Publisher Summary This chapter highlights different inorganic constituents present in Victorian brown coals. The ash forming constituents in Victorian brown coal can be divided into two groups: (1) minerals, which occur as discrete particles, principally quartz, kaolinite, and pyrite/marcasite and (2) non-mineral inorganics present as exchangeable cations on carboxyl groups and water soluble salts. The chapter presents the nature and mode of occurrence of the inorganic constituents, their distribution in the coal seams, and the chemical transformations they undergo during coal utilization. The nature of the inorganic ash-forming constituents in these coals, however, is such that they exert an important influence on the behavior of these coals during utilization. The transformation of the mineral and nonmineral inorganic species present in Victorian brown coal during its utilization in various processes depends on the relative concentrations of the individual species and the process conditions (including thermal history). The combustion of Victorian brown coal in pulverized fuel fired boilers results in the formation of fly ash and fireside ash deposits, mainly as a result of transformations sustained by the nonmineral inorganic species. A key role in the process of ash formation is that of sodium through the condensations of its vapor state species on either fly ash particles or heat transfer surfaces. The current and future areas of research related to inorganic constituents of Victorian brown coal include (1) the development of on-line methods of analysis, to provide detail of coal quality variations for process control, and (2) the influence of additives on the behavior of the coal in processes.

Publisher Summary This chapter describes the chemical structure of Victorian brown coal. Victorian brown coals represent one of the purest and most extensive concentrations of organic matter anywhere in the world with ash yields generally less than 2%. These coals typically contain 69.6% carbon, 5.0% hydrogen, 24.6% oxygen, 0.5% nitrogen, and 0.3% sulfur on a dry mineral and nonmineral-inorganic free basis. A significant amount of research interest has been directed towards the structural elucidation of Victorian brown coals. Victorian brown coals are structurally complex and heterogeneous because of their detrital origin and early stage of coalification. These coals are derived from demethylated dehydrated lignin monomers intermixed with lipid material, such as polymethylene long chain acids, esters, and triterpenoids of both higher plant and microbial origin. The presence of cellulose remnants reflects the early stage of coalification. The use of controlled degradation techniques has helped confirm the structural characteristics of Victorian brown coals as separately indicated by spectroscopic techniques. The variation in environments of deposition and decomposition, which occurred during the formation of Victorian brown coal deposits, led to significant variations in properties and structure, which further contribute to the coal's heterogeneity.

Publisher Summary This chapter discusses pyrolysis with respect to the influence of heating rates, final temperature, time at final temperature, and the presence of exchangeable cations on the yields and nature of the solid and volatile decomposition products in Victorian brown coals. Pyrolysis includes combustion, the production of carbon products, and conversion to liquid and gaseous fuels. The effects of cations on pyrolysis at rapid heating rates have been investigated using the fluidized bed and shock tube techniques. The investigations show that considerable progress has been made in understanding the details of the pyrolysis of brown coals and the factors that influence the thermal decomposition process and the nature of the residual chars and volatile products. It is evident, however, that many details remain to be learned about the pyrolytic process and how it can be manipulated to advantage to maximize the opportunities for utilizing the brown coal resources of Victoria.

This chapter provides an overview of the industrial implications of the properties of Victorian brown coals. Combustion for power generation accounts for 95% of the brown coal consumed in Victoria. The sections on drying and briquetting relate to processes largely dedicated to rendering brown coal transportable and suitable for combustion in smaller scale applications, including industrial, commercial, and household uses. These processes are also usually prerequisites for the carbonization and gasification of soft brown coals such as those found in Victoria. There has been a tendency for Victorian brown coals to be regarded as the Cinderella of fossil fuels, largely because of their high moisture content that makes transportation expensive and combustion difficult. Technological ingenuity, however, has overcome most of the inherent disadvantages to the utilization of these coals and allowed recognition of some of their merits, such as high reactivity and low sulfur content and ash yield. However, whereever possible, large scale pilot plant or commercial demonstration tests are strongly recommended before commitment to a commercial development of a particular technology on any new brown coal field.

This chapter presents the hydrogenation and reduction of Victorian brown coals to study the chemical structure of brown coal and the mechanism of coal reduction. It describes the chemical and physical processes involved in the conversion (reduction) of brown coals to liquid products with particular regard to (1) the effects of coal characteristics (organic structure and inorganic material present); (2) the role of the slurring solvent; (3) the role of the pyrolytic decomposition of the coal; (4) the nature and role of catalysts or promoters in hydrogen transfer reactions between hydrogen gas and donor solvents and/or direct transfer to the coal; and (5) the yield and nature of the primary liquid products. It has been established that Victorian brown coal is well suited as a feedstock for liquefaction. A fundamental reason for this position is the presence in brown coal of a significant amount of long chain, predominantly aliphatic, material with a high atomic H/C ratio. A good correlation has been established between the atomic H/C ratio for all coals and the yield of oil products. For a fixed atomic H/C ratio, however, the quality of the product from the higher rank coal is usually superior to that from the brown coal principally because it contains less oxygen. The subsequent hydro-treating step to upgrade the product may, therefore, require a lower reaction severity.

This chapter discusses physical structure and properties of brown coal. Brown coal is composed of a poly-dispersed collection of particulate entities ranging from small molecules such as fulvic acids, humic acids, humic acid macromolecules, small plant residues, such as spores, collapsed cells, and pieces of wax and resin right through to xylitic fragments that may themselves range from 1 μm to the size of well-preserved roots, branches, and tree trunks as large as 10 m. Victorian coals contain up to 70% moisture or conversely, the water associated with a seam contains as little as 30% brown coal solids. The water held in the pores is in a state of active interaction with the solid. Upon drying, the physical structure is collapsed and to a large extent its original properties cannot be regenerated by re-wetting. The solids fraction of brown coal is a complex, heterogeneous mixture of plant remains, and each component of the mixture has its own physical and chemical characteristics. Victorian brown coal is very low rank: It has passed through the rotting and humification stages of coalification, but it has not been subjected to the higher temperatures and pressures needed to convert it into higher rank coal. In bed-moist brown coals, or their aqueous dispersions, there is a dynamic equilibrium between the acidic functional groups of the organic matter and the aqueous medium. In its naturally occurring state, brown coal is acidic, owing to the partial dissociation of carboxylic acid groups on the coal surface.

This chapter discusses the geological occurrence of Victorian brown coal deposits. All the coals occurring in Victoria are of low rank and of tertiary age apart from a number of thin seams of bituminous coals of lower Cretaceous age, found mainly in West Gippsland. On the basis of the International Commission of Coal Petrology (ICCP) Classification, the greater part of these low rank coals are classified as soft brown coals with the remainder tending to be, or being, hard brown coals. The American ASTM classification system would designate all the coals as lignite B. Low rank coals also occur in South Australia and Western Australia; these are frequently referred to as lignite. The latter coals are mainly of similar age and equivalent to the soft brown coals of Victoria. The stratigraphy, structure, and economic resources of the brown coals are well known through extensive drilling for coal and petroleum. The sedimentational history of the Gippsland Basin has largely followed a similar sequence of events to the Otway and Murray Basins, but the scale of accumulation of coal and hydrocarbon source rocks is unprecedented and differentiates this basin, for reasons less well understood, from the others. Brown coal seam thicknesses and economically winnable reserves are huge and outrank most other brown coal basins of the world.

Publisher Summary This chapter discusses the petrology of Victorian brown coals in terms of their visible constituent elements. The Victorian brown coals occur in beds or seams ranging in thickness from a few centimeters to over 100 m extending laterally from a few meters to over 50 km. These bands are formed of coals belonging to different lithotypes (rock type). Brown coals are characterized by a high in situ moisture content that confers on these coals special characteristics not exhibited by black coals. The in situ (wet basis) moisture contents of Victorian brown coals range from 40 to 70% with the actual moisture contents at any locality being determined by the geological history, especially the depth of burial. When brown coal is air dried, the color ranges from yellow brown to black brown and is strongly influenced by coal type as well as rank. The hardness of the dry coal ranges from soft and friable to hard and brittle. The specific gravity of the coal in the dry state also varies significantly, again due to variations in type and rank. The inorganic matter in brown coals occurs, both as discrete mineral species and as cations, bound to the organic coal substance and in solution in the inseam water. The output of this unit has largely been directed to broader the State Electricity Commission of Victoria (SECV) projects where the objectives were to determine the properties of Victorian brown coal in relation to its utilization characteristics.

Publisher Summary This chapter provides an overview of the sampling, analysis, and composition of Victorian brown coal. The high moisture content and the nature of the inorganic ash forming constituents in Victorian brown coals present special challenges in their sampling, sample preparation, and analysis. These brown coals are characterized by a high moisture content, low ash yield, and high oxygen content. The average moisture contents range from 52% to 67%; the ash yield is generally less than 6% and less than 3% for the majority of the large coal fields; the oxygen content of the organic coal substance can be as high as 27%. The ash forming constituents in Victorian brown coals are mainly present either as cations associated with the carboxyl groups in the coal or as dissolved salts in the associated moisture, unlike black coals where the ash is derived from mineral species. The development of methods for the chemical analysis of Victorian brown coal is still progressing. The most elusive goal is the direct analysis of organic oxygen in coal and although a number of methods have been researched, none have proved satisfactory for routine analysis purposes. Methods for mineral and nonmineral inorganics analysis of whole coal by means other than X-ray fluorescence spectroscopy and acid extraction/atomic absorption spectroscopy (AAS) are also under active development. Extensive work over the last half century has defined and characterized all major and most minor brown coal fields in Victoria.

This chapter discusses the nature of water in brown coal. The coalification of brown coal process is accompanied by the elimination of water because of both the chemical changes associated with coalification and the physical consolidation of the deposit. This high moisture content critically impacts on virtually every facet of brown coal utilization. Thechapter discusses the problems associated with the determination of moisture content and moisture holding capacity, the factors influencing the variability of moisture content in Victorian brown coals, and the methods of moisture removal (drying). Early studies in Victoria on the brown coal-water system concentrated on the determination of the moisture content of the coal, the variation of moisture content through the Latrobe Valley deposits, and processes for the removal of the moisture. As the severity of drying increases, there is a continuum in the evolution of water from the coal, ranging from initially normal evaporation of free surface water to eventually the release of water formed during the thermal decomposition of oxygen-containing functional groups in the coal and water from the dehydration of the adventitious minerals in the coal. The equilibrium moisture content of brown coal at ambient humidity is in the relatively flat multilayer sorption section of the isotherm. Large variations in humidity are required to produce significant changes in the moisture content of the coal. The increase in the moisture content raises the temperature, due to the exothermic heat of condensation, and accelerates the rate of oxidation.