Understanding FABA composition in coal-fired power plants: Impact of operating conditions and combustion efficiency on ash characteristics – A case study in PT Bukit Asam, South Sumatra, Indonesia

Abstract

Coal-fired power plants are integral to global electricity production due to their cost-effectiveness and widespread availability of coal. This research investigates the operational dynamics of these plants, emphasizing the production of fly ash and bottom ash (FABA) as crucial by-products. The study focuses on three power plants in South Sumatra, Indonesia, operated by PT Bukit Asam Tbk. Fly ash and Bottom ash (FABA) and feed coal samples were collected to determine how the operational conditions of a power plant impact the composition of FABA. The mineralogical composition of FABA has been determined accurately with X-Ray diffraction analysis. Significant feed oxides in coal and FABA were identified using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The primary characteristics of FABA mostly consist of unburned carbon, which may exceed levels as high as 76.05 %. The existence of unburned carbon residues is evidence of an inefficient coal grinding operation and low combustion efficiency of carbon in the boiler. The abundance of quartz in the FABA corresponds to its condition of being unmelted when heated to a temperature of 850 °C. A decrease in operating temperature results in a lower percentage of amorphous glass. The presence of quartz and reduced plagioclase concentration in FABA components correspond to the utilization of boiler-incompatible sand as bed material. In addition a consequence of a decrease in combustion temperature, pyrite exhibits partial decomposition, resulting in the formation of a tiny amount of hematite, while the other pyrite is still into its original form. A relatively small amount of spinel was associated to a mineral composed of Fe-oxide. Spinel is formed as a secondary mineral through the decomposition of Fe sulfides and other Fe-bearing minerals that exist in coal. This study evaluates the combustion efficiency and operational characteristics of power plants by applying the shrinking reactive core model by the assistance of Matlab®. The results demonstrate that since the efficiency of coal combustion increases, the concentration of unburned carbon in the FABA decreases. The modeling corresponds with the current findings in the field.