Ion Exchange

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General Description

The Ion Exchange Column is used to simulate the movement of liquor through a solid phase of resin. When implemented as part of an ion exchange circuit, the interstitial liquid will be carried between stages with the effective resin flow.

The unit operates as a plug flow column, with the interstitial liquid being discharged before the incoming liquor, without any mixing.

If the reaction block is employed there is a facility allowing fractions of the solid and liquid to bypass.

The user may also implement a thermal override to set the temperature of discharge streams to a fixed value or offset from the incoming resin temperature.

Diagram

IonExchange.png

The diagram shows a drawing of the Ion Exchange Column with all connectable streams of the unit. The physical location of the streams connecting to the unit is unimportant. The user may connect the streams to any position on the unit.

Inputs and Outputs

Label Required
Optional
Input
Output
Number of Connections Description
Min Max.
Liquor Optional In 0 5 The incoming process stream.
Resin Required In 1 10 The resin solid phase and its interstitial liquid. If IL is connected, then the interstitial liquid fed here will be the interstitial liquid above IL, closest to the column inlet.
IL Optional In 0 5 The interstitial liquid closest to the outlet.
ResinOut Required Out 1 1 Resin outlet containing the solid phases and the interstitial liquid which remains associated with the resin according to the ILFactor.
Liquor1Out Optional Out 0 1 The first column discharge. This will be the interstitial liquids initially in the column.
Liquor2Out Optional Out 0 1 The second column discharge. This is the excess liquor after all the original interstitial liquid has been discharged.
ILOut Optional Out 0 1 The original interstitial liquid that has not been displaced from the column by Liquor.
Vent Optional Out 0 1 Any gases fed to the unit or produced inside the unit.

As shown in the table above, the only connections necessary for the model to work are Resin and ResinOut. The following logic is applied if the other optional outlet connections are not made:

Label If not connected send to Otherwise send to
Liquor1Out Liquor2Out ResinOut
Liquor2Out Liquor1Out ResinOut
ILOut ResinOut N/A
Vent Liquor1Out ResinOut

Behaviour when Model is OFF

If the user disables the unit, by un-ticking the On tick box, then the following actions occur:

  • All input streams will flow straight out of the 'Resin Out' outlet, including any liquors and vapours;
  • No reactions will occur.

So basically, the unit will be 'bypassed'.


Block Flow Diagram

The following diagram shows the basic solid and liquid flows of the model if all connections are made.

IX block.png

Model Theory

Plug Flow

The liquid associated with the bed volume of the solid resin phase, ResinFlow, is based on an interstitial liquid factor (ILFactor). This should include the interstitial volume supported by the resin and the space in the column between the resin meshes and the control valves.

ResinFlow*ILFactor = V1 + V2

Where V1 is the volume of liquor closest to the discharge outlet and V2 is the volume of liquid closest to the feed inlet. V1 is the liquid in IL (if present) and V2 is the liquid fed with the Resin.

If present, IL is displaced first to Liquor1Out without mixing with the incoming liquor. The flow of Liquor will typically be several times larger than IL, but in cases where Liquor < IL, there will be a residual flow that reports to ILOut. In this minimal flow case any liquid in the Resin feed will also report to ILOut as it is assumed that the two bodies of liquid become perfectly mixed. The remaining interstitial liquid volume is made up from fresh liquor according to the column properties and leaves with the Resin.

Similarly, while Liquor < (V1 + V2) then the residual V2 will report to ILOut. The user may wish to create an IL connection between columns to preserve a concentration profile. Once an entire column volume has eluted, i.e. Liquor > (V1 + V2), there will be no concentration gradient in the interstitial liquor and no need to distinguish IL from the interstitial liquid feed with the Resin. All interstitial liquid leaves with the Resin with the required column volume made up with Liquor.

Example

The Ion Exchange column has a solid resin feed of 10 m^3/h and an interstitial liquid factor of 0.85. The interstitial liquid fed with the Resin contains caustic soda and the liquor flow corresponds to one Bed Volume. The table below shows the material flows in m^3/h around the Ion Exchange column.

Material Liquor Resin Liquor1Out Liquor2Out ResinOut
H2O(l) (m^3/h) 10 8.5 8.5 1.5 8.5
NaOH(aq) (g/L water) 0 10 10 0 0
Solid Resin (m^3/h) 0 10 0 0 10
Total (m^3/h) 10 18.5 8.5 1.5 18.5


This example shows the interstitial liquor displaced by incoming fresh water to Liquor1Out. Because there is a connection to Liquor2Out this stream contains fresh water only as the incoming liquid has displaced more than the interstitial liquid volume. There is nothing present in IL or ILOut.

Thermal Override

It is assumed that the original interstitial liquid is discharged prior to any effective heat transfer occurring. Therefore the thermal override is not applied to the Liquor1Out stream.

Data Sections

The default access window consists of several sections:

  1. IonExchange tab - Contains general information relating to the unit.
  2. RB - Optional tab, only visible if the Reactions are enabled in the Evaluation Block.
  3. Info tab - Contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
  4. Links tab, contains a summary table for all the input and output streams.
  5. Audit tab - Contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.


Ion Exchange Page

Unit Type: IonExchange - The first tab page in the access window will have this name.

Tag (Long/short) Input / Calc Description/Calculated Variables / Options
Common Data on First Tab Page

Requirements

On Tickbox Toggles between having the model on or off. If the model is off then the Resin feed will report to the ResinOut and all other inputs will report to IL2Out.
ThermalOverride None No energy removed or added, the outlet temperatures will be determined by energy balance.
UserT External energy is added/removed in order to achieve a user defined temperature.
ResinFeedT External energy is added/removed in order to achieve an outlet temperature equal to the inlet temperature of the Resin feed stream/s.
TempChange External energy is added/removed in order to achieve an outlet temperature equal to the inlet temperature of the Resin minus a user defined drop in temperature.
TemperatureReqd / T_Reqd Input This is only visible if the UserT thermal override method is selected. This is the user defined temperature.
TempRiseReqd / TRiseReqd Input This is only visible if the TempChange thermal override method is selected. This is the user defined change in temperature relative the inlet temparature of the Resin feed stream/s. +ve for Temperature Rise, -ve for Temperature Drop.
Reactions List This can be used to switch on the Reaction Block (RB). If this is 'On' then the associated page, RB becomes visible and may be configured.
Note: The user does not have to configure a reaction file, even if this block is checked.
RB.LiqBypass Input The fraction of liquids that bypass the RB.
RB.SolBypass Input The fraction of solids that bypass the RB.
BedVolume
BV.Method ResinFeed The Resin Flow will be calculated by the sum of all solids in the Resin and IL feed streams.
User The Resin Flow is a user input.
BV.ResinVolFlowReqd / BV.ResinQvReqd Input The Resin Flow to be used when calculating the amount of interstitial liquid associated with the resin. This field is only present if the User option is chosen for the BV.Method.
BV.ILFactor Input The factor relating BV.ResinFlow to interstitial liquid volume including interstitial resin space and free space between feed/discharge valves.
BV.ResinVolFlow / BV.ResinQv Display The Resin Flow actually used when calculating the amount of interstitial liquid associated with the resin.
Solids Loss to Liq2Out
SolidsLoss.Method None There are no solid losses, all solids exit via the ResinOut stream.
Fraction in Liq2Out The Liquor2Out stream will have a user specified fraction of solids. NOTE: If there is no liquor sent to Liquor2Out there will be no solids loss.
Fraction to Liq2Out A user specified fraction of the solids present after any reactions are completed will be sent to Liquor2Out.
NOTE: If there is no liquor sent to Liquor2Out then the Liquor2Out stream will consist of 100% solids.
Liq2OutSolFracReqd Input The user specified fraction of solids in the Liquor2Out stream. This field is only present if the Fraction in Liq2Out option is chosen for the SolidsLoss.Method.
SolidsToLiq2Out Input The user specified fraction of solids loss to the Liquor2Out stream. This field is only present if the Fraction to Liq2Out option is chosen for the SolidsLoss.Method.
OperatingP...
Method Atmospheric outlet streams will be at Atmospheric Pressure. The atmospheric pressure is calculated by SysCAD based on the user defined elevation (default elevation is at sea level = 101.325 kPa). The elevation can be changed on the Species tab page of the Plant Model.
AutoDetect If there are any liquids AND no vapours present in the feed, outlet streams will take the highest pressure of the feeds. Else (eg. some vapours present) outlet streams will take the lowest pressure of the feeds.
LowestFeed outlet streams will take the lowest pressure of the feeds.
HighestFeed outlet streams will take the highest pressure of the feeds.
RequiredP outlet streams will be at the user specified pressure.
IgnoreLowQm Tick Box This option is only visible if LowestFeed or HighestFeed method is used. When calculating the outlet pressure and temperature of the tie, SysCAD will ignore the low flow feed streams if option is selected. The low flow limit is set in the field below.
LowQmFrac Input This is the amount any stream contributes to the total flow. For example, if the total feed to the tie is 10 kg/s, and this field is set to 1%. Then any feed streams with less than 0.1 kg/s will be ignored in the pressure calculations.
PressureReqd / P_Reqd Input This field is only visible if the RequiredP method is chosen. This is the user specified pressure.
Result Display The actual pressure used for the sum of the feeds which will also be the outlet pressure (unless further model options change the pressure).
 
ShowQRBFeed Tick Box QRBFeed and associated tab pages (eg Qm) will become visible, showing the properties of the feed to the Reaction Block (refer to Block Diagram above). See Material Flow Section. This will exclude any solids or liquids which have bypassed the reaction block.

Results

Liq.LiquidVolFlow / Liq.LQv Calc Volumetric flowrate of liquids in Liquor feed
IL.LiquidVolFlow / IL.LQv Calc Volumetric flowrate of liquids in IL feed
Resin.LiquidVolFlow / Resin.LQv Calc Volumetric flowrate of liquids in Resin feed
Resin.SolidVolFlow / Resin.SQv Calc Volumetric flowrate of solids in Resin feed and IL feed
Resin.SolidMassFlow / Resin.Qm Calc Mass flowrate of solids in Resin feed and IL feed
 
RB.BypassMassFlow / RB.BypassQm Calc Mass flowrate of material bypassing the reaction block
RB.FeedMassFlow / RB.FeedQm Calc Mass flowrate of material fed to the reaction block
RB.FeedSolFrac / RB.FeedSf Calc Mass fraction of solids in the reaction block feed
Liq1Out.LiquidVolFlowReqd / Liq1Out.LQvReqd Calc The required volumetric flowrate to Liquor 1 outlet
Liq1Out.LiquidVolFlow / Liq1Out.LQv Calc The actual volumetric flowrate to Liquor 1 outlet
ILOut.LiquidVolFlow / ILOut.LQv Calc Volumetric flowrate of IL1Out
ResinOut.LiquidVolFlowReqd / ResinOut.RqdLQv Calc The required volumetric flowrate of interstitial liquid as determined by BV.ResinFlow*BV.ILFactor
ResinOut.LiquidVolFlow / ResinOut.LQv Calc The actual volumetric flowrate of interstitial liquid sent to ResinOut. This will be equal to the required flow (as shown above), unless the liquor feed is too low.
Liq2Out.LiquidVolFlow / Liq2Out.LQv Calc The actual volumetric flowrate of liquids sent to Liquor2Out. This is the liquor which exceeds the required volumetric flowrate of interstitial liquid as determined by BV.ResinFlow*BV.ILFactor.
SolidsLoss.MassFlow / SolidsLoss.Qm Calc The actual mass flowrate of solids lost to Liquor2Out.
 
Resin.TemperatureIn / Resin.Ti Calc Incoming resin temperature for thermal override
OverrideT Calc The override temperature.
HeatFlow Calc heat flow required to achieve thermal override setting, positive value for external heat addition, negative value for heat loss.

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

 

DLL:

Separation.dll

Units/Links

Separation: Ion Exchange

or

Group:

Mass Separation

Units/Links

Separation: Ion Exchange

See Project Configuration for more information on adding models to the configuration file.


Insert into Project

 

Insert Unit

Separation

Ion Exchange

See Insert Unit for general information on inserting units.