Elucidating the mechanism underpinning ultra-clean coal production from Victorian brown coal and its application as a gasification fuel

Coal accounts for almost forty-percent of global power generation. Globally, coal is likely to retain a central role in power generation given its abundance and economic advantage over other fuels for the foreseeable future. However, current coal-fired power stations are inefficient (25-35% efficiency) and contribute to significant CO2 emissions. Therefore, there is a concerted effort to improve the efficiency of coal use, potentially resulting in reduced CO2 emissions. Amongst alternative coal-based technologies, research into the direct carbon fuel cell (DCFC) has gathered momentum over the last decade. This is largely due to the high efficiency and carbon capture and storage compatibility of this promising and novel technology. Current research efforts in the DCFC field include the trialling of various types of carbons, predominantly from coal and biomass derived fuels, and assessing the influence of fuel properties on fuel cell performance and operability. In addition, understanding carbon reaction and conversion mechanisms, long-term fuel cell operation, as well as the compatibility of critical fuel cell components with cell operating environments are all pressing issues for advancing this technology. The present work addresses some of these key areas of interest in this field, in the context of Victorian brown coal char as a fuel in physical-contact solid oxide electrolyte DCFC. The studies were mostly focussed on lanthanum strontium cobalt ferrite (LSCF), a mixed ion-electronic conducting (MIEC) anode for the cell with yttria-stabilised zirconia (YSZ) as the electrolyte and LSCF as the cathode. However, due to long term instability of the LSCF in fuel environments, an alternative anode was also investigated. Following a review of the desirable properties of solid fuels for use in a DCFC, the first investigation in this body of work directly addresses the influence of fuel-based properties on the performance of a DCFC. The results from DCFCs operated on Victorian brown coal are encouraging. A thorough characterisation and analysis of chars produced from the coal used has highlighted the contribution of inorganic species, inherent in the coal, to fuel reactivity and ultimately to fuel cell performance. These results were benchmarked against pure carbon in the form of carbon black. Subsequent investigation into extended cell operation revealed insights into potential sources of cell performance degradation. Through careful monitoring of cell performance via electrochemical impedance spectroscopy, a mechanism of carbon consumption contributing to loss of electrical conducting pathways was proposed. The state of the MIEC anode before and after cell operation was also investigated and showed that there were changes occurring to the anode phase relating to the coarsening of LSCF particles as well as minor phase instabilities. In addition, a phenomenon of power overshoots, not reported in any detail in the literature, during voltage-current density scans was observed and the influence of the fuel chamber atmosphere on this was evaluated. Noting the structural changes to the LSCF electrode over extended periods of operation in strongly reducing atmospheres, a new anode was fabricated and trialled in the DCFC. The anode, composed of nickel, Gadolinia-Doped Ceria (GDC), and YSZ, delivered promising stability and operability when using a demineralised coal char as the fuel. Ash accumulation at the anode has been proposed as a likely contributor to degradation in the cell performance with time in the case of raw coal char. In order to gain further insight into the role of coal impurities within the DCFC, carbon black was impregnated with various catalytic species (compounds of Ca, Mg and Fe) for a targeted investigation into the effect of these inorganic species on DCFC performance. Thermogravimetric analysis revealed effects of these catalytic elements on the reactivity (Ca > Fe > Mg) of the catalysed carbon fuels towards Boudouard gasification under a carbon dioxide atmosphere. The catalysed carbon reactivity translated into enhanced fuel cell performance in a similar order, supporting the relationship between carbon reactivity and cell performance identified in the earlier study. The research outcomes from this project have generated substantial knowledge in the field of fuel (Victorian brown coal) preparation and characterisation, DCFC operation, carbon oxidation mechanism, cell performance, and lifetime of critical cell components with Victorian brown coal as a fuel for power generation. The findings presented in this study are expected to contribute to the development of this technology for the operation of direct-contact solid electrolyte based DCFCs using solid carbonaceous fuels.

This is the first ever study assessing the possibility of dimethyl ether (DME) production through gasification of Victorian brown coal. This project involves gasification of Victorian brown coal and catalyst development for syngas to DME conversion process. Victoria has large reserves of brown coal, 430 billion tonnes at current estimate. Use of Victorian brown coal is currently limited mostly to mine-mouth power generation because of high moisture content of the as-mined coal and high reactivity of the dried coal; both these properties make Victorian brown coal, raw or dried, unexportable. Gasification based alternative processing paths can provide export market for brown coal derived products, and more energy efficient application of brown coal. Syngas from Victorian brown coal can be catalytically converted into DME with higher energy efficiency and at potentially lower CO₂ emission. DME is a non-toxic, non-carcinogenic and non-corrosive compound. In addition, it has wide application as a fuel in cars, gas turbines, fuel cells and household applications. A process simulation for as-mined Victorian brown coal to DME was performed using ASPEN Plus. The simulation study shaped the experimental matrix as it provided a realistic range of operating conditions (e.g. gasification temperature and syngas H₂ to CO ratio). CO₂ Gasification kinetics for raw parent coal as well as demineralised and catalyst-loaded (Ca, Fe) coals were studied using a thermogravimetric analyser. Pyrolysis and gasification of the coal was performed in an entrained flow reactor (EFR) and the solid, liquid and gaseous products were characterised. DME synthesis experiments were performed in a high pressure fixed-bed reactor, using commercial and developed catalysts, and synthetic syngas consisting H₂ and CO. A 3² factorial experimental design was used to optimise catalyst composition and syngas ratio (H₂ to CO). The developed catalysts were prepared based on the information generated from preliminary experiments with commercial catalysts. Physical mixing and coprecipitation-impregnation methods were used for the preparation of bi-functional DME synthesis catalysts. Performance (CO conversion, DME yield and DME selectivity) of the developed catalysts was compared with that of commercial catalysts. Effects of sulphur poisoning on CO-conversion, DME yield and DME selectivity were also studied. Process simulation using ASPEN plus showed that the low temperature gasification at 900 °C can produce syngas with appropriate H₂ to CO ratio. The ratio was found to be 0.81 at the gasifier outlet (before the recycle stream) and 1.41 at the DME reactor inlet (after the recycle stream). The overall process efficiency was found to be ∼ 32% after considering the energy penalty for CO₂ separation, higher than the power generation efficiency of 28% (without CO₂ separation). Two kinetic models (Grain model and random pore model) were used to find the intrinsic CO₂ gasification kinetics. Random pore model predicted the experimental results better than the grain model. The activation energy for char-CO₂ gasification was ∼189 kJ/mol. Ca-loaded coal char showed better gasification reactivity. However, addition of iron did not show any improvement. The results indicate that the effect of minerals become insignificant at 1000 °C or above and catalytic gasification showed be carried out below this temperature. EFR studies showed that the tar yield rapidly decreased as the gasification temperature was increased. The residence time and gasification temperature in the EFR were not enough for complete carbon conversion. In situ synchrotron radiation X-ray diffraction on methanol and DME synthesis catalysts showed rapid catalyst deactivation at temperatures above 300 °C, resulted from phase mobility and thermal sintering. The extent of deactivation was higher for the bi-functional DME catalyst compared to the methanol synthesis catalyst. Regression analysis on the yield data, obtained using commercial catalysts, showed that a H₂ to CO ratio of 1.45 and a catalyst consisting 58% methanol synthesis component results maximum DME yield. Among the four developed catalysts (DSC-1, DSC-2, DSC-M, DSC-1-PRE), three catalysts (except DSC-1-PRE) showed performance similar or better than the commercial catalyst mixture M1A1. CO conversion was between 67-70% for the DSC-1 catalyst, best among the developed catalysts, compared to 58-60% conversion for the M1A1 catalyst. DME yield was 36-40% and 35-38% for the DSC-1 and M1A1, respectively. A 10 hour exposure of the catalyst to 103 ppm H₂S showed at least 12% reduction in conversion and yield, indicating rapid deactivation in the catalyst activity. All the results were at least duplicated, and triplicated in most of the cases. The obtained results positively indicate that the conversion of syngas from Victorian brown coal to DME is a feasible option.

Chemical looping combustion of Victorian brown coal using Fe-based oxygen carriers

Iron is usually produced from its ores using coke in a blast furnace (BF). Coke, a hard and macroporous carbon material, is produced from special coals (coking coals) and acts as fuel, smelting agent, and the permeable support for the charge to the BF. No material can completely replace coke in a BF. Coking coals are becoming harder (and more expensive) to obtain. Victorian brown coal (VBC) is accessible, cheap, with low mineral concentrations, which is favourable for iron production in a BF. However, as-mined, it does not form coke, but a char which is too reactive to be used in a BF. The objective of this project is to produce a substitute for BF coke from VBC by physical and chemical treatments and to investigate the use of cementing agents to reduce the reactivity and strengthen the product finally formed. VBC from Loy Yang open cut, and its commercial products, briquettes and char, which were obtained from Australian Char Pty Ltd in lump form, were used as starting materials. VBC tar, coking coal tar pitch, and asphaltene (hexane insolubles from VBC tar) were used as binders. Some of the starting material was pre-treated by acid washing (0.5 M H₂SO₄), hydrothermal dewatering (HTD; 320 °C-35 min) or alkali treatment (KOH (aq), 185 °C-10 h). The elemental analysis and NMR of these materials were determined. Before pelleting, raw VBC, pre-treated VBC, or briquettes were dried at 105 °C under N₂, ground to <0.15 mm, then mixed with the binder in tetrahydrofuran (THF). THF was removed and the mixture was pelleted by a conventional hydraulic press at ambient temperature or using an INSTRON 5569 series Mechanical Tester applying a range of forces, temperatures and times. Some samples were pelleted under N₂ (350 °C-30 min) by “Hot Press Carbonization” (HPC). In some cases, samples were air cured at 200 °C for 2 h. Finally, the samples were carbonised at a range of temperatures and times under N₂ flow, at a low heating rate to minimise cracking of the pellet, then cooled under N₂. The measurements used to evaluate the suitability of the products as substitutes for BF coke were compressive strength and reactivity. The compressive strengths of pellets were measured by using an INSTRON 5569 series Mechanical Tester. Reactivity was measured using a thermogravimetric balance. The sample was heated to 1000 °C at 20 °C /min under N2 and held at 1000 °C for 1 h in a flow (70 ml/min) of 1:1 CO₂:N₂. The reactivity, R60CO₂, was calculated from the weight loss. Physical properties of the products were measured in order to understand what factors controlled the compressive strength and reactivity. Initially, VBC or commercial briquettes were impregnated with tar, pelleted at ambient temperature and carbonized. Products from VBC showed higher compressive strengths (40-60 MPa) and slightly lower reactivity (R60CO₂ 87-89 %) and surface areas (790-800 m²/g) than those from briquettes. The effects of carbonization time, temperature (900 or 950 °C) and tar addition were relatively small. The high reactivity of the samples compared to that of coke (R60CO₂ 13 %) is probably related to their higher surface areas and the smaller extent and greater disorder of their graphitic structure as shown by XRD. The poor results of ambient pelleting and recent literature suggested that hot pelleting of VBC would be advantageous. Therefore, VBC-tar mixture was hot pelleted (150 °C-20 kN for 10 or 30 min), optionally air cured then carbonized (950 °C for 3 h). Products showed higher compressive strength (90-200 MPa) and bulk density (1.17-1.27 g/cm³) than those obtained following ambient pelleting. A high concentration of tar (10-15 wt%) and air curing increased the compressive strength by a further factor of two. The compressive strength was higher than that of a BF coke (20 MPa), but the surface area remained high and the surface was rough (SEM) and the proportion of graphitic structure was small (Raman spectroscopy). These factors probably contributed to the high reactivity of even the strongest products. VBC treated by HTD resembles a higher rank coal (e.g. lower O content), suggesting that HTD coal might carbonize to a less reactive product, like a higher rank coal. HTD treatment reduced the reactivity of the carbonization products, without an unacceptable lowering of the compressive strength. More severe briquetting conditions, acid washing before HTD, air curing and severe carbonization conditions (1200 °C-8 h) all together reduced the reactivity to R60CO₂ 34 %, still much higher than that of a BF coke. The surface area was reduced, but only to 100 m²/g, (cf. 18 m2/g for BF coke) and the proportion of graphitic structure was smaller than in BF coke, so that the higher reactivity may be due to these structural factors. Alkali treated VBC (ATC) appears to melt and fuse upon carbonization, like a coking coal, suggesting that carbonised product might be similar to a BF coke. The ATC with pitch and air curing had a high compressive strength (up to 230 MPa) after carbonization (1200-1300 °C for 2-8 h). The small surface area (as low as 20 m³/g) and smooth surface (SEM) of the products under some conditions suggests that fusion occurred during carbonization. However, the proportion of graphitic structure (Raman and TEM) was lower than for a BF coke and the reactivity of the carbonized products did not fall below R60CO₂ 30 %. Possibly the alkali treatment changed the chemical structure and inhibited graphitisation. Suitable pore structure is necessary for low reactivity, but the chemical structure is also important. Empirical treatments, modifying the structure of brown coal in the direction of higher rank coals, give carbonised products which approach BF coke in reactivity, surface area and the proportion of graphitic structure while maintaining compressive strength.

Victoria has abundant brown coal resource, but they are mainly used for mine-mouth power generation units with very low efficiency and high greenhouse gas emissions. Entrained flow gasification is a technology with great potential for Victorian brown coal utilization to produce high-value products. However, little is known about entrained flow gasification of Victorian brown coal. Therefore, the major objective of this study is to obtain a better understanding of entrained flow gasification of Victorian brown coal with CO2 using different experimental and modelling approaches. The focus of this research is to examine: 1) the effect of a wide range of operational variables on gasification performance and emission of air pollutants, 2) the mineral transformation during coal pyrolysis and char gasification, 3) a comparison of entrained flow gasification behaviour of Victorian brown coal and biomass, 4) the kinetic modelling of char-CO2 gasification of Victorian brown coal.

This thesis presents a study of the morphological changes that occur in selected coal chars during oxidation at low temperature (725K-875K) and at high temperature (1400K-1600K). Gas adsorption and mercury porosimetry were the primary means by which these changes were monitored. An attempt was made to relate the observed reactivity of the char in oxygen to the evolving porous structure of the char. Initial pore structure was varied by using three different raw coals: a lignite, a subbituminous and high volatile A bituminous coal. In the case of the bituminous coal, pore structure was varied further by using different pyrolysis temperatures. Of course, while there were differences in the physical structure of the chars, there were differences in the chemical structure as well. In order to account for this, the chemical nature of the chars was monitored, using elemental analysis and oxygen chemisorption. The results of this study indicate that, at low temperatures, the rate of oxidation of the subbituminous and bituminous chars is proportional to the BET surface area beyond 20% conversion. The lignite char did not show such simple behavior because of the presence of large amounts of ash. For the high-temperature case, reaction appeared to be confined to the exterior of the particle and to the interior of the macropores. Time-temperature histories of individual lignite char particles were obtained with a two-color pyrometer. A simplified model of single- particle-char combustion was used in conjunction with statistical analysis to infer kinetic parameters from the experimental time-temperature traces.

Generation of ultra-clean coal from Victorian brown coal — Sequential and single leaching at room temperature to elucidate the elution of individual inorganic elements

The conversion of solid fuels via gasification is a viable method to produce valuable fuels and chemicals or electricity while also offering the option of carbon capture. Fluidized bed gasifiers are most suitable for abundantly available low-rank coal. The design of these gasifiers requires well-developed kinetic models of gasification. Numerous studies deal with single aspects of char gasification, like influence of gas compositions or pre-treatment. Nevertheless, no unified theory for the gasification mechanisms exists that is able to explain the reaction rate over the full range of possible temperatures, gas compositions, carbon conversion, etc. This study aims to demonstrate a rigorous methodology to provide a complete char gasification model for all conditions in a fluidized bed gasifier for one specific fuel. The non-isothermal thermogravimetric method was applied to steam and CO2 gasification from 500 °C to 1100 °C. The inhibiting effect of product gases H2 and CO was taken into account. All measurements were evaluated for their accuracy with the Allan variance. Two reaction models (i.e., Arrhenius and Langmuir–Hinshelwood) and four conversion models (i.e., volumetric model, grain model, random pore model and Johnson model) were fitted to the measurement results and assessed depending on their coefficient of determination. The results for the chosen char show that the Langmuir–Hinshelwood reaction model together with the Johnson conversion model is most suitable to describe the char conversion for both steam and CO2 gasification of the tested lignite. The coefficient of determination is 98% and 95%, respectively.

The aim of this study is to investigate about the complex phenomenology associated with the interaction of a particle-laden turbulent flow with the slag-covered wall of an entrained-flow gasifier. Recent observations, indeed, highlighted that this phenomenology can have an impact on the global gasifier performance greater than that expected from previous analyses. The design of new generation of entrained-flow coal gasifiers aims at favoring ash migration/deposition onto the reactor walls, whence the molten ash (slag) flows and is eventually drained separately at the bottom of the gasifier. In terms of efficiency, the oxidation of the volatile compounds released around the particles depends upon its mixing with the fresh oxidant mixture. Therefore combustion efficiency is influenced by the spatial distribution of the particle phase, with an homogeneous distributions favoring a better mixing. From the observation that a significant number of coal particles can spent most of the time in the gasifier close to the slag layer, where usually their concentration largely increase, leads to the need to understand the effective conditions experienced before complete conversion. An experimental evidence of a picture for the fate of coal particles has been recently assessed by analyzing the chemical composition of samples of coarse slag and slag fines generated in the ELCOGAS entrained-flow gasifier located in Puertollano, Ciudad Real (Spain). Quantitative SEM-EDX analysis of the coarse slag revealed the presence of small marks with a significant carbon content as high as 48.8%-54.2%. This fact can be explained by assuming the entrapment of not fully burned coal particles into the slag. The results of the SEM analysis performed on whole slag fines particles showed that the carbon content was larger than the value obtained from the inspection of coarse slag particles. This is particularly evident for porous particles where C-content ranged between 82.3% and 86.5%. A considerable amount of unreacted coal is therefore entrapped into the slag matrix. From this observations emerges that a certain level of spatial non homogeneity of the solid phase distribution exists. In a recently published study by Montagnaro and Salatino (2010), these data have been interpreted by assuming that different regimes of particles-slag interaction can occur: either char entrapment inside the melt or carbon-coverage of the slag may occur, depending on properties like char density, particle diameter and impact velocity, slag viscosity, interfacial particle-slag tension. Occurrence of char entrapment prevents further progress of combustion/gasification. On the contrary, if char particles reaching the wall adhere to the slag layer's surface without being fully engulfed, the progress of combustion/gasification is still permitted. The observed high rate of coal conversion can actually be explained only if this second regime establishes on the slag surface. The addressed considerations highlights the technological need to build up methods for the prediction of the mechanism particles clustering and segregation in condition representative of coal particle flying and converting into a gasifier. Actually a comprehensive numerical simulation of the whole range of spatial and temporal chemical and turbulent time scales involved in a full scale gasifier, is still unfeasible due to the high computational cost: the scales of turbulence involved in the gasification processes range from sub-micron scale up to the integral scale of a gasifier reactor chamber (of the order of tens of meters). To overcome this difficulty, the approach proposed in this study is based on the development of a multilevel approach.. In a first level, the motion of particles representing classes of partially converted coal in a 3-dimensional representation of the gasifier is modeled with a Computational Fluid Dynamic (CFD) approach.. Turbulence of the flow field is described adopting the Reynolds Averaged Navier Stokes (RANS) approach, while particle motion is resolved with a Lagrangian Particle Tracking (LPT) approach. The use of the RANS method for the gas phase coupled with the LPT for the solid phase in this analysis is twofold. Firstly it has been used to address the behavior of coarse and fine coal particles trajectories when subjected to a swirl motion which induced a turbulent field. This model, while avoiding the great complexity and computational effort required by comprehensive numerical CFD models of gasifiers already proposed in the literature, is sufficient to characterize the range of conditions, in terms of momentum possessed and direction, that the different particles show when approaching the gasifier walls. The second aspect concerns the identification of regions where different mechanisms for the coal clustering becomes foreseeable: distinct regions close to the wall have been identified: finer particles could be mainly responsible of particle layering near the solid walls as they, after their first impinging on the wall, assumes a pathway parallel to the wall; in contrast, larger particles continue to bounce over the walls along the whole length of the gasifier. The identification of these two different regions and the characterization of particle classes representative of partially burned coal particles, was the basis for the proper setup of numerical simulations based on a Large Eddy Simulation (LES) approach in two completely different configurations. This level aims at a detailed investigation of the mechanisms of slag-particle interaction. The first is a plane particle-laden channel flow, that well represents the main features of the gasifier regions where particles move parallel to the wall. The second is a periodic particle laden curved channel flow, that best represent regions close to the wall but dominated by the external swirling flow. For these two configurations the particle interaction with the slag has been treated as a rebound on a not perfectly elastic wall. A parametric study has been conducted obtaining results for different particle sizes (representing different particle inertia) and different momentum restitution in the particle-wall impact. Numerical multiphase simulations are based on the Eulerian-Lagrangian approach implemented in the OpenFOAM CFD framework. Both RANS and LES turbulence models are implemented for the gas phase. The equations of particles motion were solved via a Lagrangian particle tracking algorithm with the TrackToFace method. Simulations were performed involving a number of particles from 10^5 to 10^6, a level of detail that allowed to obtain a clear picture of the multiphase flow behavior responsible for char deposition phenomena. Numerical simulation results with the LES approach do confirm the establishment of a region near the wall slag layer (the dense-dispersed phase leading to the formation of the slag fines), in which particles impacting the slag accumulate to an extent depending on the system fluid-dynamics and on parameters such as particles Stokes number and restitution coefficient. However, particle concentration near the wall in all the simulated cases does not appear perfectly steady not evenly spatially distributed. Interestingly, the segregation of char particles near the wall is more evident for the curved channel flow geometry and is enhanced for coarser particles, making evident the role played by the effective impact with the slag not recovered by the simpler models adopted in the RANS simulations.

Catalytic gasification of carbon in a direct carbon fuel cell

The exploitation of fossil fuels and greenhouse gas emissions have brought great attention to the utilization of biomass fuel resources. The scholars researcher Were studied with thermo gravimetric mass spectrometry instrument in this paper, four kinds of biomass paralysis gas product characteristics, the small fixed bed is used for rice husk, straw paralysis experiment, the analysis of the microstructure of carob coal, element composition and phase composition of biomass and coal in fluidized bed gasification experiment. The different mixing ratio, air equivalence ratio, the influence law of water vapour in the fuel quality in the gasification process, the analysis of biomass and coal gasification mechanism are studied to explore the synergistic effect of the gasification process. The average gasification reaction rate of RH coal, DWG coal coke and YX coal coke is very different. The average gasification reaction rate of RH coal, DWG coal coke and Yx coal coke in the 0.1mpa paralysis was 1.04s-1, 0.58s-1, and 0.95 s-1. The average gasification reaction rate of the RH was 1.8 times that of DWG coal coke gasification reaction rate. Therefore, we can conclude that RH coal gasification reactivity is the best, YX coal is the second, and DWG coal is the worst. In addition, we can also compare the influence of paralysis pressure on coal coke gasification reactivity. No matter RH, DWG coal or Yx coal, the paralysis pressure increases, the average gasification reaction rate decreases and the gasification reactivity deteriorates. Especially 0.1 MPa paralysis pressure average Yx char gasification reaction rate significantly greater than 0.5 MPa, and 3. The average MPa paralysis pressure Yx char gasification reaction rate is shown in figure 2. Gasification reaction rate and the total carbon conversion rate trend is consistent.

The utilization of Victorian brown coal (VBC) is restricted domestically due to its high moisture content and handling difficultly. A stepwise pyrolysis and gasification technology was developed to promote VBC utilization in entrained flow gasifier. The process simulation was conducted using Aspen Plus, where a higher efficiency process was achieved based on exergy analysis. The co-gasification for VBC and bituminous coal has been studied experimentally in terms of reactivity and ash slagging propensity. The completion of this project provides theoretical reference and technical support for VBC industrial gasification applications. It also broadens the utilization range for low-rank fuels in the carbon-constrained future.

This paper presents reviews of studies on properties of coal pertinent to carbon dioxide (CO2) sequestration in coal with specific reference to Victorian brown coals. The coal basins in Victoria, Australia have been identified as one of the largest brown coal resources in the world and so far few studies have been conducted on CO2 sequestration in this particular type of coals. The feasibility of CO2 sequestration depends on three main factors: (1) coal mass properties (chemical, physical and microscopic properties), (2) seam permeability, and (3) gas sorption properties of the coal. Firstly, the coal mass properties of Victorian brown coal are presented, and then the general variations of the coal mass properties with rank, for all types of coal, are discussed. Subsequently, coal gas permeability and gas sorption are considered, and the physical factors which affect them are examined. In addition, existing models for coal gas permeability and gas sorption in coal are reviewed and the possibilities of further development of these models are discussed. According to the previous studies, coal mass properties and permeability and gas sorption characteristics of coals are different for different ranks: lignite to medium volatile bituminous coals and medium volatile bituminous to anthracite coals. This is important for the development of mathematical models for gas permeability and sorption behavior. Furthermore, the models have to take into account volume effect which can be significant under high pressure and temperature conditions. Also, the viscosity and density of supercritical CO2 close to the critical point can undergo large and rapid changes. To date, few studies have been conducted on CO2 sequestration in Victorian brown coal, and for all types of coal, very few studies have been conducted on CO2 sequestration under high pressure and temperature conditions.

Coal contributes to almost forty percent of global power generation. As conventional coal-fired power generation technologies result in large CO2 emission, the pursuit for new technologies focuses on either reducing CO2 emission or that allows easier capture of the emitted CO2 from coal-fired power plants. Oxy-fuel fluidized bed (Oxy-FB) combustion is one such technology due to its ability to produce concentrated CO2 stream in the flue gas. This concentrated CO2 allows easier capture for subsequent transportation and storage. Other important benefits of this technology are the potential for using any type of fuel, and the ability to control SO2 and NOX emissions. Despite its perceived advantages over conventional technologies, very little is known about the applicability of Oxy-FB for brown coal. Brown coal accounts for 91% of Victoria’s current electricity needs. Since Victoria has an estimated reserve of over 500 years of brown coal at the current consumption rate, successful application of Oxy-FB can potentially result in environment friendly power generation in Victoria. This first-ever study investigates the Oxy-FB combustion using Victorian brown coal in a combined experimental and modelling approach. The research involves designing and commissioning of a 10 kWth fluidized bed rig, carrying out experiments in laboratory scale and bench scale equipment, and performing thermodynamic and process modelling. Laboratory scale experiments using single char particle were conducted to investigate the combustion characteristics of individual and large char particle under Oxy-FB conditions. Particle temperature was observed to be higher compared to bed temperature. Up to 48°C difference was noticed between the char particle temperature and the bed temperature using 15% (v/v) steam in oxy-fuel combustion atmosphere. The temperature of the char particle during Oxy-FB combustion has practical implication for agglomeration. The bench scale experiments were carried out to evaluate combustion efficiency, agglomeration characteristics, sulphation characteristics, carbonation characteristics, NOX (NO, NO2 and N2O) emission, SOX (SO2 and SO3) emission, and trace elements (Hg, Se, As and Cr) emissions during Oxy-FB combustion of Victorian brown coal. A high level of CO2 concentration (90-94% in dry flue gas), over 99% combustion efficiency and no bed agglomeration under oxy-fuel combustion conditions including those with the addition of steam at temperatures between 800°C and 900°C. Moreover, the measured NOX and SOX concentration levels in the flue gas are within the permissible limits for coal-fired power plants in Victoria. This implies that additional NOX and SOX removal systems may not be required with Oxy-FB combustion of Victorian brown coal. The gaseous mercury concentrations, however, are considerably higher under oxy-fuel combustion compared to air combustion suggesting that mercury removal system may be required to avoid corrosion in the CO2 separation units if CO2 capture and transportation is intended. These conventional pollutants and trace elements emission characteristics are of great importance for the design of the gas cleaning systems for CO2 capture and storage (CCS) purposes. Furthermore, these results also provide information for selecting the optimum operating condition. Thermodynamic equilibrium modelling was carried out to predict the compounds formed during the combustion of Victorian brown coal under different Oxy-FB combustion conditions. It was predicted that the amount of toxic gaseous Cr6+ species was greater for oxy-fuel combustion than for air combustion. The distribution of toxic Se4+ species, however, remained almost the same in both combustion conditions within the typical temperature range for Oxy-FB combustion (800 - 950°C). A process model on Oxy-FB combustion using Aspen Plus was also developed to predict combustion performance of any coal during Oxy-FB. It was observed that the concentrations of CO and SO2 were higher in the lower dense region of the bed. These levels, however, dropped significantly with the introduction of secondary oxygen. The simulation results were consistent with the experimental data. Overall, this thesis has identified several important issues, for the first time, on Oxy-FB combustion using brown coal. The information generated is useful for academics, industry and policy makers. Future research on Oxy-FB combustion can use the findings of this study while developing Oxy-FB combustion for brown coals.

Ash free coal extracted from a bituminous coal and carbon made from Oak were served as fuels in a direct carbon fuel cell and their oxidation behaviors were compared in terms of temperature, coal to carbonate ratio, and gas compositions in the cell. The ash free coal had much higher OCV and voltage at polarization states than carbon fuel at 650oC. Dominant product gases from the coal were H2and CO, while carbon had carbon monoxide in the tested range. Therefore difference in the oxidation process would be existed between the two fuels.Coal is relatively abundant energy source compared with other fossil fuels. Regardless of its abundance and long history of usage, inconvenience of its use reduces coal consumption at present. Coal as a solid fuel has a big problem of remaining ash in its use. Ash free coal has been attempted to overcome the problem. So far, ash free coal can be produced by two ways; one is removing ash compounds with acids and alkalines in the coal, calling UCC(Ultra Clean Coal), and another one is extracting organic compounds from the coal with organic solvents, named by ash free coal.In this work, ash free coal was produced by a micro-wave method with a polar solvent of NMP. For the comparison of oxidation behavior, carbon made from Oak was employed in this work. The electrochemical oxidation behaviors of coal and carbon were investigated with respect to temperature, coal to carbonate ratio, and gas compositions in a coin type direct carbon fuel cell (DCFC).The raw coal used in this work was Berau bituminous supplied by KEPRI in Korea. Carbon was made in-house, for 2 hrs at 400oC under N2 environment. A coin type direct carbon fuel cell was fabricated by molten carbonate fuel cell technology. The diameter of electrodes was about 3 cm. The anode was porous Ni-Al alloy, and the cathode was porous Ni. The matrix was made of LiAlO2. The long alumina tube at the upside of the cell was installed for the coal supply to the anode. A mixture of 62 mol% Li2CO3 and 38 mol% K2CO3 was served as electrolyte. The cathode gas was 70 % air and 30 % CO2. More details of the DCFC operation was described in a previous work [1]. The normal H2 fuel for the anode was H2:CO2 = 0.125 L/min: 0.025 L/min with ca. 5 % of H2O. Temperature ranged from 923K to 1123K. Coal to carbonate ratios were 3g to 3g, 3g to 1g, and 1g to 3g. Gas compositions in the cell were analyzed with a gas chromatography (HP 5890II).Figures 1 and 2 show OCV behaviors of fuel change from the normal H2 fuel to carbon fuel and ash free coal, respectively at 650oC, 750oC, and 850oC. The carbon fuel was a mixture of 3 g of carbon and 3 g of Li-K carbonates, while the ash free coal was a mixture of 3 g coal and 3 g of Li-K carbonates. Before 0 s the OCV was determined by the H2 fuel. After 0 s the carbon fuel shows only one minimum in the OCV whereas the coal does two minimums. The difference was attributed to the different gas species that carbon produced mostly CO species, while the coal gave H2 and CO as dominant gas species. In particular, very low OCV is observed at carbon fuel of 650oC, which indicates that very small reaction species in the condition. Very low gasification of carbon is the reason at the condition. On the other hand, coal fuel shows much higher OCV at 650oC. Rather easy gasification of ash free coal can be the reason. The main gas species of coal were CO and H2 because the hydrocarbon species in the coal is readily gasified even at 650oC. Similar amounts of CO and H2 were measured at the coal fuel in the anode chamber. The H2gas is generally more active than CO gas in the oxidation. Then the difference in the oxidation process between coal and carbon can be existed. ACKNOWLEDGEMENT This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2011-0009748).