23-07-2014, 02:36 PM
BOILER
BOILER.pptx (Size: 1.69 MB / Downloads: 25)
INTRODUCTION
The term boiler is used for closed vessel in which water or other fluid is
heated. The older steam generators were commonly termed as boilers.
A bolier or steam generator is used whenever a source of steam is
required. The source of heat of boiler is combustion of any several
fuels, such as wood, coal, oil or natural gas. Electric steam boilers
used resistance or immersion type heating element. Nuclear fission is
also used as a heat source of generating steam.
Most boilers now depend on mechanical draught equipment rather
than natural draught. This is because natural draught is subjected to
outside air conditions and temp. of flue gasses leaving the furnace, as
well as chimney height.All these factors makes proper draught hard to
attain and therfore make mechanical draught equipment much more
economical.
WORKING OF BOILER
The burner mixes the fuel and oxygen together and, with the assistance
of an ignition device, provides a platform for combustion. This
combustion takes place in the combustion chamber, and the heat that
it generates is transferred to the water thorugh the heat exchanger.
controls regulate the ignition, burner firing rate, fuel supply, air supply,
exhaust draft, water temperature, steam pressure, and boiler pressure.
Hot water produced by a boiler is pumped through pipes and delivered
to equipment throughout the building, which can include hot water coils
in air handling units, service hot water heating equipment, and terminal
units. Steam boilers produce steam that flows through pipes from areas
of high pressure to areas of low pressure, unaided by an external energy
source such as a pump. Steam utilized for heating can be directly utilized
by steam using equipment or can provide heat through a heat exchanger
that supplies hot water to the equipment.
FIRE TUBE BOILER
In fire tube boilers, combustion gases passes through the inside of tubes with water surrounding the outside of the tube.
The most common fire tube boiler used in facility heating applications are often referred to as “scotch” or “scotch marine” boilers, as this boiler type was commonly used for marine service because of its compact size.
Fire tube boilers are:-
Relatively inexpensive
Easy to clean
Compact in size
Easy to replace tubes
The advantage of fire tube boiler are its simple construction and less rigid water treatment requirements.
The disadvantages are the excessive weight per pound of steam generated, excessive time required to raise the pressure because of relatively large volume of water, and inability to respond quickly to load changes, again, due to large water volume.
. STEAM AND CONDENSATE BOILER SYSTEM
Boilers are generally used to provide a source of steam or hot water for facility heating and process needs.
In steam and condensate system, heat is added to water in a boiler causing the water to boil and form steam.
The steam is piped to points requiring heat, and as the heat is transferred from the steam to the building area or process requiring heat, the steam condenses to form condensate.
In some very low pressure saturated steam heating application, the steam distribution piping may be sized to slope back to the boiler so that the steam distribution piping also acts as the condensate return piping.
. Feed water heaters =>
Feed water heaters are energy recovery devices generally found only in large steam generating plants where all of the steam generated is not reduced to condensate by the steam user. The boiler feed water is used as a cooling medium to reduce the steam to condensate, which increases the temperature of feed water and, thereby, increases the thermal efficiency of the boiler.
Combustion air blowers =>
In many packaged boiler installations, the combustion air fan is designed and provided by the boiler manufacturer and is integral with the boiler housing. In installations where a stand-alone fan is provided, low-pressure centrifugal blowers are commonly used.
Piping =>
Piping two inches and smaller used in steam and hot water system is typically schedule 80, American Society for Testing and Materials A 106, standard specification for seamless carbon pipe for high temperature service. Grade B, steel pipe with threaded joints and carbon steel fittings. Piping larger than two inches is typically standard weight, ASTM A106, Grade B, steel pipe with flanged joints and carbon steel fittings.