Progress in Energy and Combustion Science最新文献

Global warming is one of the most pressing environmental concerns which correlates strongly with anthropogenic CO₂ emissions so that the CO₂ decreasing strategies have been meaningful worldwide attention. As an option, natural gas hydrate reservoirs have steadily emerged as a potent source of energy which would simultaneously be the proper places for CO₂ sequestration if the method of CO₂/CH₄ replacement could be developed. On the flip side, CO₂ hydrates as safe and non-flammable solid compounds without an irreversible chemical reaction would contribute to different industrial processes if their approaches could be improved. Toward developing substantial applications of CO₂ hydrates, laboratory experiments, process modelling, and molecular dynamics (MD) simulations can aid to understand their characteristics and mechanisms involved. Therefore, the current review has been organized in form of four distinct sections. The first part reviews the studies on sequestering CO₂ into the natural gas hydrate reservoirs. The next section gives an overview of process flow diagrams of CO₂ hydrate-based techniques in favour of CO₂ Capture and Sequestration & Utilization (CCS&U). The third section summarizes the merits, flaws, and different effects of hydrate promoters as well as porous media on CO₂ hydrate systems at macroscopic and mesoscopic levels, and also how these components can improve CO₂ hydrate properties, progressing toward the more feasibility of CO₂ hydrate industrial applications. The final sector recapitulates the MD frameworks of CO₂ clathrate and semiclathrate hydrates in terms of new insights and research findings to elucidate the fundamental properties of CO₂ hydrates at the molecular level.

High lipid content and excellent CO₂ fixation capability of microalgae by photosynthesis have made microalgal biodiesel (BD) a promising carbon-neutral fuel. Nonetheless, the commercialization of BD has not yet been realized because of expensive and energy-intensive cultivation, pretreatment, and BD conversion processes in reference to 1^st generation BD production. To resolve the issues, this study comprehensively reviewed the current technical developments of microalgal BD production process and suggested promising future studies. Current microalgal BD production processes highly rely on the processes developed from 1^st generation BD process, namely base-catalyzed transesterifications. However, the base-catalyzed suffers from saponification reaction and low production yield due to high water and free fatty acid contents in microalgae. Vigorous pretreatments such as dewatering, drying, esterification of free fatty acid, and purification are required for high yield of microalgal BD production, making this process economically not attractive. As efforts to construct new transesterification platform, novel approaches tolerant to impurities such as thermally induced non-catalytic transesterifications were suggested. The thermally induced reactions allowed in situ conversion of microalgal lipid into BD (≥ 95 wt.% yield) within 1 min of reaction at ≥ 350 ˚C. This process resists to presence of water and free fatty acids and does not require lipid extraction process. To make this process more promising, it was suggested lowering reaction temperature for thermally induced transesterifications. In addition, pilot study, in-depth life cycle assessment, and economic analysis were suggested to assess economic viability and environmental impacts.

Solid oxide cells (SOC) play a major role in strategic visions to achieve decarbonization and climate-neutrality. With its multifuel capability, this technology has received rapidly growing amount of attention from researchers worldwide. Due to the great flexibility of SOCs with respect to the fuels that can be used, not only hydrogen, but also biogas, natural gas, diesel reformates and many other conventional and alternative fuels can be used. This makes it possible to couple SOCs with diverse sustainable fuel sources to generate electricity or to generate valuable fuels such as syngas when utilizing renewable electricity. In this paper, the reader is provided with a review of the existing knowledge about solid oxide fuel cell (SOFC) and solid oxide electrolysis (SOE) systems and how to safely operate them over the long-term, placing a special focus on real-world operating environments. Both the utilization and generation of real commercially available fuels are taken into consideration. Different failure modes can appear during the system operation under real-world conditions and reduce the SOC lifetime, an aspect that is extensively discussed in this review. Firstly, a detailed discussion of the difference between carbon-free and carbon-containing fuels is presented, considering different impurities and their impacts on the SOC performance, stability and lifetime. Secondly, unfavorable operating conditions are presented and possibilities for the early identification of different failure modes are explored. An overview of available conventional and non-conventional diagnostic tools and their applications is provided here. Overall, this review paper presents a guideline for all relevant degradation issues related to SOCs operated in a real-world environment, describing (i) how these issues appear and how to understand them, (ii) how to predict them, (iii) how to identify them and (iv) how to prevent them, as well as, if required, how to reverse them. To achieve this goal, individual chapters specifically address failure modes, degradation prediction, degradation prevention and performance regeneration. The reader is provided with necessary knowledge about the long-term and short-term operating stability and the degradation provoked in a compact summary. The available knowledge about specific process frequencies is summarized in one diagram, which is a novel contribution of this review. This enables researchers to rapidly identify all occurring process mechanisms with SOFCs and SOECs. Moreover, suggestions for how to accelerate degradation and how to regenerate performance are summarized in several tables.

Building on their dual functionality for solar photothermal absorption and storage, slurries/dispersions of micro/nano-encapsulated phase-change materials (ePCMs) are capable of revolutionizing the solar-thermal industry. Yet, to facilitate their transition from the research and development stage into market adoption and penetration, there is a dire need for a methodical understanding of the design criteria, fabrication techniques, application areas, and technical challenges of these novel solar concepts in light of state-of-the-art advances. This work thoroughly addresses these needs with a focus on slurries/dispersions with solid-liquid PCM cores for latent heat storage and surface-engineered shells for solar radiation extinction. By dividing this study into four parts, we start with an overview of the material types, desired attributes, and key challenges of PCMs; the different types of PCM systems; and their potential applications in the solar energy industry. We then focus in the second part on ePCMs in indirect (surface-based) and direct (volume-based) solar-absorption systems in terms of their functional requirements, encapsulation methods, stability metrics and assessment, compositional and structural characterization techniques, measurement of thermophysical properties, and key design parameters. The third part of this work is dedicated to the theoretical foundation necessary to model and simulate solar ePCM systems, including continuum, discrete, and multi-scale modeling approaches for flow and heat transfer in ePCM slurries/dispersions; thermophysical property correlations; melting theory in PCM capsules; radiation transfer and optical properties evaluation; and energy performance analysis. In the final part, recent breakthroughs in multi-functional shell engineering, molten-salt encapsulation, multi-scale modeling, contrasting ePCMs and nanofluids, and ePCM-based optical filtration are highlighted. By striking a balance between fundamentals and applications, this work aims to serve as a comprehensive foundation for newcomers into this promising field of research as well as an updated critique for experts looking to identify knowledge gaps, technical bottlenecks, latest advances, and future directions.

Shock tubes have emerged as an effective tool for applications in various fields of research and technology. The conventional mode of shock tube operation employs a frangible diaphragm to generate shock waves. The last half-century has witnessed significant efforts to replace this diaphragm-bursting method with fast-acting valves. These diaphragmless methods have good repeatability, quick turnaround time between experiments, and produce a clean flow, free of diaphragm fragments, in contrast to the conventional diaphragm-type operation. The constantly evolving valve designs target shorter opening times for improved performance and efficiency. The present review is a compilation of the different diaphragmless shock tubes that have been conceptualized, developed, and implemented for various research endeavors. The discussions focus on essential factors, including the actuation mechanism, driver-driven configurations, valve opening time, shock formation distance, and operating pressure range, that ultimately influence the shock wave parameters obtained in the shock tube. A generalized mathematical model to study the behavior of these valves is developed. The advantages, limitations, and challenges in improving the performance of the valves are described. Finally, the present-day applications of diaphragmless shock tubes have been discussed, and their potential scope in expanding the frontiers of shock wave research and technology is presented.

Waste tires are solid wastes with large annual output and with the potential for great harm to the environment. The pyrolysis of waste tires can recycle energy and produce reusable products. Although there are many reviews in the literature in regard to the pyrolysis characteristics of waste tires, no one paper focuses on reviewing and summarizing the tire char. This paper critically appraises the achievements of earlier reports and literature and assesses the current state-of-the-art for the production and application of tire char from waste tires. Initially, the thermal decomposition behavior of different tire rubbers is discussed and compared where it is shown that the different components of waste tire rubber have different thermal degradation characteristics. The influencing factors on the yield and quality of tire char are discussed and assessed in terms of different pyrolysis reactors and technologies, tire type and composition, and a range of pyrolysis process conditions. The composition of the waste tire and pyrolysis conditions are the main factors affecting the distribution of pyrolysis products. Pyrolysis technology and reactor equipment also have an effect on the distribution of pyrolysis products. The physical and chemical structural characteristics of tire char are critically reviewed in detail, including a comparison of the fundamental differences with commercial carbon black and modified tire char (physical activation and chemical activation). Finally, high-value application fields and developmental prospects of tire char are summarized. Through extensive literature review, a novel development was that tire char could be used as a source of graphene. The economic analysis of the various tire char applications should be one of the main research directions in the future. The keynote of this review is to promote intensification of waste tire recycling and treatment so that more tire char can be obtained from waste tire pyrolysis and thereby be reused in different applications to obtain more value.

Discarded plastics can be converted to various fuels and chemicals to generate positive economic value instead of polluting the environment. In the past few years, pyrolysis has attracted much attention in the industrial and scientific communities as a promising versatile platform to convert plastic waste into valuable resources. However, it is still difficult to fine-tune an efficient and selective pyrolysis process to narrow the product distribution for a feasible commercial production. Furthermore, traditional plastic-to-fuels technology looks like another expensive way to burn fossil fuels, making no contribution to the plastic circular economy. By learning from the developed plastic-to-fuels technology, achieving the conversion of plastic waste into naphtha or plastic monomers that can be used for new plastic manufacturing in a closed-loop way is a more promising resource recovery pathway. However, there is no comprehensive review so far about achieving plastic waste recycling/upcycling by pyrolysis. This article will provide a critical review about the recovery pathways of plastic pyrolysis based on the various products (fuels, naphtha, hydrogen, and light olefins). It will overview the recent advances regarding plastic pyrolysis process and reactor design, introduce various recovery pathways based on the pyrolysis process, summarize process optimization and catalyst development, discuss the present challenges for plastic pyrolysis, highlight the importance and significance of creating a plastics’ circular economy, discuss the economic feasibility, the environmental impact, and outlook for future development for plastic pyrolysis. This review presents useful information to further develop and design an advanced pyrolysis process, with an improved efficiency, desirable product selectivity, and minimum environmental impacts. It is helpful to encourage more circular economy-oriented research aimed at converting waste plastics to naphtha and plastic monomers instead of simply producing fuels from the scientific communities of chemistry, energy, and the environment.