The application of granulation to fine coal preparation

Currently fine coal recovery and characteristic improvement are attracting increasing attention. To exemplify this attention this thesis reports an investigation into the application of a size enlargement process to fine coal preparation. The application of this process was considered appropriate to overcome the existing problems associated with the storage and flow of fine coal. In particular this investigation aimed to identify the requirements for and characteristics of granulated fine coal produced from coal washery waste using a drum granulator. To this end this investigation included the examination of techniques to produce suitable granulator feed, the variables affecting granule strength and characteristics, the identification of optimal binders and additive addition rates, assessment of granule characteristics and an economic assessment of the process. Of particular concern was the assessment of the storage and flow properties of the granulated product. In this investigation, which utilized the pilot plant scale feed preparation and granulation test facility at the University of Wollongong, it was found that a saleable high quality product could be generated at high recovery rates. The production of this product required classifying the waste coal slurry at 75 μm by use of a hydrocyclone and processing the underflow and overflow by froth flotation and oil agglomeration processes, respectively. This processed material, when dried to about 18% moisture content and mixed with suitable binders, produced granules of adequate mechanical strength and durability. The latter mechanical strength and durability was assessed by measurement of granule compressive strength, impact strength, standard properties including density and particle size, flowability as assessed using a Durham Cone tester, water immersion testing, friability or abrasion resistance and dustiness. In particular it was identified that strong and stable granules could be produced by the addition of 1.5% guar gum or 1 % guar gum + 0.5% bentonite. It is subsequently shown that these granules have superior properties relative to those exhibited by the source fine coal. In addition it is found that the granules possess sufficient strength and durability to withstand the stresses imposed during storage, handling and transportation. This investigation identifies that optimum feed conditions result in optimum granule size which in turn yields optimum granule characteristics. In particular when using guar gum binder optimum granules have good characteristics including relatively low water disintegration, low friability or high abrasion resistance, low dustiness and insensitivity to ambient humidity. These characteristics are further improved by optimum bentonite addition rate. These favourable characteristics in combination with the suggested favourable process economics suggest that granulation be applied to actual coal preparation plants. Such application will attract long term economic, environmental and utilization benefits. The full scale application of which warrants further investigation