Dynamic distillation

Table 5,14 gives a digital computer FORTRAN program for this three-component batch distillation dynamic simulation. The specific example is a column with 20 trays and relative volatilities of 9, 3, and 1. The vapor flow rate is constant at 100 mol/h. 

The thermal capacity of the metalwork is important for distillation dynamics in the same way as it was for steam drum dynamics. Allowance has been made for its inclusion by providing the energy balance equation for each plate with a heat flux variable, < >/. We may follow the procedure outlined in equations (12.45) to (12.47) to calculate the temperature of the metalwork associated with each plate and hence the heat flux. 

Deshpande, P. B., Distillation Dynamics and Control, Instrument Society of America, Research Triangle Park, North Carolina, 1985. 

C. Noeres, Catalytic Distillation Dynamic Modeling, Simulation and Experimental Validation, Ph.D. Thesis, University of Dortmund, Germany, 2002. 

A very full bag of distillation dynamic simulation techniques has been developed and demonstrated in this chapter. The example considered is a simple binary ideal vapor-liquid equilibrium (VLB) column. As the remaining chapters in this book demonstrate, these techniques can be readily extended to much more complex flowsheets and phase equilibrium. 

A comprehensive review of the literature of distillation dynamics and control through about 1974 is given by Rademaker, Rijnsdorp, and Maarleveld. Tolliver and Waggoner have published an exhaustive review of more recent additions to the literature. 

Dynamic headspace GC/MS. The distillation of volatile and semivolatile compounds into a continuously flowing stream of carrier gas and into a device for trapping sample components. Contents of the trap are then introduced onto a gas chromatographic column. This is followed by mass spectrometric analysis of compounds eluting from the gas chromatograph. 

Therefore, 12.37 kg saline water are needed in this case to produce 1 kg distillate. This high dow rate incuts corresponding pumping equipment and energy expenses, sluggish system dynamics, and, because the stream level depth is limited to about 0.3—0.5 m for best evaporation rates, also requites large evaporator vessels with their associated expense. 

Distillation columns are controlled by hand or automatically. The parameters that must be controlled are (/) the overall mass balance, (2) the overall enthalpy balance, and (J) the column operating pressure. Modem control systems are designed to control both the static and dynamic column and system variables. For an in-depth discussion, see References 101—104. 

Whereas there is extensive Hterature on design methods for azeotropic and extractive distillation, much less has been pubUshed on operabiUty and control. It is, however, widely recognized that azeotropic distillation columns are difficult to operate and control because these columns exhibit complex dynamic behavior and parametric sensitivity (2—11). In contrast, extractive distillations do not exhibit such complex behavior and even highly optimized columns are no more difficult to control than ordinary distillation columns producing high purity products (12). 

Errors are proportional to At for small At. When the trapezoid rule is used with the finite difference method for solving partial differential equations, it is called the Crank-Nicolson method. The implicit methods are stable for any step size but do require the solution of a set of nonlinear equations, which must be solved iteratively. The set of equations can be solved using the successive substitution method or Newton-Raphson method. See Ref. 36 for an application to dynamic distillation problems. 

Vertical in-tube condensers are often designed for reflux or knock-back application in reactors or distillation columns. In this case, vapor flow is upward, countercurrent to the hquid flow on the tube wall the vapor shear ac4s to tliicken and retard the drainage of the condensate film, reducing the coefficient. Neither the fluid dynamics nor the heat transfer is well understood in this case, but Sohman, Schuster, and Berenson [J. Heat Transfer, 90, 267-276... 

FIG. 13-107 Binary distiUatio n column dynamic distillation of ideal binary mixture. 

TABLE 13-32 Initial and Fixed Conditions, Controller and Hydraulic Parameters, and Disturbance for Ideal Binary Dynamic-Distillation Example... 

DISTILLATION TABLE 13-33 Results for Ideal Binary Dynamic-Distillation Example of Table 13-32 ... 

FIG. 13-108 Initial steady state for dynamic azeotropic distillation of ethanol-water with benzene. 

FIG. 13-109a Resp onses after a 30 percent increase in the feed flow rate for the mnlticomponent-dynamic-distillation example of Fig. 13-100. Profiles of liquid mole fractions at several times. 

---