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In this system, the circulation pump "J" runs continuously. The
auxiliary boiler serves as steam separator for the entire system. The system is
thus kept in hot condition and is ready to start instantly. If the steam from
the exhaust boiler exceeds the steam demand onboard a steam dump valve
automatically dumps the surplus steam to a dump condenser.
The energy content of the exhaust gases is utilized optimally in this system.
In addition to generating superheated steam for driving a turbo-alternator, the
exhaust gas boiler also supplies steam for other requirements on board.
- Economizer section of the Waste Heat Recovery
Boiler
Preheats the circulating water before it enters the evaporator tubes. The
counterflow principle is applied, i.e., the hottest exhaust gasses meet the
heated feed water.
- Evaporator section of the Waste Heat Recovery Boiler
Water evaporates and emulsion of steam and water flows back to the boiler. The
counterflow principle is not applied since the evaporated
steam rises in the tube bank and it would be disadvantageous to let the steam
rise against the water flow.
- Superheater section of the Waste Heat Recovery
Boiler
Superheats the steam for the turbine. The counterflow principle is applied,
i.e., the hottest exhaust gasses meet the superheated steam.
- Heat exchanger
Preheats the boiler feedwater.
- Condenser
The exhaust steam from the turbine and excess steam from the steam system
condense and recycle.
- Condensate pump
- Cooling water pump
Seawater.
- Make-up water pump
From softener unit.
- Boiler feedwater pump
- Boiler water circulation pump
- Alternator
Deliver electric power to the ships different el-consumers.
- Steam pressure control
The pressure control loop adjusts the burner load according the steam demand.
- Water
level control
A simple control loop will do for a boiler with large amount of water and
relatively small steam output. To minimize shrink and swell at start and stop
of the burner it would be wise to have two setpoints for the water level. A
lower level (abt. 40%) when the burner is stop and a higher (abt. 50%) when
it's firing.
- Economizer inlet temperature control
The feedwater is pre-heated in order to increase the efficiency of the plant.
The circulating water to the exhaust gas boiler heats the feed water and the
three-way valve on the inlet to the heat-exchanger controls the temperature.
The economizer inlet temperature must never fall below 135°C to avoid
corrosion on the economizer tubes.
- Condenser pressure control
An absolute pressure transmitter and a controller adjust the cooling-water to
the condenser to protect the condensate from being cooled down more than
necessary.
- Condenser level control
The level controller actuates the condensate outlet control valve.
- Steam dump control valve
Takes care of excess steam from the waste heat boiler when the steam production
exceeds the steam demand.
- Feedwater tank level control
The level controller actuates the make up water control valve.
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