Stochastic methods for improving secondary production decisions under compositional uncertainty

Thesis (S.M.)--Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 77-80).A key element for realizing long term sustainable use of any metal will be a robust secondary recovery industry. Secondary recovery forestalls depletion of non-renewable resources and avoids the deleterious effects of extraction and winning (albeit by substituting some effects of its own). For most metals, the latter provides strong motivation for recycling; for light metals, like aluminum, the motivation is compelling. Along aluminum's life-cycle there are a variety of leverage points for increasing the usage of secondary or recycled materials. This thesis aims to improve materials decision making in two of these key areas: 1) blending decisions in manufacturing, and 2) alloy design decisions in product development. The usage of recycled aluminum in alloy blends is greatly hindered by variation in the raw material composition. Currently, to accommodate compositional variation, firms commonly set production targets well inside the window of compositional specification required for performance reasons. Window narrowing, while effective, does not make use of statistical sampling data, leading to sub-optimal usage of recycled materials. This work explores the use of stochastic programming techniques which allow explicit consideration of statistical information on composition. The computational complexity of several methods is quantified in order to select a single method for comparison to deterministic models, in this case, a chance-constrained model was optimal. The framework and a case study of cast and wrought production with available scrap materials are presented.(cont.) Results show that it is possible to increase the use of recycled material without compromising the likelihood of batch errors, when using this method compared to conventional window narrowing. The chance-constrained framework was then extended to improving the alloy design process. Currently, few systematic methods exist to measure and direct the metallurgical alloy design process to create alloys that are most able to be produced from scrap. This is due, in part, to the difficulty in evaluating such a context-dependent property as recyclability of an alloy, which will depend on the types of scraps available to producers, the compositional characteristics of those scraps, their yield, and the alloy itself. Results show that this method is effective in, a) characterizing the challenge of developing recycling-friendly alloys due to the contextual sensitivity of that property; b) demonstrating how such models can be used to evaluate the potential scrap usage of alloys; and (c) exploring the value of sensitivity analysis information to proactively identify effective alloy modifications that can drive increased potential scrap use.by Gabrielle G. Gaustad.S.M

Time-dependent evaluation of upgrading technologies for recycling

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 151-160).As consumption in the US grows, so does concern about sustainable materials usage. Increasing recycling is a key component within a broad arsenal of strategies for moving towards sustainable materials usage. There are many barriers to increasing recycling; one that is problematic is compositional uncertainty in the scrap stream. Repeated recycling compounds this problem through the accumulation of tramp elements in the material stream over time. Pertaining to the available operational and technological strategies that exist to mitigate accumulation, this thesis addresses the following questions: 1) How effective are these strategies at mitigating accumulation? 2) Under what conditions do upgrading technologies provide a cost efficient and environmentally effective improvement to the composition of recycled scrap streams? To answer these, a method was developed combining dynamic material flow analysis with optimal allocation of those materials into production portfolios using blending models. This methodology thus captured 1) the flow of EOL scraps, 2) how the economics of production are affected by changes in technology, and 3) a characterization of how recycling parameters influence accumulation in recycled streams. Using this methodology, optimal allocation was found to be an effective strategy for mitigating accumulation, for example, iron in the scrap stream was 69% less when compared to the value projected by conventional statistical methods. Two upgrading technology cases were examined using the time-dependent methodology developed: shredding, sorting, and dismantling of aerospace scraps and fractional crystallization.(cont.) Case results indicate that the time-dependent value of these technologies relies on whether or not the scrap stream is compositionally or availability constrained. These values were compared to analysis that does not consider repeated recycling (time-independent). Results show that undervaluing will occur in a regime where scrap availability is constrained and there is significant compositional accumulation occurring, a regime that may very well represent the reality faced by aluminum secondary producers in the US.by Gabrielle G. Gaustad.Ph.D

Characterizing Large-Scale, Electric-Vehicle Lithium Ion Transportation Batteries for Secondary Uses in Grid Applications

Lithium ion battery modules have significant capacity left after their useful life in transportation applications. This empirical study successfully tested the used modules in secondary grid applications in laboratory conditions. The selection of the secondary application was based on the construction features of the modules and the growing need for storage in grid operations. Description of the laboratory setup is provided in the context of a critical practical constraint where the battery management system and the usage and health history are not available to the secondary battery integrator. Charge and discharge profiles were developed based upon applications for peak shaving and firming renewables. Techno-economic analysis was focused on peak shaving at the utility level, considering a growing need for an affordable and environmentally friendly replacement to the traditional solutions based on environmentally costly peaker plants. The analysis showed strong evidence that near-term and future storage markets will be characterized by a large mismatch between the demand and supply of reused batteries from automotive primary applications for peak-shaving purposes in the generation side. The paper includes a discussion on successful adoption of cascaded use of batteries and their potential to reduce both economic and environmental cost of peak shaving

The Consequences of Electronic Waste Post-Disaster: A Case Study of Flooding in Bonn, Germany

Within the response and recovery phases of the disaster management cycle, debris clean-up is a well-researched topic, around which numerous policies have been developed. However, the subcategory of electronic waste is an issue that is overlooked by existing studies. A theoretical case study of a flood of the Rhine river in Bonn, Germany is used to demonstrate that while electronic waste may be a small portion of the debris generated during a disaster (by volume), it can have disproportionately large health, economic, and environmental consequences if not effectively planned for and handled. A spatial analysis of a flooding disaster scenario in Bonn was conducted to estimate the quantity of electronic waste that could be generated from residential buildings. Further modeling was done to calculate the greenhouse gas savings, energy savings, and economic impacts that can be realized through proper recovery and recycling of the electronic waste created by the flood. One key finding is that while implementation may be difficult, ensuring that effective policy is in place prior to a disaster can enable this waste stream to be managed in a manner that mitigates negative impacts on the environment and human health and keeps valuable materials in circulation

Operational Strategies for Increasing Secondary Materials in Metals Production Under Uncertainty

Increased use of secondary raw materials in metal production offers several benefits including reduced cost and lowered energy burden. The lower cost of secondary or scrap materials is accompanied by an increased uncertainty in elemental composition. This increased uncertainty for different scraps, if not managed well, results in an increased risk that the elemental concentrations in the final products fall outside customer specifications. Previous results show that incorporating this uncertainty explicitly into batch planning can modify the potential use of scrap materials while managing risk. Chance-constrained formulations provide one approach to uncertainty-aware batch planning; however, typical formulations assume normal distributions to represent the compositional uncertainty of the materials. Compositional variation in scrap materials has been shown to have a skewed distribution, and therefore, the performance of these models, in terms of their ability to provide effective planning, it may then be heavily influenced by the structure of the compositional data used. To address this issue, this work developed several approximations for skewed distributional forms within chance-constrained formulations. We explored a lognormal approximation based on Fenton’s method; a convex approximation based on Bernstein inequalities; and a linear approximation using fuzzy set theory. Each of these methods was formulated and case studies executed using compositional data from an aluminum remelter. Results indicate that the relationship between the underlying structure/distribution of the compositional data and how these distributions are formulated in batch planning can modify the use of secondary raw materials.National Science Foundation (U.S.) (Award 1133422

Comparative Analysis of Supply Risk-Mitigation Strategies for Critical Byproduct Minerals: A Case Study of Tellurium

Materials criticality assessment is a screening framework increasingly applied to identify materials of importance that face scarcity risks. Although these assessments highlight materials for the implicit purpose of informing future action, the aggregated nature of their findings make them difficult to use for guidance in developing nuanced mitigation strategy and policy response. As a first step in the selection of mitigation strategies, the present work proposes a modeling framework and accompanying set of metrics to directly compare strategies by measuring effectiveness of risk reduction as a function of the features of projected supply demand balance over time. The work focuses on byproduct materials, whose criticality is particularly important to understand because their supplies are inherently less responsive to market balancing forces, i.e., price feedbacks. Tellurium, a byproduct of copper refining, which is critical to solar photovoltaics, is chosen as a case study, and three commonly discussed byproduct-relevant strategies are selected: dematerialization of end-use product, byproduct yield improvement, and end-of-life recycling rate improvement. Results suggest that dematerialization will be nearly twice as effective at reducing supply risk as the next best option, yield improvement. Finally, due to its infrequent use at present and its dependence upon long product lifespans, recycling end-of-life products is expected to be the least effective option despite potentially offering other benefits (e.g., cost savings and environmental impact reduction)

Portfolio Optimization of Nanomaterial Use in Clean Energy Technologies

While engineered nanomaterials (ENMs) are increasingly incorporated in diverse applications, risks of ENM adoption remain difficult to predict and mitigate proactively. Current decision-making tools do not adequately account for ENM uncertainties including varying functional forms, unique environmental behavior, economic costs, unknown supply and demand, and upstream emissions. The complexity of the ENM system necessitates a novel approach: in this study, the adaptation of an investment portfolio optimization model is demonstrated for optimization of ENM use in renewable energy technologies. Where a traditional investment portfolio optimization model maximizes return on investment through optimal selection of stock, ENM portfolio optimization maximizes the performance of energy technology systems by optimizing selective use of ENMs. Cumulative impacts of multiple ENM material portfolios are evaluated in two case studies: organic photovoltaic cells (OPVs) for renewable energy and lithium-ion batteries (LIBs) for electric vehicles. Results indicate ENM adoption is dependent on overall performance and variance of the material, resource use, environmental impact, and economic trade-offs. From a sustainability perspective, improved clean energy applications can help extend product lifespans, reduce fossil energy consumption, and substitute ENMs for scarce incumbent materials

Challenges in Validation of Sustainable Products and Services in the Green Marketplace

<p>As consumer awareness of sustainability increases, companies are spending more time and money claiming their products or services are more environmentally friendly than other similar products on the market. However, a substantial number of those claims used for advertising and marketing purposes may be misleading or false. While there are organizations that currently provide environmental claim validation services to increase trust in the green marketplace, the challenges in validation of these environmental claims have not been comprehensively examined. This paper explores three major challenges in validating sustainable products and services: 1) the risk of validating erroneous environmental claims, 2) the difficulty of balancing the trade-offs in multi-attribute environmental claim validations, and 3) the challenge of developing protocols for innovative claims within a reasonable time frame. The authors use three real-world examples – evaluation of a longevity claim (and associated reduced environmental impacts) of a product, development of a multi-attribute standard, and construction of test procedures in the absence of an existing standard. Results demonstrate that validations and certifications by dedicated third parties may effectively improve perceptions of trust in greener product claims. These initial findings aim to inform a variety of policy decision-making and potentially help to lay the foundation for establishing rules and regulations for environmental claims in green markets.</p