Dust emissions conceal a major risk potential in sewage sludge drying. Sewage sludge dust is not only explosive, it also represents an increased health risk for the employees in question. Dust usually appears at transfer points, where products are being stored and, especially, during subsequent logistics.
We set ourselves the challenge of eliminating any dust emissions in the process. This begins with the acceptance of wet sewage sludge, includes the drying process and ends with the subsequent logistics. All conveyors are sealed in a dust tight way by screw feeders. The dryer works at low pressure, meaning that no emissions can escape into surroundings of the dryer. The dried sewage sludge is moved to a sealed container after the drying process. The container has a level sensor and automatically begins the pelletization process that immediately follows.
A slower gear pelletizer, that has been specially developed for this application, presses the dried sewage sludge at a compression ratio of 1:2. The pelletization system is completely closed and works in a virtually dust free manner. The dried sewage sludge is conveyed by interlocking pressure gears and compacted into a dust free, robust and wear resistant pellet using a pressure cone. This does away with any need for laborious silo storage or silo logistics. The sewage sludge is sanitized through the drying process and becomes dust free through its compression into pellets. After the pelletization process, the sewage sludge pellet can be stored in open containers and processed. It can subsequently be used for anything, be it for combustion, gasification, phosphorous recovery or as a fertilizer.