Duty ratio influence

Influence of duty ratio, machining voltage and electrolyte concentration on WOC is shown in Figs 8.17 and 8.18 at particular parametric condition, i.e., 40 kHz pulse frequency, 7 V of machining voltage and 150 pm/s feed rate. It is found from the surface plots that the WOC is minimum for lower duty ratio and machining voltage. 

In Fig. 10.16, product purity and conversion are depicted vs. heat duty varied over a wide range. The influence of different catalytic column internals is clearly seen. Here, the molar feed ratio of acetic acid and ethanol is 1.02, the reflux ratio is 4.41, and the total feed rate is 1.4kg/h. In this example, no liquid-liquid phase separation is considered. 

Constraint control is another type of selector or override that is intended to keep the controlled variable near a constraining or limiting value. Chapter 19 discusses how constraints influence the selection of operating conditions and why it is necessary in many cases to operate near a constraint boundary. Riggs (1998) has described a constraint control application for distillation columns with dual composition control, where reboiler duty Qr controls bottoms composition of xb and reflux flow R controls overhead composition The reboiler becomes constrained at its upper limit when the steam flow control valve is completely open. Several abnormal situations can result (1) the column pressure increases, (2) heat transfer surfaces become fouled, or (3) the column feed rate increases. When the reboiler duty reaches the upper limit, it is no longer able to control bottoms composition, so constraint control forces one composition (the more valuable product) to be controlled with the reflux ratio while the other product composition is left uncontrolled (allowed to float ). Computer control logic must be added to determine when the column has returned to normal operation, and thus the constraint control should be made inactive. 

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