The Duffin Creek Biosolids to Energy Experience – Lessons in Energy Recovery

The Duffin Creek Water Pollution Control Plant (WPCP) is a conventional activated sludge plant located in Pickering Ontario, Canada. The liquids module of the WPCP has a treatment capacity of 630 MLD (∼166 mgd), following the Stage 3 Liquids Expansion completed in 2010, which increased treatment capacity from 420 MLD (∼110 mgd). The Stage 3 Solids Expansion which will increase the firm solids processing capacity from 90 t/d DS (99 dtpd) to 270 t/d DS (297 dtpd), was in commissioning at the time of writing and will be in full operation in 2013. Following commissioning, the Duffin Creek WPCP will be the largest thermal processing facility with energy recovery (420 t/d DS installed capacity) in North America. The Stage 3 Solids Expansion modified the existing digesters, replaced the dewatering facility and added two fluid bed reactor (FBR) trains, as well as ash thickening and dewatering.A key component of the project was selecting an energy recovery scheme that was sustainable and cost effective. The scheme that was selected included recovering energy from the new FBRs in the form of high pressure superheated steam to drive fluidizing air blowers, with a future plan to generate electricity, following replacement of the original two FBR trains.Commissioning of this complex plant required careful planning and execution. With the selected energy recovery scheme, proper boil-out procedures were implemented to protect the waste heat boilers, as well as steam blowing to protect the steam turbine drives.