Design and evaluation of recycling and recovery infrastructures for glass and carbon fiber reinforced plastics : an application in the wind energy industry

Sommer, Valentin; Walther, Grit (Thesis advisor); Letmathe, Peter (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022


This doctoral thesis is based on three publications that were published in peer-reviewed journals. The thesis contributes to the field of waste management and sustainable material management by developing an analysis approach to ex-ante plan economically and environmentally optimal recycling and recovery infrastructures for future glass- and carbon fibre reinforced plastic (GFRP/CFRP) waste. The analysis approach is applied to a case study from wind energy industry. The thesis is composed of a framing preface, a main part presenting the three publications, and a conclusion. The preface begins by stating that waste management is considered as key to achieve a circular economy. In this respect, the need for sophisticated analyses is motivated to support the decision makers with relevant information before large quantities of novel waste masses occur. It is outlined how this specifically applies to planning the management of future GFRP/CFRP waste. The relevance of the applied case study in wind energy industry is motivated by current discussions between practitioners and academia concerning challenges in the waste management. Afterwards, the general framework of the planning activities is presented by introducing the waste materials GFRP and CFRP as well as the state-of-the-art waste treatment options and characterizing them from an economic, environmental, regulatory and technical perspective. In this respect, the planning problem of this thesis is described and the requirements for the analysis approach are derived. The subsequent literature review on Reverse Logistics places the planning problem of this thesis in the context of literature from the field of business and economics. Herein, an overview of recent research is presented and the characteristics of the planning problem for adequate modelling are classified consistent with the literature. The main part of the thesis is structured by three publications in which the analysis approach is developed. The approach consists of advanced methodologies that enable ex-ante planning of the management of waste streams. Its application generates relevant information for political decision makers and investors. First, to provide a foundation for the ex-ante planning of the waste management of GFRP/CFRP waste, the upcoming waste streams are estimated. An estimation approach is developed based on a simulation study, regression analysis and a stochastic distribution function. The results show that more than 500.000 [t] of GFRP/CFRP waste from the wind energy industry will occur in the EU between 2020 and 2030. For these waste streams, the optimal treatment paths are still unknown and the required recycling and recovery infrastructures are still missing. Second, to analyze the optimal treatment paths from an economic perspective, a decision support system to plan economically optimal recycling and recovery infrastructures for GFRP/CFRP waste is developed as an integrated mixed integer linear optimization model for location, technology and capacity selection. Herein, the resulting infrastructures are evaluated by the net present value (NPV). The impact of political regulations, such as recycling and recovery targets as well as the impact of secondary market development on the choice of treatment paths and on the NPV is analyzed. Third, to demonstrate potential differences between economically and environmentally optimal recycling and recovery infrastructures, the decision support system is extended to a multi-objective decision-making approach. Life Cycle Assessment is conducted to evaluate the environmental impact of each treatment option. The impact of political regulations on the overall economic and environmental benefit/ burden is analyzed by scenario analyses. In total, the application of the developed decision support system on the estimated GFRP/CFRP waste streams provides information for political decision makers and investors on the choice of technologies as well as the resulting economic (and environmental) burdens and benefits. The results of the evaluation from the economic and environmental perspective show that regardless of political regulations, the optimal treatment for CFRP is chemical recycling through solvolysis. In contrast, the optimal treatment for GFRP is either incineration (economically favored), mechanical recycling (environmentally favored) and chemical recycling through solvolysis (required in case of certain political regulations). Besides, it is shown that adequate recycling targets lead to good solutions from an environmental perspective at little additional costs. In contrast, high recycling targets lead to a deterioration of the solutions not only from an economic but also from an environmental perspective. In the conclusion, the main findings and the contributions of the thesis are summarized. Herein, the demonstration of the advantage of advanced methods in the ex-ante planning of waste management as well as the specific insights for stakeholders are emphasized. Although this thesis provides a comprehensive approach for analyzing the waste management of innovative materials in general and for GFRP/CFRP waste in particular, there remain limitations that are discussed. In line with this, the thesis is concluded by the outlook on further research opportunities.