3084-semin sanuri-2. basic of boilers

8/2/2019 3084-Semin Sanuri-2. Basic of Boilers

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BASIC OF BOILERS

BY: SEMIN, PHD

Dept. Marine Engineering

Faculty of Marine Technology

Institut Teknologi Sepuluh Nopember (ITS)Surabaya Indonesia


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APPLICATION IN SHIPS


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OUTLINE:

1. INTRODUCTION

2. MARINE BOILERS

3. MAIN COMPONENTS OF BOILER4. TYPES OF BOILER


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1.1 INTRODUCTION

BOILER:

BOILER or steam boilers are heating units that holdwater, wood, oil or coal to create steam.

This steam is transferred for purposes of heating,mover, locomotion and cleaning.

Steam boilers are common found in the home, wherewater is converted to steam. This is transferred fromthe unit to radiators for heating comfort.


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BOILER:


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BOILER:

Generally, steam boilers break down into two categories:

There is a "closed" system steam boiler in which the unused

steam, which has now condensed, is recycled back into thesystem and reheated for further use.

If you are concerned about contamination, you can obtain an

"open" system steam boiler, in which the steam boiler

evacuates the unused condensed liquid out of the system. This

may require a continuous flow of water to the boiler.


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A boiler or steam generator is a device used to create steam

by applying heat energy to water. Although the definitions are

somewhat flexible, it can be said that older steam generators

were commonly termed boilers and worked at low to medium

pressure (1

300 psi/0.069

20.684 bar; 6.895

2,068.427kPa), but at pressures above this it is more usual to speak of a

steam generator.

A boiler or steam generator is used wherever a source of steamis required. The form and size depends on the application:

mobile, industrial installations and power stations will usually

have a larger separate steam generating facility connected to

the point-of-use by piping.

BOILER:


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STEAM PLANTS:

Water in the form of steam has the ability to store great amounts ofenergy. With it's ease of control and delivery, steam brought theadvent of power to the shipping world.

There are still some steam powered vessels such as ULCC (Ultra

Large Crude Carrier) where steam turbines can provide thenecessary, high power shaft requirements to propel the ship.However it's time as passed, most ships nowadays use the moreeconomical diesel burning heavy fuels.

Although boilers may no longer be commonplace for ship propulsion

they are almost guaranteed to be one boiler for various duties onboard a ship. Duties like heating cargo, fuel, and accommodations.Some ships also use boilers for auxiliary power. Such as deckwinches and pumps, where electrical machines would prove to be ahazard as in the oil industry.


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STEAM THEORY:

Within the boiler, fuel and air are force into the furnace by the

burner. There, it burns to produce heat. From there, the heat (flue

gases) travel throughout the boiler. The water absorbs the heat,

and eventually absorb enough to change into a gaseous state -

steam.

The figure below are shown the basic theoretical design of a

modern boiler. Boiler makers have developed various designs to

squeeze the most energy out of fuel and to maximized its

transfer to the water. But it all boils down, pardon the pun, to the

basic design shown here.


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STEAM THEORY

Figure: Basic theoretical designof a modern boiler


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STEAM THEORY

Figure: Basic design of a

modern boiler


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STEAM THEORY:

Steam boilers are used to produce saturated or superheated

steam, which is then put to work in a variety of ways.

Steam is used for its heat energy in heating, cooking and

reboiling operations. It also is used for its pressure energy inreciprocating steam engines and steam turbines.

Steam boilers create the steam by converting heat energy

from fuel combustion, nuclear reactors, concentrated sunlight orwaste heat from other processes.


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A boiler in one form or another will be found on every type of

ship. Where the main machinery is steam powered, one or more

large watertube boilers will be fitted to produce steam at very

high temperatures and pressures.

On a diesel main machinery vessel, a smaller (usually firetube

type) boiler will be fitted to provide steam for the various ship

services. Even within the two basic design types, watertube and

firetube, a variety of designs and variations exist.

2. MARINE BOILERS


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MARINE BOILER DESIGN:

Reliability

Flexibility

Wide range of steam loads

Rapid changes

Responsive to automatic controls

Relatively compact


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Efficient operation

5 different heat exchangers

Combustion air

Economizer Furnace

Superheater

Desuperheater

Accessability for cleaning and repair

MARINE BOILER DESIGN:


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Figure: Simplified marine boiler arrangement


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1.3 MAIN COMPONENTS of BOILER

ECONOMIZER

FEED WATER INLET PIPE

DOWNCOMERS

WATER DRUM GENERATING TUBES

SUPERHEATER

DESUPERHEATER


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ECONOMIZER:

The economizer is a feed water heater deriving heat from

the flue gases discharged from the boiler. The justifiable

cost for economizer depends on the total gain in efficiency.

In turn, this depends on the gas temperature out of the

boiler and feed water temperature to the boiler.


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FEET WATER INLET PIPE:

These pipes are used for supplying boilers with hotfeed water. An important benefit of these pipes isthat most of the dissolved gases are liberated beforethe feed water enters the boiler.

The feed water flow passes through tubes which areexposed to partially expanded steam brought from,typically, one or more points in the turbine system.The turbine exhausted steam is thus used to some

advantage.


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In the steam generation process the feedwater enters the boiler

where it is heated and becomes steam. The feedwater circulates

from the steam drum to the water drum and is heated in the process.

Some of the feedwater passes through tubes surrounding the

furnace, i.e. waterwall and floor tubes, where it is heated and

returned to the steam drum. Large-bore downcomer tubes are used

to circulate feedwater between the drums. The downcomer tubes

pass outside of the furnace and join the steam and water drums.


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A boiler is used to heat feedwater in order to produce steam. The

energy released by the burning fuel in the boiler furnace is stored

(as temperature and pressure) in the steam produced. All boilers

have a furnace or combustion chamber where fuel is burnt to release

its energy. Air is supplied to the boiler furnace to enable combustion

of the fuel to take place. A large surface area between the

combustion chamber and the water enables the energy of

combustion, in the form of heat, to be transferred to the water.


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SUPERHEATER:

Steam that has been heated above the saturation

temperature corresponding to its pressure is said to be

superheated.

This steam contains more heat than does saturated steamat the same pressure and the added heat provides more

energy for the turbine for conversion to electric power, or

in the case of process steam, more energy contained in a

pound of steam for a more efficient process.

The convection superheater is placed somewhere in the

gas stream, where it receives most of its heat by

convection.


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The hot gases produced in the furnace are used to heat the

feedwater to produce steam and also to superheat the steam from

the boiler drum. The gases then pass over an economiser through

which the feedwater passes before it enters the boiler.

The exhaust gases may also pass over an air heater which warms the

combustion air before it enters the furnace. In this way a large

proportion of the heat energy from the hot gases is used before they

are exhausted from the funnel.


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The steam is produced in a steam drum and may be drawn off for

use from here. It is known as 'wet' or saturated steam in this condition

because it will contain small quantities of water, Alternatively thesteam may pass to a superheater which is located within the boiler.

Here steam is further heated and 'dried', i.e. all traces of water are

converted into steam. This superheated steam then leaves the boilerfor use in the system. The temperature of superheated steam will be

above that of the steam in the drum. An 'attemperator', i.e. a steam

cooler, may be fitted in the system to control the superheated steam

temperature.


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Figure: Superheater


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DOWN COMER:

A tube or pipe in a boiler or water wall circulating system

through which fluid flows downwards.

GENERATING TUBES:

A tube in which steam is generated.

DESUPERHEATER:

Apparatus for reducing and controlling of temperature of asuperheated vapour or of a fluid.


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A drum must be provided where steam and water can separate.

There must also be a variety of fittings and controls to ensure that

fuel oil, air and feedwater supplies are matched to the demand for

steam. Finally there must be a number of fittings or mountings which

ensure the safe operation of the boiler.


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4. TYPE OF BOILERS

Boilers can be classified in various ways dependingon firing method used, fuel fired, field ofapplication, type of water circulation employed,and pressure of steam etc.

In general there are two principle types of boilers.

A. Water tube boilers.

B. Fire tube boilers.C. Auxiliary boilers.


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A. WATER TUBE BOILER:

A water tube boiler is a type of boiler in which water circulates in tubesheated externally by the fire. Water tube boilers are used for high-

pressure boilers. Fuel is burned inside the furnace, creating hot gas which

heats water in the steam-generating tubes. In smaller boilers, additional

generating tubes are separate in the furnace, while larger utility boilers

rely on the water-filled tubes that make up the walls of the furnace togenerate steam.


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A. WATER TUBE BOILER:

The heated water then rises into thesteam drum. Here, saturated steam is

drawn off the top of the drum. In some

services, the steam will reenter the

furnace through a superheater to

become superheated. Superheatedsteam is used to drive turbines. Since

water droplets can severely damage

turbine blades, steam is superheated

to 730 F (388 C) or higher to ensure

that there is no water entrained in thesteam and pressures above 350 psi

(2.4 MPa).


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Figure : Water tube boiler schematic


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A. WATER TUBE BOILERContd:

As you can see, the Babcock MarineWater Tube Boiler in below is looks

very complicated. Thousands of tubes

are placed in strategic location to

optimize the exchange of energy

from the heat to the water in thetubes. These types of boilers are most

common because of their ability to

deliver large quantities of steam.

Figure: Babcock Marine Water Tube Boiler


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The large tube like structure at the

top of the boiler is called the

steam drum. You could call it the

heart of the boiler. That's where

the steam collects before beingdischarged from the boiler. The

hundreds of tube start and

eventually end up at the steam

drum.

Figure: Foster Wheeler D-Type boiler


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Water enters the boiler, preheated, at the top. The hot water naturallycirculates through the tubes down to the lower area where it is hot. Thewater heats up and flows back to the steam drum where the steamcollects. Not all the water gets turn to steam, so the process startsagain. Water keeps on circulating until it becomes steam.

Meanwhile, the control system is taking the temperature of the steamdrum, along with numerous other readings, to determine if it shouldkeep the burner burning, or shut it down.

As well, sensors control the amount of water entering the boiler, thiswater is know as feed water. Feed water is not your regular drinkingwater. It is treated with chemicals to neutralize various minerals in thewater, which untreated, would cling to the tubes clogging or worst,rusting them. This would make the boiler expensive to operate becauseit would not be very efficient.


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Figure: Detail of Martin Boiler


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A. WATER TUBE BOILER.Contd:

On the fire side of the boiler, carbon deposit resulting fromimproper combustion or impurities in the fuel can accumulate on

the outer surface of the water tube. This creates an insulation

which quickly decrease the energy transfer from the heat to the

water. To remedy this problem the engineer will carry out sootblowing.

At a specified time the engineer uses a long tool and insert it into

the fire side of the boiler. This device, which looks like a lance,has a tip at the end which "blows" steam. This blowing action of

the steam "scrubs" the outside of the water tubes, cleaning the

carbon build up.


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A. WATER TUBE BOILER..Contd:


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A. WATER TUBE BOILER..Contd:

Water tube boilers can have pressures from 7 bar (one bar =~15 psi) to as high as 250 bar. The steam temperature's can

vary between saturated steam, 100 degrees Celsius steam with

particle of water, or be as high as 600 - 650 degrees Celsius,

know as superheated steam or dry steam (all water particle havebeen turn to a gaseous state).

The performance of boiler is generally referred to as tons of

steam produced in one hour. In water tube boilers that could be

as low as 1.5 t/hr to as high as 2500 t/hr. The larger boilers

would be land based, your local power company would most

likely operate one. In British Columbia, large boilers are most

common at Pulp and Paper plants.


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B. FIRE TUBE BOILER:

A fire-tube boiler is a type of boiler in which hot gases from a firepass through one or more tubes running through a sealed container ofwater. The heat energy from the gases passes through the sides of thetubes by thermal conduction, heating the water and ultimately creatingsteam.

The fire-tube boiler developed as the third of the four major historicaltypes of boilers: low-pressure tank or "haystack" boilers, flued boilerswith one or two large flues, fire-tube boilers with many small tubes, andhigh-pressure water tube boilers.

Their advantage over flued boilers with a single large flue is that themany small tubes offer far greater heating surface area for the sameoverall boiler volume. The general construction is as a tank of waterperforated by tubes that carry the hot flue gases from the fire. Thetank is usually cylindrical for the most part being the strongestpractical shape for a pressurized container and this cylindrical tankmay be either horizontal or vertical.


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B. FIRE TUBE BOILERContd:

This type of boilers started it all. This is the original design ofboiler which brought the tide of power to the marine world. If

you are ever in Vancouver, BC, the SS Master, a turn of the

century tugboat, is open for the public to view at the Vancouver

Maritime Museum. It is operational, and a fine example of shipusing a fire tube boiler.

On a modern ship, the fire tube boiler meet the ship's heating

needs and is generally not used for deck machinery. The steamproduced will circulate through coils in the cargo tanks, fuel tanks,

and accommodation heating system. They are generally supplied

as a complete package, such as the one pictured in figures below.


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Figure: Fire tube boiler schema


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Figure : Fire tube boiler


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Figure: Fire tube boiler construction


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This is a single furnace, three pass type fire tube boiler. Heat - flue gases - travelsthrough three different sets of tubes. All the tubes are surrounded by water which

absorbs the heat. As the water turns to steam, pressure builds up within the boiler,

once enough pressure has built up the engineer will open main steam outlet valve

slowly, supplying steam for service. Fire tube boilers are also known as "smoke

tube" and "donkey boiler".

Figure:

Detail of

fire tube

boiler


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A fire-tube boiler is a type of boiler in which hot gases from a firepass through one or more tubes running through a sealed container ofwater. The heat energy from the gases passes through the sides of thetubes by thermal conduction, heating the water and ultimately creatingsteam.

The fire-tube boiler developed as the third of the four major historicaltypes of boilers: low-pressure tank or "haystack" boilers, flued boilerswith one or two large flues, fire-tube boilers with many small tubes, andhigh-pressure water tube boilers. Their advantage over flued boilerswith a single large flue is that the many small tubes offer far greater

heating surface area for the same overall boiler volume. The generalconstruction is as a tank of water perforated by tubes that carry thehot flue gases from the fire. The tank is usually cylindrical for the mostpart being the strongest practical shape for a pressurized container and this cylindrical tank may be either horizontal or vertical.


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C. AUXILIARY BOILER:

On smaller ships the auxiliaryboiler can be a stand alone unitand would most likely be of thefire tube boiler arrangement asdescribed above.

But on a larger vessel it is moreefficient for the auxiliary boilerto take advantage of the mainengine's flue gases to heat thewater. Basically this means that

the hot gases from the mainengine must pass through a heatexchanger (the auxiliary firetube boiler) before exiting to theatmosphere.

Figure: Auxiliary boiler


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On this diagram, look for it above, and just aft of the main engine, nearthe exhaust stake of the ship. It is called the "cargo heating boiler".

Figure: Cargo heating boiler


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THANK YOU

Q AND A

3084-semin sanuri-2. basic of boilers

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