Dr. RIYADH S. AL-TURAIHI
POWER PLANT
LEC.NO.(3)
____________________________________________________________________
Steam Generator(Boiler)
Boiler is an apparatus to produce steam. Thermal energy released by
combustion of fuel is transferred to water, which vaporizes and gets
converted into 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 is a closed vessel in which water is converted into steam by the
application of heat. Usually boilers are coal or oil fired. A boiler should
fulfill the following requirements
(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. The boiler should be capable of supplying steam
according to the requirements.
(iv) Efficiency. To permit efficient operation, the boiler should be able to
absorb a maximum
amount of heat produced due to burning of fuel in the furnace.
(v) It should be simple in construction and its maintenance cost should be
low.
(vi) Its initial cost should be low.
(vii) The boiler should have no joints exposed to flames.
(viii) The boiler should be capable of quick starting and loading.
The performance of a boiler may be measured in terms of its evaporative
capacity also called power of a boiler. It is defined as the amount of water
evaporated or steam produced in kg per hour. It may also be expressed in
kg per kg of fuel burnt or kg/hr/m2 of heating surface.
CLASSIFICATION:
1-Steam pressure:
A-Low pressure P < 2.4 Mpa
C- High pressure P>6.4
B- Medium pressure 2.4 <P<6.4
Dr. RIYADH S. AL-TURAIHI
POWER PLANT
LEC.NO.(3)
____________________________________________________________________
2-Steam output:
A-Small capacity
̇ <10 ton/hr
B-medium capacity
10 < ̇ <50 ton/hr
C-High capacity
50 < ̇ <150 ton/hr
D- Super high capacity
̇ >150 ton/hr
3- Water content:
A- With high water content.
B- With low water content.
4-Tube arrangement:
A-Fire tube (shell)
B-Water Tube Boiler
5-Material:
A-Cost Iron
B- Steel
6-Setting:
A-Brick set
B- Portable
7-flue gas travel:
A-Single pass
8- Draft:
A-direct up draft
9-fuel type:
A- oil
B-Multi pass
B-direct down draft
B-gas
C-coal
Content:
1-Water container
2-Heating device
Steam Formation And Thermal Efficiency Improvement
Methods:
1-Superheated steam:
Wet steam is passed through the superheated which consist of along tube
or series of tube suspended across the path of the hot gases from furnaces
.The degree of superheat is controlled by injection of water or steam in
the superheated steam.
2-Reheater:
Dr. RIYADH S. AL-TURAIHI
POWER PLANT
LEC.NO.(3)
____________________________________________________________________
An improvement of cycle thermal efficiency can be achieved by
installation of a reheater, to avoid wet steam in the low-pressure stages of
the turbine.
3-Economizer:
The flue gases are passed into the economizer, which is a heat exchanger
to heat feed water into the boiler.
4-Air preheater:
The flue gases are still hot, further efficiency improvement can be
obtained by passing then into the air heater which is a heat exchanger
used to heat the air ducted to the furnace to get high furnace temperature
,more steam and hence high efficiency.
5-Attemperator:
In which the steam temperature is reduced by removing heat from the
steam:
1-Tubular type: in this case, the boiler water is used as a cooling medium.
2-water injection: water from the boiler is sprayed directly into the steam
.This water is evaporated ,hence the temperature of mixture is reduced.
Steam generator:
Is a complex combination of economizer ,boiler, super heater, reheater
and preheater
Boiler heating surface:
Heating surfaces either direct or indirect:
1-Direct surfaces:
Are those through which the light or fire shines. They are effective for
heat transfer to water.
2-Indirect surfaces:
Are those in contact with flue gases. Types:
a- fire tubes boilers: in which hot gases pass through tubes surrounded by
water
b-water tube boilers: In which water circulates through tubes surrounded
by hot gases.