Energy efficiency improvement and GHG abatement in the global production of primary aluminium

Primary aluminium production is energy- and GHG-intensive in which electrolysis is by far the most energy- and GHG-intensive process. This paper’s aim is to study the effects on (1) primary energy use, (2) GHG emissions and (3) energy and CO2 costs when energy end-use efficiency measures are implemented in the electrolysis. Significant savings in final and primary energy use, GHG emissions and energy and CO2 costs can be achieved by implementing the studied measures. Vertical electrode cells and the combination of inert anodes and wettable cathodes are among the measures with the highest savings in all three areas (primary energy use, GHG emissions and energy and CO2 costs). Direct carbothermic reduction is one of the measures with the highest savings in primary energy use and energy and CO2 costs. For GHG emissions, direct carbothermic reduction is the more beneficial choice in regions with a high proportion of coal power, while inert anodes are the more beneficial choice in regions with a high proportion of low-carbon electricity. Although a company potentially can save more money by implementing the direct carbothermic reduction, the company should consider implementing the vertical electrode cells together with other energy-saving technologies since this would yield the largest GHG emission savings while providing similar cost savings as the direct carbothermic reduction. It may be necessary to impose a price on GHG emissions in order to make inert anodes cost-effective on their own, although further evaluations are needed in this regard. There is a potential to achieve carbon-neutrality in the reduction of aluminium oxide to pure aluminium.

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

The Paris Agreement includes the goals of ‘holding the increase in the global average temperature to well below 2°C above pre-industrial levels’ and ‘making finance flows consistent with a pathway towards low greenhouse gas emissions’. Industrial energy efficiency will play an important role in meeting those goals as well as becoming a competitive advantage due to reduced costs for companies. The aluminium industry is energy intensive and uses fossil fuels both for energy purposes and as reaction material. Additionally, the aluminium industry uses significant amounts of electricity. The electrolysis process in the primary production of aluminium is the most energy- and carbon-intensive process within the aluminium industry. The aim of this paper is to study the effects on primary energy use, greenhouse gas emissions and costs when three energy efficiency measures are implemented in the electrolysis process. The effects on the primary energy use, greenhouse gas emissions and costs are calculated by multiplying the savings in final energy use by a primary energy factor, emissions factor and price of electricity, respectively. The results showed significant savings in primary energy demand, greenhouse gas emissions and cost from the implementation of the three measures. These results only indicate the size of the potential savings and a site-specific investigation needs to be conducted for each plant. This paper is a part of a research project conducted in close cooperation with the Swedish aluminium 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.

Recent trends in Mexican industrial energy use and their impact on carbon dioxide emissions

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.

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

Elemental carbon (EC) and nitrogen dioxide (NO2) in air as markers for diesel exhaust (DE) emission exposure were measured in selected work environments in Norway where diesel-powered engines are in use. Two hundred and ninety personal full-shift air samples were collected in primary aluminium production, underground and open-pit mining, road tunnel finishing, transport of ore, and among airport baggage handlers. EC was determined in the samples by a thermo-optical method, while NO2 was determined by ion chromatography. Highest EC air concentrations (geometric mean, GM) were found in aluminium smelters (GM = 45.5 μg m-3) followed by road tunnel finishing (GM = 37.8 μg m-3) and underground mining activities (GM = 18.9 μg m-3). Low EC air concentrations were measured for baggage handling at an international airport (GM = 2.7 μg m-3) and in an open-pit mine (GM = 1.2 μg m-3). Air concentrations of NO2 were similar in road tunnel finishing (GM = 128 μg m-3) and underground mining (GM = 108 μg m-3). Lower NO2 values were observed in open-pit mining (GM = 50 μg m-3), at the airport (GM = 37 μg m-3), and in the aluminium smelters (GM = 27 μg m-3). Highly significant (P < 0.001) positive correlations between NO2 and EC air concentrations in underground mining (r = 0.54) and road tunnel finishing (r = 0.71) indicate a common source of these pollutants. NO2 and EC were also correlated (P < 0.01) positively at the airport. However, due to the complex air chemistry and a potential contribution of various sources, the correlation between EC and NO2 cannot be regarded as unambiguous hint for a common source. The association between EC and NO2 was not of statistical significance in open-pit mining. In the aluminium smelters, EC and NO2 were negatively correlated, although not reaching statistical significance. The substantial differences in NO2/EC ratios across the investigated industries, ranging from around 0.2 in the primary aluminium production to around 25 during spring at the airport, clearly show that exposure to DE cannot be estimated based on NO2 concentrations, at least for outdoor environments. Results in the primary aluminium production suggest that the measured EC concentrations are related to DE emissions, although the NO2 concentrations were low. Further studies are required to assess the magnitude of exposure in primary aluminium production.

Two perfluorinated carbon compounds (PFCs), tetrafluoromethane and hexafluoroethane are produced periodically as by-products in primary aluminium production. Emissions of these compounds have received considerable attention over the current decade because their strong infrared absorbing power and relatively long atmospheric lifetimes result in high GWPs. World-wide primary aluminium production has been identified as the major anthropogenic source of these emissions. Early efforts have been quite successful in making substantial reductions in PFC emissions per unit of aluminium produced through implementation of new computer control systems, control of raw materials and careful attention to work practices. Primary aluminium producers are concerned about recent initiatives to establish 1995 as an alternative baseline year for PFC emissions reductions because it would discount the major PFC emissions reductions attained during the period from 1990 to 1995. Alcoa achieved approximately 70% reduction in aluminium specific PFC emission rate during that period for U.S. operations. At that same time world-wide international reductions, as documented by the International Primary Aluminium Institute, were also quite substantial. This paper reviews the processes in which PFC compounds are produced during aluminium production and discusses best methods for actual measurement of these compounds. Results of measurements made during primary aluminium production are reviewed and comparisons are made of the efficacy of methods of predicting PFC emissions. The logic of retaining 1990 as the base year for PFC emissions for the aluminium industry is reiterated.

Energy use and CO 2 emissions in Mexico's iron and steel industry

Recycling mixed aluminum scrap usually requires adding primary aluminum to the scrap stream as a diluent to reduce the concentration of non-aluminum constituents used in aluminum alloys. Since primary aluminum production requires approximately 10 times more energy than melting scrap, the bulk of the energy and carbon dioxide emissions for recycling are associated with using primary aluminum as a diluent. Eliminating the need for using primary aluminum as a diluent would dramatically reduce energy requirements, decrease carbon dioxide emissions, and increase scrap utilization in recycling. Electrorefining can be used to extract pure aluminum from mixed scrap. Some example applications include producing primary grade aluminum from specific scrap streams such as consumer packaging and mixed alloy saw chips, and recycling multi-alloy products such as brazing sheet. Electrorefining can also be used to extract valuable alloying elements such as Li from Al-Li mixed scrap. This project was aimed at developing an electrorefining process for purifying aluminum to reduce energy consumption and emissions by 75% compared to conventional technology. An electrolytic molten aluminum purification process, utilizing a horizontal membrane cell anode, was designed, constructed, operated and validated. The electrorefining technology could also be used to produce ultra-high purity aluminum for advanced materials applications. more » The technical objectives for this project were to: - Validate the membrane cell concept with a lab-scale electrorefining cell; - Determine if previously identified voltage increase issue for chloride electrolytes holds for a fluoride-based electrolyte system; - Assess the probability that voltage change issues can be solved; and - Conduct a market and economic analysis to assess commercial feasibility. The process was tested using three different binary alloy compositions (Al-2.0 wt.% Cu, Al-4.7 wt.% Si, Al-0.6 wt.% Fe) and a brazing sheet scrap composition (Al-2.8 wt.% Si-0.7 wt.% Fe-0.8 wt.% Mn),. Purification factors (defined as the initial impurity concentration divided by the final impurity concentration) of greater than 20 were achieved for silicon, iron, copper, and manganese. Cell performance was measured using its current and voltage characteristics and composition analysis of the anode, cathode, and electrolytes. The various cells were autopsied as part of the study. Three electrolyte systems tested were: LiCl-10 wt. % AlCl3, LiCl-10 wt. % AlCl3-5 wt.% AlF3 and LiF-10 wt.% AlF3. An extended four-day run with the LiCl-10 wt.% AlCl3-5 wt.% AlF3 electrolyte system was stable for the entire duration of the experiment, running at energy requirements about one third of the Hoopes and the conventional Hall-Heroult process. Three different anode membranes were investigated with respect to their purification performance and survivability: a woven graphite cloth with 0.05 cm nominal thickness & > 90 % porosity, a drilled rigid membrane with nominal porosity of 33%, and another drilled rigid graphite membrane with increased thickness. The latter rigid drilled graphite was selected as the most promising membrane design. The economic viability of the membrane cell to purify scrap is sensitive to primary & scrap aluminum prices, and the cost of electricity. In particular, it is sensitive to the differential between scrap and primary aluminum price which is highly variable and dependent on the scrap source. In order to be economically viable, any scrap post-processing technology in the U.S. market must have a total operating cost well below the scrap price differential of $0.20-$0.40 per lb to the London Metal Exchange (LME), a margin of 65%-85% of the LME price. The cost to operate the membrane cell is estimated to be < $0.24/lb of purified aluminum. The energy cost is estimated to be $0.05/lb of purified aluminum with the remaining costs being repair and maintenance, electrolyte, labor, taxes and depreciation. The bench-scale work on membrane purification cell process has demonstrated technological advantages and substantial energy and investment savings against other electrolytic processes. However, in order to realize commercial reality, the following items need to be fully investigated: 1. Further evaluation of a pure fluoride electrolyte. 2. Investigate alternative non conductive, more mechanically robust and chemically inert membrane candidates. 3. Optimized membrane cell design to understand contribution of fluid flow patterns and the mass transfer conditions. 4. Improve current efficiency and total metallic aluminum recovery from the cell. All Tasks and Milestones were completed successfully. « less

The purpose of this paper is to articulate the immediate need for review and improvement of Kosovo Building Regulations and Codes in the field of implementation of EE measures and specifically reducing U-values for all building envelope elements, to be comparable to European Standards, and present a specific contribution for EE measures in public building stock in Kosovo as the real potential for huge energy savings. In this paper the results of the several years’ long research on the impact of implemented energy efficiency measures in the 70 selected public buildings are presented, in light of calculated U-values with a brief description of the constituent elements of the building envelope and their corresponding U-values, such as external walls, windows, doors, floors and roofs, comparing their impact in the phases before and after the implementation of Energy Efficiency measures. A building designed to use the minimum quantity of thermal energy for heating and cooling to achieve a healthy environment and thermal comfort is considered an Energy Efficient building. The U-values of the building envelope are the dominant factors in its thermal performance and play an important role in reducing the energy consumption of buildings. Many studies confirm that in cold climates, from the total annual energy consumption for heating and air conditioning of public buildings, approximately 50% of the energy is consumed through the heat transmission of the building envelope. The achieved results after implementation of EE measures have shown significant improvement of U-values for both opaque parts of building envelope and belonging fenestration compared with the referent values set in Kosovo Technical Regulation which is actually in use for designers in Kosovo. Depending on wall thickness and installed insulation achieved, results of U-values for external walls were 0.31-0.35 W/m2K, much lower than recommended in old technical Regulations, lower than recommended by ANA_IAE, but still higher than values from Finish and Norwegian building codes. Calculations have shown that in the case of implementation of improved U-values according to the Finish building code the impact of walls on U-values in overall energy savings is around 36.86%. Windows and doors look the sensitive part of the building envelope and show that it is more than the required strengthening of requirements in future Kosovo Building code reducing the U-values for doors and windows at 0.8 W/m2K. Analysis has shown huge improvement and potential increase of energy savings with 55.25 % for part of fenestration. Detailed analysis of the collected U-values data for roofs has shown that there is sufficient space for improvements in Building codes and it is a highly recommended change of existing criteria and at least application of the values from EU building codes. With this change, potential energy savings in part of roof covers might be 44.24%. Working as an EE expert in Kosovo Energy Efficiency Agency (KEEA) and World Bank (WB) and European Union (EU) projects, the author has identified the necessity of improvement of actual Kosovo legislation in the field of EE policies for public buildings, addressing the importance of the appropriate building envelope’s thermal insulation to reduce its thermal losses and stipulating the impact of the U-values in the evaluation of implemented energy efficiency measures and energy savings in public buildings. The overall energy savings with applied EE measures and potential energy savings in case of improvements of Kosovo Technical Regulation according to recommended standards and EU countries’ experiences are presented in a separate table showing economic net savings, an average payback period and overall potential reductions of CO2 emissions. The presented results indicate a recommendation for further studies that may include other building typologies and may disclose additional differences between the energy performance criteria in the analysed building codes.

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

Mapping and modeling multiple benefits of energy efficiency and emission mitigation in China’s cement industry at the provincial level

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.