With most sludges, a significant percentage of weight is water, anything up to 60%. We have developed an application of our reactor to the drying of slurries, sludges and biomass solids to produce a higher calorific value ‘fuel’.
The paper sludge drier shown dries up to 5 t/h of 55% water paper sludge from a primary paper mill in Holland (the balance of the feed is 50% mineral and 50% wood fibre). The sludge is flocculated, granulated and fed directly to this three stage drier off a conveyor belt. The dried sludge has an average water content of 5%. The hot air that is used to dry the sludge enters at 120ºC with an off gas at ~60ºC which suits a recovered/waste heat source from power generation. The TORBED technology copes with the ‘sticky’ nature of the sludge through very rapid ‘skinning’ of the particles.
The system shown here combusts some 6 t/h of paper sludge containing 50-55% water. This sludge is generated at a paper recycling mill in Ontario, Canada. This US$5m demonstration unit has been installed and operating since 2007. The ‘simple’ payback with these plants is less than 18 months in avoided disposal costs, recovered energy and mineral sales. The major issue faced in the development was that of feed consistency.