贵冶预干燥热风炉给煤装置的改造

本文介绍了贵溪冶炼厂备料车间热风炉给煤装置的工作原理及生产中存在的问题 ,并提出了有效的改进措施 ,降低了生产成本。     

Control of Molybdenum Emission by Sorbents: Equilibrium Analysis

Emissions from fossil fuel combustion containing various heavy metals such as molybdenum are of public concern due to their adverse effects on human health and the environment. In this study, thermodynamic analyses were applied to determine the potential of sorbent technology to control molybdenum emissions from combustion sources. The effectiveness of four sorbents (Ca, Fe, Mg and Na based) was assessed for a wide range of temperatures. The adverse effects of chlorine and sulfur were also examined. Ca and Na-based sorbents were identified to be effective.     

Wear characteristics of commercial gas turbine components

Wear is one of the common degradations in a commercial gas turbine. A stainless steel grade 304 (SS 304) fuel nozzle and its collar made of nickel-based superalloy (Hastelloy X) are two vital components that normally suffer from rapid wear. During an installation, the fuel nozzle is slotted into the collar of the combustion liner. In operation, these two surfaces are subjected to high pressure from the fuel combustion, hence continuously rubbing against each other causes vibrations. During the start–stop operation, these surfaces had undergone a large relative motion. The vibration is the main cause of the wear occurrence on the surfaces. Physical properties of the worn surfaces were obtained through visual observations: wear measurement, hardness and microstructure examination. Through visual observations, fretting wear was mainly suspected as the dominant wear mode, particularly after 8,000 of running hours at high temperature and vibration. In short, this paper discusses the preliminary findings of wear on the fuel nozzle and its collar. It also discusses the changes in the mechanical properties before and after the operation. Solutions for mitigating the problem were discussed.     

Effect of NaCl on the properties of Eu-doped Ca-α-SiAlON phosphors prepared by combustion synthesis

Eu-doped Ca-α-SiAlON phosphors, featuring high phase purity, uniform particle size of 3–5 μm and good luminescent properties with a yellow emission spectrum under blue light excitation, were prepared by a highly efficient combustion synthesis (CS) method. A certain amount of NaCl was applied as an innovative additive to regulate and control the properties of synthesized phosphors. Further, the effects of NaCl additive in the CS system were systematically investigated and rational proposed. It was found that the effect on accelerating nitridation and crystallization played a dominant role in the reaction as the content of NaCl was less than 6 wt%, while the effect of absorbing reaction heat through vaporization was dominant with the further-increased content of NaCl. The intensity of the emission spectrum for the sample doped with 6 wt% of NaCl was remarkably enhanced, nearly 40% more than the sample which was not NaCl-doped. Moreover, a continuous blue-shift phenomenon in emission spectra was observed with the increased content of NaCl.     

Flame spray drying: Droplet and particle flow dynamics

ABSTRACT

The work presents the fundamental research of dispersed phase flow during flame spray drying. Particle dynamics analysis and laser Doppler anemometry technique were applied to determine particle size distribution and particle velocity distribution. Results of the study showed that stable combustion and longer length of the flame were observed for coarse spray (large droplets, low atomization pressure, small spraying angle, and low concentration of droplets in spray). Particle residence time in the combustion zone is the main factor affecting the increase in particle diameters due to puffing. Complex flow dynamics of dispersed phase observed at the outward regions of the flame in recirculation zones results in the formation of particle agglomerates.     

ReaxFF molecular dynamics simulations of n-eicosane reaction mechanisms during pyrolysis and combustion

The pyrolysis and combustion mechanism of the hydrocarbon fuel has important scientific and practical significance. However, it is difficult to detect the whole intermediates and products using traditional methods, which brings trouble to the analysis of the reaction process. In this paper, the microscopic reaction mechanism and the main products of n-eicosane (C₂₀H₄₂) were simulated based on the reactive force field molecular dynamics (ReaxFF-MD). The effects of temperature (2000–3500 K) and oxygen on the initial decomposition, the distribution of main products, and the reactive pathways of C₂₀H₄₂ fuel were studied to determine its reaction mechanism. The initial decomposition of C₂₀H₄₂ was mainly initiated by small alkyl radicals in pyrolysis, and by the oxygen-containing radicals in combustion. The participation of oxygen had a greater effect on accelerating the decomposition reaction. The reactions involving oxygen of C₂₀H₄₂ initial decomposition accounted for 87.5% of the total reactions at 2000 K. Moreover, the detailed distribution and formation pathways of the main products of H₂, C₂H₄, CH₄, H₂O, CO, and CO₂ were depicted to construct the overall reaction mechanism of C₂₀H₄₂. •H radical formed from the composition of C₂H₄ was exactly consistent with the •H radical consumed by the generation of CH₄ and H₂ in the pyrolysis stage. The feasibility of the simulation method was verified by the result of thermal analysis. The results are helpful for further research on the reaction mechanism of hydrocarbon fuels.     

Combustion analysis of a spark ignition engine fueled with gaseous blends containing hydrogen

This paper presents the combustion characteristics of a naturally aspirated spark ignition engine, intended for installation in vehicles, fueled with different hydrogen and methane blends. The experimental tests were carried out in a wide range of speeds at equivalence ratios of 1, 0.8 and 0.7 and at full load. The ignition timing was maintained for each speed, independently of the equivalence ratio and blend used as fuel. Four methane-hydrogen blends were used. In-cylinder pressure, mass fraction burned, heat released and cycle-by-cycle variations were analyzed as representative indicators of the combustion quality. It was observed that hydrogen enrichment of the blend improve combustion for the ignition timing chosen. This improvement is more appreciable at low speeds, because at high speeds hydrogen effect is attenuated by the high turbulence. Also, hydrogen addition allowed the extension of the LOL, enabling the engine to run stable in points where methane could not be tested. The main inconvenience detected was the high NO_x emissions measured, especially at stoichiometric conditions, due mainly to the increment in the combustion temperature that hydrogen produces.     

Effects of nano-Ag on the combustion process of Al–CuO metastable intermolecular composite

Effects of nano-Ag with high thermal conductivity on the combustion wave behavior of Al–CuO MIC (metastable intermolecular composite) are studied in this paper by incorporating Al–CuO MIC with nano-Ag particles in different weight proportions. The physical and chemical characteristics of Al–CuO MIC are determined using scanning electron microscope (SEM), X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The combustion wave behavior is identified by high-speed video recording (HSVR). The experimental observations confirm that the presence of nano-Ag particles improves the heat transfer efficiency. With nano-Ag increasing from 1 wt% to 10 wt%, the first exothermic peak temperature decreases from 607.8 °C to 567.6 °C, and average combustion speed (ACS) increases at first and then reduces. The most suitable amount of nano-Ag is 2 wt% with the ACS and instantaneous combustion velocity on the order of 954.0 m/s, 1562.5 m/s. Moreover, heat transfer mechanisms in the combustion process of Al–CuO MIC are better understood, especially by distinguishing conduction from convection during the combustion propagation. Furthermore, three stages (ignition, acceleration and steady combustion) of reactive propagation are observed in the combustion process. And the corresponding dominative heat transfer mechanisms in the three stages are conduction, conduction to convection transition, and convection, respectively.     

Effect of natural gas enrichment with hydrogen on combustion characteristics of a dual fuel diesel engine

Environmental benefits are one of the main motivations encouraging the use of natural gas as fuel for internal combustion engines. In addition to the better impact on pollution, natural gas is available in many areas. In this context, the present work investigates the effect of hydrogen addition to natural gas in dual fuel mode, on combustion characteristics improvement, in relation with engine performance. Various hydrogen fractions (10, 20 and 30 by v%) are examined. Results showed that natural gas enrichment with hydrogen leads in general to an improved gaseous fuel combustion, which corresponds to an enhanced heat release rate during gaseous fuel premixed phase, resulting in an increase in the in-cylinder peak pressure, especially at high engine load (4.1 bar at 70% load). The highest cumulative and rate of heat release correspond to 10% Hydrogen addition. The combustion duration of gaseous fuel combustion phase is reduced for all hydrogen blends. Moreover, this technique resulted in better combustion stability. For all hydrogen test blends, COV_IMEP does not exceed 10%. However, no major effect on combustion noise was noticed and the ignition delay was not affected significantly. Regarding performance, an important improvement in energy conversion was obtained with almost all hydrogen blends as a result of improved gaseous fuel combustion. A maximum thermal efficiency of 32.5%, almost similar to the one under diesel operation, and a minimum fuel consumption of 236 g/kWh, are achieved with 10% hydrogen enrichment at 70% engine load.