Laureate Professor Behdad Moghtaderi

Here graphite was found to undergo carbon/carbonate gasification at 800 °C, resulting in exfoliation of graphite to form turbostratic carbon. The lattice distance of graphene sheets in graphite are shown to undergo marked changes following treatment with molten ternary eutectic carbonate (Li2CO3: 43.5%, Na2CO3: 31.5%, K2CO3: 25%) during slow temperature ramping rates (5 °C/min) under N2 at temperatures above 750 °C. Initial findings suggest that approximately 50 wt% of graphite experiences interlayer expansion. The conventional d spacing of 0.34 nm is modified to a range of intervals between 0.41 nm and 1.22 nm. As a consequence of high operational temperature (800 °C), cations (Li+, Na+ and K+) as well as potentially the anion (CO32¿) intercalate between graphitic layers and overcome Van der Waal force between layers. Employing a pressurized N2 environment of 5 bar and 10 bar successfully controls carbonate vaporization and decomposition, as well as inducing ordered layer manipulation to exfoliate more graphite planes from the edges towards deeper levels of the particles. Exploring parameters of both carbonate loading and treatment time in addition to pressure demonstrate that this work opens up a rich selection of parameters that can be used to produce carbons with tuned properties from graphite.

Accidental flame initiation to propagation in pipes carrying flammable gases is a significant safety concern that can potentially result in loss of life and substantial damage to property. The understanding of flame propagation characteristics caused by methane¿air mixtures within various extractive and associated process industries such as coal mining is critical in developing effective and safe fire prevention and mitigation countermeasures. The aim of this study is to investigate and visualise the fire and explosion properties of a methane¿air mixture in a straight pipe with and without obstacles. The experimental setup included modular starting pipes, an array of sensors (flame, temperature, and pressure), a gas injection system, a gas analyser, data acquisition and a control system. The resulting observations indicated that the presence of obstacles within a straight pipe eventuated an increase in flame propagation speed and deflagration overpressure as well as a reduction in the elapsed time of flame propagation. The maximum flame propagation speed in the presence of an orifice with a 70% blockage ratio at multiple spots was increased around 1.7 times when compared to the pipe without obstacles for 10% methane concentration. The findings of this study will augment the body of scientific knowledge and assist extractive and associated process industries, including stakeholders in coal mining to develop better strategies for preventing or reducing the incidence of methane¿air flame propagation caused by accidental fires.

Water scarcity is a significant issue in developing countries and remote locations, however, atmospheric water vapour is a widely available and yet underutilised water reservoir. Desiccant coated heat exchangers are a potential sorption reactor for multicyclic atmospheric water generation due to the enhanced heat and mass transfer to the desiccant. This study utilised a transient one-dimensional mathematical model for a plate-fin desiccant coated heat exchanger and adapted the model for atmospheric water generation. From this, a heat and mass transfer analysis and parametric study were conducted to determine the effect of the operational and geometric parameters on the specific water production and specific energy consumption. The heat and mass transfer analysis found that the coating at the inlet and outlet regions of the channels were underutilised. The parametric study found that the adsorption and desorption cycle times should be optimised independently, the primary air velocity should be high during adsorption and low during desorption, and secondary channel cooling during adsorption did not significantly improve performance. The highest specific water production and the lowest specific energy consumption recorded in this study were 5.8 L kg-1 day-1 and 7.7 MJ L-1 respectively. The recorded specific water production values were higher than most desiccant based atmospheric water generators in the literature. However, the performance was significantly reduced at higher ambient temperatures.

Ventilation Air Methane (VAM) refers to the release of fugitive methane (CH4) emissions into the atmosphere during underground coal mining operations. Growing concerns regarding the greenhouse effects of CH4 have led to a worldwide effort in developing efficient and cost-effective methods of capturing CH4. Among these, absorption-based processes, particularly those using Ionic Liquids (ILs) are appealing due to their advantages over conventional methods. In this study, the solubility of CH4 in various ILs, expressed by Henry¿s law constant, is first reviewed by examining a wide range of experimental techniques. This is followed by a review of thermodynamic modelling tools such as the extended Henry¿s law model, extended Pitzer¿s model, Peng¿Robinson (PR) equation of state, and Krichevsky-Kasarnovsky (KK) equation of state as well as computational (Artificial Neural Network) modelling approaches. The comprehensive analysis presented in this paper aims to provide a deeper understanding of the factors that significantly influence the process of interest. Furthermore, the study provides a critical examination of recent advancements and innovations in CH4 capture by ILs. ILs, in general, have a higher selectivity for methane compared to conventional solvents. This means that ILs can remove methane more effectively from VAM, resulting in a higher purity of the recovered methane. Overall, ILs offer several advantages over conventional solvents for the after treatment of VAM. They are more selective, less volatile, have a wider temperature range, are chemically stable, and can be made from renewable materials. As a result of their many advantages, ILs are becoming increasingly popular for the after treatment of VAM. They offer a more sustainable, efficient, and safe alternative to conventional solvents, and they are likely to continue gaining market share in the coming years.

Gas fluidized beds with bi-dispersed particles of different sizes, densities, and shapes are encountered in many industrial processes spanning the manufacture of energy, material and resources to greenhouse emissions mitigation and renewable resources utilization. The design and operation of such systems heavily rely on the prediction of minimum fluidization velocity of the mixture (Umf(mixture)) to avoid particle segregation and maximize mixing. Many correlations exist for predicting Umf(mixture); however, they exhibit limitations in accuracy and/or applicability. The limitations of these correlations are often expressed in terms of particles properties (e.g. effective size and density), flow conditions, and solids composition. This study has critically assessed highly cited correlations, delivered a comparative analysis of their applicability and predictability against a large pool of experimental data, and deepened the understanding of parameters that affect the prediction of Umf(mixture) using different correlations.

The energy transition for a net-zero future will require deep decarbonisation that hydrogen is uniquely positioned to facilitate. This technoeconomic study considers renewable hydrogen production, transmission and storage for energy networks using the National Electricity Market (NEM) region of Eastern Australia as a case study. Plausible growth projections are developed to meet domestic demands for gas out to 2040 based on industry commitments and scalable technology deployment. Analysis using the discounted cash flow technique is performed to determine possible levelised cost figures for key processes out to 2050. Variables include geographic limitations, growth rates and capacity factors to minimise abatement costs compared to business-as-usual natural gas forecasts. The study provides an optimistic outlook considering renewable power-to-X opportunities for blending, replacement and gas-to-power to show viable pathways for the gas transition to green hydrogen. Blending is achievable with modest (3%) green premiums this decade, and substitution for natural gas combustion in the long-term is likely to represent an abatement cost of AUD 18/tCO2-e including transmission and storage.

A few-layer graphene (FLG) composite material was synthesized using a rich reservoir and low-cost coal under the microwave-assisted catalytic graphitization process. X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were used to evaluate the properties of the FLG sample. A well-developed microstructure and higher graphitization degree were achieved under microwave heating at 1300¿ C using the S5% dual (Fe-Ni) catalyst for 20 min. In addition, the synthesized FLG sample encompassed the Raman spectrum 2D band at 2700 cm-1, which showed the existence of a few-layer graphene structure. The high-resolution TEM (transmission electron microscopy) image investigation of the S5% Fe-Ni sample confirmed that the fabricated FLG material consisted of two to seven graphitic layers, promoting the fast lithium-ion diffusion into the inner surface. The S5% Fe-Ni composite material delivered a high reversible capacity of 287.91 mAhg-1 at 0.1 C with a higher Coulombic efficiency of 99.9%. In contrast, the single catalyst of S10% Fe contained a reversible capacity of 260.13 mAhg-1 at 0.1 C with 97.96% Coulombic efficiency. Furthermore, the dual catalyst-loaded FLG sample demonstrated a high capacity¿up to 95% of the initial reversible capacity retention¿after 100 cycles. This study revealed the potential feasibility of producing FLG materials from bituminous coal used in a broad range as anode materials for lithium-ion batteries (LIBs).

CFD modeling of methane-air combustion and the subsequent flame and pressure wave propagations from the closed end of a detonation tube is presented, with a focus on propagation through variable concentration mixtures. A partially premixed combustion model that avoids the need to specify the flame speed is developed based upon the Flamelet Generated Manifold (FGM) model and needs no tuning to account for different methane concentrations. The numerical model is extensively validated using the experimental data collected from a large-scale detonation tube. The results show that the pressure wave propagation experiences three sequential stages: i) growth; ii) decoupling; and iii) decay. The peak overpressure is generated in the pressure wave growth stage in which the wave front transiently couples with the flame front, and the confined tube walls induce lateral wave reflections and force the flame front to transit from spherical to planar. Subsequently, the wave front starts decoupling from the flame front, with an almost constant global maximum pressure. After decoupling, the global maximum pressure drops because of the energy loss incurred through the wave propagation. The different methane concentrations introduced initially after the explosion chamber containing a stoichiometric mixture do not affect the peak overpressure or the pressure wave propagation but do affect the profile and propagation of the flame. Exponential acceleration of the flame propagation speed is found in the growth stage of pressure wave propagation, followed by the transition to a linear acceleration stage. For cases with the methane concentration becoming smaller than the stoichiometric concentration, the linear flame acceleration rate is smaller, with more pronounced flame stretching.

Energy-efficient building design needs an accurate way to estimate temperature inside the building which facilitates the calculation of heating and cooling energy requirements in order to achieve appropriate thermal comfort for occupants. Sky temperature is an important factor for any building assessment tool which needs to be precisely determined for accurate estimation of the energy requirement. Many building simulation tools have been used to calculate building thermal performance such as Autodesk Computational Fluid Dynamics (CFD) software, which can be used to calculate building internal air temperature but requires sky temperature as a key input factor for the simulation. Real data obtained from real-sized house modules located at University of Newcastle, Australia (southern hemisphere), were used to find the impact of different sky temperatures on the building¿s thermal performance using CFD simulation. Various sky temperatures were considered to determine the accurate response which aligns with a real trend of buildings¿ internal air temperature. It was found that the internal air temperature in a building keeps either rising or decreasing if higher or lower sky temperature is chosen. This significantly decreases the accuracy of the simulation. It was found that using the right sky temperature values for each module, Cavity Brick Module (CB) Insulated Cavity Brick Module (InsCB), Insulated Brick Veneer Module (InsBV) and Insulated Reverse Brick Veneer Module (InsRBV), will result in 6.5%, 7.1%, 6.2% and 6.4% error correspondingly compared with the real data. These errors mainly refer to the simulation error. On the other hand using higher sky temperatures by +10¿C will significantly increase the simulation error to 16.5%, 17.5%, 17.1% and 16.8% and lower sky temperature by +10¿C will also increase the error to 19.3%, 22.6%, 21.9% and 19.1% for CB, InsCB, InsBV and InsRBV modules, respectively.

Human health is a key pillar of modern conceptions of sustainability. Humanity pays a considerable price for its dependence on fossil-fueled energy systems, which must be addressed for sustainable urban development. Public hospitals are focal points for communities and have an opportunity to lead the transition to renewable energy. We have reimagined the healthcare energy ecosystem with sustainable technologies to transform hospitals into networked clean energy hubs. In this concept design, hydrogen is used to couple energy with other on-site medical resource demands, and vanadium flow battery technology is used to engage the public with energy systems. This multi-generation system would reduce harmful emissions while providing reliable services, tackling the linked issues of human and environmental health.

To design energy-efficient buildings, energy assessment programs need to be developed for determining the inside air temperature, so that thermal comfort of the occupant can be sustained. The internal temperatures could be calculated through computational fluid dynamics (CFD) analysis; however, miniscule time steps (seconds and milliseconds) are used by a long-term simulation (i.e., weeks, months) that require excessive time for computing wind effects results even for high-performance personal computers. This paper examines a new method, wherein the wind effect surrounding the buildings is integrated with the external air temperature to facilitate wind simulation in building analysis over long periods. This was done with the help of an equivalent temperature (known as Tnatural ), where the convection heat loss is produced in an equal capacity by this air temperature and by the built-in wind effects. Subsequently, this new external air temperature Tnatural can be used to calculate the internal air temperature. Upon inclusion of wind effects, above 90% of the results were found to be within 0¿3¿C of the perceived temperatures compared to the real data (99% for insulated cavity brick (InsCB), 91% for cavity brick (CB), 93% for insulated reverse brick veneer (InsRBV) and 94% for insulated brick veneer (InsBV) modules). However, a decline of 83¿88% was observed in the results after ignoring the wind effects. Hence, the presence of wind effects holds greater importance in correct simulation of the thermal performance of the modules. Moreover, the simulation time will expectedly reduce to below 1% of the original simulation time.

A three-dimensional hot flow model for simulating the alumina encapsulated Ni/NiO methane-air CLC system is developed. The temperature of particles (i.e., metal/metal oxides) is calculated based on exothermal/endothermal reactions and the convective heat transfer between particles and the gas mixture. The temperature of the gas mixture is solved by incorporating the energy exchange with the oxygen carrier particles into the governing equations. The motion of particles is tracked using the discrete element method, whilst the fluid flow is governed by the modified Navier-Stokes equations derived by replacing the point and fluid mechanical variables with locally averaged variables and the inclusion of local gas volume fraction. Two different CLC systems with different initial particle conversion rates have been simulated and the characteristics of the CLC hot flow system in terms of distributions of particle and gas mixture temperatures, solid circulation rate and particle conversion rate have been analysed and discussed. The results showed that the transient solid circulation rate varied but fluctuated around a certain value. Heterogeneous distributions of particle temperature and conversion rate have been observed in both fuel and air reactors. The model has been validated by comparing the predicted solid circulation rate and pressure distribution against the experimental data. The hot flow model proves capable of reproducing the CLC mechanism, i.e., transferring oxygen atom from the air reactor to the fuel reactor.

A novel slag carbon arrestor process (SCAP) was proposed to improve the heat recovery in energy-intensive steelmaking process, which typically has a low heat recovery. The proposed SCAP process introduces a tar reformer to utilise the slag - a by-product from steelmaking process - as the catalyst to convert coke oven gas and tar into hydrogen-enriched fuel gas. This is achieved by making use of the valuable carbon and/or energy contained in the coke oven gas, which otherwise being wasted, to assist in tar reforming and produce hydrogen-enriched gas. Such concept is expected to reduce the undesired tar formation in steelmaking process along with improved heat recovery efficiency and higher quality coke oven gas production. Both simulation and experimental studies on the slag carbon arrestor process were performed. The preliminary thermodynamic analysis carried out using Aspen Plus v8.4 indicates that with the tar reformer the energy content of coke oven gas was found increased from ~ 34.6 MJ/kg to ~ 37.7 MJ/kg (or by 9%). Also, with the utilisation of carbon deposition on the slag, a reduction of up to 12.8% coke usage in the steelmaking process can be achieved. This corresponds to an energy saving of 4% and a carbon emission reduction of 5.7% compared with the conventional steelmaking process. Preliminary experimental TGA-FTIR investigations revealed a reduction in the aromatic and aliphatic hydrocarbon groups and an increase in the production of CO2 and CO, attributed to the tar cracking abilities of slag.

This study investigates the suitability and effectiveness of La0.5Sr0.5Co0.8Fe0.2O3-d (LSCF5582) membrane for integration into the reduction reactor of a Nitrogen based chemical looping air separation (CLAS) process for exclusive separation of oxygen. First, the structural and chemical characteristics as well as the oxygen separation properties of LSCF5582 membranes, prepared at sintering temperatures of 1050¿1350¿°C, were examined to obtain the optimum range of sintering temperatures resulting in membranes with enhanced oxygen separation from air. This was achieved by determining the oxygen permeation properties of LSCF5582 membranes under the reducing environment of the Nitrogen based CLAS process, whereby oxygen is liberated from CuO oxygen carriers on the feed side of the membrane using nitrogen as a reducing gas. Membrane characterisation results showed that a single phase dense LSCF5582 membrane was formed at the sintering temperature range of 1200¿1225¿°C obtaining a maximum oxygen permeation flux of 0.67¿ml¿min-1¿cm-2 and oxygen recovery of 27% at the sintering and operating temperatures of 1200¿°C and 900¿°C, respectively. At the same operating temperature, under the reducing environment of nitrogen, the LSCF5582 membrane sintered at 1225¿°C was found to perform best achieving an oxygen permeation flux and oxygen recovery of 0.77¿ml¿min-1¿cm-2 and 76%, respectively.

There has been a surge of interest from the extractive industries in the application of mechanical means to the mitigation of flame deflagration. To verify the implementation and performance of passive and active mitigation protection, a comprehensive experimental investigation has been conducted on a large scale detonation tube, 30¿m long and 0.5¿m in diameter, with two mitigation valves (passive and active) and a burst panel venting system. The valves were used alternately to mitigate the flame deflagration of methane in concentrations ranging from 1.25% to 7.5%. The experimental work revealed that locating the passive mitigation valve at 22¿m distance from the ignition source mitigates the flame by fully isolating the tube. However, closing the valve structure in the axial direction generated another pressure wave upstream, which was approximately the same value as for the original pressure wave upstream. In the case of the active mitigation system, the system perfectly isolated upstream from downstream with no further pressure wave generation. When the vent was located at 6.5¿m from the ignition source, the total pressure was reduced by 0.48¿bar. Due to the counter flow of the reflected pressure wave the flame was extinguished at 12.5¿m from the ignition source.

The current work focuses on the development of a novel calcium-looping-based biomass-integrated gasification combined cycle (CL-BIGCC) process. The process is expected to improve the energy density of synthesis gas by capturing CO2 in a carbonator. Also, at the same time, the carbonator is expected to act as an ex situ tar removal unit, where tar cracking is expected to occur via catalytic reactions with CaO. The current work evaluates the feasibility of the proposed CL-BIGCC concept via thermodynamic analysis using Aspen Plus. Moreover, the tar cracking ability of CaO is demonstrated using thermogravimetric analyzer coupled to Fourier transform infrared spectrometer (TGA-FTIR) experiments. As part of the thermodynamic analysis, sensitivity analyses of the key process parameters, such as the calcium/biomass (Ca/B) ratio, steam/biomass (S/B) ratio, carbonator temperature, and calciner temperature, and their effects on net thermal-to-electricity efficiency have been studied in detail. The optimal values of key process parameters, such as a compression ratio of 5.1, an air/fuel mass ratio of 15, a Ca/B ratio of 0.53, a S/B ratio of 0.17, and carbonator and calciner temperatures of 650 and 800 °C, respectively, have been obtained. Furthermore, the CL-BIGCC process simulated in the current work was found to have a net thermal-to-electricity efficiency of ~25% based on the above optimal parameters, which is the highest among other conventional steam-based BIGCC processes. The biomass gasification (i.e., partial oxidation) experiments in a TGA-FTIR with a CaO/biomass ratio of 1:1 at different temperatures showed that CaO effectively catalyzed tar-cracking reactions.

This paper is concerned about a detailed techno-economic assessment of a hypothetical 500 MWe coal-fired power plant in New South Wales, Australia, for oxy-fuel conversion using integrated chemical looping air separation (ICLAS) technology and cryogenic air separation unit (CASU). The key objectives of this study are to (i) investigate and compare the detailed integration options for oxy-fuel conversion using ICLAS and CASU and (ii) determine the technical merits of the above integration options and the conditions at which the technologies become economically feasible. The study produced scientific evidence that confirms the viability of the CLAS process from both technical and economic points of view under certain conditions. The detailed technical analysis revealed that ICLAS with natural gas integration is energy-efficient compared to CASU running on parasitic load. This is primarily due to the fact that ICLAS needs less auxiliary power compared to CASU. Despite the fact that ICLAS natural gas integration has resulted in higher efficiencies than CASU running on parasitic load, from a series of detailed economic analyses, it was observed that both ICLAS and CASU may not be viable under the present operating and economic conditions. Nevertheless, from sensitivity analysis, it was concluded that ICLAS can become feasible if economic conditions are improved, e.g., a low natural gas market price (<$3.5/GJ), a high electricity wholesale price (>$59/MWh), and/or a high carbon tax (>$33/tonne).

The fires and explosions caused by flammable hydrocarbon air mixtures are a major safety concern in the chemical and processing industries. The thermo-physical and chemical properties of the flammable fuels in a hybrid form appear to have a significant impact on the combustion process. This usually occurs due to substantial changes in the flammability concentration regimes. The aim of this study is to investigate the fire and explosive properties of hybrid fuels in the chemical and process industries. In addition, it examines the impact of the ignition energy and vessel geometry on the magnitude of the pressure rise and flame propagation velocity. The experimental work was conducted on a cylindrically shaped explosion chamber constructed as part of this study at The University of Newcastle, Australia. The chamber was made of mild steel and was 30 m in length and 0.5 in diameter. It included a series of high resolution pressure transducers, a pyrometer, as well as a high speed video camera. Methane and coal dust were used as fuels and chemical igniters with a known energy were used to ignite the fuels.The results obtained from this study showed that both the ignition energy and the diluted combustible fuel dust have significant impacts on the Over Pressure Rise (OPR) in an explosion chamber. The significant findings included that the OPR doubled when 30 g m-3 of coal dust was added to a 6% methane/air mixture, and it increased by 60% when 10 kJ was used instead of a 1 kJ ignition source. The initial ignition energy was observed to considerably enhance the speed of both the pressure wave and the flame front, where the pressure wave speed doubled when using a 5 kJ instead of a 1 kJ ignition source. However, the pressure wave speed increased by five times when a 10 kJ was used instead of a 1 kJ ignition source. Additionally, the maximum flame front velocity observed for the ignition source with 5 kJ energy was twice the flame front velocity for the 1 kJ ignition source. Finally, it was observed that the time needed for the initial methane ignition was reduced by about 50% when using a 10 kJ instead of a 1 kJ ignition source.

Optimal thermo-physical properties of nanofluids provide an opportunity to overcome energy associated difficulties, in addition to providing new alternatives to catch, store and exchange of energy. A significant reduction in energy consumption is possible by improving the performance of a heat exchanger circuit, and may in part alleviate current energy related challenging issues such as global warming, climate change, and the fuel crisis. The objective of this work is to gain an insight into the overall stability of nanofluids with respect to pH, zeta potential, particle size distribution, and its effect on viscosity and thermal conductivity. For the purpose of this study two nanofluids were selected (water based alumina and copper oxide). Various nanoparticles concentrations as well as anionic surfactants (sodium dodecylbenzene sulfonate) were investigated for their stability, viscosity as well as thermal conductivity. The results clearly showed that nanofluid stability has a strong relation with viscosity and thermal conductivity. The stability of the nanofluid was found to be improved with a decrease in viscosity and an increase in thermal conductivity.

Ventilation Air Methane (VAM) abatement technology is recognized as a promising and value adding technique for reducing fugitive methane emissions, however, it also increases the potential fire and explosion risks of overheated coal dust. To eliminate these risks from the abatement systems it is necessary to determine the critical combustion characteristics of the minimum auto ignition temperature (MAIT) for a coal dust layer. This study investigates the auto-ignition behavior of coal dust layers in a humid environment with Relative Humidity (RH) >80%. The MAIT of four different coal dust samples (Australian coal) with particle sizes below 212 µm and dust layer thicknesses of 5, 12 and 15 mm were measured using a dust layer auto ignition temperature apparatus in accordance with the ASTM E2021 standard. It was concluded that the MAIT of the coal dust layer significantly decreases with decreasing particle size. The MAIT for the coal samples with a smaller D50 size were observed to be lower in comparison with samples with a larger D50 size. The dust layer thickness was shown to significantly impact on the MAIT. The MAIT increased proportionally with the increasing thickness of the coal dust layer. The effect of the coal dust moisture content and humidity on the MAIT for compacted dust layers was noticeable, whereas, this effect was less important with loose dust layers. In addition, this work investigated and compared the MAIT for a typical coal dust sample based on the existing ASTM and International Electrotechnical Commission (IEC) standard procedures for ignition of coal dust layers.

Theoretical modelling, design and operation of circulating and interconnected fluidized beds require an accurate prediction of solids holdup in the fully developed pneumatic conveying flow regime of the riser (i.e. the upper section of the riser). Existing empirical and semi-empirical solids holdup correlations have exhibited limited accuracy and application range. In this study, an empirical correlation was developed to predict the solids holdup at the upper section of the riser in circulating and interconnected fluidized beds with an improved level of accuracy for a broad range of operating conditions and riser dimensions. The correlation is based on a group of dimensionless quantities, which are typically used to describe the hydrodynamics of gas-solids fluidized beds, taking into account gas and particle properties, riser dimensions, and solid circulation rate. The reduced solids flux phenomenon also has been considered directly by introducing a system dependent exponent in the correlation. The correlation predicted 90% of the experimental data with an average deviation of 15%. The correlation is applicable for particle Reynolds numbers between 3.7 and 366.

Gas-solid fluidised beds are widely used in chemical, petrochemical, pharmaceutical, biochemical and powder industries. Particles used in gas-solid fluidised beds often differ in size and/or density, thus have the tendency to segregate under certain operating conditions. The results of our earlier work (Alghamdi et al., 2013) showed that for a given binary mixture, the transition from segregation to mixing occurred when the superficial gas velocity was increased over a critical value. In this study, force analysis at particle scale, including particle-particle, particle-wall and particle-fluid interacting forces, has been performed to investigate the underlying mechanisms that drive the occurrence of the transition. The results showed that as the superficial gas velocity increased, the system exhibited three sequential states: segregated, transition, and mixed. The vertical fluid force acting on the particles was found to be responsible for the occurrence of the transition from segregation to mixing, at which the bulk density of the heavy (small) particle species became smaller than the actual density of the light (large) species. After the occurrence of the transition, the particle collisional effects were dominant over the fluid viscous effects in governing the gas-solid two-phase flow. After the system became mixed, the net force of fluid and particle net weight forces conversely tended to separate the particles. However, the particle dispersion induced by particle collisions counterbalanced the particle segregation, acting as the main mechanism driving the good mixing of the binary particle species. The simulation results were in good agreement with the experimental data.

Liquid fluidised beds often operate with particles of different sizes and densities, encountering partial or complete segregation of solid particles at certain operating conditions. In this study, the segregation and dispersion of binary particle species of the same size but different densities in liquid fluidised beds have been investigated based on the analysis of computational fluid dynamics - discrete element method (CFD-DEM) simulation results.The vertical fluid drag force acting on the particles was found to be responsible for the particle segregation. The mechanisms governing the particle dispersion strongly depended upon the solid-liquid two-phase flow regime, which transited from pseudo-homogeneous to heterogeneous when the superficial liquid velocity reached a certain value. In the homogeneous or pseudo-homogeneous flow regime (Rep=40, ¿L, ave=0.74), particle collisions acted as the main mechanism that drove the dispersion of particles. However, after the system became heterogeneous, the magnitude of the vertical collision force decreased towards zero and correspondingly, the magnitude of the vertical fluid drag force was approaching that of the particle net weight force as the superficial liquid velocity increased. Therefore, in the heterogeneous flow regime (Rep>40, ¿L, ave>0.74), the local turbulence of the fluid flow and particle collisions (if there were any) were found to be the main mechanisms that drove the dispersion of particles in all directions. The dispersion coefficient of individual particles varied significantly throughout the system in the heterogeneous flow regime. The simulation results reasonably agreed with the experimental data and the prediction results by existing correlations.

The development of lignite-char-supported metal oxide catalyst for reduction of nitric oxide (NO) is investigated in this paper. The characteristics of NO reduction by copper and iron oxide catalysts supported on activated lignite chars (ALC) was studied using a fixed-bed reactor at 300 °C. The results showed that the impregnation of Cu on ALC resulted in higher catalytic reactivity during NO reduction compared with that of Fe. Chemisorption of O2 and NO on Cu/ALC catalyst was found to play an important role in denitrification. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses showed that chemically adsorbed oxygen facilitates the formation of C(O) complex and oxidation of Cu0 to Cu+ for Cu/ALC catalyst. The C(O) intermediates and C*production formed due to the fact that C/O2 reaction promoted the reduction of NO. It is suggested that the catalytic reaction of NO in this case comprised of C/O2 reaction, C(O)/NO reaction and formation of N2 and CO2. Cu seemed to have significantly promoted the C(O) formation and CO oxidation compared with Fe. The catalytic reactivity of Cu species for C(O) formation and CO oxidation followed the order of Cu0 > Cu+ > Cu2 +. Fe3O4 was believed to be the active phase in Fe catalyst. The oxygen and char-supported metal catalysts significantly promoted C/NO reaction, and therefore may lead to a lower operation temperature of NOx removal.

Polychlorinated dibenzothiophene (PCDT) and polychlorinated thianthrene (PCTA) are sulfur analogues of dioxins, such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F). In this work, we present a detailed mechanistic and kinetic analysis of PCDT and PCTA formation from the combustion of 2,4,5-trichlorothiophenol. It is shown that the formation of these persistent organic pollutants is more favourable, both kinetically and thermodynamically, than their analogous dioxin counterparts. This is rationalised in terms of the different influences of the S¿H and O¿H moieties in the 2,4,5-trichlorothiophenol and 2,4,5-trichlorophenol precursors. Kinetic parameters also indicate that the yield of PCDT should exceed that of PCDD. Finally, we demonstrate here that the degree and pattern of chlorination on the 2,4,5-trichlorothiophenol precursor leads to subtle thermodynamic and kinetic changes to the PCDT/PCTA formation mechanisms. [Figure not available: see fulltext.]

This article presents a numerical study of the explosive wave propagations from a 40¿cm long and 10.8¿cm diameter cylinder to smaller 1.7¿m and 2.6¿m long cylinders with 36¿mm diameters. Initially, the 40¿cm long cylinder was filled with 4% propane-air mixtures and ignited with a 1¿kJ sparking energy until the maximum temperature near the ignition source reached 2400/3000¿K. In the study, a 3D numerical model was established by combining compressible four-step reduced propane oxidation reaction kinetics with the k-¿ shear-stress transport (SST) turbulent model. In order to resolve the thin detonation wave front, a dynamically refined mesh near the high pressure gradient was adopted. The pressure gradient profiles, velocity magnitude contours, temperature contours and compressible wave propagation speeds across the tubes were then predicted using this 3D model.

The determination of internal building air temperature has an impact on the design and performance of a building in measuring thermal comfort and heating and cooling loads. There is software to assist with measuring internal building air temperature such as Autodesk CFD simulation. However, the use of Autodesk CFD simulation for the analysis appears to have an issue with simulations extending over a long term (i.e. months or years) as the internal air temperature in a building keeps rising with time. This paper addresses the challenges encountered using CFD simulation in the modelling of a building for long term performance. A new method to overcome the issue of the progressive rising of internal air temperature using two external air boundaries, one for the external volume (sky boundary) and the other surrounding the building, is suggested in the paper.

This review examines existing knowledge on the genesis and flame acceleration of explosions from methane-air mixtures. Explosion phases including deflagration and detonation and the transition from deflagration to detonation have been discussed. The influence of various obstacles and geometries on explosions in an underground mine and duct have been examined. The discussion, presented here, leads the readers to understand the considerations which must be accounted for in order to obviate and/or mitigate any accidental explosion originating from methane-air systems.

The void fraction of computational cells in numerical simulations of particulate flows using computational fluid dynamics-discrete element method (CFD-DEM) is often directly (or crudely) calculated assuming that the entire body of a particle lies in the cell at which the particle centroid resides. This direct method is most inexpensive but inaccurate and may lead to simulation instabilities. In this study, a modified version of the direct method has been proposed. In this method, referred to as the particle meshing method (PMM), the particle is meshed and the solid volume in a fluid cell is calculated by adding up the particle mesh volume with the basic working principle being the same as that of the direct method. As a result, the PMM inherits the simplicity and hence the computational advantage from the direct method, whilst allowing for duplicating the particle shape and accurate accounting of particle volume in each fluid cell. The numerical simulation characteristics of PMM including numerical stability, minimum particle grid number, prediction accuracy, and computational efficiency have been examined. The results showed that for a specific cell-to-particle size ratio, there was a minimum particle grid number required to reach the stable simulation. A formula of estimating the minimum particle grid number was derived and discussed. Typically, a particle grid number of about 5 times the minimum number was suggested to achieve the best computational efficiency, which was comparable or even higher than that of simulations using the analytical approach. PMM also exhibited the potential to be applied for complex computational domain geometries and irregular shaped particles.

This paper conducts a numerical study of detonation wave propagations in 30 m and 73 m long straight/varying angle bending detonation tubes with inner diameters of 0.5 m and 1.05 m, respectively, which are filled with varying stoichiometric methane-air mixtures. In the study a 3D numerical model was established by combining a compressible one-step global reaction hot model with the k-¿ shear-stress transport (SST) turbulent model. In order to resolve the thin detonation wave front, a dynamically refined mesh near the high pressure gradient is adopted. The initial conditions of the model are obtained from the 1D detonation model. The present model was first verified by comparing the numerical results against the published measurements. The pressure distributions and detonation wave speeds across the tubes and bends were then predicted by using this 3D model.

Deflagration explosions of coal dust clouds and flammable gases are a major safety concern in coal mining industry. Accidental fire and explosion caused by coal dust cloud can impose substantial losses and damages to people and properties in underground coal mines. Hybrid mixtures of methane and coal dust have the potential to reduce the minimum activation energy of a combustion reaction. In this study the Minimum Explosion Concentration (MEC), Over Pressure Rise (OPR), deflagration index for gas and dust hybrid mixtures (Kst) and explosive region of hybrid fuel mixtures present in Ventilation Air Methane (VAM) were investigated. Experiments were carried out according to the ASTM E1226-12 guideline utilising a 20 L spherical shape apparatus specifically designed for this purpose. Results: obtained from this study have shown that the presence of methane significantly affects explosion characteristics of coal dust clouds. Dilute concentrations of methane, 0.75-1.25%, resulted in coal dust clouds OPR increasing from 0.3 bar to 2.2 bar and boosting the Kst value from 10 bar m s-1 to 25 bar m s-1. The explosion characteristics were also affected by the ignitors' energy; for instance, for a coal dust cloud concentration of 50 g m-3 the OPR recorded was 0.09 bar when a 1 kJ chemical ignitor was used, while, 0.75 bar (OPR) was recorded when a 10 kJ chemical ignitor was used.For the first time, new explosion regions were identified for diluted methane-coal dust cloud mixtures when using 1, 5 and 10 kJ ignitors. Finally, the Le-Chatelier mixing rule was modified to predict the lower explosion limit of methane-coal dust cloud hybrid mixtures considering the energy of the ignitors.

We combine combustion experiments and density functional theory (DFT) calculations to investigate the formation of chlorobenzenes from oxidative thermal decomposition of 1,3-dichloropropene. Mono- to hexa-chlorobenzenes are observed between 800 and 1150. K, and the extent of chlorination was proportional to the combustion temperature. Higher chlorinated congeners of chlorobenzene (tetra-, penta-, hexa-chlorobenzene) are only observed in trace amounts between 950 and 1050. K. DFT calculations indicate that cyclisation of chlorinated hexatrienes proceeds via open-shell radical pathways. These species represent key components in the formation mechanism of chlorinated polyaromatic hydrocarbons. Results presented herein should provide better understanding of the evolution of soot from combustion/pyrolysis of short chlorinated alkenes.

Abstract Methanol economy is considered as an alternative to hydrogen economy due to the better handling and storage characteristics of methanol fuel than liquid hydrogen. This paper is concerned about a comprehensive equilibrium thermodynamic analysis carried out on methanol production via an innovative Chemical Looping Carbon Arrestor/Reforming process being developed at the University of Newcastle in order to reduce both energy consumption and carbon emissions. The detailed simulation revealed thermodynamic limitations within the Chemical Looping Carbon Reforming process however on the other hand it also confirmed that the new concept is a low energy requirement and low emission option compared to other methanol production technologies. Specifically, the mass and energy balance study showed that the Chemical Looping Carbon Reforming process typically consumes approximately 0.76-0.77 mole methane, 0.25-0.27 mole carbon dioxide, 0.49-0.50 mole water, and 0.51 mole iron oxide (in a chemical looping manner) per mole of methanol production. Moreover, the energy efficiency of Chemical Looping Carbon Reforming process was found to be ~64-70% and its emission profile was found as low as 0.14 mole carbon dioxide per mole of methanol, which is about 82-88% less than the conventional methanol production process and well below the emission levels of other emerging methanol production technologies.

Three Australian sub-bituminous coals were treated with three different ionic liquids (ILs) at a temperature of 100 °C. The thermal behaviour of these treated coals were compared against raw coals via pyrolysis experiments in a Thermogravimetric Analyser. Morphological comparisons were also made via Scanning Electron Microscopy. Among the studied ILs, 1-butyl-3-methylimidazolium chloride [Bmim][Cl] was found to perform the most consistently in being able to alter the thermal and morphological properties of most of the coals used. It is posited that this may be due to the large difference in charge density between the delocalised charge of the large bmim cation and the chloride anion which allows this IL to disrupt the cross linked network of coal. It was also found that the interactions of the ionic liquids are coal specific, for instance none of the ionic liquids were able to change the thermal properties of coal A. Moreover, the results indicated that among the studied coals, coal R showed the highest mass loss during pyrolysis in TGA and coal C showed the highest amount of swelling and fragmentation in SEM images. The results displayed in this study indicate that the potential for ionic liquids to be used as pre-treatments in coal liquefaction is promising. Crown

The larger reactor volume, additional oxygen polishing unit, and carbon stripper for the separation of oxygen carriers and ash in the chemical looping combustion (CLC) and/or chemical looping oxygen uncoupling (CLOU) processes for solid fuels are anticipated not only to incur operational complexity but also to increase the capital and operating costs. As an alternative, this paper proposes a novel hybrid process, called "Chemical Looping Oxy Combustor (CLOC)". This novel process provides an integration of chemical looping air separation (CLAS) with fluidized bed oxy-fuel combustion and is expected to eliminate the need for an additional oxygen polishing unit and carbon stripper. It can be retrofitted to any existing coal circulating fluidized bed (CFB) at low cost. The other advantages of CLOC includes less solid handling issues, flexibility in handling low-grade coal with high moisture, no/less contamination of oxygen carriers, no/less slip of CO2/SOx in an air reactor, low energy penalty, etc. Also, in the CLOC process, coal combustion will occur in a separate fluidized bed combustor with relatively faster kinetics, because of the availability of high oxygen concentration (i.e., ~25-28 vol-"%), which eliminates the need for a larger fuel reactor volume. In the current paper, thermodynamic simulations of CLOC process using Cu-, Mn-, and Co-based metal oxide oxygen carriers were performed. Their performances were also compared against the conventional air-firing and oxy-firing technologies, e.g., oxy-fuel combustion integrated with cryogenic air separation unit (CASU) and CLOU. It was identified that the CLOC process needs external heat for reduction reactor provided by either direct or indirect methane combustion. Moreover, a maximum plant thermal efficiency was achieved for CLOC using Cu-based oxygen carrier. The energy penalty of the CLOC process, compared with the air-firing base case, was found to be ~2%-3%, which is ~4-5 times smaller than those of the CASU cases and only half of that of the CLOU process, indicating that CLOC offers a promising option for the combustion of solid fuels.

A techno-economic analysis was carried out to assess the oxy-fuel conversion of eight major coal-fired power plants in the state of NSW, Australia. For this purpose, several alternative retrofit configurations, differing only in the air separation unit (ASU) but otherwise identical, were considered. More specifically, three types of oxygen plants were studied: a cryogenic-based air separation unit and integrated chemical looping air separation units using steam (ICLAS[S]) and recycled flue gas (ICLAS[FG]) as the reduction medium. The main objective of the techno-economic analysis was to determine if the economic viability of oxy-fuel operations could be enhanced by incorporating ICLAS technology. The results show that the normalized oxygen demand for the NSW fleet of coal-fired power plants was about 450-550 m3/MWh, with Bayswater having the lowest normalized oxygen demand and Munmorah having the highest one. Moreover, it was found that by replacing a cryogenic-based ASU with an ICLAS unit, the average reduction in the ASU power demand was up to 47% and 76%, respectively, for ICLAS[S] and ICLAS[FG]. Similarly, the average thermal efficiency penalty associated with the cryogenic and the ICLAS[S] and ICLAS[FG] units was found to be about 9.5%, 7.5%, and 5%, respectively, indicating that the ICLAS[FG] unit is the most energy efficient option for oxy-fuel plants. Economic analyses suggest that a retrofit cost reduction of about 32% can be achieved by incorporating an ICLAS[FG] unit. On average, the levelized cost of electricity associated with the cryogenic and the ICLAS[S] and ICLAS[FG] units for the NSW fleet of coal-fired power plants was found to be about $118/MWh, $105/MWh, and $95/MWh, respectively.

Statistical analyses are important for real-world validation of theoretical model predictions. In this article, a statistical analysis of real data shows empirically how thermal resistance, thermal mass, building design, season and external air temperature collectively affect indoor air temperature. A simple, four-point, diurnal, temperature-by-time profile is used to summarise daily thermal performance and is used as the response variable for the analysis of performance. The findings from the statistical analysis imply that, at least for moderate climates, the best performing construction/design will be one in which insulation and thermal mass arrangements can be dynamically altered to suit weather and season.

This paper describes an experimental investigation of the thermal performance of four Australian domestic walling systems (cavity brick, insulated cavity brick, insulated brick veneer and insulated reverse brick veneer) having various combinations of thermal insulation and of thermal mass location within the wall. This experimental analysis extends further the previous studies of the benefits of thermal mass on the overall thermal performance of building enclosures (Gregory et al. 2008, Luo at al. 2008, Alashaary et al. 2009). The comparison is based on the time required to maintain thermal comfort for free-floating internal conditions. The results clearly show that internal comfort levels are influenced by both the thermal resistance of the walls as well as the extent and location of the thermal mass, with neither parameter being the sole predictor. The best thermal performance is therefore obtained by an appropriate combination of thermal mass and resistance, rather than focussing on the overall wall thermal resistance (R-value) alone. A new approach of density temperature plots for comparison of temperature variation is also used in the assessment of module thermal performance.

This paper describes the development of a novel stone dust looping process that relates to the removal of ventilation air methane using stone dust. The working principle behind the stone dust looping process is incredibly simple which involves the catalytic oxidation of methane followed by carbonation and calcination reactions. In the current work, laboratory scale fluidized bed experiments and process simulations were conducted to evaluate the feasibility of the stone dust looping process. The experimental work concluded that oxidation of ventilation air methane in the stone dust looping process can be successfully achieved at temperatures between 500 and 650 °C. The experimental results indicated that oxidation of methane was found to increase at higher temperatures while carbon dioxide capture efficiency showed a declining trend with increasing temperature. Furthermore, higher methane conversion and optimum (thermodynamic) carbon dioxide capture efficiency were observed for lower ventilation air methane flow rates and higher bed inventory. The concentration of methane in ventilation air methane and stone dust particle size did not have a significant effect on methane conversion or carbon dioxide capture. Also, comparison with synthetically prepared CuO and Fe<inf>2</inf>O<inf>3</inf> catalysts has been made with CaO for VAM oxidation. CaO was found to be comparable to Fe<inf>2</inf>O<inf>3</inf> and superior to CuO. From the process simulations, it was concluded that thermal energy generation in the carbonator was increased with higher methane and carbon dioxide concentrations. However, at the same time for higher methane and carbon dioxide concentrations, a greater CaO flux was required in the carbonator and hence a larger amount of goaf gas was required for the calcination reaction. The higher thermal energy generation in the carbonator was expected to improve the autothermicity of the stone dust looping process at concentrations of methane in the ventilation stream < 0.2 vol.% (thermodynamic limit).

Abstract Greenhouses typically employ conventional burner systems to suffice heat and carbon dioxide required for plant growth. The energy requirement and carbon dioxide emissions from fossil fuel burner are generally high. As an alternative, this paper describes a novel greenhouse calcium looping process which is expected to decrease the energy requirements and associated carbon dioxide emissions. The conceptual design of greenhouse calcium looping process is carried out in the ASPEN Plus v 7.3 simulator. In a greenhouse calcium looping process, the calcination reaction is considered to take place during day time in order to provide the required optimum carbon dioxide between 1000 and 2000 ppm, while the carbonation reaction is occurred during night time to provide required heat. The process simulations carried out in ASPEN indicates that greenhouse calcium looping process theoretically attributes to zero emission of carbon dioxide. Moreover, in a scenario modelling study compared to the conventional natural gas burner system, the heat duty requirements in the greenhouse calcium looping process were found to reduce by as high as 72%.

In a chemical looping combustor (CLC) system, the solid circulation rate (SCR) is a key parameter that determines the design, operating conditions and the overall efficiency of the system. In the present work, the gas-solid flow of a CLC cold flow model (10kWth) has been simulated by the computational fluid dynamics-discrete element method (CFD-DEM). The results showed that the SCR at different locations of the system fluctuates with time with different amplitude, and the variation of SCR is periodically stable. The turbulent gas-solid flow regime in the air reactor was found to be the main mechanism driving the fluctuation of SCR and determined the fluctuation frequency and amplitude. The SCR increased with the flow rates of air/fuel reactors and loop seals, and the total solid inventory. Changes in operating conditions directly induced the change in the mass of solids that were entrained into the riser from the air reactor and how fast the solids were transported therein. A correlation was subsequently proposed to describe the SCR as a function of solid hold-up and gas flow velocity in the riser. The particle residence time decreased in a power law as the SCR increased. Reasonable agreements were obtained between simulations and experiments in terms of solid distribution, gas-solid flow patterns, pressure drop profiles and SCR.

We present a quantum chemical investigation of benzofuran and cholorobenzofuran formation mechanisms during the combustion of 1,3-dichloropropene. Density functional theory and Gaussian-n thermochemical methods are used to propose detailed mechanistic reaction pathways. These calculations indicate that oxidation of phenylvinyl radical intermediates and subsequent ring closure are key mechanistic pathways in the formation of benzofuran and chlorobenzofuran. Thermochemical and kinetic parameters presented herein will assist in further elucidation of dioxin formation mechanisms from thermolyses of hydrocarbon moieties.

Two Australian thermal coals were treated with four different ionic liquids (ILs) at temperatures as low as 100 °C. The ILs used were 1-butylpyridinium chloride ([Bpyd][Cl]), 1-ethyl-3-methylimidazolium dicyanamide ([Emim][DCM]), 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]), and 1-butyl-3-methylimidazolium tricyanomethanide ([Bmim][TCM]). Visual comparisons were made between the raw and IL-treated coals via optical microscopy. Changes in thermal behavior of these treated coals were compared against raw coals via pyrolysis experiments in a thermogravimetric analyzer (TGA). Changes in functional group composition in the treated coals were probed via Fourier transform infrared (FTIR) spectroscopy. The recovered ILs were also analyzed via FTIR and nuclear magnetic resonance (NMR) spectroscopies to observe any changes after recovery. Low-temperature IL treatment of each of the coals resulted in fragmentation and fracturing, reducing the average particle size. An increase in mass loss in the treated coals was also observed when compared to each raw coal, indicating an increase in lower molecular weight fragments after treatment. This was corroborated by a large increase in aliphatic hydrocarbons being observed in the treated coals, along with a decrease in oxygenated functional groups and mineral matter in one coal. The recovered ILs were shown to be unchanged by this treatment process, indicating their potential recyclability. These results indicate the potential for ILs to be implemented as solvent treatments for coal conversion processes.

The success of many industrial processes largely depends on the structural characteristics of aggregates. In intensive aerobic digestion process for wastewater treatment applications, the structural characteristics namely aggregate shape, size and therefore the aggregate surface area strongly influence the transfer of dissolved oxygen from the aeration process to aggregates of harmful contaminants/microorganisms. The aim of this study was to apply Discrete Element Modelling (DEM) techniques to the aggregation of suspended particles (microorganisms) to quantify the available surface area for convection and diffusion as a function of particles number concentration and surface charge. The simulation inputs included particle and fluid characteristics such as particle size and density, solid concentration, suspension pH and ionic strength. A post processing method based on the Go-chess concept was developed to quantify the surface area of aggregate structure. The simulation results showed that whilst an increase in connection points increases the total surface area of the aggregate, this does not necessarily translate into an increase in the surface area available for oxygen transfer as combinations of open and close pores are formed. Aggregate surface area was directly determined by aggregate structural characteristics, and increased rapidly when the coordination number was below 3.5 and the fractal dimension was less than 1.5. A correlation for prediction of aggregate external surface area was also proposed as a function of aggregate structural characteristics in terms of fractal dimension and coordination number.

In chemical looping combustion systems, accurate measurement of the solid circulation rate (SCR) is crucial for optimising the system performance. Conventionally, the SCR is predicted using the riser total pressure drop leading to an overestimation of up to 70%. In this work, a model has been proposed for the SCR prediction using the pressure drop at the top section of the riser. The height of this top section was determined by the riser gas-solid flow characteristics, namely, the axial solid holdup profile and lateral solid flux profile. A kinematic model was developed to predict the axial solid holdup profile and the reduced solid flux model developed by Rhodes et al. (1992) was employed to predict the mass fraction of upwards flowing solids. The prediction results of the proposed model were validated against the experimental data obtained in this work and those reported in the literature, where the prediction accuracy of SCR was significantly improved (by up to 60%) with a deviation of around 15%.

The correct calculation of cell void fraction is pivotal in accurate simulation of two-phase flows using a computational fluid dynamics-discrete element method (CFD-DEM) approach. Two classical approaches for void fraction calculations (i.e., particle centroid method or PCM and analytical approach) were examined, and the accuracy of these methodologies in predicting the particle-fluid flow characteristics of bubbling fluidized beds was investigated. It was found that there is a critical cell size (3.82 particle diameters) beyond which the PCM can achieve the same numerical stability and prediction accuracy as those of the analytical approach. There is also a critical cell size (1/19.3 domain size) below which meso-scale flow structures are resolved. Moreover, a lower limit of cell size (1.63 particle diameters) was identified to satisfy the assumptions of CFD-DEM governing equations. A reference map for selecting the ideal computational cell size and the suitable approach for void fraction calculation was subsequently developed. © 2014 American Institute of Chemical Engineers.

In a liquid fluidised bed system, the motion of each phase is governed by fluid-particle and particle-particle interactions. The particle-particle collisions can significantly affect the motion of individual particles and hence the solid-liquid two phase flow characteristics. In the current work, computational fluid dynamics-discrete element method (CFD-DEM) simulations of a dense foreign particle introduced in a monodispersed solid-liquid fluidised bed (SLFB) have been carried out. The fluidisation hydrodynamics of SLFB, settling behaviour of the foreign particle, fluid-particle interactions, and particle-particle collision behaviour have been investigated. Experiments including particle classification velocity measurements and fluid turbulence characterisation by particle image velocimetry (PIV) were conducted for the validation of prediction results. Compared to those predicted by empirical correlations, the particle classification velocity predicted by CFD-DEM provided the best agreement with the experimental data (less than 10% deviation). The particle collision frequency increased monotonically with the solid fraction. The dimensionless collision frequency obtained by CFD-DEM excellently fit the data line predicted by the kinetic theory for granular flow (KTGF). The particle collision frequency increased with the particle size ratio (dP2/dP1) and became independent of the foreign particle size for high solid fractions when the fluidised particle size was kept constant. The magnitude of collision force was 10-50 times greater than that of gravitational force and maximally 9 times greater than that of drag force. A correlation describing the collision force as a function of bed voidage was developed for Stp>65 and dP2/dP1=2. A maximum deviation of less than 20% was obtained when the correlation was used for the prediction of particle collision force. © 2014 Elsevier Ltd.

The interactions between vitrinite and inertinite-rich coals and the ionic liquid butylimidazolium chloride ([bmim][Cl]) heated to 100 C have been characterised. Differences in the interactions of coal macerals and ionic liquids have been identified. [bmim][Cl] is able to dissolve 22 wt% of a high-vitrinite coal fraction compared to 14 wt% of a high-inertinite coal fraction. The vitrinite-rich coal fraction tends to swell to a greater extent compared to the inertinite-rich coal fraction, which was fractured and fragmented rather than swelled. © 2013 Published by Elsevier Ltd. All rights reserved.

The loaded salts (NaCl, KCl, MgCl2, and CaCl2) have significantly different influence on the contribution of dehydration and depolymerization reactions to the decomposition of sugar structures during cellulose fast pyrolysis at 325 °C. The structures of salt-loaded celluloses already become cross-linked during heating-up period, largely due to the enhanced dehydration reactions catalyzed by inorganic species. As stronger Lewis acids, the alkaline earth metal ions (Mg2+ and Ca2+) are more effective than the alkali metal ions (Na+ and K+) to catalyze the dehydration reactions of sugar structures, leading to the formation of more cross-linked cellulose for the alkaline earth metal chloride-loaded celluloses. As a result, the majority of Mg and Ca are transformed into water-insoluble forms during the heating-up period, largely reducing the catalytic effects of these species on the dehydration of sugar structures during the subsequent isothermal pyrolysis. Rather, the dehydration of non-sugar structures is enhanced because the catalytic species are already bonded with non-sugar structures. In contrast, the dehydration of sugar structures during the heating-up period is less significant for the NaCl-loaded and KCl-loaded celluloses. The majority of Na and K are water-soluble after the heating-up period so that the dehydration of sugar structures is further enhanced during isothermal pyrolysis. The loaded salts have less influence on the depolymerization reactions. The contribution of depolymerization reactions to sugar conversion is relatively small during the heating-up stage, but increases substantially during isothermal pyrolysis. © 2014 Elsevier Ltd. All rights reserved.

This experimental study was conducted to investigate the rate of flame spread over an inclined porous solid (sand) wetted with finite quantities of fuel (iso-propanol). The study comprised experiments that were conducted over 15° and 30° inclined beds with depths ranging from 13.3 mm to 39.9 mm and consisting of average sand particle diameters ranging from 0.5 mm to 5 mm under quiescent, assisted and opposed airflow conditions. Analysis of the resulting data indicate that the rate of flame spread is significantly decreased by increasing the bed inclination angle or the airflow velocity and is applicable for both assisted and opposed directions. Furthermore, the rate of flame spread is decreased to the minimum value and actually ceased halfway along the bed with a 30° inclination angle. This behaviour was observed mainly for beds containing coarse sand particles. The rate of flame spread was higher for thinner beds rather coarse beds under any given airflow conditions. Finally, the rate of flame spread in upward direction was relatively quicker in comparison with downward direction counterpart. © 2014 Elsevier Ltd. All rights reserved.

Coke oven gas cleaning is an important issue in China, where it can be a source of liquefied natural gas (LNG) through the methanation process. In this study, char-supported sorbents were prepared by loading iron, cerium, and molybdenum into a Chinese lignite through co-precipitation, and the sorbents were used for dry desulfurization of coke oven gases. Desulfurization efficiency of the sorbents was examined using a fixed-bed reactor in a temperature range of 473-673 K using a simulated coke oven gas. A gas chromatograph equipped with both a flame photometric detector (FPD) and a thermal conductivity detector (TCD) was used to analyze gas composition, while X-ray diffraction and scanning electron microscopy were used to examine chemical phases and the dispersion pattern of the active constitutes of the sorbents. The experimental results showed that the highest desulfurization efficiency and sulfur capacity appeared at 673 K. The reactivity of the nanosized active components in the char increased with increasing the desulfurization temperature in the temperature range of 473-673 K. In the case of Fe-Mo-impregnated sorbents, Fe and Mo combined together to form complex Fe-Mo oxide phases. The introduction of Mo in the sorbent is found to greatly increase the sulfur capacity and desulfurization efficiency of the Fe sorbent supported on activated chars. The addition of Ce leads to noticeable improvement of the performance of Fe sorbent during sulfidation. The mechanisms and factors influencing the sulfidation reactions have also been discussed. © 2014 American Chemical Society.

Release of fugitive methane (CH) emissions from ventilation air in coal mines is a major source of greenhouse gas (GHG) emissions. Approximately 64% of methane emissions in coal mine operations are the result of VAM (i.e. ventilation air methane) which is difficult for use as a source of energy. A novel ancillary utilization of VAM was thereby proposed. In this proposal, the VAM was utilized instead of air as a feedstock to a chemical looping combustion (CLC) process of coal. In this case, FeO/FeO particles were shuttled between two interconnected reactors for combustion of syngas produced by an imbedded coal gasifier. The effect of VAM flow rate and methane concentration on the performance of CLC was analyzed thermodynamically using Aspen Plus software. Results indicated that the variations of air reactor temperature with VAM flow rate and methane concentration can be minimized as expected. The effect of temperature and inlet methane concentration on the conversion of CH was examined experimentally in a fixed bed reactor with the presence of particles of FeO/AlO. Not surprisingly, the reaction temperature put a significant influence on the conversion of CH. The conversion started at the temperature about 300 °C and the temperature to achieve full conversion was around 500 °C while the temperature in empty reactor between 665 °C and 840 °C. This is due to the catalytic effect of oxygen carriers (i.e. FeO/AlO) on the conversion of methane. Moreover, it was observed that the methane conversion rate decreased with the increase in inlet methane concentration while increasing with FeO loading content. © 2014 Elsevier Ltd. All rights reserved.

In this study the transition from homogeneous to heterogeneous flow in a solid-liquid fluidized bed (SLFB) is examined both experimentally and numerically. The experimental apparatus comprised a refractive index-matched SLFB, comprising 5. mm diameter borosilicate glass and sodium iodine solution, which allowed for both instantaneous particle image velocimetry of the liquid flow field and solids hold-up measurements to be undertaken for superficial liquid velocities in the range of 0.06-0.22. m/s. The motion of individual, spherical steel balls (with diameters 6, 7, 8, 9. mm) was then tracked as it settled through the fluidized bed for differing superficial liquid velocities. It was observed that, for all the steel balls covered in this work, there was a change in slope in their respective classification velocity curves at a superficial liquid velocity of 0.08. m/s. This value was very close to the critical velocity of 0.085. m/s predicted from 1-D linear stability analysis; and therefore deemed to be the critical condition that marked the transition from homogeneous to non-homogenous flow. It is proposed that the change in slope of the classification velocity curve is due to the encounter of the settling foreign particles with liquid bubbles whose presence marks the onset of heterogeneous flow. Additional computational analysis, involving both Eulerian-Eulerian (E-E) and Eulerian-Lagrangian (E-L) approaches, is used to confirm the presence of liquid bubbles at a critical liquid hold-up of 0.54, which corresponds to that predicted from 1-D linear stability analysis. In summary, the study has highlighted that experimentally the transition condition for a SLFB can be obtained simply by observing the behavior of the classification velocity of a single foreign particle at different superficial liquid velocities. This transition condition was found to agree with the 1D linear stability criterion, Eulerian-Eulerian CFD (3D) and Eulerian-Lagrangian DEM (3D) approaches. © 2014 Elsevier B.V.

Integrated Chemical Looping Air Separation (ICLAS) offers an energy efficient and cost effective option for large-scale oxygen generation in oxy-fuel type power plants. Oxygen production in the ICLAS is achieved by reduction of oxidised metal oxides in an environment of steam/recycled flue gas (CO2-rich) using a dedicated reduction reactor. This paper provides the results of a thermodynamic investigation into the effect of flue gas impurities on the reduction of three metal oxide oxygen carriers (Cu, Mn and Co oxides) under conditions pertinent to an oxy-fuel coal-fired power plant. Relevant calculations were carried out using the Fact-sage 6.1 thermodynamic equilibrium calculation software package. Different gas streams, namely crude/wet, dry, pure CO2 and steam were considered in the simulations together with the additional hypothetical impure flue gas stream having larger concentrations of CO, SO2 and NO. Effects of SO2, NO, CO and O2 contents of the flue gas on oxygen carrier conversion and oxygen decoupling process were investigated in detail. It was established that the successful reduction of metal oxides in the presence of flue gas impurities can only be achieved at higher temperatures due to increased partial pressure of O2 and the formation of metal sulphates at temperatures less than 800-900 °C. This may increase the operating and capital costs of the CLAS based oxygen production. © 2012 Elsevier Ltd. All rights reserved.

Performance of chemical looping combustion processes can be improved drastically by enhancing the overall redox characteristics of the system through the use of binary mixtures of oxygen carriers. However, binary mixtures of oxygen carrier particles are often found to differ in both size and density and therefore have the tendency to segregate under certain operating conditions.In this work, a numerical study was conducted to investigate the mixing and segregation behaviour of binary mixtures of particles with different sizes and densities in a bubbling fluidized bed under conditions pertinent to the fuel reactor of a cold flow model (i.e. a non-reacting replica) of a 10kWth chemical looping combustor. The motion of particles was tracked individually by discrete element model (DEM), whilst the gas flow was modelled by computational fluid dynamics (CFD). Gas-particle interactions were considered by a two-way coupling method. Further, a modified version of Lacey's method was developed to calculate the mixing index, taking into account both the heterogeneity of solids spatial distribution and particle size differences.Results showed that the modified Lacey's method provided very consistent and stable mixing indexes, proving to be effective for an in-situ quantitative description of mixing. It was also found that as the size ratio of the binary mixture of particles reduced, the mixing index increased indicating better mixing conditions. The agreement between the DEM/CFD model predictions and the experimental data was found to be satisfactory. The optimum conditions for mixing of binary mixtures appeared to be a function of bubble size, bubble rising rate and bubbling dynamics (e.g., splitting and coalescence). Application of the DEM/CFD model for prediction of layer inversion phenomenon in gas-solid fluidized beds was also demonstrated. © 2012 Elsevier B.V.

This study experimentally investigates the application of a solid-liquid micro-fluidised bed as a micro-mixing device. The experiments were performed in a borosilicate capillary tube with an internal diameter of 1.2. mm (i.e. near the upper-limit dimension of a micro-fluidic system) using borosilicate particles with a mean diameter of 98 µm. Refractive index matching technique using sodium iodide solution was employed to achieve a transparent fluidised bed. Mixing performance of the micro-fluidised bed in terms of mixing time was investigated using a dye dilution technique. Experiments were carried out in the creeping flow regime at Reynolds numbers ranging between 0.27 and 0.72. It was demonstrated that the micro-fluidised bed mixing time sharply decreases as the Reynolds number increases. That is because at relatively high Reynolds numbers, the particle oscillation is stronger creating larger disturbances in the flow. The energy dissipation rate in micro fluidised bed was estimated to be four orders of magnitude less than other passive micro mixers which operate in the turbulent regime. It was also demonstrated that the ratio of mixing time and the energy dissipation rate for fluidised bed micro-mixer was comparable to K-M, Tangential IMTEK, and interdigital micro-mixers. However, the fluidised bed micro-mixer was found to operate at much lower Reynolds numbers compared to other passive mixers, with a mixing time of the order of few seconds. © 2013 The Institution of Chemical Engineers.

Fires caused by accidental spillage of flammable liquids have been a major safety concern in industries and urban areas. There has been a recent surge of interest in the research concerning the combustion and flame spread over an inert porous media soaked with flammable liquid. This interest has been driven by the need to better understand fire and its behaviour under these conditions and improve the relevant fire safety and prevention technologies. A review of key studies in this subject area has been conducted and summarised, focussing mainly on the theory plus a notable experimental findings about combustion and the flame spread phenomena of fuel-soaked porous media. The review covers topics such as flame spread behaviour, physical flame propagation aspects, heat transfer, temperature distribution; and fuel consumption over inert porous media. The review concludes with some practical safety and environmental considerations for decontamination of land soaked with flammable liquid. © 2013 Elsevier Ltd. All rights reserved.

An experimental investigation was conducted to explore the rate of flame spread over an unconsolidated porous bed of sand wetted with 2-propanol under a range of operating conditions. Video cinematography was employed to determine the rate of flame spread and characterise the combustion behaviour of the system. The rate of flame spread strongly correlated with: (i) the ratio of fuel volume to the weight of the sand bed, referred to as FR, and (ii) the flame initiation delay, referred to as FID. The rates of flame spread associated with no initiation delay cases were found to rise with increasing FR while for cases associated with any given flame initiation delay the rate of flame spread was found to decrease with increasing FR. In addition, the rate of change in flame spread was observed to be different for beds containing finer particles in comparison to those containing coarser ones. © 2013 Elsevier Ltd.

In a typical chemical looping combustion process, the oxygen for fuel combustion is supplied by circulating metal based oxygen carriers between two interconnected fluidised bed reactors. The redox characteristics of oxygen carriers and hence the overall performance of the process can be significantly improved by utilising binary mixtures of oxygen carrier particles. The full potential of such multi-species particle systems however can be only realised when particles segregation is minimised. This study is concerned with gaining an understanding of the mixing and segregation behaviour of binary mixtures of oxygen carrier particles with different sizes and densities in a cold flow model representing a 10. kWth chemical looping combustor. The hydrodynamics of such systems were investigated and compared with a typical chemical looping combustion process where single species are used. This was followed by investigating the solids mixing and segregation behaviour in terms of segregation intensity and species weight percentage at each reactor as a function of operating parameters. It was shown that increasing the total solid inventory, particle terminal velocity ratio, composition, and air reactor superficial velocity increases the riser pressure, solid circulation rates, and riser solid holdup. Mixing and segregation regimes of the fuel reactor and the component segregation between the two reactors were also mapped. The results showed that, for mixtures of species with low terminal velocity to high terminal velocity ratios of greater than 0.7, a good mixing in the fuel reactor can be achieved by maintaining the superficial gas velocity to the mixture minimum fluidisation velocity ratio above 5. For the tested conditions, the component segregation between the two reactors was avoided by maintaining the ratio of the riser superficial velocity to the terminal velocity of the species with a high terminal velocity between 1.25 and 2. © 2013 Elsevier B.V.