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Effects of polymer char on nitridation kinetics of attrition milled silicon powder have been investigated from 1200 to 1350 C. Results indicate that at and above 1250 C, the silicon compacts containing 3.5 wt percent polymer char were fully converted to Si3N4 after 24 hr exposure in nitrogen. In contrast, the silicon compacts without polymer char could not be fully converted to Si3N4 at 1350 C under similar exposure conditions. At 1250 and 1350 C, the silicon compacts with polymer char showed faster nitridation kinetics than those without the polymer char. As the polymer char content is increased, the amount of SiC in the nitrided material is also increased. By adding small amounts (approx. 2.5 wt percent) of NiO, the silicon compacts containing polymer char can be completely nitrided at 1200 C. The probable mechanism for the accelerat...
Evaporation experiments of biomass fast pyrolysis oil and its aqueous fractions at low (TGA-10°C/min, Glass tube-100°C/min) and high (atomization ~10 6°C/min) heating rates are performed. Slow heating of pyrolysis oil produced ~28% char (on carbon basis), whereas atomization of oil droplets (~117µm) produced ~9% char in the temperature range of 500-850°C. Aqueous fractions and glucose solutions also produced less amount of char by evaporating at higher heating rates (~3% char) when compared with slower heating (~24% char). The results obtained show that not a single lumped components class in pyrolysis oil can be identified that is primarily responsible for the char formation. At low heating rate, higher concentrations of organics in the bioliquids result in higher char yields, which reveals that a certain fraction in the oil produce c...
This study characterized and removed ash from waste-derived char to improve the quality of char as fuel. Municipal solid waste (MSW) and automobile shredder residue (ASR) were carbonized at 450 ℃ and at 500 ℃ respectively in a rotary kiln with a nitrogen atmosphere for 1 h. MSW and ASR char were subjected to sieving and pulverization-sieving to screen incombustibles and the ash-rich fraction, after which float–sink separation, froth floatation, and oil agglomeration were applied to remove ash from the char. The established target quality was less than 30% ash content and more than 20000 kJ/kg heating value. However, the rate of combustibles recovery had to be lowered to produce a good quality of char along with a high heating value. MSW char attained the targeted quality level using froth floatation or oil agglomeration whereas neither...
Analysis of reacting flow of pyrolysis products through char layer of low density, nylon phenolic resin, charring ablators and porous graphite
In order to improve the understanding of the structure of char produced in a fluidized bed reactor reflectance and several Raman analyses were carried out on a set of coals with increasing rank and their char. The reflectance of the chares is discontinuous and related with coal rank. With the increasing of rank a general shift of the D band towards lower wavenumbers and an increase of the ID/IG intensity area ratio were observed on the coals. These trends are not evident in the char, since pyrolysis seems to have had a homogenizing effect on these parameters
Technique for manufacture of graphite composites uses high-char-forming processable polyimide resin systems to produce the graphitic matrix. Only three cyclic steps are required to yield a 99.7 percent graphite product.
The evaporation of pyrolysis oil was studied at varying heating rates (∼1–106°C/min) with surrounding temperatures up to 850°C. A total product distribution (gas, vapor, and char) was measured using two atomizers with different droplet sizes. It was shown that with very high heating rates (∼106°C/min) the amount of char was significantly lowered (∼8%, carbon basis) compared to the maximum amount, which was produced at low heating rates using a TGA (∼30%, carbon basis; heating rate 1°C/min). The char formation takes place in the 100–350°C liquid temperature range due to polymerization reactions of compounds in the pyrolysis oil. All pyrolysis oil fractions (whole oil, pyrolytic lignin, glucose and aqueous rich/lean phase) showed charring behavior. The pyrolysis oil chars age when subjected to elevated temperatures (≥700°C), show similar...
Gasification and combustion of porous char particles occurs in many industrial applications. Reactor-scale outputs of importance depend critically on processes that occur at the particle-scale. Because char particles often possess a wide range of pore sizes and react under varying operating conditions, predictive models which can account for the numerous physical and chemical processes and time-dependent boundary conditions to which a particle is subjected are necessary. A comprehensive, transient, spherically symmetric model of a reacting, porous char particle and its surrounding boundary layer has been developed and validated. The model accounts for heterogeneous and homogeneous reactions, pore structure evolution, gas transport in and around the porous particle, thermal annealing, fragmentation and ash behavior. To model the pore st...
In this paper a packed bed of char particles is considered for experimental study and analysis. The packed char bed is modelled by extending the single-particle analysis (Dasappa et al., 1994a, Chem. Eng. Sci. 49-2: 223-232. Dasappa et al., 1994b, Twenty-fifth Symposium (International) on Combustion, pp. 1619-1628. Dasappa et al., 1998, Twenty-seventh Symposium (International) on Combustion, pp. 1335-1342.). All the reactions related to gasification are introduced into the reaction system as in Dasappa et al. (1998). The propagation of the reaction front into the packed char bed against the air stream is modelled. The results are compared with the experimental data on a model quartz reactor using charcoal. Experimental data of propagation of the reaction front through the packed bed from the present study and of Groeneveld's charcoal g...
<p>The activation energy of Douglas ftr wood char gasified in carbon dioxide was determined. Activation energies were found for chars that had been pyrolyzed in nitrogen at 600, 750, and 900°C. A thermogravimetric analyzer provided the weight versus temperature data used to obtain the activation energies. The Coats-Redfern integral method of kinetic analysis was used to extract the activation energies from the data. This method can be used to obtain an activation energy from a single weight versus temperature trace for a constant heating rate. An overall apparent activation energy of 723 ± 60 kl/mole and a natural log of the pre exponential factor of 68.8 ± 6.2 was determined from the data collected for all three chars. The different char preparation temperatures did not appear to affect the activation energy.<p>
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