http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:12224 Research Doctorate - Doctor of Philosophy (PhD) 2013-01-24T03:00:04.068Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:680 A mathematical model for entrained flow coal gasification was developed with the objective of predicting the influence of coal properties and gasification conditions on the performance of entrained flow gasifiers operating at pressures up to 21 atmospheres (2.1MPa). The model represents gasifiers as plug flow reactors and therefore neglects any mixing or turbulence effects. Coal properties were predicted through use of correlations from a variety of literature sources and others that were developed from experimental data in the literature. A sensitivity analysis of the model indicated that errors in the calculated values of coal volatile yield, carbon dioxide gasification reactivity and steam gasification may significantly affect the model predictions. Similarly errors in the input values for gasifier wall temperatures and gasifier diameter, when affected by slagging, can cause model prediction errors. Model predictions were compared with experimental gasification results for a range of atmospheric and high pressure gasifiers, the majority of the results being obtained by CSIRO at atmospheric pressure for a range of coals. Predictions were accurate for the majority of atmospheric pressure results over a large range of gas feed mixtures. Due to the limited range of experimental data available for high pressure gasification the capability of the model is somewhat uncertain, although the model provided accurate predictions for the majority of the available results. The model was also used to predict the trends in particle reactions with gasification and the influence of pressure, gasifier diameter and feed coal on gasifier performance. Further research on coal volatile yields, gasification reactivities and gas properties at high temperatures and pressures was recommended to improve the accuracy of model inputs. Additional predictions and model accuracy improvements could be made by extending the model to include fluid dynamics and slag layer modelling. 2011-12-20T23:20:03.533Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:2862 Research Doctorate - Doctor of Philosophy (PhD) 2011-12-19T23:00:08.906Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7205 The reactivity of four pulverised Australian coals were measured under simulated air (O₂/N₂) and oxy-fuel (O₂/CO₂) environments using a drop tube furnace (DTF) maintained at 1673 K and a thermogravimetric analyser (TGA) run under non-isothermal (heating) conditions at temperatures up to 1473 K. The oxygen concentration, covering a wide and practical range, was varied in mixtures of O₂/N₂ and O₂/CO₂ in the range of 3 to 21 vol.% and 5 to 30 vol.%, respectively. The apparent volatile yield measured in CO₂ in the DTF was greater than in N₂ for all the coals studied. Pyrolysis experiments in the TGA also revealed an additional mass loss in a CO₂ atmosphere, not observed in a N₂ atmosphere, at relatively high temperatures. The coal burnout measured in the DTF at several O₂ concentrations revealed significantly higher burnouts for two coals and similar burnouts for the other two coals in oxy-fuel conditions. TGA experiments with char also revealed higher reactivity at high temperatures and low O₂ concentration. The results are consistent with a char–CO₂ reaction during the volatile yield experiments, but additional experiments are necessary to resolve the mechanisms determining the differences in coal burnout. 2011-02-09T05:10:08.478Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1930 The physical and chemical structure as well as gasification reactivities of chars generated from several biomass species (i.e. pinus radiata, eucalyptus maculata and sugar cane bagasse) were studied to gain insight into the role of heating rate and pressure on the gasification characteristics of biomass chars. Char samples were generated in a suite of reactors including a wire mesh reactor, a tubular reactor, and a drop tube furnace. Scanning electron microscopy analysis, X-ray diffractometry, digital cinematography and surface area analysis were employed to determine the impact of operating conditions on the char structure. The global gasification reactivities of char samples were also determined for a range of pressures between 1 and 20 bar using pressurised thermogravimetric analysis technique. Char reactivities were found to increase with increasing pyrolysis heating rates and decreasing pyrolysis pressure. It was found that under high heating rates the char particles underwent plastic deformation (i.e. melted) developing a structure different to that of the virgin biomass. Pressure was also found to influence the physical and chemical structures of char particles. The difference in the gasification reactivities of biomass chars at pressure was found to correlate well with the effect of pyrolysis pressure on the graphitisation process in the biomass char structure. 2010-04-27T06:58:34.644Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1390 Advanced clean coal technologies, e.g. power generation from integrated gasification combined cycle (IGCC) and pressurised fluidised bed combustor, have attracted increased interest from the scientific and technological communities over the last few decades. Pressures up to 40 atm have been applied to these technologies, which inherently result in an increase in coal throughput, a reduction in pollutant emissions and an enhancement in the intensity of reaction. Therefore, fundamental understanding of the effect of operating pressure on coal reactions is essential to the development of these technologies. In this paper, the pressure effect on a variety of aspects of coal reactions reported in the open literature has been reviewed. Major emphasis of the paper is given to experimental observations, although some theoretical modelling is reviewed. The pressure has been found to significantly influence the volatiles yield and coal swelling during devolatilisation, hence the structure and morphology of the char generated. More char particles of high porosity are formed at higher pressures. Char structure appears to play a significant role in burnout of residual char and ash formation. In general, at higher pressures, coal particles burn quicker and form finer ash particles. Increasing reactant pressure enhances char combustion and gasification reaction rate, which can be understood by an adsorption–desorption mechanism. These factors have been applied to the understanding of a practical high-pressure gasifier. Most of the work published has been at the lower temperatures (typically <1000 °C), which can be achieved in experiments involving captive particles or coal samples. Experiments in pressurised TGA and wire mesh systems at these low temperatures are the most commonly reported, with some experiments for entrained flow system reported at the higher temperatures typical IGCC conditions in entrained flow reactors. Although the difficulty and cost have restricted these experiments, the entrained flow work is the current research need. The structure of the char generated has recently been related to char reactivity and the ash formed, but the mechanisms leading to the effect of pressure on this structure are not understood. Progressing the understanding of the formation of char structure at pressure and its relation to coal properties is an obvious research need. 2010-04-27T06:52:52.367Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:248 Coal research, particularly in the area of coal utilization, has flourished in the University of Newcastle for last several decades. There have been significant developments in the area of furnace modeling and heat transfer - modeling of radiative heat transfer in pulverized coal fired boilers and aerodynamic modeling of swirl burners, blast furnace raceways, coal combustion - kinetics of devolatilisation, combustion and gasification, mineral and ash reactions - thermal behaviour of different minerals, ash formation and their implications on ash deposition and thermal performance. There have been some investigations into in situ gasification, NO_x formation and cofiring with biomass as well. Coal characterization - for organic and inorganic matter and ash has been a strong activity in the past few years. This paper presents a comprehensive review of these activities summarizing the key achievements in each area. The paper also describes possible directions and drivers for future coal research in the current environment. © 2004 Elsevier Ltd. All rights reserved. 2010-04-27T06:01:02.031Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:116 In this study, the gasification kinetics of chars from different biomass species have been investigated within the temperature range 800-950 degrees C, CO2 concentrations of 10 to 100% v/v, and pressures between 1 and 20 bar using thermogravimetric analysis (TGA). The quartz wool matrix (QWM) method was used to simulate circulating fluidized-bed (CFB) conditions. The reactivity results obtained by the QWM method were compared with those extracted using TGA data. Kinetic data from TGA analyses was found to be compatible for predicting CFB gasification reactivity. Effects of pyrolysis pressure on the chemical structure of char and char conversion reactivities were also investigated. Pressure has been found to have no effect on reactivity during char conversion while having a dramatic effect on chemical and physical structure during the pyrolysis process. The Langmuir-Hinshelwood rate equation represents the pressurized radiata pine char gasification kinetics well. The Langmuir-Hinshelwood expression for studied conditions can be described as RCO2 = 1,22.10(4)e-(163.103/RT) P-CO2/1 + (5, 84.10(-11)e(246.103/RT))P-CO (6,48.10(-4)e(56.103/RT))P-CO2 Kinetic data found in this study are in good agreement with the literature. 2010-04-27T05:58:45.503Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:170 The knowledge of biomass char gasification kinetics has considerable importance in the design of advanced biomass gasifiers, some of which operate at high pressure. The char gasification kinetics themselves are influenced by char structure. In this study, the effects of pyrolysis pressure and heating rate on the char structure were investigated using scanning electron microscopy (SEM) analysis, digital cinematography, and surface area analysis. Char samples were prepared at pressures between 1 and 20 bar. temperatures ranging from 800 to 1000 degrees C, and heating rates between 20 and 500 degrees C/s. Our results indicate that pyrolysis conditions have a notable impact on the biomass char morphology. Pyrolysis pressure, in particular, was found to influence the size and the shape of char particles while high heating rates led to plastic deformation of particles (i.e. melting) resulting in smooth surfaces and large cavities. The global gasification reactivities of char samples were also determined using thermogravimetric analysis (TGA) technique. Char reactivities were found to increase with increasing pyrolysis heating rates and decreasing pyrolysis pressure. (c) 2004 Elsevier Ltd. All rights reserved. 2010-04-27T05:57:35.456Z ]]>