Influence of oxy-fuel combustion of Ca-rich oil shale fuel on carbonate stability and ash composition

Oil shale is an unconventional low-calorific-value fossil fuel, the usage of which is increasing due to increasing energy demand. Today, Estonia's oil shale usage is the largest in the world. Approximately 90% of the electricity consumed is produced from Ca-rich oil shale. Most of the oil shale, approximately 12 million tons yearly, is used for power generation utilizing pulverized combustion (PC) and circulating fluidized bed combustion (CFBC) technologies. As a result, Estonia has one of the world's highest CO2 emission rates per capita. This study provides results of oil shale combustion in a batch reactor applying oxy-fuel conditions. The combustion experiments were performed at temperatures of 800, 850 and 900 °C while varying the N2, O2 and CO2 ratios. In addition to different temperatures and air-composition variation, water vapor was injected into the gas flow entering the furnace to study the water vapor influence on the solid combustion products. Our results indicated that elevated CO2 levels have a significant influence on the carbonate-decomposition extent and therefore on the SO2-binding properties.