Thickener 2
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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:
- 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.
- 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:
- 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.
- The resulting flows are mixed into the existing clarified liquid and mud bed volumes.
- 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.
- 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:
- Thickener2 - contains general information relating to the unit.
- Results - displays a summary of current parameters for the unit.
- PC - Optional tab that is visible if EB.Solubility.On and/or [email protected] is enabled in the Evaluation Block.
- RB - Optional tab, only visible if the Reactions are enabled in the Evaluation Block.
- EHX - Optional tab, only visible if the EnvironHX is enabled in the Evaluation Block.
- 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.
- 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.
- Bed - Optional tab, only visible if ShowBed is enabled. This page shows the contents of the Thickener Bed.
- CL - Optional tab, only visible if ShowCL is enabled. This page shows the contents of the Clarified Liquid.
- 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.
- 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.
- 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.
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
- 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.
- 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.