The current paper presents the results of incineration of pyrolytic wastewater (WW) in an oil shale fired 250 MW thermal (MWth) circulating fluidized bed combustion (CFBC) boiler. The measurements in the industrial-scale oil shale fired CFBC unit show that WW incineration did not cause the plant to exceed the gaseous pollutant or particulate matter (PM) emission limits set for large combustion plants. The data obtained is compared to previous results from a pilot-scale 60 kWth CFB combustor. In pulverized combustion (PC) units, incineration of pyrolytic WW was carried out a long time ago as it reduced SO2 emissions and improved PM removal from flue gases in an electrostatic precipitator (ESP). Regarding PM emissions, a similar result was achieved in a CFBC unit; however, a high nitrogen content in WW results in increased NOx emissions. From the practical point of view, pyrolytic WW incineration (ca 13 t/h) increases fuel (oil shale) consumption by up to 6% for the same thermal output, which consequently reduces a unit’s efficiency

Introduction

Global Energy demands are increasing and according to International Energy Agency (IEA) data, combustion with conventional fuels will still be needed to meet this energy demand (Table 1). Fuel combustion (for heat and power generation) remains the most significant source of GHG emissions, of which CO2 emissions constitute about 65% (Lee et al., 2017). Estonia has had long-term experience with oil shale. It is used for power generation (via combustion) and for shale oil production (via pyrolysis) as shown in Fig. 1. For power production, old outdated pulverized combustion (PC) combustors are still used together with new, more efficient, and environmentally friendly CFB combustors. Moving to CFB units has helped to reduce the carbon footprint in the oil shale power sector which is a problem experienced throughout the world (Klemes et al., 2017). On a national level, shale oil production is seen as the most promising option for oil shale utilization (Anon., 2016). Although shale oil production is seen as the superior option, its production is also associated with the generation of pyrolytic WW, which contains PAHs, ammonia, sulfates etc. (Maaten et al., 2017) and hence poses a considerable environmental hazard. Under the current annual shale oil production capacity (around 1 Mt), about 0.10e0.15 Mt of pyrolytic WW must be disposed of annually. Currently, there is no economically feasible solution for purification of this WW. Moreover, only limited success has been achieved in the treatment of pyrolytic WW under laboratory conditions using various WW purification processes (Klein et al., 2017).