Australian Institute of Energy 9th Australian Coal Science Conference

SOLUTIONS FOR INDUSTRY

The proceedings CD ROM $50 can be ordered by emailing the AIE 

Burning

Self-heating Rates of Australian and New Zealand Low Rank Hard Coals
B Beamish, A Coope, University of Queensland, Brisbane; M Barakat and J St George University of Auckland, New Zealand
Self-heating rates have been determined for New Zealand and Australian subbituminous coals using an adiabatic oven.  New Zealand subbituminous coals yield self-heating rate indices in excess of 14 ºC/h.  There is a distinct rank relationship in the samples tested, which shows that as rank decreases the self-heating rate increases.  Strip samples taken from the Callide Coalfield of Queensland indicate that the freshly exposed subbituminous coal has a self-heating rate index (R70) in excess of 5 ºC/h.  Intraseam variation is also present, which appears to relate to the presence of sideritic layers in the coal. The difference in self-heating propensity between the New Zealand and Australian coals can be attributed to the greater inertinite content of the Australian coals, which tends to inhibit the self-heating process.

Mathematical Modelling of Propane Combustion in a Fluidised-bed Gasifier
Davide Ross, Hong Ming Yan and Dong-ke Zhang CRC Clean Power from Lignite Melbourne
A mathematical model for a bubbling fluidised-bed coal gasifier was developed for simulating the performance of a laboratory-scale gasifier with feeds of both Yallourn char and propane by incorporating propane decomposition and combustion reactions and reaction kinetics.  Model predictions of the in-bed axial gas concentration profiles for O2, CO, CO2, CH4, and C3H8 compared well, except for the minor gas species of both C2H4 and C3H6, to the experimental data at operating bed temperatures of 850oC and 950oC, respectively.  In contrast, the predicted gas species show a poor agreement with the experimental data, particularly for the carbon oxide species at 750oC. Most importantly, the addition of propane to simulate the volatile matter released from coal devolatilisation process results in an increase in the proportion of oxygen consumed by homogeneous combustion.  This leads to an increase in an availability of char for char gasification reactions, subsequently showing an increase in carbon conversion due to gasification over the sole gasification of char.  This further demonstrates the importance of incorporating homogenous combustion into the model for correctly predicting the gasifier performance, particularly for coal with high volatile content.  However, the information regarding the measured temperature profiles of gases in the fluidised-bed coal gasifier has been neither measured in the experiments nor found in the literature, and this leads to some difficulties for the verification of the predicted temperature profiles from the model.

Thermally Induced Change in the Macromolecular Structure of Coal
H Kumagai, K Tanabe and T Chiba Hokkaido University, Japan
The effects of heating rate on the change in associated molecular structure of slightly-coking coal, Witbank coal, was investigated.  Spin-spin relaxation phenomenon of the coal during heat treatment was observed using in-situ pulsed 1H-NMR.  The fractional intensity and spin-spin relaxation time for mobile component has changed with rapid heating treatment up to 644K.  The results indicate that change in the associated macromolecular structure of coal has strongly affected with heating rate.

CAMD Study on the Change in the Pore Size Distribution of Brown Coal along with a Progress of Moisture Release 
H Kumagai Hokkaido University, Japan; and K Nakamura Osaka Gas Co Ltd, Japan
A computer-aided molecular design (CAMD) method was utilized to evaluate the change in the physical and chemical characteristics of brown coal along with a progress of moisture release.  The results indicated that the removal of water molecules results in a drastic change in the density of cell which contain coal model molecules and water molecules at the final stage of moisture removal.  Size distribution of micropore stuffed with water molecules shifted slightly toward a smaller radius up to 80% of moisture removal.  Then, the distribution became broader and mean pore radius increased from extent of moisture removal of 80%.  This increase in mean pore radius well corresponded to the change in the density of cell.  The results appeared to represent the characteristics of the brown coal, at least change in the density and pore size distribution along with a progress of moisture release.

Acidic Functional Groups in Brown Coal
L Clemow CRC for Clean Power from Lignite, Monash University, Melbourne; W Jackson Monash University, Melbourne ; R Sakurovs CSIRO Division of Energy, Sydney and
D Allardice Allardice Consulting, Victoria
The heterogeneous nature of brown coal has led to lengthy but unresolved discussions as to its structure.  To obtain some concrete information, we have been studying the acidic oxygen functional groups by aqueous and non-aqueous titrations.  These results are of practical importance in determining coal-water interactions which underpin the hydrophilic nature of the coal and could lead to improved understanding of drying processes which are critical to the development of more efficient power generation technologies.  A number of methods for determining acidic oxygen in brown coals were examined.  It was found that the best techniques for measuring the acidic oxygen functionality were barium exchange based aqueous titrations modified from well known methods.  Results obtained using these techniques and their implications for explaining the structure of brown coal will be discussed.

Percolative Fragmentation of Char particles During Gasification
B Feng and S Bhatia University of Queensland, Brisbane;
Three Australian cola chars were observed under an optical microscope after gasified at various temperatures (450 – 600 C) in air to various conversions.  Many fragments were observed at low conversions (55%) during gasification even under chemical control.  The fragments appear earlier when diffusion becomes important.  These results indicate percolative fragmentation.  This is supported by the percolations behavior of the variations of the electrical resistivity with the conversions, ie the electrical resistivity initially increase only slightly with the conversion, until at a certain conversion it rises sharply.  The percolations models satisfactorily predicted the behavior of the electrical resistivity.

Effect of Heat Treatment of Reactivity and Structure of an Australian Semi-anthracite
B Feng and S Bhatia University of Queensland, Brisbane
J C. Barry The University of Queensland Brisbane
An Australian coal was observed under a high resolution transmission electron microscopy (HRTEM) after heat treatment at various temperatures (950 – 1150 °C) for various times (2 minutes to 12 hours). While the internal structure of pure carbon in coal char is highly disordered, the carbon near the iron particles shows graphite structure. The clay in coal char also slightly enhanced the ordering of carbon at the interface of carbon/clay. The results suggest catalytic graphitization with iron being the major catalyst. This is supported by the observation that the fraction of organized carbon by x-ray diffraction (XRD) increases with the heat treatment temperature and heating time for the raw coal char, while it does not change significantly for the ash-free coal char. The electrical resistivity (ER) shows the same behavior, i.e the ER for the raw coal char decreases with heat treatment temperature and heating time,  while the ER for the ash-free coal char does not change significantly, suggesting the occurrence of catalytic graphitization.

Hydrogen Chemisorption and Desorption at Carbon Sites
Y Otake University of Queensland, Brisbane; and R Jenkins University of Vermont, USA
Edge carbon atoms responsible for the existence of oxygen surface complexes on a microporous carbon have been studied further by hydrogen chemisorption experiments.  Results indicate that hydrogen can be chemisorbed exclusively at newly created edge carbon atoms that are generated by thermal decomposition of a specific type of CO-evolving surface complex.

Leachability of Fly Ash
S McEvoy, J Killingley and L Dale  CSIRO Energy Technology, Sydney
The leachability of elements from fly ash has historically been determined using batch methods such as the Synthetic Ground Water Leaching Protocol (SGLP) or Toxicity Characteristic Leaching Procedure (TCLP) USEPA SW-846 Method 1311. These batch methods extract the fly ash with a single fixed volume of solution in a well mixed but closed system. While these methods often provide useful information as to the degree of leachability of many major and trace elements, they fail to compensate for temporal changes in conditions as fly ash is leached. The effects of changes in pH, the variation in relative solubilities and the subsequent inhibition of release of trace elements associated with phosphate and sulphate compounds have a considerable impact on composition of leachates from a dynamic open system. Additionally, the batch leaching methods, which require an extraction with a liquid to solid ratio (L:S) of 20:1, provide little indication of the true concentrations or volumes required to leach many elements.  Column leaching work in our laboratories in association with the Black Coal CRC and ACARP has indicated that leaching of many major and trace elements from fly ash is complete with as little as 0.5 to 2 L:S.
 
Other environmentally significant elements are delayed in their leaching. In some columns, for reach their maximum levels after 5 or more L:S volumes. These elements are not well characterised by the batch methods due to their poor leachability into the strong common ion environment of the batch methods.
 
This work describes some of the observations and data resulting from a comparative column / batch method study and offers the column technique as an alternative method that could provide a strong predictive tool for the long term leachability of many elements from fly ash dams associated with power stations.

Coal/Water

On the Shear Dependent Flow Properties of Victorian Brown Coal
T Kealy and C Tiu  CRC for Clean Power from Lignite, Melbourne
Victorian brown coal has complex rheological properties exhibiting gradual, irreversible changes from granular solid to stiff paste through the application of shearing forces.  It has been suspected for some time that these interesting rheological changes take place as a result of the liberation of intraparticle water, contained in the void spaces of porous, friable coal particles.
 
This work outlines a new technique for lignite rheology assessment, based on torque measurement at the shaft of a laboratory scale, instrumented kneading mixer for a typical brown coal, mined in the Latrobe Valley, Victoria, Australia.  It is demonstrated that this technique yields reliable and reproducible data, allowing prediction of the sheared coal product flow properties even at low shear rates where previous attempts at characterisation have been unsuccessful or unreliable.
 
Typical samples of run-of-mine lignite have been subjected to shearing forces in the apparatus and the effects of processing parameters such as particle size and the duration and intensity of shearing have been analysed in terms of their effect on the behaviour of lignite.  Properties such as the point at which the mixture may be said to change from a solid to a stiff paste and the interdependence of this phenomenon with particle size and measured flow properties, are documented and examined in terms of the time and power input required to obtain them.  It has been found that particle size has decreased by several orders of magnitude after low power inputs, to 7.2 mm.  Decreases are at a much reduced rate thereafter.  Tentative explanations regarding the interdependence of rheology and processing parameters are suggested.  A three-stage model is proposed, with grinding, grinding/shearing and shearing stages apparent from the experimental evidence.

Steam Reforming of Rapid Pyrolysis Char from Brown and Sub-bituminous Coals
J Hayashi, H Takahashi, M Iwatsuki, K Morishita Hokkaido Universtiy, Japan; C Li Monash University, Melbourne; A Tstsumi and T Chiba University of Tokyo, Japan
Steam gasification of nascent rapid pyrolysis char from low-rank coals was studied at 1123 – 1223 K employing a novel drop-tube/fixed-bed reactor, into which a small amount of pulverized coals was injected and it was rapidly pyrolyzed on a filter as a gas/solid separator.  The volatiles were swept in-situ out of the reaction zone through the filter by a forced flow of atmospheric nitrogen/stream (47/53 in vol/vol) while the particles remaining on the filter being exposed to the flow for a desired period.  Char from Yallourn brown coal underwent so rapid steam gasification at 1173 K that its conversion reached 26 and 32% on the basis of carbon in the nascent char in 5 and 10 s, respectively.  It was also found that the gasification decelerates drastically at the char conversion around 80%, leaving residue much less reactive that the initial char. Char from Taiheiyo sub-bituminous coals was also steam-gasified rapidly and its conversion reached about 70 and 80% in 60 s at 1173 and 1223 K, respectively.  The results of the rate analysis suggested that the rapid pyrolysis of the coals forms so-called ‘rapid carbon’ in nascent char that transforms into less reactive material in a few hundred seconds at 1173 K
 

Estimation of Pore Size for Low Rank Coals Sorbing Water Based on its Molecular Mobility
N Kudo, J Hayashi, and T Chiba  Hokkaido University, Japan  and K Norinaga Tohuku University Japan
This paper proposes an application of proton magnetic resonance relaxation analysis (MRRA) for estimating the size of pores in water-sorbing coals on the basis o f the transverse relaxation characte4ristics of water condensed in the po4res as the molecular probe.  Raw Yallourn brown coal (water content; 1.46 g-water/g-mf coal and Beulah Zap lignite (0.53) were employed as the starting materials and were partially or completely dried at 303K.  The samples with known water contents were subjected to the MRRA using a Carr-Purcel/Meiboom-Gill(CPMG) pulse sequence.  The results of the analysis revealed that the initial amplitude of the CPMG signal corresponds quantitatively to the total amount of ‘mobile’ proton.  It was also found that there are three components with different relaxation times (T2) that are attributed to free water, pore water (freezable bound water and non-freezable water) and mobile coal hydroxyls/carboxyles. The relaxation characteristics the components where further analyzed based on a theory proposed by Brownstein and Tarr, and finally the following conclusions could be reached. (i) pores filled with pore water are slit-like rather than cylindrical in shape; (ii) the dimensions of pores are about 3 nm and 2 nm for the raw Yallourn and Beulah Zap, respectively; (iii) the pore dimension decreases linearly with the content of pore water.

The Future of Brown Coal Drying Technologies for Power Generation Comparison of Products from Various Processes
G Favas, A Chaffee and W Jackson   Monash University, Melbourne
The deregulation of the Australian electrical supply industry, the increase in competition between all electricity generators (hydro-electricity, natural gas, black and brown coal) across the national grid and the need to reduce greenhouse emissions have necessitated improvements in brown coal utilisation for power generation. The competitiveness of brown coal power generation will in large part depend on the implementation of energy efficient drying technologies for existing brown coal boilers, which currently burn coal with a moisture content of 60%.
Three major drying technologies, Steam Drying (SD), Hydrothermal Dewatering (HTD) and Mechanical Thermal Expression (MTE), were investigated in batch and bench scale units.
 
Steam drying is an evaporative drying technology that utilises superheated steam to remove water from high moisture coals at much lower temperatures than HTD and MTE; however, the metal ash forming elements remain in the final product. HTD and MTE are non-evaporative energy efficient drying technologies that remove water from the coal as a liquid, thus saving energy. An added advantage of these process is that some of the water soluble inorganics, in particular Na, are leached out from the coal, thus decreasing the inorganic content of the product coal. The temperatures used in the HTD process are higher than in SD and MTE (i.e. up to 320°C). In HTD, soluble organic material can also leach out into the wastewater that, therefore, may require substantial treatment. In the MTE process, in addition to heat, a mechanical force is also applied to the system to facilitate the removal of water and destroy the internal pore structure of the coal. A disadvantage of this system is the high mechanical forces (e.g., 12MPa); but processing temperatures are much lower (180°C to 200°C) than for HTD.
 
Products from each process have been subjected to a range of analyses, including proximate and ultimate analysis, the composition of the inorganics, helium density, surface area (CO2 adsorption), pore volume (mercury porosimetry) and calorific value. The effectiveness of each of the drying technologies in relation to the chemical and physical structure of the coal has been evaluated.

Production of High Quality Coal Product from a Low Quality Coal using a Modified Hydrothermal Dewatering Technique
G Favas and W Jackson Monash University, Melbourne
A novel method of producing a very low porosity coal material from highly porous Latrobe Valley raw brown coals has been developed using a combination of hydrothermal and evaporative drying. Low porosity coal was made in three different batch autoclave systems at temperatures of 320°C. Higher temperatures (up to 350°C) gave a small additional decrease in porosity but these conditions were found undesirable as the water vapour pressure and the loss of organic material were significantly increased. Residence times as low as 5min were found to be sufficient to give a densified coal product. The total organic carbon leached into the wastewater during the process was significantly lower than under pure hydrothermal dewatering conditions. The low porosity coal product was found to give a coal water mixture with a maximum coal concentration for a pumpable slurry of greater than 60%wt.d.b. in comparison to 45%wt.d.b. using conventional hydrothermal dewatering. This paper will discuss the method of preparation, the chemical transformations of the raw coal and the production of very highly concentrated coal water slurries, with and without the use of chemical additives.

Bound Water in Brown Coal
L Clemow W Jackson, CRC for clean power from lignite, Monash University, Melbourne;
R Sakurovs CSIRO Division for Energy Technology, Sydney; and D Allardice Allardice Consulting Victoria
A well known characteristic of brown coals is their strong affinity to water, which is demonstrated by their high moisture content as mined, high monolayer water capacity and high non-freezing water content.  It is therefore important to establish how these quantities relate to the coal structure.  For several coals, monolayer water capacity was measured by equilibration at 15% relative humidity at 30°C and the non-freezing water content by 1H nuclear magnetic resonance spectroscopy (nmr) and differential scanning calorimetry (DSC).  These properties have been correlated with structural characteristics of the same coals (elemental analysis, carboxyl and phenol content determined by aqueous titration).  It was found that both of these properties and their ratio were primarily dependent on the carboxylic acid concentration of the coal.  The phenol groups were less significant in this regard.  Therefore to improve the characteristics of brown coals, attention should be concentrated on processes which enhance decarboxylation.

The Chemistry of Coal-Water Interactions: and Theoretical and Experimental Investigations
A Chaffee, T Vu CRC for Clean Power from Lignite, Melbourne; and I Yarovshy RMIT University, Melbourne
Compared to other coals, Victorian lignite is remarkably clean, typically possessing low concentrations of inorganics and mineral matter. Unfortunately, the high moisture content (60 – 70% wet basis) means that a pre-drying process is required to remove most of the water in the coal prior to combustion. Drying processes that remove the water evaporatively require substantial energy, reducing the efficiency of power generation from this fuel.
To assist the optimisation of drying processes it is important that details of the coal structure and coal-water interactions be understood in as full detail as possible.
 
Since lignite is a very complex heterogeneous material, the complexity of the problem has been reduced through the use of ‘megafossil’ samples taken from the coal. Megafossils are the discrete macroscopic remains of wood, leaves, resins, etc that can be visually identified and hand-picked from the coal seam. Such megafossils are chemically less heterogeneous than lignite as a whole.
 
The physical structure of these fossil woods has been probed by techniques such as helium pycnometry, mercury porosimetry and gas adsorption. Likewise, the organic structure has been probed by elemental analysis, DRIFT-IR, SS-NMR and TGA. On the basis of these results, structural models of fossil wood are constructed and coal-water interactions are simulated.  The simulated results are compared with measured isotherms of water adsorption.

Upgrading of Coal Derived Oil as Transportation Fuels
S Azuma and S Wasaka New Energy and Industrial Technology Development Organization, Japan
The New Energy and Industrial Technology Development Organization (NEDO) has been developing coal liquefaction technology as part of the “New Sunshine Programs” planned by the Agency of Industrial Science and Technology, a division of the Ministry of International Trade and Industry in Japan.  The developed “NEDOL” process showed advantages such as applicability to a wide range of coal ranks, a high oil yield and reliability of plant facilities.
 
Parallel to the development of the coal liquefaction process, development of product upgrading technology has been proceeding to make use of the liquefied products as transportation fuels.  Based on the laboratory study of the upgrading process, a 40 bbl/d process development unit (PDU) was designed and constructed.  The PDU is composed of a two-stage hydrotreating unit, an atmospheric distillation unit and a reforming unit to produce gasoline and diesel fractions.  First-stage hydrotreating of coal derived crude oil was carried out successfully in the PDU.

Coking

Fifty years of Coking
T Callcott and R Callcott Callcot Consulting, Newcastle
This paper is an idiosyncratic and personal view of cokemaking in Australia over the last fifty years. It covers the state of the coal and coke industry, coke-making and iron-making, and the place of research throughout.

Effects of Low-temperature Oxidation on Caking Property of Coal
H Ota and T Takarada  Gunma University Department of Biological and Chemical Engineering, Japan
Low-temperature oxidation is a well-known but important process to change the caking property of coal. In this paper, we aim at investigating the mechanism of coal oxidation and the effect of oxidation treatment on the caking property. Particle size of coal sample showed a pronounced effect on the oxidation reaction. The oxidation reaction occurred more severely in the outer layer of coal particles than inside the coal particles. FT-ir was used to characterize the oxidized samples, and it was observed that carbonyl functional group (C=O and COOH) and ether functional group ( -O- ) were the main products formed during the oxidation. The isotope 18O2 was used to trace the dynamics of the oxygen inherent in coal and that absorbed during oxidation. It was found that during the oxidation treatment, not only the oxygen adsorption occurred on the coals but also the reaction took place between oxygen and the hydrogen in coal with the release of H2O (m/z=20), and the two interactions may change the chemical bonds and the amount of hydrogen in coal and thus affect the caking property of coal.

Coal Petrography by Low Cost Imaging
B Jenkins Jenkins-Kwan Technology Brisbane; G O’Brien, H Beath, and J Esterle CSIRO Exploration and Mining and CSIRO Minerals, Brisbane
A new coal petrography technique is being developed to characterise coking and thermal coals.  It involves the analysis of micrographic images of coal to produce a characteristic reflectance signature or ‘fingerprint’ called a full phase maceral reflectogram.  This can be used for several purposes: to qualitatively compare coals, to quantify maceral group proportions, to determine rank from vitrinite reflectance distributions, and to provide utilisation modelling parameters.  A low cost system has been designed to retro-fit to existing petrographic microscopes.  Similar to manual techniques, a petrographer is required to calibrate the illumination system and manually collect images which takes about 45 minutes. The calibration data is stored to assist with the image processing which takes a further 45 minutes offline. A reflectogram and report are generated in MS Excel.  Current developments and testing are aimed at expanding the rank range for quantitative analyses (0.4 – 2.2 at present) and determination of blend proportions.

Factors Affecting the Coking Properties of Blends
R Sakurovs, E Gawronski and L Burke CSIRO Division of Energy Technology, Sydney
The aim of this work was to determine which of a number of factors suspected to affect coke properties do in fact affect them.
 
Eleven Australian coals were used to prepare eight blends, which where coked in a 400 kg Research Coke Oven.  The blend compositions were chosen such that effective rank and fluidity of the blends were the same but other factors were allowed to vary.  The strength, abrasion resistance and reactivity of the cokes were examined
It was found that cokes prepared to the same effective rank and fluidity had similar overall quality though the variation in some coke properties was significant.  Tow factors that some consider responsible for the variations in coke quality had no effect on any coke property: variations in reflectance (or V-step) distribution and the presence of high volatile poorly-coking coals, even at additions as great as 25% wt.
 
One source of variation was due to the presence of one low-volatile coal.  When this coal was present in the blend there was a marked decrease in the resistance to abrasion as measured by severe abrasion tests although no other indices were significantly affected.  It is hypothesized that the cokes containing this coal tend to flake on extended abrasion, owing to the relatively large domain sizes in the coke generated by this coal, but that this form of abrasion has no effect on strength or reactivity.
 
There were significant variations in D1150/15 that were not due to rank, rank distributions or fluidity of the blend and remained unexplained.  Additionally, the significant variations in CRI and CSR were observed that were not due to variations in the elemental composition of the ash.

Mining

Alternate Management Options for the Control of Acid Materials at Coal Mines in the Bowen Basin Queensland
C Hanahan  University of Queensland, Brisbane
The management of acid mine drainage at coal mines in the Bowen Basin depends on low rainfall to minimise transport of the products of the oxidation of sulphide minerals, primarily pyrite.  Thus, generation of acid mine drainage (AMD) occurs mainly during rain events.  Management involves channeling run-off from rain events into active pits and then either pumping the generated AMD out to evaporation ponds or in some cases pumping into underground shafts no longer in use.  Acid-generating tailings are stored in ponds with water covers.  Alternative management options are proposed here.
 
Red mud, the iron-rich residue from the caustic extraction of alumina from bauxite ore using the Bayer process, is a highly alkaline waste produced in large quantities.  At the Queensland Alumina Ltd. (QAL) refinery in Gladstone, QLD, the 8,000 dry tonnes of residues produced daily are neutralised with seawater, resulting in a reaction pH (1:5) of 8.6 - 8.8.  The author’s PhD project has investigated the abilitites of seawater neutralised red mud to neutralise acidity and trap trace metals associated with acid mine drainage.
 
The study reported here trials the use of seawater neutralised red mud to treat surface waters collected from three sites at two coal mines in the Bowen Basin.  Alternative management options are proposed to treat the AMD from storm events and to treat and enhance rehabilitation of tailings.  A leaky dam lined with red mud for the slow infiltration of collected storm run-off could replace evaporation ponds.  Co-disposal of red mud with dewatered tailings could enhance rehabilitation potential and eliminate the need to maintain water covers.  The reduction in transport costs of the red mud, a waste product with its own management costs, by using the coal trains returning empty to the Bowen Basin coal mines from Gladstone lends an additional cost benefit to these management options.

Brown Coal Derived Pproducts for Ameliorating Soil Acidity
J Issa, A Patti and W Jackson Monash University,  Melbourne
High acidity in soil is directly related to high toxic aluminium levels.  An increase in pH is desirable down to the root zone of crops (>10 cm).  Typical treatments such as lime and gypsum only increase pH near the soil surface unless they are physically incorporated; this is labour and cost intensive, and may also cause soil degradation.
Humic acid derived from brown coal, with added calcium, when applied to the soil surface, can increase pH deeper into the soil profile.  The humates can move down with water percolating the soil.  As they move down, the added calcium bound to the humate’s cation exchange sites (the acidic oxygen functional groups) can exchange with toxic aluminium ions and ions on exchange sites in the soil.  Thus the soil pH is buffered, nutrient transport to plants assisted, and phytotoxic aluminium bound and rendered harmless to plants.
 
Humic material fractions obtained from brown coal can be classified according to their solubility in acid and base.  These fractions differ in their ability to decrease soil acidity.  The ‘humin’ fraction (base-insoluble) has a low acid group content and moves slowly through the soil.  Humic acid (base-soluble, acid-insoluble) and fulvic acid (base and acid-soluble) move more rapidly; fulvic acid has more acidic groups than humic acid, but its lower molecular weight makes it more susceptible to microbial degradation, so that it is destroyed before benefiting the soil.

K Humate is a commercially available source of humate (ex HRL Agriculture Pty Ltd, Australia) derived from brown coal.  It can be obtained by the treatment of brown coal with potassium hydroxide.  Calsulmag is a commercial treated coal fly ash (also ex HRL Agriculture Pty Ltd) which can be used instead of lime due to its high inorganic calcium and magnesium content.  When K humate and Calsulmag are combined in an aqueous mixture, and applied to the surface of an acidic soil, pH is increased (from 3.8 to 4.5) as is exchangeable calcium (30-50%), while exchangeable aluminium is decreased (30-50%), down to a 5 cm depth.
 

Optimisation of Underground Coal Gasification for Improved Performance and Reduced Environmental Impact
A Beath and C Mallett CSIRO Exploration and Mining, Brisbane
Development of improved UCG processes has been performed using two complementary methods.  The first of these is the utilisation of detailed models of the gasification of coal under the conditions experienced in UCG.  The development of these models is discussed and the sensitivity of the models to variables such as temperature, pressure, water ingress and feed gas composition input is analysed.  In the second stage of the optimisation various process arrangements for the surface plant were simulated using a commercial process modelling software package.  The objective was to determine process arrangements that had both high efficiency and minimal emission of greenhouse gases.  The processes were all specifically designed for electricity generation, however the techniques used could also be applied to synthesis gas production.  The preferred process developed allows for separate combustion of hydrogen, with a stream comprised of methane, carbon monoxide and other gases being burnt separately in oxygen, allowing for sequestration of a carbon dioxide rich stream.  Disposal of the carbon dioxide could possibly be in spent underground gasification sites.  As the majority of the gas processing is carried out at high pressures, there is minimal expenditure of energy in recompression of the carbon dioxide for sequestration.