The very best way to get redundancy in a
steam boiler plant would be to have two completely independent
one-boiler-systems, and a good Marine Steam Boiler Control System should at
least comprise the following:
- Each boiler provided with a control cubicle with starters and stand-by
functions for the fuel oil pumps and the feed water pumps. For each boiler two
feed water pumps, and two fuel oil pumps etc.
- Only a cable for the master/slave system between the two boiler control
cubicles.
- A master-slave system that forces the burners' load to follow the
performance curves of the boilers. The master-slave function may be
disconnected and allow the boilers to operate independently.
- At inert gas firing the master burner's load is limited to operate between
50% and 100%. A steam dump controller should automatically take over the steam
pressure control and by means of a control valve dump the excess steam to a
steam dump condenser.
- The combustion air fan stop-delayed for ten minutes to minimize the number
of fan starts at low steam demand.
- The burner forced to minimum firing if the boiler is cold or the pressure
is lower than 1 bar.
- Two set points for the water level; 40% level when the burner is stop and
50% when it's firing; to minimize shrink and swell at start and stop of the
burner.
- Supply for chemical dosing pump only when the feed water pump runs and the
feed water control valve is open.
- Separate automatic fuses for all, not short circuit proof, external
circuits.
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