Flash Tank 2 in Dynamic Mode

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Navigation: Models -> Energy Transfer Models

Flash Tank 2 Flash Tank 2 in Dynamic Mode

Related Link: Flash Train Control


General Description

This section is for the Flash Tank 2 model when used in Dynamic mode.

For help on the Flash Tank model in Steady State mode and general theory on how this model operates, please see Flash Tank 2.

The Flash Tank 2 serves as Flash vessel with a simple content in the Dynamic mode:

  • The level can vary and hence Flow In is not always equal to Flow Out;
  • It is commonly used to flash off vapour by specifying a flash pressure;
  • It can be used with Shell and Tube Heat Exchanger 2 and the Flash Train Control to form flash train calculations.
  • User is allowed to define volume and shape for the flash tank.

Shape.png

Data Section

The default access window consists of several sections:

  1. FlashTank2 tab. This section contains the variables that will be visible in dynamic mode.
  2. Cont tab. This section allows the user to define the shape and volume of the flash tank.
  3. RB - Optional tab, only visible if the Reactions are enabled.
  4. EHX - Optional tab, only visible if the EnvironHX is enabled in the Evaluation Block.
  5. VLE - Only visible if the VLEquilibrium is enabled (If it is NOT enabled, then the Flash Tank will operate as a pipe)
  6. MU - Optional tab, or multiple tabs if more than 1 Makeup is selected. Only visible if one of more Makeup is enabled in the Evaluation Block.
  7. 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.
  8. 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.
  9. Info tab - Contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
  10. Links tab, contains a summary table for all the input and output streams.
  11. Audit tab - Contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.

Flash Tank 2 Page

Unit Type: FlashTank2 - 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:
  • 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) This is the only method available, user needs to specify the flash tank pressure or use a controller to adjust the pressure.
WithContents Tickbox This will add a simple contents section to the flash tank, where user can specify the shape, volume and height of the flash tank.
TargetMethod Stand Alone No Target method, the flash tank pressure will be used for the flash calculations. NOTE: Select this option when using a Flash Train Control model to balance the pressure in the flash train.
Vapour MassFlow This allows user to specify an expected flash vapour flow, and the pressure of the flash tank will be adjusted to give this targeted flow.
Condensing Duty This allows user to specify an expected condensing duty, and the pressure of the flash tank will be adjusted to meet this target duty.
VapQmReqd Input Visible with the Vapour MassFlow method, allows user to specify an expected flash vapour flow.
DutyReqd Input Visible with the Condensing Duty method, allows user to specify an expected condensing duty.
TargetDamping Input Visible with the Vapour MassFlow and Condensing Duty methods, allows user to specify the damping for the required target.
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.
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 Calc 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.

EB(Evaluation Block)...

EvaluationSequence
/ EvalSequence
Display The sequence in which the sub models (which are part of the evaluation blocks) will be calculated. The sequence is determined by the priority selection for the individual sub-models. If none are selected, the default evaluation sequence is MU,RB,EHX,VLE.
Makeups Input The number of makeup blocks required. Extra dropdown options Makeup1, Makeup2, etc will be added to allow these to be switched on.
Makeup1 List This can be used to switch on the Makeup Block (MU). If this is 'On' then the associated page, MU1 becomes visible and may be configured.
Note: This field is only visible if the entry for 'Makeups' is greater then 0.
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.
EnvironHX List This can be used to switch on the Environmental Heat Exchanger (EHX). If this is 'On' then the associated page, EHX may become visible and may be configured.
Note: The user does not have to configure an environmental heat exchange, even if this block is checked.
VLEquilibrium Display This shows that the Vapour Liquid Equilibrium (VLE) is always on for the Flash Tank2 model. The associated page, VLE may be configured.
Note: This option may automatically adjust the species make-up.

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%.

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.
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 Calc Displays the flash vapour mass flow.
FlashTrainTag Calc If the flash tank is being referenced and controlled by any Flash Train Control unit, the flash train control tag will be displayed here.

Cont Page

Tag (Long/Short) Input / Calc Description/Calculated Variables / Options

Requirements

Shape...
Type Simple No shape is defined, assumed to be a uniformed shape, therefore the level and volume are directly proportional.
LookUp Allows user to define and look up a table for volume, height and / or surface area.
Cone bottom Assumes the flash tank is made up with cylindrical body and cone bottom.
hemisphere bottom Assumes the flash tank is made up with cylindrical body and hemisphere bottom.
Volume Input The volume of the flash tank.
Height Input The height of the flash tank. This is the total height, includes Cone or hemisphere heights. Note that for hemisphere bottom shape, minimum height applies, where the Height >= radius.
ConeHeight Input Only visible with Cone Bottom Option. The height of the Cone bottom section.
Diameter Calc The diameter of the flash tank - cylindrical section.
Meas ...
Volume Calc The current volume of the flash tank contents.
VolumeFrac Calc The flash tank contents volume fraction.
Height Calc The height of the flash tank contents.
Level Calc The level of the flash tank contents.
area Calc The diameter of flash tank based on the area and assuming a circular cross-section.

LL...

Tags associated with the Look Up type are listed in the this section. Please click here for more information.

PresetData ...
UsePresetImg Tickbox PresetImg will become visible if this is enabled. The user may define the composition required in the flash tank on this tab and this composition will be used when the flash tank contents are preset.
If this is disabled, then the actual composition in the flash tank will be used to adjust the masses in the flash tank when the flash tank contents are preset.
Setpoint.Level Input The required level that is used when the flash tank contents are preset.
Safty.MaxQmRatio
Safty.MinQmRatio

Results Summary

Temperature Calc The temperature of the flash tank contents.
Density Calc The Density of the flash tank contents.
Vol Calc The volume of the flash tank contents.
Level Calc The level of the flash tank contents.
TotalMass Calc The total mass of the flash tank contents.
InitTtlMass Calc The initial total mass of the flash tank contents.
DeltaTtlMass Calc The delta total mass of the flash tank contents.
MassRateOfChange Calc The mass rate of change of the flash tank contents.
MtAcc Calc The mass accumulation in the flash tank.