Falcon Lead Lag Appendix E
E-60
- The operating point is below the setpoint by an amount greater than
or equal to Add-stage error threshold
When the Add-stage condition is false then AddStageDetectTimerN is set to zero. (If the condition is true then
AddStageDetectTimerN is not zeroed and thus allowed to run.) If this timer reaches or exceeds LL- Add-stage
detection timeN then AddStageRequestN is true.
RATE THRESHOLD
For rate based staging, a stage is added based on the rate of the modulating stage.
ADD-STAGE CONDITION:
The modulating burner is at a rate that is at or above the rate which is calculated by adding the Add-stage rate
offset to the maximum position per the rate allocation rules.
Examples:
rate offset = 20% The add-stage condition will occur if the modulating stage is 20% above base load for
unlimited allocations, or, if limited, when there is 20% more rate to distribute than can be absorbed by firing
the stages at base load.
rate offset = -20% The add-stage condition will be as described just above, but the threshold is now 20%
below the modulating stage's base load rate.
To support this, the current Rate Allocation method asks for the current "Overflow rate" - see the Rate Allocator
section.
Drop Stage Methods
Various methods can be used to determine when a stage should be dropped. The internal algorithms that generate
DropStageRequests are called Drop-stage methods.
One or two methods may be active at any time. If two are active then their requests are OR'd together.
All methods work by observing various criteria such as the Firing stages, the commanded rate, or Setpoint.
Dropping Stages Parameters:
DROP-STAGE DETECTION TIME: MM:SS
This provides time thresholds. They differ only in that:
Drop-Stage detection time is used with DropStageDetectTimer
In the descriptions below, the relevant parameter is referred to as LL – Drop Stage detection timeN}.
Drop-Stage method:
Disable,
Error threshold,
Rate threshold,
dError/dt and threshold,
dRate/dt and threshold
DROP-STAGE ERROR THRESHOLD: DEGREES
This provides the error threshold as defined by the methods below.
DROP-STAGE RATE OFFSET: -100% TO +100%
This provides the rate offset threshold as defined by the methods below.
LL boiler off options:
Options disabled,
Enable all boilers off (ABO)
Enable lead drop-stage on error (LDSE)
Enable both ABO and LDSE
This provides options for customizing the way stages are dropped, as described below.
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