Given the potential of oxyfuel combustion for carbon capture, the impact of flue gas recirculation on oxyfuel combustion in Waste-to-Energy is investigated using a combined modeling and thermoanalytical approach, providing the basis for technical implementation. The oxyfuel combustion model reveals distinct gas compositions and flow rates for different recirculation strategies. Recirculation before flue gas treatment results in high pollutant concentrations in the oxidizer mixture but reduces the volume flow in downstream units. Recirculation after flue gas treatment lowers pollutant levels and, as in the first case, shows high H2O concentrations in the oxidizer mixture. Dry flue gas recirculation achieves the highest CO2 concentration but also the highest relative N2 content in the clean, dry flue gas. By recirculating a larger absolute amount of O₂ to the oxidizer mixture, dry recirculation reduces the O₂ demand by 11.6% compared with wet recirculation. Thermogravimetric and differential thermal analysis of refuse-derived-fuel examines the influence of O2 and H2O concentrations on combustion performance. Increasing O2 concentration strongly promotes char combustion, while devolatilization is slightly affected. Achieving similar combustion and burnout as with air, requires 32–35 vol-% O2 in CO2. Higher H2O content slightly enhances char combustion, indicating a positive effect of the wet recirculation.

Carbon capture, utilization and storage is crucial to mitigate the inevitable fossil and biogenic CO₂ emissions from Waste-to-Energy (WtE) plants. Oxyfuel combustion represents a promising technology, as it produces a CO₂-rich flue gas stream suitable for purification and compression. Although core design principles from coal-fired systems are largely transferable, the heterogeneous nature of municipal solid waste (MSW) and the combustion in grate-firing systems require dedicated evaluation.The transition to a CO₂-dominated atmosphere alters key physical properties in the combustion chamber, resulting in delayed combustion at identical oxygen concentrations. To achieve air-like combustion characteristics, oxygen concentrations of around 30 vol% are typically required, although fuel-specific deviations have been determined. Experimental studies on MSW have examined combustion behavior, emissions and ash formation, while simulative studies on implementation in WtE have focused on the impact of flue gas recirculation (FGR) strategies, oxygen excess, oxygen purity, and air leakage.This review evaluates process-level impacts, critical operational parameters, and remaining research gaps relevant for retrofit implementation in grate-fired WtE plants. Despite recent progress, further experimental investigations are required to assess the effects of optimized fuel-specific O2/CO2 ratio on emissions and ash formation. To enable reliable large-scale implementation, integrated studies that couple pilot-scale investigations with validated process models are essential. Further research should address the robustness of oxyfuel WtE systems under fluctuating waste compositions, the interaction of advanced process regulations as well as technical process optimization.

Ökologische Vergleiche technischer Verfahren scheitern häufig daran, dass zwar Umweltindikatoren wie Treibhausgasemissionen oder Energieverbräuche benannt werden, die zugrunde liegenden Rahmenbedingungen – insbesondere die erforderlichen Massen- und Energiebilanzen – jedoch nicht veröffentlicht sind. Zwar kann ein in einer Ökobilanz untersuchtes Szenario reale Gegebenheiten wie Logistik, Energieversorgung und Nebenproduktverwertung berücksichtigen, doch bleibt dadurch ein Rückschluss auf die konkret eingesetzten Verfahren sowie ein systematischer Vergleich dieser meist verwehrt. Um eine belastbare Vergleichbarkeit technischer Verfahren zu ermöglichen, ist es daher erforderlich, einen realitätsnahen, aber einheitlichen Bilanzraum sowie identische – auch wenn fiktive – Rahmenbedingungen für alle betrachteten Verfahren zu definieren. Im ReFo-Plan-Forschungsvorhaben Abschätzung der Potenziale und Bewertung der Techniken des thermochemischen Kunststoffrecyclings wurde ein solcher Ansatz für verschiedene chemische Recyclingverfahren umgesetzt. Dabei zeigte sich, dass klassische ingenieurtechnische Massen- und Energiebilanzen auch als Referenzansatz für vergleichende ökologische Bewertungen in Form von Lebenszyklusanalysen (LCAs) geeignet sind. Die Gültigkeit dieses Vorgehens wurde durch Abgleich mit veröffentlichten Ökobilanzen verifiziert. Zur operativen Anwendung dieses Vergleichsrahmens wurde ein Python-basiertes Bilanzierungstool entwickelt, das eine einheitliche Eingabe, Auswertung und Gegenüberstellung verschiedener Verfahren auf Basis strukturierter Stoff- und Energiedaten erlaubt. Dies ermöglicht eine schnelle, fundierte Einordnung und Bewertung existierender LCAs sowie eine vergleichende Beurteilung technischer Verfahren im Gesamtkontext.

The limited usage of fermentation residues, due to increasingly stringent legal requirements, demands novel routes of utilization for these feedstocks. To the best of our knowledge, for the first time, a mixture of fermentation residues and wood chips is used as feedstock in a fixed-bed gasifier, using only O2/CO2 mixtures as gasifying agent. The maximum O2 concentration achieved was 31.6 Vol.-%. Pronounced process stability was achieved with a cold gas efficiency of about 94%, possibly due to CO2 conversion within the process. The heating value of the produced synthesis gas was 8.5 MJ/m3i.N.dry, with increased amounts of carbon monoxide and methane when compared to air-blown operations.

With increasing efforts to lower CO2 emissions globally, the demand for carbon-based resources in industries remains on a high level, leading to new technologies being able to provide those essential carbon sources. To the best of our knowledge, we were able to show for the first time the adaption of a readily available gasifier for the gasification of wood chips using only O2 (18.4–23.1 Vol.-%) and CO2 as gasification agents, creating a nitrogen-free product gas. It was found that the setup used was able to convert up to 27.2% of the CO2 from the gasification agent to CO, creating a promising route for the production of renewable carbon sources for future carbon-based applications. Furthermore, no decrease in gasification performance was observed as the cold gas efficiency was at 83.5–95.5% with only minor formation of tar.

Chemie Ingenieur TechnikVolume 95, Issue 7 p. 1182-1182 VorschauFree Access Vorschau: Chem. Ing. Tech. 8/2023 First published: 21 June 2023 https://doi.org/10.1002/cite.202370706AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume95, Issue7Special Issue: KEEN – Artificial Intelligence Incubator Labs in the Process IndustryJuli 2023Pages 1182-1182 RelatedInformation

Chemical recycling offers the opportunity to foster the transition towards a circular economy for plastics as a complementary strategy for mechanical recycling. For the implementation of chemical recycling technologies, there are still significant challenges ahead that - besides the definition of binding legal frameworks - need for intensified research: knowledge-based methods for both the identification of suitable process technologies considering decentralized waste conditions and the design of conversion steps and downstream processing are strongly needed for process development and process evaluation.

The plastic crisis requires drastic measures, especially for the plastics' end-of-life. Mixed plastic fractions are currently difficult to recycle, but microbial metabolism might open new pathways. With new technologies for degradation of plastics to oligo- and monomers, these carbon sources can be used in biotechnology for the upcycling of plastic waste to valuable products, such as bioplastics and biosurfactants. We briefly summarize well-known monomer degradation pathways and computed their theoretical yields for industrially interesting products. With this information in hand, we calculated replacement scenarios of existing fossil-based synthesis routes for the same products. Thereby, we highlight fossil-based products for which plastic monomers might be attractive alternative carbon sources. Notably, not the highest yield of product on substrate of the biochemical route, but rather the (in-)efficiency of the petrochemical routes (i.e., carbon, energy use) determines the potential of biochemical plastic upcycling. Our results might serve as a guide for future metabolic engineering efforts towards a sustainable plastic economy.

The use of carbon fibre (CF)-reinforced plastics has grown significantly in recent years, and new areas of application have been and are being developed. As a result, the amount of non-recyclable waste containing CF is also rising. There are currently no treatment methods for this type of waste. Within this project different approaches for the treatment of waste containing CF were investigated. Main subject of the research project were large-scale investigations on treatment possibilities and limits of waste containing CF in high temperature processes, with focus on the investigation of process-specific residues and possible fibre emission. The results showed that the two conventional thermal waste treatment concepts with grate and rotary kiln firing systems are not suitable for a complete oxidation of CFs due to the insufficient process conditions (temperature and dwell time). The CFs were mainly discharged via the bottom ash/slag. Due to the partial decomposition during thermal treatment, World Health Organization (WHO) fibres occurred in low concentrations. The tests run in the cement kiln plant have shown the necessity of comminution for waste containing CF. With respect to the short testing times and moderate quantities of inserted CF, a final evaluation of the suitability of this disposal path was not possible. The use of specially processed waste containing CF (carbon-fibre-reinforced plastic (CFRP) pellets) as a carbon substitute in calcium carbide production led to high carbon conversion rates. In the unburned furnace dust, which is marketed as a by-product of the process, CFs in relevant quantities could be detected.

Increased media coverage of plastic pollution in the environment and import bans on plastic waste in several countries have resulted in plastic waste becoming one of the most discussed waste streams in recent years. In the European Union (EU), only about one-third of the post-consumer plastic waste is recycled; the rest goes to energy recovery and landfilling in equal parts. In connection to the necessary increase in efforts to achieve the ambitious EU recycling targets, chemical recycling is currently receiving more and more attention. The assumption is that chemical recycling processes could open up new waste streams for recycling and generate valuable raw materials for the chemical industry. Although there exists no legal definition for chemical recycling, there is more or less agreement that it covers the conversion of plastic polymers into their monomers or chemical building blocks. Techniques such as gasification, pyrolysis and liquefaction as well as solvolysis can be used for chemical recycling. So far, only few large-scale plants for chemical recycling exist worldwide. This article presents the different processes by means of examples from (formerly) running installations and their suitability for plastics recycling is assessed. However, to date, only few chemical recycling plants are in continuous operation, and further scientific evidence for the ecological and economic benefits is still necessary for final evaluation.