EXERGY ANALYSIS OF COAL THERMAL CONVERSION PROCESSES

To develop energy-saving technologies and facilities that use coal, it is essential to evaluate the energy potential of the resulting products. Additionally, it is necessary to determine their suitability for specific technologies, processes, and installations. Alongside the energy method, it is proposed to use the exergy method, which allows for the assessment of not only the quantitative but also the qualitative aspects of thermal conversion processes. Thermal conversion methods such as combustion and gasification are of interest for both energy and industrial applications. The study includes calculations of the exergy efficiency of coal thermal conversion products, based on which material and exergy balances were compiled for the gasification process under air and oxygen blast conditions, as well as for the combustion process. An analysis was conducted to evaluate the impact of process temperatures on the characteristics of coal thermal conversion products (composition, output, exergy). Additionally, the exergy efficiency coefficients (overall, chemical and physical exergy) for these thermal conversion methods were calculated. Based on the analysis, optimal operating modes for coal thermal conversion processes were determined, depending on the final goals of the obtained products. The advantages of high-temperature oxygen and air gasification were identified, characterized by low exergy losses (24.9–28.9 %) and high chemical potential (12–13.46 MJ/kg of coal). The exergy efficiency of the oxygen gasification process is 68.3–71.2 %, while for air gasification, it is 70.2– 76.3 %. It was also established that, to achieve the highest fuel utilization efficiency, it is advisable to utilize the heat of the produced syngas. The utilization of 1 MJ/kg of coal from the physical exergy of the gas increases the overall exergy efficiency of air gasification by 3.5 % and that of oxygen gasification by approximately 0.7 %. A comparison of the exergy efficiency of the processes was conducted, revealing that coal gasification is a more rational method of thermal conversion compared to traditional combustion. This is because the highest losses are observed during the combustion process, with an exergy efficiency of 64.8 %. During coal combustion, irreversible losses account for 35 % of its initial exergy.