PCC production from calcium-rich oxy-fuel CFBC ash

Yearly, approximately 12 million tons of oil shale (OS) are used in Estonia for power generation utilizing pulverized combustion (PC) and circulating fluidized bed combustion (CFBC) technologies that produce nearly 6 million tons of calcium-rich ash. Implementation of CFBC has decreased environmental impact of OS combustion; oxy-fuel technology promises a further decrease of CO2 emissions. Using oxy-fuel CFBC technology alters the ash properties, including decomposition of carbonate minerals. By means of producing precipitated calcium carbonate (PCC) from Ca-rich ash, CO2 can be stored safely and leakage-free for a very long time, and at the same time a valuable product is produced. We applied so-called slag2PCC technology to CFBC OS ash produced in Tallinn University of Technology. Batch and semi-continuous experiments were conducted. The PCC yields were 20 – 167 kg of PCC per t of OS CFBC ash. PCC yield from oxy-fuel ashes was smaller than from regular CFBC ashes. The PCC consisted of >98% CaCO3; the main impurity was CaSO4. Traces of iron, potassium, chloride, magnesium and sodium were registered. Experiments on semicontinuous device showed that an inclined settler is sufficient for separating ~99% of the solids from the Carich solution. Estonian OS ashes can be used for PCC production.