The MiMiC Distillation Object is a rigorous first-principles, dynamic model of distillation column, reboiler, reflux condenser and stripper unit operations designed for high-performance simulations for operator training or automation system testing.

The MiMiC Distillation Modeling Object is part of the MiMiC Advanced Modeling Objects License that adds sophisticated modeling objects into the MiMiC Simulation Studio modeling palette. These Objects can be used on MiMiC systems for application software testing or operator training. The MiMiC Advanced Modeling Objects License provides:

• Medium-High to High Fidelity Simulation Performance
• Rigorous First Principles process modeling using proven dynamic, real-time modeling methods
• Unit Operation modeling objects
• Easy handling of individual stream component physical properties using MiMiC Component Sets
• Block to block communications of all parameters with one connection using MiMiC Streams
• MiMiC OTM Process Snapshot support
• MiMiC OPC Server Access to all model parameters

In MiMiC Simulation Studio, process models using these objects can be integrated with any other models or MiMiC dynamic modeling blocks. All modeling objects in MiMiC are IEC1131 function blocks. Models can be built off-line and then viewed executing on-line with real-time values from the MiMiC Simulation engine. The process of going from off-line model building to on-line model tuning is fast and intuitive.

Distillation Object Overview

The Distillation Object provides a high-fidelity dynamic model for a wide range of the distillation column configurations. The configuration features supported by the Distillation Object include:

• Multi-sectional columns: up to three column sections (in current design version) with different tray/column diameters, tray spacing, and weir heights. Up to 75 trays can be configured per column section.
• Multiple feeds and side withdraws: up to five feed streams and five side draw streams per column.
• Total Condenser and Partial Condenser with automatic switching between the modes depending on current operational conditions.
• Choice of the Reboiler: reboiler heat exchanger with a heating agent (steam) flow, controlled by valve, or an external reboiler heater (for instance, fired heater) with manipulated heat duty.
• One or Two liquid phases in the Reflux Drum: an option with two liquid phases pro-vides simulation of separation of the light and heavy liquids in the Drum and knocking out the heavy liquid from the process.
• Flexible configuration of the column over-head section, matching to most of the connection schemes for the condenser and reflux drum (reflux receiver).

Distillation Object Configuration in MiMiC Simulation Studio

The overhead section layout, implemented in the column model, makes possible simulation of a variety of the pressure control loops used in the distillation. Particularly, the column pressure can be controlled:

• By manipulation of cooling agent flow rate to the condenser
• Using control valve on the vapor bypass around condenser to the reflux drum
• Using directly control valve on the vapor stream to the condenser
• By manipulation of flow rate of the outside vapor stream from/to reflux drum (split range control commonly used with the partial condenser)

Cold Startup, Warm Startup of Column Model

The distillation column model built with the MiMiC Distillation Object has the ability to be initialized and started from a Cold or Warm (near steady-state) status. User controls within MiMiC allow users to perform initialization off-line and then launch the object online.

Stripper/Reboiled Absorber Configuration

The configuration of the Distillation Object as a Stripper/Reboiled Absorber provides a dynamic model of the separation and reboiler sections.

Overhead of the column includes a vapor product piping with valve (if specified) and a liquid feed stream to the column top. All functionality, related to the separation and reboiler / sump sections, is available in the Stripper/Reboiled Absorber also.

The Stripper/Reboiled Absorber configuration has a vapor feed stream (optional) beneath the tray #1. This stream is a part of the absorber configuration, but can be used also in a general case for modeling of a direct vapor (steam) injection into the column bottom.

Distillation Column Configuration

A dynamic model of a distillation column can be implemented with different options depending on needs and scope of the particular simulation. The user can control the level of the model complexity by means of the following options.

• Tray Pressure Drop – The column tray pressure drop can be chosen constant or variable. At the constant pressure drop the user specifies the tray delta P value. If the variable pressure drop is selected, the delta P is calculated for each tray according to hydraulics correlations.
• Column Pressure – The column pressure calculation option can be also specified as constant or variable. If the variable pressure is selected, the pressure at the column overhead is defined by a vapor-liquid equilibrium in the Reflux Drum and the column pressure is calculated using pressure-flow interaction between main vapor volumes of the column. The choice of the constant pressure for this object allows the column overhead pressure to be assigned constant or externally calculated. In this way, the user can create his custom modeling calculation for the column overhead pressure and use this value instead of the Object value.
• Component Activities – If the constant activity option is chosen, the model updates the tray component activities with the given constant values equal for all trays, the variable activity option makes all the tray component activities equal to one.
• Tray Efficiency – If constant tray efficiency was selected, the predefined value of the Murphee tray efficiency coefficient is assign to all trays of the column. Otherwise (the variable efficiency), the efficiency coefficient is calculated individually for each tray using a semi-theoretical tray efficiency formula.
• Liquid Weeping at the tray – The Liquid Weeping coefficient can be set in the range of 0.0 – 1.0 gradually. At weeping coefficient equal to 1.0, the flow rate of the tray weeping liquid is calculated using Lockett-Banik correlation. At the coefficient value less than 1.0, only specified fraction of weeping flow is taken into consideration, at the value equal to 0.0 – no weeping flow from the tray.
• Material Balance Correction – This option indicates the use of a simplified automatic correction of the vapor flow balance at the top of column. If the option is chosen, the reflux drum holdup is corrected by the value of difference between two vapor flows: the flow leaving a top tray of the column, calculated from equilibrium conditions on the tray, and flow entering the condenser, calculated from pressure-flow conditions. Note that for properly chosen column pressure option the balance correction can be safely disabled.
• Detailed or Simplified Partial Condenser – This option defines an algorithm used for calculation of the column partial condenser. With the simplified option the vapor fraction of the condensing stream is calculated directly using ratio of the available condenser heat duty to the duty needed for total condensation, the vapor composition is assumed to be equal to the liquid one. The calculation is fast, but of the limited accuracy. With the detailed option the iterative partial condenser algorithm is employed for a precise evaluation of the vapor fraction, vapor and liquid compositions.
• Two liquid phase separation in Reflux Drum – This option defines an algorithm (module) used for calculation of the column reflux drum. With the two liquid phase option, the model calculates holdup and composition for both light and heavy liquids in the drum (heavy liquid component is specified by user). Heavy liquid is accumulating, primarily, in the drum boot and exiting at its bottom. With one liquid phase option the model calculates just an overall liquid holdup and composition, and a liquid exits the drum through the nozzle in its bottom.
• Water in Hydrocarbons – This option indicates the use of a simplified automatic correction of the vapor-liquid equilibrium constant for water (K-value, K = Ywat/Xwat) by the value of water solubility in heavy hydrocarbons. If the option is enabled, the correction is calculated using temperature correlations for the water solubility in hydrocarbons. The option is applied, mainly, to the refinery distillations, where the direct steam injection is used to decrease partial pressure of heavy hydrocarbons and increase column separation.

Distillation Column with Two Liquid Phase in Reflux Drum

Column View

Column View is a new user view that contains column performance data from MiMiC that would normally not be availlable at the control system HMI.  For control system testing or operator training, it provides an inside view of the performance and dynamics of the distillation column,  The user does not have to configure Column View,  It can be launched from MiMiC Explorer or from the Distillation Object in MiMiC Simulation Studio.  Performance data available in column view includes:

• Selectable Tray Pressure / Temperature Trend
• Vapor / Liquid Flowrate, Liquid Holdup, and Liquid Enthalpy Trends for three user-selected trays
• Overhead Section Temperature, Pressure, and Liquid Holdups Trends
• Vapor and Liquid Flow and Valve Posittion Trends for Overhead Sections
• Reboiler Temperature, Pressure Trends
• Vapor and Liquid Flow and Liquid Holdup for Reboiler
• Vapor Composition Trend for One Selected Tray
• Column Input and Output Flowrate Trends including Feed, products, and Side Withdraws
• On-line profile (tray by tray) of Liquid and Vapor Flowrates, Liquid Holdups, and Liquid Enthalpy
• On-line Liquid Composition X-Profile (tray-by-tray)
• On-line Vapor Composition Y-Profile (tray-by-tray)
• On-line Pressure / Temperature Profile (tray-by-tray)
• On-line table of performance parameters of trays including temperatures, pressures, holdups, and flooding indicators

Distillation Tower Tray-By-Tray Liquid Composition, X-Profile, in MiMiC Column View

Ordering Information

The MiMiC Advanced Modeling Distillation / Separation Objects License can be added to any MiMiC system with a MM3-7111, Advanced Modeling Objects Core license.  The MiMiC system must also be current on MiMiC Software Support.