Greenhouse gas emissions and future development trends of primary aluminum in China

Trajectory, driving forces, and mitigation potential of energy-related greenhouse gas (GHG) emissions in China's primary aluminum industry

Aluminum production is a major energy consumer and source of greenhouse gas (GHG) emissions. The regional transfer of the primary aluminum (PA) industry, which mainly consists of the processes of electrolysis and aluminum ingot casting, is currently an important international trend in aluminum industrial development. However, the changes in GHG emissions from aluminum production for such transfers are unclear. This study has established a life cycle assessment model of aluminum industry based on regional transfers in the context of China, determined the GHG emissions of PA and secondary aluminum (SA) production, examined the GHG emission changes of PA production based on regional industry transfer between the years 2007 and 2017, and explored seven driving factors that affect GHG emissions in the aluminum industry. GHG emissions per unit PA and SA production in China decreased by 18.6% and 6.3%, respectively, but the total GHG emissions from aluminum industry still increased by 2.2 times between the years 2007 and 2017. The driving factor analysis showed that the major positive effects of GHG emissions from China's aluminum industry from 2007 to 2017 included the production scale effect of SA and the energy structure effect. Existing regional transfers (between the years 2007 and 2017) did not deliver significant annual GHG emissions reductions. Currently, Xinjiang, Henan, Shandong, and Inner Mongolia are the main PA production provinces in China, although regional transfers have been implemented. This study provides a basis for the improvement and sustainable development of the aluminum industry, suggests policies for regional aluminum development, and proposes a beneficial layout of the aluminum industry.

Technologies for CO2 emission reduction and low-carbon development in primary aluminum industry in China: A review

Primary aluminium production is a highly energy-intensive and greenhouse gas (GHG)-emitting process responsible for about 1 % of global GHG emissions. In 2009, the two most energy-intensive processes in primary aluminium production, alumina refining and aluminium smelting consumed 3.1 EJ, of which 2 EJ was electricity for aluminium smelting, about 8 % of the electricity use in the global industrial sector. The demand for aluminium is expected to increase significantly over the next decades, continuing the upward trend in energy use and GHGs. The wide implementation of energy efficiency measures can cut down GHG emissions and assist in the transition towards a more sustainable primary aluminium industry. In this study, 22 currently available energy efficiency measures are assessed, and cost-supply curves are constructed to determine the technical and the cost-effective energy and GHG savings potentials. The implementation of all measures was estimated to reduce the 2050 primary energy use by 31 % in alumina refining and by 9 % in primary aluminium production (excluding alumina refining) when compared to a “frozen efficiency” scenario. When compared to a “business-as-usual” (BAU) scenario, the identified energy savings potentials are lower, 12 and 0.9 % for alumina refining and primary aluminium production (excluding alumina refining), respectively. Currently available technologies have the potential to significantly reduce the energy use for alumina refining while in the case of aluminium smelting, if no new technologies become available in the future, the energy and GHG savings potentials will be limited.

Aluminum production is a major energy consumer and important source of greenhouse gas (GHG) emissions globally. Estimation of the energy consumption and GHG emissions caused by aluminum production in China has attracted widespread attention because China produces more than half of the global aluminum. This paper conducted life cycle (LC) energy consumption and GHG emissions analysis of primary and recycled aluminum in China for the year 2020, considering the provincial differences on both the scale of self-generated electricity consumed in primary aluminum production and the generation source of grid electricity. Potentials for energy saving and GHG emissions reductions were also investigated. The results indicate that there are 157,207 MJ of primary fossil energy (PE) consumption and 15,947 kg CO2-eq of GHG emissions per ton of primary aluminum ingot production in China, with the LC GHG emissions as high as 1.5–3.5 times that of developed economies. The LC PE consumption and GHG emissions of recycled aluminum are very low, only 7.5% and 5.3% that of primary aluminum, respectively. Provincial-level results indicate that the LC PE and GHG emissions intensities of primary aluminum in the main production areas are generally higher while those of recycled aluminum are lower in the main production areas. LC PE consumption and GHG emissions can be significantly reduced by decreasing electricity consumption, self-generated electricity management, low-carbon grid electricity development, and industrial relocation. Based on this study, policy suggestions for China’s aluminum industry are proposed. Recycled aluminum industry development, restriction of self-generated electricity, low-carbon electricity utilization, and industrial relocation should be promoted as they are highly helpful for reducing the LC PE consumption and GHG emissions of the aluminum industry. In addition, it is recommended that the central government considers the differences among provinces when designing and implementing policies.

CO2 emission trends of China's primary aluminum industry: A scenario analysis using system dynamics model

This paper presents an analysis of the smelting trends and potential opportunities to reduce the overall greenhouse gas emissions from the primary aluminum industry in total, both direct emissions from the production processes and indirect emissions from the electric power used. Presently, 71% of the aluminum is produced with electricity from fossil fueled power plants, and while the introduction of wind and solar generation of electricity is accelerating, these have technical constraints and limitations. On average, indirect emissions from the power used dominate as emission source, so de-carbonizing the electricity production through low-emission power sources is crucial for the primary aluminum production in order to meet carbon emission targets. Globally the best result will be achieved by maximizing aluminum production in regions that can provide low emission power. However, national or political objectives can sometimes counter this by re-directing the use of existing hydro power used by aluminum smelters to eliminate local emissions from the process, in order to meet national goals. While this may reduce carbon emissions regionally, the result may be an increase in the industry’s global emissions through increased production capacity using non-renewable high emission level power sources in other regions. Indeed, the carbon footprint of primary aluminum production has increased significantly this century due to an increasing transition of the energy mix towards fossil based power.

Current Status, Future Expectations and Mitigation Potential Scenarios for China's Primary Aluminium Industry

GHG emissions from primary aluminum production in China: Regional disparity and policy implications

A hybrid process structure, a continuous flow followed by a batch process, is used in the primary aluminum production. The continuous flow provides a steady stream of Work-In-Process (WIP) to the process; but the WIP is usually delayed before it can move to the batch process. This leads to increased flow times, increased inventories, and inefficient use of resources. In such hybrid structures, process synchronization can be achieved by carefully scheduling the production and allocating the resources. We study the performances of two alternative production-scheduling policies and two alternative resource allocation mechanisms in the primary aluminum production process, which is a hybrid process. First, we build a simulation model that can represent a nearly realistic primary aluminum production setting under various design parameters. Second, we show that the production scheduling policy led by the latter stage of the production, significantly improves the process performance compared to a decentralized policy, in which each stage makes its own schedule. Third, we show that the amount of resources at the buffer zone in between the two stages of the process is very critical for the process performance; and we quantify its benefits through numerical work. Finally, we suggest that dedicating common resources, such as trucks, to individual stages of the process slightly improves the process performance as opposed to pooling those resources.

Overcapacity of primary aluminium is local surplus. In traditional aluminium producing provinces such as Henan and Shandong, excess capacity does exist; but in western China, the industry still has large room for development. The claim that primary aluminium industry in the whole country suffers overcapacity lacks theoretical and data supports. The coastal regions of China have high population density, and developed industry, leading to shortage of electricity and higher electricity bills. Production of primary aluminium consumes large amount of electricity; therefore, to optimize the allocation of resources, the distribution of aluminium producers should be adjusted. The center of primary aluminium production should be moved to the resource-rich west. This adjustment is in line with laws of economics, and will help energy saving, emission reduction, and environment protection. Storage of primary aluminium is storage of energy. The government should enlarge China’s strategic stockpile of primary aluminium. Light-weighted, durable in use, and easy to store, aluminium products may be widely used in the production of automobiles and doors and windows of constructions. If the government builds more low-rent housings for low-income groups, primary aluminium industry will not face overcapacity; instead, it will scale new heights.

Low-carbon production of iron and steel: Technology options, economic assessment, and policy

Aluminum is an essential material for the construction and development of national economy, however the GHG (greenhouse gas) emissions caused by its production have been noticed by China’s government gradually. In this study, the life cycle energy consumption and GHG emissions caused by the production of primary aluminum in different years in China were calculated, and the correlation between GHG emissions and some important factors i.e. resource consumption and procedure energy consumption was analyzed. The final results show that for GHG emissions, electricity is the major contributor that accounts for 68.5% of the total, followed by the emissions of anode effect and calcination of limestone, which accounts for 7.9% and 6.8% respectively, and the percentages other factors account for less than 6%. The results also show that the calcination of limestone, combustion of coal gas and consumption of electricity are the three main factors which have the largest correlation degree with GHG emissions, and their correlation degrees are 0.96, 0.94 and 0.90 respectively. Therefore, decreasing the consumption of coal gas and improving the efficiency of the calcination of limestone are effective ways to decrease the GHG emissions of primary aluminum production.

CO2 emission and mitigation potential estimations of China's primary aluminum industry

Many individual polycyclic aromatic hydrocarbons (PAH) are genotoxic carcinogens. One of the parent PAH, pyrene, undergoes simple metabolism to 1-hydroxypyrene. 1-Hydroxypyrene and its glucuronide are excreted in urine. Biological monitoring of exposure to PAH has rapidly been expanded since urinary 1-hydroxypyrene was suggested as a biological index of dose of pyrene. Since pyrene is always present in PAH mixtures, the biological indicator is not only an indicator of uptake of pyrene, but also an indirect indicator of all PAH. At present, several hundreds of papers reporting on urinary concentrations of 1-hydroxypyrene in workers' urine are available. It appeared that urinary 1-hydroxypyrene is a sound biomarker and that the analytical method is robust and non-laborious. Since epidemiological studies of cancer mortality related to long-term average urinary 1-hydroxypyrene concentration are lacking, a sound health-based limit value of 1-hydroxypyrene in urine cannot be set as yet. Since PAH exposure is widespread and the dermal uptake is substantial among exposed workers, an attempt was made to propose a three-level benchmark guideline for urinary 1-hydroxypyrene. The reference value as a 95th percentile in non-occupational exposed controls is 0.24 micromol mol(-1) creatinine and 0.76 micromol mol(-1) creatinine for non-smokers and smokers, respectively. This is the first level of the benchmark guideline. A no-biological-effect-level of 1-hydroxypyrene in urine of exposed workers was found at 1.4 micromol mol(-1) creatinine. It is the lowest reported level at which no genotoxic effects were found and therefore the estimate for the second level of the benchmark guideline. In two types of industry, coke ovens and primary aluminium production, the regression of airborne PAH concentrations and urinary 1-hydroxypyrene concentrations in exposed workers has been studied. The correlation of airborne concentrations and urinary 1-hydroxypyrene in urine of workers from coke ovens and in the primary aluminium industry was used to estimate the level of urinary 1-hydroxypyrene equal to the present occupational exposure limit (OEL) of PAH. The concentration of 1-hydroxypyrene in urine equal to the OEL is 2.3 micromol mol(-1) creatinine and 4.9 micromol mol(-1) creatinine, respectively, in these two industries. These latter values present the third level of the benchmark guideline.