Production cost of mining enterprises can be significantly reduced when using secondary heat. A large volume of secondary heat sources has a temperature potential of no higher than 50°C. To generate additional electricity using secondary heat it has been proposed to use installations with the Rankine thermodynamic cycle in mining enterprises. The paper aim is to study the thermodynamic efficiency of using R-1234yf and R-744 in the equipment, which uses the secondary heat of mining technologies for evaporation of these working fluids. R-1234yf is a freon that belongs to the class of hydrofluoroolefins and has a much lower level of global warming potential than other ozone-depleting substances. R-744 is carbon dioxide, which belongs to a natural, non-toxic and non-flammable working substance. It has been determined that the thermodynamic efficiencies of using R-1234yf and R-744 are 10% and 6.3%, respectively. The thermodynamic efficiency has been calculated for the temperature range from 50° to 20°C, which is typical for a large volume of secondary heat sources in mining technologies.

The article analyses the process of making the coal-water slurry fuel. The main factors influencing the slurry rheological characteristics and, therefore, energy costs during its transportation are determined. The main attention is paid to the original coal ash content efficiency influence on the energy characteristics of the coal-water slurry fuel. In the work, the transformations of classical rheological equations were carried out taking into account the experimental dependence of the coal-water fuel effective viscosity on the feedstock ash content. As a result of the conducted transformations the dependence to determine the specific pressure loss due to the feedstock ash content was obtained. This has enabled to supplement the eligibility determination techniques for the grade of the coal used as the feedstock for the preparation of the coal-water fuel with rational energy and rheological characteristics. To substantiate the theoretical calculations, the article presents the results of the experimental studies on the effect of coal ash content on the specific pressure losses.