View source for Filter Press

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{{Filter header table|currentpage=3}}
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{{TOC}}
== 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 ===

[[Image: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 ==

{| border="1" cellpadding="5" cellspacing="0"  
|- 
| '''Label''' || '''Required / Optional''' || '''Input /Output ''' ||  colspan="2"   | '''Number of Connections''' || '''Description'''
|- 
| &nbsp; || &nbsp; || &nbsp; || '''Min''' || '''Max''' || &nbsp;
|-
| 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>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 (i.e. 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> \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>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 (i.e. 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> \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>\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> \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>\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> \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.

{| border="1" cellpadding="5" cellspacing="0" 
|-
|Width=100|'''Material''' ||Width=100|'''Feed'''||Width=100|'''Wash Water'''||Width=100|'''Cake'''||Width=100|'''Filtrate''' ||Width=100|'''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      ||&nbsp;          ||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 ==

[[Image: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:

# '''[[#Filter Press Page|FilterPress]]''' tab - Contains general information relating to the unit.
# '''[[#WashCalc|WashCalc]]''' tab - {{Available139|30498}} Optional second tab which allows the user to specify parameters for wash water requirement calculations.
#{{ShowQout|Cake}}
#{{ShowQout|Filtrate}}
# '''[[Common Data Sections#Common Data on Info Tab Page|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 Table|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.

===Filter Press Page===
'''Unit Type: FilterPress''' - The first tab page in the access window will have this name.

{|   border="1" cellpadding="5" cellspacing="0" align="center"
||<div style="text-align: center;">'''Tag (Long/Short)'''</div>||<div style="text-align: center;">'''Input / Calc/ Options'''</div>||<div style="text-align: center;">'''Description'''</div>
|-
{{Common Data on First Tab Page}} 
|-
|  colspan="3" font style="background: #ebebeb"    |

=== 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%.
|-
|font style="background: #ebebeb" colspan="3" |&nbsp; 
|-
|rowspan="3" valign="top"|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.  <br>'''Note'''<nowiki>: If the user specifies 1%, then the filtrate stream will contain 1% of the solids in the feed.</nowiki>
|-
| 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||{{Available139|30498}} Allows model to calculate required wash water. When selected, the '''WashCalc''' tab page will become visible.
|-
|  colspan="3" font style="background: #ebebeb"    |

=== Wash Efficiency ===
|-
|rowspan="4" valign="top"| 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 || {{Available139|30316}} Use a constant volume-based wash efficiency for the filter.
|-
| Based on Volume Wash Ratio || {{Available139|30316}} 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}}
|-
|  colspan="3" font style="background: #ebebeb"    |

=== Options===

{{ShowQout DataSection|Cake}}
{{ShowQout DataSection|Filtrate}}
|-
||TrackStatus||Tickbox||Allows warning messages be displayed if requirements are not met. For example, if the required and actual wash efficiencies are different.
|-
|  colspan="3" font style="background: #ebebeb"    |

=== Results ===
|-
| Cake.SolidFrac / Cake.Sf ||  font style="background: #ebebeb" | Calc || The calculated percentage of solids in the filter cake.
|-
| Cake.SolidConc25 ||font style="background: #ebebeb"| Calc || Displays the concentration of solids in the final Cake from the Filter Press at 25°C.
|-
| Filtrate.SolidFrac / Filtrate.Sf ||  font style="background: #ebebeb" | Calc || The calculated percentage of solids in the filtrate.
|-
| Filtrate.SolidConc25 ||font style="background: #ebebeb"| Calc || Displays the concentration of solids in the filtrate from the Filter Press at 25°C.
|-
|  colspan="3" font style="background: #ebebeb" |''Calculated Wash Values (Mass Basis)''
|-
| WashRatio ||  font style="background: #ebebeb" | Calc || The ratio of Wash Water to Feed Liquor in the un-washed cake on a mass flow basis.<br>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 ||  font style="background: #ebebeb" | Calc || The ratio of Wash Water to Solids in the feed to the Filter Press on a mass flow basis.
|-
| WashEfficiency / WashEff ||  font style="background: #ebebeb" | 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 ||  font style="background: #ebebeb" | Calc || The calculated single volume wash efficiency, based on the actual Wash Efficiency and Wash Ratio.<br> SingleWashEff = 1-(1-WashEff)^(1/WashRatio)<br> If this number is different to the required efficiency, and the TrackStatus box is ticked, then the unit will flag a warning.
|-
| WashWaterToCake.Qm || font style="background: #ebebeb" | Calc || The mass flow of wash water which ends up in the final cake.
|-
| FeedLiquorToCake.Qm || font style="background: #ebebeb" | Calc || The mass flow of feed liquor which ends up in the final cake.
|-
|  colspan="3" font style="background: #ebebeb" |''Calculated Wash Values (Volume Basis)''
|-
|  colspan="3" font style="background: #ebebeb" | (note: all volume flows are calculated at the product temperature)
|-
| VolWashRatio ||  font style="background: #ebebeb" | Calc || {{Available139|30186}} The ratio of Wash Water to Feed Liquor in the un-washed cake on a volume flow basis.<br>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 ||  font style="background: #ebebeb" | Calc || {{Available139|30498}} The ratio of '''volume''' of Wash Water to '''mass''' of Solids in the feed to the Filter Press.
|-
| VolWashEfficiency / VolWashEff ||  font style="background: #ebebeb" | Calc || {{Available139|30316}} 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 ||  font style="background: #ebebeb" | Calc || {{Available139|30316}} The calculated single volume wash efficiency, based on the actual Wash Efficiency and Wash Ratio.<br> VolSingleWashEff = 1-(1-VolWashEff)^(1/VolWashRatio)<br> If this number is different to the required efficiency, and the TrackStatus box is ticked, then the unit will flag a warning.
|-
| FeedLiquorToCake.Qv || font style="background: #ebebeb" | Calc || {{Available139|30316}} The volume flow of feed liquor which ends up in the final cake, calculated at the feed liquor temperature.
|-
|  colspan="3" font style="background: #ebebeb" |''Calculated Wash Values''
|-
| RemainingLiquor / RemainLiq ||  font style="background: #ebebeb" | 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||  font style="background: #ebebeb"   |Display||The Component/species chosen for the calculation of Wash efficiency on a concentration base.
|-
||CompWashEfficiency / CompWashEff|| font style="background: #ebebeb"   |Calc||The calculated wash efficiency of the unit for the chosen component. 

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

|}

=== WashCalc ===

{{Available139|30498}}  This page is only visible if the '''TargetWashCalc''' option is chosen on the first tab page.

{|   border="1" cellpadding="5" cellspacing="0"
|    Width=200|'''Tag (Long/Short)''' || Width=150|'''Input / Calc'''||'''Description/Calculated Variables / Options'''
|-
|  colspan="3" font style="background: #ebebeb"    |'''Calculation of wash required to achieve a Target condition'''
|-
|  colspan="3" font style="background: #ebebeb"    |'''WashCalc...'''
|-
|  colspan="3" font style="background: #ebebeb"    |'''Requirements'''
|-
|  valign="top" rowspan="4"  |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).
|- 
|  valign="top" rowspan="3"  |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 [[Demand|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|| font style="background: #ebebeb"   |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|| font style="background: #ebebeb"   |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|| font style="background: #ebebeb"   |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|| font style="background: #ebebeb"   |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).
|- 
|  colspan="3" font style="background: #ebebeb"    |'''Calculated Wash Flow Demand'''
|-
|WashWater.QvReqd||  font style="background: #ebebeb"   |Calc||The required volume flow of wash water in order to achieve the Target Ratio.
|-
|WashWater.QmReqd||  font style="background: #ebebeb"   |Calc||The required mass flow of wash water in order to achieve the Target Ratio.
|-
|WashWater.Qm||  font style="background: #ebebeb"   |Calc||The actual mass flow of wash water.
|-
|WashWater.Error||  font style="background: #ebebeb"   |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 ==

{{Adding Model to a Project | DllName=Separation | DllSubGroup=Separation | UnitOp=Filter - Filter Press | Group=Mass Separation}}