Boiler Operation and Types

Boilers

• Boilers provide steam for on board heating.
• Steam is water in gaseous state when heated to boiling point, needing water and heat to produce.
• Boilers use external heat from burners or waste heat from the main engine.
• Combustion requires the correct balance of key elements, and will not occur if one is missing.
• Boilers allow the elements of combustion and steam production to come together.

Basic Principles of Boiler Operation

• Heat naturally moves from hotter to colder objects.
• Radiation transfers heat via electromagnetic waves, such as from the sun to the earth.
• Convection transfers heat within a medium, like air conditioning.
• Conduction transfers heat through a solid object via direct contact.

Types of Boilers

• Water tube boilers flow water inside tubes heated externally by fire from the burner.
• Fuel burning in the furnace creates radiant energy and electromagnetic waves that heats the water tubes.
• Hot gases from the burner transfer heat through convection.
• Conduction heat transfer occurs when the heated tube surface transfers heat to the inner tube surface.
• Fire tube boilers route hot combustion gases inside the tubes instead of water, inside a water drum shell.
• The water level stays above the fire tubes to prevent overheating.
• Combustion gases pass through tubes which then transfers heat to the water.
• Steam rises above waterline because it is lighter and routed towards machineries.

Boiler Functions

• Boilers provide working fluid for steam engines or turbines which provide main propulsion.
• They heat fuel oil.
• They satisfies accommodation heating requirements by heating water and space.
• They heat to meet various heating requirements of heat exchangers such as freshwater generators and jacket-cooling water.
• They are used as a cleaning medium.
• They meet various Cargo heating requirements on board tankers.

Air Compressors

• Air compressors replenish loss of compressed air inside the reservoir for the next sequence.
• Air compressors are like small engines with crank shafts and cylinder heads that contain valves for pistons, cylinders, crank air inlet and outlet.
• Large electric motors turn the moving parts in a marine setting.
• An air compressor works like an internal combustion engine, moving up and down along the cylinder.
• When the piston goes down, air is routed to the chamber because a vacuum is created which pushes the inlet valve to open and fill the cylinder.
• When the piston moves upwards, it compresses the collected air.
• The compressed air which is then trapped closes the inlet valve and opens the outlet/discharge valve at a certain point.
• Air moves out through pipes to collecting tank
• The cycle continues until the pressure prompts the compressor to stop.
• This principle applies to both single-stage compressors.
• Two stage compressors first cycle the air to pass through another, smaller piston and cylinder to attain a higher range of pressure.
• Compressors use a pressure switch in a storage tank to shut off the compressor when pressure reaches the limit.
• If the switch fails, air reservoirs have a safety valve to release excessive air.
• A pressure gauge on each tank shows the present pressure and is repeated remotely at the ECR panel.
• An emergency air compressor uses an internal combustion engine and fills the emergency air reservoir necessary for starting the emergency generator, which is pneumatically started.

Types of Air Compressors

• Reciprocating compressors are the most common type used, which resemble small internal combustion engines, and are positive displacement compressors.
• They can be single-stage or two-stage compressors.
• Rotary screw compressors are also positive displacement compressors.
• They use spiral or helical lobe screw to compress air.
• Rotary centrifugal compressors are dynamic displacement types.
• They rely on energy transfer from the rotating impeller to the air.

Air Compressor Function

• Air compressors produces pressurized air for main propulsion, generator, and emergency generator.
• Compressed air is a separate system with further uses.
• Provides control air for PID controllers.
• For deck and engine service air use, including maintenance.
• Used as a cleaning medium.
• Powers the air horn and alarm.
• Seals the stern tube.
• Compressed air is vital for machinery on board and for initial startup of the emergency and regular generator engines.