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