Machinery Spaces.com

Home || Diesel engines ||Boilers||Feed systems ||Steam turbines ||Fuel treatment ||Pumps ||Valves ||Refrigeration ||

Steam turbines and gearing - operating principle

What is energy conversion in a steam turbine ?
The steam turbine has until recently been the first choice for very large power marine propulsion units. Its advantages of little or no vibration, low weight, minimal space requirements and low maintenance costs are considerable.



Furthermore a turbine can be provided for any power rating likely to be required for marine propulsion. However, the higher specific fuel consumption when compared with a diesel engine offsets these advantages, although refinements such as reheat have narrowed the gap.

The steam turbine is a device for obtaining mechanical work from the energy stored in steam. Steam enters the turbine with a high energy content and leaves after giving up most of it.

The high-pressure steam from the boiler is expanded in nozzles to create a high-velocity jet of steam. The nozzle acts to convert heat energy in the steam into kinetic energy. This jet is directed into blades mounted on the periphery of a wheel or disc (Figure above).

The steam does not 'blow the wheel around'. The shaping of the blades causes a change in direction and hence velocity of the steam jet. Now a change in velocity for a given mass flow of steam will produce a force which acts to turn the turbine wheel, i.e. mass flow of steam (kg/s) x change in velocity (m/s) = force (kgm/s2).

steam turbine

Fig: Energy conversion in a steam turbine

This is the operating principle of all steam turbines, although the arrangements may vary considerably. The steam from the first set of blades then passes to another set of nozzles and then blades and so on along the rotor shaft until it is finally exhausted. Each set comprising nozzle and blades is called a stage.

Steam Turbines Warming Through

The turbines are to be warmed through gradually following a stay in port or other occasion when they have been shut down. The bulkhead, stop, and manoeuvring valves are to remain shut. Warming through is to commence, not less than 12 hours prior to the estimated time of departure. The Deck Officer of the watch, or Duty Deck Officer is to be contacted and permission to turn the turbines/propeller requested.

Once the Deck Officer has confirmed that this can safely be carried out then and only then can the turbines be turned.

Lubricating oil circulation is to be started, and low vacuum created. Rotation can then commence after which the gland steam can be opened gradually. On no account is gland steam to be admitted with the turbine rotors stationary. The temperatures are to be raised to the manufacturers recommendations. Once this has been achieved the turning gear can be disengaged.

It is the responsibility of the Chief Engineer Officer to ensure that disengagement of the turning gear is physically sighted. No reliance is to be placed on any remote indicating devices. A request is then to be made to the Officer of the watch on the bridge for permission to turn the engine on live steam.

Once permission is obtained, then the main bulkhead stop, guardian, valves etc. may be opened. All nozzle control valves are to be opened.

With gland steam on and a low vacuum the turbines can be turned on the ahead manoeuvring valve for several propeller revolutions every five minutes. Astern movement is not necessary for warming purposes and the use of astern steam is to be restricted to the necessary amount to check astern rotation. Care should be exercised to ensure that the turbines do not come to rest for too long a period during the warming through procedure.


Normal Operation

The main engine is to be operated within the limits of power, maximum evaporative capacity and pressure of the boilers, and the revolutions per min set out in the commissioning letter issued when the vessel entered Company service.

Only if subsequent specific instructions have been issued by the Company, are the original commissioning letter parameters to be countermanded.


Stand By Manoeuvring

The Officer of the watch on the Bridge must give the Engine Department at least one hours notice before Stand By for manoeuvring. Regardless of the time of day or type of vessel i.e. unmanned engine room or conventional watchkeeping, the Chief Engineer Officer, and the Engineer Officer of the watch or Duty Engineer Officer are to be informed.

Reduction in speed from full speed to the recognised manoeuvring speed is to be as gradual as possible and in accordance with the manufacturer’s instructions. The operating parameters are to be maintained avoiding sudden variations of boiler loading etc.


Cooling Down

When the main turbines are stopped and "Finished with Engines" has been rung, the nozzle control, manoeuvring, guardian, bulkhead and stop valves are to be shut and verified as shut. As soon as the above mentioned valves are verified as shut, permission is to be sought from the Officer of the watch on the Bridge to turn the turbines/propeller.

Once permission is granted, then the turning gear is to be engaged and the turbines rotated with the lubricating oil supply maintained, low vacuum, and gland steam on, over a minimum period of 4 hours.


Maintaining Temperatures during Short Stays in Port

If the ETD is six hours or less then the following procedure is to be adhered to. Following "Finished with Engines" permission is to be sought to turn the turbines/propeller on live steam. With the lubricating oil supply maintained, low vacuum, and gland steam on the turbines are to be turned on ahead steam for approximately 2 propeller revolutions every five minutes, using astern steam as appropriate for checking ahead rotation only.


Control Systems Maintenance

Testing and maintenance of any turbine control system alongside a berth is strictly forbidden under live steam conditions. The main steam stop, guardian and bulkhead stop valves are to be shut prior to maintenance work being carried out.

In the case where a simulated test would be unsatisfactory and operation with live steam has to be carried out, then the vessel is to be suitably anchored or stopped at sea, before maintenance or testing is carried out. Running Hours for Turbines and Boilers should be recorded in the “Turbine and Boilers Running Hours” and returned to the Managing Office on a monthly basis.



Related Info:

  1. Marine steam turbines operating procedure

  2. The steam turbine has until recently been the first choice for very large power marine propulsion units. Its advantages of little or no vibration, low weight, minimal space requirements and low maintenance costs are considerable. Furthermore a turbine can be provided for any power rating likely to be required for marine propulsion.
    More.....

  3. Impulse steam turbine and reaction steam turbine

  4. The steam turbine is a device for obtaining mechanical work from the energy stored in steam. There are two main types of turbine, the 'impulse' and the 'reaction'. The names refer to the type of force which acts on the blades to turn the turbine wheel.
    More.....

  5. Turbine control and protection

  6. A turbine protection system is provided with all installations to prevent damage resulting from an internal turbine fault or the malfunction of some associated equipment. Arrangements are made in the system to shut the turbine down using an emergency stop and solenoid valve.
    More.....

  7. Various turbine gearing -Epicyclic gearing,Helical gearing,Flexible coupling &Turning gear

  8. Helical gears have been used for many years and remain a part of most systems of gearing. Epicyclic gears with their compact, lightweight, construction are being increasingly used in marine transmissions.
    More.....

  9. Construction of the steam to steam generator - how it works

  10. Steam-to-steam generators produce low-pressure saturated steam for domestic and other services. They are used in conjunction with watertube boilers to provide a secondary steam circuit which avoids any possible contamination of the primary-circuit feedwater. .
    More.....

  11. Cross compound steam turbine arrangement for marine use

  12. Compounding is the splitting up, into two or more stages, of the steam pressure or velocity change through a turbine. Pressure compounding of an impulse turbine is the use of a number of stages of nozzle and blade to reduce progressively the steam pressure..
    More.....




Marine machineries - Useful tags

Marine diesel engines ||Steam generating plant ||Air conditioning system ||Compressed air ||Marine batteries ||Cargo refrigeration ||Centrifugal pump ||Various coolers ||Emergency power supply ||Exhaust gas heat exchangers ||Feed system ||Feed extraction pump || Flow measurement || Four stroke engines || Fuel injector || Fuel oil system || Fuel oil treatment ||Gearboxes || Governor || Marine incinerator || Lub oil filters || MAN B&W engine || Marine condensers || Oily water separator || Overspeed protection devices || Piston & piston rings || Crankshaft deflection || Marine pumps || Various refrigerants || Sewage treatment plant || Propellers || Power Plants || Starting air system || Steam turbines || Steering gear || Sulzer engine || Turbine gearing || Turbochargers || Two stroke engines || UMS operations || Drydocking & major repairs || Critical machinery || Deck machineries & cargo gears || Control and instrumentation ||Fire protection ||Engine room safety ||






Machinery Spaces.com is about working principles, construction and operation of all the machinery items in a ship intended primarily for engineers working on board and those who working ashore . For any remarks please Contact us

Copyright © 2010-2016 Machinery Spaces.com All rights reserved.
Terms and conditions of use
Read our privacy policy|| Home page||