Advanced Process Modelling for separation systems

Bringing new accuracy and sophistication to separation modelling

“With gPROMS we made remarkable progress compared to the tools that we used in the past”.

- Linde Engineering,
following a three-month evaluation

Vapour-liquid and liquid-liquid separation are fundamental processes in the Chemical Process Industries. Distillation operations alone are responsible for some 40% of energy usage.

Despite this, the modelling of separation processes remains relatively unsophisticated, and is not well catered for by current simulation software. PSE's tools, libraries and services overcome these limitations.

PSE approach to separation modelling

Distillation simulation PSE's approach is to use as rigorous models as possible, coupled with formal optimisation.

This ensures that all key effects are captured and the calculated optimal values (or trajectories) for design variables take into account all relevant interactions.

The result of using these high accuracy techniques is significantly better design and operation.

This leads to capital and operational savings, increased yield and throughput, improved product characteristics, greater operational flexibility and reduced operational risk.

PSE tools and capabilities

PSE brings a powerful combination of state-of-the-art tools and expert services to the market:

– The gPROMS Advanced Process Modelling environment

– The gPROMS Advanced Model Library for Gas Liquid Contactors (AML:GLC)

– PSE's expert ModelCare configuration and consulting services

Collectively these overcome all of the deficiencies described above, to provide high-accuracy predictive models for all types of vapour-liquid separation.

The Advanced Model Library for Gas-Liquid Contactors (AML:GLC)

For standard rate-based modelling – steady-state or dynamic – PSE's Advanced Model Library for Gas Liquid Contactors (AML:GLC) allows virtually any configuration to be modelled with a high degree of accuracy.

The AML:GLC models take into account mass and heat transfer limitation, liquid and vapour film diffusion effects, hydrodynamics and reaction mechanisms using detailed physical property calculations. Models can be applied to any vapour-liquid or liquid-liquid separation.

PSE also has an extensive set of models that can be supplied under ModelCare agreements, for applications such as full hydraulic modelling for tray-to-tray columns, or pressure-swing adsorption and membrane processes.

Typical application areas

Some typical application areas are described below.

High-accuracy conventional tray-by-tray or packed distillation columns and absorbers

gPROMS provides extensive capabilities for modelling of distillation columns and absorbers, as well as a state-of-the-art rate-based separation library.

The AML:GLC allows the construction of full non-equilibrium dynamic models of distillation columns and absorbers, for accurate modelling of start-up, shut-down and transition as well as steady-state operation.

gPROMS' mixed-integer optimisation facilities will determine the optimal feed location and number of stages, while simultaneously optimising design and operational parameters.

Detailed tray-by-tray hydraulic models

PSE's detailed hydraulic tray models are used when complex questions of hydraulics need to be answered.

An example is PSE's analysis of the Texas City Refinery accident, where the startup of the column involved was modelled using rigorous tray hydraulic relationships. Similar gPROMS models are used to train operators in the start-up of Air Separation Units.

Falling-film equipment

Falling film evaporators, condensers and reactors involve heat and mass transfer over a continuous transfer surface. Operation – usually involving heat-sensitive foodstuffs or pharmaceutical materials – must take place within a very tightly-defined envelope to avoid spoiling product or creating dry patches.

gPROMS is the only tool capable of easily dealing with the complex interaction of hydrodynamics, heat and mass transfer and reaction kinetics.

Reactive distillation and absorption and liquid-liquid extraction

PSE's AML:GLC caters for reactive distillation and absorption in both tray and packed columns. The AML:GLC is capable of modelling reaction in the liquid bulk phase and both liquid and vapour films, to provide the highest possible accuracy for both steady-state and transient operation.

One application for Linde Engineering accurately predicted the CO2 removal from a reactor gas feed stream down to ppb levels, without any need for data fitting.

Heat-integrated distillation columns (including partition and divided wall columns)

Heat-Integrated Distillation Columns (HIDiCs) represent a major breakthrough in energy efficiency. By exchanging heat between the rectifying and stripping sections, energy savings of nearly 50% can be achieved.

gPROMS is the only commercial tool capable of modelling the complex heat transfer and non-equilibrium operations involved.

Heat and mass transfer operations

Heat and mass exchangers are an interesting separation option, capable of separating at a much higher efficiency than even concentric-tube HIDiC configurations.

The gPROMS AML:GLC models provide easy modelling of this type of system.

Pressure-Swing Adsorption

gPROMS is an ideal tool for modelling and optimisation of pressure-swing adsorption (PSA) systems, an inherently dynamic operation. gPROMS·dynamic simulation, task language, dynamic optimisation (to optimise the cyclic steady state) and robust solution techniques are essential advantages.