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Abstract

Significant quantities of coal sludge are created during the coal enrichment processes in the mechanical processing plants of hard coal mines (waste group 01). These are the smallest grain classes with a grain size below 1 mm, in which the classes below 0.035 mm constitute up to 60% of their composition and the heat of combustion is at the level of 10 MJ/kg. The high moisture of coal sludge is characteristic, which after dewatering on filter presses reaches the value of 16–28% (Wtot r) (archival paper PG SILESIA). The fine-grained nature and high moisture of the material cause great difficulties at the stage of transport, loading and unloading of the material. The paper presents the results of pelletizing (granulating) grinding of coal sludge by itself and the piling of coal sludge with additional material, which is to improve the sludge energy properties. The piling process itself is primarily intended to improve transport possibilities. Initial tests have been undertaken to show changes in parameters by preparing coal sludge mixtures (PG SILESIA) with lignite coal dusts (LEAG). The process of piling sludge and their mixtures on an AGH laboratory vibratory grinder construction was carried out. As a result of the tests, it can be concluded that all mixtures are susceptible to granulation. This process undoubtedly broadens the transport possibilities of the material. The grain composition of the obtained material after granulation is satisfactory. Up to 2 to 20 mm granules make up 90–95% of the product weight. The strength of the fresh pellets is satisfactory and comparable for all mixtures. Fresh lumps subjected to a test for discharges from a height of 700 mm can withstand from 7 to 14 discharges. The strength of the pellets after longer seasoning, from the height of 500 mm, shows different values for the analyzed samples. The values obtained for hard coal sludge and their blends with brown coal dust are at the level from 4 to 5 discharges. The strength obtained is sufficient to determine the possibility of their transport. At this stage of the work it can be stated that the addition of coal dust from lignite does not cause the deterioration of the material’s strength with respect to clean coal sludge. Therefore, there is no negative impact on the transportability of the granulated material. As a result of mixing with coal dusts, it is possible to increase their energy value (Klojzy-Karczmarczyk at al. 2018). The cost analysis of the analyzed project was not carried out.
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Abstract

The new legislative provisions, regulating the solid fuel trade in Poland, and the resolutions of provincial assemblies assume, inter alia, a ban on the household use of lignite fuels and solid fuels produced with its use; this also applies to coal sludge, coal flotation concentrates, and mixtures produced with their use. These changes will force the producers of these materials to find new ways and methods of their development, including their modification (mixing with other products or waste) in order to increase their attractiveness for the commercial power industry. The presented paper focuses on the analysis of coal sludge, classified as waste (codes 01 04 12 and 01 04 81) or as a by-product in the production of coals of different types. A preliminary analysis aimed at presenting changes in quality parameters and based on the mixtures of hard coal sludge (PG SILESIA) with coal dusts from lignite (pulverized lignite) (LEAG) has been carried out. The analysis of quality parameters of the discussed mixtures included the determination of the calorific value, ash content, volatile matter content, moisture content, heavy metal content (Cd, Tl, Hg, Sb, As, Pb, Cr, Co, Cu, Mn, Ni, and W), and sulfur content. The preliminary analysis has shown that mixing coal sludge with coal dust from lignite and their granulation allows a product with the desired quality and physical parameters to be obtained, which is attractive to the commercial power industry. Compared to coal sludge, granulates made of coal sludge and coal dust from lignite with or without ground dolomite have a higher sulfur content (in the range of 1–1.4%). However, this is still an acceptable content for solid fuels in the commercial power industry. Compared to the basic coal sludge sample, the observed increase in the content of individual toxic components in the mixture samples is small and it therefore can be concluded that the addition of coal dust from lignite or carbonates has no significant effect on the total content of the individual elements. The calorific value is a key parameter determining the usefulness in the power industry. The size of this parameter for coal sludge in an as received basis is in the range of 9.4–10.6 MJ/kg. In the case of the examined mixtures of coal sludge with coal dust from lignite, the calorific value significantly increases to the range of 14.0–14.5 MJ/kg (as received). The obtained values increase the usefulness in the commercial power industry while, at the same time, the requirements for the combustion of solid fuels are met to a greater extent. A slight decrease in the calorific value is observed in the case of granulation with the addition of CaO or carbonates. Taking the analyzed parameters into account, it can be concluded that the prepared mixtures can be used in the combustion in units with flue gas desulfurization plants and a nominal thermal power not less than 1 MW. At this stage of work no cost analysis was carried out.
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