Flowsheet FS2 with Furnace

In this flowsheet the presence of the furnace provides an additional control degree of freedom, and there are now two controllers. The first G( (X) controls 7 lmx by manipulating bypass flow Fby. The second Gc2(s) controls Tm by manipulating furnace firing QF. The second controller sees the furnace transfer function GF2(S) which we assume to be a furnace first-order lag and three small lags (see Fig. 7.4b)  

The first controller GCuS) sees a coupled openloop transfer function in which the second controller is nested, because the controller Gq , is on automatic. The 67 i(v) controller is tuned by finding the ultimate gain and period and using the Tyreus-Luyben settings. The settings of this PI controller are Kc2 = 2.13 and r/2 = 1.94. 

---