Efficiency Screen

Summary

The Efficiency Screen model is an empirical screening model that splits the feed stream into undersize and oversize products from a user-defined undersize efficiency, screen opening and oversize bypass.

The model builds a size-by-size partition curve to oversize. Material coarser than the screen opening reports to oversize, material finer than a calculated minimum-size point reports according to the bypass, and the interval between the minimum-size point and the screen opening is represented by a log-linear transition.

The model should be used when screen performance is known by an overall undersize efficiency rather than by equipment geometry or a detailed partition curve. It is suitable for calibrated flowsheet studies, simplified screening stages and cases where measured or assumed efficiency is the main available performance parameter.

DPSIM model key: DPSIM.Classification.EfficiencyScreen
Category: Classification
Subcategory: Screens
Display name: Efficiency Screen

Parameters

Derived parameters

Model Description

The Efficiency Screen model receives one feed stream and generates two product streams. In DPSIM, the product port represents the undersize stream and the tail port represents the oversize stream.

The screen opening is converted from millimetres to micrometres:

h=1000h_mm

Where:

If the variable efficiency curve is disabled, the correlated efficiency is the user-defined undersize efficiency:

η_corr=η_set

If the variable efficiency curve is enabled, the correlated efficiency is calculated by linear interpolation between points A and B:

η_corr=η_A+(η_B-η_A)(M_S^F-M_A)/(M_B-M_A)

Where:

An optional random perturbation can be applied around the correlated efficiency:

η_target=η_corr+δ

with:

-Δη≤δ≤Δη

The target efficiency is then limited to the range from 0 to 100%.

Where:

The model searches for the minimum-size point d_min that gives the requested undersize efficiency when combined with the selected bypass and screen opening. This point defines the lower end of the transition region in the partition curve.

The partition curve gives the fraction of each size class reporting to oversize:

E_i^O=1, d_i>h

E_i^O=B, d_i<d_min

E_i^O=B+(1-B)(log d_i-log d_min)/(log h-log d_min), d_min≤d_i≤h

Where:

The partition curve is limited internally to the interval from 0 to 1.

The undersize efficiency associated with a trial partition curve is calculated as:

η=100 sum_i M_i^F(1-E_i^O)/sum_(d_i<h) M_i^F

Where:

After the partition curve is established, the oversize and undersize retained masses are calculated size by size:

M_i^O=E_i^O M_i^F

M_i^U=M_i^F-M_i^O

Where:

The retained size distributions are normalized as:

p_i^O=M_i^O/sum_i M_i^O

p_i^U=M_i^U/sum_i M_i^U

The same partition curve is applied to the component-by-size matrix. For each component c:

M_(c,i)^O=E_i^O M_(c,i)^F

M_(c,i)^U=M_(c,i)^F-M_(c,i)^O

Where:

The model calculates the water assigned to the oversize stream from the requested coarse stream solids percentage:

W_O=M_S^O(1-X_O)/X_O

with:

X_O=S_O/100

Where:

If the calculated oversize water is greater than the feed water, all feed water is assigned to the oversize stream and the undersize stream receives no water. If the target oversize solids percentage is zero, the model also assigns all feed water to the oversize stream.

The model preserves total solids and water by splitting the feed into undersize and oversize streams. The separation response is empirical and should be calibrated against screen survey data when used for design or reconciliation.

The model does not calculate screen capacity, deck loading or geometric correction factors. For capacity-based screen calculations, use the King Screen model. For a Karra partition-based screen model, use the Karra Screen model.