Environmental impact of Estonian oil shale CFB firing

Abstract

Oil shale based power production has been the basement of Estonias̀ energetical independency and economy for over 60 years. At the same time oil shale power plants emissions still give the biggest share of Estonian stationary source pollution, having significant impact to the environment. Thanks to the introduction of oil shale large scale CFB firing, reduction of the total environmental impact was achieved in last years. Detailed information about emissions from CFB power units was collected during several research projects in last years. The paper reviews this new data and compares it with former information. Analysis and estimation of changes of charges of all main polluting components at CFB firing compared to former pulverized firing (PF) are presented. It concerns mass balance of trace metals in initial fuel and in formed ash, emissions of PCDD/F, PCB, PAH, PM 2,5/10, plus conventional air emissions as NOx, SO2, CO2, CO, HCl, TSP. Eg.it was found out, that the relative share of very small (<2,5 μm) particulates is higher in case of oil shale CFB firing, what could be explained with very efficient milling effect of relatively soft minerals of oil shale at CFB furnace. In relation of emission studies also mass distribution of CFB boiler ash between different separation points along the flue gas duct (ash mass balance) was determined and analyses of sampled ashes were provided. This information is important from the point of view of better understanding of thermochemical processes and emission formation in CFB boiler, wider reuse of the ashes of CFB unit.