The Experts below are selected from a list of 123 Experts worldwide ranked by ideXlab platform
Rafael Kandiyoti - One of the best experts on this subject based on the ideXlab platform.
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Development of a bench-scale high-pressure fluidized bed reactor and its sequential modification for studying diverse aspects of pyrolysis and gasification of coal and biomass
Energy and Fuels, 2008Co-Authors: A Cousins, A. George, Nigel Paterson, Y. Zhuo, Denis R. Dugwell, Rafael KandiyotiAbstract:This paper reviews the design, operation, and sequential modifications of a bench-scale high-pressure fluidized bed reactor system, capable of diverse pyrolysis and gasification applications, all based on the same hardware platform. The reactor is small: 34 mm i.d. and 504 turn high. The mechanical design is relatively simple and inexpensive, featuring direct electrical heating to avoid the use of a separate furnace. The reactor body is made of a high-strength alloy, with 1000 h creep resistance at maximum design conditions (1000 degrees C and 3.0 MPa). The design thus obviates the use of a "cold" pressure casing. The system can be operated by a single person and has demonstrated ability to generate fuel reactivity and product distribution data rapidly and cheaply, using a wide range of solid fuels. In batch operation, conversions achieved during coal pyrolysis and gasification experiments were comparable with results from a high-pressure wire-mesh reactor, indicating nearly single-particle behavior. The system has been modified for continuous feeding (similar to 3 g min(-1)), to study the effect of reaction conditions on the fate of fuel-N, during the gasification of coal and sewage sludge (to 3.0 MPa). The work showed that steam plays a primary role in the formation of NH3 from both volatile-N and char-N. HCN concentrations were found to depend strongly on the residence Time at temperature and on the extent of contact with heated bed solids. A quartz lining allowed the determination of extents of trace element emissions during gasification. Above 900 degrees C, enhanced depletion of Ba, Pb, and Zn in bed solids was accompanied by enrichment of fines, collected in a downstream filter. The system was subsequently modified to enable a slug of coal to be injected and bed solids discharged (1-3.0 MPa) from the fluidized bed under controlled conditions and precise solid residence Times in the bed. The reactivities of the chars were measured as a function of "residence Time at temperature" and were observed to decrease with increasing temperature, Time, pressure, and particle size. at 1000 degrees C, coal char reactivities were found to diminish by nearly a factor of 4 within 10 s. The study confirmed and extended prior work carried out in a high-pressure wire-mesh reactor. The system was subsequently configured for pyrolyzing waste plastic material at low temperatures. Altering the electrode positions enabled changing the position of the heated zone, enabling trouble-free injection of polymer samples at temperatures up to 600 degrees C. The aim of these experiments was to investigate the potential to produce liquid fuel precursors from pure and mixed waste plastics. In its latest incarnation the system has been further modified for performing oxy-fuel gasification experiments.
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Conversion of coal particles in pyrolysis and gasification: comparison of conversions in a pilot-scale gasifier and bench-scale test equipment☆
Fuel, 2000Co-Authors: Y. Zhuo, R. C. Messenböck, A. Megaritis, Denis R. Dugwell, A.-g. Collot, N.p Paterson, Rafael KandiyotiAbstract:Abstract Comparison with bench-scale experiments has been used to evaluate strategies by which fuel conversion could be improved in a pilot-scale air blown fluidised bed gasifier. Bench-scale data clearly showed that lower overall conversions observed in the pilot scale gasifier do not correspond to levels of reactivity expected from the properties of the original feedstock. Increasing particle sizes were found to affect conversions adversely. Conversions also depended on the reactivity of the gaseous medium ( steam > CO 2 ) and increased with reactive gas pressure. Relative combustion reactivities of residual chars diminished rapidly with Time-at-temperature: at 1000°C, char reactivities declined sharply between 0 and 10 s holding Time. The adverse effect of increasing pressure and of secondary char deposition on char reactivity were experimentally significant but small. In low temperature gasifiers, the combined effect of longer Times required for consuming larger char particles and the rapid deactivation of chars by (∼10 s) exposure to gasification temperatures tends to lead to appreciable levels of residual char removal. Our findings indicate that coal/char reactivities decrease appreciably during the first 10 s at peak temperature—underlining some the difficulties of establishing reactor simulations, which include fundamental kinetic models of coal gasification. The kinetics of char deactivation as a function of Time-at-temperature and particle size would appear to play an important role in determining eventual gasification conversions as well as the gasification kinetics itself.
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High-pressure pyrolysis and CO2-gasification of coal maceral concentrates: conversions and char combustion reactivities
Fuel, 1999Co-Authors: A. Megaritis, R. C. Messenböck, Denis R. Dugwell, I.n. Chatzakis, Rafael KandiyotiAbstract:The gasification behaviour of maceral concentrates was examined in a fixed-bed and a wire-mesh reactor. 'Extents of gasification' were calculated by subtracting sample weight loss during pyrolysis (He) from weight loss in CO2-gasification. The effect of holding Time (10 and 200 s) and pressure (1 and 20 bar) on conversions and on combustion reactivities of chars were studied. During short hold-Time gasification experiments (10 s), liptinites gave the highest conversions, followed by the vitrinites and the inertinites. Vitrinite conversions decreased sharply above 90% elemental-C content. Extents of gasification were found to be in the order: vitrinites > liptinites > inertinites. However, at 200 s, a marked increase in inertinite conversion translated into a clear change of relative ordering to: inertinites > vitrinites > liptinites. The high gasification reactivities of inertinites at longer Times appear to be related to a more rigid and porous structure, but the late surge suggests that an induction period is needed. More detailed Time series data are required. Relative combustion reactivities of chars were generally observed to decrease with (i) pressure, (ii) Time at temperature and (iii) increasing elemental carbon content. The data indicated that orders of gasification reactivities may be predicted from the order of combustion reactivities of pyrolysis chars. Inertinite concentrate chars were more reactive. However, the difference in reactivity between inertinite chars and other samples was reduced when the inertinites were heated rapidly - possibly owing to melting at the higher heating rates.
Zarita Zainuddin - One of the best experts on this subject based on the ideXlab platform.
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influence of pulping variables on the properties of elaeis guineensis soda pulp as evaluated by response surface methodology
Wood Science and Technology, 2004Co-Authors: W D Wanrosli, Zarita ZainuddinAbstract:Response surface methodology with central composite design was used to investigate the influence of pulping conditions, viz. cooking temperature, Time-at-temperature and alkali charge for alkaline pulping of oil palm empty fruit bunch fibres, on the properties of the pulp and paper obtained (screened yield, Kappa number, tensile and tear indices). Quadratic models consisting of the three independent variables were found to accurately describe the pulping of this material with correlation between the actual and predicted values of the response variables having a relatively good degree of R2. The delignification of oil palm empty fruit bunch fibre can be achieved with ease using sodium hydroxide as the sole cooking agent to about 30–45% yield with the process greatly enhanced by an increase in temperature. Although, a relatively low temperature (about 160°C) within the limits of pulping Time (60–120 min) and of alkali charge between 20 and 30% is generally sufficient.
Helen V. Atkinson - One of the best experts on this subject based on the ideXlab platform.
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Wettability of silica substrates by silver-copper based brazing alloys in vacuo
Journal of the American Ceramic Society, 2000Co-Authors: Jorge López-cuevas, Howard Jones, Helen V. AtkinsonAbstract:The sessile drop method has been used to determine the Time dependence of the contact angle at 850°C in vacuo for Ag-28 wt% Cu, Ag-35 wt% Cu-1.5 wt% Ti, and Ag-27 wt% Cu-12 wt% In-2 wt% Ti on vitreous and devitrified fused quartz substrates. Nonwetting behavior (θ > 90°) was observed for Ag-28 wt% Cu on both substrates with no evident effect of Time at temperature. The silica substrate structure, whether crystalline or amorphous, as well as its surface condition, whether smooth or rough, made no significant difference. In contrast, with Ag-35 wt% Cu-1.5 wt% Ti and Ag-27 wt% Cu-12 wt% In-2 wt% Ti the contact angle continuously decreased with Time for both silica substrates, and the structure and surface condition of the substrates had a negligible effect in the case of Ag-27 wt% Cu-12 wt% In-2 wt% Ti, which produced essentially the same contact angles on both silica substrates at a given Time of hold at 850°C. The contact angles produced by Ag-35 wt% Cu-1.5 wt% Ti on devitrified fused quartz were consistently higher than those produced on the vitreous substrates, with increasing holding Time at 850°C. This is attributable to the presence of extensive cracks in the α-cristobalite layer at the surface of the devitrified substrates, which obstruct wetting and spreading. These results, when correlated with the wettability of preoxidized silicon carbide by the same alloys reported in previous work, could account for the adverse effect on wetting of the high-temperature silica films formed on the surface of the SiC in that work.
S Celotto - One of the best experts on this subject based on the ideXlab platform.
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tem study of continuous precipitation in mg 9 wt al 1 wt zn alloy
Acta Materialia, 2000Co-Authors: S CelottoAbstract:Abstract The development of continuous precipitate morphology in heat-treated Mg–9 wt%Al–1 wt%Zn alloy (AZ91) for a range of ageing temperatures is investigated in detail using TEM. The matrix/precipitate orientation relationships (ORs), sizes, shapes and the number of precipitates per unit volume (NV) are described for ageing at temperatures from 70 to 300°C. Most of the continuous precipitates have a Burgers OR and are plate-shaped with the primary habit plane parallel to the basal plane of the matrix. These precipitates are initially lozenge-shaped plates that elongate with Time at temperature to become long laths. Two other smaller populations of precipitates that have ORs different from the Burgers OR are also present. These precipitates are rod-shaped with their long direction either perpendicular to or inclined to the basal plane. The relationship between the continuous precipitate morphology and the hardness response is discussed and comparisons are made with high-strength aluminium alloys.
W D Wanrosli - One of the best experts on this subject based on the ideXlab platform.
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influence of pulping variables on the properties of elaeis guineensis soda pulp as evaluated by response surface methodology
Wood Science and Technology, 2004Co-Authors: W D Wanrosli, Zarita ZainuddinAbstract:Response surface methodology with central composite design was used to investigate the influence of pulping conditions, viz. cooking temperature, Time-at-temperature and alkali charge for alkaline pulping of oil palm empty fruit bunch fibres, on the properties of the pulp and paper obtained (screened yield, Kappa number, tensile and tear indices). Quadratic models consisting of the three independent variables were found to accurately describe the pulping of this material with correlation between the actual and predicted values of the response variables having a relatively good degree of R2. The delignification of oil palm empty fruit bunch fibre can be achieved with ease using sodium hydroxide as the sole cooking agent to about 30–45% yield with the process greatly enhanced by an increase in temperature. Although, a relatively low temperature (about 160°C) within the limits of pulping Time (60–120 min) and of alkali charge between 20 and 30% is generally sufficient.
