Optimal Scheduling of Automatic Flushing Devices in Water Distribution System

Abstract

Maintaining sufficient chlorine residual in a water distribution system is important for water quality and system integrity. Discharging stagnant water from the pipeline through automatic flushing device (AFD) is a feasible method to maintain water quality. This paper presents a simulation-based optimization method to minimize total AFD discharge volume during a 24-h horizon. EPANET 2.0 is used as a hydraulics and water quality simulator. This is formulated as a single-objective optimization problem. The decision variables are the AFD operation patterns. The methodology has three phases. In the first phase, AFD discharge capacities are calculated to evaluate whether the existing AFDs are able to maintain chlorine residuals in the water network. In the second phase, the decision variables are converted to AFD discharge rates. A reduced gradient algorithm is used to quickly explore and narrow down the solution space. At the end of this phase, decision variables are switched back to the AFD operation patterns. In the third phase, simulated annealing is used to search intensively to exploit the global minimum. The method is demonstrated on the water system located at the south end of Pinellas County, Florida, where AFD optimal operation patterns are achieved.