Filter Press

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Navigation: Models ➔ Mass Separation Models ➔ Filter Press


General Description

The filter press is used to separate the solids from the liquids in the feed stream. There is the facility to wash the solids using wash water. This water will displace a percentage of the liquid in the cake from the filter press.

The user defines the following parameters:

  • The amount of moisture retained in the filter cake,
  • The amount of solids reporting to the filtrate,
  • The fraction of wash water that bypasses the filter cake, and
  • The required wash efficiency. The wash efficiency may be specified as either an overall wash efficiency, or as a single volume wash efficiency.

If the user specifies an constant wash efficiency, then the model will use this value to calculate the percentage of the feed liquid remaining in the washed cake. For example, an constant wash efficiency of 100% represents complete displacement of the feed liquor from the filter cake. If the constant wash efficiency is set at 80%, then 20% of the cake moisture will consist of feed liquor.

If the user specifies a single volume wash efficiency then the model will use this value together with the wash ratio to calculate the percentage of feed liquid remaining in the cake.

If there is no Washings stream connected to the Filter Press, then all of the filtrate and the wash water from the unit will report to the Filtrate stream. In this case the wash water will dilute the Filtrate stream.

If the user connects the 'Washings' stream to the unit, then the liquor from the washing stage will report to the washing stream.

Diagram

Filter-Press-Image001.gif

The diagram shows the default drawing of the Filter Press, with all of the streams that are available for operation of the unit. The user does not have to connect a stream to the 'Wash Water' or 'Washings' connections, as the Filter Press will operate without wash water. The user may have a wash water stream without a washings stream, as the wash water which does not remain in the cake will report to the Filtrate stream.

The physical location of the streams connecting to the Filter Press 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 1 Required In 1 20 The slurry feed to the Filter Press
Wash Water Optional In 0 10 Wash water to the Filter Press.
Filtrate Required Out 1 1 Filtrate outlet from the unit.
Cake Required Out 1 1 Solids outlet from the unit.
Washings Optional Out 0 1 Wash stream outlet.
Vent Optional Out 0 1 Vent Stream (Vapour Only).

Behaviour when Model is OFF

If the user disables the unit, by un-ticking the On tick box, then the following actions occur:

  • The field MassFracToCake becomes visible and the user may set the fraction of the feed stream that reports to the 'Cake' outlet. The default is 100%.
  • All streams connected to the 'Feed' inlet will flow out of the 'Cake' outlet, unless the user has changed the above field from 100%. In which case the user defined fraction of the Feed will report to the Filtrate stream;
  • All streams connected to the 'Wash Water' inlet will flow straight out of the 'Washings' outlet, if connected, otherwise out of the 'Filtrate' outlet;
  • Normally no mixing will occur. If the user sends some, or all, of the Feed to the Filtrate stream, then this will mix with the Wash stream, if the Washings stream is not connected.

So basically, the unit will be 'bypassed' without the user having to change any connections.

Model Theory

The Filter Press is based on user defined variables that define the solids / liquids split, as well as the efficiency of the washing action.

The user may specify a fraction of the wash water to bypass the filter cake. This amount of wash water will not be involved in the displacement of feed liquor from the filter cake and will not be used in any of the wash efficiency calculations.

The user may specify the wash efficiency of the filter in four ways (volume based methods are only available in recent versions of Build 139):

NOTE: For the volume flows calculated, volume is calculated at the product temperature (not the feed wash temperature).

(1) Constant Wash Efficiency (by Mass)

In this case, the calculation used to determine the amount of feed liquid remaining in the washed cake is simply:
[math]\displaystyle{ R = 1 - E }[/math]
where
R = Mass Fraction of Feed liquid remaining in Washed Cake
E = Wash Efficiency
If there is sufficient wash water to replace the required amount of feed liquor (ie. mass of wash water >= mass of unwashed feed liquor), then the amount of wash water does not affect the wash efficiency.
If mass of wash water < mass of unwashed feed liquor, then the maximum wash efficiency is:
[math]\displaystyle{ \frac {\mbox{Mass of Wash Water}}{\mbox{Mass of Cake Liquor prior to washing}} }[/math]

(2) Constant Wash Efficiency (by Volume)

In this case, the calculation used to determine the amount of feed liquid remaining in the washed cake is simply:
[math]\displaystyle{ R = 1 - E }[/math]
where
R = Volume Fraction of Feed liquid remaining in Washed Cake
E = Wash Efficiency
If there is sufficient wash water to replace the required amount of feed liquor (ie. mass of wash water >= mass of unwashed feed liquor), then the amount of wash water does not affect the wash efficiency.
If mass of wash water < mass of unwashed feed liquor, then the maximum wash efficiency is:
[math]\displaystyle{ \frac {\mbox{Mass of Wash Water}}{\mbox{Mass of Cake Liquor prior to washing}} }[/math]

(3) Based on Wash Mass Ratio

In this case the washing efficiency of the filter depends on both the single wash efficiency and the mass ratio of wash water to residual cake moisture. The formula used is:
[math]\displaystyle{ \cfrac{R}{100} = \left(1 - \cfrac{E}{100}\right)^n }[/math]
where
R = Percentage of Feed liquid mass remaining in Washed Cake
E = Percentage Single Wash Efficiency
n = mass wash ratio = [math]\displaystyle{ \frac {\mbox{Mass of Wash Water}}{\mbox{Mass of Cake Liquor prior to washing}} }[/math]
Note: If there are no solids in the Wash Water stream then the wash ratio is the same for the washed cake.

(4) Based on Wash Volume Ratio - Reference 1

In this case the washing efficiency of the filter depends on both the single volume wash efficiency and the volume ratio of wash water to residual cake moisture. The formula used is:
[math]\displaystyle{ \cfrac{R}{100} = \left(1 - \cfrac{E}{100}\right)^n }[/math]
where
R = Percentage of Feed liquid volume remaining in Washed Cake
E = Percentage Single Volume Wash Efficiency
n = volume wash ratio = [math]\displaystyle{ \frac {\mbox{Volume of Wash Water}}{\mbox{Volume of Cake Liquor prior to washing}} }[/math]
Note: If there are no solids in the Wash Water stream then the wash ratio is the same for the washed cake.

This model is designed to emulate a Filter Press, which is normally operated on a batch basis:

Step 1. The feed stream containing liquids and solids is sent to the Filter Press for a given length of time. During this time, the filtrate is removed and sent on to the next process. The filter cake, with retained moisture, remains in the unit.
Step 2. The feed to the Filter Press is stopped and the cake is washed with a wash water stream. The washings stream may either be combined with the filtrate, or sent to a different destination.
Step 3. The washed cake is removed from the unit.

Therefore, the liquid in the filtrate stream from the Filter Press will consist entirely of feed liquor. The washings stream will contain the feed liquor that was displaced from the cake as well as the excess wash water.

The solids reporting to the filtrate will be divided between the filtrate and washings streams, in proportion to the stream flows.

Example

The Filter Press shown in the Diagram in 2 is configured to give 10% moisture in the cake, 1% of the feed solids to the filtrate, and 90% constant washing efficiency. The table below shows the material flows around the Filter Press with this configuration.

Material Feed Wash Water Cake Filtrate Washings
H2O(l) 9.4 5.0 1.09 8.37 4.94
NaCl(aq) 0.6 0.0 0.01 0.53 0.06
Total Liquid 10.0 5.0 1.1 8.9 5.0
Solids 10.0   9.9 0.064 0.036
Total Mass 20.0 5.0 11.0 8.964 5.036

The amount of liquor from the feed stream which reports to the Filtrate is reduced by the percentage moisture retained in the cake, in this case 1.1t/h. The wash water stream then displaces 90% of this moisture into the washings stream.

References

1. Merritt, R.C, The Extractive Metallurgy of Uranium

Flowchart

Filter-Press-Image003.gif

Data Sections

The default sections and variable names are described in detail in the following tables. The default Filter Press access window consists of 3 sections:

  1. FilterPress tab - Contains general information relating to the unit.
  2. WashCalc tab - Only available in Build 139.30498 or later. Optional second tab which allows the user to specify parameters for wash water requirement calculations.
  3. QCake - Only available in Build 139 or later. Optional tab, only visible if ShowQCake is enabled. This page shows the properties of the Cake stream. The tags in the QCake tab are valid even when the ShowQCake option is not selected.
  4. QFiltrate - Only available in Build 139 or later. Optional tab, only visible if ShowQFiltrate is enabled. This page shows the properties of the Filtrate stream. The tags in the QFiltrate tab are valid even when the ShowQFiltrate option is not selected.
  5. Info tab - Contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
  6. Links tab, contains a summary table for all the input and output streams.
  7. Audit tab - Contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.

Filter Press Page

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

Tag (Long/Short)
Input / Calc/ Options
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 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 unit class ID.

Requirements

On Tick box Switch the model on or off. If the unit is 'Off' then by default all Feed reports to the Cake outlet and all wash streams report to the Filtrate stream. If the user specifies a value (less than 100%) in the MassFracToCake field, then some feed may report to the Filtrate stream.
MassFracToCake_WhenOff / MassFracToCake Input This field becomes visible when the unit is switched off. The user may set the fraction of the feed stream that reports to the Cake outlet. The default is 100%.
 
Method SolidsToFiltrateFraction Specify the percentage of solids in the feed that report to the filtrate. If a washings stream is connected then this fraction of solids will be the total which reports to the filtrate and the washings stream in proportion to their flows.
FiltrateConcAt25C Specify the required filtrate solids concentration at 25°C.
SolidsFractionInFiltrate Specify the solids fraction in the filtrate.
SolidsToFiltrate Input The required percentage of the feed solids that reports to the filtrate - visible with SolidsToFiltrateFraction method.
Note: If the user specifies 1%, then the filtrate stream will contain 1% of the solids in the feed.
FiltrateSolidConc25Reqd Input The required filtrate solids concentration, measured at 25°C - visible with FiltrateConcentration method.
FiltrateSolidFracReqd Input The required fraction of solids in the filtrate - visible with SolidsFractionInFiltrate method.
CakeMoistReqd Input The required percentage of liquids in the filter cake.
WashWaterBypass Input The fraction of wash water that bypasses the filter cake. This will emulate wash water "channeling" through the filter cake.
TargetWashCalc Tickbox Only available in Build 139.30498 or later. Allows model to calculate required wash water. When selected, the WashCalc tab page will become visible.

Wash Efficiency

WashEfficiencyMethod / WashEffMethod Constant Efficiency Use a constant mass-based wash efficiency for the filter.
Based on Wash Ratio Use the single wash efficiency, together with the ratio of wash water to cake moisture, mass wash ratio, to determine the actual wash efficiency of the filter.
Constant Volume Efficiency Only available in Build 139.30316 or later. Use a constant volume-based wash efficiency for the filter.
Based on Volume Wash Ratio Only available in Build 139.30316 or later. Use the single volume wash efficiency, together with the ratio of wash water to cake moisture, volume wash ratio, to determine the actual wash efficiency of the filter.
WashEfficiencyReqd / WashEffReqd Input The constant mass-based wash efficiency - visible with the Constant Efficiency wash method. For example, 90% wash efficiency means that the liquid in the cake consists of 90% wash water and 10% feed liquor by mass.
SingleWashEffReqd Input The single wash efficiency - visible with the Based on Wash Ratio wash method. In this case, 90% single wash efficiency may give a final wash efficiency of more or less than 90% depending upon the mass ratio of wash water to cake moisture.
VolWashEfficiencyReqd / VolWashEffReqd Input The constant volume-based wash efficiency - visible with the Constant Volume Efficiency wash method. For example, 90% wash efficiency means that the liquid in the cake consists of 90% wash water and 10% feed liquor by volume.
VolSingleWashEffReqd Input The single volume wash efficiency - visible with the Based on Volume Wash Ratio wash method. In this case, 90% single volume wash efficiency may give a final wash efficiency of more or less than 90% depending upon the volumetric ratio of wash water to cake moisture.
WashComponent / WashComp Input Choose Component/species from the drop down list for the calculation of Wash efficiency on a concentration base. This calculation is for display purposes only.
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 (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).

Options

ShowQCakeTickbox Only available in Build 139 or later. When selected, the QCake and associated tab pages (eg Sp) will become visible, showing the properties of the Cake stream. See Material Flow Section. Tags in the QCake tab can be used for controllers (eg: PGM files) and reports even when this option is not selected.
ShowQFiltrateTickbox Only available in Build 139 or later. When selected, the QFiltrate and associated tab pages (eg Sp) will become visible, showing the properties of the Filtrate stream. See Material Flow Section. Tags in the QFiltrate tab can be used for controllers (eg: PGM files) and reports even when this option is not selected.
TrackStatus Tickbox Allows warning messages be displayed if requirements are not met. For example, if the required and actual wash efficiencies are different.

Results

Cake.SolidFrac / Cake.Sf Calc The calculated percentage of solids in the filter cake.
Cake.SolidConc25 Calc Displays the concentration of solids in the final Cake from the Filter Press at 25°C.
Filtrate.SolidFrac / Filtrate.Sf Calc The calculated percentage of solids in the filtrate.
Filtrate.SolidConc25 Calc Displays the concentration of solids in the filtrate from the Filter Press at 25°C.
Calculated Wash Values (Mass Basis)
WashRatio Calc The ratio of Wash Water to Feed Liquor in the un-washed cake on a mass flow basis.
Note: If there are no solids in the Wash Water, then this is also the ratio of Wash Water to Feed Liquor in the final washed cake.
SolidsWashRatio / SolWashRatio Calc The ratio of Wash Water to Solids in the feed to the Filter Press on a mass flow basis.
WashEfficiency / WashEff Calc The calculated wash efficiency, based on the mass fraction of feed liquor in the cake moisture. If this number is different to the required efficiency, and the TrackStatus box is ticked, then the unit will flag a warning.
SingleWashEff Calc The calculated single volume wash efficiency, based on the actual Wash Efficiency and Wash Ratio.
SingleWashEff = 1-(1-WashEff)^(1/WashRatio)
If this number is different to the required efficiency, and the TrackStatus box is ticked, then the unit will flag a warning.
WashWaterToCake.Qm Calc The mass flow of wash water which ends up in the final cake.
FeedLiquorToCake.Qm Calc The mass flow of feed liquor which ends up in the final cake.
Calculated Wash Values (Volume Basis)
(note: all volume flows are calculated at the product temperature)
VolWashRatio Calc Only shown in Build 139.30186 or later. The ratio of Wash Water to Feed Liquor in the un-washed cake on a volume flow basis.
Note: If there are no solids in the Wash Water, then this is also the ratio of Wash Water to Feed Liquor in the final washed cake.
SolidsVolWashRatio / SolVolWashRatio Calc Only shown in Build 139.30498 or later. The ratio of volume of Wash Water to mass of Solids in the feed to the Filter Press.
VolWashEfficiency / VolWashEff Calc Only shown in Build 139.30316 or later. The calculated wash efficiency, based on the volume fraction of feed liquor in the cake moisture. If this number is different to the required efficiency, and the TrackStatus box is ticked, then the unit will flag a warning.
VolSingleWashEff Calc Only shown in Build 139.30316 or later. The calculated single volume wash efficiency, based on the actual Wash Efficiency and Wash Ratio.
VolSingleWashEff = 1-(1-VolWashEff)^(1/VolWashRatio)
If this number is different to the required efficiency, and the TrackStatus box is ticked, then the unit will flag a warning.
FeedLiquorToCake.Qv Calc Only shown in Build 139.30316 or later. The volume flow of feed liquor which ends up in the final cake, calculated at the feed liquor temperature.
Calculated Wash Values
RemainingLiquor / RemainLiq Calc The calculated fraction of feed liquor remaining in the final washed cake. This equivalent to the 'R' value in the wash ratio calculation above.
WashComponentUsed / WashCompUsed Display The Component/species chosen for the calculation of Wash efficiency on a concentration base.
CompWashEfficiency / CompWashEff Calc The calculated wash efficiency of the unit for the chosen component.

CompWashEff = (Conc Feed - Conc Cake) / (Conc Feed - Conc wash)

WashCalc

Only available in Build 139.30498 or later. This page is only visible if the TargetWashCalc option is chosen on the first tab page.

Tag (Long/Short) Input / Calc Description/Calculated Variables / Options
Calculation of wash required to achieve a Target condition
WashCalc...
Requirements
TargetCalc Wash Ratio (Mass) The target ratio will be the mass-based wash ratio (mass of wash water/mass of cake liquor).
Wash Ratio (Volume) The target ratio will be the volume-based wash ratio (volume of wash water/volume of cake liquor).
Solids Wash Ratio The target ratio will be the solids wash ratio (mass of wash water/mass of solids in feed).
Solids Wash Ratio (Volume) The target ratio will be the solids wash ratio (volume of wash water/mass of solids in feed).
TargetControl None (Info) The required flow (WashWater.QmReqd) will be calculated but not used by the model. The required flow will be considered a target and the user will not receive any warning messages if WashWater.Qm does not equal WashWater.QmReqd.
External Control The required flow (WashWater.QmReqd) will be calculated but not used by the model. A condition warning message is given if the target is not achieved. It is up to the user to use an external controller to fetch this value.
General Demand The required flow (WashWater.QmReqd) will be passed back through the wash water feed stream using the General Demand functionality. Note: If this option is used, only 1 wash water feed stream can be connected.
WashRatioReqd Input This field is only visible if Wash Ratio (Mass) is chosen for TargetControl. The required mass-based wash ratio (mass of wash water/mass of cake liquor).
VolWashRatioReqd Input This field is only visible if Wash Ratio (Volume) is chosen for TargetControl. The required volume-based wash ratio (volume of wash water/volume of cake liquor).
SolWashRatioReqd Input This field is only visible if Solids Wash Ratio is chosen for TargetControl. The required solids wash ratio (mass of wash water/mass of solids in feed).
SolVolWashRatioReqd Input This field is only visible if Solids Wash Ratio (Volume) is chosen for TargetControl. The required solids wash ratio (volume of wash water/mass of solids in feed).
WashRatio Calc This field is only visible if Wash Ratio (Mass) is chosen for TargetControl. The actual mass-based wash ratio achieved (mass of wash water/mass of cake liquor).
VolWashRatio Calc This field is only visible if Wash Ratio (Volume) is chosen for TargetControl. The actual volume-based wash ratio achieved (volume of wash water/volume of cake liquor).
SolWashRatio Calc This field is only visible if Solids Wash Ratio is chosen for TargetControl. The actual solids wash ratio achieved (mass of wash water/mass of solids).
SolVolWashRatio Calc This field is only visible if Solids Wash Ratio (Volume) is chosen for TargetControl. The actual solids wash ratio achieved (volume of wash water/mass of solids).
Calculated Wash Flow Demand
WashWater.QvReqd Calc The required volume flow of wash water in order to achieve the Target Ratio.
WashWater.QmReqd Calc The required mass flow of wash water in order to achieve the Target Ratio.
WashWater.Qm Calc The actual mass flow of wash water.
WashWater.Error Calc The difference between the required mass flow and the actual mass flow of wash water (WashWater.QmReqd - WashWater.Qm).

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

  DLL:
Separation.dll
Units/Links Separation: Filter - Filter Press
or Group:
Mass Separation
Units/Links Separation: Filter - Filter Press

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


Insert into Project

  Insert Unit Separation Filter - Filter Press

See Insert Unit for general information on inserting units.