Behavior of the components of carbon-containing ash from the combustion of power coals under the conditions of chlorination roasting

Abstract

On the basis of thermodynamic calculations of interaction reactions between mullite, oxides of titanium, iron, and Cl2 (gas) in the presence of carbon, the values of the Gibbs free energy are determined in the current work. It has been established that the probability of reactions occurring in the temperature range 1073–1473 K is very high. The most negative value ΔG°Т = –1029.9 kJ/mol is typical for the titanium oxide reduction reaction at the roasting tem- perature (1100 °С). The value of the Gibbs free energy of the destruction reaction of mullite (Al2SiO5), which is important for practice, is ΔG°Т = –269.2 kJ/mol. This makes it possible to predict the complete decomposition of mullite from ash to easily soluble aluminum chloride under the conditions of chlorination roasting. The study of the behavior of carbon under the conditions of chlorination roasting of ash with CaCl2 in an oxidizing atmosphere is also important. The results of the differential thermal analysis of the non-magnetic fraction of ash, previously separated from the TPP ash by magnetic separation, showed clearly defined manifestations on the DTA, DTG and TG curves, caused by the presence of various types of reactions in the system. Low-temperature (20–115 °C) sample dehydration and ash dehydration were determined in the temperature range of 115–375 °C. In the range of further heating of the sample (375–685 °C), an exothermic projection was found on the DTA curve, which is characteristic of the oxidation of thermally active carbon present in the powder. The amount of carbon removed from the ash established as 6.75% by weight of the sample. The research was carried out within the framework of grant funding from the Committee of Science of the Ministry of Education and Science of the Republic of Kazakhstan for 2021–2023 in the priority area “Geology, mining and processing of mineral and hydrocarbon raw materials, new materials, technologies, safe products and structures” of project No. АР09259637 “Development of a highly efficient wastefree technologies for the utilization of ash from coal combustion with the production of marketable products.