Aspen separation system

Aspen Split synthesis and design of non-ideal separation systems. 

Te mentioned control loops have been implemented in Aspen Dynamics (Fig. 13.37) that includes the control of the heat integration loop around the reactor (Fig. 13. 27) and of the separation system (Fig. 13.9). The following scenario was used to evaluate the performance of the control system initially, the production rate is set to 120 kmol/h, after 2 hours, increased to 150 kmol/h, later, reduced in two steps to 90 kmol/h. 

For the design study of a particular separation system, we typically start by using the Aspen built-in parameters of a suitable physical property model. The phase equilibrium behavior predicted by the Aspen built-in parameters should be compared with experimental data for validation purpose. It is obvious that an inaccurate description of the phase equilibrium behavior of a separation system will give flowsheet results that do not match the results of the true system. The worst case may be a failure of the separation task in the proposed design flowsheet. Thus, the validation stage is important before doing any design study. The experimental data that can typically be found in hterature include the Txy and yx data, binary and ternary LLE data, VLLE data, and azeotropic information. 

Application of a Hierarchical Approach for the Synthesis of Biorefineries 49 Table 2.7 Specification for separation system used in Aspen Plus... 

This is the fun (and frustration) of chemical reaction engineering. While thermodynamics, mass and heat transfer, and separations can be said to be finished subjects for many engineering apphcations, we have to reexamine every new reaction system from first principles. You can find data and construct process flowsheets for separation units using sophisticated computer programs such as ASPEN, but for the chemical reactors in a process these programs are not much help unless you give the program the kinetics or assume equihhrium yields. 

The simulator packages such as Aspen Plus and Hysys may be useful in analyzing distillation column systems to improve recovery and separation capacity, and to decrease the rate of entropy production. For example, for the optimization of feed conditions and reflux, exergy analysis can be helpful. A complete exergy analysis, however, should include both an examination of the exergy losses related to economic and environmental costs and suggestions for modifications to reduce these costs. Otherwise, the analysis is only theoretical and less effective. 

The basic principle of one-column process is identical to four-zone SMB. The performance of the process for the amino acids separation was compared with four-zone SMB by computer simulation using Aspen Chromatography. The system and operating parameters are listed in Table 1. It was set that T2, T3 and T4 are initially filled with desorbent and T1 is empty in the simulation. Liquid in each tank is ideally mixed. Liquid of the average solute concentration in a tank is introduced into the column. The simulated concentration profile of two amino acids in the one-column process is presented in Figure 3. 

In this chapter we begin at the beginning. We take a simple binary separation and go through all the details of setting up a simulation of this system in Aspen Plus using the rigorous distillation column simulator RadFrac. 

V. Pressure effects—Azeotropes. Switch the system to isopropanol and water. Use NRTL or NRTL-2 as the VLB package. We want to look at the analysis at different pressures. To do this, you need to set up a column (dimensions and so forth are arbitrary). Run the simulation so that Aspen Plus will let you use Analysis. Look at the T-y,x and y,x diagrams at p = 1.0 atm, p = 10.0 atm, and p = 0.1 atm Notice how the concentration of the azeotrope shifts. (In the Binary Analysis Results Table the azeotrope occurs when Ki p = 1.000. Record the azeotrope mole fractions). This shift maybe large enough to develop a process to separate azeotropic mixtures (see Chapter 81. 

A typically way to separate a binary mixture containing an azeotrope is to add a third component to the system. Aspen can easily generate the following useful ternary diagrams for the purpose of analysis and design. 

In Part 3 of this book an extrainer is added to the system so that liquid-liquid sphtting can appear in the top decanter and also maybe in the top few stages of the azeotropic column. The LLE behavior in the decanter, or the VLLE behavior in the top stages of flie azeotropic column, can be predicted by Aspen Plus. The system of separating an isopropanol-water mixture using cyclohexane as the entrainer will be used as an example to demonstrate the way to generate a LLE envelope in Aspen Plus. 

The separation in the extractive column depends on the amount of solvent circulating around the system. Figure 12.4 shows that high solvent flowrates reduce the impiuity of chloroform in the distillate acetone product. For each solvent flowrate, there is a nonmonotonic effect of reflux ratio. To achieve the desired distillate purity of 99.5 mol% acetone, the minimum solvent flowrate is 145kmol/h (solvent-to-feed ratio of 1.45). These results are obtained with the impurity of acetone in the bottoms held at 0.1 mol% acetone using the design spec/vary feature of Aspen Plus and manipulating distillate flowrate. 

The purpose of this chapter is to study the dynamie eontrol of a pervaporator system coupled with a distUlation column. The example system is the important ethanol-water separation. The commercial simulation tools of Aspen Technology are used in this study. 

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. 

---