Energy losses in hydraulic systems of water treatment plants: An application to Vombverket in south Sweden

Sammanfattning: Sydvatten AB is a municipally owned company producing and supplying drinking water to about 900,000 inhabitants in southern Sweden through two water treatment plants (WTP), Ringsjöverket and Vombverket. At Vombverket, the present capacity is somewhat reduced because of pressure losses in the pipe systems of the WTP. Parts of the WTP was built already in the 1950’s and it was significantly expanded in the 1990’s. In connection with the latter expansion, the transport of water through the WTP was extended before it is pumped to the main pipe system for distribution to the customers. This extension caused increased hydraulic losses in the system, resulting in reduced capacity. The WTP was typically not optimized for the new process design with regard to the hydraulic conditions, but substantial pressure losses were introduced through bends, valves, and other hydraulic components. An alternative to add a pump for overcoming the additional energy losses was to perform a detailed analysis of the flow and establish the location and properties of these losses. This study could form a basis for modifications of the hydraulic system that would reduce the losses and eliminate the need for pumping. The study begun with a literature review on energy losses in hydraulic systems of WTPs with focus on components present in Vombverket. A thorough investigation of the existing hydraulic system was performed based on available drawings and other additional information, and a comparison made of the system before the WTP was expanded. Measurements of the pressure were carried out at selected points in the hydraulic system in order to quantify the losses occurring in the system. Based on the knowledge established about the system and the measurement datasets obtained, the hydraulic system was schematized coming up with a simplified conceptual model involving the most important components that were expected to have an effect to the flow. Certain coefficient values were estimated from the collected data on pressure. Using Pipe Flow Expert, a hydraulic model that had more details and effective description of the complex system was obtained. The model was calibrated, and validated using measured datasets from the plant. The validated model was then modified to optimize its performance. Financial implications of each modification were done. There were two significant modifications recommended; (1) To remove specific components from the system, like; weirs, gate valve, and Venturi meters. (2) To directly connect the hydraulic system in filter block 1 and 2 to the reservoir, thus shortening the water pathway and reducing energy losses.