ASPEN models

Shah V.B. ASPEN Models for Solid Oxide Fuel Cell, Molten Carbonate Fuel Cell and Phosphoric Acid Fuel Cell Prepared by EG G Washington Analytical Services Center for the Morgantown Energy Technology Center under Contract No. DE-AC21-85MC21353, 1988. 

All ASPEN models allow solids to be in inlet streams. The user does not need to take special precautions. The solids are normally assumed to be non-distributing in the liquid and vapor phases. That is, the phase equilibria is unaffected by the solid phase. However, the system does allow for the case of solids distributing into other phases. Solids are taken into account in the energy balance around each equipment model. 

For final evaluation of the biomass hydrogasification concept (proof of principle), it is important to integrate the experimental results, within the developed ASPEN model. 

Tie-line data of the ternary system containing of (water + propionic acid + 1-octanol) were obtained at temperature from (293.15 to 308.15) K. Experimental LLE data of this work analyzed and predicted using UNIQUAC and ASPEN model. The average RMSD value between the observed and calculated mole fractions was 12.94% for the UNIQUAC and ASPEN model. It can be concluded that 1-octanol has high separation factor, very low solubility in water, low cost, high boiling point which may be an adequate solvent to extract propionic acid from its dilute aqueouse solutions. 

National Renewable Energy Laboratory. (2004). Corn Stover to Ethanol. Aspen Plus Backup file. Available at http //www.nrel.gov/extranet/biorefinery/aspen models/... 

The optimization of empirical correlations developed from the ASPEN-PLUS model yielded operating conditions which reduced the steam-to-slurry ratio by 33%, increased throughput by 20% while maintaining the solvent residual at the desired level. While very successful in this industrial application the approach is not without shortcomings. The main disadvantage is the inherent assumption that the data are normally distributed, which may or may not be valid. However, previous experience had shown the efficacy of the assumption in other similar situations. 

Aspen Technology, Inc. Aspen Plus, Aspen Custom Modeler, Dynaplus, Split, Advent, Adsim. Cambridge, MA (1998). 

The non-random two-liquid segment activity coefficient model is a recent development of Chen and Song at Aspen Technology, Inc., [1], It is derived from the polymer NRTL model of Chen [26], which in turn is developed from the original NRTL model of Renon and Prausznitz [27]. The NRTL-SAC model is proposed in support of pharmaceutical and fine chemicals process and product design, for the qualitative tasks of solvent selection and the first approximation of phase equilibrium behavior in vapour liquid and liquid systems, where dissolved or solid phase pharmaceutical solutes are present. The application of NRTL-SAC is demonstrated here with a case study on the active pharmaceutical intermediate Cimetidine, and the design of a suitable crystallization process. 

The first step in building a solubility model in Aspen Properties is to define the solute as a new component in two instances, one for the solid phase and the other for the liquid phase. Acetylsalicylic acid is used as a convenient basis for new drug molecules in the Aspen template, because it includes data for all of the necessary thermodynamic methods to satisfy the simulation engine and avoid run time errors. 

The Aspen Properties implementation of the NRLT-SAC method is available as a template. aprbkp file to license holders of Aspen Properties or Aspen Plus release 12.1 or above, by contacting Aspen s support centre or regional sales offices. The template is distributed with an Excel interface to simplify the data regression process and is suitable for non-expert users of Aspen Properties. Numerous Excel templates are available for data analysis and design calculations, based on the NRTL-SAC model. 

Before the raw data can be fitted to a thermodynamic model it must first be converted into mass or mole fractions. This operation can be accomplished quickly using a Microsoft Excel spreadsheet that is linked to the Aspen. aprbkp file in order to obtain the solvent molecular weights and temperature dependent densities. The molar volume of Form A Cimetidine is also required for this conversion, however, as is often the case it was not available so a density of 1 g/ml has been assumed. 

Two regression cases have been run on the Cimetidine data, the first uses all of the data points, whilst the second uses a sub-set of the data, to confirm the predictive power of the model. The reduced data set consists of the single solvents in Table 5. which adequately cover the range of conceptual segment types. Where solubility data is supplied in mixed solvents it is necessary to enter the data directly into the Aspen Properties interface before regression. 

The procedure described in section 4 will now be applied to the case of Cimetidine, using the NRTL-SAC model of the full regression case presented in section 6.2. The following screening calculations were built into a Microsoft Excel spreadsheet, using the Aspen - Excel interface to calculate the solubility data. 

Khogeer (2005) developed an LP model for multiple refinery coordination. He developed different scenarios to experiment with the effect of catastrophic failure and different environmental regulation changes on the refineries performance. This work was developed using commercial planning software (Aspen PIMS). In his study, there was no model representation of the refineries systems or clear simultaneous representation of optimization objective functions. Such an approach deprives the study of its generalities and limits the scope to a narrow application. Furthermore, no process integration or capacity expansions were considered. 

Table I. MWD of Acetylated Aspen Lignins and Model Compounds from Universal Calibration with Narrow Standards 1...

To study different operating conditions in the pilot plant, a steady-state process simulator was used. Process simulators solve material- and energy-balance, but they do not generally integrate the equations of motion. The commercially-available program, Aspen Plus Tm, was used in this example. Other steady-state process simulators could be used as well. To describe the C02-solvent system, the predictive PSRK model [11,12], which was found suitable to treat this mixture, was applied. To obtain more reliable information, a model with parameters regressed from experimental data is required. 

As a consequence, corporations operating PUREX plants have been using sophisticated process simulation codes, including the PAREX code in France (45-47), SpeedUp (Aspen Plus) in the UK (48), and SIMPSEX code in India (49-51). Argonne Model for Universal Solvent Extraction (AMUSE) code in the United States was contrived not only for PUREX, but for UREX+ processes (52), which will be mentioned later. In Japan, similar efforts have also been made (53-55). 

This structure assures correct pressure-flow solutions and, thus keeps the model consistent. Software packages, such as ASPEN Dynamics , will ensure this correct coupling. In general, two flow calculating devices cannot be connected directly, but must have a pressure (typically a volume) element in between. Two flow devices can be connected if a single equation can be written that describes the pressure drop over the connected section. For instance, some programs allow two pipe models to be connected. 

Hybrids from the Big Three are on the roads and in the pipeline for additional releases. 2008 models included the Chevrolet Tahoe and Malibu hybrids, the Chrysler Aspen and Dodge Durango hybrids and the GMC Silverado, Sierra and Yukon hybrids. 2009 hybrid models include the Cadillac Escalade, the Chevrolet Silverado Crew Cab, the Ford Fusion and the Mercury Milan. 

The example CO2 capture process, shown in Figure 8 as an Aspen Plus EO model representation, is part of an ammonia plant. Designed to scrub CO2 from ammonia synthesis gas, it includes an absorber and two solution regeneration columns, one stripping the rich, C02 laden solution leaving the absorber to semilean concentration of absorbed CO2, and the other cleaning the solution even further to lean solution... 

Figure 8 Aspen Plus EO model for an MDEA/PZ C02 capture unit.

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