Shortcuts

The best few nonintegrated sequences can be identified most simply using the total vapor load as a criterion. If this is not satisfactory, then the alternative sequences can be sized and costed using shortcut techniques. 

The program uses all the standard controls in Windows programs. In addition, the use of an extensive number of shortcuts and function keys makes it possible to control the system without the use of a mouse, which is convenient for operating the system in the field. 

The basic function of the JME Editor is to allow the creation and modification of molecules and reactions directly within a web page. The editor has all the standard chemical drawing and editing capabilities, mduding a rich set of keyboard shortcuts for adding common structural fragments easily (Figure 2-130). 

Organic chemists have devised a number of shortcuts to speed the writing of structural formulas Sometimes we leave out unshared electron pairs but only when we are sure enough m our ability to count electrons to know when they are present and when they re not We ve already mentioned representing covalent bonds by dashes In condensed structural formulas we leave out some many or all of the covalent bonds and use sub scripts to indicate the number of identical groups attached to a particular atom These successive levels of simplification are illustrated as shown for isopropyl alcohol ( rub bmg alcohol )... 

This approach attempts to permit the designer to evaluate and optimize alternatives quickly, using shortcut hand calculations. However, if it is to be adopted by practicing design engineers it must be complemented by software for at least the analysis, evaluation, and optimization stages. 

Discussions of shortcut methods have appeared many times in the Hterature (16,36), accompanied by the usual admonition to use such methods only for approximate designs or analyses. For multicomponent systems having significant nonideaUties, the shortcut methods can be grossly in error. 

Methods are available for making detailed estimates of working capital (15). Shortcut ratios for estimating working capital are 15—20% of the fixed capital, 15% of the total capital, or 10—30% of annual sales. 

No single method or algorithm of optimization exists that can be apphed efficiently to all problems. The method chosen for any particular case will depend primarily on (I) the character of the objective function, (2) the nature of the constraints, and (3) the number of independent and dependent variables. Table 8-6 summarizes the six general steps for the analysis and solution of optimization problems (Edgar and Himmelblau, Optimization of Chemical Processes, McGraw-HiU, New York, 1988). You do not have to follow the cited order exac tly, but vou should cover all of the steps eventually. Shortcuts in the procedure are allowable, and the easy steps can be performed first. Steps I, 2, and 3 deal with the mathematical definition of the problem ideutificatiou of variables and specification of the objective function and statement of the constraints. If the process to be optimized is very complex, it may be necessaiy to reformulate the problem so that it can be solved with reasonable effort. Later in this section, we discuss the development of mathematical models for the process and the objec tive function (the economic model). 

Published data and shortcut estimating methods can be used to calculate the approximate manufacturing cost of a new product. However, most companies have extensive data on various items of cost such as overheads, property taxes, etc. These data should be used whenever possible to give the estimate that is most vahd for a particular company. 

Unfortunately, there are no satisfactory shortcut methods for doing this. When the utilities cost is relatively small, it may be possible to make an intelhgent guess on the basis of known costs for similar processes in the company. Alternatively, published data for the consumption of utihties per unit of production for various processes may be used. 

For preliminary studies of batch rectification of multicomponent mixtures, shortcut methods that assume constant molal overflow and negligible vapor and liquid holdup are useful. The method of Diwekar and Madhaven [Ind. Eng. Chem. Res., 30, 713 (1991)] can be used for constant reflux or constant overhead rate. The method of Sundaram and Evans [Ind. Eng. Chem. Res., 32, 511 (1993)] applies only to the case of constant remix, but is easy to apply. Both methods employ the Fenske-Uuderwood-GiUilaud (FUG) shortcut procedure at successive time steps. Thus, batch rectification is treated as a sequence of continuous, steady-state rectifications. 

For shortcut calculations the partition ratio K in Bancroft [Phys. Rev., 3, 120 (1895)] coordinates using the weight ratio of solute to extraction solvent in the extract phase Y and the weight ratio of solute to feed solvent in the raffinate phase X is preferred [Eq. (15-3)]. 

In shortcut calculations the slope of the equilibrium line in Bancroft (weight-ratio) coordinates m is also used [Eq. (15-4)]. 

For the McCabe-Thiele type of graphical calculations and shortcut methods, the Bancroft (weight-ratio) concentrations can be used on... 

Example 3 Shortcut Calculation Case A Let us solve the problem in Example 2 by using the shortcut calculation method assuming immiscible solvents, case A. 

Example 4 Shortcut Calculation Case B Let iis solve the problem in Example 2 hy assuming case B. The solute (acetic acid) concentration is low enough in the extract so that we may assume that the mutual solubilities of the solvents remain nearly constant. The material balance can be calculated by an iterative method. 

For the first time through a liqmd-liquid extrac tion problem, the right-triangular graphical method may be preferred because it is completely rigorous for a ternary system and reasonably easy to understand. However, the shortcut methods with the Bancroft coordinates and the Kremser equations become valuable time-savers for repetitive calculations and for data reduction from experimental runs. The calculation of pseudo inlet compositions and the use of the McCabe-Thiele type of stage calculations lend themselves readily to programmable calculator or computer routines with a simple correlation of equilibrium data. 

Assuming that natural gas is used to fire the burner with a known heating value of HVc, calculate the available heat at the operating temperature. A shortcut method usually used for most engineering purposes is ... 

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