Vytiahanets V. Optimising the operating mode of a mine furnace for limestone production in the metallurgical industry

The dissertation study is devoted to determining the optimal parameters of the process of calcining limestone in mine furnaces to ensure the maximum yield of quality products with minimal consumption of raw materials and energy and reduce the negative impact on the environment. The development of effective thermal engineering and hardware solutions will make it possible to implement the process of burning lime for the metallurgical industry in a mine furnace with the production of steelmaking lime. In the introduction, the relevance of the work is substantiated, the goal, idea and tasks to be solved are defined, and the main provisions, scientific novelty and practical significance are defined. The first chapter performs a brief scientific and technical analysis of the current state and prospects for developing the theory and practice of lime production in mine furnaces. The second chapter presents an analysis of the limestone firing process in mine furnaces, including mathematical models to describe the dissociation of calcium carbonate granules and aspects of thermophysics related to the operation of mine 3 furnaces. In the third section, research was conducted on the improvement of the technological process of limestone firing in mine furnaces: the design of mine furnaces using gaseous fuel was developed and the peculiarities of the process were investigated developed a method of experimenting with a detailed analysis of the process of calcination of limestone; the results of experimental studies were obtained, which were analysed to improve the technological process further. It is shown that for the heat treatment of polydisperse rocks with an adjustable heat carrier temperature, the fuel should be burned outside the material layer, obtaining gaseous combustion products (heat carrier) at 1200‒1250°C. A certain relationship has been established between the total composition of mixtures of all colour varieties of limestone and the value of the reflection coefficient, which allows the enrichment of limestone by colour. It was investigated and established that the most rational separation threshold corresponds to a reflection coefficient of about 33%. In the fifth chapter, research was carried out to optimise the firing of limestone in a mine furnace. Optimisation technologies in lime production are considered, and 4 optimisation models are presented. The research results aimed at maximising the firing of limestone in the kiln are discussed. A study of material movement in the mine furnace was carried out to optimise the technological process further. The research results showed that the main positive consequence of the reconstruction was a reduction in fuel consumption by 2.1‒2.3 times and an increase in the total content of CaO and MgO in lime by an average of 7%. An important conclusion is that, despite the different residence times of the material in the heating and firing zones, which affect the uniformity of dissociation, the difference in the actual movement speeds is less significant. The results of these studies were presented, including the results of scanning electron microscopy (SEM), physical adsorption and X-ray structural analysis of the obtained lime. The key factors influencing the dissociation of lumpy limestone and the efficiency of firing in mine furnaces were studied. According to the conclusions regarding the effectiveness of the dissertation research, the following scientific results were noted: 1) an improved mathematical model of a limestone kiln is proposed, thanks to which the task of optimising the process is solved taking into account technological parameters; 2) a refined mathematical description of the firing of a single granule of calcium carbonate was obtained, which takes into account the influence of temperature, the concentration of carbon dioxide in the gas phase, and the size on the rate of dissociation 5 of chunky limestone at different stages of firing, and the limiting factors were identified; 3) for the first time, the possibility and intended ways of increasing the thermal efficiency of the mine furnace due to changes in the characteristics of raw materials, reconstruction of loading and unloading systems, transfer of heating zones, mode setting, and multi-parameter optimisation of the thermal regime of the mine furnace were shown for the first time; 4) the method of intensification of firing in a mine furnace and improvement of the quality characteristics of the product using the direct-countercurrent principle of heat exchange in combination with the lower circuit of recirculation of furnace gases is substantiated.