Equation-oriented optimization of reaction distillation column considering tray hydraulics

Extension of the Equilibrium Stage Model to Include Rigorous Liquid Holdup Calculations for Reactive Distillation

“…The choice to adopt the inside-out algorithm was made to include tray hydraulic correlations in the solution of the MESH equations. Here, we show how the liquid holdup calculations influence the solution procedure with calculation examples and briefly discuss the reasoning for this choice compared to existing implementations using an equationoriented approach [6]. The MESH equations for steady-state distillation modelling form a set of nonlinear algebraic equations that are typically solved by Newton-Raphson methods.…”

“…Consequently, the majority of (initial) RD column design studies still rely on the EQ stage model. The addition of tray hydraulic relations to the EQ model has been explored before to more accurately describe the pressure profile throughout the RD column, thereby evaluating the reaction kinetics, chemical equilibrium and vaporliquid equilibrium at their correct pressure and temperature [6]. The weir height used to evaluate the hydraulics of the trays are also used to calculate the liquid holdup calculation in this work.…”

“…This can be contrasted to the workflow of commercial flow sheeting software implementations of the EQ model (e.g., Aspen Plus), where the liquid holdup is specified as a constant value per stage to be estimated separately by the user, which may happen independently of considering the tray weir height, diameter and other tray parameters. Liquid holdup (for defining a tray reaction rate) is often estimated by taking the geometric volume available on a tray (bubbling area x weir height) [6][7][8][9]. However, correlations used in conventional distillation predict the liquid fraction of the froth (clear liquid height) to be only 10-40% of the weir height under typical distillation conditions, depending on tray type, design and vapor and liquid traffic on the trays [10].…”