Column Product Streams
Information for the column product streams must be supplied via the drop-down list boxes in the list of product streams table. There is no limit on the number of products from a column and, with the exception of decanted water, a draw product may be taken from any tray. Only product streams which have been connected to the column in the simulation flowsheet appear in this window. Every column must have an Overhead product from tray one and a Bottoms product from the bottom tray.
Note: For Columns with thermosiphon reboilers (without baffles), the bottoms product is taken from the second to last tray, N-1, instead of the last tray, N. See
Thermosiphon without Baffles for more information.
Product
The product stream identifier from the simulation flowsheet in the main PFD window.
Type of Product
Overhead : Product from tray one, required for every column.
Bottoms : Product from bottom tray, required for every column.
Fixed rate draw : Side draw product. The allowable draws depend on the selected Column Algorithms and Calculated Phases.
Total phase draw : Total draw of designated liquid phase. The allowable draws depend on the selected Column Algorithms and Calculated Phases.
Pseudoproduct : Column Pseudoproduct (excluded from column material balance) . See Column Pseudoproducts for further details.
Phase
Vapor : Equilibrium vapor from tray
Liquid : Equilibrium liquid mixture from tray
Decanted water : Total water phase draw
Liquid 1 : Light liquid product for vapor-liquid-liquid or liquid-liquid systems
Liquid 2 : Heavy liquid product for vapor-liquid-liquid or liquid-liquid systems
Tray
Tray number from which product is withdrawn. Note that all columns must have products from the top tray and the bottom tray.
Rate
The product rate. This entry is required for all fixed rate draw products. An estimated value for column overhead or bottoms rate (or both) must be provided. For total phase draws, the rate is always assumed to be an estimate and all of the specified phase present on the tray is removed. The dimensional units for rates may be changed using the Unit-Of-Measure Selection Window which is displayed when the UOM button on the Toolbar is pushed.
The estimated value for the Overhead or Bottoms rate should be as accurate as possible. For many cases, the quality of the initial estimate is strongly influenced by this estimated rate. It is good practice to estimate Overhead or Bottoms products that have small flows.
To specify a desired flow for the Overhead or Bottoms product it is necessary to define a column performance specification.
Automatic Estimate Normalization
Providing estimates for both the overhead and bottom product rates (which may be redundant), initiates automatic normalization of all column products. For the first execution of the column model, the rate estimates are normalized so the summation of all the column products matches the total feed (when the column solves for the first time). For columns in recycle, the same normalization is applied whenever the column was not converged in the immediately previous recycle iteration. (Note a column can reach a converged state and still not be solved because it does not satisfy all specifications and constraints.)
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