Input Experts guide you through the installation of a Column. The Input Experts are available for the following six standard column templates:
l Absorber
Details related to each column template are outlined inTemplates. Each Input Expert contains a series of input pages whereby you must specify the required information for the page before advancing to the next one. When you have worked through all the pages, you have specified the basic information required to build your column. You are then placed in the Column property view which gives comprehensive access to most of the column features.
It is not necessary to use the Input Experts to install a column. You can disable and enable the Input Experts option on the Options page in the Simulation tab of the Session Preferences property view.
If you do not use the Input Experts, you move directly to the Column property view when you install a new column.
Templates
HYSYS contains a number of column templates which have been designed to simplify the installation of columns.
A Column Template is a pre-constructed configuration or “blueprint” of a com-mon type of Column, including Absorbers, Reboiled and Refluxed Absorbers, Distillation Towers, and Crude Columns. A Column Template contains the unit operations and streams that are necessary for defining the particular column type, as well as a default set of specifications.
All Column templates can be accessed using the Model Palette.
When you add a new Column HYSYS gives you a choice of the available tem-plates. Simply select the template that most closely matches your column con-figuration, provide the necessary input in the Input Expert property view (if applicable), and HYSYS installs the equipment and streams for you in a new Column subflowsheet. Stream connections are already in place, and HYSYS provides default names for all internal streams and equipment. You can then make modifications by adding, removing or changing the names of any streams or operations to suit your specific requirements.
Clicking the Side Ops button on the final page of the Column Input Expert opens the Side Operations Input Expert wizard, which guides you through the process of adding a side operation to your column.
In addition to the basic Column Templates which are included with HYSYS, you can create custom Templates containing Column configurations that you com-monly use.
HYSYS Column Conventions
Column Towers, Overhead Condensers, and Bottom Reboilers are each defined as individual unit operations. Condensers and Reboilers are not numbered stages, as they are considered to be separate from the Tower.
Note: By making the individual components of the column separate pieces of equipment, there is easier access to equipment information, as well as the streams connecting them.
The following are some of the conventions, definitions, and descriptions of the basic columns:
Column Component
Description
Tower A HYSYS unit operation that represents the series of equilibrium stages in a Column.
Column Component
Description
Stages Stages are numbered from the top down or from the bottom up, depending on your preference. The top stage is 1, and the bottom stage is N for the top-down numbering scheme. The stage numbering pref-erence can be selected on the Connections page of the Design tab on the Column property view.
Overhead Vapor Product
The overhead vapor product is the vapor leaving the top stage of the Tower in simple Absorbers and Reboiled Absorbers. In Refluxed Absorbers and Distillation Towers, the overhead vapor product is the vapor leaving the Condenser.
Overhead Liquid Product
The overhead liquid product is the Distillate leaving the Condenser in Refluxed Absorbers and Distillation Towers. There is no top liquid product in simple Absorbers and Reboiled Absorbers.
Bottom Liquid Product
The bottom liquid product is the liquid leaving the bottom stage of the Tower in simple Absorbers and Refluxed Absorbers. In Reboiled Absorbers and Distillation Columns, the bottom liquid product is the liquid leaving the Reboiler.
Overhead Condenser
An Overhead Condenser represents a combined Cooler and separation stage, and is not given a stage number.
Bottom Reboiler
A Bottom Reboiler represents a combined heater and separation stage, and is not given a stage number.
Default Replaceable Specifications
Replaceable specifications are the values which the Column convergence
algorithm is trying to meet. When you select a particular Column template or as you add side equipment, HYSYS creates default specifications. You can use the specifications that HYSYS provides or replace these specifications with others more suited to your requirements.
The available default replaceable specifications are dependent on the Basic Column type (template) that you have chosen. The default specifications for the four basic column templates are combinations of the following:
l Overhead vapor flowrate
l Distillate flowrate
l Bottoms flowrate
l Reflux ratio
l Reflux rate
Note: The specifications in HYSYS can be set as specifications or changed to estimates.
The provided templates contain only pre-named internal streams (streams which are both a feed and product). For instance, the Reflux stream, which is named by HYSYS, is a product from the Condenser and a feed to the top stage of the Tower.
Note: The pressure for a Tower column section, condenser, or reboiler can be specified at any time on the Pressures page of the Column property view.
In the following schematics, you specify the feed and product streams, includ-ing duty streams.
Absorber Template
The only unit operation contained in the Absorber is the Tower, and the only streams are the overhead vapor and bottom liquid products.
The following is a schematic representation of the Absorber:
There are no available specifications for the Absorber, which is the base case for all tower configurations. The conditions and composition of the column feed stream, as well as the operating pressure, define the resulting converged solu-tion. The converged solution includes the conditions and composition of the vapor and liquid product streams.
Note: The Liquid-Liquid Extraction Template is identical to the Absorber Template.
Note: The remaining Column templates have additional equipment, thus increasing the number of required specifications.
Reboiled Absorber Template
The Reboiled Absorber template consists of a Tower and a bottom reboiler. Two additional streams connecting the Reboiler to the Tower are also included in the template.
Figure 2.11
When you install a Reboiled Absorber (in other words, add only a Reboiler to the Tower), you increase the number of required specifications by one over the Base Case. As there is no overhead liquid, the default specification in this case is the overhead vapor flow rate.
Note: The Column Input Expert for Reboiled Absorber offers advanced pre-configurations for the reboiler including the HYSYS Shell and Tube Heat Exchanger. See the Reboiled Absorber section of the Aspen HYSYS online help for updated information on these func-tions.
Refluxed Absorber Template
The Refluxed Absorber template contains a Tower and an overhead Condenser (partial or total). Additional material streams associated with the Condenser are also included in the template. For example, the vapor entering the
Condenser from the top stage is named to Condenser by default, and the liquid returning to the Tower is the Reflux.
Figure 2.12
When you install a Refluxed Absorber, you are adding only a Condenser to the base case. Specifying a partial condenser increases the number of required spe-cifications by two over the Base Case. The default spespe-cifications are the over-head vapor flow rate, and the side liquid (Distillate) draw. Specifying a total condenser results in only one available specification, since there is no overhead vapor product.
Either of the overhead vapor or distillate flow rates can be specified as zero, which creates three possible combinations for these two specifications. Each combination defines a different set of operating conditions. The three possible Refluxed Absorber configurations are listed below:
l Partial condenser with vapor overhead but no side liquid (distillate) draw.
l Partial condenser with both vapor overhead and distillate draws.
l Total condenser with distillate but no vapor overhead draw.
Distillation Template
If you select the Distillation template, HYSYS creates a Column with both a Reboiler and Condenser. The equipment and streams in the Distillation
tem-plate are therefore a combination of the Reboiled Absorber and Refluxed Absorber Templates
Figure 2.13
Note: The Column Input Expert for the Distillation column offers advanced pre-con-figurations for the reboiler including the HYSYS Shell and Tube Heat Exchanger. Refer to Column Property Viewfor further details.
Reflux Ratio
The number of specifications for a column with both a Reboiler and Condenser depends on the condenser type. For a partial condenser, you must specify three specifications. For a total condenser, you must specify two specifications. The third default specification (in addition to Overhead Vapor Flow Rate and Side Liquid Draw) is the Reflux Ratio.
(1)
The Reflux Ratio is defined as the ratio of the liquid returning to the Tower divided by the total flow of the products (see the figure above). If a water draw is present, its flow is not included in the ratio.
As with the Refluxed Absorber, the Distillation template can have either a Par-tial or Total Condenser. Choosing a ParPar-tial Condenser results in three replace-able specifications, while a Total Condenser results in two replacereplace-able
specifications.
The pressure in the tower is, in essence, a replaceable specification, in that you can change the pressure for any stage from the Column property view.
Note: The pressure remains fixed during the Column calculations.
The following table gives a summary of replaceable column (default) spe-cifications for the basic column templates.
Templates Vapor Draw Distillate Draw Reflux Ratio Reboiled Absorber X
Templates Vapor Draw Distillate Draw Reflux Ratio Refluxed Absorber
Total Condenser X
Partial Condenser X X
Distillation
Total Condenser X X
Partial Condenser X X X
Three Phase Distillation Template
If you select the Three Phase Distillation template, HYSYS creates a Column based on a three phase column model.
Note: The same standard column types exist for a three phase system that are available for the “normal” two phase (binary) systems.
Using the Three Phase Column Input Expert, the initial property view allows you to select from the following options:
l Distillation
l Refluxed Absorber
l Reboiled Absorber
l Absorber
Each choice builds the appropriate column based on their respective standard (two phase) system templates.
If the Input Expert is turned off, installing a Three Phase column template opens a default Column property view for a Distillation type column equipped with a Reboiler and Condenser.
The key difference between using the standard column templates and their three phase counterparts lies in the solver that is used. The default solver for three phase columns is the “Sparse Continuation” solver which is an advanced solver designed to handle three phase, non-ideal chemical systems, that other solvers cannot.
When using the Three Phase Column Input Expert some additional spe-cifications can be required when compared with the standard (binary system) column setups.
Clicking the Side Ops button on the final page of the Three Phase Column Input Expert opens the Side Operations Input Expert wizard, which guides you through the process of adding a side operation to your column.