Environmental lifetime optimization and closed-loop recycling potential of circular products
Loading...
Author / Producer
Date
2022
Publication Type
Doctoral Thesis
ETH Bibliography
yes
Citations
Altmetric
Data
Rights / License
Abstract
Humans have come to influence the global Earth system to such an extent that their economic activities exceed ecological limits. Resource extraction and processing contribute significantly to global environmental impacts. Fundamental changes in human behavior are urgently needed but not readily possible in the current economic system since most activities and products of modern society rely on raw materials. Therefore, the transition to a Circular Economy (CE) is often promoted as one path to ensure sustainable material cycles. CE aims to close material loops based on nature’s example, thus avoiding waste and protecting natural resources. Generally, a distinction is made between two major CE strategy groups: (1) slowing down and (2) closing resource cycles.
The transition to (sustainable) CE is facing several challenges. Some of them are addressed in this dissertation. First, there is the question of when to apply which product lifetime extension strategy for energy using products (EuP). However, lifetime extension strategies only delay products from being discarded. Accordingly, the questions remain about how well material quality can be maintained during recycling and how it can be improved through product and service design. Based on these questions, recommendations for a circular product and service design are derived in this dissertation.
The aim of CE should be to optimize the lifespan and not necessarily to maximize it. The latter only results in reduced resource consumption in the production phase and thus manufacturing-related impact. However, if the entire life cycle is considered, the environmental impact is not necessarily minimal. The first question of optimal environmental lifetime (OEL) is answered in chapter 3 with non-linear optimization using a dynamic programming approach. This approach allows taking into account various dynamics affecting the OEL of (circular) products and considering several irregular, unordered replacements over the optimization horizon. The approach is used to calculate the OEL of residential heating systems as an example of EuP. Only full substitutes of the gas boiler technology are considered with new evolved or re-manufactured products as replacement options. The efficiency progress of this cohort of products is little within a given period. In this case, the highest savings potential comes from an optimized replacement schedule that includes frequent replacement with re-manufactured products to eliminate unavoidable efficiency degradation at low investment costs. In addition, an optimized replacement policy also exploits some efficiency gains across the product cohort.
While the OEL can serve as a target for new product development and the best replacement time for old products, it does not provide by itself any information on how much the environmental impacts increase when deviating from it. Therefore, a Life Cycle Assessment (LCA) based lifespan indicator ϕ is introduced in chapter 4. This indicator allows evaluating how far away a given lifetime of a product is from the optimal replacement scenario, thus revealing unsustainable throughput of materials and waste of resources. Such a lifespan indicator requires a simple and efficient calculation method that must deal with path dependencies of non-linear dynamics. The indicator builds on the considerations on substitutes from chapter 2. With the indicator ϕ, it is possible to make informed decisions about the selection and optimal timing of CE strategies and to communicate the results clearly. The application of the indicator is illustrated for residential heating systems considering also the technology switch to heat pumps. The replacement of gas heating appliances should be done in short intervals with the same technology at OEL. It is similarly beneficial to wait until the more efficient product becomes available. However, replacing with new, more efficient or re-manufactured gas boilers brings only little savings potential. More effective is the replacement with heat pumps.
Material quality degrades through use and especially during recycling, e.g., due to contamination with other materials during shredding. In order to maintain material quality and thus material functionality for as long as possible, it is crucial to maintain material quality when closing material loops. For the second research question, the first step is to analyze how much of the material embodied in a product can hypothetically come from the same recycled product for given material quality. Based on this, the fitness for closed-loop material recycling indicator Θ is developed, which indicates how well the material quality can be preserved (chapter 5). In a case study, the new approach is also applied to gas heating appliances to analyze their recyclability and quantify potential material quality losses. Retaining material quality requires dilution of contaminants with less contaminated material, which significantly limits Θ.
The results are summarized in recommendations for the design of circular products and services. Longevity only makes sense when neither more mature product versions with reduced energy requirements during the use phase nor better, more environmentally friendly alternative technologies are available, and efficiency degradation during use can be neglected. Therefore, re-manufacturing of EuP only makes sense if the technology is mature; otherwise, the lifespan should be optimized. Products and services should therefore be designed so that their environmental lifespan is optimized and recycling is improved. This dissertation provides methods for this.
Permanent link
Publication status
published
External links
Editor
Contributors
Examiner: Hellweg, Stefanie
Examiner : Dewulf, Jeroen
Book title
Journal / series
Volume
Pages / Article No.
Publisher
ETH Zurich
Event
Edition / version
Methods
Software
Geographic location
Date collected
Date created
Subject
Organisational unit
03732 - Hellweg, Stefanie / Hellweg, Stefanie