• Energy Research

Over the past two decades, the use of machine learning (ML) methods to model biomass and waste gasification/pyrolysis has increased rapidly. Only 70 papers were published in the 2000s compared to a total of 549 publications in the 2010s. However, the approaches and findings have yet to be systematically reviewed. In this work, the machine learning methods most commonly employed for modelling gasification and pyrolysis processes are discussed with reference to their applications, merits, and limitations. Whilst coefficients of determination (R2) can be difficult to compare directly, due to some studies having greatly different approaches and aims, most studies consistently achieved a high prediction accuracy with R2 > 0.90. Artificial neural networks have been most widely used due to their potential to learn highly non-linear input-output relationships. However, a variety of methods (e.g. regression methods, tree-based methods, and support vector machines) are appropriate depending on the application, data availability, model speed, etc. It is concluded that ML has great potential for the development of models with greater accuracy. Some advantages of machine learning models over existing models are their ability to incorporate relevant non-numerical parameters and the power to generate a multitude of solutions for a wide range of input parameters. More emphasis should be placed on model interpretability in order to better understand the processes being studied.

Syngas and biochar are two main products from biomass gasification. To facilitate the optimization of the energy efficiency and economic viability of gasification systems, a comprehensive fixed-bed gasification model has been developed to predict the product rate and quality of both biochar and syngas. A coupled transient representative particle and fix-bed model was developed to describe the entire fixed-bed in the flow direction of primary air. A three-region approach has been incorporated into the model, which divided the reactor into three regions in terms of different fluid velocity profiles, i.e. natural convection region, mixed convection region, and forced convection region, respectively. The model could provide accurate predictions against experimental data with a deviation generally smaller than 10%. The model is applicable for efficient analysis of fixed-bed biomass gasification under variable operating conditions, such as equivalence ratio, moisture content of feedstock, and air inlet location. The optimal equivalence ratio was found to be 0.25 for maximizing the economic benefits of the gasification process.

AbstractPlastic pollution is a global issue that severely threatens the environment if not managed properly. Plastic waste is widely treated in unsustainable ways such as landfill and incineration that generally do not contribute to the circular economy or to the principles of the United Nation's sustainable development goals. Catalytic pyrolysis of plastic waste is considered an alternative solution with its potential of recovering fuels and chemicals from the plastic waste that is not recyclable. Here, we described for the first time the main steps required for running an operational pyrolysis plant from a whole system perspective. The recent advancement of plastic pyrolysis technologies is also described to guide the selection of relevant catalysts. The practical applications of products from the plastic pyrolysis are succinctly reviewed. This review will facilitate the development of the capacity to make better decisions upon the design and analysis of plastic pyrolysis processes and systems.This article is categorized under: Sustainable Energy > Bioenergy Climate and Environment > Circular Economy Emerging Technologies > Materials Sustainable Energy > Energy Efficiency

La digestion anaérobie à haute teneur en solides (HSAD) est une méthode attrayante d'élimination des déchets organiques pour la récupération de bioénergie et l'atténuation du changement climatique. Le développement de la HSAD est confronté à plusieurs défis tels que de faibles rendements en biogaz et en méthane, de faibles taux de réaction et une facilité d'inhibition du processus en raison de la faible diffusion de masse et des limites de mélange du processus. Par conséquent, les progrès récents de la HSAD sont examinés de manière critique en mettant l'accent sur les phénomènes de transport et la modélisation des processus. Plus précisément, le travail discute des phénomènes hydrodynamiques, des mécanismes biocinétiques, des simulations de réacteurs spécifiques à HSAD, des conceptions de réacteurs multi-étapes à la pointe de la technologie, des ramifications industrielles et des paramètres clés qui permettent un fonctionnement durable des processus HSAD. Des recherches supplémentaires sur de nouveaux matériaux tels que les bio-additifs, les adsorbants et les tensioactifs peuvent augmenter l'efficacité du processus HSAD, tout en assurant la stabilité. De plus, un outil de simulation générique est urgent pour permettre un meilleur couplage entre les phénomènes biocinétiques, l'hydrodynamique et le transfert de chaleur et de masse qui justifierait une mise à l'échelle du processus HSAD. La digestión anaeróbica de alto contenido de sólidos (HSAD) es un método atractivo de eliminación de residuos orgánicos para la recuperación de bioenergía y la mitigación del cambio climático. El desarrollo de HSAD se enfrenta a varios desafíos, como los bajos rendimientos de biogás y metano, las bajas velocidades de reacción y la facilidad de inhibición del proceso debido a la baja difusión de masa y las limitaciones de mezcla del proceso. Por lo tanto, el progreso reciente en HSAD se revisa críticamente con un enfoque en los fenómenos de transporte y la modelización de procesos. Específicamente, el trabajo analiza los fenómenos hidrodinámicos, los mecanismos biocinéticos, las simulaciones de reactores específicos de HSAD, los diseños de reactores de múltiples etapas de última generación, las ramificaciones industriales y los parámetros clave que permiten el funcionamiento sostenido de los procesos de HSAD. La investigación adicional sobre materiales novedosos como bioaditivos, adsorbentes y tensioactivos puede aumentar la eficiencia del proceso HSAD, al tiempo que garantiza la estabilidad. Además, se necesita urgentemente una herramienta de simulación genérica para permitir un mejor acoplamiento entre los fenómenos biocinéticos, la hidrodinámica y la transferencia de calor y masa que justifique la ampliación del proceso HSAD. High-solid anaerobic digestion (HSAD) is an attractive organic waste disposal method for bioenergy recovery and climate change mitigation. The development of HSAD is facing several challenges such as low biogas and methane yields, low reaction rates, and ease of process inhibition due to low mass diffusion and mixing limitations of the process. Therefore, the recent progress in HSAD is critically reviewed with a focus on transport phenomena and process modelling. Specifically, the work discusses hydrodynamic phenomena, biokinetic mechanisms, HSAD-specific reactor simulations, state-of-the-art multi-stage reactor designs, industrial ramifications, and key parameters that enable sustained operation of HSAD processes. Further research on novel materials such as bio-additives, adsorbents, and surfactants can augment HSAD process efficiency, while ensuring the stability. Additionally, a generic simulation tool is of urgent need to enable a better coupling between biokinetic phenomena, hydrodynamics, and heat and mass transfer that would warrant HSAD process scale-up. الهضم اللاهوائي عالي الصلابة (HSAD) هو طريقة جذابة للتخلص من النفايات العضوية لاستعادة الطاقة الحيوية والتخفيف من آثار تغير المناخ. يواجه تطوير HSAD العديد من التحديات مثل انخفاض إنتاج الغاز الحيوي والميثان، وانخفاض معدلات التفاعل، وسهولة تثبيط العملية بسبب انخفاض انتشار الكتلة وقيود الخلط للعملية. لذلك، تتم مراجعة التقدم الأخير في HSAD بشكل نقدي مع التركيز على ظواهر النقل ونمذجة العمليات. على وجه التحديد، يناقش العمل الظواهر الهيدروديناميكية، وآليات الحركية الحيوية، ومحاكاة المفاعلات الخاصة بـ HSAD، وتصميمات المفاعلات متعددة المراحل الحديثة، والتداعيات الصناعية، والمعايير الرئيسية التي تمكن من التشغيل المستدام لعمليات HSAD. يمكن أن يؤدي إجراء المزيد من الأبحاث حول المواد الجديدة مثل الإضافات الحيوية والممتزات والمواد الخافضة للتوتر السطحي إلى زيادة كفاءة عملية HSAD، مع ضمان الاستقرار. بالإضافة إلى ذلك، هناك حاجة ملحة إلى أداة محاكاة عامة لتمكين اقتران أفضل بين الظواهر الحركية الحيوية، والديناميكا المائية، ونقل الحرارة والكتلة التي من شأنها أن تضمن توسيع نطاق عملية HSAD.

The auto-regressive distributed lag (ARDL) bound testing approach was used to study the relationships between the monthly household electricity consumption and outdoor PM2.5 concentration with the consideration of ambient temperature and the number of rainy days for Singapore and Shanghai. It is shown that there are significant long-run relationships between the household electricity consumption and the regressors for both Singapore and Shanghai. For Singapore, a 20% increase in the PM2.5 concentration of a single month is in the long-run significantly related to a 0.8% increase in the household electricity consumption. This corresponds to an electricity overconsumption of 5.0 GWh, a total of 0.7–1.0 million USD in electricity cost, and 2.1 kilotons of CO2 emission associated with electricity generation. For Shanghai, a 20% decrease in the PM2.5 concentration of a single month is in the long-run significantly related to a 2.2% decrease in the household electricity consumption. This corresponds to a 35.0 GWh decrease in the overall household electricity consumption, 1.6–5.1 million USD decrease in electricity cost, and 17.5 kilotons of CO2 emission. The results suggest that the cost of electricity consumption should be included in the economic cost analysis of PM2.5 pollution in the future. A 1 °C increase in the monthly temperature is in the long-run significantly related to a 13.6% increase in the monthly electricity consumption for Singapore, while a 30 degree days increase in heating & cooling days (HCDD) is in the long-run significantly related to a 24.9% increase in the monthly electricity consumption for Shanghai. A 5-day increase in the number of rainy days per month is in the long-run significantly related to a 3.0% and 5.8% increase in the monthly electricity consumption for Singapore and Shanghai, respectively.

Net carbon management of agro-residues has been an important pathway for reducing the environmental burdens of agricultural production. Converting agro-residues into biochar through pyrolysis is a prominent management strategy for achieving carbon neutrality in a circular economy, meeting both environmental and social concerns. Based on the latest studies, this study critically analyzes the life cycle assessment (LCA) of biochar production from different agro-residues and compares typical technologies for biochar production. Although a direct comparison of results is not always feasible due to different functional units and system boundaries, the net carbon sequestration potential of biochar technology is remarkably promising. By pyrolyzing agro-residues, biochar can be effectively produced and customized as: (i) alternative energy source, (ii) soil amendment, and (iii) activated carbon substitution. The combination of life cycle assessment and circular economy modelling is encouraged to achieve greener and sustainable biochar production.

This work developed a framework to predict the energy and economic impacts of solar photovoltaic soiling. This framework includes the effects of relative humidity, precipitation and tilt angle on solar photovoltaic soiling. A concept of relative net-present value change was introduced to determine the optimal cleaning interval. The uncertainties in the economic analysis were accounted for using a Monte Carlo simulation method. The framework was used to study the soiling-induced efficiency and economic losses of solar photovoltaic modules in seven cities (i.e. Taichung, Tokyo, Hami, Malibu, Sanlucar la Mayor, Doha, and Walkaway). Overall, the efficiency loss (in ascending order) for Tokyo/Walkaway < Taichung < Sanlucar la Mayor < Malibu/Hami < Doha for a one-year study period. Doha experiences an efficiency loss over 80% for a 140-day exposure, while Tokyo has an efficiency loss less than 4% for a one-year exposure. Malibu has longest optimal cleaning intervals (70 days for manual cleaning and 49 days for machine-assisted cleaning) that leads to the relative net-present value changes of 1.7% and 1.1%. Doha has the shortest optimal cleaning intervals (23 days for manual cleaning and 17 days for machine-assisted cleaning) that leads to the relative net-present value changes of 21% and 19%. The work serves as an effective tool for designing optimal cleaning protocols for solar photovoltaic systems.

Bioenergy production is one of the most reliable strategies for replacing fossil fuels and reducing CO2 emissions. Gasification-based bioenergy generation has been extensively studied; however, it is still facing the challenges of limited energy efficiencies, especially upon small-scale development. Concentrated solar thermochemical gasification of biomass (CSTGB) where the endothermic reactions of gasification are driven by concentrated solar thermal energy serves as a promising solution to improve the efficiency of gasification. This review summarized recent development in modeling concentrated solar thermochemical gasification of biomass, the method of concentrated solar thermal for gasification, and applications and development of concentrated solar thermal biomass gasification. The influences of operating parameters toward the performance of the technology were studied, which determine the optimum parameters for maximizing the energy conversion efficiency of the technology. CSTGB could improve the utilization of biomass feedstocks and the total energy efficiency by 30% and 40%, respectively by effectively storing solar energy in the producer gas as compared to conventional gasification.