The very best way to get redundancy in a
steam boiler plant would be to have two completely independent one boiler
control 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.
- Install a ten minutes stop-delay on the combustion air fan motor to
minimize the number of 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.
After some years of use the boiler control system ought to be optimized.
Minor problems have led to adjustments and after a lot of small adjustments the
system needs to be tuned up.
Modifying old boilers control systems might be very profitable
measures.
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