Advances in Thermal Conversion: Integrating and Intensifying Waste/Biomass-to-Energy Processes

Dear Colleagues,

This Special Issue focuses on the innovative and emerging field of waste/biomass-to-energy processes, with a particular emphasis on process integration and intensification through thermal conversion methods. This Issue will explore the latest advancements in thermal technologies such as torrefaction, pyrolysis, gasification, and combustion, as well as their role in efficiently converting waste and biomass into energy, including carbon capture and storage (BECCS). The Issue will delve into the optimisation of these processes, addressing challenges related to efficiency, scalability, and environmental impact. It will also highlight the integration of these processes into existing industrial frameworks, examining how they can contribute to sustainable energy production and waste management.

Contributions are invited from research into technological developments, process design and optimisation, life cycle analysis, economic feasibility, and environmental sustainability in the field of waste/biomass-to-energy processes.

Dr. Fatih Gulec
Dr. Yavuz Gokce
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• thermal conversion technologies
• waste-to-energy processes
• biomass energy conversion
• process integration
• process intensification
• pyrolysis
• gasification
• combustion technologies
• sustainable energy production
• environmental impact assessment
• industrial waste management
• life cycle analysis
• techno-economic feasibility
• energy efficiency
• scalability of conversion processes
• bioenergy with carbon capture storage
• BECCS

Title: Classification of biochars produced by hydrothermal carbonisation of rapeseed and whitewood
Authors: Fatih Güleç; Orla Williams; Teshan Rezel; Emily T. Kostas; Abby Samson; Edward Lester
Affiliation: University of Nottingham
Abstract: Biomass feedstocks are defined as inexpensive, clean, and environmentally friendly energy sources and present three major components – hemicellulose, cellulose, and lignin. These components can partially be decomposed by thermal conversion technologies such as pyrolysis, torrefaction and hydrothermal conversion and produce a coal-like structure named biochar. Biochars could play a crucial role in clean energy production and reach the 2 °C climate targets. The morphologies of biochar provide a lot of information about the combustion characteristics but there is limited information about the biochar classification. In this study, biochar formation was investigated in a semi-continuous hydrothermal process rig using three different biomass feedstocks (Rapeseed and Whitewood). To investigate the potential of biohar formation at different conditions, hydrothermal conversion of Rapeseed and Whitewood was investigated at 200-300°C (55-240bar) for hydrothermal carbonisation for ~1.5 h. The biochars were collected from the reactor and dried in an oven at 100 °C for overnight. To classify the biochars, scratch-free, polished blocks were prepared using epoxy liquid resin for each biochar sample to be characterized. A Zeiss Leitz Ortholux II POL-BK microscope with a 32x (and an internal 10x lens) providing a total of 320X magnification was used to analyse particle morphology. Composite images (3090×3900 pixels) from mosaics of 10×10, representing a total area of 4mm×3.3 mm, were obtained from the Zeiss AxioCam digital camera attached to the microscope and operated with KS400 V3.1 software. As previously suggested for the biomass chars, the biochar were classified based on three morphological characteristics: i – aspect ratio (the ratio of length to width: high aspect ratio or low aspect ratio), ii – wall thickness (thin-walled chars or thick-walled chars), iii – porosity (cellular porosity: based on typical initial cell walls or the porous: more like open rounded pores). The results provide a comprehensive understanding of the impact of subcritical conditions of hydrothermal conversion on biochar classifications and their potential in energy production. Figure 1 demonstrates an example for each classification.

Title: Thermochemical Characterization and Environmental Evaluation of Personal Protective Equipment
Authors: Umut Güçlü; Italo Pisano; Anna Trubetskaya; Ayman Hijazi; James J. Leahy; Feyza Kazanç
Affiliation: a Mechanical Engineering Department, Middle East Technical University, 06800 Ankara, Turkey b Department of Chemical Sciences, Faculty of Sciences and Engineering, University of Limerick, Castletroy, V94 T9PX Limerick, Ireland c Department of Biosciences, Nord University, 7713 Steinkjer, Norway d Department of Engineering, University of Limerick, Castletroy, V94 T9PX Limerick, Ireland e Micro and Nanotechnology Department, Middle East Technical University, 06800 Ankara, Turkey
Abstract: The COVID-19 pandemic dramatically expanded the use of Personal Protection Equipment (PPE). The most commonly used PPEs against the COVID-19 virus were masks, gloves, face shields, and protective gowns. The disposable nature of most PPE generated a waste problem soon after the pandemic started. This waste problem and the constant usage of these PPE in hospitals have made it clear that there was an urgent need to investigate the thermochemical characteristics and environmental effects of the associated medical wastes. This study investigated the pyrolysis and combustion characteristics, gaseous emissions, and ash compositions of the most commonly used PPEs. In contrast to previous studies, which have focused on the characterization of these waste materials individually, the present study investigated the co-combustion of PPE, which provided a realistic analysis of the ongoing waste disposal procedures. A specific combination of the medical waste blend, consisting of face mask, medical gown, and nitrile glove, was prepared based on the actual waste compositions of the intensive care services of several local hospitals. Thermogravimetric analysis was conducted on both the combined waste and the individual components. The results showed a synergistic effect during the co-combustion of polypropylene-based materials with nitrile gloves, as a decrease in polypropylene-based materials' peak and burnout temperatures. Resulting ash compositions were investigated with SEM-EDX and ICP-OES analyses. The slagging inclination of the bottom ash was evaluated with conventional methods, and the results showed that slagging risks have decreased in the co-combustion of the medical wastes.