| Water distribution system is an important part of modern urban infrastructure,and storage tank plays a key role in water distribution system.The main function of the storage tank is to regulate the water quantity,keep the pressure of the pipe network and the stability of the pump working condition.It can also be used to store reserve water and improve the reliability of water distribution system.To a certain extent,the scale and location of storage tank determine the investment and operation of water supply network,secondary pump station and booster pump station,and have an impact on water supply reliability,water quality safety and environment.Therefore,it is necessary to study the optimal design of the storage tank and confirm the scale of the storage tank in the water distribution system.Based on the operational characteristics of storage tank,the secondary pumping stations and the peak-valley time-of-use electricity prices(TOU),a multi-objective optimization model of storage tank was built.The model was established with the objective of minimizing annual cost of the system,reliability index,water age and greenhouse gas emission.The constraints included the hydraulic conditions of pipe network,water supply capacity of pumping station,storage capacity and water level of storage tank.The linear weighted sum method was used to transform the multi-objective into a single objective,and the weight of each objective was determined by the analytic hierarchy process(AHP).The dynamic programming method was used to solve the model.MATLAB and EPANET 2.0 software were used for programming calculation.Taking Shexian County’s Water Distribution Network Planning in 2030 as an example,two kinds of total storage volume were set according to the curves of water supply and consumption,and different storage structure schemes were formulated.According to the storage volume of clear water tank and elevated tank,the respective water supply areas were divided,the flow distribution was carried out,and the pipe diameter of each scheme section was determined by the calculation formula of economic pipe diameter.Through the calculation of each scheme and the evaluation function value,the optimal scheme is that the total storage volume is 14%,in which the storage volume of clear water tank is 11% and the storage volume of elevated tank is 3% when the TOU is implemented.Furthermore,the hourly water level of clear water tank and elevated tank,and the hourly water supply of the secondary pumping station were obtained.On the basis of the calculation results,the paper analyzed the influence of the total storage volume of the system and the storage volume change in the elevated tank on each target: When the total storage volume is fixed,the storage volume in the elevated tank increases,the total annual cost first decreases and then increases,the reliability of the pipe network is improved,the water age increases,water quality is getting worse,and emission of greenhouse gas is reduced;the annual cost of storage tank and the water age increased while the annual cost of pipe network and power cost,the system reliability and the emission of greenhouse gas decreased with the increase of the total storage volume of water distribution system;when TOU is implemented,the storage volume in the pipe network can be used to cut the peak and fill the valley,so that the total annual cost can be significantly reduced.It is proved that the model can reasonably determine the scale of storage tank in urban water supply system,and optimize the operation of pipe network. |
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