MARINE PROPULSION STEAM TURBINE

Roof Firing • Advantages : – Increased efficiency due to the longer length allowed for the flame giving more time for complete combustion. This also allows more heat to be released as radiant rather than convective cutting down the required number of screen wall generating tubes • The longer period allowed for complete combustion means that less excess air is required, this has the knock on effect of lowering the Dew Point of the flue gasses. • Equal length flames – Better gas flow.

Reheat Boilers Advantages : • Efficiency of steam cycle increases with rise in average temperature at which heat is supplied. • By reheating the steam from some appropriate temperature in the cycle to a higher temperature, effectively means raising the average temperature at which heat is added to steam. • This results in the increase in cycle efficiency and hence saving in fuel consumption. • Typical value of gain in specific fuel consumption due to reheating for a 18500 tons tanker is about 5-7 % of total fuel consumption.

Contd • Since the work output per kg of steam with reheat increases, the plant size reduces considerably for the same maximum power demand. • Since, the steam condition is less wet due to reheating, erosion of blades considerably reduces.

Disdavantages • Boiler installation becomes more complex. • Problem of protecting reheater during astern maneuver is to be considered.

Typical Reheat Type Boiler

Reheat Type Boiler for Tanker

Reheat Boiler integrated to main boiler









Definition ▪ Components which are directly mounted on the boiler body for its safe operation ▪ Gauge Glass ▪ Safety valves ▪ Blowdown valves ▪ Main/aux steam stop valves ▪ Vent valve ▪ Pressure/temperature gauges ▪ Feed Regulator ▪ Feed water Drain Valves

Water Gauge Glass ▪ In small low pressure boilers (below 20 bar) gauge glass directly attached to drum by screwed connections ▪ Sometimes a water column may be used to attach gauge glass ▪ Water column is a vessel to which gauge glass or other level indicating devices are attached ▪ Water columns must be provided with a blow down line of ¾ inch minimum diameter ▪ Two gauge glass for boilers operating over 400 psi

Contd ▪ Water column permits the gauge glass to be located where it can be seen easily and repair/maintenance becomes easy. ▪ Water columns minimise error in level reading due to rolling effect of ship ▪ Gauge glass connections are fitted with ball valves at top and bottom to prevent steam and hot water to escape in engine room. Ball valves open by gravity effect

Contd ▪ In some gauge glass ball valves are fitted only in the water side. ▪ In the event of damage to gauge glass the water will not escape and provide cooling to the hot boiler metal

High pressure boiler Gauge glass ▪ For high pressure boilers, (above 20 bar) water columns are made of flat glass having mica sheet to protect the water side of the glass from etching action of steam ▪ Water column is provided with high-low level alarm that gives whistle when water level crosses limits either way. ▪ Whistle tones indicate if lower or upper level has been breached

contd ▪ Whistle operates by a float located in the gauge glass unit. ▪ Movement of float up and down opens steam to a valve which admits steam to the the whistle

Bi-colour Gauge glass ▪ It is constructed in sections and in port assembly units can be replaced without removing gauge glass from boiler. ▪ Normally only one port need to be serviced at a time. ▪ Water is green and steam red, and water level is indicated where the two colours meet. ▪ For safety, gauge cock handle must point downwards in normal operating conditions.

Putting Gauge Glass in Operation Warming-up by : ▪ Open drain cock ▪ Crack open water cock ▪ Crack open steam cock After warming-up : ▪ Drain cock fully closed ▪ Steam and water cocks are fully open

What happens if Gauge Glass Breaks ▪ Gauge glass connections are provided with two shut off valves ▪ One valve is located on top and other at the bottom ▪ These valves can be shut off automatically by boiler pressure if gauge glass breaks ▪ These valves can be also closed manually to isolate the the boiler and replace the gauge glass while boiler is steaming

contd Q. What will happen, If water cock is kept open and steam cock closed during boiler operation A. Water from boiler will channel to the gauge glass and fill it indicating a false high water level Q. Why will it happen so? A. Since there is no steam inlet to the gauge glass, a diff. pressure is set up between water in boiler and in gauge glass. Boiler water pressure being higher it will force its way up in the gauge glass tube

contd Q. Why steam connection of gauge glass is not lagged but water connection is lagged. A. To keep a small condensate flow through gauge glass to ensure that gauge glass remains active all the time B. Q. Escape of steam or water which is more dangerous C. A. Water, because water provides cooling to the drum against residual heat in the boiler metal

Fusible Plug ▪ Fusible plugs are used on small boilers to provide protection against low water failure ▪ They are constructed of brass or bronze with tapered hole drilled through the plug ▪ The hole is filled with low melting point material ▪ Fusible plug is located at the lowest permissible water level in the steam drum.

Fusible Plug ▪ Fitted to save the boiler from damage due to overheating ▪ When the fusible material melts it allows high pressure steam to escape into the furnace and put off the flame ▪ Also gives audible warning to watchkeeper

Blowdown Q. What is blowdown A. Removal from a boiler unit a fraction of the boiler water to prevent excess concentration of dissolved substances B. To remove solid scales settled at the bottom of the boiler C. To remove oil and floating impurities in steam drum

contd Q Purpose of continuous blowdown A. To prevent concentration of dissolved salts beyond a definite level Q.Purpose of intermittent blowdown A. To remove sludge from boiler drums

Sootblowers ▪ Sootblowers basically consists of ▪ A tube element or lance that is entered into the boiler and carries a pressurised medium ▪ Nozzles in the tip of lance to direct the cleaning medium and increase its velocity ▪ A mechanical system for insertion and rotation of the lance ▪ A control system

Cleaning medium ▪ Saturated steam ▪ Superheated steam ▪ Compressed air ▪ Water ( coal fired boilers) ▪ In most cases Superheated steam is preferred because it eliminates erosion

Types of Sootblowers ▪ Fixed position blowers ▪ Short retractable furnace wall blowers ▪ Long retractable blower, from 2-50 ft range ▪ Operation of sootblower can be manual or automated in programmed sequence

When to soot blow? ▪ High funnel temperature is indication of dirty boiler tubes necessitating soot blowing ▪ Sparks coming out of the funnel is indication of excessive carbon deposits in the furnace, necessitating soot blowing ▪ Soot blowing improves furnace cooling because clean water walls improve heat absorption ▪ After soot blowing superheat steam temperature falls because percentage of heat absorbed by superheater reduces

Soot Blowing Process ▪ Inform bridge to change ship’s course if necessary to avoid flue particles fall on deck ▪ Increase blower speed to force carbon particles out of furnace ▪ Reduce ships speed to decrease load on boiler ▪ Use superheated steam at reduced pressure to blowdown carbon particles/dust ▪ Commence blowdown from funnel top down to the furnace at last

Reference book ▪ Steam Plant operation (7 th Edition) McGraw- hill) by Everett B Woodruff Herbert B Lammers Thomas F Lammers ▪ Boiler Operation Engineering, Questions and answers, By P Chattopadyay, Mc grawhill

Md Redzuan Zoolfakar

2 3 GENERATION EXPANSION FEEDWATER CONDENSATION 1 4

 Compounding - When turbine have two or more stages. 1) Pressure compounding - an impulse turbine, nozzle/s in used with moving blade each stage. 2) Velocity compounding - an impulse turbine, a nozzle with an arrangement of several moving blades. Between the moving blades are fitted guide blades which are connected to the turbine casing. 3) The two arrangements may be combined to give what is called 'pressure-velocity compounding'.

 The reaction turbine - result from blade arrangement between fixed and moving blades with consequent gradual steam pressure reduction.  ‘Cross-compound' – arrangement of a high pressure and a low pressure turbine.  Reheating - improving the thermal efficiency of the complete turbine plant by reheat the steam.

 Parsons. A reaction turbine where steam expansion takes place in the fixed and moving blades.  Curtis. An impulse turbine with more than one row of blades to each row of nozzles, i.e. velocity compounded.  Rateau. An impulse turbine with several stages, each stage being a row of nozzles and a row of blades, i.e. pressure compounded.











Marine steam turbines need to be reversible. This is achieved by the use of several rows of astern blades fitted to the high pressure and low-pressure turbine shafts. About 50% of full power can be achieved through the astern turbines. When the turbine is operating ahead, the astern blades acts as an air compressor.

 The advantages of a steam turbine include little or no vibration, low weight, minimal space requirements and low maintenance costs.  The main disadvantage of turbines is that they have a higher specific fuel consumption than diesels.  A typical main propulsion turbine would consist of both a high-pressure turbine and a low-pressure turbine to improve the efficiency of the steam usage.







 Acts as shaft, transmits the mechanical power produced to propeller shaft via gearing.  Maybe a single piece, wheels integral with shaft or built up, shaft and wheels are separate, for large dimensions.  Rotor ends have labyrinth gland sealing system  Journal bearings fitted at each end of rotor  One end has a thrust collar for correct longitudinal alignment.  The other end has a flange or flexible coupling for rotor and gearbox pinion.  Blades fitted into grooves of various designs cut into wheels.