PHREEQC Flash Tank

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Navigation: Models -> TPS Models -> PHREEQC Models -> PHREEQC Flash Tank

PHREEQC
Overview
PHREEQC
Model Configuration
PHREEQC
Direct Calc Model
PHREEQC
Side Calc Model
PHREEQC
Reactor
PHREEQC
Evaporator
PHREEQC
Flash Tank
PHREEQC
Reverse Osmosis

See Also PHREEQC SysCAD Project Workflow


New for Build 138. Currently in BETA - contact SysCAD for demonstrations or further information.


General Description

The PHREEQC solver is called to determine the state of a SysCAD stream. The composition, temperature and pressure of the 'Feed' stream are based on the feed to the unit. The unit will then determine the equilibrium conditions of the resulting stream. The results can be applied to the product stream or just performed as a side calculation (similar to use of the PHREEQC Side Calc Model).

  • The PHREEQC Flash Tank is used to 'flash' a feed stream to produce a liquid and vapour product at a set pressure or temperature.
  • There are two operational modes for the PHREEQC Flash Tank: (1) as a stand-alone unit; or (2) as part of a Flash Train. The user sets the operational mode of the Flash Tank. However, if the user sets the mode as Flash Train and the Flash Tank is NOT connected to any Flash Train aware destination unit, the model will go to an error state.
  • The PHREEQC Flash Tank model may be used as a Crystallizer. Vapour is flashed off and the remaining solution is then supersaturated with the required species. This species then precipitates out as the crystal product.

Notes

  1. The user MUST have added and configured a PHREEQC Model Configuration unit in the SysCAD project before this unit can function.
  2. The user MUST have installed a version of PHREEQC on their computer to make use of the PHREEQC functionality in SysCAD. Please see wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc for more information.

Diagram

PHREEQC Flash Tank.png

The diagram shows a drawing of the PHREEQC Flash Tank unit, with Feed, Product, Overflow and Vapour streams. When the user inserts the PHREEQC Reactor unit into a flowsheet, a different graphics symbol can be selected from a pull down menu. The streams may be connected to any area of the drawing without affecting the actual connection point as SysCAD ignores the physical position of the connection.

Inputs and Outputs

Label Input / Output No. of Connections Description
    Min Max  
Feed Input 1 10 Feed Stream
Overflow Output 0 1 Overflow liquor Stream
Product Output 1 1 Product Slurry Stream - this stream normally contains the majority of the solids.
Vapour Output 1 1 Optional Vent Stream

Behaviour when Model is OFF

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

  • All material in streams connected to the 'Feed' will flow straight out of the 'Product' outlet, with no change in phase;
  • No sub-models will be called.

So basically, the unit will be 'bypassed' without the user having to change any connections.

Model Theory

The PHREEQC flash tank uses the PHREEQC algorithms and data to determine the status of the aqueous solution.

The PHREEQC flash tank can be incorporated into a SysCAD flowsheet, it can be connected with SysCAD inlet and outlet streams.

  1. User connects the PHREEQC flash tank with SysCAD input streams,
  2. The SysCAD feed stream(s) using SysCAD species is converted into PHREEQC "Input" using PHREEQC Species. The species mapping is defined in the corresponding PHREEQC Model Configuration unit model.
  3. The PHREEQC Reactor calls the PHREEQC algorithms to determine the status of the mixture using the converted PHREEQC "input" data.
  4. The PHREEQC results are displayed in the "output" tab using PHREEQC species.
  5. The resulting mixture is then separated into vapour, overflow, product streams based on user specification on the Separ Tab page.

NOTES:

  • This model uses the VLE model of SysCAD, not PHREEQC, for calculating the vapour. The liquid fraction of the stream is fed to PHREEQC to determine the ionic solution properties, which are then used in an iterative manner to calculate the BPE, and ultimately, the temperature, pressure, amount of vapour generated, etc. Thus PHREEQC is used for calculating the liquid and solid fractions of the stream, and SysCAD VLE is used to calculate the vapour.
  • The Input, Output and Diff tab pages are displayed using PHREEQC species, as defined in the PHREEQC database file (.dat) specified in the corresponding PHREEQC Model Configuration unit model.
  • The species used in the SysCAD project are shown on the optional Sp pages, shown as part of the QFeed, QUnmapped, QRxnBypass and QProd pages.

WorkFlow

The suggested workflow for configuring the model is:

  1. Make sure the project contains at least one of the PHREEQC Model Configuration model, and the model is loaded with the correct PHREEQC database you would like to use for the PHREEQC Reactor.
  2. On the PHREEQCFlashTank Tab page, select the correct "ChemModel" (to match step 1)
  3. Set the operating pressure (and any other sub-models)
  4. Perform an equilibrium calculation by pressing Solve in SysCAD.
  5. The Results are displayed in the Results and Output tabs.
  6. Check and fix any species mapping issues. (PHREEQC resulting species may change if the operating conditions change, so it is likely a change of temperature or feed composition will result in different PHREEQC species.)

Data Sections

The default access window consists of several sections:

  1. PHREEQC Flash Tank tab. This first tab contains general information relating to the unit.
  2. Separ - Only visible if the Overflow stream is connected. The tab allows the user to specify the split between the Product and Overflow streams.
  3. VLE - Always visible.
  4. CFE - Optional tab, only visible if the UseCFE option is enabled on the first tab page.
  5. Results tab - This tab displays the key results of the calculations.
  6. Input tab - This tab displays a summary of the mapped Input stream as PHREEQC species.
  7. Output tab - This tab displays the Output stream results including the amounts of each PHREEQC species present in the final mixture.
  8. Diff tab - This tab displays the amounts of each species which are formed or reacted as part of the calculations.
  9. ElemBal tab - This tab displays an elemental balance between the Input and Output streams.
  10. Deportment tab - This tab shows the mass movement of elements for the Solid, Liquid and Gas phases.
  11. ParamSweep tab - This tab allows the user to generate sets of data.
  12. SelectSpForPlot tab - Optional tab, only visible if the SelectSp option is enabled on the ParamSweep tab. This tab allows the user to select which species to be reported in the sets of data to be generated.
  13. QUnmapped - Optional tab, only visible if ShowQUnmapped is enabled on the first tab page.
  14. QFeed - Optional tab, only visible if ShowQFeed is enabled. This page shows the properties of the mixed stream as the feed to the tank.
    • This is before any Evaluation Block models are evaluated.
  15. QProd - This page shows the properties of the Flash Tank discharge as a single stream.
    • This is AFTER the flash calculations, but before the split to liquid and vapour streams.
  16. Info tab - Contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
  17. Links tab, contains a summary table for all the input and output streams.
  18. Audit tab - Contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.

PHREEQC Flash Tank Tab Page

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

Tag (Long/Short) Input/ Calc Description
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:
  • For pipes, SysCAD will use the text in the 'ConnectDesc' field - this displays the Source and Destination tags of the pipe;
  • For Feeders/Cross Page Connectors, SysCAD will display the state of the unit, i.e. if it is a Feeder or a Sink, etc.;
  • For other units SysCAD will display the unit class ID.
Requirements
On Tickbox This variable in used to enable flashing in the unit. If this not selected, the material will flow out of the liquor outlet with no change in state, i.e. the unit acts as a pipe.
Mode Stand Alone (Manual) The flash tank will not form part of a flash train.
Flash Train The flash tank will form part of a Flash Train if appropriate units are connected to it. The OperatingP - Method will be set to Saturated.
OperatingP...
Method Atmospheric This method is only available if 'Stand Alone' Mode is chosen. All flash calculations will be done 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 This method is only available if 'Stand Alone' Mode is chosen. All flash calculations will be done at the user specified pressure.
RequiredT This method is only available if 'Stand Alone' Mode is chosen. All flash calculations will be done at the user specified temperature.
Saturated The OperatingP - Method will be set to Saturated if 'Flash Train' Mode is chosen. All flash calculations will be done at the saturated pressure.
PressureReqd / P_Reqd Input The Required Flash Pressure - This is only visible if the RequiredP Method is selected.
TemperatureReqd / T_Reqd Input The Required Flash Temperature - This is only visible if the RequiredT Method is selected.
Result Display This field displays the operating pressure of the flash Tank.
MinFlashP Input This is only visible when 'Flash Train' Mode is chosen. The Minimum Flash Pressure.
Environmental Heat Transfer
HeatLossMethod None No heat transfer between the unit and the environment.
Fixed HeatFlow The user specifies a fixed heat loss between the unit and the environment.
Ambient SysCAD calculates the overall heat loss based on user specified HTC and Area and the temperature difference between the Feed and environmental temperatures. The environmental temperature is assumed to remain constant.
EHX.HeatLossReqd Input Visible when the HeatLossMethod = Fixed HeatFlow. The required heat loss.
EHX.HTC Input Visible when the HeatLossMethod = Ambient. The Overall Heat Transfer coefficient.
EHX.Area Input Visible when the HeatLossMethod = Ambient. The Heat Transfer area.
EHX.AmbientT Display Visible when the HeatLossMethod = Ambient. The ambient temperature. The ambient temperature is specified in the Plant Model - Environment_Tab
EHX.HeatLoss Calc Visible when the HeatLossMethod = Ambient. The calculated heat flowrate.
Options
VapStandardSpModel Tick Box If ticked then the Standard (default) species model will be used in the vapour exit stream. This selection has no effect on the model operation.
ShowQFeed Tick Box QFeed and associated tab pages (eg Sp) will become visible if this is enabled. These tabs will show the properties of the combined feed stream to the Unit. These values are BEFORE any flashing calculations or other sub-models occur.
ShowQProd Tick Box QProd and associated tab pages (eg Sp) will become visible if this is enabled. These tabs will show the properties of the combined product streams from the Unit. These values are after any flashing calculations or other sub-models occur but before the final phase split is made.
Vapour Entrainment
FlashVapToLiquid Input This field allows the user to set a proportion of the flash vapour bypassing to the liquid stream. The default is 0%.
OtherGasToLiquid Input This field allows the user to set a proportion of any non-condensable gas bypassing to the liquid stream. The default is 0%.
======== BETA VERSION ========
This program contains PHREEQC Copyright U.S. Geological Survey (USGS)
Requirements
Chemistry Model
ChemModel...
UnitTag List The tag of the relevant PHREEQC Model Configuration unit model- this may be chosen from the drop down list of all PHREEQC Model Configuration unit models available in the project.
ChemModel.Selected Display The tag of the relevant PHREEQC Model Configuration unit model.
Check Check Tag.png If the user clicks on this button, SysCAD will check that the UnitTag is a valid PHREEQC Model Configuration unit model.
ConnOK Tickbox If SysCAD finds a valid PHREEQC Model Configuration unit model, then this field will be enabled.
Status OK The specified chemistry model (PHREEQC Model Configuration) has been initialised correctly and the database file has been found and loaded correctly.
ChemModel Tag not Specified No tag has been specified for the Chemistry Model. Specify the desired Chemistry Model (PHREEQC Model Configuration) in the UnitTag field.
Valid ChemModel Tag Required The tag specified for the Chemistry Model in the UnitTag field is invalid and needs to be corrected.
Init Required The specified Chemistry Model (PHREEQC Model Configuration) needs to be initialised.
ChemModel Load Required The database of the specified Chemistry Model ((PHREEQC Model Configuration) needs to be loaded.
DLL or Version Error There is a problem with the PHREEQC DLL or version.
Init Failed Initialisation of the specified Chemistry Model ((PHREEQC Model Configuration) has been attempted but failed.
UseCFE Tickbox If this is ticked, then the CFE (Constrained Free Energy) tab page will appear.
  • If CFE is not available, this ticked box will be greyed out.
  • This option allows a portion of a species to be locked up and not allowed to react.
  • Applying CFE can have a significant effect on the final composition, use of this feature requires detailed knowledge of the process chemistry.
WithBypass Display Always ticked, H2O(g) will be bypassed.
PhaseElemDeportment Tickbox If this is ticked, then the Deportment tab page will appear. This tab shows the mass movement of elements for the Solid, Liquid and Gas phases.
ShowQUnmapped Tickbox Allows the user to view the QUnmapped and associated tab pages. See Material Flow Section. This is the SysCAD species flows which are not mapped to PHREEQC species, and therefore are not taken into account in the PHREEQC calculation.
ShowQBypass Tickbox Only visible when WithBypass is ticked. Allows the user to view the QBypass and associated tab pages. See Material Flow Section. This is the SysCAD species flows which bypass the PHREEQC calculation.
ShowQRxnBypass Tickbox Only visible when WithBypass is ticked. Allows the user to view the QRxnBypass and associated tab pages. See Material Flow Section.
ShowRxnDiff Tickbox Allows the user to view the Diff tab page. This shows the difference between the mapped input stream seen by PHREEQC and the PHREEQC calculation results.
ShowPlotter Tickbox Allows the user to perform a parameter sweep using the product stream of the reactor. If this is ticked, then the ParamSweep tab page will appear.
PHREEQCInput PHREEQCInput button.png If the user clicks on this button, SysCAD will create the files PHREEQC_outputIn.pqi and PHREEQC_outputOut.pqi in the CfgFiles folder of the project. These files contain information relating to the PHREEQC input and output streams used in the model and can be opened with the PHREEQC software.
Results
TemperatureIn / Ti Calc The flash tank feed temperature.
PressureIn / Pi Calc The flash tank feed pressure.
BPE Calc The Boiling Point Elevation of the Flash Tank discharge. This is the BPE value that is used for the Flash calculations.
HeatFlow Calc Any environmental heat loss will be displayed here.
FlashT Calc The calculated temperature at the operating pressure of the Flash Tank.
FlashP Calc The calculated operating pressure of the Flash Tank.
VapourMassFlow / VQm Calc The mass flow of flashed vapour.
Flash Train Macro Model

These extra fields are only visible if the unit is part of a Flash Train.

PressureReqd / P_Reqd Calc The required flash pressure calculated by the Flash Train.
TotalPressChange / TotaldP Calc
FlashTrain Display A unique tag assigned to the Flash Train by SysCAD. Each unit in the Flash Train will have the same tag in this block.
FlashTearBlock Display Displays the name of the tear block that is part of the Flash Train.
FlashTrainEqp List This contains a list of all of the equipment tags in this Flash Train. For example, the list might be as follows:

Heat_Exchanger_2

Flash_Tank_1

PAdvBase Input Additional damping or acceleration for calculated pressure change (DP) for the iteration. DP = DP * PAdvBase when PAdvExtra=0.
PAdvExtra Input Additional damping or acceleration for calculated pressure change (DP) for the iteration. DP = DP * (PAdvBase + PAdvExtra*(VQmReqd-VQm)/Max(VQmReqd,VQm)).