Multi-Time-Scale Optimization and Control Method for High-Penetration Photovoltaic Electrolytic Aluminum Plants

Price determination in the electrolytic aluminum industry: The role of electricity prices

The aluminum electrolysis industry is a typical high-energy-consumption and high-carbon-emission sector, and its low-carbon transformation is crucial for achieving “dual-carbon” goals. However, aluminum electrolysis is constrained by thermodynamic safety limits, and conventional dispatch models also often overlook carbon emission trading and the integrated utilization of waste heat. To address these challenges, a low-carbon economic dispatch method considering production safety constraints is proposed in the paper for integrated energy systems in aluminum electrolysis, aiming to enhance wind power utilization and ensure operational safety. First, a load model incorporating thermodynamic safety constraints is developed, and a thermal dynamics equation of electrolytic cells is established to characterize the temperature dynamics of aluminum loads. Then, a bi-level optimization framework for the power–aluminum system is constructed: the upper level minimizes grid power-supply costs by coordinating thermal, wind, and photovoltaic generation, while the lower level maximizes enterprise profit, balancing production safety and economic efficiency to achieve coordination between the system and enterprise layers. Finally, a tiered carbon trading mechanism and waste heat heating model are integrated into the framework, combined with a second-order RC building thermal inertia model to realize coordinated optimization among electricity, heat, and carbon flows. The simulation results demonstrate that the proposed method effectively reduces carbon emissions while ensuring electrolytic cell safety: with carbon trading, emissions decrease by 7.2%; when incorporating waste heat utilization reduces boiler heating emissions, they decrease by 74.7%; and further considering building thermal inertia increases wind power utilization to 99.6%, achieving the coordinated optimization of electricity–heat–carbon systems.

With the development of electrolytic aluminum in our country, sulphur content in aluminum anode increased year by year, thus there is the risk of SO2 discharge over standard in exhaust gas treatment in electrolytic aluminum industry. Further, the waste heat from exhaust gas of electrolytic aluminum has not been made full use at present. It is necessary to development new exhaust gas treatment and utilization technology. In this study, a scheme about electrolytic aluminum exhaust gas cascade utilization has been proposed according to the characteristics of electrolytic aluminum exhaust gas. The electrolytic aluminum exhaust gas after dry treatment could be sent to power plant boiler as combustion air, as the discharge of electrolytic aluminum exhaust gas and air pollutants could be decreased greatly. After the comparison of techno-economic analysis, the discharge by the scheme of cascade utilization was less than that with desulfurization, with more economic benefit. Thus it is worth to be extended, since the scheme of electrolytic aluminum exhaust gas cascade utilization showed good techno-economy.

High temperature superconducting (HTS) dc power cable shows a wide application prospect in the field of power transmission for its nearly lossless and rather high capacity. IEE has installed a 360-meter long high temperature superconducting (HTS) dc power cable at the self-supply power plant of Zhongfu Industrial Company Ltd. in Gongyi, Henan and the system has operated for two years. The cable connects a 19.5 MVA/1.5 kA silicon-controlled rectifier, which connects with a 110 kV/1 kV transformer, to the bus bar of an electrolytic aluminum cell. It is designed to carry 10-kA current and the voltage is 1300 V. The HTS dc power cable core consists of five conductor layers wound with the spliced Bi-2223 wires with the length of 40 km. The cable core has five layers and 23 HTS wires in each layer with the outer diameter of 45 mm. The HTS dc power cable is fabricated with the spliced superconducting wires which will have effect on the overall superconductivity. Also, since dc output of the rectifier contains a proportion of the ac harmonic ripple, the large dc and small ac will generate the loss in the cable core. In the operation of the 10 kA HTS dc power cable, anode effect will occur in electrolytic aluminum tank, which will lead to a large fault current in the cable and even lead to the power off protection. In this paper, stability of the spliced Bi-2223 wire, stability of the cable core under the cold shrinkage force, loss under the large dc and small ac ripple are analyzed by the theoretical and experimental methods. The test results of ac ripple loss, anode effect, and stable operation are also presented.

The unit energy consumption and its price have become the main obstacles for the future development of the aluminum electrolysis industry in China. Meanwhile, wind power is widely being abandoned because of its instability. In this study, a novel idea for wind power accommodation is proposed to achieve a win-win situation: the idea is for nearby aluminum electrolysis plants to absorb the wind power. The features of the wind power distribution and aluminum electrolysis industry are first summarized, and the concept of wind power accommodation by the aluminum industry is introduced. Then, based on the characteristics of aluminum reduction cells, the key problems, including the bus-bar status, thermal balance, and magnetohydrodynamics instabilities, are analyzed. In addition, a whole accommodation implementation plan for wind power by aluminum reduction is introduced to explain the theoretical value of accommodation, evaluation of the reduction cells, and the industrial experiment scheme. A numerical simulation of a typical scenario proves that there is large accommodation potential for the aluminum reduction cells. Aluminum electrolysis can accommodate wind power and remain stable under the proper technique and accommodation scheme, which will provide promising benefits for the aluminum plant and the wind energy plant.

As a high energy-consuming industry, electrolytic aluminum industry consumes too much social resources, which needs to further improve its energy efficiency. This paper analyzes the different views of evaluating the energy efficiency level of electrolytic aluminum industry, and presents it in the form of constructing energy efficiency evaluation index system. Through the calculation of the index and the determination of weight, the level of energy efficiency in the typical scene of electrolytic aluminum industry is evaluated. Finally, an example is given to verify the effectiveness of the evaluation method. This study provides guidance for the improvement of energy efficiency of electrolytic aluminum, and lays the foundation for the implementation of the follow-up energy efficiency improvement scheme.

Herein, the characteristics, research progress, and application prospects of ionic liquid-based electrolytic aluminum deposition are reviewed and analyzed in comparison with the Hall-Héroult method. The reaction conditions and production procedures of this material are discussed alongside the problems ionic liquids face in the electrolytic aluminum industry. Ionic liquid-based electrolytic aluminum deposition realizes the electrolytic aluminum reaction at low temperatures, achieving a reaction energy consumption close to the theoretical minimum value. The reaction also avoids harmful CO2 or HF emissions, demonstrating a green and environmental-friendly approach to the production of electrolytic aluminum. In the future, in-depth work on the implementation of ionic liquid electrolytes should be carried out, establishing the necessary technical criteria and laying the foundation for the integration of this approach.

IEE has installed a 360-m-long high-temperature superconducting (HTS) dc power cable at the self-supply power plant of Zhongfu Industrial Co., Ltd. in Gongyi, Henan. The cable connects a 19.5 MVA/1.5 kA silicon-controlled rectifier, which connects with a 110 kV/1 kV transformer, to the bus bar of an electrolytic aluminum cell. It is designed to carry 10 kA current and the voltage is 1300 V. The HTS dc power cable core consists of five conductor layers wound with the spliced Bi-2223 wires with the length of 40 km. The cable core has five layers and 23 HTS wires in each layer with the outer diameter of 45 mm. As the items in this project, testing of 4 to 5 m length prototype cables, including a 5 m prototype cable fabricated before the 360 m power cable and a 4 m prototype cable intercepted from the 360 m HTS power cable, is conducted. These prototypes are used to assess the design program, fabrication process, and performance of the 360 m/10 kA HTS power cable including steady state operation at the 10 kA design current and overcurrent fault capability. The critical current of the 5 and 4 m HTS power cable reach 14.3 kA and 13.8 kA at 77 K, 1 μV/cm, respectively. In this paper, the design parameters and fabrication of the 360 m/10 kA HTS dc power cable conducted by IEE are presented. The cable system, installation process and the summary of the results from the testing of 4 and 5 m prototype cables are described. In addition, details of the initial cool-down process and energizing are presented.

Spent carbon anode (SCA) is a dangerous solid waste that is continuously discharged from the aluminum electrolysis industry and has a large number of valuable resources and a high risk of environmental pollution. Its safe disposal and resource utilization have become a resource and environmental problem that must be solved urgently. Current methods for SCA disposal include flotation, vacuum metallurgy, physical activation, roasting, bubbling fluidized bed combustion, alkali fusion, alkali leaching, and chemical leaching combined with high temperature graphitization. In this paper, the material composition, resource properties, and environmental risks of SCA are discussed. Working principle, treatment process, advantages and disadvantages of the above methods are also briefly described and compared. Results showed that flotation is the safest disposal and comprehensive utilization technology that is suitable for characteristics of SCA raw materials and has the most large-scale application potential. In addition, characteristics of SCA recovery products are correlated to the recycling of aluminum reduction cells. This technology can alleviate the shortage of high-quality petroleum coke resources in China’s carbon material industry and the high cost of raw materials in aluminum electrolysis industry.

Superheat identification is very important in aluminum electrolysis industry. In order to realize the real-time identification of superheat, this paper proposes a novel dual-stream multidimensional network (DM) model, which is composed of an efficient stream and an accuracy stream. In efficient stream, a mobilenet is equipped on Artificial Intelligence of Things (AIoT) devices to achieve quick superheat identification as normality or abnormality. In accuracy stream, a two-stream information sharing 3D residual network is equipped on a cloud computing service to achieve accurate identification through abnormal frames. Experiments are conducted on the aluminum electrolysis datasets, and the results verify that our DM model can realize efficient and accurate identification under resource saving condition.

Evaluation of fluoride emissions and pollution from an electrolytic aluminum plant located in Yunnan province

Formation mechanism and treatment status of perfluorocarbon in the electrolytic aluminum industry: A review

To address the curtailment phenomenon caused by the high penetration of renewable energy in the system, an optimization scheduling strategy is proposed, considering the full process of electrolytic aluminum production and the integration of thermal power and energy storage. Firstly, to explore the differentiated response capabilities of various devices such as high-energy-consuming electrolytic aluminum units, thermal power units, and energy storage devices to effectively address uncertain variables in the power system, a Variational Mode Decomposition method is introduced to construct differentiated response methods for its low-frequency, medium-frequency, and high-frequency components. Secondly, based on the real production regulation characteristics of the high-energy-consuming electrolytic aluminum load, and considering various influencing factors such as current, temperature, and output, a scheduling model involving electrolytic aluminum load is established. Then, the power generation characteristics in other processes of electrolytic aluminum production are fully exploited to achieve energy storage conversion, replacing the energy storage batteries that respond to high-frequency components. Finally, by combining the deep peak-shaving model of thermal power units, an optimization scheduling model is established for the joint operation of the full electrolytic aluminum production load and thermal-power-storage systems, with the goal of minimizing system operating costs. The case study results show that the proposed model can significantly enhance the system’s renewable energy absorption capacity, reduce energy storage installations, and enhance the economic efficiency of the system’s peak-shaving operation.

Low carbon operation is one of the goals of the energy revolution, and the thermal power units are required to achieve more carbon emission reduction for achieving the carbon peaking and carbon neutrality goals. To help thermal power units participating in both electricity spot trading and carbon trading to optimize their operational decisions, a cost-benefit model for thermal power units that take into account both electricity spot trading and carbon trading is built from two perspectives: low-carbon technology and low-carbon policy, combining low-carbon instruments with market mechanisms. The objective is to maximize the profitability of the unit, and the effectiveness of the proposed model is proved by simulation using actual measurement data. The results proves that the proposed model can balance low carbon target and economic aspects, and is also useful for thermal power units to optimize their operational decisions under different scenarios.

Product tending machine (PTM) is one of the most important equipment in the aluminum electrolysis production process, for the problem of PTM optimization, a queuing system model of aluminum electrolysis PTM is proposed for the first time. According to the actual production situation of the aluminum electrolysis industry, a non-preemptive priority M/G/1 aluminum electrolysis PTM queuing system model is defined, and the general calculation formula of the operating index of the non-preemptive priority PTM queuing system is given, including queuing system length, waiting time, optimal service rate, etc. According to the actual production data of an aluminum factory, the relevant indicators were calculated and analyzed, and the relationship between the operating indicators and the number of electrolysis cells was drawn. Finally, under the conditions of meeting different operating indicators, the optimal matching scheme of PTM and aluminum electrolysis cells was given.