Unit 1 - Purifier and Fuel Oil Treatment

1. Purifier and fuel oil treatment

Describe the following with the aid of sketches:

 bowl assembly
 operating water
 seal water
 gravity disk
 valve cylinder
 Separation disk/plate

State principles of purifying to eliminate water or dirt particles from oil

Explain why fuel oil treatment is necessary
Describe the following types of filter, which are used in fuel oil lines
Describe the following types of filter, which are used in fuel oil lines
• mesh/gauze elements
• magnetic elements
• fiber assemblies
Explain how the force of gravity is used to separate out liquids and solids of
different densities
Describe the operation principles of an oil purifier
Explain why the use of centrifugal separation is much faster and more effective
than gravity in the separation process
Describe, with the aid of simple sketches, a bowl separator and a tube
separator, showing the main components and the principal differences
between the two
State the rotation speeds used in the equipment described in the above
objective
Page 1
Fuel oil service tank – An oil fuel tank that contains only the required quality
of fuel ready for immediate use. Two oil fuel service tanks, for each type of
fuel used on board, necessary for propulsion and generator systems, are to be
provided. Each tank is to have a capacity for at least eight hours operation, at
sea, at maximum continuous rating of the propulsion plant and/or generating
plant associated with that tank. The arrangement for oil fuel service tank is to
be such that one tank can continue to supply oil fuel when the other is being
cleaned or opened for repair (according to Lloyd’s Register). Where main
engine, auxiliary engines and boilers are operated on heavy fuel oil, the
following equivalent arrangement may be accepted:

Marine Fuel Oil Purifier: Working Principle of Centrifugal Separator

Purifier Parts and Functions #purifier #marine oil

1. Centrifuge 1 – UNITROL system

2. Centrifuge 2 – SECUTROL system

3. Compressed air cut-off valve

4. Operating and filling water cut-off valve

5. Fuel oil cut-off valve before supply pump

6. Fuel oil cut-off valve behind supply pump

7. Fuel oil regulating valve before centrifuge 1

8. Fuel oil regulating valve behind centrifuge 1

9. Fuel oil cut-off valve before service tank

10. Centrifuge 1 by-pass valve

11. Fuel cut-off valve before centrifuge 2

12. Fuel oil regulating valve before centrifuge 2

13. Fuel oil regulating valve behind centrifuge 2

14. Fuel oil cut-off valve before service tank

15. Three/two-way piston valve for dirty oil feed to centrifuge 1

16. Three/two-way piston valve for dirty oil feed to centrifuge 2

17. Centrifuge 1 pre-heater

18. Centrifuge 2 pre-heater

19. Solenoid valves:

a. Centrifuge 1 operating-water valve

b. Centrifuge 1 filling and displacement water valve

c. Centrifuge 2 operating-water valve

d. Centrifuge 2 filling and displacement water valve

20. Fuel oil contamination slide-switch ( LO-low, Hi-high )

1. Describe the following with the aid of sketches:

• bowl assembly - Bowls have Been Thoroughly Cleaned and Inspected for
Corrosion, Erosion and Impact Damage. all Sealing Faces are Checked and
Machined Where Necessary. Bowl Tapers are Carefully Checked for Play and
Wobble. Lock Rings Large and Sum all are Checked for Wear and are
Remarked. Bowl Discs are Mechanically Polished, Removing Surface Scratches
Which Cause Sludge to Stick Creating Balancing Problem.
 Fuel Oil Purifier Construction - Purifier Bowl and Drive

Marine Mitsubishi Selfjector Purifier Bowl Overhaul 2

• Operating Water

Marine Mitsubishi Selfjector Purifier Water Suplying Device Removal

Marine Mitsubishi Selfejector Purifier Water Supplying Device Overhaul

• Seal Water – For disludging bowl has to slide open, supply of operating
water is stopped. Desludging water is supplied which acts on the lower surface
of the pilot valve having a larger surface area, thereby opening the pilot valve
to the counter radial direction ( opposite to centrifugal force ).

This causes all the operating water to drain from the drain orifice which is
normally kept closed by the pilot valve. The bowl slides down and accumulated
sludge and water at the bowl periphery is thrown out. The desludging water is
stopped and operating water is simultaneously started to fill the water
chamber. Causing the bowl to lift and again return to normal working
position. And the pilot valve also loses water pressure which was forcing it to
remain open in counter radial direction. Therefore the drain orifice is also
closed by the pilot valve. This completes the desludging operation. Water is
distributed by a water paring disc. Water sequence and timing are controlled
by solenoid valves. Water from the hydrophore or in some cases, Header tanks
are used.
The difference between partial and total discharge operations of Mitsubishi self
ejector series is only the time duration for which the bowl remains opened.
This is achieved by supplying desludging water for shorter time duration.

Alpha Laval ALCAP design in marine centrifugal purifiers claims it can purify
high density residual fuels. Its flow control disc eliminates the need to change
gravity disc based on differing fuel densities. It used transducers to detect
water in oil side and oil in water side and thereby signaling the microprocessor
to desludge automatically upon detecting changes in the interface.
 Marine Mitsubishi Purifier Operation Explained

Marine Mitsubishi Selfjector Purifier Water Supplying Device Mounting

Marine Mitsubishi Purifier Operation Explained

Marine Mitsubishi Selfjector Purifier Water Supplying Device Overhaul

Page 4
• Gravity Disc

Gravity disc or dam ring – Purifiers have great role in marine ships. A ring
fitted at the top of disc stack from where water is passing out is called gravity
disc. Oil which is for purification may not be of same type it is of different
densities or viscosity, so the interface change. To create the correct interface
between and oil it is very important to select correct gravity disc size.

Functions of gravity Disc

1. Gravity disc in purifier is the one which controls the output of the quality of
the fuel.

2. Dam ring is responsible for creating the interface between the oil and water

3. Back pressure is maintain by gravity disc.

Purifier gravity disc selection

Selection of gravity disc is depends on specific gravity, Temperature and

feed rate

There are two method to find the correct size of Dam ring

1. Using monogram

2. By trial and error method

Using monogram – to find the correct gravity disc monograms are using on
board ship .
Method of using monogram

For better understanding refer the example:

Specific gravity of treated oil 0.925 @ 15 degrees Celsius

Treating temperature 70 degrees Celsius

Feed rate 300 L/h

Selection method

From an intersection between falling curve 1 of specific gravity of 0.925 and

the vertical line of 70 degrees Celsius, draw horizontal line II to reach the
vertical line of 100 degrees Celsius.

 Connect between the right end of line II and the point of 3000 L/h on the
treating capacity scale using straight line III.
 Read within which section of gravity disc inside diameter scale the
intersection made by line III falls.
 For this select a gravity disc having diameter of 79.
 GRAVITY DISC

Bigger the diameter of the disc, the possibility of having water mix with fuel is
high while if the diameter of the disc is smaller then the better fuel you get. If
we are to use so small diameter disc, this will cause some good fuel oil to be
thrown to the sludge tank. There is also a drawback if you use to much large
diameter disc because there is a possibility that the water will be mixed with
fuel. So it is very important that the size of gravity disc should be correct.

Fuel Purifier Operation

Valve Cylinder (Pilot valve)

Marine Mitsubishi Selfjector Purifier Sludge Discharge Mechanism

Source: https://www.marinesite.info/2014/04/what-is-gravity-disc-of-
purifier.html

• Separation disk/plate - disc-stack centrifuge efficiently separates the solid

and liquid phases from each other. Traditional settling tanks use gravity to
separate phases. Due to the high rotational velocity, the centrifuge separators
speed up separation by 5,000 times using centrifugal force instead of just
gravity.

2. State principles of purifying to eliminate water or dirt particles from

oil

The force presses heavy particles outwards against the separator walls. The
disc stack inside the separator bowl ensures lighter particles follow the heavier
ones instead of the liquid, making separation more precise and efficient.
Separation takes place between the bowl discs where the liquid phase
gravitates towards the center of the bowl and the solids move towards the
periphery. The gas-tight design of the center-to-center flow fully encloses the
process liquid and eliminates the risk of gas flashing. The separated liquid
leaves the bowl through the hermetically sealed outlet at the top of the
separator and is further boosted by an impeller. The solids are discharged via
the discharge ports when the sliding bowl bottom moves
downwards. Discharged solids leaves the separator via the sludge cyclone.

3. Explain why fuel oil treatment is necessary - Fuels supplied to a ship

must be treated on board before use in order to remove solid as well as liquid
contaminants. The solid contaminants in the fuel are mainly rust, sand, dust
and refinery catalysts. Liquid contaminants are mainly fresh or salt water. The
settling tank is the first step in fuel treatment process. Water and sediments
can be separated by gravity and drained off at the bottom of the tank.
Effective cleaning of residual fuels can only be ensured by centrifuges: a
clarifier to separate particles and/or a purifier to separate water. In order to
remove any solid particles not separated by centrifuging, fine filters are placed
directly after the centrifuge, or in the supply line to the engine.

The oil fuel system provides the means for delivering fuel from the receiving
stations at upper deck level, port and starboard, to double-bottom or deep
bunker tanks. Sampling cocks are fitted at the deck connections to obtain a
representative specimen for (a) shore analysis; (b) on board testing; and (c)
retention on the ship. A filter on the downpipe removes large impurities.

Transfer of Fuel oil

The fuel oil can be pumped from storage to settling tanks and also transferred
if necessary, between forward and aft, port and starboard storage tanks, by
means of heavy oil and diesel oil fuel transfer pumps. Transfer from settling to
service tanks (Figure 1) in motor ships, is via centrifuges. The latter are
arranged as purifiers or clarifiers.

Marine Fuel Oil Purifier: Working Principle of Centrifugal Separator

Page 6
4. Describe the following types of filter, which are used in fuel oil lines -

Trouble-free operation of a diesel injection system is possible only with filtered

fuel. Fuel filters help reduce damage and premature wear from contaminants
by retaining very fine particles and water to prevent them from entering the
fuel injection system. As shown in Figure 1, fuel systems can contain one or
more stages of filtration. In many cases, a course screen is also located at the
fuel intake located in the fuel tank.

Fuel Oil Duplex Filter

Two stage filter system typically uses a primary filter on the inlet side of the
fuel transfer pump and a secondary filter on the outlet side. The primary filter
is required to remove larger particles. The secondary filter is required to
withstand higher pressures and remove smaller particles that can damage the
engine components. One-stage systems remove larger and smaller particles in
a single filter.

Filters can be a box-type or replacement element design, as shown in Figure

2. The box-type filter is that which can be completely replaced as needed and
does not require cleaning. Filters with a replaceable element have to be
thoroughly cleaned when replacing elements and care must be taken to avoid
any dirt residue that could migrate to the intricate parts of the fuel injection
system. Filters can be constructed of metal or plastic.
 Figure 2. Two Types of Fuel Filters

(a) Box type; (b) Element type

Common materials for modern fuel filter elements are synthetic fibres and/or
cellulose. Micro glass fibres can also be used but because of the risk of
migration of small glass fibre pieces broken off from the main element into
critical fuel system components, their use in some applications is
avoided [Petiteaux 2009]. In the past, pleated paper, packed cotton thread,
wood chips, a mixture of packed cotton thread and wood fibres and wound
cotton have also been used [Brady 1996].

The degree of filtration required depends on the specific application. In

general, when two filters are used in series, the primary filter retains particles
down to about 10 - 30 µm, while the secondary filter is capable of retaining
particles greater than 2-10 µm. As fuel systems evolve, clearances and
stresses on high pressure components increase and the need for clean fuel
becomes event more critical. Both the capability of fuel filters to keep up with
demands for cleaner fuel [Salvador 2009] as well as methods quantifying
acceptable fuel contamination levels have needed to evolve [van Stockhausen
2009].

In addition to keeping solid particles out of the fuel supply and injection
equipment, water in fuel must also be prevented from entering critical fuel
injection system components. Free water can damage fuel lubricated
components in the fuel injection system. Water can also freeze in cold
temperature conditions and ice may block small fuel injection system passages
thus cutting off the fuel supply to the rest of the fuel injection system.

Water can be removed from the fuel using two common approaches. The
incoming fuel can be subject to centrifugal forces that separates the denser
water from the fuel. Much better removal efficiencies can be achieved with a
filter media that separates water. Figure 3 shows a filter using a combination
of media-type and centrifugal approaches.
 Figure 3. Fuel Filter Equipped with Water Separator

Different water separation media operate under different

principles. Hydrophobic barrier media, such as silicone treated cellulose,
rejects water and causes it to bead up on the upstream surface. As the beads
become larger, they run down the face of the element into a cup under the
force of gravity. Hydrophilic depth coalescing media, such as glass micro-fibre,
has a high affinity for water. The water in the fuel associates with the glass
fibres and over time as more water enters from the upstream side, massive
droplets are formed. The water moves through the filter with the fuel and on
the downstream side, falls out of the fuel flow into a collection cup.

Fuel filters can also contain additional features such as fuel heaters, thermal
diverter valves, de-aerators, water-in-fuel sensors, filter change indicators.

A fuel preheater helps minimize the accumulation of wax crystals that can
form in the fuel as it cools to low temperatures. Common heating methods use
electric heaters, engine coolant or recirculated fuel. Two approaches that use
warm return fuel to heat the incoming fuel are shown in Figure 1.

Fuel overflow and leak-off fuel returning to the tank also carries air and fuel
vapor. The presence of gaseous substances in the fuel can cause difficulties in
starting as well as normal engine operation in high temperature environments.
Therefore, bleeder valves and de-aerators are used to rid the fuel supply of
vapors and air to ensure trouble-free engine operation.
5. Describe the following types of filter, which are used in fuel oil lines

• Mesh/gauze elements - The filter is a fine mesh screen which is used to

remove impurities from oil, water, and air on the ship. Filters are mounted in
pairs as a duplex system so that one can be used and other is kept on standby
at a time. The filter can be utilized both in low pressure (suction) and
discharge (high pressure) side of the system and is used to remove the
smallest part of dirt which is carried away in the system. The cleaning
frequency of filters depends on the type of the filter and is decided by the
manufacturer. The schedule is generally included in the planned maintenance
system on board. Fine Mesh Screen Filter: It is the most commonly used filter
in lube and fuel oil systems on board. It can be used both on suction and
discharge side of the system. It is used in cylinder lube oil line, main engine
and auxiliary engine fuel oil line & diesel oil line, boiler fuel oil line and in
different lube oil systems on board, etc.

• Magnetic elements - This normally consists of filter elements which are

magnetic in nature and which help in catching fine metal or ferrous particles
that run in the system. These elements are surrounded by a basket screen
which also acts as a filter and simplifies the cleaning of the filter. Magnetic
filters are used in lube oil system.

• Fibre assemblies - Fiber optic cable assemblies consist of an optical fiber, a

reinforcement strand for support, and fiber optic cable connectors. While copper wires
depend on electrical pulses to transmit data, fiber optic systems rely on light pulse
transmissions carried through the cable which delivers data at a quicker rate.
Page 7
6. Explain how the force of gravity is used to separate out liquids and solids of
different densities

Ship Purifier System: How the Marine Fuel Oil Purification System Works?

7. Describe the operation principles of an oil purifier

8. Explain why the use of centrifugal separation is much faster and more
effective than gravity in the separation Process

Marine Fuel Oil Purifier: Working Principle of Centrifugal Separator

9. Describe, with the aid of simple sketches, a bowl separator and a tube
separator, showing the main components and the principal differences
between the two

10. State the rotation speeds used in the equipment described in the above
objective

For complete overview of overhauled purifier Marine Mitsubishi Selfjector

Purifier Vertival Shaft Mounting
 Unit 2 - Marine Boiler

Page 1
Topic: Marine Boiler - Steam boiler fuel atomization and combustion

Explain the part played by nitrogen in the combustion process

Combustion refers to the rapid oxidation of fuel accompanied by the

production of heat, or heat and light. Complete combustion of a fuel is possible
only in the presence of an adequate supply of oxygen. Oxygen (O2) is one of
the most common elements on earth making up 20.9% of our air. Rapid fuel
oxidation results in large amounts of heat. Solid or liquid fuels must be
changed to a gas before they will burn. Usually heat is required to change
liquids or solids into gases. Fuel gases will burn in their normal state if enough
air is present. Most of the 79% of air (that is not oxygen) is nitrogen, with
traces of other elements. Nitrogen is considered to be a temperature reducing
dilutant that must be present to obtain the oxygen required for combustion.

Nitrogen reduces combustion efficiency by absorbing heat from the

combustion of fuels and diluting the flue gases. This reduces the heat
available for transfer through the heat exchange surfaces. It also increases
the volume of combustion by-products, which then have to travel through the
heat exchanger and up the stack faster to allow the introduction of additional
fuel air mixture.

This nitrogen also can combine with oxygen (particularly at high flame
temperatures) to produce oxides nitrogen (NOx),which are toxic
pollutants.. The primary nitrogen pollutants produced by combustion are nitric
oxide (NO) and nitrogen dioxide (NO2) and are generally referred to
collectively as NOx. Increasing evidence suggests that NOx has a direct
negative effect on the human respiratory system and when exhausted into the
atmosphere, reacts with moisture to produce ozone and acid rain.

State that State that the elements carbon and hydrogen combine
chemically with oxygen during combustion to form the gaseous
products carbon dioxide and water vapour, to ensure that the
combustion process is as compete as possible, excess air is normally
supplied

A combustion reaction is a type of chemical reaction in which a compound and

an oxidant are reacted to produce heat and a new product. The general form
of a combustion reaction can be represented by the reaction between a
hydrocarbon and oxygen, which yields carbon dioxide and water: hydrocarbon
+ O2 → CO2 + H2O

Products of Combustion

Carbon Dioxide.

Carbon Monoxide.

Sulfur Dioxide.

Nitrogen Oxides.

Lead.

In addition to heat, it's also common (although not necessary) for a

combustion reaction to release light and produce a flame. For a combustion
reaction to begin, the activation energy for the reaction must be
overcome. Often, combustion reactions begin with a burning match or another
flame, which provides the heat needed to initiate the reaction.

Once combustion starts, enough heat might be produced to sustain the

reaction until it runs out of either fuel or oxygen. Combustion, like all chemical
reactions, does not always proceed with 100% efficiency. It's prone to
limiting reactants the same as other processes. As a result, there are two
types of combustion you're likely to encounter:

Complete Combustion: Also called "clean combustion," complete combustion is

the oxidation of a hydrocarbon that produces only carbon dioxide and water.

Supply of air & fuel mixing

Combustion is the burning of fuel in air in order to release heat energy. For
complete and efficient combustion the correct quantities of fuel and air must
be supplied to the furnace and ignited. About 14 times as much air as fuel is
required for complete combustion.
Page 2
State that the excess of air must be kept to a minimum, consist
ent with good combustion

The air and fuel must be intimately mixed and a small percentage of excess air
is usually supplied to ensure that all the fuel is burnt. When the air supply is
insufficient the fuel is not completely burnt and black exhaust gases will result.

The flow of air through a boiler furnace is known as 'draught'. Marine boilers
are arranged for forced draught, i.e. fans which force the air through the
furnace. Several arrangements of forced draught are possible. The
usual forced draught arrangement is a large fan which supplies air along
ducting to the furnace front.

The furnace front has an enclosed box arrangement, known as an 'air register',
which can control the air supply. The air ducting normally passes through the
boiler exhaust where some air heating can take place. The induced draught
arrangement has a fan in the exhaust uptake which draws the air through the
furnace. The balanced draught arrangement has matched forced draught and
induced draught fans which results in atmospheric pressure in the furnace.

State that either the percentage of carbon dioxide or the percentage of

oxygen in the exhaust gas should be continuously recorded

Documenting your measurements is fundamental to insure short and long

term understanding of your combustion process. As the boiler changes with
time, it is important to compare today`s measurements to pass data to
identify components in combustion system that justify replacing to maximize
the combustion efficiency of the process.

You should be aware that under various regulations applicable to the area your
vessel is in, it may be an offence to emit dark smoke. The Master should
therefore request appropriate detailed information from the local agent
concerning the area emission regulations and pass the information to the Chief
Engineer. Careful consideration should be given to the location and operational
circumstance of the vessel before soot blowing. Permission should be sought
from the bridge before soot blowing.

Emissions of smoke, soot and exhaust gases such as COx, NOx and SOx
(Carbon, nitrogen and sulphur) is minimised by controlled running, systematic
maintenance and inspection routines of machinery, boilers and funnel. The
emissions of exhaust gases contribute to pollution and environmental
problems such as acidification and global warming. We aim to focus on control
and reduction of the emission of these harmful gases. Reference is made
to MARPOL Annex VI and of the Company’s Safety and Environmental
Procedures.

State that although excess air is supplied, there may be some

incomplete combustion of carbon to carbon monoxide (CO)

Excess air is the extra air supplied to the burner beyond the air required for
complete combustion. Excess air is supplied to the burner because a boiler
firing without sufficient air or “fuel rich” is operating in a potentially dangerous
condition. Therefore, excess air is supplied to the burner to provide a safety
factor above the actual air required for combustion.

State that in practice the products of combustion are normally a

gaseous mixture of carbon dioxide, sulphur dioxide, water-vapour,
possibly carbon monoxide and an ash, possibly containing sodium and
vanadium

Since sulfur emissions are proportional to the sulfur content of the fuel, an
effective means of reducing SOx emissions is to burn low-sulfur fuel such as
natural gas, low-sulfur oil, or low-sulfur coal. Natural gas has the added
advantage of emitting no particulate matter when burned.

NO2 is not only an important air pollutant by itself, but also reacts in the
atmosphere to form ozone (O3) and acid rain. It is important to note that the
ozone that we want to minimize is tropospheric ozone; that is, ozone in the
ambient air that we breathe.

State that poor combustion creates smoke, which pollutes the

atmosphere and wastes fuel and reduces the efficiency of the engine
or boiler

The efficiency of the boiler depends on the ability of the burner to provide the
proper air to fuel mixture throughout the firing rate, day in and day out,
without the need for complex set-up or adjustments. The actual air/fuel ratio
allowing for normal excess in the furnace of a steam boiler. Complete
combustion will occur when the proper amount of fuel and air ratio are mixed
for the correct amount of time under the appropriate conditions of turbulence
and temperature. A proper ratio can prevent boiler from producing excessive
soot and emission gases that cause a serious accidents. The recommended
percentage of oxygen is at 3.0% with a corresponding of 13% of excess air.
The actual ratio is 2.5kg/hr to 1.0kg/hr the minimum ratio of consumption of
1,000 kg/hr and maximum ratio of consumption 3,200kg/hr.
Lesson 2 - Marine Boiler Fundamentals
Page 1
Describe, with the aid of diagrams, an auxiliary boiler steam
system together with identifying the services supplied by steam

Main stop valve -- The steam generated in the boiler is supplied to

ship’s system through this valve. It usually is non-return type of valve directly
mounted on the steam space of the boiler shell. The body is made of cast iron,
and the valve seat is of gunmetal.

Auxillary steam valve -- In most of the steam system on ships, a

separate steam line provided from the boiler for the small auxiliary system is
supplied through this valve. The valve is smaller in size and usually of a non-
return type
State typical pressures of steam produced in auxiliary boilers and
average system supply pressures

Types of boiler by pressure

Low pressure boiler – up to 10Kg / Cm2

Medium pressure boiler – 10-25 Kg /Cm2

High pressure boiler – Over 25 Kg / Cm2

Marine boilers are of two types namely the water tube boiler and the fire
tube boiler. The water tube type boiler is used for high-pressure, high-
temperature, high-capacity applications. The water-tube boiler is employed
for high-pressure, high-temperature, high-capacity steam applications, e.g.
providing steam for main propulsion turbines or cargo pump turbines. Firetube
boilers are used for auxiliary purposes to provide smaller quantities of low-
pressure steam on diesel engine powered ships.

The construction of watertube boilers, which use small-diameter tubes

and have a small steam drum, enables the generation or production of steam
at high temperatures and pressures. The weight of the boiler is much less than
an equivalent firetube boiler and the steam raising process is much quicker.

State that auxiliary steam boilers range from simple fire-tube

boilers to self-contained fully automated package units

Composite boiler – A firetube boiler which can generate steam by oil

firing or the use of diesel engine exhaust gas. Exhaust gas boiler, or
Economiser – An exhaust gas heat exchanger is a row of tube banks circulated
by feed water over which the exhaust gases from main diesel engine flow. A
boiler drum is required for steam generation and separation to take place. For
this purpose, the drum of an auxiliary boiler is usually used.

Most fire tube boilers are now supplied as a completely packaged unit,
which includes oil burner, fuel pump, FD fan, fuel pumps and auto controls.
The other names of fire-tube boilers are tank boiler, smoke tube or
donkey boiler.

Explain simply and briefly, with the aid of diagrams, the principal
differences between a fire-tube boiler, a water-tube boiler and a
packaged boiler

The main difference between fire tube and water tube is that in fire tube
boiler the flue gases flow in the tubes and water flows from the outside of tube
and in water tube boiler, water flows from the tubes and the flue gases from
the shell or passes over the tubes.

Lesson 3 - Marine Boiler Construction Part 1

Page 1
Marine boiler construction

Describe the material commonly used for construction in a fire-

tube boiler

Describe, with the aid of sketches, the general constructional

details of a fire-tube boiler, showing how the parts are connected to
form a compete Structure

These tubes consist of a large number of small diameter tubes installed in the
direction of the gas flow. For roof-fired boilers, the generating bank may
consist of one or two rows of closed-pitched tubes. In some latest modern
radiant heat boilers, the generating bank has been omitted to allow the
replacement of the water drum by a distribution header. The generation bank
is normally heated by convection rather than radiant heat. For a set water
circulation the tube diameter is limited to minimum as the ratio of steam to
water can increase to a point where the possibility of overheating can occur as
a result of low heat capacity of the steam. The number of tubes is limited to
prevent undercooling of the gas flow, leading to dew point corrosion.

Screen tubes - These are larger bore tubes that receive the radiant heat
of the flame and the convective heat of the hot gasses. The large diameter
keeps the steam/water ratio down and thus prevents overheating. The main
purpose of these tubes is to protect the superheater from the direct radiant
heat. On modern marine radiant heat boiler, the screen tube wall is formed
out of a membrane wall.

Water-wall tubes - Contains the heat of the furnace, thus reducing the
refractory and insulation requirements. Water wall tubes normally comes in
three designs:

 Water-cooled with refractory covered studded tubes

 Close pitched exposed tubes
 Membrane wall tubes

Downcomers - These are large diameter unheated tubes i.e. they are
fitted external to the furnace; their purpose is to feed water from the steam
drum to the water drum and bottom headers.
 Riser/Return tubes - These tubes return steam from the top water wall
headers to the steam drum.

Superheater tubes - These are small diameter tubes in the gas flow after
the screen tubes. Due to the low specific heat capacity of the saturated steam
they require protection from overheating in low steam flow conditions, for e.g.
when flashing.

Superheater support tubes - These are large diameter tubes designed to

support part of the weight of the superheater tubes. Tube temperature for the
water-cooled sections is considered to be saturation temperature + 15°C.
Solid drawn mild steel is generally used for the construction of superheater
support tubes.

Tube temperature for convection superheater sections is considered to be

final superheat temperature + 300°C. For radiant heat, higher temperature is
considered. For Superheater tubes operating above 450°C a
chrome Molybdenum alloyed steel is required. Boiler tube is a type of seamless
steel tube, which shares the same production technique –hot rolled or cold
drawn. It can be both of carbon steel and alloy steel.

Page 2
State that, for pressure vessels:

• shells of cylindrical form give a higher strength/weight ratio

than other shapes

• the cylindrical shell can be sited vertically or horizontally

• dished or spherical end-plates give a higher strength than flat

end-plates of similar thickness

• all flat surfaces must be properly stayed to resist deformation

• stays can have the form of solid bars, thick tubes or plate
girders

• corrugated furnaces provide higher strength and flexibility

than plain furnaces of similar thickness

When under steam, a cylindrical shell is strained by internal pressure

in two directions, namely : transversely, by a circumferential strain due to the
pressure tending to burst the shell by enlarging its circumference,
and longitudinally, by the pressure on the ends. If a boiler were spherical it
would require no stays, because a sphere subjected to internal pressure tends
to enlarge but not to change its shape. All flat surfaces in boilers must be
stayed, otherwise the internal pressure would bulge them out and tend to
make them spherical in shape. The ends of steam drums on high-pressure
water-tube boilers are often made hemispherical.

The first and most important point in staying is to have a sufficient

number of stays so that they will entirely support the plate without regard to
its own stiffness. The second is to have them so placed as to present the least
obstruction to a free inspection, and third, to have them so arranged as to
allow a free circulation of water. Too much care cannot be taken in fitting
stays and braces, as they are out of sight for long periods, and a knowledge of
their exact condition is not always easily obtained. In the ordinary fire-tube
boiler the principal surfaces stayed are: the flat ends, crown sheets, flat sides
of locomotive boilers and combustion chambers of cylindrical marine boilers. In
t h e case of most marine or Scotch boilers, the diameter is large compared to
the length ; hence the flat surface is considerable, and needs careful staying.
All the plates that are not cylindrical or hemispherical must be stayed. The
details should be arranged for each boiler ; a few general methods
and cautions can, however, be given.

The most common and simple form of stay. is a plain rod. It is used to
stay the flat ends of short boilers. This stay is a plain rod passing through the
steam space and having the ends fastened to the heads. The ends are
fastened and the length adjusted in a variety of methods ; the simplest being
nuts on both sides of the plate.

strengthen the plate and prevent abrasion by the nuts. In place of the
nuts the rod is often bolted to angle irons, which are riveted to the plates. In
this case, turn buckles similar to the one shown in Fig. 29 are used for
adjusting the length

Staying for Construction of Boilers

The stays are usually from 1/4 inch to an inch in diameter, and are made
of wrought iron or steel, with an allowable stress of 5,000 to 7,000 pounds per
square inch. If the ends are fastened to riveted angle irons, the combined area
of the rivets is made a little greater than that of the rod.

If a boiler is long, that is, more than 20 feet, long stays would sag in the
middle and not take up the full stress on the end plates. For long boilers,
gusset and diagonal stays are used. This form of boiler stay, shown in Fig. 30,
is made of wroughtiron plate riveted to angle irons ; the angle irons being
riveted to the end and shell. Boilers of the Cornish, Lancashire and Galloway
types often have this kind of stay. These boilers are internally fired, and as the
'variation of temperature causes expansion and contraction, great care should
be used in placing the gusset stay. If the stay is too near the flange or too
many stays are used, the head will be too rigid and have a tendency to crack.

Source: http://gluedideas.com/Collected-Works/Cyclopedia-of-Mechanical-
Engineering-Vol-4-p1/Staying-for- Construction-of_P1.html
Page 3
Corrugation: The plain boiler furnace geometry is corrugated to
strengthen and to increase the heated surface area. Due to their shape, they
can withstand elevated operating parameters of a high pressure boiler.

State why boiler is usually installed on board diesel engine ships

Boilers are one of the essensial equipments onboard ships. It's purpose is
to provide heating to the main diesel propulsion engine, to the bunker F.O.
tanks (to make it less viscous for transfer purposes as well as easy ignition).

The steam generated by the boiler can also be use for cleaning, and
heating of the seawater in the freshwater generator thus evaporating it to
make it potable water. Marine boilers used in ships today are mostly
for auxiliary purposes in vessels that run on marine diesel engines or diesel
electric propulsion. In case of ships using steam turbines (mostly found in high
speed vessels used by navies), boilers are a part of the main
propulsion system. However, in this article, we will focus on auxiliary boilers,
i.e. boilers used for running auxiliary systems in a ship.

To look at this from a ship designer’s point of view, he/she should be able
to choose the right kind of boiler for a particular ship depending on the
requirement for that particular project. The process is pretty much
an application of first principles, but in a somewhat different way.

Explain and
outlines a boiler system listing associated systems including their
components

Boiler Safety valve: - This is one of the most critical boiler fitting used
in the event of unsafe excessive pressure inside the boiler. The boiler safety
valve is designed to come into action to release the overpressure. The lifting
pressure of the valve is set prior to its installation and locked in the presence
of a surveyor so that it cannot be changed later on. Boiler safety valves are
installed in pairs with one valve set at a little higher pressure to ensure boiler
does not explode of overpressure in the event of failure of any one boiler
safety valve.

Boiler level gauge glass: - Boiler gauge glasses are fitted in pairs for
manually checking the water level inside the boiler drum. It is on the basis of
the boiler pressure that the construction of the gauge glass is decided. The
boiler water level indicator is an important boiler fitting as it tells the status of
water level inside the steam drum of the boiler.
 Air release valve or boiler vent: - This valve is fitted in the headers, boiler
drum etc., to avoid imploding of the boiler when it is depressurized or when
initially raising the steam pressure. The term implosion is just opposite of an
explosion. In this scenario, the pressure inside the boiler will reduce
sufficiently below atmospheric pressure to cause the shell to buckle inwards.

Feed check and control v/v: - This valve controls the supply of steam
supply as per the demand and is fitted in both main and auxiliary steam line
after the stop valve. They are non-return valves with a visible indication of
open and closed position.

Pressure gauge connection: - The pressure gauge can be fitted in the

superheater, boiler drum and wherever it is necessary to read the real-time
pressure reading from the local station.

Boiler blowdown valve: - A bottom blowdown valve is used to empty the

boiler either completely for maintenance purpose or partially for water
treatment of boiler when the chloride level in the boiler water is on a higher
side.

Scum blow down valve: - It’s a shallow dish type arrangement fitted at the
normal water level which allows the blowdown of floating impurities, oil
foaming etc. from the water surface.

Sampling connection: - Generally, a sampling water cock arrangement is

also fitted with the cooler, in series, so that water sample can be collected at
any time for feed water analysis.

Whistle valve: - If there is a provision for the steam whistle in the ship, then
steam is supplied directly from the boiler through a small bore type non-return
valve known as whistle valve.

Low-Level alarm: - This is a device used to initiate audible warning at low

water level condition. Another shut down alarm (burner cut off) is fitted below
this level (Low-Low Level alarm) to prevent overheat of boiler drum.

Soot blowers: - Required to blow the soot and the combustion products from
the tube surfaces. It is operated by steam or compressed air.

Automatic feed water regulator: - This device is essential to ensure

appropriate water level in all load conditions and is fitted in the feed line.
Multiple element feedwater control system is used in boilers with high
evaporation rate.
 Manhole: - The boiler is provided with multiple manhole doors, allowing
inside access to the crew for inspection, cleaning and maintenance of boiler
tubes and internal parts. Usually, one door is provided in the steam drum and
one in the water drum.

Mud box: - The mud box in the boiler is provided at the bottom of the water
drum to collect the mud (muddy impurities) of the water drum

TDS Sensor and Probe: - Nowadays, most of the modern boilers are
provided with this arrangement to monitor the total dissolved solids within the
boiler water continuously. The sensor compares the true value with the set
point, and if the value is on the higher side, an audio-visual alarm is given. A
manual blowdown can be done to introduce fresh feedwater to the system to
lower the total dissolved solids.

Page 4
Explain the relationship between a boiler and exhaust gas economizer

The exhaust gas boiler and economizer are heat recovery units and
types of water tube boiler. The flue gases from the exhaust of the engine are
used to heat water in the tubes at a specific temperature and limited pressure
loss.

A circulation pump is used to continuously circulate the hot water in the water
tubes of the economizer. The auxiliary steam boiler serves as a steam
separator for the entire system and is thus kept hot and ready to start
instantly. The excess steam produced by the economizer when the main
engine is running at high load, is dumped back to the hot-well using a steam
dump condenser.

COMPOSITE BOILER

Another most common type of boiler found on ships is the composite boiler,
where the exhaust heat of the main engine or generator engine is used to
additionally heat the water or generate the steam. Technically, composite
boiler is an integration of exhaust gas boiler and oil-fired boiler. A composite
boiler can be a water tube or a smoke tube boiler divided in two different
sections. One section of the boiler is heated by the burner and the other by
the exhaust gases produced by ship’s engine

Time 4:15 Economizer

Explain ignition system including the function of burner control

 In some marine boilers with main burner firing in heavy fuel oil, it is
very difficult to initially start the boiler with the main burner. For start up of
such boiler, a separate pilot or ignition burner is provided which uses diesel oil
as fuel. This enables the pilot burner to ignite even at the coldest condition the
ship faces at sea. The pilot burner has a separate diesel oil piping and pump
arrangement. The heat source is provided by two electrodes, which are used
for igniting the pilot flame and are fitted to a high voltage ignition transformer.
The pilot burner is allotted with a limited time of ignition, during which it acts
as a source of heat for the main burner and once the time is over, the pilot
flame goes off.

A marine boiler is commissioned with several automation systems so as to

generate the required steam pressure with independent automatic operation.
The automation includes monitoring and alarm systems, automatic feed supply
system, level control system, fuel control system, electrical system and
sequence operation system. The boiler local control panel is provided with a
selector knob to choose between 3 modes of the operation– “Auto”, “Manual”
and “Stop”. In some ships, instead of operating from control panel,
computerized operating program is designed to operate the boiler. When not
in use, the knob is selected to stop position, which de-energizes all electrical
power to the boiler. Feed water pump and fuel pump has a separate power
switch which needs to be operated in stop position if there is no requirement
of fuel and water.

Automatic operation: - When the selector knob is positioned to “Auto”,

considering the fuel pump system, pilot burner diesel oil pump and feed water
system are already running in auto, following steps will occur:

Once the auto operation is selected, the panel will send a signal to the starter
of FD fan to operate. The forced draught (FD) fan will start for a set period of
time controlled by the timer switch. Normally 3 to 4 minutes of time is allotted
pre purging. After the pre purging operation, power is supplied to the
electrodes of pilot burner.

The solenoid valve installed in the line of pilot burner fuel line is energized and
opened to allow the flow of fuel. Fuel is supplied in the combustion chamber
via pilot burner with electrodes creating spark. Air is supplied in a controlled
way through the air register in the furnace. In the presence of heat source
(spark), oxygen and fuel- flame is created inside the furnace. The flame eye
which is located in the furnace detects the pilot flame and sends a signal to the
boiler control panel. If there is a problem in pilot burner flame, the flame eye
will not detect any flame which will trip the boiler. If the eye detects flame,
after a set period of time it sends a signal to the control panel, which then
energizes the main burner fuel line solenoid valve and opens it. Fuel is
supplied to the main burner, which generates the flame in the presence of pilot
flame and air registers.

A timer is installed and set to switch off the pilot burner after a period of time
once the burner solenoid valve is open. Flame eye is continuously monitoring
the flame condition inside the boiler and if it does not detect any flame, a trip
signal is send to boiler control panel. A pressure transmitter is also installed
with minimum and maximum pressure settings. Once the maximum set
pressure is reached, it sends a signal to the boiler control panel for stopping
the main burner. Since the boiler main burner is now off, due to the steam
consumption the boiler pressure will reduce and once the minimum set
pressure in the pressure transmitter is reached, it will give a signal to the
control panel to start the overall operation again.

Page 5
Explain feed water system including the function of feed water
control

The water is supplied to the boiler water drum through feed water pump. For
an automatic operation, the feed water pump must know when to start and
when to stop. If the feed pump runs continuously it may overflow the boiler
which can cause priming or if the pump does not cope up with the demand,
the water level will reduce below the required, leading to severe thermal
stresses and overheating of the boiler. The feed water system is provided with
a level control system, which commands the start and stop of the feed water
pump to maintain the boiler water level. In a marine boiler, the following
water level control systems are prominently used:

Level control float/ probe: This type of system is fitted either on the top of the
boiler drum or in a water chamber attached to the boiler drum, which shows
the actual water level as of the drum. In probe type system, a metal rod is
suspended in the boiler water drum with electrical voltage along with an
ammeter included in the circuit.

Float Type Level Sensor

With the probe immersed in the water, current will flow through the circuit. If
the probe is lifted out of the water, current will not flow through the circuit.
The probe can be used to control starting and stopping of the feed water pump
or to open the feed water valve integrated with level alarm (depending on the
design of the system).
In a float type system, a float is suspended over the water and moves up or
down as per the actual boiler level. The float is connected to a metal rod fitted
with magnetic switches for starting or stopping the pump or opening and
closing of the feed valve.

Alarms can also be integrated in this system by adding more magnetic

switches in the desired level. Both float and probe type water level devices
may give erratic readings in the presence of foam or oil in the boiler water.

Source: http://mirmarine.net/stati-na-anglijskom/marine-
boiler/699-boiler-automation-and-control

Explain steam temperature control system usually used for main

boiler

Steam temperature is normally controlled by spraying water into the steam

between the first and second-stage superheater to cool it down. Water
injection is done in a device called an attemperator or desuperheater. The
spray water comes from either an intermediate stage of the boiler feedwater
pump (for reheater spray) or from the pump discharge (for superheater
spray). Other methods of steam temperature control include flue gas
recirculation, flue gas bypass, and tilting the angle at which the burners fire
into the furnace. This discussion will focus on steam temperature control
through attemperation. The designs discussed here will apply to the reheater
and superheater, but only the superheater will be mentioned for simplicity.
Because of the slow response of the main steam temperature control loop,
improved disturbance rejection can be achieved by implementing a secondary
(inner) control loop at the desuperheater. This loop measures the
desuperheater outlet temperature and manipulates the control valve position
to match the desuperheater outlet temperature to its set point coming from
the main steam temperature controller (Figure 2). This arrangement is called
cascade control.
Lesson 3 - Marine Boiler Construction Part 2
Page 6
State what is meant by ABC and ACC

Inside the ABC is also equipped with Supervising Instrument Boiler in the form
of recorder recording data - boiler operation data. The ABC system has
functions for operation and thermal power plant control as follows: The ABC
system is composed of a microprocessor with high reliability and maintenance
levels. These tools or control modules are installed in 4 cabinet systems with a
power supply. 2-wire electric transmitters and pneumatic actuators are used in
this ABC system.
The essential requirement for a combustion control system is to correctly
proportion the quantities of air and fuel being burnt. This will ensure complete
combustion, a minimum of excess air and acceptable exhaust gases. The
control system must therefore measure the flow rates of fuel oil and air in
order to correctly regulate their proportions.

A combustion control system capable of accepting rapid load changes is shown

in Figure . Two control elements are used, 'steam flow' and 'steam pressure'.
The steam pressure signal is fed to a two-term controller and is compared with
the desired value. Any deviation results in a signal to the summing relay.

The steam flow signal is also fed into the summing relay. The summing relay
which may add or subtract the input signals provides an output which
represents the fuel input requirements of the boiler. This output becomes a
variable desired value signal to the two-term controllers in the fuel control and
combustion air control loops.

A high or low signal selector is present to ensure that when a load change
occurs the combustion air flow is always in excess of the fuel requirements.
This prevents poor combustion and black smokey exhaust gases. If the master
signal is for an increase in steam flow, then when it is fed to the low signal
selector it is blocked since it is the higher input value.

When the master signal is input to the high signal selector it passes through as
the higher input. This master signal now acts as a variable desired value for
the combustion air sub-loop and brings about an increased air flow. When the
increased air flow is established its measured value is now the higher input to
the low signal selector. The master signal will now pass through to bring about
the increased fuel supply to the boiler via the fuel supply sub-loop. The air
supply for an increase in load is therefore established before the increase in
fuel supply occurs. The required air to fuel ratio is set in the ratio relay in the
air flow signal lines.
Describe how a tube is expanded into a tube plate

How to Expand, Bead and Re-Roll Boiler Tubes In One Seamless

Operation

Rolling a Boiler Tube - Boiling Point

Describe the principles of construction, operation and control of a

packaged boiler

Formation of marine boiler : 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.

The air and fuel must be intimately mixed and a small percentage of excess air
is usually supplied to ensure that all the fuel is burnt. When the air supply is
insufficient the fuel is not completely burnt and black exhaust gases will result.

The flow of air through a boiler furnace is known as 'draught'. Marine boilers
are arranged for forced draught, i.e. fans which force the air through the
furnace. Several arrangements of forced draught are possible. The usual
forced draught arrangement is a large fan which supplies air along ducting to
the furnace front.

The furnace front has an enclosed box arrangement, known as an 'air register',
which can control the air supply.

The air ducting normally passes through the boiler exhaust where some air
heating can take place. The induced draught arrangement has a fan in the
exhaust uptake which draws the air through the furnace. The balanced
draught arrangement has matched forced draught and induced draught fans
which results in atmospheric pressure in the furnace.

The essential requirement for a combustion control system is to correctly

proportion the quantities of air and fuel being burnt. This will ensure complete
combustion, a minimum of excess air and acceptable exhaust gases. The
control system must therefore measure the flow rates of fuel oil and air in
order to correctly regulate their proportions.

http://www.machineryspaces.com/boiler.html - Marine boiler mountings and

steam distribution

Page 7
Describe the principles of construction, operation and control of a
packaged boiler

Formation of marine boiler : 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.
The air and fuel must be intimately mixed and a small percentage of excess air
is usually supplied to ensure that all the fuel is burnt. When the air supply is
insufficient the fuel is not completely burnt and black exhaust gases will result.

The flow of air through a boiler furnace is known as 'draught'. Marine boilers
are arranged for forced draught, i.e. fans which force the air through the
furnace. Several arrangements of forced draught are possible. The usual
forced draught arrangement is a large fan which supplies air along ducting to
the furnace front.

The furnace front has an enclosed box arrangement, known as an 'air register',
which can control the air supply.

The air ducting normally passes through the boiler exhaust where some air
heating can take place. The induced draught arrangement has a fan in the
exhaust uptake which draws the air through the furnace. The balanced
draught arrangement has matched forced draught and induced draught fans
which results in atmospheric pressure in the furnace.

The essential requirement for a combustion control system is to correctly

proportion the quantities of air and fuel being burnt. This will ensure complete
combustion, a minimum of excess air and acceptable exhaust gases. The
control system must therefore measure the flow rates of fuel oil and air in
order to correctly regulate their proportions.

http://www.machineryspaces.com/boiler.html

Marine boiler mountings and steam distribution

The use of boiler mountings - Safety valves, Mam steftm stop valve, Auxiliary
steam stop valve etc.

: Certain fittings are necessary on a boiler to ensure its safe operation. They
are usually referred to as boiler mountings. The mountings usually found on a
boiler are: safety valves, main steam stop valve, feed check valve, water level
gauge, pressure gauge connection, air release cock, sampling connection, blow
down valve, scum valve, etc.

Identify the following boiler fittings and position on boiler shell

(supply shell diagram for fitting to be married/drawn and identified):

• main stream outlet (or "stop") valve -

• auxiliary steam stop valve
• safety valves and easing gear
-Safety valves and pressure-relief valves are automatic pressure-relieving
devices used for overpressure protection of piping and equipment. Safety
valves (Fig. A) are generally used in gas or vapor service because their
opening and reseating characteristics are commensurate with the properties
and potential hazards of compressible fluids. The valves protect the system by
releasing excess pressure. Under normal pressure, the valve disc is held
against the valve seat by a preloaded spring. As the system pressure
increases, the force exerted by the fluid on the disc approaches the spring
force. As the forces equalize, fluid begins to flow past the seat.
The valve disc is designed in such a way that the escaping fluid exerts a lifting
pressure over an increased disc surface area, thereby overcoming the spring
force and enabling the valve to rapidly attain near-full lift. An added benefit to
the safety valve disc design is that the pressure at which the valve reseats is
below the initial set pressure, thereby reducing the system pressure to a safe
level prior to resealing. The ratio of the difference between the set pressure
and the resealing pressure to the set pressure is referred to as the blowdown.
Pressure-relief valves (Fig. A) are used primarily in liquid service. These
valves function in a way similar to safety-relief valves, except that as liquids
do not expand, there is no additional lifting force on the disc and, therefore,
the valve lift is proportional to the system pressure. Also, the valves reseat
when the pressure is reduced below the set pressure.

A third type of pressure-relieving valve is a safety-relief valve, which can be

used with both compressible and incompressible fluids. It combines the design
features of a safety- and a relief-valve into one. Therefore, when it is used
with compressible fluids, such as steam or a gas, it pops open to release the
overpressure, and when used with incompressible fluids, such as water or
other liquids, it opens gradually, proportional to the increase in pressure over
the set pressure, to safeguard the vessel, tank, heat exchanger, piping, or
other equipment.
Page 8
 • water level gauges

• feed inlet valve

• blow-down valve

• scumming valve

• soot blowers

• connections for pressure gauges

• air release valve

sampling valve

Explain the importance of boiler mounted valves

Just installing a boiler on a ship doesn’t guarantee efficient working of a boiler.

When a boiler installation is done on board a ship, it can only be considered as
complete, when different types of boiler mountings, including boiler controls,
are fitted to ensure safe and efficient operation of a gas boiler.
Identify the following internal boiler fitting and internal position
within boiler shell:

• feed water distribution unit

• scumming pan - A boiler mounting used to remove scum from the

water surface. A shallow dish is positioned at the normal water level and
connected to the valve.

https://www.wartsila.com/encyclopedia/term/scum-valve

• blow-down dip pipe (Refer to the diagram below)

https://maritime.org/doc/merchant/engineering/part2.htm

http://www.machineryspaces.com/boiler.html

Explain the purpose of the valves and fittings listed in the above
objectives, comparing the differences, where applicable, between
water - tube and fire - tube boilers

The boiler steam drum is fitted with several internal and external mountings
for ensuring the safety and efficiency of the boiler steam system. These
mountings are important mechanical components that need to be maintained
for trouble-free operation. Following are the important external mountings
fitted over the boiler:

Safety Valves: Safety valve are fitted in two numbers (pairs) to ensure that
the boiler does not over-pressurize else it may lead to explosion of the
pressure vessel.

http://mirmarine.net/stati-na-anglijskom/marine-boiler/693-marine-boiler-
mountings

Explain the purpose of a reducing valve

Every steam pipe and every connecting fitting through which steam passes
must be designed, constructed and installed to withstand the maximum
working stresses to which it may be subjected. Means shall be provided for
draining every steam pipe in which dangerous water hammer action might
otherwise occur. If a steam pipe or fitting can receive steam from any source
at a higher pressure than that for which it is designed, a suitable reducing
valve, relief valve and pressure gauge must be fitted.

Describe the operation of a reducing valve, using a single line sketch

Page 9
Explain how steam pipes are supported

Clips and supports are used to hold pipes in position and to prevent movement
or vibration. A vibrating pipe can ‘work harden’ and fail. Pipes can fracture
when there is insufficient support. There are no hard and fast rules about the
number of clips required in a length of pipe as this will depend on the pipe’s
diameter, length, position and the density of fluid conveyed.

The contact area at the surface of the pipe requires protection. Failures often
occur as a result of mechanical wear when the clip loosens or a clip supporting
weld fractures, allowing the pipe to move. Inspection procedures must be
designed to ensure that all clips are checked regularly, including those hidden
from sight behind insulation or under engine room floor plates. Special
attention should be paid to clips in concealed places.

https://www.standard-
club.com/media/24158/AMastersGuidetoShipsPiping2ndedition.pdf

Explain how expansion and contraction are allowed for in steam

pipes

Expansion loops or bellows are fitted to compensate for thermal expansion or

contraction and for the flexing of the ship. Pipe joints are kept to a minimum.
The piping system, including bellows, is normally welded but with sufficient
flanges to allow for maintenance and removal of equipment.

Describe the different methods of joining lengths of a steam pipe

Steam is used for indirectly heating oils, water and air. It is also used as a
scavenge fire-fighting medium on some slow speed engines. The steel piping
that carries the steam must be of seamless construction and joined by flanges
with suitable steam-resistant gasket materials.

Explain the purpose of drains and steam traps

Shall be provided for draining every steam pipe in which dangerous

water hammer action might otherwise occur

https://www.standard-
club.com/media/24158/AMastersGuidetoShipsPiping2ndedition.pdf

Describe the operation of steam traps

A steam trap is a special type of valve which prevents the passage of steam
but allows condensate through. It works automatically and is used in steam
heating lines to drain condensate without passing any steam. The benefit
gained with a steam trap, is that steam is contained in the heating line until it
condenses, thus giving up all of its latent heat. There are three main types
which are the mechanical, the thermostatic and the thermodynamic. There is
also the vacuum trap or automatic pump.

http://generalcargoship.com/valves-traps.html

Describe the procedure for warming through a steam line and

explains the cause, in simple terms, of water hammer and how water
hammer can be avoided

Water hammer can affect any pipe but is most common in steam pipes. It is a
problem in pipes where internal condensation occurs. Water hammers are
impulse pressures that happen when steam enters a cold pipe containing a
small amount of water. The resulting stresses, along with possible rapid
expansion, can cause pipe joints to fail. Prevent water hammer by draining
fluid from pipes before injecting steam gradually.

Steam systems are most prone to damage by water hammer because they
operate at high temperature and pressure, and because condensed steam will
remain in them, unless regularly drained.

Note:Steam heating coils on tankers are particularly susceptible to damage by

water hammer.

https://www.standard-
club.com/media/24158/AMastersGuidetoShipsPiping2ndedition.pdf

Explain the outline of steam supply system including its

components/installations

Every steam pipe and every connecting fitting through which steam passes
must be designed, constructed and installed to withstand the maximum
working stresses to which it may be subjected. Means shall be provided for
draining every steam pipe in which dangerous water hammer action might
otherwise occur. If a steam pipe or fitting can receive steam from any source
at a higher pressure than that for which it is designed, a suitable reducing
valve, relief valve and pressure gauge must be fitted.

There have been many accidents resulting in serious injury or death from
working on or near steam pipework. Always ensure that the steam line is
completely vented with double valve isolation or blank flange before opening a
pipe. Always wear the appropriate personal protective equipment (PPE) when
opening the pipe, as even when vented, scalding water may still be present in
the line. Always carry out a risk assessment and ensure a permit to work is
issued. Valve isolation and venting must be cross-checked by another senior
engineer.

https://www.standard-
club.com/media/24158/AMastersGuidetoShipsPiping2ndedition.pdf

Describe the means used to minimize the possibility of oil

contaminating the boiler feed water

The most common sources of oil contamination observed on boilers originate

from leaking heating coils fitted in fuel oil tanks, fuel/lub oil heaters, cylinder
lub oil from reciprocating steam engines for pumps and heating coils in DB
tanks dedicated for sludge/waste oil tanks. It is also not rare for cargo tank
heating coils and tank cleaning heaters fitted on the cargo side to contribute to
the contamination in some cases.

However, main propulsion boiler plants with a segregated saturated steam

system as the main source of heating medium are least likely to be
contaminated by oil.

Compensatory and precautionary measures include derating the boiler's steam

generating capacity by reducing the firing rate/heat input in conjunction with
the design working pressure.

Boiling out the water side of the boiler using recommended chemicals and/or
mechanical cleaning are normal procedures undertaken to facilitate
satisfactory cleaning. This may be additionally supported by hardness checks
and a hydrostatic pressure test at 1.5 times the design working pressure to
ensure the expected safety factor at the design temperature.

In view of the oil deposits on the water side, it is also imperative that the
impulse piping to the level transmitters is blown through and safety functions
verified for satisfactory operation.

https://safety4sea.com/oil-contamination-of-marine-boilers/