Hot Flash Tie

Navigation: Models ➔ Energy Transfer Models ➔ Hot Flash Tie

Evaporative Dryer	Multi-Stage Counter Flow Tie	Hot Flash Tie

---

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 to 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 gases 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.

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.

Diagram

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.

Behaviour when Model is OFF

If the user disables the unit by unticking the On checkbox, the following actions occur:

1. When only the Product stream is connected (Vent not present)
   • The input streams will mix and reach an average temperature.
   • No water will be flashed.
   • All material will be sent to the Product stream.
2. Both Vent and Product streams are connected
   • When both outlet streams are present, the BypassAll checkbox becomes available.

BypassAll NOT checked

• The input streams will mix and reach an average temperature.
• No water will be flashed.
• All gas will be sent to the Vent stream.
• All liquids and solids will be sent to the Product stream.
• The split of solids and liquids can be adjusted using SolFracToVent and LiqFracToVent.

BypassAll checked

• No mixing occurs.
• HotFeed goes directly to the Vent stream.
• WetFeed goes directly to the Product stream.
• No heat exchange occurs.
• No water is evaporated.
• Streams retain their original temperature but are adjusted to the unit pressure.

Flowchart

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 [email protected] 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.
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
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	An automatically generated description for the unit. If text is entered in the 'EqpDesc' field on the Info tab (see below), this is displayed here. Otherwise, SysCAD will display the UnitType or SubClass.
Requirements
On	Tickbox	This variable in used to enable flashing in the unit. If this unchecked, auto flashing of water is disabled.
BypassAll	Tickbox	Visible only when both Vent and Product streams are connected. Use this option to prevent the feed streams from mixing. See Behaviour when Model is OFF for detailed behaviour.
SolFracToVent	Input	Visible only when both Vent and Product streams are connected. 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	Visible only when both Vent and Product streams are connected. Allows the user to set a proportion of the liquids to go out with the Gas stream (Liquid entrainment). The default is 0%.
OperatingP - NOTE: this pressure is applied to the (combined) feed, before sub-models (if any). DirectLink feeds, for example from Makeup Blocks, are excluded in determining the pressure. Typically the specified or calculated OperatingP pressure is also the unit operating pressure and outlet stream pressure, but in some models further changes are made to the pressure.
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 (e.g. 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 pressure and temperature of the mixture, 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 required for any stream to contribute to the total flow when calculating the mixture pressure. For example, if the total feed to the unit 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).
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.
[email protected]	Tickbox	Only visible if Phase Change at Temperature has been defined for at least one species in the project and Plant Model - Species Tab - PhaseChange@T = OFF. Allows the user to switch on any predefined phase changes at temperature in the unit.
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 than 0. If there is one makeup then X=1. If there are two makeups, then X=1 and X=2, etc.
Reactions	List	Reaction Block (RB) - Enable or disable Reactions and set the sequence in relation to the other sub-models. 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	Environmental Heat Exchanger (EHX) - Enable or disable Environmental Heat Exchange and set the sequence in relation to the other sub-models. 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	Evaporation Block (Evap) - Enable or disable the Evaporator and set the sequence in relation to the other sub-models. 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	Vapour Liquid Equilibrium (VLE) - Enable or disable Vapour Liquid Equilibrium and set the sequence in relation to the other sub-models. 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.
Discard	Input	The number of discard blocks required. Extra dropdown options Discard1, Discard2, etc. will be added to allow these to be switched on.
DiscardX	List	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 (e.g. Qm) will become visible, showing the properties of the combined feed stream. See Material Flow Section. This will be prior to any sub-model (e.g. reactions) actions.
ShowQProd	Tick Box	QProd and associated tab pages (e.g. 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

Add to 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 Model Selection for more information on adding models to the configuration file.

Insert into Project Flowsheet

Insert Unit

→

Heat Transfer

→

Tie - Hot Flash Mixer

See Insert Unit for general information on inserting units.

Example Project

Boiler & Combustion Project