03929 Mass transfer kinetic model of cracking of large coal particle during combustion

03929 Mass transfer kinetic model of cracking of large coal particle during combustion

09 Mesa transfer kinetic model of cracking of large 95103929 coal particle during combustion Gu, F. and Shen, H. Meiran Zhuanhuu, 1994, 17, (4), 21-25...

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09 Mesa transfer kinetic model of cracking of large 95103929 coal particle during combustion Gu, F. and Shen, H. Meiran Zhuanhuu, 1994, 17, (4), 21-25. (In Chinese) Describes theoretical analysis of the ignition and cracking of large coal particle.

Mathematical modeling of a spouted bed coal 95103930 gaaifier Tsuji, T. et al., Kagaku Kogaku Ronbunshu, 1994, 20, (6), 820-826. (In Japanese) A mathematical model for a continuous spouted-bed coal gaisifer, which had been developed previously by the authors, is based on a gasification rate and mass balance eauations. and assumes that the suout and the annulus to be well-mixed taiks. The. devolatilization data aid steam-semicoke reaction rate of Taihyeiyo coal were measured using small-scale fixed-bed equipment. The results were compared with the previous work on Taiheiyo coal.

Mathematical modelllng of devolatilizatlon of large 95103931 coal particles In a convective environment Adesanya, B. A. an&Pham, H. N. Fuel, Jun. 1995, 74, (6), 896-902. A geneialized model for devolatilization of large coal paiticles typically encountered in a gasifier has been developed. The model predicts a timetemperature history of the particle in a cbnvective heat tiansfer environment. Thermal decomposition of volatile matter is treated as a series of indeoendent chemical reactions in which the rate constants differ onlv in act&ation energy. The activation energy is expressed as a Gaussian dibtribution. Experimental data obtained in a flow reactor are presented and used 10 validate kinetic and transport parameters of the model. Devolatilization time predicted by the modkl with updated parameters is also compared with that obtained from a pilot fixed-bed gasifier.

Mathematically reduced reaction mechanisms 95103932 applied to adiabatic flat hydrogen/air flames Eggels, R. L. and De Goey, L. P. Combusrion & Flame, Mar. 1995, 100, (4), 559-570. Several hydrogen/air reaction systems are reduced mathematically to onestep schemes, using the method introduced by Maas and Pope. The reduction is obtained by assuming fast reaction groups of the reaction system lo be in steady state. The authors developed a method to apply the reduced schemes to adiabatic flat flames. The results are compared with those of detailed chemistry calculations.

95JO3933 Method for fuel flow determination and improving thermal efficiency In a fossil-fired Dower plant Lang, F. D. (Assigned to) Exergetics Systems Inc., US Pat. US.5,367,470, Nov. 1994. A process where fuel flow rate, pollutant flow rates, and boiler efficiency for a fossil-fired steam generator system are determined from analysis of the composition of the dry fuel bas and composition of the combustion effluents.

Model of nitrogen oxide generation during coal95JO3934 powder combustion In steam boilers iaichik, L. I. et al., Teploenergetika (Moscow), 1994, (6), 32-37. (In Russian) A mathematical model was derived lo describe coal combustion in steam boilers on the basis of analysis of various kinetic models of NO, formation during combustion of solid fuels.

95/03935 Nitrous oxide formation mechanisms In coal combustion Moritomi, H. et al., Kagaku Kogaku Ronbunshu, 1994, 20, (6), 849-856. (In Japanese) Four mechanisms of formation of N,O from low-temperature combustion of coal and petroleum coke, studied in a batch reactor are discussed.

95103936 Nonldeal vaporization of dilating binary droplets with radiation adsorption Laee. P. L. er al.. Combustion & Flame. Aor. 1995. 101. (1). 36-44. A &ently developed liquid vaporization model for m;lticd~p&ent droplets has been enhanced in order lo study the effect of thermal radiation absorption in binary droplet vaporization. The possible coupling beween radiation absorption and droplet microexplosion is also investigated. The results show that radiative absorption can influence droplet vaporization in combustion environments. In addition to this, the results serve lo explain some experimental findings on microexplosion phenomena, such as the radical location of the onset of bubble formation. The vaporization model including radiation absorption also predicts the experimentally observed sparkle at the end of droplet combustion (flash vaporization).

Combustion (burners, combustion systems)

95103937 Numerical investigation of chemical reaction-turbulence Interaction in compressible shear layers Kim, S. W. Combustion & Flame, May 1995, 101, (3), 197-208. Calculations of mixing of hydrogen and vitiated supersonic airstream with and without chemical reactions are presented. The Favre-averaged compressible flow equations and convection-diffusion equation for the chemical species are solved by a finite volume method that incorporates an incremental pressure equation for the conservatin of mass. Thd chemical reactions are described by 9 chemical species and 24 pairs of reactionsteps. The turbulence field is described by multiple-time scale turbulence equations. It is shown that the multiple-time-scale turbulence equations successfully predict the increased shear layer thickness caused by the chemical reaction-turbulence interaction.

95103938 Numerical modeling of turbulent jet diffusion flames in the atmospheric surface layer Hernandez, J. et al., Combustion & Flame, Apr. 1995, 101, (I), 113-131. The evolution of turbulent jet diffusion flames of natural gas in air is predicted using a finite-volume procedure for solving the flow equations. The model is three dimensional, elliptic and based on the conserved-scalar approach and the laminar flamelet concept. A laminar flamelet prescription for temperature, which is in agreement with measurements in methane/air flames and accounts for radiative heat losses, has been modified and adapted to natural-gas flames. The k-e-g turbulence model has been used. Different probability-density functions for the conserved scalar and an alternative method which does not require the use of a pdf are employed.

On the oscillation of combustion of a laminar spray 95103939 E;.Y;~:. and Bulzan, D. L. Combustion & Flame, Mar. 1995, 100, (4), A spray combustor, with flow velocities in the laminar range, exhibits a unique operating mode where large amplitude, self-induced oscillations of the ilame shape occur. The phenc?menoh, not previously encountered, only occurs when fuel is supplied in the form of fine liquid droplets and does not occur when fuel is supplied in gaseous form. Several flow mechanisms are coupled in such a fashion as 10 trigger and maintain the oscillatory motion of the flame. These mechanisms include heat transfer and evaooration processes, dynamics of two-phase flows, and effects of gravity (duoyancy forces). An interface volume, lying between the fuel nozzle and the flame was found lo be the most susceptible lo gravity effects, and postulated lo be responsible for inducing the oscillatory motion. Heptane fuel was used in the majority of the tests.

95103940 On the structure, stabilization, and dual response of flat-burner-flames En& J. A. er al., Combustion & Flame. Mar. 1995. 100. (41. 645-652. A comprehensive computational and experimental study. ias been conducted on the structure and stabilization dynamics of the classical planar flame over a flat, porous burner. The specific issue addressed is the apparem dual response’nature of the flat-bummer flames in that previous stbhies have shown the existence of two flame speeds for either a given heat loss rate or a given flame standoff distance. The present study demonstrates that the flame response is actually unique when the flame burning rate is considered to be the indepenedent variable, that the turning point behaviour of the flame response is a manifestation of system nonmonotonicity rather than extinctidn, and that the flat-burner flame does not appear to-possess distinct extinction states.

95103941 Palladium-catalyzed combustion of methane: Slmulated gas turbine combustion at atmospheric pressure Griffin, T. et al., Combustion & Flame, Apr. 1995, 101, (l), 81-90. Atmospheric pressure tests were performed in which a palladium catalyst ignites and stabilizes the homogeneous combustion of methane. Palladium e>hibited a reversible deactiv&on at temperatures above 75O”C, which acted to ‘self-regulate’ its operating temperature. A properly treated palladium catalyst could be employed to preheat a methane/air mixture lo temperatures required for ignition of gaseous combustion (ca. 800°C) without itself being exposed to the mixture adiabatic flame temperature. The operating temperature of the palladium was found to be relatively insensitive to the methane fuel concentration or catalyst inlet temperature over a wide range of conditions. Thus, palladium is well suited for application in the ignition and stabilization of methane combustion.

95103942 RaDid miCrOWaVe DVrOiVSiS Of Coal Monsef-Mirzai, P: et al., IChemy Res: Event, Two-Day Symp., Inst. Chemical Engineers, Rugby, UK, 1994, 2, 646-648. Substances sich as CuO, magnetite and even coke will heat rapidly in a microwave oven and will reach temperatures in the range of 1055-1210°C in a N atmosphere. When mixed with coal (Creswell) rapid pyrolysis of the coal occurs and after 3 min final temperatures in the range 1180-1310°C are recorded. Yields of condensable material (tar) range from 20% (coke) lo up to 49% (CuO). Transfer of noncarbon elements in the tar phase is efficient; the H content of the tar is aliphatic rich, but it is likely that much is associated with side chains on aromatic nuclei.

Fuel and Energy Abstracts

July 1995

281