Feed Forward Control
Feed Forward Control
(OP)
Hi,
We have a 80 t/hr bagasse fired boiler operating at 30 Bar 450 deg C. Actually, the output of the master pressure controller feeds the ID fan Inverter through a ratio controller. We have been advised to use feed forward control instead. Basically, what is a feed forward control ?
Thanks.
Bob
We have a 80 t/hr bagasse fired boiler operating at 30 Bar 450 deg C. Actually, the output of the master pressure controller feeds the ID fan Inverter through a ratio controller. We have been advised to use feed forward control instead. Basically, what is a feed forward control ?
Thanks.
Bob





RE: Feed Forward Control
David Baird
mrbaird@hotmail.com
Sr Controls Designer
EET degree.
Journeyman Electrician.
RE: Feed Forward Control
Bagasse is a slow burning fuel , and it is possible that the current air flow control is primarlily based on feedback to hold Oxygen in the exhaust at 3% O2. If so, then one problem with feedback control of air flow is that you will get spikes in CO if there is a large increase in bagasse input ( following a demand for more fuel due to low drum pressure).
If the above is a correct interpretaion of your problem, then you will need to modify the air flow control logic to something similar to what is used for faster burning fuels ( such as oil, nat gas). That is , when the drum pressure drops below setpoint and increases demand for more bagasse, you should increase airflow in parrellel with increases in fuel flow without waiting for O2 to drop. For firign rte decreases, though, you must lag the decrease in air flow to avoid CO spikes or flame out. This may be mandated by NFPA.
RE: Feed Forward Control
Quoting from Shinskey's Process Control Systems (McGraw Hill):
It is the intent of a feed forward system to force the process to respond as it was designed, to follow the set points as directed without regard to load upsets.
The book brings a variety of examples of feed forward control worth reading.
Paul W, Murrill's Application Concepts of Process Control (ISA) brings a conceptual definition:
"Feedback control worked to eliminate errors bur feed forward control operates to prevent errors from occurring in the first place."
RE: Feed Forward Control
rmw
RE: Feed Forward Control