Carbon Paste Mixing Process for Electrode Densification
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Solution Overview
Problem
Current methods for producing carbonaceous pastes for high-density electrodes, particularly for aluminum electrolysis, face challenges in achieving optimal densification due to incomplete binder penetration and coating of aggregates, leading to residual porosities and reduced electrical conductivity and durability.
Innovation Solution
A two-stage mixing process is employed, using bituminous binders with different softening points in each stage to enhance binder penetration and coating, where the first stage focuses on pre-impregnating the coarse fraction and the second stage ensures thorough filling and distribution of fines, optimizing binder distribution and quality for improved electrode density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single bituminous binder is used for mixing the granular mixture, then the process is simple and cost-effective, but the binder cannot sufficiently penetrate aggregates and fill intergranular voids, resulting in residual porosities and reduced electrode density
Solution Approach 1:
The mixing process is segmented into two distinct stages: first mixing coarse aggregates with binder, then adding fine fraction. This segmentation allows the binder to penetrate aggregates and fill voids more effectively without requiring complex equipment modifications.
Solution Approach 2:
The coarse aggregates are pre-mixed with the bituminous binder before adding the fine fraction. This preliminary action ensures that the binder has sufficient time and opportunity to penetrate the aggregates and begin filling intergranular voids before the fines are introduced, thereby improving overall penetration quality.
2Manufacturing precision
If the granular mixture is mixed without separating fractions, then the mixing process is fast and simple, but the binder distribution is non-uniform with poor penetration into aggregates and voids
Solution Approach 1:
The granular mixture is segmented into coarse aggregates and fine fraction, which are introduced to the mixer at different times. This segmentation enables uniform binder distribution by allowing the binder to first coat and penetrate aggregates, then subsequently coat the fine fraction, resulting in homogeneous final mixture.
Solution Approach 2:
The coarse aggregates are preliminarily mixed with the binder before adding fines. This preliminary mixing action ensures that the binder is uniformly distributed on and within the coarse fraction, creating a foundation for subsequent uniform distribution when fines are added.
3Manufacturing precision
If bituminous binder is added to cold granular mixture, then energy consumption is reduced, but the binder freezes on aggregate surfaces preventing proper coating and penetration
Solution Approach 1:
The granular mixture is preliminarily heated before adding the bituminous binder. This preliminary heating action prevents the binder from freezing on cold aggregate surfaces, ensuring proper coating and penetration while minimizing the total energy required during the mixing process itself.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly enhances the densification of electrodes by ensuring better binder penetration and coating, resulting in improved electrical conductivity and durability by minimizing residual porosities and maintaining the coking rate of the binder.
Implementation Method 1
The bituminous binder is fed onto the load of preheated dry granular mixture... to promote its 'coating' and 'penetration' properties... penetration into the open porosities of the aggregates
Implementation Method 2
the processing temperature must typically be at least 30°C above the SP obtained by the Mettler method... to sufficiently lower the viscosity of the binder, on the one hand, for pumping and flowing needs
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3a~3b
AI summary
The process according to the invention proposes, for the mixing of a solid and dry granular mixture and of a liquid bituminous binder, in an amount required for the manufacture of the electrodes (6), the solid and dry granular mixture being a mixture of two fractions of constituents, of which one is referred to as a coarse fraction (1a, 2a) that includes aggregates, and the other fraction is a fraction of submillimetric fines (1b, 2b), that the mixing comprise at least two consecutive mixing steps, a first (102a) of which, referred to as a step of preimpregnating the aggregates, consists in mixing the coarse fraction (2a) of the granular mixture with a portion (3a) of the bituminous binder, in an amount that is at least sufficient to coat the aggregates and at least partially fill open porosities of the aggregates, and is followed by a second mixing step (102b), referred to as a packing step, which consists in mixing the coarse fraction (4a) preimpregnated with bituminous binder and derived from the first mixing step (102a), with the remainder (3b) of the bituminous binder, required for the manufacture of the electrodes (6), and with the fraction of fines (2b) of said granular mixture. The process of the invention may be carried out by equipment comprising two mixer stages, in continuous mode or batch mode, with the aid of two mixers, each of which carries out one of the two mixing steps, or with the aid of a single mixer.