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
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, including any excess IL in the feed (>ResinFlow*ILFactor). |
| 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.
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:
- IonExchange tab - Contains general information relating to the unit.
- RB - Optional tab, only visible if the Reactions are enabled in the Evaluation Block.
- QRBFeed - Optional tab, only visible if ShowQRBFeed is selected. Shows the properties of the feed to the Reaction Block (refer to Block Diagram above). This excludes any solids or liquids which have bypassed the reaction block.
- Info tab - Contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
- Links tab, contains a summary table for all the input and output streams.
- 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 |
| Tag | Display | This name tag may be modified with the change tag option. |
| Condition | Display | OK if no errors/warnings, otherwise lists errors/warnings. |
| ConditionCount | Display | The current number of errors/warnings. If condition is OK, returns 0. |
| GeneralDescription / GenDesc | Display | This is an automatically generated description for the unit. If the user has entered text in the 'EqpDesc' field on the Info tab (see below), this will be displayed here. If this field is blank, then SysCAD will display the UnitType or SubClass. |
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 (also refer to Hints and Comments) | ||
| 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 - NOTE: this pressure is applied to the (combined) feed, before sub-models (if any). | ||
| Method | AutoDetect | If there are any liquids AND no vapours present in the feed, outlet streams will take the highest pressure of the feeds. Else (e.g. 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. | |
| 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 Environment tab page of the Plant Model. | |
| RequiredP | Outlet streams will be at the user specified pressure. | |
| IgnoreLowMassFlow / IgnoreLowQm | Tick Box | This option is only visible if the AutoDetect, LowestFeed or HighestFeed methods are chosen. When calculating the outlet pressure and temperature of the tank, SysCAD will ignore the low flow feed streams should this option be selected. The low flow limit is set in the field below. |
| LowMassFlowFrac / LowQmFrac | Input | This field is only visible if the IgnoreLowQm option is selected. This is the amount any stream contributes to the total flow. For example, if the total feed to the tank 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 user specified pressure. |
| Result | Calc | The actual pressure used for the sum of the feeds which will also be the outlet pressure (unless further model options change the pressure). |
| Options | ||
| ShowQRBFeed | Tick Box | QRBFeed and associated tab pages (e.g. 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
Add to 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 Model Selection for more information on adding models to the configuration file.
Insert into Project Flowsheet
| Insert Unit | → | Separation | → | Ion Exchange |
See Insert Unit for general information on inserting units.
Hints and Comments
- Any solids in the feed streams (Resin, IL or Liquor) will always end up in the ResinOut product stream (unless the Solids Loss method is enabled). If the Resin is recycled, this may lead to a build up of any solid impurities. Suggest adding a filter to the Liquor stream prior to being fed to the IX circuit to remove any solid impurities.
- The Bed Volume (BV) group of tags are used to calculate the required volume of liquor to be sent out with the Resin in the ResinOut stream. Note that this is independent of the actual volumetric solids flow in the ResinOut stream which is simply all the solids from the unit (minus any lost to Liquor2Out if the Solids Loss method is enabled).
- If BV.Method = User, the model will NOT limit the flow of solids to the ResinOut stream.
- If BV.Method = Resin Feed, the volumetric flow of solids in the ResinOut stream may be different to the Resin feed stream due to solid impurities in the Liquor feed and/or differences in solids composition (due to reactions), where the solids have different densities.
Example Project
Please see IX Column Uranium Example