Tank

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Navigation: Models -> General Models

Related Links: Tank - Dynamic Mode

This section is for the Tank model when used in Steady State, mode. For help on the Tank model in Dynamic mode, please see Tank - Dynamic Mode (There are significant differences in the tank behaviour between Steady State and Dynamic).

General Description

In Steady State the tank model is very similar to the tie model. When materials are mixed in the tank, a homogeneous product is produced.

Available Sub-Models

Evaluation Block:

  1. Makeup Blocks (one or more) may be enabled in a Tank. This allows the user to control the addition of streams such as reagents, water, air, etc to the tank, often without having to use a PID or General controller.
  2. The Reaction Block (RB) allows the user to configure any number of reactions within the tank.
  3. The Environmental Heat Exchanger Block allows the user to add or remove energy from the tank using a number of different methods.
  4. The Evaporation Block allows the user to set the evaporation of either water only or a mixture of water and all other species that are specified as both liquid and vapour.
  5. The Vapour Liquid Equilibrium Block will attempt to ensure that the vapours and liquids of the selected species will be in equilibrium in the Tank. For example, if the equilibrium species is water and the tank is at atmospheric pressure, then SysCAD will maintain the temperature at, or below, the saturated temperature of 99.97°C by evaporating water if required.
  6. Discard Blocks (one or more) may be enabled in a Tank. This allows the user to control the discarding of material from the Tank, usually without having to use a PID or General controller. This is available in Build 138 or later.

Options:

  1. The General Model (GM) may be enabled in the tank in Steady State, allowing the user to control the split between the outgoing stream flows.
  2. The Thermal Split may also be enabled in Steady State IF the General Model is enabled. This option is used to adjust the temperatures of the outgoing streams from the unit.
  3. The Heat Exchanger (HX) may be enabled. The user must also connect links to the HX input and the HX output. The Heat Exchange page needs to be configured with the relevant heat exchange area and overall heat transfer coefficient. The model combines all of the incoming streams, performs any reactions, and then carries out the heat exchange operation. Please note that the fluid in the heat exchanger will transfer energy via sensible heat ONLY. There is NO condensing or boiling in the heat exchanger.

Model Procedures

Model Procedures allows the user to implement code directly within the Tank.

To enable this, on the Info tab page tick the "Procedures" tickbox.

Diagram

Tank.jpg

The diagram shows a drawing of the tank, with a number of connecting streams. When the user inserts the tank 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. In dynamic mode, you can set the connection height of the links.

Inputs and Outputs

Label Required
Optional
Input
Output
Number of Connections Description
Min Max.
Input 1 Required In 0 20 General purpose inlet
Output 1 Required Out 0 20 General purpose outlet
HX_in Optional In 0/1* 1 Heat exchanger inlet. *This is required only if the HX block is selected.
HX_Out Optional Out 0/1* 1 Heat exchanger outlet. *This is required only if the HX block is selected.


Model Theory

In Steady State, all the input streams (excluding the HX streams) are perfectly mixed, then any sub-model actions occur on the mixture. This is very similar to the Tie model.

Flowchart

The following flowchart shows the sequence of events if any Evaluation Block sub-model options or the HX Block are enabled:

Tank-ProBal.png

Data Sections

Summary of Data Sections

The tank access window may consist of a number of sections. This number may increase or decrease, based on user configuration and / or number of species.

  1. Tank-1 tab - Contains general information relating to the unit.
  2. PC - Optional tab that is visible if EB.Solubility.On and/or EB.PhaseChange@T.On is enabled on the first tab.
  3. RB - Optional tab, only visible if the Reactions are enabled in the Evaluation Block.
  4. HX - Optional tab, only visible if streams (in and out) have been connected to the Tank.HeatExchange IO connection ports.
  5. EHX - Optional tab, only visible if the EnvironHX is enabled in the Evaluation Block.
  6. Evap - Optional tab that is visible if Evaporator is enabled.
  7. VLE - Optional tab, only visible if the VLEquilibrium is enabled in the Evaluation Block.
  8. MU - Optional tab, or multiple tabs if more than 1 Makeup is selected. Only visible if one of more Makeups are enabled in the Evaluation Block.
  9. DB - Optional tab, or multiple tabs if more than 1 Discard Block is selected. Only visible if one of more Discard Blocks are enabled in the Evaluation Block. Only available in Build 138 or later.
  10. Split - Optional tab, only visible if SplitFlows (or General Model) is enabled.
    • This tab is only available for Steady State mode.
  11. SplitT - Optional tab, only visible if SplitThermal (or General Thermal Model) is enabled.
    • This may only be enabled after GM has been enabled.
    • This tab is only available for Steady State mode.
  12. QFeed - Optional tab, only visible if ShowQFeed is enabled. This page shows the properties of the mixed stream as the feed to the tank. If user has specified a required pressure in the tank, the mixed feed will be set to this pressure. This may cause the temperature of the mixture to change if the delta P is significantly different.
  13. QProd - Optional tab, only visible if ShowQProd is selected. This page shows the properties of the mixed output stream as the product before separation to outlet streams of the tank.
    • This is after any Evaluation Block sub-models or the HX are evaluated, but before flow splits.
    • This tab is only available for Steady State mode.
  14. Info tab - Contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
  15. MP tab - Optional tab, only visible if Procedures have been enabled on the Info tab page.
  16. Links tab, contains a summary table for all the input and output streams.
  17. Audit tab - Contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.
  18. Additional fields are shown in Dynamic mode. These are described in the Tank - Dynamic Mode.

Tank Page

Unit Type: Tank-1 - The first tab page in the access window will have this name.

Tag (Long/Short) Input/ Calc Description

Common Data on First Tab Page

Requirements

OperatingP - NOTE: this pressure is applied at QFeed, before sub-models.
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 (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.
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).

ResTime (Residence Time)

Volume Input The operating volume of the tank. This will be used to calculate the apparent residence time in the tank. In ProBal this is based on the QProd volumetric flow from the tank. In Dynamic mode it is based on the flow into the Tank Content.
Slurry Calc The residence time of the slurry in the tank.
Total Calc The residence time for the slurry and the vapours in the tank. If there are any vapours in the Product discharge, then this value will be smaller than the Slurry figure.

EB (Flow Evaluation Block)

Solubility.On Tickbox Only visible if Solubility has been defined for at least one species in the project. Allows the user to switch on any predefined solubility curve to adjust the composition of material in the unit.
PhaseChange@T.On Tickbox Only visible if Phase Change at Temperature has been defined for at least one species in the project. Allows the user to switch on any predefined phase changes at temperature in the unit.
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.
Note: If the user chooses On-AutoSequence then SysCAD will determine the sequence of the sub-models. The sequence followed will be MU1, MU2, etc., RB, EHX, Evap, VLE, DB1, DB2, etc.
Makeups Input The number of makeup blocks required. Extra dropdown options Makeup1, Makeup2, etc will be added to allow these to be switched on and off and prioritised in relation to the other sub-models.
MakeupX List This can be used to switch the Makeup Block (MU) on or off and prioritise it in relation to the other sub-models. If this is 'On' then the associated page, MUX becomes visible and may be configured.
Note: This field is only visible if the entry for 'Makeups' is greater then 0. If there is one makeup then X=1. If there are two makeups, then X=1 and X=2, etc.
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.
HeatXChg List This can be used to switch on the Heat Exchanger (HX). If this is 'On' then the associated page, HX becomes visible and may be configured.
Note: The user does not have to configure the heat exchange, 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 becomes visible and may be configured.
Note: The user does not have to configure an environmental heat exchange, even if this block is checked.
Evaporation List This can be used to switch on the Evaporation Block (Evap). If this is 'On' then the associated page, Evap becomes visible and may be configured.
Note: The user does not have to configure an evaporator, even if this block is checked.
VLEquilibrium List This can be used to switch on Vapour Liquid Equilibrium (VLE). If this is 'On' then the associated page, VLE becomes visible and may be configured.
Note: This option may automatically adjust the species make-up.
Discards Input Only available in Build 138 or later. The number of discard blocks required. Extra dropdown options Discard1, Discard2, etc will be added to allow these to be switched on.
DiscardX List Only available in Build 138 or later. This can be used to switch the Discard Block (DB) on or off and prioritise it in relation to the other sub-models. If this is 'On' then the associated page, DBX becomes visible and may be configured.
Note: This field is only visible if the entry for 'Discards' is greater than 0. If there is one discard then X=1. If there are two discards, then X=1 and X=2, etc.

Options

SplitFlows Tick Box This can be used to enable the Flow separate for output streams. If this box is checked then the associated page, Split, becomes visible and may be configured.
Notes:
  1. This option is used to adjust the outgoing streams from the unit. It cannot be changed while the model is solving.
  2. This option is not available in Dynamic mode.
SplitThermal Tick Box This option is only visible if the SplitFlows option has been chosen. This can be used to enable the uneven Energy distribution for output streams. If this box is checked then the associated page, SplitT, becomes visible and may be configured.
Notes:
  1. This option is used to adjust the temperatures of the outgoing streams from the unit. It cannot be changed while the model is solving.
  2. This option is not available in Dynamic mode.
ShowQFeed Tick Box QFeed and associated tab pages (eg Sp) will become visible, showing the properties of the combined feed stream. See Material Flow Section. This will be prior to any sub-model (eg reactions) actions.
ShowQProd Tick Box QProd and associated tab pages (eg Sp) will become visible, showing the properties of the products. See Material Flow Section. This will be after the actions of any sub-models and before any flow splits with the GM model. This option is not available in Dynamic mode.

Dynamic Mode Data Sections

The fields which appear in the access window for the tank in Dynamic mode only are shown in Tank - Dynamic Mode.

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

 

DLL:

Basic1.dll

Units/Links

Process: Tank(1)

or

Group:

General

Units/Links

Process: Tank(1)

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


Insert into Project

 

Insert Unit

Process

Tank(1)

See Insert Unit for general information on inserting units.

Hints and Comments

  1. If the user configures the GM, and then at a later stage adds or removes a stream (input or output), this may have an impact on the GM configuration. It is recommended that the user check the GM every time a stream change is made.
  2. In Steady State, the Tie model is almost identical to the tank model, except that the Tie does not have the Heat Exchanger (HX) sub-model.
  3. In Steady State, the tank model can be used with Demand.
  4. There may be mass entering or leaving the tank via the Reaction Block source or sink, so if the outgoing mass is not the same as the incoming mass, this may be a place to check first.
  5. If the user 'Resets' or uses the 'Empty Process' SetState option, then all connecting flanges will also be set to zero flow.
  6. If the user defined pressure is very different to the feed stream pressure, then this may cause the temperature change to be quite significant. If the inlet temperature is already high, then it is possible for the temperature to go above the critical temperature of water. In this case, the unit will return an energy imbalance error message. To avoid this issue, please consider using the Flash Tank so that VLE, T and P can be solved simultaneously in an iterative process.