Alumina 1 vs Alumina 3

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Navigation: Alumina Models -> Converting Alumina Project

Related Links: Converting Alumina 1 to Alumina3, Alumina1, Alumina3

Detailed Bayer Species Model are documented in these two linked pages. Alumina1 and Alumina3. Please refer to these pages for full explanation of correlations, limitation and description of variables used.

IMPORTANT NOTE: Alumina1 is not distributed and supported with release of SysCAD 9.3. Projects should be converted to Alumina3. However, a SysCAD 9.3 version of Alumina1 library is available on request.

The sections below only highlight the difference in the two models and also give some pointers to user wanting to convert existing Alumina1 project to Alumina 3.

Model Implemented

Species Representation

Alumina 1 Alumina 3 Description
Al2O3(l) NaAl[OH]4(aq) Dissolved Alumina
SiO2(l) Na2SiO3(aq) Dissolved Reactive Silica
Al2O3.3H2O(s) Al[OH]3(s) Gibbsite (THA)
Na2O(s) Na2O(s) Occluded Soda
NaOH*(s) Bound Soda (NOTE: This is only required when using the Precipitation3 unit operation, if NaOH* is not present, Na2O will be used)
Na2C5O7*(s) Bound Organics (NOTE: This is only required when using the Precipitation3 unit operation as a percentage of the total bound soda)

Global Method

Global Method and Constants selection change:

Alumina1 : Located on Feeder Access Window (Access window on the left in picture below)
Alumina3 : Located on View - PlantModel - Globals Tab. (Access window on the right in picture below)

Alumina3Conversion2.png

Method Alumina 1 Alumina 3
ASat Rosenberg 1) Rosenberg
2) RosenbergUser
Specific Heat MulloyDonaldson 1) MulloyDonaldson
2) LM_1985
Density MulloyDonaldson MulloyDonaldson
Boiling Point Elevation 1) Dewey
2) Adamson		 1) Dewey
2) Adamson
3) Dewey All Liq
Viscosity - 1) EMA1962
2) Alexandrov

When comparing projects, make sure the global method selection match, refer to Alumina1 and Alumina3 model documentation for correlations used.

Define Liquor Calculator

The differences of the Bayer Liquor Calculator is listed below. They are also marked with a red dot on the picture below.

Alumina1 : Allows user to define the required organic carbon in terms of Sodium Organic or Total Organic Carbon. Solids Fraction can only be entered in terms of %Solids.
Alumina3 : The required organic carbon can only be specified in terms of Total Organic Carbon. Solids in the stream can be defined as %Solids or g/L solids.
Oxalate Concentration input differences:
  • Alumina 1 uses oxalate concentration expressed as g/L Na2CO3.
  • Alumina 3 uses oxalate concentration expressed as g/L Na2C2O4.
NaF Concentration input differences:
  • Alumina 1 does not include NaF in the Calculator.
  • Alumina 3 allows the input of g/L NaF if NaF is used in the project.

Alumina3Conversion3.png

Property Model Display

General Tag Changes, all Alumina3 Bayer property tags need to have Props. added to the Tag.

Example of Alumina 1 property tags: SL1.Qo.A (g/L)
Example of Alumina 3 property tags: SL1.Qo.Props.A (g/L)

Other Tags that are different are highlighted in the following screen print. Alumina1 on the left and Alumina3 on the Right:

AluminaConversion4.png


Variable Difference

Input Variable Difference:

  1. Oxalate concentration input in the Define Liquor Calculator, see Define Liquor Calculator


Calculated Variable Difference:

  1. A/CSat
  2. Boiling Point Elevation

In Alumina1, [email protected] calculations were referenced to the boiling point of water rather than the liquor, which gave a small difference in the vapor pressure and boiling point. This has been corrected in Alumina3, but the previous interpretations are available for backward compatibility. TotalNa as used in the BPE correlations in Alumina3 includes NaF and Na2SiO3.

BPE A3.png

  1. Solids Cp
    • Alumina1: Applies a minimum total solids phase Cp of 1.05kJ/kg.C
    • Alumina3: No minimum is applied to the total solids phase Cp.
  2. FC(Free Caustic)
    • Alumina1: Caustic expressed as g/L Na2CO3, excluding the amount that is associated with Al2O3 (in the form of NaAl[OH]4). This does not adjust for any Caustic associated with Silica.
    • Alumina3: Caustic expressed as g/L Na2CO3, excluding the amount that is associated with Al2O3 (in the form of NaAl[OH]4). Also excludes the amount associated with Silica.
  3. TotalSoda Calculation
    • Alumina 1: Silica concentration is represented by SiO2, so Total Soda calculation does not account for Na associated with Si.
    • Alumina 3: Silica concentration is represented by Na2SiO3, so Total Soda calculation does account for Na associated with Si.

NOTE - The total Soda Calculation in Alumina3 will show a difference if data entry is made via the Bayer Calculator (with Si Concentration specified), as Silica will bring to the feed extra Na and causing the total soda higher. However, this generally would not be a problem if the plant is fully connected and Si is not added via the Bayer calculator.

Known issues in the two models

  1. Alumina1 Bayer Species model represents dissolved Alumina as Al2O3(l).
    One flaw with this representation is that user can write the Gibbsite dissolution as:

    Al2O3.3H2O(s) = Al2O3(l) + 3H2O(l)

    Although this reaction is valid in terms of elemental balance, it is not realistic since Gibbsite cannot dissolve without Caustic. Therefore, if the Gibbsite dissolution reaction is written this way, it is possible for the Alumina concentration to be higher than what can be realistically achieved. In some extreme cases, the A/C ratio can be very large and cause some property correlations to return unrealistic values. To safe guard this, the Bayer 1 model has a maximum limit for A/C = 0.96.
    See Stream Property Limits for more information.
  2. Kaolin Dissolution in Alumina3 may be limited by the availability of NaOH(aq).
    This is not a common problem, but may exist when:
    • Predesilication occurs just after Milling
    • Predesilication slurry has a high solids content (thus limiting the amount of NaOH(aq) present)
    • Kaolin dissolution reaction is written first, followed by DSP formation.

      For Example:
      Reaction 1: 1 Al2O3.2SiO2.2H2O(s) + 6 NaOH(aq) = 2 Na2SiO3(aq) + 2 NaAl[OH]4(aq) + 1 H2O(l)
      Reaction 2: 6 NaAl[OH]4(aq) + 6 Na2SiO3(aq) = 3 4/3Na2O.Al2O3.2SiO2.2H2O(s) + 10 NaOH(aq) + 1 H2O(l)

    • Under these conditions, it is possible that there is not enough NaOH available to first fully dissolve the Kaolin into Na2SiO3. To avoid this situation, it is recommended the two reactions are combined and rewritten as:

      Combined Reaction: 1 Al2O3.2SiO2.2H2O(s) + 8/3 NaOH(aq) = 1 4/3Na2O.Al2O3.2SiO2.2H2O(s) + 4/3 H2O(l)

Converting Existing Alumina 1 Project to Alumina 3

For an example work flow of how to convert an existing Alumina 1 project to Alumina 3, please see Converting Alumina 1 to Alumina3.

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