler's furnace area can be easily altered to meet the fuel requirements.

Demerits

1. It is less suitable for impure and sedimentary water as a small deposit of scale may causewater, as a small deposit of scale may cause the overheating and bursting of tube. Therefore use of pure feed water is essentialTherefore, use of pure feed water is essential.

2. They require careful attention. The i hi hmaintenance costs are higher.

3. Failure in feed water supply even for short period is liable to make the boiler over‐heated.

Water tube Vs Fire tube

Water tube Vs Fire tube

Water tube boilers classification

1. Horizontal straight tube boilersL it di l da. Longitudinal drum

b. Cross‐drum.

2. Bent tube boilersa. Two drum b. Three drumc. Low head three drum d. Four drum.

3. Cyclone fired boilersy

BABCOCK WILCOX BOILERBABCOCK WILCOX BOILER

Features• 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.

• The draught loss is minimum compared with other boilers.h d f b b l d l• The defective tubes can be replaced easily.

• The entire boiler rests over an iron structure, independent of brick work, so that the boiler may expand or contract freely.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.

Stirling Boiler

High pressure Boilers

Lamont Boiler

Loeffler Boiler

Benson Boiler

Schmidt-Hartmann Boiler

Velox Boiler

Reference

Business

Boilers