Evaluation of binders in briquetting of coal fines for application in combustion processes

Fine coal (-1 mm top size) is a global problem in terms of handling and pollution. It is expected that at least 6 percent of run-of-mine coal will be fines, and this does not include the fines generated in mining, beneficiation, and transportation processes. Fines can be processed through various means, which include recirculation with lump coal products to increase product quality. Alternatively, the coal can be sent to agglomeration processes; these include extrusion (pelletizing), spherical agglomeration, and briquetting. When considering briquetting, binders may be required if the coal has low caking properties, which is the case for some South-African bituminous coals. The briquettes can be used as a feedstock in thermal processes such as steam generation for electricity production or in fuel gas synthesis plants. In this study briquettes were manufactured with the aim of alleviating the handle-ability problems associated with coal fines, and then using these briquettes in combustion processes for steam generation. South African bituminous medium rank C coal was used, and its low vitrinite content necessitated the use of a binder. The binder used was of a novel composition consisting of two polymeric components (components A and B) with an added cross-linker to start the reaction (component XL). The study comprised of four phases namely, general mechanical testing (using an FED), an investigation into the optimal concentration and poly-acrylic binder composition, reactivity testing, and finally modelling of the binder formulation to the inherent properties of the coal used, which alluded to the behaviour of a briquette as a result of the maceral and mineral composition of the coal used. It was found that the poly-acrylic (PA) binder bound briquettes were comparably strong relative to briquettes formed using a polyvinyl alcohol (PVA) binder. The briquettes formed using a binder yielded compressive strengths that were twice as strong as the binderless briquettes. None of the briquettes were able to reach lump coal compressive strengths, but achieved the recommended 350 kPa set out by Richards (1990) for transportation requirements. The binderless briquetteing process produced briquettes that had a fines production tendency of 5 ± 2 percent, which was close to the 5 percent recommended value by Richards (1990). The briquettes formed using a binder achieved fines-generation potentials below 5 percent at a 0.4 and 1.2 weight percent addition. None of the briquettes were found to be water resistant at these binder additions, however, when the concentration of the poly-acrylic binder was increased to 5 weight percent, the resulting briquettes yielded an average wet compressive strength of 318 kPa. The addition of binder did not hinder the combustion value of the briquettes. Therefore, the PA formulation could provide an alternative to PVA in the fines briquetting process, yielding briquettes that are stronger than binderless briquettes; that are transportable, and combustible. The resulting briquettes will have to be stored in dry conditions, and in terms of initial financial feasibility will be comparable to PVA.