Design and application of multidimensional decision system for aluminum electrolysis
Aluminum electrolysis is a complex process, the outputs of the controller are hard to decide. This paper described a system for the decision of the setting voltage, AlF3 addition and aluminum tapping amount in aluminum electrolysis process according to the equivalent superheat which is regarded as the main parameter. The system has four sub-systems, which are the fault diagnosis, equivalent superheat calculation, control extent decision, decision quantity correction. The cell state diagnosis was implemented based on the frequency characteristics of cell resistance, which helps to select the decision strategy. The superheat soft measurement model was given by the analysis and calculation of electrolyte composition after the aluminum fluoride volatilization rate model was built, and it was on-line corrected by the actual measured value. The outputs of the controller were got by the equivalent differential diagram. At last, the decision content was corrected by the prediction of temperature. This system have been applied in a 300kA aluminum production control system, and the results showed that the temperature can be controlled between 945 degree celsius and 960 degree celsius, and the superheat can be controlled within 12 degree celsius, the current efficiency increased and power consumption reduced.
Diagnosis System for Alumina Reduction Based on BP Neural Network
The diagnosis system for the alumina reduction was developed on the basis of BP neural network with optimization by genetic algorithm. The neural network used the characteristic vectors composed of the frequency energy calculated from cell resistance as 10 inputs and three cell statuses as 3 outputs. The neural network was certified by industrially sampling data. The results showed the accuracy ratio was larger than 80%, which can meet the requirements in the aluminum production. The diagnosis software was designed and applied in an aluminum smelter.
Liquidus temperatures for primary crystallization of cryolite in molten salt systems of interest for aluminum electrolysis
AbstractTemperatures for primary crystallization of Na3AlF6 in multicomponent electrolyte systems of interest for the aluminum electrolysis process were determined by thermal analysis. The results are presented as binary and quasibinary diagrams and discussed in view of the literature data. An empirical equation describing liquidus temperatures for primary crystallization of Na3AlF6 was derived:
$$\begin{gathered} t/(^\circ C) = 1011 + 0.50[AlF_3 ] - 0.13[AIF_3 ] - \frac{{3.45[CaF_2 ]}}{{1 + 0.0173[CaF_2 ]}} \hfill \\ + 0.124[CaF_2 ] \cdot [AlF_3 ] - 0.00542([CaF_2 ] \cdot [AlF_3 ])^{1.5} \hfill \\ - \frac{{7.93[Al_2 O_3 ]}}{{1 + 0.0936[Al_2 O_3 ] - 0.0017[Al_2 O_3 ]^2 - 0.0023[AlF_3 ] \cdot [Al_2 O_3 ]}} \hfill \\ - \frac{{8.90[LiF]}}{{1 + 0.0047[LiF] + 0.0010[AlF3]^2 }} - 3.95[MgF_2 ] - 3.95 \hfill \\ \end{gathered} $$
 wheret is the temperature in degree Celsius and the square brackets denote the weight percent of components in the system Na3AlF6-AlF3-CaF2-Al2O3-LiF-MgF2-KF. The composition limitations are [AlF3] ≈ [CaF2] ≈ [LiF] < 20 wt pct, [MgF2] ≈ [KF] < 5 wt pct, and [A12O3] up to saturation.