DRYING – PELLETIZING AND FLUIDIZED BED COMBUSTION, A FLEXIBLE AND SUSTAINABLE SOLU TION FOR THE CITY OF BRUGGE, BELGIUM

The calorific value of mechanically dewatered sludge is often not sufficient in order to sustain a fully auto- thermal combustion process. Therefore, sludge combustion processes either require partial thermal drying of the sludge, the use of high calorific waste (e.g. RDF) or an additional fossil fuel source (e.g. coal) to sustain the combustion. However, it is possible to install a sludge pelle tizing process prior to fluidized bed combustion. Sludge hard pelletizing results in a hard and round granule that is easy and safe to store and handle. Combining sludge fluidized bed combustion with hard pelletizing results in a better energy balance and offers higher flexibility.The Bruges plant (owned by AQUAFIN) manages sludge from the Bruges WWTP and from most other WWTP in the West part of Flanders. The paper will discuss the rationale for selecting the co-joined thermal processes, its operating history, public and governmental perception of the technology, and decision to continue with the technology and increase its capacity.The paper will also present the technical aspects of the plant, including sludge dewatering, materials handling, sludge pelletizing, fluidized bed combustion, energy recovery, safety features, and emissions. The paper will also highlight the concept of “zero-fuel” as additional external fuel sources are not required for the process.