Boilers

BoilersBy: Khalid Nawaz Institute Of Chemical Engineering And Technology University Of the Punjab Lahore Pakistan

What is a boiler/steam generator..??• A closed vessel made up of steel to transfer heat

produced by combustion of fuel to water and ultimately generate steam .

It may be defined as: A steam generator or boiler is usually a closed vessel

made of steel. Its function is to transfer the heat produced by the combustion of fuel to water and ultimately to generate steam.

What should characteristics of boiler..? Generate maximum steam.

Light in weight and not occupy large space.

Proper safety regulations.

Cheaper in cost.

Easy cope up with fluctuating demands of

requirements.

Easily accessible for inspection and repair.

Where Steam is Used

Steam is used in steam generators for production of electricity.

It is used as heating source for different purposes Steam is used for production of different products

in chemical industry.

Sources of heat in boiler..??

WOOD

COAL

DIESEL

NATURAL GAS

NUCLEAR ENERGY

 : 

Classification of boilers

Method of firing

Boilers

Pressure of steam

Circulation of water

Tube contain

Water tube

Fire tube

HighExternally

Natural Forced

LowInternally

Classification of Boilers:Boilers may be classified according to the following-

1. Relative position of Hot gases and Watera) Fire tube boiler: The hot gases passes through the tubes that are

surrounded by water. Fire tube boilers are also known by certain common names-

i) Horizontal return tubular ii) Locomotive fire box iii) Scotch marine and, iv) Vertical tubular

b) Water tube Boiler:

The water passes through the tubes and the hot gases produced by combustion of fuel, flow outside. This type of Boilers designated by the following common names:

i) Babcock and Wilcox Boiler (straight but inclined tubes which connect the headers).

ii) Stirling Boiler (multitubular boiler having bent tubes that connect boiler drums to headers).

BOILER MOUNTINGS AND ACCESSORIES

Boiler Accessories for efficient operation:

1. Water heating devices.2. Water feeding devices.3. Super heater4. Economizer5. Air preheater

Mountings..??

The boiler mountings are the part of the boiler and are required for proper functioning.

In accordance with the Pakistan Boiler regulations, of the boiler mountings is essential fitting for safe working of a boiler.

Water level indicator..?? Water level indicator

is located in front of boiler in such a position that the level of water can easily be seen by attendant. Two water level indicators are used on all boilers.

Pressure gauge..??

A pressure gauge is fitted in front of boiler in such a position that the operator can

conveniently read it. It reads the pressure of steam in the boiler and is connected to steam

space by a siphon tube. The most commonly,

the Bourdon pressure gauge is used

Safety valve..??

Safety valves are located on the top of the boiler. They guard the boiler against the excessive

high pressure of steam inside the drum. If the pressure of steam in the boiler drum exceeds

the working pressure then the safety valve allows blow-off the excess quantity of steam to

atmosphere. Thus the pressure of steam in the drum falls. The escape of steam makes a

audio noise to warm the boiler attendant. There are four types of safety valve. 1. Dead weight safety valve. 2. Spring loaded safety valve 3. Lever loaded safety valve 4. High steam and low water safety valve

Dead weight safety valve Spring loaded safety valve

Lever loaded safety valve

Fusible Plug It is very important safety device, which protects the fire tube boiler against overheating. It is located just above the furnace in the boiler. It consists of gun metal plug fixed in a gun metal body with fusible molten metal. During the normal boiler operation, the fusible plug is covered by water and its temperature does not rise to its melting state. But when the water level falls too low in the boiler, it uncovers the fusible plug. The furnace gases heat up the plug and fusible metal of plug melts, the inner plug falls down The water and steam then rush through the hole and extinguish the fire before any major damage occurs to the boiler due to overheating.

Blow-Off Cock

The function of blow-off cock is to discharge mud and other sediments deposited in the bottom most part of the water space in the boiler, while boiler is in operation. It can also be used to drain-off boiler water. Hence it is mounted at the lowest part of the boiler. When it is open, water under the pressure rushes out, thus carrying sediments and mud.

Feed Check Valve

The feed check valve is fitted to the boiler, slightly below the working level in the boiler. It is used to supply high pressure feed water to boiler. It also prevents the returning of feed water from the boiler if feed pump fails to work.

Steam Stop Valve

The steam stop valve is located on the highest part of the steam space. It regulates the steam supply to use. The steam stop valve can be operated manually or automatically.

Boiler Accessories: Air preheater : It utilize the heat of exhaust gases.

Economizer: Heat is used to raise the temperature of feed water supplied to the boiler.

Steam super heater: Used to super heat the steam.

Feed pump: Raise the pressure of water and force it into the boiler.

Injector: Used to feed water in boilers.

Economizer Function:

An economizer is a device in which

the waste heat of the flue gases is

utilized for heating the feed water.

Economizer are of two types :

a) Independent type, and

b) Integral type

Injector:

Function:

The function of an injector is to

feed water into the boiler. It is also

used where the space is not

available for the installation of a

feed pump

Feed pump Function:

Its is a pump which is used to deliver

feed water to the boiler.

The appliances in common use for

delivering the feed-water into the

steam boilers are:

a) Reciprocating pump

b) Rotary pump

Boiler efficiency

Ratio of heat actually utilized in the generator to the heat supplied by the fuel.

Efficiency= ma ( h – hf)/c

Where, C is the calorific value of the fuel.

Conclusion:

Boilers are most important part of chemical industry.99 % boilers used in Pakistan chemical industries are water tube boilers because of their high efficiency and safety.so we should have cler understanding about the boilers.