Hot Flash Tie

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General Description

The Hot Flash Tie is used to mix a very hot stream, usually hot gases, with cooler streams containing water (quenching) or moist solids. The main reason for using this model it to prevent the situation where the unit mixes a very hot stream and a cooler feed stream that contains liquid water, and the resulting temperature is above the critical temperature for water. The Hot Flash Tie will flash sufficient water to prevent the situation where water exists above the critical temperature.

When the two streams mix, heat is transferred from the hot stream to heat up and, if necessary, flash the moisture in the wet stream. This is the 'automatic' flash that occurs in this unit. The user may enable other sub-models, such as reactions or Vapour Liquid Equilibrium (VLE), in the unit. All sub models will be evaluated after the initial feed mixing and 'automatic' flashing of moisture.

NOTES

  1. The Unit will only flash sufficient water achieve a mix temperature below the Critical temperature - in some cases only a part or none of the feed water may be flashed.
  2. It is recommended that the VLE sub model is enabled to ensure that the discharge mixture is at the correct saturated conditions for the given pressure and any gasses present.
  3. The behaviour of this unit is very similar to a normal Tie unit operation, with the exception that it has a built-in Water Flash reaction and has limited splitting options.

This unit operation is available in SysCAD 9.2 Builld 135.15990 or later.

Available Sub-Models

  1. Makeup Blocks (one or more) may be enabled. This allows the user to control the addition of streams such as reagents, water, air, etc to the Hot Flash Tie, often without having to use a PID or General controller.
  2. The Reaction Block (RB) allows the user to configure any number of reactions in the Hot Flash Tie.
    NOTE: The hot flash tie has a built in water flash reaction that will occur to the combined feed stream to the unit. Any user defined reactions will occur after this step.
  3. The Environmental Heat Exchanger Block allows the user to add or remove energy from the Hot Flash Tie 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 unit. For example, if the equilibrium species is water and the unit 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. This allows the user to control the discarding of material from the Hot Flash Tie, usually without having to use a PID or General controller. This is available in Build 138 or later.

Diagram

HFT.png

The diagram shows the default drawing of the Hot Flash Tie, with a number of connecting streams.

Inputs and Outputs

Label Required / Optional Input
Output
Number of Connections Description
Min Max.
Hot Feed 1 Required Input 1 20 High temperature feed stream, e.g. Hot Air.
Wet Feed Optional Input 0 10 Wet feed stream, containing water, e.g. Calciner Feed.
Product 1 Required Output 1 1 Mixed stream after flashing of water, e.g. Calcined Solids.
Vent Optional Output 0 1 Optional Vent for the gas phase, e.g. Hot Air + Flash Vapour.

Flowchart

Model-HFT-flowchart.png

Data Sections

Summary of Data Sections

  1. HotFlashTie tab - Contains general information relating to the unit.
  2. PC - Optional tab, only visible if EB.Solubility.On and/or EB.PhaseChange@T.On is enabled in the Evaluation Block.
  3. RB - Optional tab, only visible if the Reactions are enabled in the Evaluation Block.
  4. EHX - Optional tab, only visible if the EnvironHX is enabled in the Evaluation Block.
  5. Evap - Optional tab that is visible if Evaporator is enabled.
  6. VLE - Optional tab, only visible if the VLEquilibrium is enabled in the Evaluation Block.
  7. 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.
  8. 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.
  9. QFeed - Optional tab, only visible if ShowQFeed is enabled. This page shows the properties of the mixed stream as the feed to the tie.
    • This is before any Evaluation Block models are evaluated.
  10. 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 tie.
    • This is after any Evaluation Block models are evaluated, but before flow splits.
  11. Info tab - contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
  12. Links tab - contains a summary table for all the input and output streams.
  13. Audit tab - contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.

HotFlashTie Page

Unit Type: HotFlashTie - 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

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.
SolFracToVent Input Allows the user to set a proportion of the solids to go out with the Gas stream (solid entrainment). The default is 0%.
LiqFracToVent Input Allows the user to set a proportion of the liquids to go out with the Gas stream (Liquid entrainment). The default is 0%.

OperatingP

Method

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.

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.

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 Display The actual pressure used for the sum of the feeds which will also be the outlet pressure (unless further model options change the pressure).

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 Calc 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.
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.
Evaporation List This can be used to switch on the Evaporation Block (Evap). If this is 'On' then the associated page, Evap may become 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

ShowQFeed Tick Box QFeed and associated tab pages (eg Qm) 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 Qm) 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.

Results

HotFeed.MassFlow / HotFeed.Qm Result The total mass flow of the combined Hot Feed streams entering the model.
HotFeed.TemperatureIn / HotFeed.Ti Result The temperature of the combined Hot Feed streams entering the model.
HotFeed.TemperatureOut / HotFeed.To Result The temperature of the combined Hot Feed streams after providing heat to flash the water in the wet feed stream.
WetFeed.MassFlow / WetFeed.Qm Result The total mass flow of the combined Wet Feed streams entering the model.
WetFeed.TemperatureIn / WetFeed.Ti Result The temperature of the combined Wet Feed streams entering the model.
WetFeed.TemperatureOut / WetFeed.To Result The temperature of the combined Wet Feed streams after the flashing of water.
Mix.Temperature / Mix.T Result The combined Hot and Wet Feed streams temperature after flashing has occurred.
Mix.Pressure / Mix.P Result The pressure of the combined mixture.
VapFlashed.MassFlow / VapFlashed.Qm Result The amount of flashed vapour.
VapFlashed.Energy Result The energy that is required to flash any water in the wet feed streams to achieve a final temperature below the critical temperature of water. This energy is obtained from the Hot Feed stream.
In cases where there is no requirement for water to be flashed, then this value will be zero.

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

 

DLL:

HeatExchange.dll

Units/Links

Heat Transfer: Tie - Hot Flash Mixer

or

Group:

Energy Transfer

Units/Links

Heat Transfer: Tie - Hot Flash Mixer

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


Insert into Project

 

Insert Unit

Heat Transfer

Tie - Hot Flash Mixer

See Insert Unit for general information on inserting units.

Hints and Comments

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