Fluidized Bed Combustion of Pelletized Sewage Sludge in a Pilot Scale Reactor

Thermal conversion of sewage sludge is a viable route to reduce the amount of waste to dispose. A pilot scale bubbling fluidized bed combustor (FBC370) was used to investigate the combustion of dried and pelletized sewage sludge particles. An experimental campaign was carried out to study gaseous and particulate emissions and stable thermal regimes during the combustion of dried and pelletized sewage sludge in the thermal power ranging from 45 to 65 kWth. The results show that, under the experimental conditions investigated, a stable and efficient combustion behavior was obtained in terms of low emissions of unburnt species, but a train of cleaning processes is necessary to reduce gaseous and particulate emissions. A two stage de-dusting system for the capture of fine and ultrafine particles and the proper units for the abatement of the NOx, SO2 and HCl produced in high concentrations are needed. The temperature profile in the post-combustion zone and stable combustion conditions are critical for the formation of dioxins.