7.2.6 Reboiler Model
Equations (7.40)-(7.47) describe the dynamic equilibrium stage model which was used to model the partial reboiler in the reactive distillation system. The most important aspect of this model is that the stage pressure is determined implicitly from other models or fixed as a boundary condition. There are no equations relating the reboiler pressure to other pressures within the column. This distinction is required to prevent the formation of a subsystem of equations that yields a dependent equation. A dependent equation requires another variable relationship to be defined and it is suggested that this cannot be done without increasing the problem index above one.
The material hold-up in the reboiler sump is likely to be much larger than the other equilibrium stages in the column (unless a large reflux accumulator is specified) and subject to different forces. Consequently, the hold-up function (equation 7.47) should be expressed differently although this is not essential for the integrity of the global model. The Francis weir formula was used here and is recommended to relate the liquid outflow to the hold-up.
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