The Column module allows you to perform thermal analysis of distillation columns. This analysis is based upon a Pinch Technology technique called the column grand composite curve.

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The column grand composite curve will clearly show how (and if) heat loads can be redistributed in a column in order to reduce utility costs or exchange heat with an existing process stream. Column will enable you to explore column modifications in a systematic way, rather than attempting improvements in an ad-hoc manner.

Over 95% of all distillation columns will be targeted automatically, for refinery, petro-chemical and chemical processes. Difficult columns can be analysed successfully using advanced features, reports, graphs and other analytical methods available in Column.

One of the most important results from a Column analysis is an understanding of the ideal thermal distribution in the column. This is gained through the following graphs:

	The column grand composite curve (Stage - Enthalpy)
	This shows a plot of the minimum reboiler and condenser loads distributed over the temperature range of the column. The existing reboiler and condenser loads are super-imposed on this. From this combination you can see the scope for increasing existing loads or introducing new loads at different levels. This allows you to optimise pump-arounds, reduce utility costs or exchange heat with an existing process stream.
	The column grand composite curve (Temperature - Enthalpy)
	This is similar to the plot just described but shows stage number on the Y axis rather than temperature.
	The column composite curves
	These allow the user to visualise the distribution of driving forces within the column. This gives a qualitative "feel" for how a proposed modification may affect the number of stages required.

Exergy targeting

As well as thermal targeting, Column provides an additional technique called exergy loss analysis. This technique compares the minimum thermodynamic exergy loss within the column against the actual exergy loss in the real column. This can be done for the column as a whole or on a stage by stage basis. Column provides the following features for this:

	Exergy loss summary
	This presents the results as a table, including an overall exergy balance.
	Exergy loss profiles
	These show the distribution of exergy loss within the column. These can be plotted as temperature vs. exergy loss or stage vs. exergy loss.

Exergy Loss Analysis allows you to see the main causes of exergy loss and to consider appropriate action. For example, a large exergy loss at the feed stage may suggest feed heating or cooling (as appropriate) or relocation of the feed stage. Exergy analysis is particularly important for cryogenic columns.

Push button column targeting

One of the most significant improvements in the Column module in SuperTarget 5 is the ability to perform column targeting at the push of a button. For example, after importing data from a simulator the user can immediately display the column grand composite curve, without needing to make further choices. This is made possible by a statistical analysis of the column data and automatic selection of key components. These are described in the sections below.

Automatic key selection

The automatic key selection is implemented using two different methods:

A method based on "K-values", which lumps components together to form different keys on each stage. This is used for distributed separations, such as refinery towers.

A method which divides the column into zones between feed or product streams. Different key selections are chosen for each zone. This is used for sharp separations, such as those typically found in a petro-chemical plant.

Automatic identification of separation type

The section above has described two different methods for automatic key selection. For any column, the user is free to choose between these methods. However, by default the system will do a statistical analysis of a particular column and decide for itself which method is appropriate. In other words, it will automatically decide if the column separation is sharp or distributed. It will then automatically choose the key selections appropriately.

Complex distillation towers

SuperTarget Column is very good at handling complex distillation towers and multi-product columns. This is because of the following features:

	There are no hard limits on the number of stages or the number of components in a column. All memory is allocated dynamically according to the column configuration
	A column can have multiple feeds and multiple products per stage
	Pump-arounds are properly represented throughout the program, instead of being treated as a pseudo feed and a pseudo product
	Compositions can be added together during key selection without actually needing to create a completely new lumped component. This makes it easy to select different groupings on each stage of a refinery column

Column has been designed for two different data entry methods:

Process provides the following simulation features:

	Direct import of data from a simulation file -
	The format of this file has been defined by Linnhoff March. Interfaces are currently available to PRO/II and HYSYS. Please see your Linnhoff March representative for the latest information.
	Manual data entry using a step by step Wizard -
	This has been designed so that data can be easily pasted in from a commonly available format, such as Aspen Plus output. In addition, there are graphs that help the user to understand the separation that is taking place in the column. These are as follows:
	A graph of component split factors -
	This shows the fraction of each component going to each product.
	A graph of product component flowrates -
	This shows the molar flow of each component going to each product.

Advanced key selection

By default, Column does all key selection automatically. This means that you can display the column grand composite curve at the push of a button. However, advanced key selection is still available for users who want more control. This is useful in the following circumstances:

	So that experts can fine-tune the choices from the automatic key selection
	For dealing with problem columns, particularly those with heat or mass balance errors
	To gain an understanding of the choices that the system has made

In these circumstances the following features are available to the user:

	An editor for excluding certain components from the automatic key selection. A common use is to exclude water from the analysis in a refinery tower
	An editor that allows the user to choose the key selection method (see above)
	A key map that displays the current key selections throughout the column
	A stage-wise plot of the mole fractions of the selected keys throughout the column

Key ratio profiles

The key ratio is the mole fraction ratio of the selected light key to the selected heavy key components in the chosen phase. Key ratio profiles are plots of the key ratio against stage number on a semilog scale. These graphs can be useful in analysing the separation performance of a column. For example, the slope of the curve gives a measure of the relative separation accomplished per stage in various locations in a column. For a well behaved separation at high reflux, distillation theory implies that the plot will be a smooth, almost straight, sloping line.