Progress in Energy and Combustion Science最新文献

The utilization of low calorific value gases (LCVG) in combustion devices presents particular challenges in terms of ignition and sustained combustion stability due to the presence of non-combustible components. Moderate or intense low-oxygen dilution (MILD) combustion has emerged as a promising technology for LCVG combustion, offering numerous advantages such as high combustion efficiency, reduced pollutant emissions, and increased fuel flexibility. However, the current body of research in this area is fragmented, making it challenging to draw meaningful comparisons between studies and hindering its practical application. This paper provides a comprehensive review of conventional and MILD combustion of LCVG. To understand the impact of composition on combustion, the fuels are classified based on their composition of hydrogen, carbon monoxide, methane, carbon dioxide, nitrogen, and water. We also delve into the chemical and physical effects of composition, including reaction kinetics and turbulence mixing, and provide an overview of the burners and methods used in establishing MILD combustion. Furthermore, computational fluid dynamics (CFD) models and chemical kinetics in MILD combustion are also thoroughly discussed.

The presence of a large amount of dilution gas in LCVG increases the self-ignition temperature and ignition delay time of the mixture, making preheating the reactants a critical consideration. In MILD combustion, it is crucial to have an inlet reactant temperature higher than the self-ignition temperature ($T_{\text{in}}>T_{\text{si}}$) to mitigate the difficulties associated with ignition and unstable combustion. The heat release in MILD combustion should be moderate to ensure that the combustion temperature does not become too high. The non-combustible components of LCVG are beneficial in this regard, as they allow for a temperature increase of less than the self-ignition temperature ($\Delta T<T_{\text{si}}$). Hydrogen is the most reactive component in LCVG, and its content directly impacts the establishment, efficiency, and pollutant emissions of MILD combustion. Carbon dioxide, nitrogen, and water act as diluents, helping to reduce NOx emissions in MILD combustion. Although a burner may have the potential to be used for MILD combustion, it must be optimised for LCVG with variable composition in order to achieve the lowest pollutant emissions. Further research is necessary to verify and improve simulation models and chemical kinetics. This article provides theoretical support for the practical application of MILD combustion of LCVG with variable composition.

Increasing global energy consumption has created an urgent need to address climate change and consequently, the need for sustainable and renewable energy has increased. Simultaneously, the pervasive presence of crude oil hydrocarbons in the ecosystem, stemming from exploration and extraction activities, underscores the urgency for developing effective and environment-friendly remediation technologies. Hence, here we describe use of non-edible second-generation energy crops for rhizoremediation of oil contaminated soil, to yield plant biomass for bioenergy and carbon sequestration. This could address the restoration of petroleum hydrocarbon contaminated soil, along with waste management for biofuel production. This strategy could also save the agricultural land that is under threat as a consequence of crude oil contamination. The strategies for enhanced rhizoremediation with bioenergy crops have been elaborated, including soil, and microbiome engineering. Furthermore, the article delves into recent technological advancements aimed at enhancing the efficiency of biofuel production with bioenergy crops, employing methodologies such as synthetic biology, systems biology, and metabolic engineering. Despite the promising aspects of this approach, challenges in biofuel production using bioenergy crops are acknowledged, including issues such as N₂O emissions, biodiversity loss, and water quality management. The article not only outlines these challenges but also proposes remedial strategies to address them. Through this comprehensive discussion, valuable insights are provided on the potential of petroleum hydrocarbon-contaminated soils for biomass production within the framework of achieving sustainable bioenergy generation. This approach has potential to mitigate CO₂ emissions, remediate polluted lands, and significantly contribute to the global effort to combat climate change.

Direct absorption solar collectors (DASCs) based on nanofluids offer a promising solution for achieving the dual goals of solar energy utilization: maximizing solar absorption and minimizing thermal losses. In contrast to conventional surface absorption solar collectors, which suffer from substantial heat losses, DASCs operate by replacing elevated-temperature absorption surfaces with nanofluid bulk for volumetric absorption. To bridge the gap between theoretical research and commercialization, a comprehensive understanding of DASCs is essential. This includes modeling approaches, the impact of design and operational parameters, recognizing limitations, and evaluating future prospects. This study provides a comprehensive review with a focus on resolving disagreements regarding low-flux DASC responses to specific design and operational variations that have sparked conflicting interpretations in the literature. This review, by addressing these discrepancies, serves as an invaluable resource for researchers seeking a more nuanced understanding of this evolving field, facilitating its advancement into practical applications.

This review comprehensively examines the field of DASCs across eight distinct sections. Section 1 provides an overview of solar energy's potential, the evolution of solar collectors, and the rationale for the review. Section 2 focuses on theoretical modeling approaches for simulating colloidal suspensions in solar thermal systems, including optical properties, radiative transport, and heat transfer mechanisms. The strengths and limitations of these models are critically evaluated to assist researchers in selecting the most suitable one for specific colloidal systems. Additionally, a critical assessment of analytical and numerical studies in the existing literature is presented in this section. Section 3 offers a detailed view and critical assessment of experimental efforts in the field. The stability of nanofluids is discussed in section 4, while sections 5 and 6 analyze the impact of operating conditions, geometry, design parameters, and flow properties on DASC performance criteria. We address contradictions and ambiguities in the effects of some operating variables in the DASC literature, considering state-of-the-art simulation techniques. Section 7 focuses on economic and environmental analyses related to DASCs, providing insights into their feasibility and sustainability. Finally, Section 8 synthesizes conclusions from the reviewed literature, identifies research gaps, and proposes future directions based on recent advancements in DASC technology.

Fischer-Tropsch Synthesis (FTS) allows the conversion of syngas to high-density liquid fuels, playing a key role in the petrochemical and global energy sectors over the last century. However, the current Global Challenges impose the need to recycle CO₂ and foster green fuels, opening new opportunities to adapt traditional processes like FTS to become a key player in future bioenergy scenarios. This review discusses the implementation of CO₂-rich streams and in tandem catalysis to produce sustainable fuels via the next generation of FTS. Departing from a brief revision of the past, present, and future of FTS, we analyse a disruptive approach coupling FTS to upstream and downstream processes to illustrate the advantages of process intensification in the context of biofuel production via FTS. We showcase a smart tandem catalyst design strategy addressing the challenges to gather mechanistic insights in sequential transformations of reagents in complex reaction schemes, the precise control of structure-activity parameters, catalysts aging-deactivation, optimization of reaction parameters, as well as reaction engineering aspects such as catalytic bed arrangements and non-conventional reactor configurations to enhance the overall performance. Our review analysis includes technoeconomic elements on synthetic aviation fuels as a case of study for FTS applications in the biofuel context discussing the challenges in market penetration and potential profitability of synthetic biofuels. This comprehensive overview provides a fresh angle of FTS and its enormous potential when combined with CO₂ upgrading and tandem catalysis to become a front-runner technology in the transition towards a low-carbon future.

Carbon capture and storage is recognized as one of the most promising solutions to mitigate climate change. Compared to conventional separation technologies, supersonic separation is considered a new generation of technology for gas separation and carbon capture thanks to its advantages of cleaning and efficient processes which are achieved using energy conversion in supersonic flows. The supersonic separation works on two principles which both occur in supersonic flows: the energy conversion to generate microdroplets and supersonic swirling flows to remove the generated droplets. This review seeks to offer a detailed examination of the cutting-edge technology for gas separation and carbon dioxide removal in the new-generation supersonic separation technology, which plays a role in carbon capture and storage. The evaluation discusses the design, performance, financial feasibility, and practical uses of supersonic separators, emphasizing the most recent progress in the industry. Theoretical analysis, experiments, and numerical simulations are reviewed to examine in detail the advances in the nucleation and condensation characteristics and the mechanisms of supersonic separation, as well as new applications of this technology including the liquefaction of natural gas. We also provide the perspective of the challenges and opportunities for further development of supersonic separation. This survey contributes to an improved understanding of sustainable gas removal and carbon capture by using the new-generation supersonic separation technology to mitigate climate change.

Solid oxide fuel cells (SOFCs) have witnessed significant advancements in recent years, emerging as potential alternatives to low-temperature fuel cells for mobile applications owing to their wide fuel flexibility and high efficiency. This paper offers a comprehensive assessment of the progress achieved thus far and the challenges faced in transitioning from stationary to mobility sectors. Three pivotal aspects are highlighted across different levels: enhancing fuel tolerance and flexibility at the anode level, achieving rapid start-up at the cell level, and realizing compact integration at the stack level. This review can lay a theoretical foundation for the development of SOFC systems tailored to unique requirements, such as high power density and rapid start-up, crucial for mobile applications. This review will facilitate commercial breakthroughs and advances in the mobility of SOFCs, which holds substantial strategic importance.

Solar and other renewable energy driven gas-solid thermochemical energy storage (TCES) technology is a promising solution for the next generation energy storage systems due to its high operating temperature, efficient energy conversion, ultra-long storage duration, and potential high energy density. Experimental and theoretical studies suggest that the respective gravimetric and volumetric TCES energy storage densities vary from 200 to 3000 kJ kg⁻¹ and 1–3 GJ m⁻³. Solar radiation or heat generated from electric furnaces powered by renewable electricity can be stored in the form of chemical energy through endothermic reactions, while the stored chemical energy can be converted to thermal energy via an exothermic reaction when needed. The design of highly effective reactors requires a deep understanding of materials, thermodynamics, chemical kinetics, and transport phenomena. At time of writing, TCES reactors are yet to be deployed at commercially relevant scales, leaving a substantial gap between development efforts and commercial feasibility. Therefore, this review aims to examine the state-of-the-art design and performance of particle-based TCES reactors with different reactive materials. Fundamentals related to TCES reactive materials, reaction conditions, thermodynamics and kinetics, and transport phenomena are reviewed in detail to provide a comprehensive understanding of the reactor design and operation. Five major types of TCES reactors have been comprehensively reviewed and compared, including fixed, moving, rotary, fluidized, and entrained bed reactors. Most reported prototype reactors in the literature operate at lab scale with thermal inputs below 40 kW, and scaled TCES reactors (e.g., at megawatt level) are yet to be demonstrated. The nominal reactor operating temperatures range from 300 to 1500 °C, depending on the selected chemistry, reactive material, and heat sources. To evaluate their designs, the reactors are assessed in aspects of performance, cost, and durability. Discrepancies in performance indicators of energy storage density, extent of reaction, and various energy efficiencies are highlighted. The scale-up of reactors and power block integration, which hold the key to the successful commercialization of TCES systems, are critically analyzed. Advanced materials (both reactive materials and ceramic reactor housing materials), effective particle flow control, advanced modeling tools, and novel system design may bring significant improvement to the energy efficiency, storage density and cost competitiveness of particle-based TCES reactors.

Non-thermal plasma appears as a promising alternative technology to develop the electrification of the petrochemical industry. Non-thermal plasma has the advantage of operating at atmospheric pressure and room temperature in “on/off” mode. The high-energy electrons generated are able to activate many reactants allowing thermodynamically unfavorable reactions to occur. Methane coupling is particularly important to produce C₂ hydrocarbons, especially ethylene known as a platform chemical for the synthesis of many products. In this review, the state-of-the-art of plasma and plasma-catalysis for methane coupling is described. Focus is given on plasma chemistry and the influence of different parameters related to plasma reactors and gas composition are discussed. The role of a catalyst coupled with plasma is detailed and synergies are explained for various catalytic compositions.