از دست دادن کمی کیفیت و بهره وری منابع بازیافت با استفاده از تجزیه و تحلیل اکسرژی

Contaminants cause a decrease in the quality of materials with each recycling step. These quality losses should be minimized to increase the sustainability of resources use. Quality losses cannot be measured using weight-based recovery definitions alone, as the quality degradation cannot be translated by mass measures. Therefore, a better measure of the efficiency of resource use is investigated in the present work. Exergy is a measure of the quality of the energy and of resources in systems. The exergy losses are a thermodynamic measure of exhaustion and thus, of the quality losses in the resource systems. We describe a method to calculate the exergy content and exergy losses of metals during recovery and recycling of a concept car. The exergy losses attributed to recycling (the pollution with other metals) and the consequent need for dilution can be used as indicators of the quality loss of materials and of the efficiency of resource use in product systems.

Life Cycle Impact Assessment of the average passenger vehicle of the Netherlands has been previously performed [1], with emphasis on the current dismantling and recycling practice in the Netherlands. According to the Eco-indicator 99 (EI99) [2], the largest environmental impact of the passenger vehicle's life cycle occurs in the use phase – over 90% – due to the combustion and depletion of fossil fuels. Also, in the other life cycle phases, the use of fossil fuels is the dominant impact, even for the production phase. Resource depletion due to the use of the materials employed in the vehicle causes a comparatively lower environmental impact, namely due to the high recovery rate and efficiency of the metallurgical recycling, that accounts for about 30% the total impacts of the materials. Therefore, the automotive industry has been making efforts to reduce vehicle weight as a way to reduce fuel consumption and hence emissions. The use of lightweight materials can contribute to a significant weight reduction as they replace traditionally used heavier materials. There is a tendency to use more polymers, aluminium, magnesium and various composite materials. Other attempts to reduce vehicle weight include considering the use of newly developed ultra-strong steel alloys in a different body design, as is the case of the ULSAB [1]. Lightweight metals are recyclable and have relatively high prices in the scrap markets, but other lightweight materials such as polymers and composites represent a challenge for the recycling industry. Their recycling is economically unattractive, as a satisfactory recycling technology has not yet been developed [3]. When a mixture of all these materials is present in the End-of-Life Vehicle (ELV), recycling becomes even more complex and costly. During shredding, the joints between the different materials are not completely liberated, resulting in contamination of the recovered streams [4]. In many cases, such contaminations cause the recycled material to lose its properties or to be downgraded and therefore cannot be used for the original applications. As a consequence large quantities of materials are buried in landfills. The EU target of recycling is 85% on a mass basis. However, the quality decrease of the material is not taken into account. This has been addressed by Reuter et al. [5], where they investigated the fundamental limits of recycling by developing recycling models for ELV. Furthermore, these models are being applied to argue recycling legislation that is reflected in an EU stakeholder report to the EU commission [6]. In general, the materials lose quality with each step of recycling. A common remedy is to add high purity primary resources during recycling to dilute the undesired contaminations and thereby to bring the material back to a higher quality. This is necessary because the contaminants cannot be removed because of thermodynamic constraints of the current process routes. These quality losses are not taken into account in the weight-based recovery targets established by the European ELV legislation, because the quality degradation cannot be translated by mass measures alone. Additionally, the recovery targets do not include the downstream recycling processes required to bring the materials back to the resource cycles. In the present work, the quality of recycling streams is quantified by exergy, which also demonstrates the efficiency of resource use, in the case of a concept light car. Various scenarios for dilution of recycled streams are assessed by this thermodynamic life cycle methodology.

Recycling is a major component in closing the cycle between industrial products and the environment. Actually, End-of-Life legislation is designed to accomplish this purpose and set targets for the recycling rate of discarded products. The EU legislation, for example, requires 85% of cars to be recycled [16], however, recycling can create streams with a lower quality which are un-economical to recycle partially due to the limitations of thermodynamics, which makes refining difficult. Weight-based recovery targets are shown not to be adequate to monitor the possible quality degradation of the metals during the recycling. Furthermore, the current LCA methodologies are unable to accurately demonstrate the resource efficiency. Exergy analysis is used in the present work as a possible indicator to quantify the exergy losses of metals in recycling of a concept car DutchEVO. As the metals mix with contaminants in the process of recycling, the entropy increases and consequently there is loss of quality, which is shown as exergy loss in the present work and also by Reuter et al. [7] during physical recycling. It is obvious that it is sometimes impossible to bring the metal quality back to the original quality due to thermodynamic limits. In the case considered in the present work, wrought and cast aluminium are mixed and further contaminated with Fe (via steel). Hence, it becomes “degraded” possibly to casting quality. The results of calculations show that the chemical exergy content decreases during several recycling steps and consequently quality loss during smelting, which necessitates the dilution process since the removal of iron from aluminium is thermodynamically difficult. The third order loss accounts for the exergy removed from resource reserve as a consequence of the contaminations. The third order losses are shown to be high when pure aluminium is added to the recycled material. The exhaustion of natural resources is responsible for sustainability of resource use. The exergy efficiency and resource input ratio are used as new measures to quantify the efficiency of recycling compared to the conventional mass-based recycling efficiency. It is shown that when pure aluminium is used as a diluting agent, the exergy efficiency is low with high resource input ratio. The results indicate that using scrap aluminium alloys leads to high resource efficiency and environmental sustainability.