Emeritus Professor Terry Wall

Thermoplasticity is a determining factor for the development of the coke structure and coke strength. Mobile phase, whether vaporizable or not, may significantly affect thermoplasticity during coal coking. This work studies the effect of the mobile phase, including the volatile tar and extractable metaplast generated from one bituminous coking coal, on the thermo-swelling of the raw coal. The volatile tar was collected when the raw coal was heated from room temperature to 450 °C at a heating rate of 5 °C/min, while the metaplast was extracted from the heated char. Molecular properties of the tar and metaplast were characterized using a laser desorption/ionization-time of flight-mass spectrometry technique (LDI-TOF-MS). Thermo-swelling of the raw coal and its blends with the volatile tar and extractable metaplast was investigated using a computer-aided thermal analysis (CATA). The volatile (C and H) evolution rate of the heating coal samples was tracked using a dynamic elemental thermal analysis (DETA), and the weight loss rate was investigated using thermogravimetric analysis (TGA). It was found that the extracted metaplast has a higher molecular weight distribution than that of the volatile tar. The swelling and thermal changes of the heating coal increased with the addition of tar or metaplast. The weight loss rate prior to coal swelling increased with the additives, while the raw coal showed a higher volatile release after maximum swelling than the blends. The addition of metaplast into the raw coal led to greater swelling, increased exothermicity, and resulted in a higher thermal conductivity than the addition of volatile tar during the primary devolatilization, particularly when the additive was 20 wt % in the blend. Different influences of thermoplasticity of the blends indicated that the interactions between the additive and the coal are affected by the molecular weight distribution of the additive. These findings will aid in the selection of the additive for improving thermoplasticity of low-caking coals to benefit coke production.

A suit of nitrogen-dried maceral concentrates derived from a coking coal and a non-coking coal was investigated to reveal the impact of varying coal main organic constituent, the vitrinite, on their thermoplasticity and pyrolysis products. The thermoplastic development of maceral concentrates during pyrolysis was evaluated via their thermo-swelling and dynamic volatile release. These measurements were then linked to molecular weight distributions of vaporised tars and tetrahydrofuran (THF) extracts obtained from heat-treated samples. Regardless of the vitrinite content, only coking macerals agglomerated during pyrolysis while non-coking macerals retained their powdered structure. This result indicated that although concentrating the vitrinite could alter the extent of coal thermoplasticity, such process could not grant or remove thermoplasticity from a maceral concentrate. This was reflected in the similar molecular weight distribution of solvent extracts produced between the parent coals and their concentrates. In specific, coking concentrates generated extractable materials with a relatively more complex structure, consisting of a bimodal molecular weight distribution with 12¿14 Da repeating structures at <600 Da and 24 Da reoccurring units between 600 and ~1500 Da. Solvent extracts isolated from non-coking concentrates, on the other hand, possessed a unimodal molecular weight distribution with only 12¿14 Da repeating structures extending to ~800 Da. The absence of high-range molecular weight materials (the 24 Da repeating units) in non-coking coal and its concentrates was speculated to play a vital role to their inability to exhibit thermoplastic behaviour during pyrolysis.

This study outlines a novel thermal extrusion system and methodologies for evaluating the potential to manufacture carbon fiber directly from thermoplastic coals. It is envisioned that the intermediate product will be further refined by spinning down to commercial fiber sizes and thermal annealing. Commercial melt spinning is used for manufacturing carbon fibers from pitch-based feed materials, and a similar approach for plasticized coal is likely to be a lower risk option. However, the critical aspect of using coal for this purpose is its behavior inside a higher pressure extrusion unit and the need to characterize its rheology. This work has evaluated the thermoplastic development needed for extrusion of a single coking coal in terms of the heating rate and residence time and characterized the extruded fiber product. It was observed that the coal underwent a preliminary softening phase prior to extruding at significant speed. This phase appeared necessary to develop the critical viscosity for extrusion and was affected by the heating rate. The size of the orifice that the coal was extruded through also impacted the point of extrusion, with the smaller 0.5 mm hole requiring lower viscosity to be developed to flow at steady state. Other operating modes were developed to examine the thermoplastic properties of the coal over an extended residence time, and it was found that the coal could be maintained up to 60 min at selected temperatures. The product fiber was larger than the commercial size, appearing slightly larger than the orifice size. Internal porosity and surface roughness were observed as coal-based fiber qualities in need of controlling, along with the mineral content and size.

This work has used high range imaging mass spectrometry to study a coal sample that has undergone heating with a temperature gradient. A custom made hotplate was heated to 1000°C and the coal was allowed to heat naturally through conduction to produce a large thermal gradient typical of conditions in a coke oven. The sample was quenched, sectioned and analysed using laser desorption time of flight imaging mass spectrometry (LDI-TOF-IMS) to study the molecular changes that occur within the plastic layer and in the semi-coke. The raw coal was observed to have a molecular weight range between 500 and 20,000 Da with a peak occurring at 2000 Da. The plastic layer was observed to have a prevalence for increasing 500-1000 Da structures though this formed part of the larger molecular weight range. Resolidification of the plastic layer coincided with a rise in 4000 Da structures. The semi-coke spectrum had a series of repeating peaks separated by 24 Da extending from 1000 Da to 3000 Da. This was considered evidence of broad molecular ordering. A second phenomenon was observed in the semi-coke associated with low range molecular weights (50-300 Da). This appeared as high intensity signals in a molecular range typically considered as ion fragments (being too low in size to remain in the high vacuum environment). It was speculated that these low range structures may be associated with the coking of volatile tars exiting the hot-side of the plastic layer through high temperature semi-coke. Overall, this preliminary work provides a novel methodology to study the heating impacts during coking on a molecular level.

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.

The thermoplastic development of an Australian coking coal was investigated by linking thermal swelling with changes in molecular weight of its pyrolysis products. Coal thermal swelling was investigated together with volatiles evolution and characterization of generated volatiles (including volatile tar and light gases). The molecular weight distributions of coal and its solvent extracts were measured by using laser desorption/ionization time of flight mass spectroscopy (LDI-TOF-MS). Solvent extraction (by acetone and tetrahydrofuran (THF)) was initially used on the raw coal to aid interpretation of thermoswelling by volumetric expansion measurements. The removal of ~2% solvent-soluble matter from the raw coal (the mobile phase) reduced its swelling extent during heating by up to 22% (from 86% down to 68% and 64% for acetone- and THF-residues, respectively). Volatile release after solvent treatment remained unaffected. This suggested that the majority of the coals swelling behavior could be attributed to the formation of heat-generated liquid matter (the Metaplast) during pyrolysis. Broad molecular weight changes were found in the solvent extractable component (metaplastic material extracted by acetone and THF) of the semicoke. Prior to softening (350 °C), the extractable components were composed of molecules mainly <500 Da. The upper limit in molecular weight distribution of solvent extracts increased significantly to 1800 Da at the onset of swelling (400-450 °C) and decreased back to ~500 Da at the end of swelling (500 °C). The spectra showed that the volatile tar and acetone extract (the light solvent extract) consisted of similar repeating structures separated 12-14 Da apart. As the treatment temperature increased, the molecular weight distribution of volatile tar increased in molecular mass, approaching that of the acetone extract distribution (~600 Da). The THF extract molecular weight distribution was a mixture of 12-14 and 24 Da repeating units which only became apparent at molecular weight above 600 Da. The LDI-TOF-MS analysis of the solid coal showed that it contained a distribution of molecular structures centered at 2000 Da and spanning between 500 and 7000 Da. This raw coal spectrum also contained multiple repeating mass lines every 24 Da apart. Overall, these results suggested that the coal consisted of complicated structures which subsequently degraded into smaller fragments capable of forming a complex intermediate liquid phase and a distribution of lighter volatile tar species.

Coal-fired utility boilers are the single largest anthropogenic source of mercury emissions. Mercury is a naturally occurring trace element in coal and, when combusted, may exist in three different forms: Hg0, Hg2+, or Hg particulate. During oxy-fuel combustion, impurity concentrations, such as SOx, NOx, and Hg, can be up to 4 times higher than concentrations in air combustion. An increased mercury concentration is of concern because mercury is known to attack aluminum heat exchangers required in the compression of CO2. As a result of the elevated concentrations during oxy-fuel conditions, interactions of Hg and SOx were investigated in this study to verify if there is any competition between SOx and Hg. The effect of Hg, SOx, H2O, and temperature on the native capture of Hg by fly ash was assessed using a quartz flow reactor packed with fly ash to simulate a bag filter. Doubling Hg in the system from 5 to 10 µg/Nm3 doubled the amount of Hg captured in the fly ash from 1.6 to 2.8% and increased the amount of Hg unaccounted from 5.8 to 18.1%. Increased SO2 decreased the proportion of Hg0 in the flue gas. The temperature in the bag filter was found to have a large impact on the mercury capture by fly ash. As the temperature was increased from 90 to 200 °C, Hg0 in the flue gas was found to increase from 77.9 to 98.3%, indicating better capture of Hg at lower temperatures.

Dynamic measurements of physical, chemical and thermal changes in the transformation of coal maceral concentrates were made during heating at a rate of 10°C/min to 1000°C. The endothermic and exothermic processes were identified by measurements of apparent specific heat while the fluidity was indicated by the estimated thermal conductivity. Measurements of swelling and bed permeability were made, with continuous quantitative elemental analysis of gases and tars as they evolved. Data for two coal concentrates of high and moderate vitrinite indicate that the same reactions and events are occurring for the two samples, but to a greater extent for the high vitrinite sample. The research has noted the significance of evolved tars in the early events, being the lowest temperature event identified, with rapid tar evolution prior to the onset of swelling associated with permeability change. Further tar release and gas evolution is associated with a rapid swelling event, this event being substantially greater for the high vitrinite sample. The data has also quantified contraction at higher temperatures following swelling which is associated with the release of hydrogen containing gases. Evolved tars from the high vitrinite sample showed elevated H/C ratio indicating that vitrinite tars appear to be more aliphatic than those evolved from inertinite. A comparison of measured swelling with estimated volumetric flow rate of the volatiles has indicated that thermo-expansion of coal utilised up to 21% of the volatiles to drive bubble growth. This utilisation rate varied significantly across the plastic temperature range.

The desulfurization properties of Fe-Zn sorbent prepared by impregnating Fe and Zn into lignite char via ultrasonic-assisted impregnation (UAI) were investigated in comparison with the mechanical stirring (MS) method. The sulfidation experiments were carried out using a fixed-bed quartz reactor under ambient pressure. The amounts of metals loaded into char were measured by inductively coupled plasma atomic emission spectrometry (ICP-AES). The crystalline phases and chemical structure of sorbents before and after sulfidation were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. The morphology of sorbents was analyzed by using scanning electron microscope (SEM) with an energy dispersive X-ray (EDX) auxiliary. The experimental results showed that metal oxides as the active components were evenly dispersed on char as nanoparticles. The impregnation of active components was significantly improved by the ultrasonic-assisted impregnation method. When sorbents were prepared by ultrasonic-assisted impregnation, the metal oxide particles became smaller and more evenly dispersed on the char matrix which resulted in higher desulfurization efficiency and sulfur uptake capacity of the sorbents. The BET results showed that the physical properties of sorbents (surface area and pore volume) significantly improved when prepared by UAI method compared to MS method. The sulfidation temperature had a significant effect on desulfurization performance of char supported sorbents. The Fe:Zn molar ratio of 2:1, and impregnation time of 9 h were suggested as the optimal preparation conditions during ultrasonic-assisted impregnation.

A fundamental study was undertaken to characterize the changes in solvent-extracted matter formed during the thermoplastic phase of coking. Coal samples were heated to fixed temperatures within the pyrolytic plastic range of 400-500 °C, and the volatile material was extracted in a two-stage extraction with acetone (light extract) and then tetrahydrofuran (THF heavy extract). The extracted material was analyzed using laser desorption ionization (time-of flight) mass spectrometry (LDI-TOF-MS). The LDI-TOF-MS results showed that three extracted fractions could be broadly classified here as overlapping molecular weight ranges as volatile tars (200-450 Da), light acetone-soluble extract (250-500 Da), and heavy THF-soluble extract (300-1200 Da). A further class of compounds was identified from THF extraction of the raw coal in the range of 600-2500 Da that required higher laser powers to ionize and was not observed in the thermally generated samples. Negligible changes were observed in the composition of the acetone-soluble extracts with temperature, while the THF-soluble extract showed smaller proportions of larger molecules with higher treatment temperatures. It was observed that each molecular weight spectrum showed repeating structural units forming peaks every 12-14 Da (homologous series), with distributions of species around each peak. The volatile tar and acetone-soluble material shared common repeating structures also evident in the raw coal extract. This suggested that the material in this fraction was thermally stable over the analyzed temperature range. The repeating features of the THF-soluble extract species appeared to be structurally different. Overall, this work has indicated that development of extractable matter expected to be associated with fluidity during coking and subsequent resolidification relies on <1000 Da compounds. The results showed that >600 Da compounds are thermally sensitive. Compounds with molecular weights of <450 Da may be removed during coking, possibly as a vapor, resulting in a reduction in fluidity. There has been speculation that the thermally stable (acetone-soluble) material identified in both raw coal extract and those from thermally treated samples may be capable of undergoing a phase change to initiate plastic deformation.

A new technique that allows dynamic measurement of thermal properties, expansion and the elemental chemistry of the volatile matter being evolved as coal is pyrolysed is described. The thermal and other properties are measured dynamically as a function of temperature of the coal without the need for equilibration at temperature. In particular, the technique allows for continuous elemental characterisation of tars as they are evolved during pyrolysis and afterwards as a function of boiling point. The technique is demonstrated by measuring the properties of maceral concentrates from a coal. The variation in heats of reaction, thermal conductivity and expansion as a function of maceral composition is described. Combined with the elemental analysis, the results aid in the interpretation of the chemical processes contributing to the physical and thermal behaviour of the coal during pyrolysis. Potential applications in cokemaking studies are discussed. © 2013 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda. All rights reserved.

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.

Ash produced during oxy-fuel combustion is expected to differ from ash produced during air combustion because of the higher CO2 and SO 2 atmospheres in which it is generated. For a quantitative understanding of the sulfation behavior of fly ash in oxy-fuel combustion, fly ash from three commercial Australian sub-bituminous coals was tested and decomposed under an inert atmosphere. Thermal evolved gas analysis was completed for ash produced in both air and oxy-fuel environments. Pure salts were also tested under the same conditions to allow for identification of the species in the ash that capture sulfur, along with thermodynamic modeling using FactSage 6.3. Sulfur evolved during the decomposition of air and oxy-fuel fly ash was compared to the total sulfur in the ash to close the sulfur balance. Both total sulfur captured by the ash and sulfur evolved during decomposition were higher for oxy-fuel fly ash than their air counterparts. Correlations of capture with ash chemistry are presented. © 2014 American Chemical Society.

A novel technique is described which provides quantitative and continuous analysis of light gas and condensable tar components as they are evolved in terms of carbon, hydrogen and oxygen. The technique has also been used to directly characterise the total tar sample in terms of carbon distribution and boiling point. It has been found that changes to the dynamic tar-H/C ratio correspond well with particular temperatures measured by Geiseler Plastometer for softening, maximum fluidity and re-solidification. This technique can enhance the chemical understanding of mechanisms occurring during de-polymerisation and cross-linking of coal (i.e. metaplast development and the transfer of hydrogen) while also monitoring tar evolution. A tar collection and re-vaporisation method provides a means of identifying tar groups that contribute towards the metaplast phase and temperatures at which they evolve. Both methods are unique in studying chemical aspects of coal and tar behaviour with heating, in a field based on thermo-physical techniques (e.g. H1 NMR, high temperature rheology, Geiseler plastometry, dilatation). Overall, the Dynamic Elemental Thermal Analysis (DETA) technique can give new insight into the fundamental mechanisms prevalent in coal pyrolysis and provides quantitative chemical assessment of tar nature (i) during the heating of coal and (ii) as a final (total) condensed product. © 2012 Elsevier Ltd. All rights reserved.

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.

A fundamental study on the behaviour of heating coal macerals has been undertaken using two novel thermal analysis techniques. The apparent specific heat was determined during heating using an inverse calorimetric method (computer aided thermal analysis, CATA) and combined with pressure and displacement measurements to correlate endothermic and exothermic behaviour with measurement of swelling. The second technique used a post-oxidation stage to combust the tars and gases into products which were analysed. This method was used to study the elemental character of volatiles release from coal maceral concentrates in terms of carbon and hydrogen. Extents of swelling and exothermicity during primary devolatilisation were found to be correlated with vitrinite content and were associated with tar evolution. For the highest vitrinite fraction (of 86.4% vitrinite) swelling was initiated at the same temperature range for exothermic reactions, and maximum swelling coincided with the peak release of light gases. Tar evolution was found to change in chemical character (as defined by H/C ratio) during progressive heating, initially rising in the early stages of tar formation (<430°C) to a maximum of 1.24, then gradually decreasing to a minimum of 0.64 at 550°C. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

The paper proposed a two-step desulphurization process using iron-based high temperature sorbents for removal of hydrogen sulfide from hot coal gases after coal gasification. The authors use the mixture of iron oxide with other metal oxides (e.g. Ce) supported by ash from a coalgangue- fired power plant to prepare high temperature desulphurization sorbents. The two-step desulphurization process is comprised of a first-stage desulphurization of removing majority of sulfur followed by a second-stage desulphurization to remove the remaining sulfur species. The process is integrated with effective sulfur recovery through direct elemental sulfur production during the regeneration of Fe/Ce based sorbents. Preliminary studies on sulfidation using a quartz fixed-bed reactor demonstrated that the Fe/Ce-based sorbents prepared in this study was able to remove >97% sulfur in the temperature range of 400-600°C. Simultaneous removal of organic and inorganic sulfur species was achieved.

Char structures evolved during the devolatilization process have been found to play a significant role in the subsequent processes (e.g., char combustion and gasification) and to influence the ash formation mechanisms. In the present paper, a mathematical model has been developed based on the multibubble mechanism to simulate the char structure evolution process. The model is the first to provide predictions of heterogenous char structures evolved during devolatilization (e.g. cenospheric char, foam structure, or dense char structure) as well as transient particle swelling ratios, based on the ultimate and proximate data of the given coal. The devolatilization process is divided into the preplastic stage, plastic stage, and resolidified stage. Bubble number conservation, mass, and force balance are formulated during the plastic stage to predict the transient swelling ratio and resultant char structures. Experiments have been conducted using a single coal particle reactor (SPR) and a drop tube furnace (DTF) with density-separated coal samples prepared using the sink-float method. The SPR experiments confirm that bubble behavior is responsible for the swelling of the particles that develop plasticity on heating. The analysis of the DTF chars shows that the swelling ratio and porosity decrease with increasing the coal density. Chars from lowdensity samples are mainly Group I chars (porosity >80%), while high-density samples yield mainly Group III chars (porosity <50%), and the medium-density samples contain a mixture. The predicted swelling ratio, porosity, and char type distribution of the chars of the density-separated samples are consistent with the experimental data.

Chars were made from four Australian coals of varying vitrinite content at pressures of 5, 10, and 15 atm. The morphology of the chars was correlated with the petrography of the parent coal. The intrinsic reaction rates of the chars at high pressures were measured, and no systematic effect of pyrolysis pressure or maceral concentration was found. It is concluded that observed variations in conversion rates under process conditions are likely to be due to char structural properties and not a result of variation in the intrinsic reactivity of the carbon in the chars. Consequently, this paper presents a char structural submodel that is integrated into an existing char combustion model to account for the combustion behavior of char particles of different morphologies. The char morphology used in the model was predicted using the developed correlation with parent coal petrography, so that a petrographic analysis as well as the proximate and ultimate analyses is required for model input. Validation of the model shows that chars produced at high pressure with a high percentage of cenospherical types burn more rapidly under process conditions than those at low pressure, with model predictions matching measurements. It is suggested that incorporating the char structural submodel into the existing char combustion model improves its predictability.

Consumption of fossil fuels (i.e., oil, gas, coal) is the major source (86%) for meeting the world's energy needs and is projected to be so for some time to come. Coal accounts for 73% of the world's recoverable reserves of fossil fuels. World consumption of coal is increasing, particularly in Asia. Yet, clean and efficient use of coal presents important research challenges. This paper provides a comparative review of thirteen combustion centers in eight nations, where each has significant research components devoted to coal. Other active combustion centers doing similar work are not included in this review for various reasons. Following an introduction, a section of this review is devoted to each of the thirteen participating centers. In these sections, mission, objectives, research program, representative accomplishments, and directions are addressed. Data are also provided relating to center history, budget, size, and areas of emphasis. Collectively, these centers expend about $72 million per year, conduct over 600 research projects involving 1500 researchers, interact with 700 organizations, and provide an estimated 1000 reports and manuscripts annually. Though centers vary substantially in years of existence, budget size, personnel, and otherwise, on average, centers have 22 years of experience, involve over 110 research personnel, spend over $5 million per year, and conduct nearly 50 projects. All centers are involved in experimental measurements and applications of computerized combustion models, all work on environmental issues, all do substantial work relating to coal combustion, and all work on transferring center technologies. However, research on other fuels, focus on processes and systems, and emerging technologies vary substantially among the participating centers. Directions for centers' research typically include increasing international activity, strong environmental focus, more work on biomass and waste materials, emerging coal energy technologies, and improvement in conversion efficiencies. © 1998 Elsevier Science Ltd. All rights reserved.

Mineral matter in coals contributes to operational and environmental problems associated with coal utilization processes such as pulverized coal combustion. With the aid of QEMSCAN technology, mineral matter in a suite of Australian pulverized coals has been measured in Particle Mineralogical Analysis (PMA) mode. In this paper, information on mineral-mineral associations for these coals has been presented for first time. Statistical results based on pixel-by-pixel mode show that usually oxides associate with silicates; silicates associate with silicates; carbonates associate with carbonates. In addition, Ca-bearing minerals prefer to associate with other Ca-bearing minerals; Fe-bearing minerals prefer to associate with other Fe-bearing minerals. The results can be explained by geological environment and processes in which Australian coals and mineral matter in coals formed. For combustion engineering practice, a new definition of mineral-mineral association has been adopted to describe how mineral grains associate with each other inside a single coal particle. The mineral-mineral association for included mineral grains was used as an input into an ash formation model at two limiting extremes, i.e. (A) one coal particle to one ash particle and (B) one mineral grain to one ash particle. Size and chemistry of ash particles were predicted and compared by two ash formation models.

Chars were made from four Australian coals of varying vitrinite content at pressures of 5, 10, and 15 atm. The morphology of the chars was correlated with the petrography of the parent coal. The intrinsic reaction rates of the chars at high pressures were measured, and no systematic effect of pyrolysis pressure or maceral concentration was found. It is concluded that observed variations in conversion rates under process conditions are likely to be due to char structural properties and not a result of variation in the intrinsic reactivity of the carbon in the chars. Consequently, this paper presents a char structural submodel that is integrated into an existing char combustion model to account for the combustion behavior of char particles of different morphologies. The char morphology used in the model was predicted using the developed correlation with parent coal petrography, so that a petrographic analysis as well as the proximate and ultimate analyses is required for model input. Validation of the model shows that chars produced at high pressure with a high percentage of cenospherical types burn more rapidly under process conditions than those at low pressure, with model predictions matching measurements. It is suggested that incorporating the char structural submodel into the existing char combustion model improves its predictability.