Progress in Energy and Combustion Science最新文献

Progress in recent years has opened the door for yet another area of application for the lattice Boltzmann method: Combustion simulations. Combustion is known to be a challenge for numerical tools due to, among many other reasons, a large number of variables and scales both in time and space. The present work aims to provide readers with an overview of recent progress and achievements in using the lattice Boltzmann method for combustion simulations. The article reviews some basic concepts from the lattice Boltzmann method and discusses different strategies to extend the method to compressible flows. Some of the lattice Boltzmann models developed to model mass transport in multi-species system are also discussed. The article provides a comprehensive overview of models and strategies developed in the past years to simulate combustion with the lattice Boltzmann method and discuss some of the most recent applications, remaining challenges and prospects.

Conventional diesel combustion is a mixing-limited process that passes through high temperature and fuel-rich zones, leading to oxides of nitrogen (NO_x) and particulate matter (PM) formation. Simultaneous reduction of NO_x and PM is difficult due to NO_x-PM trade-off. As alternative fuels, emulsions of water-in-diesel offer several advantages, including a simultaneous reduction in NO_x and PM formation. There are, however, disparities in the reported engine performance and emission characteristics, as they appear to depend on the constituents and microstructure of the emulsion fuel used and engine conditions. Studies on engine performance and exhaust emissions were often carried out without adequate characterization of the emulsions. Therefore, the paucity of cohesive data can be circumvented by standardizing the protocols for emulsion fuels, tailoring their morphology, structure, and characterization, and optimizing engine conditions. This review article recapitulates the salient features of emulsion fuels, from their synthesis, microstructure, characterization, and macroscopic spray characteristics to performance and emissions in diesel engines. A critical analysis of the current state of knowledge is also presented, emphasising the tunability of droplet size and characterization of emulsion stability. The review concludes by suggesting the path forward to utilizing emulsion fuels.

Alkali metals, mainly K and Na, which are present in solid fuels such as biomass and coal, play an important role during their thermal conversion, e.g., in combustion or gasification. At high temperatures, alkali elements will be released in gas phase as alkali atoms, alkali chlorides, alkali hydroxides and alkali sulphates. In biomass/coal-fired boilers, the release of these alkali species can cause problems such as corrosion, slagging and fouling, threatening the safe operation of the facilities. The information on the release dynamic is important for developing proper models for alkali metal transformation in solid fuel combustion and gasification. Therefore, accurate quantitative measurements of the release of different alkali species during thermal-chemical conversion processes of biomass/coal are important. In this paper, we review literatures published over the last few decades in the field of quantitative optical measurements of alkali metals performed in combustion/gasification processes, and the release modeling based on those optical measurements. Firstly, the current situation of biomass and coal utilization is discussed, including the speciation of alkali metals in biomass/coal and their adverse effects on facilities. Secondly, requirements for optical measurements as well as several quantitative optical techniques are introduced including the general principles, typical setups, calibration methods and major advantages and drawbacks. In contrast to off-line techniques, these optical techniques provide nonintrusive measurements with high temporal and spatial resolution, which are indispensable for alkali release modeling. Furthermore, the alkali release behaviors based on optical measurements in thermochemical conversion processes are discussed. Based on the experimental results, the kinetic data for alkali release were summarized. Alkali release modeling was fulfilled relying on the knowledge of alkali release mechanisms and the kinetic data. In addition, simulations of alkali metal release with computational fluid dynamics during the biomass/coal combustion processes are also discussed, providing valuable information for industrial processes. Finally, typical examples of industrial applications of optical measurement methods in solid fuel thermochemical conversion processes as well as waste incineration and other processes are presented.

Capturing CO₂ from air (DAC) is becoming an attractive technological route to face the climate crisis. This paper reviews the existing research efforts to integrate DAC with conversion technologies to transform the captured CO₂ into chemicals or fuels. The approach can potentially lead to net zero carbon emissions, thus being of interest in a circular economy framework. A growing amount of research has been devoted to the combination of DAC with CO₂ conversion, leading to creative strategies which start to be scaled up. In this review, we have critically analysed the existing approaches by the degree of process integration. From the point of view of process intensification, the integration of both capture and reaction in the same vessel can potentially lead to equipment and energy cost savings besides other synergistic effects. In this vessel, the DAC and conversion can occur either in consecutive stages with change of feed or spontaneously in a cascade reaction without changing the conditions. As a side effect, the benefits entailed by process intensification in different levels of integration may be a decisive driving force for the widespread deployment of DAC. This paper discusses the ongoing research and perspectives to guide researchers in this promising new field.

The massive combustion utilization of fossil fuel in human industrial activities, such as power plants, waste incineration, and kiln combustion for cement production, would emit serious gaseous pollutants (SO₂, NO_x, VOC, and mercury), aerosols and CO₂. There is a growing interest in using novel solid sorbents, i.e., activated carbon (AC), zeolites, carbon nanotube, carbon molecular sieve, and MOFs (metal-organic frameworks), for their ability to capture gaseous pollutants from combustion flue gas through adsorption processes. However, these emerging alternatives are generally expensive, limiting large-scale industrial utilization. Biochar, as a stable carbon-rich solid by-product from biomass thermal treatment, is not only capable of replacing coal as fuel in power plants but also widely reported to be an effective and cheap sorbent for removing the gaseous pollutants in flue gas, including SO₂, NO_X, Hg, CO₂ and VOC, due to its high porosity and specific surface area and surface functional groups. In this review, the physical activation, chemical activation, and novel modification methods including microwave, ultrasonic, plasma, ball-milling, and molten salts were introduced as their optimization to the porous properties and active surface functional groups for biochar sorbents. The functionalized treatments including metal, ammonia/amines, and halogen modification on activated biochar were reviewed to observe the further improved adsorption performance of biochar, for possible engineering application. The abundant amounts of the oxygenic functional group increase the number of active sites onto which NH₃ or Hg can be adsorbed, resulting in higher NO and Hg removal efficiencies. Oxygenated anchoring sites are also effective intermediate stage to introduce the nitrogen functional groups, which are generally more effective than the porous texture for acidic SO₂ and CO₂ adsorption, especially at adsorption temperature higher than ∼100 °C. The redox reactions of metal catalyst in biochar and the improved adsorption ability of NH₃ and Hg mainly determine the removal performance of biochar for NO_x and Hg⁰. The halogen addition to form C-halogen groups can transform Hg⁰ into mercury halide retained on the biochar. The practical removal performance of various gaseous pollutants is affected by the adsorption conditions, such as adsorption temperature, humidity and impurities concentrations in simulated flue gas, selectivity, synergistic adsorption of typical gases, and regeneration capacity. The adsorption isotherm models and the adsorption kinetic models are helpful for predicting the adsorption amount and controlling mechanism and calculating the energy of adsorptio