Hypothetical components

The reaction rates in Equation (5.17) are positive and apply to the reaction. That is, they are the rates of production of (possibly hypothetical) components having stoichiometric coefficients of -bl. Similarly, the heats of reaction are per mole of the same component. Some care is needed in using literature values. See Section 7.2.1. 

H Denotes possibly hypothetical component with a stoichiometric coefficient of -1-1 2.41... 

The reactions considered in previous sections have involved hypothetical components A, B, C, and I) for which arbitrary physical properties and kinetics could be selected to illustrate various phenomena. Simple Matlab programs can be easily generated for these systems. 

Table 1 gives the components present in the crude DDSO and their properties critical pressure (Pc), critical temperature (Tc), critical volume (Vc) and acentric factor (co). These properties were obtained from hypothetical components (a tool of the commercial simulator HYSYS) that are created through the UNIFAC group contribution. The developed DISMOL simulator requires these properties (mean free path enthalpy of vaporization mass diffusivity vapor pressure liquid density heat capacity thermal conductivity viscosity and equipment, process, and system characteristics that are simulation inputs) in calculating other properties of the system, such as evaporation rate, temperature and concentration profiles, residence time, stream compositions, and flow rates (output from the simulation). Furthermore, film thickness and liquid velocity profile on the evaporator are also calculated. 

The Kb method. For updating the tray temperatures, the theta method relies on the Kb method. The Kb method takes advantage of the near-linear dependence of the logarithm of the K-values and the relative volatilities on temperature over short temperature spans. Relative volatilities (a s) are calculated with respect to a base component K-value, K.bj k, at the stage temperature of the current column trial, Tjk. The base component is usually a middle boiler or a hypothetical component, The K-value of the base component for the next trial, Kbjk + 1( is calculated using a form of the bubble-point equation unique to the Kb method ... 

Thus, for first-order systems, the rate, r, is proportional (via k) to the amount present, tij, in the system at any particular time. Although at first glance, first-order reaction rates may appear too simple to describe real reactions, such is not the case (see Table 1.5.1). Additionally, first-order processes are many times used to approximate complex systems, for example, lumping groups of hydrocarbons into a generic hypothetical component so that phenomenological behavior can be described. 

This latter point and other similar concerns represent such a major problem that some scientists abandoned the idea of just using chondrites as a starting point and instead invoked the former presence of completely hypothetical components... 

In UniSim Design, nonconventional solids can be defined as hypothetical components (see Section 4.4.4). The solid phases of pure components are predicted in the phase and reaction equilibrium calculations and do not need to be identified separately. 

In UniSim Design, new molecules are added as hypothetical components. The minimum information needed to create a new hypothetical pure component is the normal boiling point, although the user is encouraged to provide as much information as is available. If the boiling point is unknown, then the molecular weight and density are used instead. The input information is used to tune the UNIFAC correlation to predict the physical and phase equilibrium properties of the molecule, as described in Chapter 8. 

The phase equilibrium coefficients are calculated next rigorously based on the latest mole fractions and stage temperatures and pressures (Chapter 1). These F-values are used to update the stage temperatures (step 8). A reference (hypothetical) component r is used to define the relative volatility ... 

The apparent symmetry of proton uptake and release on either side of the purple membrane suggests that proton release at the extracellular side and its reverse reaction may be manifest as a displacement photocurrent (a hypothetical B2 component). This signal is blocked in a Trissl-Montal bacteriorhodopsin film because the Teflon film precludes access of aqueous protons at the extracellular side. If, however, bacteriorhodopsin is reconstituted in a lipid bilayer membrane, this hypothetical component, which represents proton release at the extracellular side, might be observable. A complication arises from the expected polarity of the B2 signal, which should be the same as that of the B2 component (both are of opposite polarity to the B1 component). Therefore, a method must be devised to distinguish the B2 from the B2 component. The following kinetic analysis provides the rationale for such a method. 

Aspen HYSYS used the concept of the fluid package to contain all necessary information for performing flash and physical property calculations. This approach allows you to define all information (property package, components, hypothetical components, interaction parameters, reactions, tabular data, etc.) inside a single entity. 

Click the Hypothetical menu item in the Add Component box to add a hypothetical component to the Fluid Package... 

Hypothetical Components Available-Available Hypo Groups ... 

Click Quick Create a Hypo Component to create a hypothetical component. 

A hypothetical component can be used to model non-library components, defined mixtures, imdefmed mixtures, or solids. You will be using a hypothetical component to model the component in the gas mixture heavier than hexane. 

Since you do not know the structure of the hypothetical component and you are modeling a mixture, the Structure Builder will not be used. 

Click Estimate Unknown Props to estimate all the other properties and fully define the hypothetical component. 

Concentration can be converted to mole fraction from the gas law and after combining the resulting equation with Equation (3.11) for a single hypothetical component A appearing in reaction j only, the result can be combined with Equation (3.5). The mass velocity G=u-p, which is independent of conversion, can be inserted to obtain the final equation for reaction j ... 

Figure 1 r/ic dependence of aquation rate constants ik) on acid concentration for the [Fe(ppi)3] + cation. Curve (a) shows the actual results curves (b) and (c) show the hypothetical components... 

Includes both top-down techniques oriented to tracing back from potential real-world hazards to the sources of failures which could lead to accidents, and bottom-up techniques which follow through hypothetical component failures to determine their hazardous consequences. (Strictly these are middle-out because one also looks at how the component could come to fail.)... 

When we work with the crude in the process simulator, we deal with specific cuts based on the boiling point distribution of a particular cmde feed as shown in Figure 2.7. Each individual bar represents a hypothetical component with pseudo properties (such as critical points, heats of vaporization, heat capacity) calculated from a correlation. These correlations typically rely on boiling point and specific gravity or density. The goal is to find a minimum number of hypothetical compo-... 

Table 2.3 Hypothetical components for each boiling-point range.

Boiling-Point Range Suggested Number of Hypothetical Components... 

Throughout this work, we have used Aspen HYSYS [13] and related software products quite extensively. Despite this fact, the techniques described in this work are applicable almost directly to many other simulation and modeling products. The most important considerations are the availability of a robust implementation of inside-out method, ability to deal with pseudo (or hypothetical) components and associated thermodynamics in the software chosen. Most modem process simulators meet these criteria. Aspen HYSYS implements hypothetical components through an Oil-Manager feature shown in Figure 2.13. The Oil-Manager allows us to manage multiple types of assays and blends of different assays. 

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