Energy savings, higher efficiency, extended cell life: RuC technology applied in 600 kA aluminium reduction cells enables stable and efficient operation at lower cell voltages.

The ready to use cathode (RuC) technology has transformed the cathode assembly method, and by optimizing the cathode assembly and upgrading the collector bar material with copper, the average horizontal current in the aluminium pad has decreased by nearly 70% compared to cathode designs with steel collector bars, which significantly improved the magnetohydrodynamic (MHD) stability of the aluminium reduction cell.

Cutting carbon emissions

Aluminium reduction is a major consumer of electricity, consuming more than 580 TWh of electricity in China (7.5% of China's total electricity consumption). Electrolytic aluminium CO₂ emissions account for about 75% of the total emissions in the non-ferrous metal industry and about 3.5% of the total carbon dioxide emissions in China. With the deepening implementation of the national “dual carbon” strategy in China and related industrial policy requirements, the electrolytic aluminium industry is facing the challenge of reducing carbon dioxide emissions. Accelerating the technology research and major demonstration projects for energy-saving and carbon reduction in electrolytic aluminium is the important task for the survival and development of smelters in China. Based on the requirements of government policies, starting from 2025, the comprehensive AC power consumption of liquid aluminium has to be lower than 13,300 kWh/t Al.

R&D: energy-saving and low-carbon technologies in China

In 2024, the industry’s average comprehensive AC power consumption was about 13,400 kWh/t Al, a decrease of 600 kWh/t Al compared to 2013. In recent years, under the requirements of the national “dual carbon” emissions policy, the research and technology development in China’s aluminium reduction industry have developed energy-saving technologies for the design of aluminium reduction cells, such as graphitized cathode blocks, large cross-section high conductivity collector bars, copper insert collector bars, etc., which have achieved varying degrees of energy-saving.

In order to achieve further energy saving and carbon reduction, Shandong Weiqiao group, NEUI, Tokai Cobex and NFC collaborated to develop the “RuC energy-saving, long life, and high yield aluminium technology” with Tokai Cobex patented Ready-to-Use cathode (RuC) technology at its core.

Low cathode voltage drop (CVD) is achieved through an enhanced design and utilisation of copper even though the contact area between the collector bar and carbon block is reduced by up to 60% less. Sustaining this low CVD of cell life proves the robustness of the cathodic system and the RuC technology. Due to excellent electrical conductivity of RuC, the simulated voltage drop of the 600 kA RuC cell is only 149 mV, which is much lower than the conventional cathode design with steel collector bars, creating favorable conditions for stable and efficient operation of the reduction cell at low working voltage.

This technology has been in industrial trials on NEUI 400 and 600 kA cells technologies at Weiqiao Group since December 2016, achieving significant energy-saving, production increase, and pot life extension. In order to better respond to the policy requirements of “dual control” of energy consumption and lead industry technological progress, Weiqiao Group has started to expand the application of RuC technology in 600 kA potlines (Fig. 1).

Improving MHD stability

The RuC technology has transformed the cathode assembly. By optimizing the cathode structure and upgrading the collector bar material to copper, due to the high electrical conductivity, the average horizontal current has decreased by 65.3% compared to traditional cathode assemblies. This reduction in the electromagnetic forces in the aluminium pad, slows down the aluminium pad oscillations, significantly improving MHD stability of the aluminium reduction cell. This allows for reduced Anode-cathode distance (ACD) operation and ultimately enables a reduction in cell voltage.

Fig. 2 shows the CVD trend of 600 kA RuC cells compared to reference cells with steel collector bars over 54 months. The average CVD of the RuC cells is 162 mV, which is 48 mV lower than that of the conventional reference cells. The CVD of RuC cells is more stable than the reference cells, with an average increment of 4 mV per year, 5 mV lower than the increment of the reference cells. Projected over the cell’s lifetime, the average CVD is 167 mV, assuming a cell life of 2,600 days based on the lower measured cathode wear.

In addition, actual measurements show that the 600 kA RuC cell maintains good uniformity of cathode current distribution. The current pick-up ratio between upstream and downstream side is measured between 49–51%. This balance is achieved with the improved design and assembly mechanisms of the RuC cathode. This uniform distribution of cathode current creates favourable conditions for the stable operation of the 600 kA RuC cells.

Fig. 2: Cathode voltage drop comparison between RuC and reference cells.

Contribution of RuC to extending pot life

The RuC technology homogenises the current distribution on the cathode working surface, significantly improving the uniformity of the current distribution within the cathode block. According to simulation results, the maximum current density of the cathode working surface has decreased by nearly 30%. Since current density drives the electrochemical wear, it is expected that the wear rate in critical areas at the end of the cathodes has been considerably reduced.

RuC uses full copper collector bars instead of steel collector bars, reducing the cross-section of the conductive bars by about 80%, which can significantly reduce the thermal stress and deformation of the collector bar structure. The reduced metal volume of the collector bar is replaced by cathode material, increasing the distance from the collector bars to the cathode working surface. Due to these structural advantages, the effective carbon height and overall strength of cathode blocks can be significantly improved while maintaining the same outer dimensions, which is beneficial for improving cell life. To assess cathode erosion, measurements were performed on operational cells using Tokai Cobex’s Lancelot equipment. Fig. 3 shows the on-site cathode wear measurement for 600 kA reduction cells. It shows the comparison of typical test results for cathode wear between 600 kA RuC and reference cells. After operating 4.5 years, the maximum annual wear of 600 kA RuC cells is 25.5 mm, while the maximum annual wear of reference 600 kA cells is 34.8 mm. 600 kA RuC cells maximum annual wear is 9.3 mm smaller than the reference cells, a maximum wear rate reduction of 26.7%. Based on this results, the service life of RuC cells is expected to be significantly extended.

Fig. 3: Comparison of cathode working surface erosion measurements between RuC cathodes and Reference cathodes.

Lining configuration and thermal balance design

The lining design of the 600 kA RuC cell enhances insulation in each area of the cell. The insulation space at the bottom and end of the cathode has been improved, increasing insulation in these areas. Additionally, and an embedded insulation design on the Si₃N₄-SiC side blocks is used. Simulations show an even temperature distribution and ideally placed isotherms, preventing phenomena such as cold cathodes that are often caused by introducing copper into the collector bar. By optimizing the lining configuration and thermal balance design, RuC cells can maintain an ideal thermal balance at low voltages ranging from 3.85 to 3.90 V. This showcases the advantage of RuC cells to operate with high MHD stability and low CVD.

Production process optimization technology

In response to the technical characteristics of MHD stability, low CVD, and low heat loss of 600 kA RuC cells, the implementation of this project has led to an update of the complete set of process specifications, including lining construction, preheating, start-up and production technical specifications.

As of the end of May 2025, two 600 kA RuC cells have been operating for more than 54 months and achieved excellent technical and economic indicators. The operating voltage range of the cells during the normal period is between 3.85–3.90 V, while the operating voltage range of the reference cells with steel collector bars is between 3.95–4.02 V. Therefore, the average operating voltage of the RuC cells is about 100 mV lower than that of the reference cells.

The average current efficiency of two 600 kA RuC cells during the normal period is 94.1%, while the average current efficiency of the reference cells is 92.5%. The current efficiency of the RuC cells is 1.6% higher than the reference cells. Consequently, the average DC energy consumption is 12 288 kWh/t Al during the normal period, compared to 12 851 kWh/t Al in the reference cells. The average DC energy consumption of RuC cells is 563 kWh/t Al lower than that of the reference cells.

Stable and efficient reduction cells

The RuC technology has successfully overcome the bottleneck of MHD stability core technology, enabling the reduction cells to operate stable and efficiently at lower cell voltages. This achievement has led to long-term energy savings, increased current efficiency, and extending cell life of 600 kA cells. It is currently the most promising energy-saving technology in the industry to achieve significant energy-savings, carbon reduction, and extended cell life. Based on the trial results achieved, Weiqiao has increased the number of RuC cells in its smelters and is currently operating more than 110 RuC cells. The intention is to significantly increase this number.

By Dr Yungang Ban, (Northeastern University Engineering & Research Institute Co., Ltd. ‘NEUI’), Xintao Zhang, Xizhong Cui, (Shandong Hongtuo Industrial Co., Ltd.), Dr Till Reek, Tokai Cobex GmbH

Source：INTERNATIONAL ALUMINIUM JOURNAL