Screen 2
Navigation: Models ➔ Size Distribution Models ➔ Screen 2
General Description
The Screen 2 model allows the user to specify a single screening unit with a number of individual decks, up to a maximum of 8 decks.
The user must connect streams to the Screen 2 Undersize and at least one of the Oversize connections. The Screen 2 unit will contain as many screening decks as connections to the decks, for example:
 If the user requires 5 decks, then they may connect streams to the Undersize and to Deck1_OS, Deck2_OS, Deck3_OS, Deck4_OS and Deck5_OS.
 The user must then configure each of the 5 decks separately.
Each deck of the Screen 2 unit may be defined as a simple splitter (does not require any Size Distribution data) or as a full screening model. If the Simple mode is chosen, the solids in the screen feed need not have a size distribution, as the model will separate the solids and liquids based on a user defined split.
If a screening method is selected then the main requirement for using this option is that the Screen 2 unit feed must contain solids with size distribution information. Please see Size Distribution (PSD) and Size Configuration for more information on including a size distribution in the project.
 The model will calculate the split of solids between each deck oversize and deck undersize based on the cut point (either calculated or defined) and the size distribution of the feed to the deck.
 The user may specify different screening methods on each deck, i.e. the one deck may have a userdefined partition curve and another may use the Karra method to calculate the solids split.
 The user must define the amount of feed liquid reporting to the oversize product on each deck. The balance of the liquid will report to the undersize stream.
There are a number of screening methods available to define the solids split:
 Simple, no PSD;
 A partition curve is used to calculate the screen products;
 Whiten method;
 Karra method (Note that this method is only valid for cut apertures > 1mm),
Diagram
The diagram shows the default drawing of the Screen 2 unit, with connections to 4 screening decks. The physical location of the streams connecting to the Screen 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  10  The slurry feed to the Screen 
Undersize  1 Required  Out  1  1  The undersize from the Screen 2 unit. 
Deck1_OS  Optional  Out  0  1  The Oversize from Deck 1. 
Deck2_OS  Optional  Out  0  1  The Oversize from Deck 2. 
Deck3_OS  Optional  Out  0  1  The Oversize from Deck 3. 
Deck4_OS  Optional  Out  0  1  The Oversize from Deck 4. 
Deck5_OS  Optional  Out  0  1  The Oversize from Deck 5. 
Deck6_OS  Optional  Out  0  1  The Oversize from Deck 6. 
Deck7_OS  Optional  Out  0  1  The Oversize from Deck 7. 
Deck8_OS  Optional  Out  0  1  The Oversize from Deck 8. 
Model Theory
The model will simulate a Screen using one of the user defined methods. The Simple method does not use Size Distribution, and will not be discussed here.
All of the Size Distribution models calculate the solids separation based on the feed size distribution. The liquids separation is defined by the user as the amount of moisture reporting to the over size. The balance of the feed liquid will flow through the screen.
All of the models use a Partition Curve to determine the solids split between the Over and Under size products from the deck. This partition curve may be directly specified by the user (Partition Curve method), or it may be determined from a d_{50 } value.
The d_{50 }is defined as the particle size that has a 50% probability of reporting to either the Screen over or under size product. The majority of the particles finer than this size will report to the under size, while the majority of those coarser will report to the over size.
The Karra method will calculate the d_{50 } value based on the user specified cut aperture and screen area.
In all cases, the user must be aware that many factors may influence the screening efficiency and the actual d_{50} obtained from the physical screen.
There is no substitute for experience when specifying the expected d_{50 } from a screen. In many cases the screen d_{50} is approximately equal to the cut aperture of the screen, but this is not always the case. Many factors will influence the actual screen d_{50 }, such as:
 The screen cut aperture;
 The screening area;
 The size distribution of the screen feed, specifically
 the amount of near size material,
 the amount of half size material, and
 the amount of oversize material;
 If this is a wet screening application;
 The shape of the material in the screen feed.
The user may also specify further parameters to handle the behaviour of the large particles (> aperture size) and fine particles:
 The Maximum particle size that will report to the Screen undersize. This allows the user to take into account the fact that large particles will not pass through the screen aperture; and
 The Minimum fraction of ALL size intervals that will report to the screen Oversize. This takes into account fine particles adhering to coarse particles or following the liquid phase (in the case of wet screening) and so reporting to the screen oversize.
The following typical efficiency curve for a vibrating screen illustrates the influence of the d_{50 } value and the Maximum particles to Oversize and Minimum fraction to undersize factors:
User Defined Partition Curve
In the case of the partition curve, the model will distribute the feed material based on the user defined partition curve. The user defines the screen partition curve as the fraction of the feed to the screen reporting to the over size product. The screen model will ensure that the products follow this curve.
Whiten Method
This method is based on a model proposed by Whiten. The user may either specify:
 The d_{50} of the screen; or
 The Screen aperture and Efficiency.
The Reduced Efficiency curve to the oversize is given in equation (1):
(1) [math]\displaystyle{ \mathbf{\mathit{E_{o a i}=\cfrac{exp(\alpha x_i)1}{exp(\alpha x_i)+exp(\alpha)2}}} }[/math]
 where
 [math]\displaystyle{ \mathbf{\mathit{x_i = \cfrac{Particle Diameter_i}{d_{50}}}} }[/math]
 Particle Diameter_{i} = geometric mean of the size interval i.
 d_{50} = cutsize or separation size, the size which divides equally between oversize and undersize.
 alpha(α) = efficiency parameter. High values of α (>9) indicate good separations. (The value of α will change the slope of the screen efficiency, or partition curve.)
If the user specifies the Screen aperture and efficiency, then the model calculates the theoretical d_{50} using the following equation:
(2) [math]\displaystyle{ \mathbf{\mathit{d_{50}=\cfrac{\alpha A}{ln \left[\left(\cfrac{100}{100E}1\right)exp(\alpha)+\left(\cfrac{100}{100E}\right)2\right]}}} }[/math]
 where
 A = Nominal screen aperture.
 E = Screen Efficiency at aperture size, typically 95%.
Fines Bypass
The mass of solid material reporting to the over size product may be influenced by the amount of liquid reporting to the over size. The fine material often bypasses to the over size with the liquid, or by adhering to the coarse material.
The corrected recovery to over size is calculated using equation (3):
(3) [math]\displaystyle{ \mathbf{\mathit{E_{oci}=E_{oai}+R_f*(1E_{oai})}} }[/math]
where:
 E_{oci} = corrected recovery to the over size
 E_{oai} = actual recovery to the over size (calculated in equation (1) above)
 R_{f} = fraction of feed liquid reporting to the over size product.
Note: The R_{f} is only used to adjust the solids fine fraction to the screen oversize and NOT to set the fraction of liquid reporting to the oversize stream.
The Fraction of feed liquor reporting to the under size, C, can be found using equation (4):
(4) C = 1  R_{f}
Whiten Beta Method
This is the modified method by Whiten to accommodate some abnormal "bumps" in the fine size end of the Efficiency curve.
The Reduced Efficiency curve to the oversize is then as follows:
(5) [math]\displaystyle{ \mathbf{\mathit{E_{o a i}=C\left[\cfrac{(1+\beta\beta^*x_i)(exp(\alpha)1)}{exp(\alpha\beta^*x_i)+exp(\alpha)2}\right]}} }[/math]
 where:
 Beta (β)  is the term introduced to control the initial rise in the curve at fine sizes. If this term is set to 0 then the equation is the same form as (1) in the previous heading.
 BetaStar (β*) is derived iteratively from β so that E_{oai} = (1/2)C when d_i = d_{50}
References:
NapierMunn et al "Mineral Comminution Circuits  Their Operation and Optimisation", Chapter 12, which references:
 Whiten W.J. "Lecture notes for winter school on mineral processing." Dept. Min & Eng, University of Queensland, Aug 1966 (Lynch and Bull)
 Whiten W.J. Private communication (JKMRC), 1996.
Karra Method
This method is based on a model proposed by V.K Karra^{1} and is only valid for screen cut apertures greater than 1mm. The solids split is calculated using the d_{50} of the screen. This may either be defined by the user (when CalcMethod=d50) or calculated by the model (when CalcMethod=Area) using the physical screen dimensions and feed size distribution.
With the Karra.CalcMethod set to 'd50' the user defines the cut point of the Screen, the d_{50}. The model then calculates the solids split directly, as shown in equation (8).
With the Karra.CalcMethod set to 'Area' the user defines:
 The Screen area
 The cut aperture (> 1mm  the model will not allow the user to specify a smaller aperture), and
 Whether it is a wet screening application.
The model will then calculate the d_{50} based on these userdefined parameters and on the size distribution of the feed. This d_{50} is then used to calculate the solids split, as shown in equation (8).
The model calculates the d_{50} of the Screen from the following equations^{1}
(6) [math]\displaystyle{ \mathbf{\mathit{d_{50} = h_T * Factor * \left[\cfrac{ \left( \cfrac{Theoretical Undersize (tph)}{Screen Area (m^2)} \right)} {ABCDEFG}\right]^{0.148}}} }[/math]
 where
 The Cut aperture h_{T}, in mm, is given by (7): [math]\displaystyle{ \mathbf{\mathit{h_T=\left(h+d\right)cos\varphid}} }[/math]
 h  Aperture of square mesh, mm
 d  Wire diameter, mm
 [math]\displaystyle{ \mathbf{\mathit{\varphi}} }[/math]  Screen angle of inclination to the horizontal
 Factor is a tuning factor (default value is 1)
 the Theoretical Undersize is the mass of solids (in t/h) with sizes less than h_{T}
The modifying factors in the denominator of equation (6) are obtained as follows:
Factor A. h_{T} < 50.8mm A = 12.1286 * (h_{T})^{0.3162}  10.2991 h_{T} >= 50.8mm A = 0.3388 * h_{T} + 14.4122 Factor B. Where Q  % Oversize in feed to screen deck. Q =< 87 B = 1.6  0.012 * Q Q =< 87 B obtained from values in Nordberg reference manual. (Previously from equation: B = 4.275 + 0.0425 * Q) Factor C Where R  % half size feed to the screen deck. R =< 30 C = 0.012 * R + 0.7 30 < R < 55 C = 0.1528 (R)^{0.564} 55 =< R < 80 C = 0.0061 (R)^{1.37} R >= 80 C = 0.05 * R  1.5 Factor D. Where S is deck location, top deck S = 1, second deck S = 2 D = 1.1  0.1 * S Factor E. Wet Screening Factor, T = 1.26 * h_{T} T < 1 E = 1.0 1 =< T =< 2 E = T 2 < T < 4 E = 1.5 + 0.25T 4 =< T =< 6 E = 2.5 6 < T =< 10 E = 3.25  0.125T 10 < T < 12 E = 4.5  0.25T 12 =< T =< 16 E = 2.1  0.05T 16 < T < 24 E = 1.5  0.125T 24 =< T =< 32 E = 1.35  0.00625T T > 32 E = 1.15 Factor F F = U/1602, where U = Solids Density (kg/m^{2}) Factor G NearMesh factor G = 0.844 * (1.0  X_{n}/100)^{3.453}, where X_{n} = % near size feed to the screen deck, % in the size interval 1.25h_{T} to 0.75h_{T}
Split Efficiency
The model then uses either the calculated or user defined d_{50} of the screen to calculate the recovery to the over size in each size range (y_{i}) using the RosinRammler equation with sharpness of 5.846:
(8) [math]\displaystyle{ \mathbf{\mathit{y_i = 1exp\left(0.693147(x_i)^{5.846}\right)}} }[/math]
 where
 [math]\displaystyle{ \mathbf{\mathit{x_i = \cfrac{Particle Diameter_i}{d_{50}}}} }[/math]
 [math]\displaystyle{ Particle Diameter_i }[/math] is the geometric mean for the size interval
Notes:
 The Karra method is only valid for screen cut apertures greater than 1mm.
 When 'Area' is selected for Karra.CalcMethod the model is a form of "load based screen" and performance is a function of feed flowrate. Care should be taken, especially in steady state modelling, that the feed flowrate is representative of the expected operational flowrate.
Assumptions
 The equations are based on screening crushed stone. While the characteristics of metallic ores are very similar, this may not be true for sand and gravel applications.
 The Cut Aperture, of the screen deck is greater than 1mm.
Reference:
 V.K.Karra., "Development of a model for predicting the screening performance of a vibrating screen", CIM Bulletin, April 1979.
RosinRammler Method
This method is based on a RosinRammler type of function with the efficiency curve expression derived by Reid and Plitt.
The Efficiency curve to the oversize is given in equation (10):
(10) [math]\displaystyle{ \mathbf{\mathit{y_i' = 1exp\left(0.693147(x_i)^{m}\right)}} }[/math]
 where
 [math]\displaystyle{ \mathbf{\mathit{x_i = \cfrac{Particle Diameter_i}{d_{50}}}} }[/math]
 Particle Diameter_{i} = geometric mean of the size interval i.
 d_{50} = cutsize or separation size, the size which divides equally between oversize and undersize.
 m = sharpness parameter. High values of m for sharper separation.
References:
 L.R.Plitt, A mathematical model of the hydrocyclone classifier, CIM Bulletin, December 1976
 K.J. Reid, Derivation of an equation for classifier performance curves, Canadian Metallurgical Quarterly (1971)
Lynch Method
(11) Recovery to underflow on a corrected basis for the size interval
 [math]\displaystyle{ \mathbf{\mathit{y_i'=\cfrac{exp\left(\alpha\cfrac{d_i}{d_{50}}\right)1}{exp\left(\alpha\cfrac{d_i}{d_{50}}\right)+exp(\alpha)2}}} }[/math]
where: d_{i}  geometric mean of the size interval
 α = (1.54 * m)  0.47
 m = measure of the sharpness of separation
Note: The Lynch method is effectively the same as the simple Whiten method (without Beta), except alpha is calculated from m.
(12) The actual recovery to the underflow, y, is then calculated using the same equation for both of the above methods:
 [math]\displaystyle{ \mathbf{\mathit{y=y'+R_f(1y')}} }[/math]
where R_{f} = fraction of feed liquid reporting to the underflow product.
Reference:
L.R.Plitt, A mathematical model of the hydrocyclone classifier, CIM Bulletin, December 1976.
Del Villar and Finch Method
This method includes a term for the "fish hook" effect for entrainment.
(13) [math]\displaystyle{ \mathbf{\mathit{y_i = a_i+(1a_i)(1exp\left(0.693147(x_i)^{m}\right)}} }[/math]
 where
 [math]\displaystyle{ \mathbf{\mathit{x_i = \cfrac{Particle Diameter_i}{d_{50}}}} }[/math]
 [math]\displaystyle{ \mathit{a_i = R_f*\left(1\cfrac{Particle Diameter_i}{d_{50}}\right)} }[/math] for [math]\displaystyle{ d_i \lt d_0 }[/math]
 [math]\displaystyle{ \mathbf{\mathit{a_i = 0}} }[/math] for [math]\displaystyle{ d_i \gt d_0 }[/math]
 ParticleDiameter_{i} = geometric mean of the size interval i.
 d_{50} = cutsize or separation size, the size which divides equally between oversize and undersize.
 d_{0} = largest particle size affected by the fishhook for entrainment function.
 R_{f} = Proportion of feed liquid reporting to the over size product.
 m = sharpness parameter. High values of m for sharper separation.
Notes:
 At the finest particles the recovery approaches Rf. When Rf is equal to the liquid fraction to over size product then the finest particles are approaching the liquid split.
 If d_{0} is less than or equal to the smallest size then this method is equivalent to the RosinRammler Method.
References:
 M.Frachon, J.J.Cilliers, A general model for hydrocyclone partition curves, Chemical Engineering Journal 73 (1999)
 R.Del Villar, J.A.Finch, Modelling the cyclone performance with a size dependent entrainment factor, Minerals Engineering (1992)
Data Sections
The default access window consists of 4 or more sections,
 Screen2  The first section allows the user to enable submodels and it also contains some general information relating to Global displays for the unit.
 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.
 Evap  Optional tab that is visible if Evaporation is enabled.
 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.
 DB  Optional tab, or multiple tabs if more than 1 Discard Block is selected. Only visible if one of more Discard Blocks are enabled in the Evaluation Block. Only available in Build 138 or later.
 QEBFeed  Optional tab, only visible if ShowQEBFeed is enabled. This page shows the properties of the mixed stream as the feed to the Screen.
 This is before any Evaluation Block models are evaluated.
 Deck n  Each screening deck will be displayed on a separate tab, Deck1, Deck2, etc. These tabs will display the relevant input and results fields for the that particular deck of the screen.
 PartCrv n  There is a Partition Curve tab for each of the screen decks.
 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.
Screen 2
Unit Type: Screen2  The first tab page in the access window will have this name.
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  Tickbox  This variable in used to turn the unit ON or OFF. This will affect ALL of the screening decks of the unit. If this not ticked, the material will flow out of the Undersize outlet with no change in state, i.e. the unit acts as a pipe. 
EB (Evaluation Block)  
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 submodels. Note: If the user chooses OnAutoSequence then SysCAD will determine the sequence of the submodels. 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 submodels. 
MakeupX  List  This can be used to switch the Makeup Block (MU) on or off and prioritise it in relation to the other submodels. 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 submodels. 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 submodels. If this is 'On' then the associated page, EHX becomes visible and may be configured. Note: The user does not have to configure an environmental heat exchange, even if this block is checked. 
Evaporation  List  Evaporation Block (Evap)  Enable or disable the Evaporator and set the sequence in relation to the other submodels. If this is 'On' then the associated page, Evap becomes visible and may be configured. Note: The user does not have to configure an evaporator, even if this block is checked. 
Discard  Input  The number of discard blocks required. Extra dropdown options Discard1, Discard2, etc. will be added to allow these to be switched on. 
DiscardX  List  This can be used to switch the Discard Block (DB) on or off and prioritise it in relation to the other submodels. If this is 'On' then the associated page, DBX becomes visible and may be configured. Note: This field is only visible if the entry for 'Discards' is greater than 0. If there is one discard then X=1. If there are two discards, then X=1 and X=2, etc. 
Options  
ShowQEBFeed  Tick Box  QEBFeed and associated tab pages (e.g. Sp) will become visible, showing the properties of the combined feed stream to the Evaluation Block. See Material Flow Section. This will be prior to any submodel (e.g. reactions) actions. 
SizeForPassingFracCalc  Input  The particle size to be used for the percent 'Passing' display for ALL units in the Project. 
FracForPassesSizeCalc  Input  The fraction percent passing to be used for the 'Passes' display for ALL units in the Project. 
Intervals  
The user may toggle between displaying the size intervals ascending or descending. This will change the display on all decks of the Screen. 
Results  
Deck Count  Display  The number of decks available in this unit, up to a maximum of 8. This will be determined by the number of streams connected to the OS connections. 
Feed.Distribution  Display  The Size Distribution of the solids in the feed to the Screen. (This field is normally hidden) 
Feed.MassFlow / Feed.Qm  Display  The total mass flow in the Feed to the Screen. 
Feed.SolidMassFlow / Feed.SQm  Display  The solids mass flow in the Feed to the Screen. 
Feed.LiquidMassFlow / Feed.LQm  Display  The liquids mass flow in the Feed to the Screen. 
Feed.VolFlow / Feed.Qv  Display  The volumetric flow of the Feed to the Screen. (This field is normally hidden) 
Feed.Temperature / Feed.T  Display  The temperature of the Feed stream to the Screen. (This field is normally hidden) 
Feed.Density / Feed.Rho  Display  The density of the Feed stream to the Screen. (This field is normally hidden) 
Feed.SolidFrac / Feed.Sf  Display  The mass fraction of solids in the Feed to the Screen. (This field is normally hidden) 
Feed.LiquidFrac / Feed.Lf  Display  The mass fraction of liquids in the Feed to the Screen. 
Feed.Passing  Display  The mass fraction of material in the Feed stream passing the user defined SizeForPassingFracCalc. (This field is normally hidden) 
Feed.Passes  Display  The particle size passing the user defined FracForPassesSizeCalc. 
Screen Decks Result Summary The following table gives a summary of the Oversize and Undersize flows for each individual deck.  
OS.SolidMassFlow / OS.SQm  Display  The solids mass flow in the Oversize stream from each deck. 
US.SolidMassFlow / US.SQm  Display  The solids mass flow in the Undersize stream from each deck. 
OS.LiquidMassFlow / OS.LQm  Display  The liquids mass flow in the Oversize stream from each deck. 
US.LiquidMassFlow / US.LQm  Display  The liquids mass flow in the Undersize stream from each deck. 
OS.LiquidFrac / OS.Lf  Display  The liquids mass fraction in the Oversize stream from each deck. 
US.LiquidFrac / US.Lf  Display  The liquids mass fraction in the Undersize stream from each deck. 
OS.Passes  Display  The particle size passing the user defined FracForPassesSizeCalc in each deck Oversize stream. 
SolFracToOS  Display  The solids mass fraction in the feed to the individual deck that reports to the Oversize stream. 
LiqFracToOS  Display  The liquids mass fraction in the feed to the individual deck that reports to the Oversize stream. 
Deck n
Tag (Long/Short)  Input / Calc  Description/Calculated Variables / Options 
 
On  Tickbox  This variable in used to turn the current screening deck ON or OFF. If this not ticked, the material will flow straight through the deck, i.e. the deck will not be used. 
Off.SolFracToOS  Input  Fraction of Deck Feed Solids reporting to the over size product. This field is only visible if the current Screen Deck is Off. 
Off.LiqFracToOS  Input  Fraction of Deck Feed liquids reporting to the over size product. This field is only visible if the current Screen Deck is Off. 
Off.VapFracToOS  Input  Fraction of Deck Feed Vapours reporting to the over size product. This field is only visible if the current Screen Deck is Off. 
Solid Separation Requirements.  
SolidMethod  Simple (no PSD)  The feed does not need size distribution for this method and the unit acts as a simple mass splitter. If the user chooses this mode then they must define the solids and liquids split from the unit. (This option is visible for the Screen 2 model only) 
Partition Curve  The user inputs a Partition curve (fraction of feed solids per size interval reporting to the oversize) on the PartCrv(deck number) tab. The screen will use this curve, so the size distribution in the feed to the screen has no effect on products. Note: A single partition curve is used for all the size distributions.  
Whiten  The screen model will calculate the solids split using the Whiten method. The user must specify the d_{50} and alpha, a measure of the sharpness of separation.  
Karra  The screen model will calculate the solids split using the Karra method. The user may specify either the d_{50} or the Screen area and Cut aperture.  
RosinRammler  This method is based on a RosinRammler type of function with the efficiency curve expression derived by Reid and Plitt. User must specify d_{50}, sharpness of separation, maximum size allowed to undersize and minimum percent of solids reporting to oversize.  
Lynch  This method is based on a Lynch type of function. User must specify d_{50}, sharpness of separation (m), maximum size allowed to undersize and minimum percent of solids reporting to oversize.  
DelVillarFinch  This method is similar to RosinRammler, but includes a term for the "fish hook" effect for entrainment.  
Solid Method  Whiten  
Whiten.CalcMethod  d50  The user specifies the d50 of the screen. 
d50 with Beta  The user specifies the d50 of the screen and uses the Beta method to adjust for uncertainties in the finer fractions.  
Aperture, Eff  The user specifies the Screen Aperture and Efficiency. The unit then calculates the d50 of the Screen deck.  
Aperture, Eff with Beta  The user specifies the Screen Aperture and Efficiency and uses the Beta method to adjust for uncertainties in the finer fractions. The unit then calculates the d50 of the Screen deck.  
Whiten.Aperture  Input  Only visible if one of the two Aperture CalcMethods are chosen. The Screen Aperture, used to calculate the d50. 
Whiten.Efficiency / Eff  Input  The Whiten Efficiency of the Screen.

Whiten.d50  Input/Calc  If either of the d50 methods are chosen, this is entered by the user. If the Aperture method is chosen, this is a calculated value. This is the particle size with a 50% probability of reporting to the over or under size. 
Whiten.Alpha  Input  The Efficiency parameter, alpha. An alpha value of between 8 and 15 is normal for screening. However, this does depend on the screening conditions and hence experience and/or test or plant data is required for accurate results. 
Whiten.Beta  Input  Only visible if the d50 with Beta or Aperture,Eff with Beta CalcMethods are chosen. The Beta Efficiency parameter. This value takes into account uncertainties in the finer size fractions. 
Whiten.Beta*  Calc  Only visible if the d50 with Beta or Aperture,Eff with Beta CalcMethods are chosen. Efficiency parameter. 
Whiten.MaxSizeToUS  Input  The model will ensure that all particles LARGER than this size all report to the Screen deck oversize product. This value is often = Screen Deck Aperture. (See Model Theory). 
Whiten.MinToOS  Input  The model will ensure that a minimum fraction of solids in each size distribution reports to the oversize product. For example, if the user specifies a minimum of 5%, then at least 5% of each size distribution will report to oversize. (See Model Theory). 
Whiten.Rf  Input  The proportion of feed liquid reporting to the over size product to be used in the fines calculation. Note: This value is only used to adjust the solids fine fraction to the screen oversize and NOT to set the fraction of liquid reporting to the oversize stream. 
If the user has selected SolidMethod=Whiten and Whiten.CalcMethod = d50 or d50 with Beta, the following fields will be visible:  
Theoretical Nominal Screen Aperture  
Whiten.Efficiency / Eff  Input  The Whiten Efficiency of the Screen. Used to calculate the Screen aperture. 
Whiten.TheorAperture  Calc  The calculated screen aperture, based on the specified d50, alpha and efficiency. Refer to equation 2 in Whiten Method. 
Solid Method  Karra  
Karra.CalcMethod  d50  The user specifies the d50 of the screen. 
Area  The user specifies the Area and Cut aperture of the screen and the model calculates the d50 of the screen.  
Karra.d50  Input  Only visible if CalcMethod=d50. The user specified d_{50} of the screen. 
Karra.TotalArea  Input  Only visible if CalcMethod=Area. The deck area. 
Karra.Aperture  Input  Only visible if CalcMethod=Area. The deck cut aperture. 
Karra.Wet  Tick Box  Only visible if CalcMethod=Area. This must be ticked if this is a wet screening application. 
Karra.Factor  Input  Only visible if CalcMethod=Area. This is a tuning factor that may be used to adjust the calculated d50 of the screen deck. The default value is 1. 
Karra.MaxSizeToUS  Input  The model will ensure that all particles LARGER than this size all report to the Screen deck oversize product. This value is often = Screen Deck Aperture. (See Model Theory). 
Karra.MinToOS  Input  The model will ensure that a minimum fraction of solids in each size distribution reports to the oversize product. For example, if the user specifies a minimum of 5%, then at least 5% of each size distribution will report to oversize. This accounts for fines adhering to coarse particles or fines in the liquid. 
Karra.Calc_d50  Calc  Only visible if CalcMethod=Area. The calculated d50 of the deck, using the Karra equations. 
Karra.d50  Calc  Only visible if CalcMethod=Area. The d50 that is used to determine the screen partition curve. This is normally equal to the field above. But, if the calculated d50 > screen deck aperture, then the model will use the screen deck aperture. 
Karra.FeedOversize  Calc  Only visible if CalcMethod=Area. The fraction of oversize material (Q) in the Feed to the deck. 
Karra.FeedHalfsize  Calc  Only visible if CalcMethod=Area. The fraction of half size material (R) in the Feed to the deck. 
Karra.FeedNearsize  Calc  Only visible if CalcMethod=Area. The fraction of near size material (Xn) in the Feed to the deck. 
Karra.SolQmPerArea  Calc  Only visible if CalcMethod=Area. The calculated solids flow rate divided by the screen area. 
Solid Method  RosinRammler  
RR.d50  Input  The user specifies the d_{50} of the screen, the size which divides equally between oversize and undersize. 
RR.Sharpness  Input  The user specifies the sharpness factor for separation, high values for sharper separation 
RR.MaxSizeToUS  Input  The maximum size allowed to report to undersize. 
RR.MinToOS  Input  The minimum percent solids (from feed) to report to oversize. 
Solid Method  Lynch  
Lynch.d50  Input  The user specifies the d_{50} of the screen, the size which divides equally between oversize and undersize. 
Lynch.Sharpness (m)  Input  The user specifies the sharpness factor for separation, high values for sharper separation. 
Lynch.Alpha  Calc  Calculated from the Sharpness (m), refer to Lynch Method for more information. 
Lynch.MaxSizeToUS  Input  The maximum size allowed to report to undersize. 
Lynch.MinToOS  Input  The minimum percent solids (from feed) to report to oversize. 
Solid Method  DelVillarFinch  
Finch.d50  Input  The user specifies the d_{50} of the screen, the size which divides equally between oversize and undersize. 
Finch.Sharpness  Input  The user specifies the sharpness factor (m) for separation, high values of m for sharper separation 
Finch.d0  Input  The largest particle size affected by the fishhook for entrainment function. 
Finch.MaxSizeToUS  Input  The maximum size allowed to report to undersize. 
Finch.MinToOS  Input  The minimum percent solids (from feed) to report to oversize. 
Finch.Rf  Input  Proportion of feed liquid reporting to the over size product. 
Solid Method  Simple  
ReqdSolFracToOS  Input  Fraction of Feed solids reporting to the over size product. 
The following field is visible for all SolidMethods:  
TrackNoSolids  Tick Box  If this tick box is enabled and there are NO solids in the feed to the Screen, a warning message will be generated. If the box is not ticked, there will not be a warning message. 
Liquids Separation Requirements  
LiquidMethod  Follow Solids  The liquid mass split will exactly match the solid mass split. So the Liquid Fraction in the Feed = Liquid Fraction in Oversize = Liquid Fraction in Undersize. 
Liquids To OS  The user may specify the mass fraction of liquids in the feed that report to the Oversize product.  
OS Moisture  The user may specify the mass fraction of liquids in the Oversize product.  
Use Rf  Only visible for SolidMethod=Whiten or DelVillarFinch. The mass fraction of liquids in the feed that report to the Oversize product will be equal to the user specified Rf value.  
ReqdLiqFracToOS  Input/Calc  Only visible if LiquidMethod=Liquids To OS or Use Rf. The fraction of Deck Feed liquids reporting to the over size product. If LiquidMethod=Liquids To OS, this will be an input field. If LiquidMethod=Use Rf, then this will be a result field, showing the user specified value of Rf. 
ReqdOSMoist  Input  Only visible if LiquidMethod=OS Moisture. Fraction of liquids in the over size product. 
TrackOSMoist  Tick Box  Only visible if LiquidMethod=OS Moisture. If this tick box is enabled and the oversize moisture requirement is not met, a warning message will be generated. If the box is not ticked, there will not be a warning message. 
Vapours Separation Requirements  
ReqdVapFracToOS  Input  Fraction of Feed vapours reporting to the over size product. 
Results  
Status  Display  The current status of the screen deck. If there are no problems or errors, then this will display 'OK'. 
MaxSizeToUS_Used  Calc  Visible with all SolidMethods except Simple and Partition Curve. The maximum particle size used to force all particles LARGER than this size to report to the Screen deck oversize product. 
SolFracToOS  Calc  The fraction of solids in the feed that reports to the deck Oversize stream. 
LiqFracToOS  Calc  The fraction of liquids in the feed that reports to the deck Oversize stream. 
VapFracToOS  Calc  The fraction of vapours in the feed that reports to the deck Oversize stream. 
Deck n Stream Results Table
The following table displays the results for the individual Deck Feed, Oversize (OS) and Undersize (US)  
MassFlow / Qm  Display  The total mass flow. 
SolidMassFlow / SQm  Display  The solids mass flow. 
LiquidMassFlow / LQm  Display  The liquids mass flow. 
VolFlow / Qv  Display  The total volume flow. 
Temperature / T  Display  The total volume flow. 
Density / Rho  Display  The temperature of the stream. 
SolidFrac / Sf  Display  The solids fraction in the stream. 
LiquidFrac / Lf  Display  The liquids fraction in the stream. 
Passing  Display  The fraction of material passing the user defined particle size. (This is a global value defined on the first tab of the Screen 2 unit) 
Passes  Display  The particle size in each stream at which the user defined fraction passes. (This is a global value defined on the first tab of the Screen 2 unit) 
Partition Curve Section
Each screen deck has a section showing the partition curve values.
If the 'Partition Curve' option is chosen for screening the user must input the values for the partition curve here.
 The user configures the partition curve as fraction to Oversize per size interval.
Otherwise, the model will display the screen deck partition curve values in a table:
 The Mid size on each size interval is displayed in the first column;
 The Feed mass flow in each size interval is displayed in the second column;
 The fraction of feed reporting to the Over size stream is displayed in the third column.
If the user ticks the 'ShowBottomAndTopSize tickbox, then the table will display the Top and Bottom size of each Size Interval in 2 additional columns.
Adding this Model to a Project
Add to Configuration File
Sort either by DLL or Group:
DLL:  Separation.dll 
→  Units/Links  →  Size Separation: Screen2  
or  Group:  Size Distribution 
→  Units/Links  →  Size Separation: Screen2 
See Model Selection for more information on adding models to the configuration file.
Insert into Project Flowsheet
Insert Unit  →  Size Separation  →  Screen2 
See Insert Unit for general information on inserting units.