Computer programs ChemCad

The material balance from Problem 3-6 and either ASPEN PLUS or CHEMCAD-III computer software is used to develop the energy balance around each piece of equipment in the ethylene separation section. For example, around distillation column, C-601, the computer program establishes the heat content 6f streams 533, 602, and 603 above a selected datum plane. The distillation calculation indicates the flow rates of the oveiiiead and bottoms streams. The reflux and reboil then indicate the flow rates of the streams that are returned to the column and permits evaluation of the condenser and reboiler duties. In kW " this pan be expressed as... 

Most distillation and equilibrium parts of process-design computer programs (e.g.. Aspen, ChemCad, ProMax) report A, values for each species in the VLE data for mixtures, and some distillation programs report a. It must be clear from their definitions that they are made up from values of the y, and Xi. The computer programs mostly first compute the y and Xi, by the methods shown in the rest of this chapter and the next, and then compute and report the A, and a values for the convenience of users who prefer that formulation the, x, and y are the basic values. The common hand-calculation methods of estimating VLE are presented in terms of the A values in Section 8.9. 

In recent years, property information systems have become widely available in computer packages. Some are available on a stand-alone basis, such as PPDS2 (1997), while others are available within the chemical process simulators, such as ASPEN PLUS, HYSYS.Plant, PRO/n, CHEMCAD, BATCH PLUS, and SUPERPRO DESIGNER. Commonly, constants and parameters are stored for a few thousand chemical species, with programs provided to estimate the property values of mixtures, and determine the constants and parameters for species that are not in the data bank using estimation methods or the regression of experimental data. Virtually all of the property systems estimate the properties of mixtures of organic chemicals in the vapor and liquid phases. Methods are also provided for electrolytes and some solids, but these are less predictive and less accurate. 

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