Composite boilers are combination of
and exhaust gas
economizers. When the diesel engine is at full load the fuel oil burner
only starts if the steam demand exceeds the steam production achieved from the
diesel engines exhaust gases.
Most composite boilers nowadays have separated sections for the diesel engines
exhaust gases and the flue gases from the fuel oil burners.
Composite boilers also works as a silencer for the diesel
engine, but often an additional silencer is required.
Composite boilers that mixes the diesel
engines exhaust gases and the flue gases from the fuel oil burner have existed,
and may still exist.
Using the diesel engines exhaust gases as combustion air for the fuel oil
burner is quite economically although it makes a rather complicated unit.
Starting, stopping and modulating the burner normally controls the steam
pressure in the composite boiler. In the old days a huge damper was used to
by-pass the composite boiler when the steam demand was less than the steam
quantity produced by the diesel engines exhaust gases. Nowadays a pressure
governed control valve dumps excess steam into a steam dump condenser.