Complex processing of ash and slag wastes from coal-fired CHP plants
The paper focuses on both Russian and international practices concerning the solution of ash and slag wastes processing and prospective areas of their application. The results of lab and pilot plant tests on concentration ability of ash and slag wastes wh
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Springer International Publishing Switzerland 2016 V. Litvinenko (ed.), XVIII International Coal Preparation Congress, DOI 10.1007/978-3-319-40943-6_52
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S.A. .Prokopev et al.
In Russia, there are over 170 current coal-fired CHP plants. Ash and slag wastes are produced by coal combustion and are disposed of in ash dumps. Annual generation of ash and slag wastes accounts for approximately 30 mln*tons. The dumps have accumulated over 1.5 billion tons, and they have an area of 30,000 ha. A number of ash dumps are overfilled. Additionally, the construction costs for a new ash dump will be, up to RUB 4 billion. The operating costs for ash and slag wastes annually increase and represent around 7% of power and heat production cost at a coal-fired plant. Therefore, a solution to the problem ash and slag wastes processing is of high importance in Russian Federation [1,2]. Currently, the level of ash and slag wastes processing and utilization is still insufficient. Slightly over 11% (3.5-4.0 MTPA) of ash and slag wastes are used. At the same time, ash and slag wastes are fully utilized in other countries. For example, both Germany and Denmark use up to 100% of ash wastes annual yield to produce construction materials. More than 300 processing and utilization methods of ash and slag wastes are known, with the major use occurring in building industry and for construction materials production. However, the recovery of valuables as saleable concentrates has not yet been extensively studied [4,5]. It was found that they contain numerous valuables, such as ferrous, base, rare and precious metals. This is shown in Figure 1. Burning coal is a natural adsorbent. This results in the increase of valuables, up to 5-6 times, in the ash during its combustion. The use of the wastes as secondary raw materials is a major issue and, first of all, requires process design. Technologies which can quickly and efficiently produce a competitive and saleable product from ash and slag wastes are needed. Metals in the coal can be found as components of various minerals and metallorganic compounds. Their major portion converts to fly ash during coal combustion. In order to recover aluminum oxides from ash materials as a source for manufacture of metallic aluminum, the technologies were developed. Ferrosilicon is an alloy of iron and silicon the formation of which is observed due to the lack of air and the presence of unburned coal particles in a molten slag. Germanium and uranium may be recovered from the fly ash. Recovery of gallium, lead, zinc, molybdenum, selenium, gold, silver, rhenium and rare-earth elements is considered to be prospective. Aluminum silicate hollow spheres are arguably the most original and valuable components of fly ash. They are hollow, almost perfectly shaped silicate beads with a smooth surface. They have diameters ranging from >10 up to hundreds μm. Their average diameter is approximately 100 μm. The wall thickness is 2-10 μm [3]. Complex processing of ash-slag of Ekibastuz coal was studied by Kazakh National Researc
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