The shortcut column is used to separate multicomponent solvent mixtures. It uses a simplified algorithm FUG (Fenske-Underwood-Gilliland) with Kirckbride equation for optimum feed plate determination. The equipment offers a first overview of the separation process but the results should be accepted carefully, especially for highly non-ideal systems.

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Data Description

Equipment Properties

Data Description

Data		Unit		Description
Set	Item	Type	Native	Description
Equipment Properties	Light Key in Feed	String		Combo box which lets the user to choose the light key in the inlet mixture. Light key is the most volatile (e.g. ethanol), while heavy key is the less volatile (e.g. water).
	Heavy Key in Feed	String		Combo box which lets the user to choose the heavy key in the inlet mixture.
	Light Key Removed	Fraction or Percent	Fraction	The light key mass fraction of the feed light key, removed in the top product.
	Heavy Key Removed	Fraction or Percent	Fraction	The heavy key mass fraction of the feed heavy key, removed in the top product.
	Medium Tray Efficiency	Fraction or Percent	Fraction	The medium efficiency of the trays. used in calculation of real trays no .
	Reflux Ratio	Fraction or Percent	Fraction	Fraction to determinate the top recirculation flow as multiplication factor of the minimum reflux ratio calculated.
	Column Pressure	Pressure	psia	The pressure in column also is the pressure for the outlet streams (distillate and bottom product).
	Heat Loss in Column	Fraction or Percent	Fraction	The total heat loss of the column, fraction of the reboiler heat duty.
	Condenser Type	Boolean		Total Condenser or Partial Condenser
	Coolant Outlet Temperature	Temperature	F	The outlet temperature for the cooling medium in the top.
	Heating Medium Out Temp	Temperature	F	The outlet temperature for the heating medium (bottom).
	Reboiler Pressure Drop	Pressure	psia	The pressure drop in reboiler on the heating medium side (usually steam pressure drop).
Output Data	Minimum Reflux Ratio			The minimum reflux ratio, determined from minimum recirculation flow on the top.
	Actual Reflux Ratio			The actual recirculation flow on the top ratio, multiplication of the minimum reflux ratio.
	Minimum Number of Trays at Total Reflux			The number of ideal stages, calculated at total reflux.
	Minimum Number of Trays at Actual Reflux			The number of ideal stages, calculated considering the actual reflux ratio.
	Feed Tray			Optimum feed plate location, counted from the top.
	Number of Real Trays			The number of real plates calculated using the specified medium tray efficiency.
	Feed q			The thermal condition of the feed flow.
	Condenser Duty	Energy Flow	BTU/hr	The condenser heat that is removed by the coolant.
	Reboiler Duty	Energy Flow	BTU/hr	The reboiler heat that is supplied by the heating medium (steam).
	Heat Losses	Energy Flow	BTU/hr	The heat losses of the column (the units will be the energy flow units, e.g. GJ/h).
	Steam Per Feed			The steam amount used for 100 mass units of feed.
	Distillate Temperature	Temperature	F	The outlet temperature of the distillate stream.
	Bottom Temperature	Temperature	F	The outlet temperature of the bottom stream.
	Height	Length	ft	The estimated height of the column.
	Diameter	length	ft	The estimated diameter of the column.

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Equipment Properties

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Example of using equipment

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Method&Equations

Objective of any distillation process is to recover pure products. In case of multicomponent mixtures we may be interested in one, two or more components. Unlike in binary distillation, fixing molefraction of one of the components in a product does not fix the mole fraction of other components .On the other hand fixing compositions of all the components in the distillate and the bottoms product, makes almost impossible to meet specifications exactly.

FUG (Fenske-Underwood-Gilliland) algorithm is a widely used shortcut method.

First step is to establish if the separation is sharp or no. This will decide if the non-key components (if multicomponent mixture is involved) are distributed or undistributed. Components with negligible concentration in one of the products are called undistributed.

The components are arranged by their relative volatility refered (usually) to the heavy key component selected. If the key components are adjacents and the relative volatility of the other components are sensible different, the separation is a sharp one.

The FUG shortcut method assumes constant relative volatility and constant molar overflow.

The number of minimum ideal stages at total reflux is calculated using the Fenske equation:

The distribution of the non key components is evaluated using the equation:

A trial end error algorithm is used till the distribution of the non key components does not change significantly between two iterations of Nmin calculation.

The minimum reflux ratio is calculated in two steps, considering the Underwood I and Underwood II equations:

q is the thermal feed condition.

For a given q, and the feed composition we are looking for A satisfies this equation (usually A is between a LK and a HK) .

Once A is found, the minimum reflux ratio is calculated:

The number of ideal stages at actual reflux is calculated using the Gilliland correlation:

Kirkbride equation calculates the optimum feed stage location, as division between the number of ideal plates required in the rectification zone and the number of ideal plates required for stripping:

Where B is the molar flow of the bottom product and D is the molar flow od the distillate stream.

The dimensions of the column (height and diameter) are estimated using the following correlations:

Where NT is the number of real trays calculated uing the specified medium efficiency.

The diameter is computed from the geometry of the column area, assuming the free area required is 90% of total column area. The free area is calculated using the equation: