10.10. Combined Feed-Forward and Cascade
In Section 10.6, a fired heater was used to provide motivation for feed-forward control. In the example it was assumed that the fuel gas flow was directly manipulated. In practice a flow controller would be used, resulting in the feed-forward, feedback, and cascade-control strategy shown in Figure 10-17.
Figure 10-17. Feed-forward, feedback, and cascade control of a fired heater.
Notice that each “mode” is used to reject a different type of disturbance. The feed-forward controller is used to reject feed flow rate disturbances. The fuel gas flow controller is used to reject disturbances in the fuel gas header ...
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