Batch Distillation Simulations with Aspen Plus: A Practical Guide

In the previous blog on batch distillation, we gained a comprehensive understanding of its principles and applications across various industries. In this blog, our focus shifts to the practical aspects: designing batch distillation in Aspen Plus, understanding the key requirements for designing and simulating it effectively, and exploring the outputs that Aspen Plus provides.

BatchSep is a specialized feature in Aspen Plus designed specifically for simulating batch distillation columns. This tool is particularly useful in industries where batch processing is preferred due to the production of small quantities of high-purity products or when continuous operation is impractical. In this blog post, we will explore the BatchSep column in Aspen Plus, including its features, setup requirements, and how to effectively utilize it for simulating batch distillation processes.

Features of BatchSep in Aspen Plus

Thermodynamic Models and Properties:

• Accurate Predictions: Uses Aspen Plus’ thermodynamic models (e.g., NRTL, UNIQUAC) to predict vapor-liquid equilibrium accurately.
• Physical Properties: Requires precise physical property data for all components to ensure simulation accuracy.

Dynamic Simulation:

• Time-Dependent Profiles: Allows dynamic simulation, capturing changes in composition and temperature over time during the batch distillation process.

Flexibility in Operation:

• Multiple Feeds and Withdrawals: Supports multiple feed and withdrawal points, accommodating complex batch scenarios.
• Variable Reflux Ratios: Enables adjustments in reflux ratios and other parameters throughout the batch cycle for better control over product quality.

Required inputs to setup a BatchSep column

• setup
• Heat transfer
• Initial conditions
• Column internals
• Operating steps

Setup includes:

• Equipment type
• Valid Phases
• Model Detail
• Stream connections
• Pressure and holdups

Heat transfer includes:

• Select equipment used for heating or cooling the pot  (Jacket/Coils/External exchangers)
• Specify equipment mass/heat capacity data for modeling thermal inertia
• Specify details required for modeling heat loss to the environment
• Specify options for calculating film heat transfer coefficients

Initial conditions

• Empty: Pot or column is filled with an inert gas at the specified temperature and pressure at the start of the batch
• Total reflux: Column is at total reflux at the start of the batch
• Initial charge: Pot contains a specified amount of charge. The rest of the column contains an inert gas at the specified initial temperature and pressure.

Choose the initial condition with care. With the Empty and Initial charge initial conditions, a noncondensable pad gas is added to reach the specified initial temperature. These conditions cannot be used with a total condenser because of the unrealistic cryogenic conditions required to condense these gases. An alternative, to condense all of the condensable components, is to specify a partial condenser with degrees of subcooling set to zero.

With the Total reflux or Initial charge conditions, you can also specify the initial column contents here.

Column internals

This form is required only when Pressure profile and holdups are Calculated. It is disabled if Configuration (on Setup | Configuration sheet) is Pot.

In this section, user need to specify the internal type (trayed/packed), tray spacing/HETP, internal diameter and detailed geometry to calculate pressure profiles and holdups in column.

Opreating steps

The Operating Steps form lets you enter any number of operating steps to define how the batch distillation column is operated. Each operating step defines one or more changes to the simulation, and the end condition which specifies when the operating step will complete. The operating steps are processed in sequence until the last active operating step completes. The simulation then ends.

In this blog post, we have delved into the practical implementation of batch distillation using Aspen Plus, focusing on its specialized tool, BatchSep. The flexibility of BatchSep allows for intricate setups with multiple feeds and varying reflux ratios, catering to diverse industrial needs where batch processing is essential.

In our next blog, we will tackle an intriguing industrial case study to explore more in the subject. The real-world scenario will provide practical insights into overcoming challenges and optimizing processes with BatchSep.

Stay tuned to discover how theoretical knowledge translates into practical solutions in the field of batch distillation.