Falcon Lead Lag Appendix E
E-40
The firing rate is sent to the slaves as a percentage apportioned according to the rate allocation algorithm selected by
the Rate Allocation Method parameter.
For some algorithms this rate might be common to all slave units that are firing. For others it might represent the total
system capacity and be allocated proportionally.
For example, if there are 4 slaves and the LL master's percent rate is 30%, then it might satisfy this by:
firing all four slaves at 30%,
or
by operating the first slave at 80% (20% of the system’s capacity) and a second slave at 40% (10% of the system’s
capacity).
The LL master may be aware of slave Falcons’ minimum firing rate and use this information for some of its algorithms,
but when apportioning rate it may also assign rates that are less than this. In fact the add-stage and drop-stage
algorithms may assume this and be defined in terms of theoretical rates that are possibly lower than the actual
minimum rate of the Falcon control. In any case a unit that is firing and is being commanded to fire at less than its
minimum modulation rate will operate at its minimum rate: this is a standard behavior for a Falcon control in stand-
alone (non-slave) mode.
If any slave under LL Master control is in a Run-Limited condition, then for some algorithms the LL master can
apportion to that stage the rate that it is actually firing at.
Additionally when a slave imposes its own Run-limited rate this may trigger the LL Master to add a stage, if it needs
more capacity, or drop a stage if the run-limiting is providing too much heat (for example if a stage is running at a
higher-than commanded rate due to anti-condensation).
By adjusting the parameters in an extreme way it is possible to define add-stage and drop-stage conditions that
overlap or even cross over each other. Certainly it is incorrect to do this, and it would take a very deliberate and non-
accidental act to accomplish it. But there are two points in this:
1. LL master does not prevent it, and more important;
2. it will not confuse the LL master because it is implemented as a state machine that is in only one state at a time;
for example:
• if its add-stage action has been triggered, it will remain in this condition until either a stage has been added,
or
• the criteria for its being in an add-stage condition is no longer met; only then will it take another look around to
see what state it should go to next.
Assumptions:
Modulating stage The modulating stage is the Falcon that is receiving varying firing rate requests to track the load.
First stage This is the Falcon that was turned on first, when no slaves were firing.
Previous stage The Falcon that was added to those stages that are firing. Just prior to the adding of the unit that is
under discussion.
Next stage The Falcon that will or might be added as the next unit to fire.
Last stage The Falcon that is firing and that was added the most recently to the group of slaves that are firing.
Typically this is also the modulating stage, however as the load decreases then the last-added stage will be at its
minimum rate and the previous stage will be modulating.
Lead boiler The Lead boiler is the Falcon that is the first stage to fire among those stages which are in the equalize
runtime (Lead/Lag) group. If a boiler is in the "Use first" group it may fire before the Lead boiler fires.
First boiler A Falcon may be assigned to any of three groups: "Use First", "Equalize Runtime", or "Use Last". If one or
more units are in the "Use First" category, then one of these (the one with the lowest sequence number) will
always be the first boiler to fire. If there is no Falcon in the "Use First" category and one or more are in the
"Equalize Runtime" category, then the First boiler is also the Lead boiler.
Add-stage method
Add-stage detection timing
To Next Page
Loading...
