MARINE ENGINEERING – 1

BOILER
Boiler
A boiler in one form or another will be found on every type of ship. On a diesel main machinery vessels, a
smaller boiler will be fitted to provide steam for the various ship services. Even within the two basic design
types, water tube and firetube, a variety of designs and variations exist.

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 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.
PARTS OF BOILER
PARTS OF BOILER
Furnace
•A furnace or also called a furnace is a device used for heating.
•The name comes from the Latin Fornarx, which means the same as the oven. Sometimes people also refer to kilns.
•The process of heat transfer in a furnace occurs in three ways:
•Heat transfer by conduction, heat flows through the conductor from the side of the pipe, which receives heat into the side
of the pipe, which gives heat to the water.

Membrane Wall
•The wall consists of tubes/pipes that are joined by a membrane, therefore called the membrane wall. Inside the
Membrane wall flows water to be boiled.
•Tube/pipe construction is from the bottom up where the bottom of the pipe is filled with heavier water mass, and it is
expected that at the top, it has become steam through a combustion process where lighter mass steam will rise to the top
naturally.
•To prevent the spread of heat and to minimize contact with humans, the outer side of the membrane wall is mounted on
an insulating wall made of rock wool wire blanket.
PARTS OF BOILER
Shell Boilers
• The boiler shell in the picture above is the type of fire tube. In a firetube boiler, hot gas passes through
the pipes, and boiler feedwater is in the shell to be turned into steam.

Reversal chambers
• Change the direction of the exhaust gasses as they exit one pass and are directed into another. Reversal
chambers located away from the burner are ' rear reversal chambers ' whilst those closest to the burner
are ' front reversal chambers ‘.

Flue-Gas Stack
• Also known as a smoke stack, chimney stack or simply as a stack, is a type of chimney, a vertical pipe,
channel or similar structure through which combustion product gases called flue gases are exhausted to
the outside air.

Boiler Framer
• Support structure connecting the boiler to the ground

Pressure Switch
• Is a device that is activated by the pressure of fluids, air, or gas when it reaches a threshold or setpoint
PARTS OF BOILER

Main Stop Valve

• Boiler stop valves A steam boiler must be fitted with a stop valve (also known as a crown valve) which
isolates the steam boiler and its pressure from the process or plant. It is generally an angle pattern globe
valve of the screw-down variety.

Manhole
• Is an opening that is used to access the inside of the boiler body.

Feed Water Valve

• Opens and closes to provide fresh water into the system

Blow Down Valve

• The primary function of a blowdown valve is to control the concentrations of suspended & total dissolved
solids (TDS) in the boiler. Boiler blowdown is a severe service application which results in rapid erosion
and wearing out of conventional valves.
PARTS OF BOILER

Low-Water Fuel Cutoff

• used on both steam and hot water boilers to shut off the fuel or source of heat when the water
drops below a predetermined, safe operating level.

Pressure gauge
• is used to determine the inside pressure of the vessel

Sight Glass or Water Gauge

• is a type of level sensor, a transparent tube through which the operator of a tank or boiler can
observe the level of liquid contained within. Simple sight glasses may be just a plastic or glass
tube connected to the bottom of the tank at one end and the top of the tank at the other.
Boiler Types
Two basically different types of boiler exist, namely the water tube. In the
water tube the feedwater is passed through the tubes and the hot gases pass
over them. In the firetube boiler the hot gases pass through the tubes and
the feed water surrounds them.

Water tube Boiler is employed for high pressure, high temperature high
capacity steam applications steam for main rpropulsion turbines or cargo
pump turbines.

The construction of water tube 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.
Design arrangements are flexible, efficiency is high and the feedwater has a SCHEMATIC DIAGRAM MARINE
good natural circulation. These are some of the many reason why the water ENGINE WATER TUBE BOILER
tube boiler has replaced the firetube boiler as the major steam producer.
Firetube Boiler
The firetube boiler is usually chosen for low- pressure steam production on vessels requiring steam for
auxiliary purposes. Operation is simple and feedwater of medium quality may be employed. The name tank
boiler’s is sometimes used for firetube boilers because of their large water capacity. The terms “smoke tube
and donkey boiler are also in use.

SCHEMATIC DIAGRAM MARINE ENGINE

FIRETUBE BOILER
Boiler Mountings
Certain fittings are necessary on the boiler to ensure its safe operation. They are usually reffered to as boiler
mountings. The mountings usually found on boiler are:
Main Steam Stop Valve
-This valve is fitted in the main steam supply line and is usually of the non-return type.
Auxiliary Steam Stop Valve
-This is a smaller valve fitted in the auxiliary steam
supply line, and is usually of the non-return type.

Feed Check or Control Valve

- A pair of valves are fitted, one is the main
valve, the other the auxiliary or standby. They
are non-return valves and must give an
indication of their open and closed position.
 Air Release Cock
-These are fitted in the headers, boilers
drum etc. to release air when filling the
boiler or initially raising steam.

Blow Down Valve

-This valve enables water to be blown
down or emptied from the boiler. It may be
used when partially or completely
emptying the boiler.

Sampling Connection
-A water outlet cock and cooling arrangement is
provided for the sampling and analysis of feed
water. A provision may also be made for injecting
water treatment chemicals.
 Water Level Gauge
-Water level gauges or gauge glasses are fitted in
pairs, at opposite ends of the boiler. The construction
of the level gauge depends upon the boiler pressure.

Pressure Gauge Connection

-Where necessary on the boiler drum
superheaters, etc. pressure gauges are fitted in
pairs, at opposite ends of the boiler. The
construction of the level gauge depends upon
the boiler pressure.
Boiler Mountings (Water Tube Boilers)
Water tube boilers, because of their smaller water content in relation to their steam raising capacity, require
certain additional mountings

Automatic Feed Water Regulator

Fitted in the feed line prior to the main check valve, this device is essential to ensure the correct water level in
the boiler during all load conditions. Boilers with a high evaporation rate will use a multiple-element feed
water control system.

Low Level Alarm

A device to provide audible warning of low water level conditions.

Superheater Circulating Valves

Acting also as air vents, these fittings ensure a flow of steam when iniatially warning through and raising
steam in the boiler.

Soot blowers
Operated by steam or compressed air they act to blow away soot and the products of combustion from the tube
surfaces. Several are fitted in strategic places. The sootblower lance is inserted soot is blown and the lance is
withdrawn.
Safety Valves

Safety Valve are fitted in pairs, usually on a single valve chest. Each valve must be able release all the steam
the boiler can produce without the pressure rising by more than 10% over a set period.
Spring-loaded valves are always fitted on board ship because of their positive action at any inclination. They
are positioned on the boiler drum in the steam space.

The spring pressure, once set is fixed and sealed by a surveyor. When the steam exceeds this pressure once set
is fixed and sealed by the surveyor. When the stream exceeds this pressure the valve is opened and the spring
compressed. The escaping steam is then led through a waste pipe up the funnel and out of the spring and open
the valve further, To some extent this is countered by a lip arrangement on the valve is open. A manually
operated easing gear enables the valve to be opened in an emergency.
Safety Valves
-These are mounted in pairs to protect the boiler against
overpressure. Once the valve lifting pressure is set in the
presence of a Surveyor it is locked and cannot be changed.
The valve is arranged to open automatically at the pre-set
blow-off pressure.
Common Impurities

Various amounts of different metal salts are to be found I water. These include the chlorides, sulphates and
bicarbonates of calcium, magnesium, and to some extent Sulphur. These dissolved salts in water make up what
is called the hardness of the water. Calcium and magnesium salts are the main causes of hardness.

The bicarbonates of calcium and magnesium are decomposed by heat and came out of solution as scale
forming carbonates. These alkaline salts are known as temporary hardness. The chlorides, sulphate and nitrate
are not decomposed by boiling and are known as permanent hardness and gives a measure of the scale-forming
salts present in the boiler feedwater.
Boiler Operation
The procedure adopted for raising steam will vary from boiler to boiler and the manufacturers instructions
should always be followed. A number of aspects are common to all boilers and a general procedure might be as
follows.

Preparations

The uptakes should be checked to ensure a clear path for the exhaust gases through the boiler; any dampers
should be operated and then correctly positioned. All vents, alarm,water and pressure gauge connections
should be opened. The superheater circulating valves or draines should be opened to ensure a flow of steam
through the superheater. All the other boiler drains and blow-down valves should be checked to ensure that
they are closed. The boiler should then be filled to slightly below the working level with hot de-arenated water.
The various header vents should be closed. The economizer should be checked to ensure that it is full of water
and all air vented off.

The operation of the forces draught fan should be checked and where exhaust gas air heaters are fitted they
should be bypassed. The fuel oil system should be checked for the correct positioning of valves,etc. The fuel
oil should then be circulated and heated.
 THANK YOU!

END OF DISCUSSION