Fuel Processing Technology (v.74, #3)
The effect of inherent and added inorganic matter on low-temperature oxidation reaction of coal by Wiwik S Watanabe; Dong-ke Zhang (145-160).
The influence of inherent and added inorganic matter on low-temperature oxidation reactions of coal and the effectiveness of the additives to affect the oxidation reactions are examined in this paper. A Victorian brown coal was selected for this study. Samples of the raw coal, water-washed coal, and acid-washed coal were prepared. The acid-washed coal was also doped with seven additives, respectively, by both wet-mixing (5% wt.) and ion-exchanging with the additives. Each of the samples was then tested in a wire-mesh reactor to determine its critical ambient temperature, above which thermal runaway occurred. The critical ambient temperatures of the acid-washed and water-washed coals were higher than that of the raw coal, indicating that the inherent inorganic matter in the coal catalysed low-temperature oxidation. Of the seven additives used, Cu(Ac)2, KAc, and NaAc were found to promote the oxidation reaction, while NaCl, CaCl2, and Mg(Ac)2 inhibit the reaction. Ca(Ac)2 showed a very little effect. Furthermore, it was observed that the promotion effects of Cu(Ac)2 and KAc were stronger when they were ion-exchanged into the coal, while the inhibition effect of Ca(Ac)2 was stronger when it was wet-mixed with the coal. Low-temperature oxidation kinetics of various samples were also estimated and compared. Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) quantitative analysis of the samples respectively wet-mixed and ion-exchanged with Cu(Ac)2 indicated that the pore volume of the ion-exchanged sample was greater than that of wet-mixed sample, and the amount of copper ion absorbed in the ion-exchanged coal particle was higher and more uniformly distributed in the coal matrix than that in the wet-mixed coal particle.
Keywords: Additive; Coal; Ion-exchange; Low-temperature oxidation;
CO2 gasification of Argentinean coal chars: a kinetic characterization by J Ochoa; M.C Cassanello; P.R Bonelli; A.L Cukierman (161-176).
A kinetic characterization of the CO2 gasification of chars from Argentinean low-rank coals, subbituminous (SB) and high volatile bituminous (HVB), is performed by isothermal thermogravimetry. Temperatures in the range 1173–1433 K and CO2 concentrations among 50% and 70% v/v are employed. Experimental data obtained for both chars for the whole range of experimental conditions explored were satisfactorily described by a single master curve. Reactivity differences between chars are discussed in terms of carbon content, microporosity and crystallinity of the char carbonaceous part. In addition, potential catalytic effects of inherent minerals on chars gasification reactivity are examined by demineralizing the chars. For the subbituminous char, catalytic effects due to mineral matter content are detected up to 1333 K, whereas at higher temperatures they become considerably less pronounced. For the bituminous char, reactivity seems to depend more on structural and textural features than on catalysis over the whole range of operating conditions. Intrinsic gasification rates for both chars are properly represented by the well-known random capillary and random pore models (RPM). Recent models based on modifications introduced to the latter are also applied and kinetic data description is discussed.
Keywords: Coal char gasification; CO2 gasification kinetics; Random pore models; Argentinean coal chars;
Studies on nitric oxide removal in simulated gas compositions under plasma-dielectric/catalytic discharges by B.S Rajanikanth; Satyabrata Rout (177-195).
Application of pulsed electrical discharges for gas cleaning is gaining prominence, mainly from the energy consideration point of view. This present paper presents recent work on applying the electrical discharge plasma technology for treating gaseous pollutants, in general, and nitric oxide, in particular, as this is one of the major contributors to air pollution. The present work focuses attention on pulsed electrical discharge technique for nitric oxide removal from simulated gas compositions and study of effect of packed dielectric pellets, with and without a coating of catalyst, on the removal process. Experiments were conducted in a cylindrical corona reactor energized by repetitive high voltage pulses. The effects of various parameters, viz. pulse voltage magnitude, pulse frequency, initial nitric oxide concentration and gas mixture composition on nitric oxide removal efficiency, are discussed. When the reactors were filled with different dielectric pellets like, barium titanate, alumina, and alumina coated with palladium catalyst, the improvement in nitric oxide removal efficiency is studied and discussed. The power dissipated in the reactor and the energy consumed per nitric oxide molecule removed was calculated. Further results and comparative study of various cases are presented in the paper.
Keywords: Non-thermal plasma; Pulsed discharge; Dielectric discharge; NO removal; Catalytic discharge; Gas cleaning; Packed dielectrics;
Author Index (213).
Subject Index (215).
Contents of Volume 74 (2001) (217-218).