MARINE PROPULSION STEAM TURBINE

 Due to high rotor speeds, turbine blades are subjected to:  Centrifugal force  Tangential force on blade which cause rotation introduces a bending moment at the rotor blade  Axial force introduce bending moment at the root  Expansion and contraction during operation leading to thermal stress Because of that different shapes and sizes of roots are used to fix the blades with the rotor disc.



Impulse turbines run at high speed and hence root fixing must be strong to overcome centrifugal forces which tend to remove blades from the roots

• Reaction turbines run at slower speed hence root fixing is not a major problem. • Side strips of brass inserted to tighten blades • Packing pieces maintain distance between adjacent blades

 Fitting the blades involves placing the blade root into the wheel through a gate or entrance slot and sliding it into position.  Successive blades are fitted in turn and the gate finally closed with a packing piece which is pinned into place.  Shrouding is then fitted over tenons on the upper edge of the blades. Alternatively, lacing wires may be passed through and brazed to all the blades.



 Blades are secured at one end hence act like cantilever  The tip end of the blade is free to vibrate due to impact of steam jet  Intensity of vibration in long LP turbine blades can be dangerously high and require some restraining device  Vibration can be reduced by interconnecting the free end of the blades by running a metal strip known as shroud.

 Vibration can be also restricted by making the blades more rigid and strong  Sometimes one or two lacing wires are used instead of shroud strips, particularly in the last stage LP blades  Lacing wire is a simple small diameter steel wire which pass through holes drilled in the middle height of each blade and is soldered with each blade

 Steam is prevented from leaking out of the rotor high- pressure end and air is prevented from entering the low-pressure end by the use of glands.  A combination of mechanical glands and a gland sealing system is usual.  Mechanical glands are usually of the labyrinth type. A series of rings projecting from the rotor and the casing combine to produce a maze of winding passages or a labyrinth. Any escaping steam must pass through this labyrinth, which reduces its pressure progressively to zero.



Only impulse turbines have diaphragms. Diaphragms are circular plates made up of two semi-circular halves.

• A central semi-circular hole in each is provided for the shaft to pass through. • The diaphragm fits between the rotor wheels and is fastened into the casing. • The nozzles are housed in the diaphragm around its periphery. • Central hole arranged with projections to produce a labyrinth gland around the shaft



 Drains  Steam will condense and accumulate at various places  wDraateinr schmaumsbt ebre provided to clear this water away and return it to the  Bearings  Turbine bearings are a special type  cAastuinrgbitnheanbeaadriinegsehl aesnagignreeabteearrcilnegarance between the shaft and the  Lubricating oil system  Reduce friction between moving parts  Remove heat generated in the bearings or along the shaft  Expansion arrangement  A turbine engine spins very fast and so generates a lot of heat  Any pipes or couplings connected to the turbine must be flexible to allow uniform free expansion  Gearing  Double reduction gears are the type most commonly used in ships

Steam turbines rotate at speeds of up to 6000rpm. The most efficient propeller operating speed is from 100-120 rpm. Thus the rotation need to be reduced accordingly, hence required reduction gear.













Feed Water & Condensate System Md Redzuan Zoolfakar

Reduction HP SG/ Boiler Gears Turbine GENERATIONEconomizer SMhaaEifnt XPANSION Superheater LP DFT Turbine MU Feed Feed Tank Pump CONDENSATIONCondenser FEEDBooster Pump Condensate Pump Air Ejector Condenser

GENERATION (Boilers) SG/ Boiler Economizer Superheater

The Generation Phase  Transformation of chemical to thermal energy  Pressure - temperature relationships for both steam drum and superheater (include phase change)  Reason for superheater – increase thermal efficiency – reduction of corrosion – reduction of erosion  Desuperheated steam production

GENERATION (Boilers)  Transfers heat by convection or radiation to tubes then by conduction to water  Pressure is at 60 bar in steam drum for steam temperature (515 oC)

Cont…  Before water gets to Steam Drum, it goes through the Economizer – uses the thermal energy normally wasted and going up the stack – Adds about 140 degrees  Superheater – Gives added thermal energy needed to operate ME, TG, and MFP’s at best efficiency – Minimizes erosion to blading

EXPANSION (Turbines) Reduction HP Gears Turbine Main Shaft LP Turbine

The Expansion Phase  Transformations of thermal energy to mechanical kinetic energy (at nozzles) to mechanical work (at blades)  General differences between HP and LP turbines  Pressure-temperature relationships throughout turbines

EXPANSION (Turbines)  Goes first to the high pressure turbines  Converts thermal energy to mechanical energy  Steam first goes through “nozzles” to increase steam speed then through “blades” which does the actual work  Then goes through low pressure turbine

EXPANSION (Turbines)

CONDENSATION (Condenser, MCP, AEC) Condenser MU Feed Tank Condensate Air Ejector Pump Condenser

The Condensation Phase  Condense steam to water for re-use in plant ◦ Why a vacuum?  Pump condensate from main condenser to DFT  Provide cooling for air ejector condenser

Why a Vacuum?  Creates a difference in pressure to enhance the flow from the LPT  Allows for greater expansion in the LPT => increasing the amount of work produced by the turbine  Allows for more efficient removal of latent heat of vaporization

Seawater Cooling  Main Seawater Circulating System ◦ Main Seawater Circulating Pump  propeller type (high flow rate; low HP)  used when  going astern or stopped  slow ahead (< 5 knots)  also to de-water engineroom in case of flooding ◦ Scoop Injection System  used when moving ahead at speeds over 5 kts

Components  Main Condenser ◦ Shell and tube, cross flow, single pass heat exchanger ◦ Operates at a vacuum to lower the condensation temperature => increasing the efficiency ◦ Cooled by SW



Regenerative Condenser

Main Condensate Pump  Removes condensate from the main condenser hotwell through the air ejector condensers to the DFT  Electric driven centrifugal pump

Condenser Scoop



PUMP vs SCOOP  Why do we have both? ◦ Why used extra energy if we have free solution for high speed? ◦ Scoop doesn’t work well at slow speeds ◦ Scoop doesn’t work astern  Scoop is used at speeds > 5 knots

Air Ejectors  Draw vacuum on the main condenser by removing the air and non-condensable gases  Jet pump based on bernoulli’s principle  Uses steam (> 10 bar)  The steam air mix is condensed in the air ejector condenser (inter or after condenser)





Deaerator  Deaerating Feed Tank: ◦ Removes Oxygen ◦ Preheats ◦ Stores Water  MFP takes suction on DFT and discharges it at 5 bar (Prevents hot feedwater at 150oC from flashing to steam in the MFP)

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