Automatic Boiler Start-up and Hot Standby
When the main boiler trips, the clock that matters is not the one on the boiler. It is the one on the refinery, which needs 16 bar steam back before its units start shutting themselves down.
Starting a boiler by hand ties up an operator for hours and produces a different result every time, because the sequence depends on who is running it. Under emergency conditions, with the main boiler already down, it also depends on how that operator is doing.
The target
Start the standby gas and fuel-oil boiler within twenty minutes of the circulating fluidized bed boiler tripping, and have 16 bar steam back to consumers within forty-five.
What that took
One control system for both boilers
The CFB boiler and the standby gas boiler run under a single Emerson Ovation ACS, so the standby boiler's start can be triggered by the fact of the CFB boiler stopping, without a hand-off between systems.
An automatic safe light-off sequence
Designed with the national boiler engineering institute: draft fans started and the furnace and gas passes purged; the gas line filled and automatically sampled for analysis; the tightness of the shut-off gas valve train verified; igniter burners lit; the remaining burners lit and parameters raised along the defined start-up and loading curve.
Continuous insulation resistance monitoring
On the draft fan motors, so the machines that the start depends on are known to be startable before the start is called for, not discovered otherwise during it.
Periodic automatic nitrogen tightness testing
Of the boiler's protective gas valve train. A leak check that happens on a schedule without an operator is a leak check that actually happens.
Automatic gas sampling
From the gas line as part of the sequence.
Hot standby, and the heat that was being thrown away
A twenty-minute start is only possible from a warm boiler. The standby boiler is held in hot standby using heat that the CFB boiler was already rejecting: continuous blowdown and soot-blower drains.
A 100/16 bar reducing and desuperheating station was installed with emergency automation that starts it when the CFB boiler trips, holds pressure in the steam headers and runs the tripped boiler's cooldown regime.
Together these brought the time to restore 16 bar steam to consumers down to one hour, from a cold-start figure measured in hours.
Why this is process engineering, not sequencing
The ramp is limited by the thermal stress the drum will take, not by how fast the valves can move. The blowdown heat is only usable if the standby boiler's water chemistry allows it. The decision to hold one boiler warm at all follows from the plant's own technical and economic indicators — running on a single CFB boiler is the efficient case, and hot standby is what makes it safe.
Related
Island mode operation on the same plant is under Island Mode Operation. Boiler load control, fuel allocation and combustion optimisation are covered under Process Optimisation. The efficiency calculations that decide how the plant is run are under Plant Performance.