Washer

From SysCAD Documentation

Jump to: navigation, search

Navigation: Main Page -> Models -> Mass Separation Models

Contents

General Description

The Washer is used to separate the solids from the liquids in the feed stream. This unit is similar to the Thickener and the Counter Current Washer.

  • The user may set a bypass as either:
    • a fraction of the incoming wash water (Input streams) to the overflow stream or
    • a fraction of the incoming slurry (Feed streams) to the underflow stream.
  • The user defines the percentage solids in both the underflow and the overflow from the unit. The Washer will calculate the liquid split to the underflow to satisfy the user defined solids percentages.
  • If there is insufficient solids in the feed to the Washer to satisfy both the under and over flow requirements, the unit will try to satisfy the underflow solids / liquids requirements first.
  • The model allows reactions to be specified via a reaction file. The reactions only act on the stream(s) connected to the Feed input and the portion of the wash streams that are not bypassed. Any solids generated by the reaction(s) report to the underflow.
  • The temperature of the solids and liquids is calculated after any reactions and/or heat loss has occurred.

Note: The Counter Current Washer Project, which is distributed with SysCAD in the Examples folder, demonstrates the use of this model.

Diagram

Image:Washer image001.gif

The diagram shows the default drawing of the Washer, with all of the streams that may be connected for the unit to operate.

The physical location of the streams connecting to the Washer is unimportant. The user may connect the streams to any position on the unit.

Inputs and Outputs

Label Input / Output No. of Connections Description
    Min Max  
Feed In 1 4 The slurry feed / Washing Stream to the Washer, see NOTE below.
Input In 0 20 The slurry feed / Washing Stream to the Washer, see NOTE below.
Overflow Out 1 1 Washer overflow
Underflow Out 1 1 Washer underflow
Vent Out 0 1 Vent Stream (Vapour Only)


NOTE on the washer configuration, the "input" connection refers to the stream you want to bypass. Therefore,

  1. If the washing efficiency is calculated based on some liquor being trapped in mud, slurry to washer should be connected to the "Input" IO. All other streams should be connected to the Feed IO
  2. If the washing efficiency is calculated based on some wash water reporting straight to the O/F, then those washing streams should be connected to the "input" IO. The other streams including the mud to be washed should be connected to the Feed IO.

Model Theory

The liquid associated with the solids in the Feed stream and the liquid in the Input streams is imperfectly mixed, based on the user defined mixing efficiency. If the mixing efficiency is set at 90%, then 10% of the liquid in the Input streams will bypass directly to the Washer overflow (or Underflow) stream, based on the BypassOpt selected.

NOTES:

  1. See notes on Inputs and outputs section regarding connection IO.
  2. Reactions will only occur in the perfectly mixed portion.
  3. Any vapours in the Feed/Input stream or being produced by the reactions will report to the vent stream.


The Scandrett Wash Efficiency is calculated and displayed as an output. This shows the efficiency of washing for a selected specie (e.g. Caustic), from the liquor associated with the solids in the underflow from the unit.

As described in the notes above the bypass (or mixing efficiency) is based on the "Input" stream connection. Therefore depending on if the slurry (or mud) streams are connected to the "Feed" or "Input" connection, the user would need to select the appropriate ScanEffCalc option.

\mathbf{\mathit{\boldsymbol{\varepsilon}=\frac{C_{Slurry}-C_{underflow}}{C_{Slurry}-C_{overflow}}}}

Where:

CSlurry - concentration of the user defined species in the "Feed" or "Input" stream (depending on ScanEffCalc selection) to the washer
Cunderflow - concentration of user defined species in the underflow
Coverflow - concentration of user defined species in the overflow

References

H.F. Scandrett, "Equations for Calculating Recovery of Soluble Values in a counter current Decantation Washing System"

Flowchart

The following shows the sequence of events if sub model options are switched on. See next heading for more information. Note this only shows the flowchart for washing bypass to the overflow. For washing bypass to the underflow, the flowchart is the same except for the overflow and underflow outlets are swapped around.

Image:Washer image002.gif

Data Sections

The default access window consists of several sections,

  1. The first tab has the same name as the model tag, contains general information relating to the unit.
  2. RB - Optional tab, only visible if the Reactions are enabled.
  3. EHX - Optional tab, only visible if the EnvironHX is enabled.
  4. Info tab - contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
  5. Links tab, only visible in SysCAD 9.2, contains a summary table for all the input and output streams.
  6. Audit tab - contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.

First Tab - Washer-1 - The first tab page in the access window will have this name.

Tag / Symbol
Input / Calc
Description/Calculated Variables

Common First Data Section

Requirements

On Tick Box This allows the user to enable or disable the unit. If the unit is disabled, this is equivalent to bypassing the unit, as the following behaviour will occur:
  • All material in the streams connected to the Feed connections will flow out of the underflow;
  • All material in the streams connected to the Input connections will flow out of the overflow.

This functionality is only available in SysCAD 9.2 Build 132.

BypassOpt

None

This assumes the mixing efficiency is 100% and hence there is no bypass.

Overflow

This assumes some of the washing streams (connected as Inputs) will not be in contact with the Mud (connected as Feed) and reports directly to the overflow stream.

Underflow

This assumes some liquids in the Mud (connected as Inputs) is trapped and will not be washed by washing streams (connected as Feed) and will thus report directly to the underflow stream.

Mixing Eff

Input

The required mixing efficiency of the Feed and Input streams. This field is not visible if BypassOpt = None.

MixEffLiqOnly

Tick Box

If MixEffLiqOnly is enabled then the Mix Efficiency will apply to the liquid components only. Otherwise the Mix Efficiency applies to the slurry (Liquid and Solid) components. This field is not visible if BypassOpt = None.

RqdUFSolids

Input

The required percentage of solids in the underflow stream.

Method

OverFlow Solids Fraction

The user specifies the fraction of solids in the overflow.

OverFlow Solids Concentration

The user specifies the overflow solids concentration.

RqdOFSolids

Input

The required percentage of solids in the overflow stream. This is only visible if the user has chosen OverFlowSolidsFraction above.

RqdOFSolConc25

Input

The required overflow Solids concentration measured at 25°C. Visible only with the OverFlowSolidsConcentration method.

IntOFSolidsUsed

Calc

Shows the value used by SysCAD for the O/F solids in the solver.

 

Reactions

list

This can be used to enable Reaction Block (RB). If "On" is selected then the associated page, RB becomes visible and may be configured. Note: The user does not have to configure a reaction file, even if reactions are turned On.

EnvironHX

List

This can be used to enable Environmental Heat Exchanger (EHX). If "On" is selected then the associated page, EHX will become visible and may be configured. Note: The user does not have to configure an environmental heat exchange, even if the environmental heat exchange is turned On.

TrackStatus

Tick Box

This is used to enable warning messages.

OperatingP... (available in SysCAD 9.2 or later)

Method

Atmospheric

Outlet streams will be at Atmospheric Pressure. The atmospheric pressure is calculated by SysCAD based on the user defined elevation (default elevation is at sea level = 101.325 kPa). The elevation can be changed on the Species tab page of the Plant Model.

LowestFeed

Outlet streams will take the lowest pressure of the feeds.

HighestFeed

Outlet streams will take the highest pressure of the feeds.

RequiredP

Outlet streams will be at the user specified pressure.

Result

Display

The actual pressure used for the sum of the feeds which will also be the outlet pressure (unless further model options change the pressure).

Results

BypassQm

Calc

Shows the amount being bypassed based on the mixing efficiency.

UFSolids

Calc

The actual percentage solids in the underflow stream.

OFSolids

Calc

The actual percentage solids in the overflow stream.

UFSolConc25

Calc

The actual solids Concentration@25C in the underflow stream.

OFSolConc25

Calc

The actual solids Concentration@25C in the overflow stream.

Scandrett Efficiency

ScanEffCalc

None

The user does not require a Scandrett efficiency calculation to be performed.

Slurry in Feed Connection

Use the concentration in the Feed connection to the unit as the feed concentration when performing the calculation.

Slurry in Input Connection

Use the concentration in the Input connection to the unit as the feed concentration when performing the calculation.

ScanEffSpecie

List

Choose the liquid species from the drop down list for the calculation of Scandrett efficiency.

ScandrettEff

Calc

The calculated Scandrett efficiency of the unit. See Model Theory for equation used in calculating this value.

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

 

DLL:

Separ1.dll

→

Units/Links

→

Separation: Washer(1)

OR

Group:

Mass Separation

→

Units/Links

→

Separation : Washer(1)

See Project Configuration for more information on adding models to the configuration file.

Insert into Project

 

Insert Unit

→

Separation

→

Washer(1)

See Insert Unit for general information on inserting units.

Hints and Comments

  1. There may be mass entering or leaving the Washer via the Reaction Block source or sink, so if the outgoing mass is not the same as the incoming mass, this may be a place to check first.
  2. If the reaction block is enabled in the model, there may be small errors resulting in the calculation of Overflow/underflow solids due to the feed composition change.
  3. See notes on Inputs and Outputs section regarding how to correctly connect up inlet streams when using imperfect mixing.
Retrieved from "http://help.syscad.net/index.php/Washer"
Personal tools
Document Sections