Screen 2

Navigation: Models ➔ Size Distribution Models ➔ Screen 2

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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.

1. 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.
2. The user may specify different screening methods on each deck, i.e. the one deck may have a user-defined partition curve and another may use the Karra method to calculate the solids split.
3. 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:

1. Simple, no PSD;
2. A partition curve is used to calculate the screen products;
3. Whiten method;
4. 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	Required	Out	1	1	The undersize from the Screen.
Deck1_OS	Required	Out	1	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 d₅₀ value.

The d₅₀ 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 d₅₀ 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 d₅₀ obtained from the physical screen.

There is no substitute for experience when specifying the expected d₅₀ from a screen. In many cases the screen d₅₀ is approximately equal to the cut aperture of the screen, but this is not always the case. Many factors will influence the actual screen d₅₀ , 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:

1. 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
2. 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 d₅₀ 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 d₅₀ 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.

d₅₀ = cut-size 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 d₅₀ using the following equation:

(2) [math]\displaystyle{ \mathbf{\mathit{d_{50}=\cfrac{\alpha A}{ln \left[\left(\cfrac{100}{100-E}-1\right)exp(\alpha)+\left(\cfrac{100}{100-E}\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*(1-E_{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 = d₅₀

References:

Napier-Munn 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 Karra¹ and is only valid for screen cut apertures greater than 1mm. The solids split is calculated using the d₅₀ 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 d₅₀. The model then calculates the solids split directly, as shown in equation (8).

With the Karra.CalcMethod set to 'Area' the user defines:

1. The Screen area
2. The cut aperture (> 1mm - the model will not allow the user to specify a smaller aperture), and
3. Whether it is a wet screening application.

The model will then calculate the d₅₀ based on these user-defined parameters and on the size distribution of the feed. This d₅₀ is then used to calculate the solids split, as shown in equation (8).

The model calculates the d₅₀ of the Screen from the following equations¹

(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\varphi-d}} }[/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.	hT < 50.8mm	A = 12.1286 * (hT)0.3162 - 10.2991
	hT >= 50.8mm	A = 0.3388 * hT + 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 * hT
	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/m2)
Factor G Near-Mesh factor		G = 0.844 * (1.0 - Xn/100)3.453, where Xn = % near size feed to the screen deck, % in the size interval 1.25hT to 0.75hT

Split Efficiency

The model then uses either the calculated or user defined d₅₀ of the screen to calculate the recovery to the over size in each size range (y_i) using the Rosin-Rammler equation with sharpness of 5.846:

(8) [math]\displaystyle{ \mathbf{\mathit{y_i = 1-exp\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

1. 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.
2. 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.

Rosin-Rammler Method

This method is based on a Rosin-Rammler 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' = 1-exp\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.

d₅₀ = cut-size or separation size, the size which divides equally between oversize and undersize.

m = sharpness parameter. High values of m for sharper separation.

References:

1. L.R.Plitt, A mathematical model of the hydrocyclone classifier, CIM Bulletin, December 1976
2. 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(1-y')}} }[/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+(1-a_i)(1-exp\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.

d₅₀ = cut-size or separation size, the size which divides equally between oversize and undersize.

d₀ = largest particle size affected by the fish-hook 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 d₀ is less than or equal to the smallest size then this method is equivalent to the Rosin-Rammler Method.

References:

1. M.Frachon, J.J.Cilliers, A general model for hydrocyclone partition curves, Chemical Engineering Journal 73 (1999)
2. 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,

1. Screen2 - The first section allows the user to enable sub-models and it also contains some general information relating to Global displays for the unit.
2. RB - Optional tab, only visible if the Reactions are enabled in the Evaluation Block.
3. EHX - Optional tab, only visible if the EnvironHX is enabled in the Evaluation Block.
4. Evap - Optional tab that is visible if Evaporation is enabled.
5. 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.
6. 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.
7. 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.
8. 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.
9. PartCrv n - There is a Partition Curve tab for each of the screen decks.
10. Info tab - contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
11. Links tab - contains a summary table for all the input and output streams.
12. 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 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.
Evaporation	List	Evaporation Block (Evap) - Enable or disable the Evaporator and set the sequence in relation to the other sub-models. 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 sub-models. 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 sub-model (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
The Screen 2 unit can have up to 8 decks. The number of decks is determined by the number of Oversize connections, i.e. if the user connects streams to Deck1_OS, Deck2_OS and Deck7_OS, then the unit will have 3 decks with the tabs Deck1, Deck2 and Deck7. The parameters in this section change depending on the Screen mode chosen by the user. The parameters for each mode will be detailed separately.
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 d50 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 d50 or the Screen area and Cut aperture.
	Rosin-Rammler	This method is based on a Rosin-Rammler type of function with the efficiency curve expression derived by Reid and Plitt. User must specify d50, 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 d50, sharpness of separation (m), maximum size allowed to undersize and minimum percent of solids reporting to oversize.
	DelVillar-Finch	This method is similar to Rosin-Rammler, 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. If the user selects one of the 'Aperture' methods, then this is used to calculate the d50. If the user selects one of the 'd50' methods, then this value is used to calculate the Screen aperture (see Theoretical Nominal Screen Aperture).
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 d50 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 - Rosin-Rammler
RR.d50	Input	The user specifies the d50 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 d50 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 - DelVillar-Finch
Finch.d50	Input	The user specifies the d50 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 fish-hook 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 DelVillar-Finch. 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.