Coal is the most important source of heat energy in all sectors of the national economy. In Ukraine coal is actually the only energy carrier of domestic origin, which resources (47-50 billion tons) will last hundreds of years under the present-day rates of consumption. Coal has been used as a fuel material for thermal power stations, railway and water transport, and community demand for decades. The main coal consumer is by-product-coking industry and electricity production. At present, energy and coking coal deficiency arises from low coal production and its poor quality. As a result, processing of secondary raw materials contained in waste dumps and sludge tanks, which are man-caused fields, has been of increased interest to researchers in Ukraine. It is conditioned by several reasons:

-     high content of combustible mass – up to 20% in dumps, up to 50% and more in sludge tanks;

-     simplicity of the extraction and its low first cost;

-     criticality of the most functioning sludge tanks, that significantly complicates processing plant operation.

         At present sludge tanks exploitation is being yielded by some commercial and national enterprises according to the following flowsheets:  

         Flowsheet  #1.

         The extraction of flotation tailings from sludge tanks is done by suction-tube dredges, then coarse-grained low-ash sludge is yielded from the extracted substance with the help of screens. The material (class +0.1mm) is used as a power-plant fuel. Fine high-ash sludge (class –0.1mm) is returned into the sludge tank.

         Flowsheet #2.

         The extraction of flotation tailings from sludge tanks is done by suction-tube dredges, then coarse-grained low-ash sludge is yielded from the extracted substance with the help of screens. The extracted with the screens or hydraulic cyclones coarse-grained sludge (class +0.1mm) undergoes enrichment in spiral separators, dehydration and is used as a power-plant fuel. Cleaning rejects with fine sludge (class –0.1mm) and products of dehydration are returned into the sludge tank.  

         Flowsheet #3.

         The extraction of flotation tailings from sludge tanks is done by suction-tube dredges, then coarse-grained low-ash sludge is yielded from the extracted substance with the help of screens. The extracted with the screens or hydraulic cyclones coarse-grained sludge (class +0.1mm) undergoes enrichment in spiral separators, dehydration and is used as a power-plant fuel. Cleaning rejects with fine sludge (class –0.1mm) and products of dedehydration after inspissation are dehydrated in press-filters with layer shipment to the waste dump.

         The drawback of flowsheets #1 and #2 is the fact that higher-ash tailings are discharged into the sludge tank again, that doesn’t solve the problem of tank emptying and worsens their solid components value because of increasing sludgy fractions content.

         Flowsheet #3 is devoid of this drawback but in this case, material with 60-65% ash content is discharged to the waste dump, i.e. there is combustible mass wastage.

         At the same time, fuel with the indicated ash content can be used in steam generating units equipped with boiling bed furnaces.

         In view of the listed drawbacks of sludge tanks flowsheets, a complex flowsheet of flotation tailings processing of Mospino Coal Processing Plant sludge tank has been suggested, which provides for tank desludging and full-scale utilization of combustible waste for power-producing (flowsheet #4).  

         Flowsheet #4.

         The extraction of flotation tailings from sludge tanks is done by suction-tube dredges, then coarse-grained low-ash sludge is yielded from the extracted substance with the help of screens. The extracted with the screens or hydraulic cyclones grained sludge (ash content up to 25%) (class +0.1mm) undergoes briquetting and is sold as a fuel for domestic purposes; all the fine classes (–0.1mm) undergo granulating to the required fineness and are used as a fuel for boiling bed furnaces.

       Conclusion

         The application of the suggested sludge tanks processing flowsheets will enable to solve the problem of sludge tanks emptying and complex usage of raw materials, providing people with fuel for domestic purposes, and will give an opportunity to reduce costs of industrial premises heating and of process heat demand.