Electrowinning Cell

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General Description

The electrowinning cell converts metal in solution into solid elemental metal. The user specifies the reaction in the normal way using the Reaction Block (RB). In the dynamic mode, the solids are removed separately in a batch process, to emulate the removal of cathodes on a plant. The energy required by the cell is calculated from the heats of reaction and the efficiency of the cell. The excess energy is used to heat the contents of the unit.

Diagram

Electrowinning Cell.jpg

The diagram shows the default drawing of the Electrowinning Cell, with all of the streams that are available for operation of the unit.

The physical location of the streams connecting to the Electrowinning Cell 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 20 The feed to the Electrowinning Cell
Anolyte Required Out 1 1 The Liquid outlet from the unit
Cathodes Required Out 1 1 Solids, or cathode, outlet from the unit
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 MassFracToCath becomes visible and the user may set the fraction of the feed stream that reports to the 'Cathode' outlet. The default is 100%.
  • All streams connected to the unit will flow out of the 'Cathode' outlet, unless the user has changed the above field from 100%. In which case the user defined fraction of the feed streams will report to the Anolyte stream;
  • No reactions or heating will occur.

So basically, the unit will be 'bypassed' without the user having to change any connections.


Model Theory

The Electrowinning Cell is modelled as a tank that contains an electrolytic reaction, where a metal is plated out onto a cathode from an aqueous solution. The reactions occurring in electrowinning require energy to proceed and the amount of energy is calculated as follows:

At 100% efficiency the energy value calculated by the model is the amount of energy required to maintain the material in the cell at the temperature of the cell feed.

If the cell is less than 100% efficient, then the extra energy increases the temperature of the products from the cell.

The energy required by the electrowinning cell is governed by the enthalpy of the electrolytic reaction occurring the unit. This enthalpy of the reaction is calculated in one of two ways:

  1. Enthalpy of Reaction = Sum of Heats of formation of the products - Sum of Heats of formation of reactants. (This is the default method of calculating the heat of reaction.) The heats of formation of the species are defined in the species database.
  2. The Heat of Reaction is specified in the reaction file. This method is often used when the heats of formation are not known.


Flowchart

The following shows the sequence of events if sub model options are switched on. See next heading for more information.

Electrowinning Cell Sequence of Events.gif

Data Sections

The default access window consists of a number of sections, depending on user specifications. The tabs that may be visible are:

  1. ECell tab - Contains general information relating to the unit.
  2. RB - Optional tab, only visible if the Reactions are enabled in the Evaluation Block.
  3. QFeed - Optional tab, only visible if ShowQFeed is enabled. This page shows the properties of the mixed stream as the feed to the electrowinning Cell.
  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, 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.


Electrowinning Cell Page

Unit Type: ECell - The first tab page in the access window will have this name.

Tag (Long/Short)

Input / Calc

Description/Calculated Variables / Options

Common Data on First Tab Page

Requirements

On Tick box Switch the model on or off. If the unit is 'Off' then by default all Feed reports to the Cathodes outlet. If the user specifies a value (less than 100%) in the MassFracToCath field, then some feed may report to the Anolyte stream.
MassFracToCath_WhenOff / MassFracToCath 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 Cathodes outlet. The default is 100%.
CellEfficiency / CellEff Input The required energy efficiency of the cell. This is used to calculate the energy required by the cell, and the temperature rise in the cell.
 
Reactions List This can be used to switch on the Reaction Block (RB). If this is 'On' then the associated page, RB becomes visible and may be configured. Note: The user must configure the reaction block, if the Electrowinning cell is to do any work.
 
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.
AutoDetect If there are any liquids AND no vapours present in the feed, outlet streams will take the highest pressure of the feeds. Else (eg. some vapours present) outlet streams will take the lowest pressure of the feeds.
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.
IgnoreLowQm Tick Box This option is only visible if the AutoDetect, LowestFeed or HighestFeed methods are chosen. When calculating the outlet pressure and temperature of the tank, SysCAD will ignore the low flow feed streams should this option be selected. The low flow limit is set in the field below.
LowQmFrac Input This field is only visible if the IgnoreLowQm option is selected. This is the amount any stream contributes to the total flow. For example, if the total feed to the tank is 10 kg/s, and this field is set to 1%. Then any feed streams with less than 0.1 kg/s will be ignored in the pressure calculations.
PressureReqd / P_Reqd Input This field is only visible if the RequiredP method is chosen. This is 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).
ShowQFeed Tick Box QFeed and associated tab pages (eg. Sp) will become visible, showing the properties of the combined feed stream. See QFeed. This will be prior to any reactions occurring.
 

Results

ElecEnergyTotal Calc The calculated electrical energy requirements of the cell. This is based on the heat of reaction and the efficiency of the cell. This is the sum of ElecEnergyReact and ElecEnergyHeat.
ElecEnergyReact Calc The calculated energy requirements of the cell based on the heat of reaction. This represents the energy required for a 100% efficient cell.
ElecEnergyHeat Calc The calculated amount of energy that is converted to heat. This is based on the cell efficiency.
 
Feed.Temperature / Feed.T Calc The feed temperature.
Prod.Temperature / Prod.T Calc The final temperature of the cell after the required energy is added (calculated above).

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

 

DLL:

Separ1.dll

Units/Links

Separation: Electrowinning Cell

OR

Group:

Mass Separation

Units/Links

Separation: Electrowinning Cell

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

Insert into Project

 

Insert Unit

Separation

Electrowinning Cell

See Insert Unit for general information on inserting units.

Example Project

Please see Solvent Extraction Project OR Nickel Copper Project