Flash Tank 2 in Dynamic Mode
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Navigation: Models ➔ Energy Transfer Models ➔ Flash Tank 2 ➔ Dynamic Mode
Related Link: Flash Tank 2, 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.
Important: Note that VLE calculations are performed instantaneously on the incoming feed stream. Liquid phase from the VLE Evaluation Block (and any solids) are added to the flash tank contents if WithContents is enabled. Gas/vapour phase is immediately removed, with no storage of gas/vapour allowed in the tank. The vapour-liquor equilibrium of tank contents are not affected by subsequent changes in tank conditions (e.g. concentration, temperature, pressure).
Data Section
The default access window consists of several sections:
- FlashTank2 tab. This section contains the variables that will be visible in dynamic mode.
- Cont tab. This section allows the user to define the shape and volume of the flash tank.
- RB - Optional tab, only visible if the Reactions are enabled.
- EHX - Optional tab, only visible if the EnvironHX is enabled in the Evaluation Block.
- VLE - Only visible if the VLEquilibrium is enabled (If it is NOT enabled, then the Flash Tank will operate as a pipe)
- 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.
- 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.
- 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.
- 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.
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 SysCAD will display the UnitType or SubClass. |
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 (e.g. 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 (e.g. 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. |