Current Issue : October - December Volume : 2013 Issue Number : 4 Articles : 4 Articles
Carbon combustion in the forward stagnation flowfield has been examined through experimental comparisons, by conducting\r\naerothermochemical analyses, with the surface C-O2 and C-CO2 reactions and the gas-phase CO-O2 reaction taken into account.\r\nBy virtue of the generalized species-enthalpy coupling functions, close coupling of those reactions has been elucidated. Explicit\r\ncombustion-rate expressions by use of the transfer number in terms of the natural logarithmic term, just like that for droplet\r\ncombustion, have further been obtained for the combustion response in the limiting situations. It has been confirmed that before\r\nthe establishment of CO flame, the combustion rate can fairly be represented by the expression in the frozen mode, that after\r\nits establishment by the expression in the flame-attached or flame-detached modes, and that the critical condition derived by\r\nthe asymptotics can fairly predict the surface temperature for its establishment. The formulation has further been extended\r\nto include the surface C-H2O and gas-phase H2-O2 reactions additionally, so as to evaluate the combustion rate in humid\r\nairflow. Since those expressions are explicit and have fair accuracy, they are anticipated to make various contributions not only\r\nfor qualitative/quantitative studies, but also for various aerospace applications, including propulsion with high-energy-density\r\nfuels....
The analysis of gas evolving during the pyrolysis of two very different rank coals was studied by using FT-IR spectroscopy.These\r\ncoals, coming from Sulcis (Sardinia, Italy) and from South Africa, respectively, were subjected to progressive heating up to 800�°C in\r\nvacuum.The thermal destruction of coal was followed by monitoring the production of gases in this range of temperature.The gases\r\nevolving in the heating fromroom temperature to 800�°C were collected at intervals of 100�°C and analysed by infrared spectroscopy.\r\nThe relative pressures Pr(i) = P(i)/P max(i)T) were plotted against temperature. These graphs clearly show the correlation among\r\nqualitative gas composition, temperature, and the maximum value of emissions, thus confirming FT-IR analysis as a powerful key\r\nfor pyrolysis monitoring....
Pyrolysis, combustion, and gasification properties of pulverized coal and char in CO2-rich gas flow were investigated by using\r\ngravimetric-differential thermal analysis (TG-DTA) with changing O2%, heating temperature gradient, and flow rate of CO2-rich\r\ngases provided. Together with TG-DTA, flue gas generated from the heated coal, such as CO, CO2, and hydrocarbons (HCs), was\r\nanalyzed simultaneously on the heating process.The optimum O2% inCO2-rich gas for combustion and gasification of coal or char\r\nwas discussed by analyzing flue gas with changing O2 from 0 to 5%. The experimental results indicate that O2% has an especially\r\nlarge effect on carbon oxidation at temperature less than 1100�°C, and lower O2 concentration promotes gasification reaction by\r\nproducing CO gas over 1100�°C in temperature.The TG-DTA results with gas analyses have presented basic reference data that show\r\nthe effects of O2 concentration and heating rate on coal physical and chemical behaviors for the expected technologies on coal\r\ngasification in CO2-rich gas and oxygen combustion and underground coal gasification....
Experiments on cofiring dried sewage sludge, wet sewage sludge with coal and polyethylene (PE) were carried out on a pilot scale\r\n0.15MWt circulating fluidized bed combustion (CFBC) plant, and the influence of furnace temperatures, cofiring rates on N2Oand\r\nNO emissions was investigated. Temperature is an effective parameter influencing N2O emission, and higher temperature leads to\r\nsignificant N2O reduction and decrease of conversion ratio of fuel-N to N2O. Increasing in cofiring rates leads to higher nitrogen\r\ncontent in the mixed fuel,which could result in higherNOandN2Oemissions fromcombustion.Withmore sewage sludge addition,\r\nhigherNObut lowerN2Oemissions are observed.N2Oemission fromcofiring wet sewage sludge with coal is higher than that from\r\ncofiring dried sewage sludge with coal and PE, and fuel-N conversion ratio to N2O and NO is much higher in cofiring wet sewage\r\nsludge with coal than that in cofiring dried sewage sludge with coal and PE....
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