共查询到20条相似文献,搜索用时 15 毫秒
1.
Paola Ammendola Riccardo Chirone Giovanna Ruoppolo Fabrizio Scala 《Proceedings of the Combustion Institute》2013,34(2):2735-2740
This work reports on a study, carried out in a lab-scale fluidized bed apparatus, on fragmentation and attrition of two biomass fuels, namely wood chips and wood pellets, under both combustion and gasification conditions. The aim was to highlight the effect of their different mechanical strength on the fuel particle size distribution and overall carbon conversion. Primary fragmentation tests showed that for wood pellets limited fragmentation occurred during devolatilization, with a fragmentation probability around 30% and particle multiplication factor of 1.4. On the contrary, wood chips were subject to extensive fragmentation as witnessed by large values of the particle multiplication factor and of the fragmentation probability.Results of char attrition experiments carried out under inert, combustion and gasification conditions showed that the carbon loss by elutriation is critical only during gasification, especially for the wood chips char. A gasification-assisted attrition mechanism was proposed to explain the experimental results, similar to the well known combustion-assisted attrition patterns already documented for coal under oxidizing conditions. The higher mechanical strength of the wood pellets appears to be beneficial for reducing carbon elutriation and for obtaining a higher carbon conversion. 相似文献
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Jobin K. Antony Nilesh J. Vasa S.R. Chakravarthy R. Sarathi 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(17-18):2509-2516
Nano-aluminum particles are produced by a wire explosion process in different inert gas ambience. It is observed that generated particles have different sizes and it follows log–normal probability distribution. The particle size produced by the wire explosion process varies depending on the thermal conductivity of the medium and the operating pressure of the gas. To understand the mechanism of nano-particle formation, the optical-emission spectroscopic technique is used for measuring characteristics of plasma generated during the wire explosion process. Strong emission lines were observed from the species formed during the wire explosion process. Plasma temperatures are estimated based on local thermal equilibrium principle and using Al emission lines. Plasma temperature of more than 8000 K is observed in an Ar ambient. The optical emission study clearly indicates that the intensity of plasma increases with an increase in the ambient pressure. Further, it is observed that an increase in the pressure of the gas, the plasma temperature also increases. The study shows that the plasma temperature in the He gas is lesser than in the Ar gas. The plasma temperature due to the discharge plays a significant role on nano-particle formation. In addition, it is observed that irrespective of polarity, emission characteristics are almost the same. 相似文献
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Thermal spray coatings are affected by various parameters. In this study, the finite element method with volume of fluid (VOF) procedure is used to investigate the deposition process which is very important for the quality of sprayed coatings. The specific heat method (SHM) is used for the solidification phenomenon. A comparison of the present model with experimental and numerical model available in the literature is done. A series of numerical calculations is carried out to investigate the effect of the surrounding gas temperature on the splat formation. The variation of the surrounding gas temperature has a significant effect on splat morphology and can affect the adhesion of the splat on the substrate. 相似文献
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Selma Zahirović Robert Scharler Pia Kilpinen Ingwald Obernberger 《Combustion Theory and Modelling》2013,17(1):61-87
While reasonably accurate in simulating gas phase combustion in biomass grate furnaces, CFD tools based on simple turbulence–chemistry interaction models and global reaction mechanisms have been shown to lack in reliability regarding the prediction of NOx formation. Coupling detailed NOx reaction kinetics with advanced turbulence–chemistry interaction models is a promising alternative, yet computationally inefficient for engineering purposes. In the present work, a model is proposed to overcome these difficulties. The model is based on the Realizable k–? model for turbulence, Eddy Dissipation Concept for turbulence–chemistry interaction and the HK97 reaction mechanism. The assessment of the sub-models in terms of accuracy and computational effort was carried out on three laboratory-scale turbulent jet flames in comparison with the experimental data. Without taking NOx formation into account, the accuracy of turbulence modelling and turbulence–chemistry interaction modelling was systematically examined on Sandia Flame D and Sandia CO/H2/N2 Flame B to support the choice of the associated models. As revealed by the Large Eddy Simulations of the former flame, the shortcomings of turbulence modelling by the Reynolds averaged Navier–Stokes (RANS) approach considerably influence the prediction of the mixing-dominated combustion process. This reduced the sensitivity of the RANS results to the variations of turbulence–chemistry interaction models and combustion kinetics. Issues related to the NOx formation with a focus on fuel bound nitrogen sources were investigated on a NH3-doped syngas flame. The experimentally observed trend in NOx yield from NH3 was correctly reproduced by HK97, whereas the replacement of its combustion subset by that of a detailed reaction scheme led to a more accurate agreement, but at increased computational costs. Moreover, based on results of simulations with HK97, the main features of the local course of the NOx formation processes were identified by a detailed analysis of the interactions between the nitrogen chemistry and the underlying flow field. 相似文献
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Understanding the synergistic effect of mixed solvent annealing on perovskite film formation
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Morphology control of perovskite films is of critical importance for high-performance photovoltaic devices. Although solvent vapor annealing (SVA) treatment has been widely used to improve the film quality efficiently, the detailed mechanism of film growth is still under construction, and there is still no consensus on the selection of solvents and volume for further optimization. Here, a series of solvents (DMF, DMSO, mixed DMF/DMSO) were opted for exploring their impact on fundamental structural and physical properties of perovskite films and the performance of corresponding devices. Mixed solvent SVA treatment resulted in unique benefits that integrated the advantages of each solvent, generating a champion device efficiency of 19.76% with improved humidity and thermal stability. The crystallization mechanism was constructed by conducting grazing-incidence wide-angle x-ray diffraction (GIWAXS) characterizations, showing that dissolution and recrystallization dominated the film formation. A proper choice of solvent and its volume balancing the two processes thus afforded the desired perovskite film. This study reveals the underlying process of film formation, paving the way to producing energy-harvesting materials in a controlled manner towards energy-efficient and stable perovskite-based devices. 相似文献
7.
Dunxi Yu Minghou Xu Hong Yao Xiaowei Liu Ke Zhou Lin Li Chang Wen 《Proceedings of the Combustion Institute》2009,32(2):2075-2082
Ash particles produced from pulverized coal combustion are considered to be tri-modally distributed. These include the well-known ultrafine and coarse modes, and a central mode that is less reported but attracts increasing attention. This work presents a preliminary study on the formation mechanisms of the central mode particles during pulverized coal combustion. Experiments of four sized and density-separated coal samples were carried out in a laboratory drop-tube furnace under various controlled conditions. Experimental data show that the ash particle size distributions have an evident central mode at 4 μm for all coal samples. Increasing combustion temperature leads to an increase in the central mode particle formation, which is thought to be due to enhanced char fragmentation. The small-size coal sample produces a larger amount of the central mode particles, reasonably due to abundant fine particles in the parent coal sample. Under similar combustion conditions, both the Heavy (>2.0 g/cm3) and Light (<1.4 g/cm3) coal fractions produce a central mode, indicating that not only the included minerals but also the excluded minerals contribute to the formation of the central mode particles. 相似文献
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Slow scan voltammery (SSV), electrochemical impedance spectroscopy (EIS) and galvanostatic cycling (GC) were used to characterize
the formation of the Solid Electrolyte Interphase (SEI) on a graphite electrode during lithiation and delithiation and during
thermal aging. The SSV and GC results show the irreversible character of the first reduction peak/semi-plateau at 0.8 V. After
aging, a new irreversible plateau appears in the GC curves. Concomitantly the interfacial resistances as determined from the
Nyquist plots increased then decreased as the signature of SEI transformation. We suggest the SEI is subjected to precipitation/dissolution
processes.
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001. 相似文献
13.
N.V. Petrova I.N. Yakovkin 《The European Physical Journal B - Condensed Matter and Complex Systems》2013,86(7):1-5
The electronic structures of Sn and SnO x layers adsorbed on the Pd(110) surface have been calculated by DFT. In agreement with available results of photoemission studies, it is found that the formation of the oxides induces pronounced changes in the related peak in the DOS. In particular, it is shown that the formation of SnO2 adsorbed layers leads to a transformation of the Sn 4d spin-orbit doublet into a quadruple peak, while for SnO the peak retains its shape. Due to this feature, the shape of the Sn 4d peak in photoemission spectra can serve as an unambiguous indicator of the degree of oxidation of Sn layers on transition metal surfaces. 相似文献
14.
Lei Pang Yingjuan Shao Wenqi Zhong Hao Liu 《Proceedings of the Combustion Institute》2021,38(3):4121-4129
Oxy-coal combustion with pressurized fluidized beds has recently emerged as a promising carbon capture and storage (CCS) technology for coal-fired power plants. Although a large number of energy efficiency analyses have shown that an increase in combustion pressure can further increase the net plant efficiency, there are few experimental studies of pressurized oxy-coal combustion conducted on fluidized bed combustors/boilers with continuous coal feeding. In this study, oxy-coal combustion experiments with lignite and anthracite were conducted with a 30 kWth pressurized fluidized bed combustor within the pressure range of 0.1 MPa to 0.4 MPa. The investigation focused on the elucidation of the impacts of combustion pressure on the combustion performance, pollutant emissions and desulfurization of oxy-coal combustion in fluidized beds. The results showed that an increase in pressure increased the combustion efficiency and combustion rate of coal particles, and the promoting effect of pressure increase was more significant for the high rank coal with smaller particle size and the high O2 concentration atmosphere. For both coals, NOx emissions decreased with pressure but N2O emissions increased with pressure and accounted for a considerable part of the nitrogen oxide pollutants under high pressure oxy-coal combustion conditions. The pressure had insignificant impact on the SO2 emissions of oxy-coal combustion but an increase in pressure enhanced the direct desulfurization of limestone. 相似文献
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First principle calculations of the conductance of gold atomic wires containing chain of 3–8 atoms each with 2.39 Å bond lengths are presented using density functional theory. Three different configurations of wire/electrodes were used. For zigzag wire with semi-infinite crystalline electrodes, even–odd oscillation is observed which is consistent with the previously reported results. A lower conductance is observed for the chain in semi-infinite crystalline electrodes compared to the chains suspended in wire-like electrode. The calculated transmission spectrum for the straight and zig-zag wires suspended between semi-infinite crystalline electrodes showed suppression of transmission channels due to electron scattering occurring at the electrode-wire interface. 相似文献
16.
Qi Gao Shuiqing Li Yingqi Zhao Qiang Yao 《Proceedings of the Combustion Institute》2019,37(3):2831-2839
In this paper, the correlations between coal/char fragmentation and fly ash formation during pulverized coal combustion are investigated. We observed an explosion-like fragmentation of Zhundong coal in the early devolatilization stage by means of high-speed photography in the Hencken flat-flame burner. While high ash-fusion (HAF) bituminous and coal-derived char samples only undergo gentle perimeter fragmentation in the char burning stage. Simultaneously, combustion experiments of two kinds of coals were conducted in a 25?kW down-fired combustor. The particle size distributions (PSDs) of both fine particulates (PM1-10) and bulk fly ash (PM10+) were measured by Electrical Low Pressure Impactor (ELPI) and Malvern Mastersizer 2000, respectively. The results show that the mass PSD of residual fly ash (PM1+) from Zhundong coal exhibits a bi-modal shape with two peaks located at 14?µm and 102?µm, whereas that from HAF coal only possesses a single peak at 74?µm. A hybrid model accounting for multiple-route ash formation processes is developed to predict the PSD of fly ash during coal combustion. By incorporating coal/char fragmentation sub-models, the simulation can quantitatively reproduce the measured PM1+ PSDs for different kinds of coals. The sensitivity analysis further reveals that the bi-modal mass distribution of PM1+ intrinsically results from the coal fragmentation during devolatilization. 相似文献
17.
Zhonghua Zhan Andrew Chiodo Minmin Zhou Kevin Davis Dave Wang Jacob Beutler Marc Cremer Yueming Wang Jost O.L. Wendt 《Proceedings of the Combustion Institute》2021,38(3):4013-4022
The future use of coal as a fuel for power generation in the US depends on the availability of financially viable technologies for capture and storage of CO2 emissions from power plants. Key second-generation candidates for CO2 capture include high temperature and pressurized oxy-firing of coal, which has the potential to increase efficiency, lower capital costs, avoid air ingress and reduce oxygen requirements. However, unquantified challenges, such as flame behavior, heat transfer, ash transformation, ash deposition and char oxidation, still exist for those technologies. This study specifically focuses on the formation of submicron particles and initial layer ash deposition during high temperature oxy-coal combustion. Previous work has shown that the initial layer deposits are mainly formed of submicron size ash aerosols transported by thermophoresis. Unfortunately, the importance of submicron particle deposition has not received much attention, probably due to the insignificant deposit mass and difficulty in prediction of the submicron particles formation. In this work, models including mineral matter vaporization model, scavenging model and deposition model are developed and applied into a three-dimensional CFD framework to predict the submicron particles formation and subsequent initial layer deposits formation. The model results are comparable to experimental data. The merits of this work are that it has led to the development of a novel approach to predict both submicron particle formation and initial layer ash deposition during oxy-coal combustion. 相似文献
18.
Ould-Ehssein C Serfaty S Griesmar P Le Huérou JY Caplain E Martinez L Wilkie-Chancellier N Gindre M 《Ultrasonics》2006,44(Z1):e875-e879
The behavior of weak gels during their formation singularly attracts attention of dairy products factories. In our study we investigate acidified pre-heated milk gels formation that are fairly often used to product yoghurts. The gel formation requires a tight control of the first step of micelles modification process and the kinetics reaction parameters. The most current rheological parameters used to achieve the monitoring are the storage G' and the loss G' shear moduli and the gelation time. The study of these parameters is commonly performed at very low frequencies (1 Hz). Our technique uses a 6 MHz AT-cut quartz crystal immersed in an acidified milk solution kept at a constant temperature. This method is singularly effective to ensure a complete and a reliable follow-up of the viscoelastic parameters of casein gels. A suitable new model enables a complete follow-up of the micelles evolution from the viscoelastic properties. The experimental results of the G' and G' moduli versus temperature and versus glucono-delta-lactone (GDL) added to milk are analyzed. In order to understand the micelles modifications, an analysis of the viscoelastic evolution try to explain the validity of the various models of micelles modification. In addition a new accurate kinetics characteristic time is proposed. This time corresponds to the moment for which the elastic effect of material becomes significant. From the kinetics study of casein gels at various temperatures, the Arrhenius relationship and a modified Flory-Stockmayer relationship give us access to the activation energy. By using the proposed technique and the suitable models developed, the structure thus quality of dairy products may be better controlled. 相似文献
19.
Frank Neese 《Journal of Physics and Chemistry of Solids》2004,65(4):781-785
The broken symmetry (BS) concept is an extremely useful tool for the prediction of exchange coupling constants in molecules with interacting paramagnetic centers. An analysis of the BS wavefunctions is presented and the relationship between the overlap of magnetic orbitals and the exchange coupling is stressed. The corresponding orbital transformation is introduced as a useful tool in order to determine the non-orthogonal ‘valence bond’-like magnetic orbital pairs in many electron systems. 相似文献
20.
Chang Wen Minghou Xu Dunxi Yu Changdong Sheng Hongwei Wu Ping’an Zhang Yu Qiao Hong Yao 《Proceedings of the Combustion Institute》2013,34(2):2383-2392
The formation of PM10 (particles less than or equal to 10 μm in aerodynamic diameter) during char combustion in both air-firing and oxy-firing was investigated. Three Chinese coals of different ranks (i.e., DT bituminous coal, CF lignite, and YQ anthracite) were devolatilized at 1300 °C in N2 and CO2 atmosphere, respectively, in a drop tube furnace (DTF). The resulting N2-chars and CO2-chars were burned at 1300 °C in both air-firing (O2/N2 = 21/79) and oxy-firing (O2/CO2 = 21/79). The effects of char properties and combustion conditions on PM10 formation during char combustion were studied. It was found that the formation modes and particle size distribution of PM10 from char combustion whether in air-firing or in oxy-firing were similar to those from pulverized coal combustion. The significant amounts of PM0.5 (particles less than or equal to 0.5 μm in aerodynamic diameter) generated from combustion of various chars suggested that the mineral matter left in the chars after coal devolatilization still had great contributions to the formation of ultrafine particles even during the char combustion stage. The concentration of PM10 from char combustion in oxy-firing was generally less than that in air-firing. The properties of the CO2-chars were different from those of the N2-chars, which was likely due to gasification reactions coal particles experienced during devolatilization in CO2 atmosphere. Regardless of the combustion modes, PM10 formation in combustion of N2-char and CO2-char from the same coal was found to be significantly dependent on char properties. The difference in the PM10 formation behavior between the N2-char and CO2-char was coal-type dependent. 相似文献