Bayer3 Species Model Theory

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Alumina 3 Bayer Species Model Species Model Theory General Discussion

Nomenclature and Units

The calculations for liquor and slurry densities, heat capacity and boiling point elevation are evaluated using the following formulae:

The variables used in the calculations are described below:

A = Sodium Aluminate NaAl[OH]4 concentration, expressed as grams of Al2O3/L liquor @ slurry temperature
C = Caustic Soda concentration in NaOH + NaAl[OH]4, expressed as grams Na2CO3/L liquor @ the slurry temperature
A25 = Sodium Aluminate NaAl[OH]4 concentration, expressed as grams of Al2O3/L liquor @ at 25°C.
C25 = Caustic Soda concentration in NaOH + NaAl[OH]4, expressed as grams Na2CO3/L liquor @ 25°C.
T = Temperature in °C
Tk = Temperature in K
TOC25 = Total Organic carbon (Na2C5O7 + Na2C2O4) expressed as g/L Carbon @ 25°C;
TNa = The sum of all sodium salts, caustic, sodium aluminate, carbonate, organics, NaCl, Na2SO4, sodium silicate all expressed as Na2CO3 @ 25°C. The engineering units for this is Concentration (mass/mass) wt%.
[math]\mathbf{\mathit{T_{Na}=\left([Na_2CO_3]+\left(\frac{[NaOH]}{2\times MW_{NaOH}}+\frac{[NaAl[OH]_4]}{2\times MW_{NaAl[OH]_4}}+\frac{[Na_2C_2O_4]}{MW_{Na_2C_2O_4}}+\frac{[Na_{org}]}{MW_{Na_2C_5O_7}}+\frac{[NaCl]}{2\times MW_{NaCl}}+\frac{[Na_2SO_4]}{MW_{Na_2SO_4}}+\frac{[Na_2SiO_3]}{MW_{Na_2SiO_3}}+\frac{[NaF]}{2\times MW_{NaF}}\right)\times MW_{Na_2CO_3}\right)\times \frac{100}{L_m}}}[/math]
where: Lm - Liquor mass flow (engineering units need to be the same as individual salts in the equation.)

TAl2O3 = Total concentration (mass/mass) wt% of Alumina.

[math]\mathbf{\mathit{T_{Al203}= [NaAl[0H]_4] \times \left( \frac{MW_{Al_2O_3}}{2\times MW_{NaAl[OH]_4}}\right)\times \frac{100}{L_m}}}[/math]
where
Lm - Liquor mass flow.
NaAl[0H]4 - NaAl[OH]4 mass flow.


Method Selection for Property Calculations

For many of the property calculations described below, more than one method is available. The user can make a selection of which method should be used. This is applied globally, so you cannot use different methods in different areas in the same project. The method is selected globally from the View - PlantModel access window Globals Tab as illustrated below.

Alumina3Global.png

NOTE

  1. For very dilute solutions, ie, solutions containing >=98% water (or H2OTestFrac0), SysCAD will automatically use the "Standard Species model" to calculate its properties. This includes Density, Heat Capacity Saturation T and P etc.
  2. For solutions >=95%(or H2OTestFrac1) water and <=98% (or H2OTestFrac0) Water, a proportional result of "Bayer3 and Standard" Species properties are used to calculate the stream properties.
  3. Boiling Point Elevation must be greater or equal to 0.

See Global Properties Calculation Method Selection for more information.

Density Calculations

Mulloy-Donaldson equation. - This is based on a correlation for density at standard conditions (25°C) and a correction for temperature. NOTE: for very dilute solutions, ie >98% water, this density equation is not used. SysCAD will use the Standard Species model to calculate its properties.

Liquid SG

[math] LSG_T =LSG_{25} \big\{ 1 - \left[e_0 \times 0.85(T - 25) \right] - \left[e_1 \times 0.85(T - 25)^2 \right] \big\} [/math]
where: LSG25 -- liquid SG @ 25°C
[math] LSG_{25} = a_0 + (b_0 T_{Na} + b_1 T_{Na}^2 + b_2 T_{Na}^3) + (c_0 T_{Al_2O_3} + c_1 T_{Al_2O_3}^2 + c_2 T_{Al_2O_3}^3) + (d_0 T_{Na} \times T_{Al_2O_3}) [/math]
where:
TNa = Total concentration (mass/mass) wt% of Sodium, reported as Na2CO3. (See Nomenclature and Units)
TAl2O3 = Total concentration (mass/mass) wt% of Alumina. (See Nomenclature and Units)
a0 = 0.982
b0 = 0.01349855
b1 = -0.00024948
b2 = 0.00000273
c0 = 0.00208035
c1 = 0.00004113
c2 = -0.00000728
d0 = 0.00033367
e0 = 0.0005021858
e1 = 0.0000011881

User Specified Parameters

New in Build 135.14711

The constants in the Mulloy Donaldson density equation maybe adjusted by selecting the MulloyDonalsonUser Method.

MD UserConstants.png

Slurry SG

[math]\mathbf{\mathit{S_LSG_{T}=\frac{SolidsMass+LiquidsMass}{SlurryFlow}}}[/math]
[math]\mathbf{\mathit{SlurryFlow=\frac{SolidsMass}{SolidsSG}+\frac{LiquidsMass}{LSG_T}}}[/math]


[math]\mathbf{\mathit{S_LSG_{25}=\frac{SolidsMass+LiquidsMass}{SlurryFlow\ 25^{\circ} C}}}[/math]
[math]\mathbf{\mathit{SlurryFlow=\frac{SolidsMass}{SolidsSG}+\frac{LiquidsMass}{LSG_{25}}}}[/math]

Heat Capacity Calculations

NOTE: for very dilute solutions, ie >=98% (H2OTestFrac0) water, these Cp equations are not used. SysCAD will use the Standard Species model to calculate its properties.

See Selecting alternative methods for Property Calculations

Liquid Heat Capacity

Method 1: LM_1985 (Langa method from Light Metals 1985)

[math]\mathbf{\mathit{Cp_L=4.184 \left[K1 + T \left(K2 + T K3 \right) \right]}}[/math]
where
[math]\mathbf{\mathit{K1=0.99639 - 3.90998e^{-4}C_{25} - 5.3832e^{-4}A_{25} + 2.46493e^{-7}C_{25}^{2} + 5.7186e^{-7}C_{25} \times A_{25} }}[/math]
[math]\mathbf{\mathit{K2 = -1.51278e^{-4} - 1.86581e^{-7} A_{25} - 1.07766e^{-7} C_{25} }}[/math]
[math]\mathbf{\mathit{K3 = 2.1464e^{-6 } }}[/math]


Method 2: Mulloy Donaldson

[math]\mathbf{\mathit{Cp_L=\begin{pmatrix}1.0275057375729-0.020113606661083 T_{Na_2O}\\ +0.001081165172606 T^2_{Na_2O}-0.000022606160779 T^3_{Na_2O}\\ -0.004597725999883 T_{Al_2O_3}-0.000001053264708 T^2_{Al_2O_3}-0.00000218836287 T^3_{Al_2O_3}\end{pmatrix}\times 4.184}}[/math]
where [math]\mathbf{\mathit{T_{Na_2O}=T_{Na} \frac{MW(Na_2O)}{MW(Na_2CO_3)}}}[/math]
This is scaled for dilute liquors where [math]\mathit{T_{Na_2O}}[/math] as liquid weight % is less than 0.19.


Method 3: Langa (Langa method using T_NA instead of C)

NOTE:This variation is temporarily available in 9.1 for backward compatibility with some old projects. Discontinued in 9.2.
[math]\mathbf{\mathit{Cp_L=4.184 \left[K1 + T \left(K2 + T K3 \right) \right]}}[/math]
where
[math]\mathbf{\mathit{K1=0.99639 - 3.90998e^{-4} T_{Na} - 5.3832e^{-4} A_{25} + 2.46493e^{-7}T_{Na}^{2} + 5.7186e^{-7} T_{Na} \times A_{25} }}[/math]
[math]\mathbf{\mathit{K2 = -1.51278e^{-4} - 1.86581e^{-7} A_{25} - 1.07766e^{-7} T_{Na} }}[/math]
[math]\mathbf{\mathit{K3 = 2.1464e^{-6 } }}[/math]

Solids and Vapours Heat Capacity

Solids Cp (Cps) and Vapours Cp (Cpv) are calculated from Cp values as given in the species database (ie using Standard Species Model).

Stream Heat Capacity

[math]\mathbf{\mathit{Cp=\frac{SolidsMass*Cp_s+LiquidsMass*Cp_L+VapoursMass*Cp_V}{SolidsMass+LiquidsMass+VapoursMass}}}[/math]

Entropy

Method 1: Standard

Entropy values are not calculated by the Bayer model and hence will be the same as calculated by the Standard Species Model.

Method 2: LM_1985

Implemented In Build 137.

Based on the LM_1985 specific heat equation:

[math] S(T) = S^{25} + \int_{298.15}^T Cp/T dT[/math]

Please see Entropy for some caution notes on using this method.

Boiling Point Elevation

See Selecting alternative methods for Property Calculations

Method 1: Dewey Equation2

[math]\mathbf{\mathit{BPE=\begin{matrix}&0.00182+0.55379\times \left(\frac{M}{10}\right)^7+0.0040625\times M\times T_K\\ &+\frac{1}{T_K}\times \left(-286.66\times M+29.919\times M^2+0.6228\times M^3\right)-0.032647\times M\times \left(M\times \frac{T_K}{1000}\right)^2\\ &+\left(\frac{T_K}{1000}\right)^5\times \left[5.9705\times M-\left(0.57532\times M^2\right)+\left(0.10417\times M^3\right)\right] \end{matrix}}}[/math]
Where M is the Total Molality of the solution, calculated using the following species:
Al2O3, NaOH, Na2CO3, NaCl, Na2SO4, Na2C5O7, Na2C2O4, Na2SiO3 and NaF.
Tk is the liquor temperature.

In the original Dewey paper, Tk is the saturated temperature for the liquor , see the notes on Boiling Point Elevation Discussion. The Dewey relation correlates the liquor boiling temperature with the water boiling point at liquor saturation pressure.

Method 2: Adamson Equation

[math]\mathbf{\mathit{BPE=\begin{matrix}&0.007642857+0.006184282X+2.92857e^{-5}*T+0.00010957X^2-3.80952e^{-8}T^2\\ &+0.000208801.XT-8.61985e^{-10}X^3-8.61985e^{-10}T^3+1.7316e^{-10}XT^2-2.49763e^{-7}X^2T\end{matrix}}}[/math]
Where:-- X = Total Soda concentration expressed as g/L Na2O @ 25C; and
T = temperature in degree C. T is the saturated temperature for the liquor, see the notes on Boiling Point Elevation Discussion. The Adamson implementation correlates the liquor boiling temperature with the water boiling point at liquor saturation pressure.

Constants in the above equation were determined by data fitting of published Adamson data.

Optional Scale and Offset

Optionally, a scale and/or offset can be globally applied to the BPE value calculated by the selected BPE method. This is specified in Plant Model on the Globals Tab page - Global Properties Calculation Method Selection.

Alumina1 backward compatibility

For backward compatibility in SysCAD 9.2 only, modified versions of Dewey and Adamson are available that use the calculation method (and produce identical results) to those in Alumina1. In Alumina1, BPE@T 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. In Alumina1 implementation the TotalNa used excludes NaF and Na2SiO3.

BPE A3.png

Saturated Alumina Concentration

Rosenberg-Healy3

[math]\mathbf{\mathit{A^{*} = \cfrac{0.96197 C_{25}} {1+\cfrac{ 10 ^{\left(\cfrac{\alpha_o \sqrt{I}} {1+ \sqrt{I}} \right)- \alpha_3 I - \alpha_4 I^{\frac{3}{2}} }} {{exp \left({\cfrac{\Delta G_{rxn}}{RT}}\right)}}}}}[/math]
Where a, a3, and a4 are constants (see table 1)
DGRXN is the Gibbs energy of dissolution (-30960 kJ/kmol)
R is the Universal Gas Constant (8.314472 J/K/mol)
I is the ionic strength, calculated using the following equation:
[math]\mathbf{\mathit{I=0.01887C_{25}+\frac{k_1\left[NaCl\right]}{MW(NaCl)}+\frac{k_2\left[Na_2CO_3\right]}{MW(Na_2CO_3)}+\frac{k_3\left[Na_2SO_4 \right]}{MW(Na_2SO_4)}+k_4 \times 0.01887TOC_{25}}}[/math]
Where k1,k2, k3 and k4 are constants (see Table 1)
Note: Concentration of salts and carbonate are @ 25°C.
Table 1
[math]\alpha_0[/math] [math]\alpha_3[/math] [math]\alpha_4[/math] k1 k2 k3 k4
-9.2082 -0.8743 0.2149 0.9346 2.0526 2.1714 1.6734

User Specified Parameters

The constants in the Rosenberg-Healy equation may be specified by the user by selecting the RosenbergUser option: [math]\alpha_0[/math] = ASat.a0 etc.

ACSat01.png

Oxalate Equilibrium

Calculates the equilibrium concentration (g/l) of oxalate, based on stream properties.


[math]\mathbf{\mathit{OxEquil=7.62 \times Exp\left[0.012T-\left(\frac{MW_{Na_2O}}{MW_{Na_2CO_3}}\right) \times \left(0.016C_{25}+\frac{0.011Qm_{Na_2CO_3}} {Qv}\right)\right]}}[/math]
Where Qv = Liquor Volume at 25 °C.
QmNa2CO3 = Mass flowrate of sodium carbonate
T = temperature in °C.


Note: This equation was developed by British Aluminium Burnt Island refinery. There is no further references for the equation and it should be used with caution.

Viscosity

See Selecting alternative methods for Property Calculations

Method 1: EMA1962

Correlation from Extractive Metallurgy of Alumina, 1962., and is fitted to data with A25 and C25 up to 250 gpl and temperatures up to 80°C. Extrapolating past 80°C fails. Correlation is only valid for liquid phase

[math]\mathbf{\mathit{Visc_{Liq}=10^{Power}}}[/math]
Where:
[math]\mathbf{\mathit{Power=\left(\begin{matrix}&0.0857 + T(-0.00658 + 2.3e^{-6}T)+\frac{C_{25}}{1000}*\left[3.56+T(-0.0357+1.84e^{-4}T)\right]\\ &+\frac{A_{25}}{1000} \left[ 3.23-C_{25}0.0034-0.1246T+T^{2}(0.00204-1.107e^{-5}T) \right] \end{matrix}\right)}}[/math]
  1. The engineering units for viscosity is cP.
  2. T is in degrees of Celsius.
  3. A@25 is in terms of g/L Al2O3.
  4. C@25 is in terms of g/L NaOH.

Method 2: Alexandrov

Alexandrov Viscosity method for Caustic, this method is only available in SysCAD 9.3.
Correlation from : "Equations for Thermophysical Properties of Aqueous Solutions of Sodium Hydroxide" 14th Intl Conf Props Water Steam, Kyoto 2004.
This reference states: Viscosity of solutions at molality up to 3 mol/kg in temperature range from 273 to 548 K and under pressures up to 6 MPa. Please see reference for more information on accuracy of the viscosity prediction.

[math]\mathbf{\mathit{Viscosity{solution}=WaterViscosity \times exp{(t \times m (Term1 + m(Term2 + Term3 \times m) )}}}[/math]

Where:

  1. WaterViscosity is calculated at the same pressure and temperature as the solution
  2. m is the molality of solution in mol/kg
    [math]\mathbf{\mathit{m = (\frac{Mass_{NaOH}}{MW_{NaOH}} + \frac{Mass_{Aluminate}}{MW_{Aluminate}}) \div Mass_{Water} \times 1000}}[/math]
  3. t is temperature ratio
    [math]\mathbf{\mathit{t = \frac{T_{0}}{T}}}[/math]
    • T is solution temperature in Kelvin
    • T0 is 293.15 K
  4. Terms and Constants for the equation are:
    • [math]\mathbf{\mathit{ Term1 = b_{11}+t[b_{21}+t(b_{31}+b_{41}t)] }}[/math]
    • [math]\mathbf{\mathit{ Term2 = b_{12} + t(b_{22}+b_{32}t) }}[/math]
    • [math]\mathbf{\mathit{ Term3 = b_{13} + b_{23}t }}[/math]
b11 = 5.7050102e-1 b12 = -2.9922166e-1 b13 = 4.9815412e-2
b21 = 4.9395013e-1 b22 = 3.7957782e-1 b23 = -4.8332728e-2
b31 = -2.0417183 b32 = -7.423751e-2
b41 = 1.1654862

Correction for solids

When solids are present the viscosity will be greater than for liquor alone. The behavior may or may not be Newtonian and this will depend on the type of liquor and solids as well as the solids concentration. Particle size and shape will also influence the viscosity. Suspensions of rounded particles over 50 microns will tend to have Newtonian behavior, while irregularly shaped particles exhibit Bingham plastic behavior even at larger particle sizes.

There is thus no single correlation that we can use to correct for solids in a liquor; the viscosity will depend on many factors. For Newtonian behaviour (large, rounded particles), Heiskanen and Laapas present

[math] Viscosity Ratio = \frac {\mu_{slurry}}{\mu_{liquid}} = 1 + 2.5 v_s + 14.1 v_s^2 + 0.00273 e^{16v_s}[/math]
where vs is the volumetric fraction of solids in the slurry. This is implemented in the Alumina3 model.

CAVEAT: Calculations using the viscosity model supplied should be treated as indicative only and use of the numbers in detailed design should be discouraged. Laboratory testing of liquors should be undertaken to provide accurate viscosity measurements for design of settlers, classifiers and heat transfer equipment.

References

  1. Molloy-Donaldson Model
  2. Dewey, J.K.L. Boiling Point Rise of Bayer Liquors. Light Metals 1981. The Metallurgical Society of AIME pp 185 -- 197.
  3. Rosenberg S.P and Healy S.J. A Thermodynamic Model for Gibbsite Solubility in Bayer Liquors. Fourth International Alumina Quality Workshop. June 1996.