3. Steam Plant & Boiler31!12!09

D1MC Semester 2 / Ship Stability / March 2007/LSC /STEAM PLANT 1

To Be A Leader In Maritime Education & Training

Steam Turbines



Steam plant - content

Describe Steam plant layout & function

Describe Turbine operation- impulse & reaction

Describe Pressure & velocity compounding

Describe Boiler construction & mountings

Describe procedure to warm-up boiler

Describe steam plant preparation procedures.



Steam Turbines

Function :- Convert steam energy into mechanical work.

Advantages: Low machinery weight.

Low maintenance cost.

Low vibration.

Minimum space required

Disadvantage: High fuel consumption compared to diesel

engine. ( about 300 g / KWh vs 180 g/ KWh)3



Steam Plant Layout



Layout of Steam Propulsion Plant

Steam from the boiler is superheated before it is supplied to the high pressure (HP) and low pressure (LP) turbine during ahead operation.

Astern manoevring valve is opened only for astern operation of the astern turbine.

Waste steam from the turbine is cooled by sea water and condensed to water in the condenser.

Condensate pump transfer the water to de-aerator where air is removed from the condensate water.

Main feed pump transfer the water to heaters and economiser for heating before it is sent to the boiler



Cross - Compound

It is used to describe a steam turbine unit made up of a high pressure and a low pressure turbine.

This is the usual main propulsion turbine arrangement.

The alternative is a single cylinder unit which would be usual for turbo-generator sets.



Impulse Turbine De Laval

Steam supplied to a nozzle box and through the nozzle box to a group of nozzles.

Steam expands in passing through the nozzles with a fall in pressure and gain in velocity.

The high velocity steam jet is angled and directed to enters rows of blades without shock.

The change of momentum produces a force tangential to blades and a turning moment to rotor spindle.



De Laval Impulse Turbine



Reaction Turbine

One stage consists of fixed blades acting as nozzles followed by a row of moving blades fixed on rotor.

Pressure drops equally while the steam passes on fixed blades and moving blades.



Reaction Turbine



Parsons Reaction Turbine



MAIN TURBINE



TURBINE FOR GENERATOR



TURBINE SIDE

GENERATOR

REDUCTION

GEAR

WHY?



Compounding of Turbine

The pressure or velocity drop or both takes place in a controlled manner in a number of successive steps or stages.

The turbine becomes long but efficient and practicable.

(Compounding overcome high energy of steam liberated which is practically impossible to utilise)



Pressure Compounded Impulse

Turbine Made up of large number of stages.

Each stage consists of a row of nozzles followed by a row of moving blades attached to the wheel of the rotor.

Each stage has the same pressure but the pressure varies in successive stages.



Pressure Compounded Impulse

Turbine

Advantages:

Steam velocity lower due to smaller heat drop

Efficiency increased

Disadvantages:

Increase in first cost

Increase in length



Pressure Compounded Impulse Turbine



Velocity Compounded Turbine

Consists of a row of nozzles in which all the pressure drop takes place followed by alternate rows of moving and fixed blades.

Pressure remains uniform through the stage but velocity drops.



Velocity Compounded Turbine

Advantages:

Large pressure drop obtained through the nozzle smaller heat drop

Reduction in turbine length

Reduction in costs less materials required

Disadvantages:

Low efficiency

Increase steam consumption



Velocity Compounded Impulse Turbine



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Compounding for Pressure and

Velocity Suitable for High Pressure (HP) turbine. Steam expended through a set of nozzles.

The first stage is velocity compounded through two or three rows of moving blades.

Steam now enters the second row of nozzles, expanded to lower pressure and passed on to successive stages.



Compounding for Pressure and Velocity



Fundamentals of steam generation

Boiling point of water depends strictly upon the pressure exerted on it:

Pressure (bar) 10 20 100

Boiling Point (0C) 180 212 311

The saturated steam at 100 bar, 311 0C , when subjected to further heating will increase the dryness of the steam but does not increase its temperature

If steam flow passes out of the boiler to externally heated elements, its temperature can be increased and the steam becomes superheated



Foster Wheeler D type water Tube boiler

Consists of two horizontal cylindrical drums.

* Top steam and water drum

(referred as steam drum)

* Bottom water drum

The drums are connected directly by vertical generating tubes and by other tubes via headers.

One set of tubes from steam drum are bent to form part of roof of combustion chamber and lower portion forms the side walls.



Water Tube Boiler



Boiler Mountings

Main and Auxiliary Steam Stop Valve Steam outlet

Main and Auxiliary Feed Check Valve water inlet

Feed Water Regulator regulate water to boiler

Water Gauges indicate water level

Pressure Gauge Cock steam to pressure gauge



Boiler Mountings

Safety Valve release excessive pressure

Blow Down Valve remove dissolved contaminants

Scum Valve- remove surface contaminants

Salinometer Cock sample water for test

Air Cock release air in system

Soot Blower remove soot/carbon from boiler tubes



Regenerative Condenser



Closed Feed System

Feed water circuit from condenser to boiler is completely closed.

Main function is to prevent the condensate from contact with atmospheric air before entry boiler.

The de-aerated water would absorb air if any part of circuit was open to atmosphere.

In regenerative condenser, the air is taken out separately to the condensed water.

The air is extracted by a steam jet air ejector.

The water is taken out by a condensate pump.



Closed Feed System



Procedure for Raising Steam

Water in boiler and at correct level.

Air to burners and furnace for combustion and purging.

Fuel supply adequate and at correct pressure and temperature.

Means of ignition.

Light the burner.

Steam flow at correct pressure and signal is used to vary the firing rate as the demand requires.



Warming through Steam Turbine

Turbine must be thoroughly heated up as near as possible to working temperature before starting.

Assuming auxiliary steam line is already in use:

All drains on engine and main steam line open.

Start all lubricating pumps, check oil pressure at brgs. etc

Open main injection and discharge valves and start main condenser circulation pump.



Warming through steam turbine

Run condenser extraction pump to maintain low vacuum of about 200 mmHg

Change over auxiliary exhaust from auxiliary condenser to main condenser.

See the propeller is clear and turn the engine a little then take out the turning gear.

Ease main steam valve off its face to allow steam into main steam pipe.




Check the drain until water is driven out , open the steam valve very slowly and closed when the drains are blowing freely.

Check there is no obstruction to sliding feet and take expansion readings.

Put on gland steam and crack open

manoeuvring valves to allow a little steam into

engine.




After about 3 hours, raise vacuum to about 350 mmHg .

Operate manoeuvring valve carefully to slowly turn the engine a few revolutions ahead and then astern.

Repeat this operation about every 10 15 minutes for the next 2 hours.

At ready for stand-by, after 4 hours of heating up, pumps are brought up to normal speed, vacuum lifted up and expansion readings checked.



Manoeuvring of Steam Turbine

During manoeuvring , turbine drains are regulated as required and shut off at full-away.

Once warm through, turbine rotor must not remain stationary more than a few minutes at a time.

The rotor need to be rotated regularly to prevent failure from sag and distortion.

Astern running should be limited to prevent temperature rise, noise levels ,bearing overheating etc



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Turbine Nozzles and Turbine Control

Nozzles serve to convert the high pressure and energy of the steam into a high velocity jet of steam with reduced pressure and energy content.

Steam inlet nozzles are arranged in several groups with all but the main group having control valves.

The power produced by the turbine can be varied, depending on how many nozzle valves are opened .

Valves admitting steam to turbine are called manoeuvring valves i.e ahead, astern and guardian valve



Akademi Laut Malaysia Malaysian Maritime Academy

Turbine Nozzles and Turbine Control

Guardian valve is an astern steam isolating valve.

Speed sensitive control device acts on ahead manoeuvring valve to hold the turbine speed constant at desired value.

Manoeuvring revolutions are usually about 80 % of the full away or full speed condition.

Once full away command received, turbine can gradually be brought up to full power operation.



Full Away - Steam Turbine

This operation will take about 1-2 hours.

This involves bringing into use turbo-alternators which use steam removed or bled at some stage from main turbine

Check expansion arrangement, drains shut, astern steam valve shut, condensate re-circulation valve after air ejector shut.



Emergency Astern Operation

Safe operating procedures must be ignored.

Ahead steam shut off, may be by an emergency trip, and astern steam valve is partly opened to admit steam gradually.

The turbine can be brought quickly to stopped condition and if required operated astern.

The stopping of the turbine or astern operation will occur about 10-15 minutes.

The use of emergency procedures can lead to serious damage to turbine, gearing and boiler.



Turbine Protection

Emergency self closing stop valve close automatically and shut off steam supply to turbine as a result of the following faults:a. loss of lubricating oil pressure

b. turbine overspeed

c. emergency stop

d. low condenser vacuum

e. high or low boiler water level

f. high condensate water level in condenser

Alarms - turning gear in (turbine cannot start)

- main thrust bearing wear down.



Main steam plant

Q & A session



Auxiliary boilers - content

1 Types of boilers

Water tube vs fire tube

2

Boiler construction & mountings

Fuel oil burning installation

3

Feedwater system

Procedures related to steam plant



Boiler

Two distinct types used on board:

(a) Fire Tube or Smoke Tube Boiler

(b) Water Tube Boiler

Fire Tube Boiler

Hot gases from furnace pass through the tubes while the water is on the outside.

Water Tube Boiler

Water flows through the inside of tubes while the hot furnace gases pass around the outside.



Boiler

Groups of Boiler

Main Boiler

Supply steam directly for main propulsion purposes

Auxiliary Boiler

Supply steam for auxiliaries which are essential for main propulsion e.g. fuel tank heating, main engine warming up, purifier heating etc.

Donkey Boiler

Supply steam for hotel and port services.



Composite Boiler

Often fitted where the generation of steam can be maintained by oil firing when the exhaust gas temperature falls e.g. engine stopped

Separate uptakes are provided for:

* the engine exhaust and

* the products of combustion from oil fire



Composite Boiler



Exhaust Gas Boiler



Boiler Fuel Oil Supply System



Contamination of Feed Water

1. Dissolved Salt (calcium & magnesium make water hard, other salt may produce acid and attack metal )

2. Oil (from leakages of oil tank heating coil form scum on water surface - cause priming of water )

3. Dissolved Gases (oxygen causes corrosion of boiler)



Contamination of Feed Water

Remedies

Blow- down ( surface and bottom)

Chemical Treatment

No leakage in system

Note: Carry over of water with steam due to priming result in Damage to valve , pump and turbine.



Auxiliary boilers

Q & A session

3. Steam Plant & Boiler31!12!09

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