Boiler Draught PDF

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Boiler Draught Boiler  A boiler or steam generator is a closed vessel in which water under pressure, is converted into steam.  Boiler is a closed vessel in which water or other fluid is heated.  The fluid does not necessarily boil.  The heated or vaporized fluid exits the boiler for use in vario...

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Boiler Draught Durgesh Chaurasia

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Boiler Draught

Boiler 

A boiler or steam generator is a closed vessel in which water under pressure, is converted into steam.



Boiler is a closed vessel in which water or other fluid is heated.



The fluid does not necessarily boil.



The heated or vaporized fluid exits the boiler for use in various processes or heating applications.



E.g. water heating, central heating, boiler-based power generation, cooking, and sanitation.

Boiler :-

Boilers Are Of Two Types :

According to what flows in the TUBE :-

Fire tube boiler 2) Water tube boiler 1)

Fire Tube Boiler :-

Water Tube Boiler :-

Boiler Draught :

The draught is one of the most essential systems of thermal power plant which supplies required quantity of air for combustion and removes the burnt products from the system



To move the air through the fuel bed and to produce a flow of hot gases through the boiler, economizer, preheater and chimney require a difference of pressure.



This difference of pressure for to maintaining the constant flow of air and discharging the gases through the chimney to atmosphere is known as DRAUGHT.

Types Of Draught : Natural

Draught  Artificial Draught

Natural Draught :

The Draught required for the flow of air & gas inside the boiler is created by Chimney



It does not require any external power for producing the draught.



The capital investment is less.



It has long life.

Limitations Of Natural Draught :

Pressure :- maximum is 15 – 20 mm of water under normal atmospheric Temp.



The draught decreases with increase in outside air temperature and for producing sufficient draught.



The flue gases have to be discharged at comparatively high temperatures resulting in the loss of overall plant efficiency. And thus maximum utilization of Heat is not possible.



Combution is very poor.

Artificial Draught :

Because of insufficient head and lack of flexibility, The use of natural draught is limited to small capacity boilers only.



The draught required in actual power plant is sufficiently high (300 mm of water) and to meet high draught requirements, some other system must be used which are known as artificial draught.

Classification of Artificial Draught :1.Forced 2.Induced 3.Balanced

Advantages over natural draught :

It is better in control and more economical than natural draught.



The rate of combustion is high.



The air flow can be regulated according to the requirement.



It prevents the formation of smoke as complete combustion is possible

Limitations of Artificial Draught :

The major disadvantage of the artificial draught is the high capital cost required and high running and maintenance costs.

Importance :

For the proper and the optimized heat transfer from the flue gases to the boiler tubes draft holds a relatively high amount of significance.



The combustion rate of the flue gases and the amount of heat transfer to the boiler are both dependent on the movement and motion of the flue gases.



A boiler equipped with a combustion chamber which has a strong current of air (draft) through the fuel bed will increase the rate of combustion.

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