Thickener 2

Navigation: Models ➔ Mass Separation Models ➔ Thickener 2

Related Links: Thickener

---

General Description

The Thickener 2 model is mainly used in Dynamic solver mode to represent a thickener, settler, decanter or washer. This solid-liquid separation unit model is used to separate feed slurry into two volumes within the unit representing the mud Bed and clarified liquid (CL) zones. Outflow from these volumes produces an underflow with high solids concentration and an overflow with low solids concentration.

• Reactions, Makeups, energy transfer and Solubility may be added to the combined feed stream of this unit.
• The required percentage solids in the underflow and overflow are specified. The Thickener will calculate solid/liquid split of the new feed flow into the mud bed and clarified liquid volumes according to these values.
• A specified fraction of solids and liquids in the Input stream (usually the wash stream) may be bypassed directly to the Clarified Liquid portion of the unit.
• If there is insufficient solids in the feed to the Thickener to satisfy both the underflow and overflow requirements, the unit will try to satisfy the underflow solids / liquids requirements first.

There are 2 dynamic operating modes:

1. Calculated underflow rate - The model calculates the required underflow rate to maintain the specified bed level. The underflow rate is set by the model and may not be adjusted. This is useful for projects with large step sizes that require the thickener to act as solid/liquid splitter with volume, but no control.
2. User-defined underflow rate - The underflow rate from the thickener is specified by the user. This can be input manually or via a controller in the project. This mode is useful when the project has smaller step sizes and the thickener bed level control must be emulated.

Note: The UF Pipe Demand option allows both pull and/or capacity (including batch capacity) in the underflow pipe. Where both are present it uses the minimum. When the capacity is off or unrestricted, the logic falls back to unit operation settings for that outlet.

Diagram

The diagram shows the default drawing of the Thickener, with all of the streams that have to be connected for the unit to operate.

The physical location of the streams connecting to the Thickener is unimportant. The user may connect the streams to any position on the unit.

Inputs and Outputs

Label	Required / Optional	Input /Output	Number of Connections		Description
			Min	Max
Feed	Required	In	1	20	The slurry feed to the Thickener
Input	Optional	In	0	20	The wash water or liquid input to the Thickener
Overflow	Required	Out	1	1	Thickener overflow
Underflow	Required	Out	1	1	Thickener underflow
Vent	Optional	Out	0	1	Vent Stream (Vapour Only)

Model Theory

The Thickener 2 model represents two volumes, the mud bed and the clarified liquid. These may be visualised as two independent perfectly-mixed tanks. Note that this is not a layered tank, nor is there a "turbid" zone.

Broadly, the order of calculation is:

1. Feed and Input streams are mixed (accounting for any Input stream bypasses or Feed Evaluation Block calculations) and then split into two internal streams according to the specified overflow and underflow solids fractions.
2. The resulting flows are mixed into the existing clarified liquid and mud bed volumes.
3. Material is removed from the thickener underflow depending on the operating mode:
   • With Calc UF, the degree of freedom is the UF rate. The model will maintain the target bed level by removing material from the bed (or by stopping flow to allow the level to build up).
   • With User UF, the degree of freedom is the bed level. The model will always deliver the required flowrate. If the bed runs too low, the UF will start to take from the clarified liquid volume. Using this method, a separate control on the bed level is required.
4. Finally, any residual material over the total volume of the tank is then removed from the overflow point. This is usually from the clarified liquid volume, but can include bed material if the bed level is too high.

Each iteration, the internal flows of feed material added to the mud bed and clarified liquid volumes will be at the specified solids fractions. However, the contents of these volumes (and therefore the resulting overflow and underflow streams) may differ if the underflow and overflow solids targets have been changed. The solids fractions in the two volumes will trend towards the target value as material is removed and new material is mixed in. This speed of this effect will depend on the relative flow entering the bed/CL versus the volume of the bed/CL zones.

Flowchart

The following diagram shows the sequence of events in the Thickener 2 model.

Data Sections

The default access window consists of a number of sections:

1. Thickener2 - contains general information relating to the unit.
2. Results - displays a summary of current parameters for the unit.
3. PC - Optional tab that is visible if EB.Solubility.On and/or [email protected] is enabled in the Evaluation Block.
4. RB - Optional tab, only visible if the Reactions are enabled in the Evaluation Block.
5. EHX - Optional tab, only visible if the EnvironHX is enabled in the Evaluation Block.
6. 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.
7. QEBFeed - Optional tab, only visible if ShowQEBFeed is enabled. This page shows the properties of the mixed stream as the feed to the Evaluation Block sub-model.
   • This is before any Reactions are evaluated.
8. Bed - Optional tab, only visible if ShowBed is enabled. This page shows the contents of the Thickener Bed.
9. CL - Optional tab, only visible if ShowCL is enabled. This page shows the contents of the Clarified Liquid.
10. PresetBed - Optional tab, only visible if UsePresetImg option is enabled on the first tab page under PresetData heading. Allows user to define the Preset Image composition of the Bed.
11. PresetCL - Optional tab, only visible if UsePresetImg option is enabled on the first tab page under PresetData heading. Allows user to define the Preset Image composition of the Clarified Liquid.
12. Info tab - contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
13. Links tab, contains a summary table for all the input and output streams.
14. Audit tab - contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.

Unit Type: Thickener2 - The first tab page in the access window will have this name.

Thickener2

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	Tick Box	This allows the user to enable or disable the unit.
OpMode (Only available in Dynamic)	Calc UF	The thickener model calculates the underflow rate required to maintain the bed level. This rate is set by the thickener and the user cannot set the underflow rate.
	User UF (Qm)	This operating mode allows the user to set the thickener underflow mass rate.
	User UF (Qv)	This operating mode allows the user to set the thickener underflow volumetric rate.
	UF pipe demand	This operating mode allows the thickener underflow rate to be set by the capacity setting in the underflow pipe.
UFQmReqd	Input	Only visible if OpMode = User UF (Qm). The required mass underflow rate.
UFQvReqd	Input	Only visible if OpMode = User UF (Qv). The required volumetric underflow rate.
OFSolidFracReqd	Input	The required overflow solids fraction.
UFSolidFracReqd	Input	The required underflow solids fraction.
LiqBypassFrac	Input	The fraction of liquid in the Input stream (usually wash water / liquor) that must bypass straight to the clarified liquid layer. Any material in this bypass will NOT be involved in any Evaluation Block submodels such as reactions.
SolBypassFrac	Input	The fraction of solids in the Input stream (usually wash water / liquid) that must bypass straight to the clarified liquid layer. Any material in this bypass will NOT be involved in any Evaluation Block submodels such as reactions.
(The following options are only available in Dynamic.)
Capacity.Defn	None	Only visible if OpMode = Calc UF. The thickener will operate like a steady-state unit model with no surge.
	Total Mass	Requires specification of the total mass of the thickener and the fraction occupied by the solids bed.
	Total Volume	Requires specification of the total volume and height of the thickener as well as the fraction occupied by the solids bed.
Capacity.Mass	Input	Only visible if Capacity.Defn = Total Mass. The total mass of material that the thickener can hold.
Capacity.Volume	Input	Only visible if Capacity.Defn = Total Volume. The total volume of the thickener.
Capacity.Height	Input	Only visible if Capacity.Defn = Total Volume. The total height of the thickener.
BedSizeFrac	Input	Only visible if Capacity.Defn = Total Mass or Total Volume. The target fraction occupied by the solids bed. This is the bed height used at reset of the tank conditions, or PresetData.Method = Full. For OpMode = Calc UF this is also the target bed level.
(The following options are only available in Dynamic. Available from Build 139.)
OpModeOF	OF at Level	The user can set the level from which the overflow stream is taken.
	OF pipe demand	In addition to setting the level at which the overflow stream is taken from, the thickener overflow rate to be set by the capacity setting in the overflow pipe.
OFSizeFrac	Input	The height fraction of the tank for the overflow outlet point.
OperatingP - NOTE: this pressure is applied to the (combined) feed, before sub-models (if any).
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 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).
EB (Evaluation Block) (NOTE: These submodels act on the combined feed to the thickener, EXCLUDING any material which is bypassed.)
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.
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 auto evaluation sequence followed will be the order the sub models are listed below.
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.
Evap...
Method	None	There is no evaporation from the unit.
	MassFlow	The user may specify the mass flow of water vapour from the unit.
	VolumeFlow	The user may specify the volume flow of water vapour from the unit.
MassFlowReqd / QmReqd	Input	Only visible if the evaporation method is MassFlow. The required mass flow of evaporated water from the unit.
VolFlowReqd / QvReqd	Input	Only visible if the evaporation method is VolumeFlow. The required volume flow of evaporated water from the unit.
PresetData...
UsePresetImg	Tick Box	If this is enabled then the user may use the preset image to initialise contents of the Thickener. The PresetBed and PresetCL tab pages will be available for the user to configure the compositions of both the bed and clarified liquid layers of the Thickener.
(The following fields will only be displayed if the UsePresetImg option has been enabled.)
Method	Empty	The contents of the Thickener will be emptied when Preset is enabled.
	Full	The Thickener will be full (maximum capacity) when Preset is enabled. The bed fraction is taken from BedSizeFrac.
	Mass	The user may specify the preset bed and total mass.
	Volume	The user may specify the preset bed and total volume.
	Level	The user may specify the preset bed and total level.
Temperature	Input	Only visible if the preset method is NOT set to Empty. The required temperature of the thickener contents after a Preset.
Bed.Mass	Input	Only visible if the preset method is set to Mass. The required mass of material in the bed after a Preset.
Mass	Input	Only visible if the preset method is set to Mass. The required total mass of material in the thickener after a Preset.
Bed.Volume	Input	Only visible if the preset method is set to Volume. The required volume of material in the bed after a Preset.
Volume	Input	Only visible if the preset method is set to Volume. The required total volume of material in the thickener after a Preset.
Bed.Level	Input	Only visible if the preset method is set to Level. The required level of material in the bed after a Preset.
Level	Input	Only visible if the preset method is set to Level. The required level of all material in the thickener after a Preset.
Options
ShowQEBFeed	Tick Box	If this is enabled then the unit will display the combined feed stream to the thickener evaluation block. This will NOT include any material which is bypassed.
ShowBed	Tick Box	If this is enabled then the unit will display the contents of the Bed.
ShowCL	Tick Box	If this is enabled then the unit will display the contents of the Clarified Liquid layer.
Empty_Bed	Button	Clicking on this button will empty the contents of the Bed.
Empty_CL	Button	Clicking on this button will empty the contents of the Clarified Liquid layer.
Empty_All	Button	Clicking on this button will empty the total contents of the unit - both the Bed and Clarified Liquid layers.
FillNextIter	Button	If this is clicked then the unit will be set to 100% capacity in the next step.

Results tab page

Tag (Long/Short)	Input / Calc	Description/Calculated Variables / Options
Results
(The following options are only available in Dynamic.)
BedMassReqd	Calc	Only visible when Capacity.Defn = Total Mass. The required bed mass in the thickener.
CLMassReqd	Calc	Only visible when Capacity.Defn = Total Mass. The required clarified liquid mass in the thickener.
CLMassAvail	Calc	Only visible when Capacity.Defn = Total Mass. The available mass in the thickener. This is non-zero when the thickener is filling up. During normal operation this value is zero.
CLSurgeMassAvail	Calc	Available from Build 139. Only visible when Capacity.Defn = Total Mass. The available mass of the thickener above the overflow level, based on the total capacity of the thickener and the setting of OFSizeFrac. This is zero when OFSizeFrac is at 100%.
BedVolumeReqd	Calc	Only visible when Capacity.Defn = Total Volume. The required bed volume in the thickener.
CLVolumeReqd	Calc	Only visible when Capacity.Defn = Total Volume. The required clarified liquid volume in the thickener.
CLVolumeAvail	Calc	Only visible when Capacity.Defn = Total Volume. The available volume in the thickener. This is non-zero when the thickener is filling up. During normal operation this value is zero.
CLSurgeMassAvail	Calc	Available from Build 139. Only visible when Capacity.Defn = Total Volume. The available volume of the thickener above the overflow level, based on the total capacity of the thickener and the setting of OFSizeFrac. This is zero when OFSizeFrac is at 100%.
TotalMass / Mt	Calc	The total mass of material in the thickener.
InitTtlMass / InitMt	Calc	The initial mass of material in the thickener.
DeltaTtlMass / DeltaMt	Calc	The change in mass of material in the thickener from the beginning of the run (TotalMass - InitTtlMass).
TotalVol / Vt	Calc	The total volume of material in the thickener.
Bed.Level / Lvl	Calc	The Bed level. During normal operation this will be equal to the user specified BedSizeFrac.
Level / Lvl	Calc	The thickener level. During normal operation this is 100%.
OFSurge.Level / Lvl	Calc	Available from Build 139. The overflow surge thickener level. This is 0% when Level = OFSizeFrac. This is 100% when the Level is at 100%.
MassRateOfChange / QmAcc	Calc	The net mass flow of material into the thickener.
(The following are always shown.)
BypassMassFlow / BypassQm	Calc	The mass flow of material in the bypass streams.
VentMassFlow / VentQm	Calc	The mass flow of material in the vent stream.
EvapMassFlow / EvapQm	Calc	The mass flow of water evaporated.
EvapDuty	Calc	The energy required to evaporate the required amount of water at the current temperature.
HeatFlow	Calc	The external energy added (or removed) from the unit model.
EB.FeedMassFlow / FeedQm	Calc	The total mass flow of material in the feed to the Evaluation Block (EB).
EB.FeedSolidFrac / FeedSf	Calc	The fraction of solids material in the feed to the Evaluation Block (EB).
EB.ProdSolidFrac / ProdSf	Calc	The fraction of solids material in the product from the Evaluation Block (EB).
(The following options are only available in Dynamic.)
Bed and Clarified Liquid layers
(The following parameters are shown in a table with columns for the Bed and Clarified Liquid (CL) layers.)
FeedQm	Calc	The mass flow of material into the layer.
FeedSf	Calc	The solids mass fraction of the feed to the layer.
Temperature / T	Calc	The temperature of the layer.
TotalMass / Mt	Calc	The mass of material in the layer.
TotalVol / Vt	Calc	The volume of material in the layer.
Density / Rho	Calc	The density of the material in the layer.
SolidFrac / Sf	Calc	The solids mass fraction of the material in the layer.
LiquidFrac / Lf	Calc	The liquid mass fraction of the material in the layer.
Outlet Streams
(The following parameters are shown in a table with columns for the Underflow (UF) and Overflow (OF) streams.)
MassFlow / Qm	Calc	The mass flow of material in the stream.
VolFlow / Qv	Calc	The volume flow of material in the stream.
SolidFrac / Sf	Calc	The solids mass fraction of the stream.
Density / Rho	Calc	The density of the stream.
SolidConc	Calc	The solids concentration of the stream at product temperature.
SolidConc25	Calc	The solids concentration of the stream at 25°C.
Internal
SolFracToUF	Calc	The fraction of solids in the feed which is sent to underflow stream.
LiqFracToUF	Calc	The fraction of liquids in the feed which is sent to underflow stream.
CalcBedMassReqd	Calc	Only visible in Dynamic. The calculated required mass of material in the Bed layer.

PresetBed tab page

The PresetBed page contains a Copy to Clipboard button which copies the current temperature, pressure and composition of the Preset Bed Image to the clipboard for pasting into external programs such as Excel.

The associated DSp page is used to set the required composition of the Bed when it is Preset. This is identical in functionality to the DSp page used in Feeders.

PresetCL tab page

The PresetCL page contains a Copy to Clipboard button which copies the current temperature, pressure and composition of the Preset Clarified Liquid (CL) Image to the clipboard for pasting into external programs such as Excel.

The associated DSp page is used to set the required composition of the tank when it is Preset. This is identical in functionality to the DSp page used in Feeders.

Adding this Model to a Project

Add to Configuration File

Sort either by DLL or Group:

	DLL:	MatHand2.dll	→	Units/Links	→	Separation: Thickener - Thickener(2)
or	Group:	Mass Separation	→	Units/Links	→	Separation: Thickener - Thickener(2)

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

Insert into Project Flowsheet

Insert Unit

→

Separation

→

Thickener - Thickener(2)

See Insert Unit for general information on inserting units.

Hints and Comments

1. There may be mass entering or leaving the Thickener 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.
2. If the reaction block is enabled in the model, there may be small errors resulting in the calculation of overflow/underflow solids due to the feed composition change.