THE INFLUENCE OF PRESSURE ON THE BEHAVIOR OF OIL-SHALE CARBONATES

The utilization of solid fuels with high carbonate content in mineral matter has some peculiarities, specially at burning in pressurized con ditions. In the combustion process the sulphur oxides are usually capt ured by the addition of limestone (CaCO3) or dolomite (CaMg(CO3)(2)) i nto the combustor. In the case when the fuel mineral matter itself con tains carbonates, no additional impurities are needed to capture sulph ur oxides from flue gas. The carbon dioxide partial pressure in the fl ue gas has a significant influence on the fuel mineral matter behaviou r and sulphur dioxide capturing mechanism. The CO2 partial pressure in the flue gas has also remarkable influence on the fuel heating value and carbon dioxide emission. Estonian oil shale is a fuel that itself contains a considerable amount of carbonates. Nowadays Estonian oil sh ale is utilized only in power plants using pulverized firing (PF) tech nology. Utilization of oil shale as solid fuel with high content of ca rbonates by pressurized fluidized ed combustion (PFBC) technology has some advantages. Burning Estonian oil shale in atmospheric pressure co mbustors the carbonate decomposition rate is in the range 0.85-0.98. A ccording to the theoretical calculations the carbonate decomposition r ate should be much lower burning oil shale in pressurized conditions. The aim of this paper is to investigate the behaviour of the fuel carb onates in pressurized combustion conditions, experimental determinatio n of the carbonate decomposition rate and its influence on the fuel he ating value and carbon dioxide concentration in the flue gas. for thes e purposes the laboratory pressurized combustion facility was erected in Thermal Engineering Department of Tallinn Technical University.