After completion of the section you'll be able to identify all major components
and explain their design and function
the boiler is a complicated construction of steel tubes pipes and drums the
primary boiler of the d-type has an upper and a lower drum connected
together with hundreds of tubes and pipes the upper drum is the steam water
drum and the lower one the water drum water is circulating inside the pipes
that are arranged as warz
inside the furnace the water in the risers is heated by the flames from the
oil burners as the density of waters 30 times the density of steam the mixture
of steam and water will flow to the top drum the heavier water in the top drum
will flow back to the lower drum through the downcomers
outside the furnace Wars the steam water mixture travels around in the boiler to
velocity of zero point three to one meters per second in the epiderm the
steam will leave the water saturated steam the water content of approximately
0.25 percent primary steam is entering the evaporating coil in the secondary
steam drum and is condensed as the energy is transferred to the secondary
steam system this steam is heated above boiling temperature and is passing the
super heater in the furnace close to the burners the temperature can reach to a
thousand degrees centigrade so it is very important that we always have a
sufficient flow steam through the super heater when we are firing the boiler
you the feed water coming from the
economizer is always colder than the water in the boiler it is mixed to the
hot water by a long perforated feed pipe inside the upper drum
approximately 30% of the energy the fuel oil to the diesel engine is lost in the
exhaust gas to utilize some of this energy loss we install exhaust gas
boilers and yep take
exhaust gas dampers control the amount of heat allowed through to the
evaporating coils in the boiler as this boiler is an integrated part of the
total steam plant a set of circulation pumps forced the feed water through the
exhaust gas boiler when we are firing the boiler the exhaust gas boiler is
equipped with such blowers to keep it clean and efficient to minimize the loss
of energy in the exhaust gas several types of air preheater
have been developed young strums rotating air preheater is a common type
several thousands of steel plates are arranged in a large cylindrical housing
an electrical motor turns the preheater at a rate of two to five revolutions per
minute the exhaust gas heats about 60% the steel plates and at the same time
the air cools the remaining 40% the air preheater works according to the counter
flow principle bypassed dampers on the air and exhaust side controlled the flow
exhaust temperature below 110 degree centigrade results in the formation of
sulfuric acid the economizer is placed in exhaust gas uptake below the air
preheater this can be a single unit or several units working together the feed
water pump pushes the feed water through the economizer before it enters the
steam water drum the water temperature can increase to above 230 degrees
centigrade
if the economizer temperature gets too high the feed water will start to
evaporate and the steam may reduce the free flow of feed water to increase the
energy content of the steam and thereby the steam plant thermal efficiency and
dry it completely the saturated steam passes the super heater before it leaves
the boiler
like the economizer the superheater can be arranged differently from one type of
boiler to another usually the superheater tubes are protected by one
or more walls of risers in this way the hottest gases past these risers first
and a combustion temperature is less harmful to the superheated tubes the
steam outlet temperature from the super heater can be well above 500 degrees
centigrade not all machinery and equipment are operated by superheated
steam we still want to keep the high pressure and therefore we only want to
reduce the temperature this is done by adi super heater
a simple and common way of de-superheating is to inject water in a
steam flow
some boilers have a separate steam cooling coil inside the lower water drum
D superheated steam can be used for reciprocating machinery heating and
optimising steam the purpose of the D aerator is to be an expansion tank for
the condensate from the condenser as the flow of water to the boiler vary with a
load to remove air and other non condensable gases from the feed water
feed water pre heater as it is mixing steam and water it may be a condenser
for several - steam consumers the deaerator is placed approximately 10
metres above the feed water pump and will by that to protect the pump from
the steam flashing and cavitation by heating the feed water with steam the
air will boil off and be led to the atmosphere a level control system will
maintain a constant water level in the deaerator during normal operation of the
boiler there would always be soot and other deposits on the heat surface and
in the uptake of the boiler the suit is mostly carbon from incomplete combustion
of fuel oil that Ash and vanadium can also be a problem
search blowing has to take place regularly to maintain the thermal
efficiency of the boiler an increase in exhaust temperature after the air
preheater of 10 degrees centigrade is a good indication and when to start such
blowing the suit blower equipment on a large boiler is complicated and needs a
lot of maintenance the number and types of such blowers depend on the type and
the make of the boiler we have suit blower types like a long-stroke
retractable blower this can be electrical or a operated and
is usually placed in hot gas areas like the super heater section the multi dual
nozzle blower this is placed in lower temperature areas like air preheater and
economizer typical steam consumption per blower can be 2 kilos 4 seconds and air
consumption 130 cubic meters per minute the operation will take approximately
one minute but there will only be sucked blowing for 20 seconds
an electrical driven centrifugal type of blower supplies combustion air through a
short duct to the air preheater
from the air preheater the ducting follows the boiler front to the oil
burners even if the blowers have a controlled damper on the suction side
they may have a two to four step revolutions per minute controller this
is because it can have a major difference in boiler load during normal
operation on its way to the furnace the air passes control dampers or air
registers before it is mixed thoroughly with the fuel oil the fuel oil will only
be present in the furnace for a fraction of a second ask for a diesel engine tis
therefore very important that the fuel oil is properly atomized and mixed with
a combustion air if the fuel oil is not completely and immediately burning small
particles of oil will form soot and other deposits in the furnace and
exhaust uptake this will reduce the heat transfer and excessive search blowing is
necessary to maintain the boiler efficiency to obtain the best possible
atomizing several types of burners have been developed pressure atomizing using
high pressure oil pumps
steam or air atomizing using low pressure saturated steam when there is
no steam available for fuel oil heating and atomizing we use diesel oil to start
firing the boiler and later on changed fuel oil
rotating burners driven by an electrical motor possible reasons for combustion
problems can be poor atomizing check change burner tip to low atomizing steam
pressure too much water in the steam fuel oil too low oil pressure check pump
and filters wrong fuel oil viscosity too little combustion air to low speed on
air blower malfunction of air damper control deposits on air blower deposits
in the air preheater air or exhaust side tuning of air oil ratio controller
deposits on economizer all boilers shall be provided with at least two safety
valves on the steam drums so last chapter two one if it is possible to
close off super heater and economize a sections during firing and they are
still subject to combustion gases they must have separate safety valves the
size of the safety valve should at least be sufficient to prevent the steam
pressure from increasing more than 10% above normal pressure even if the oil
burners are working at full capacity for 15 minutes and all steam valves are
closed the safety valves must have an arrangement that makes it possible to
release the boiler pressure from deck and engine room
on boilers with working pressure after 20 bar the safety valve is normally of
the spring-loaded type the tension of the spring can be adjusted when the
steam pressure increases above the spring load the valve will open and the
steam will act on a ring in the valve housing the valve keeps open until the
steam pressure is reduced below normal operating pressure another type of
safety valve is the full stroke valve a small spring-loaded valve is first
activated by the increased steam pressure this valve is a pilot valve for
the full stroke valve and the steam pressure would push a piston that opens
the safety valve
to convert the heat and pressure energy in the steam entering the turbine the
steam passes one or several groups of nozzles these nozzles can be of the
convergent or the convergent divergent type in the convergent nozzle the
velocity of steam increases until the velocity of sound of that particular
pressure the pressure drop in the nozzle is called the critical pressure drop to
obtain the total pressure drop this type of turbine has several wheels with an
increasing diameter on the blades towards the outlet side of the turbine
the convergent divergent type of nozzle also called the Laval nozzle has an
expansion of the steam volume in the divergent part of velocity and can be as
high as 800 meters per second typical turbines of this type of feed
water turbines cargo pump turbines and turbine driven generators this type of
turbine is often called the Curtiss turbine the steam velocities brought
down in two steps from the Laval nozzle the steam enters the first rotating
wheel and leaves this in the opposite direction
passing through the fixed nozzles then entering the second rotating wheel and
the steam velocity is now close to zero when it leaves the last blade the
working principle of this turbine is called the impulse type because of the
high esteem velocity this type of turbine is not very efficient and
consequently not used as main propulsion machinery turbines can also be
categorized as back pressure or vacuum condenser types some of the energy in
the steam is converted to a cinematic energy in the nozzles and enters the
turbine rotor blades with a velocity of several hundred meters per second for
each turbine wheel the steam pressure drops until most of the available energy
in the steam is converted to mechanical work exhaust steam enters the condenser
at low pressure temperature and a volume up to 500 times higher than on the inlet
side of the turbine the condensate is pumped by a condensate pump to the
deaerator
we have several types of feed water pumps depending on the size and type of
the boiler installation on a large installation we normally have two
identical steam turbine driven centrifugal pumps each of the pumps have
a capacity well above the total boiler capacity in addition to the two main
pumps we also have an auxilary pump this can be a reciprocating type and used to
fill the boiler aft inspection and maintenance work