Research On Robust Scheduling Of Reverse Osmosis Desalination System Under Uncertain Factors

The development of seawater reverse osmosis(SWRO)desalination technology has effectively alleviated the shortage of fresh water resources in the coastal areas.With more and more large-scale reverse osmosis desalination projects put into operation,the reasonable production scheduling has become an important way to reduce the cost of freshwater making and enhance the competitiveness of enterprises.However,there are many uncertainties in the actual operation,which poses a new challenge to the robustness and effectiveness of the production process scheduling.How to take account of the stability and economy of the system has become the current research hotspot.Aiming at the large-scale SWRO desalination plant,the robust scheduling problem under two typical uncertain factors is studied in this paper.The main research contents and conclusions are as follows:(1)The whole water producing process of large SWRO system is analyzed.The models of the key parts,RO unit,water network and produced freshwater storage tank,are built.The relationship between the salt amount,water flux and recovery rate are analyzed.The total cost of large-scale SWRO desalination plant is analyzed,which is divided into two parts of the project construction cost and operation cost,and the precise model of operation cost is established.(2)In view of the uncertain factors in the operation of the SWRO system,the robust scheduling problem is analyzed,and the robustness evaluation index of the scheduling scheme is given.The prediction of water consumption is studied.The grey Markov chain prediction model is used to predict the water consumption.The simulation results show that the grey Markov chain model has higher prediction accuracy.Aiming at two typical uncertain factors,freshwater demand fluctuation and RO unit fault,a two stage robust scheduling framework is put forward,which includes two stages: pre scheduling and rescheduling.The pre scheduling mainly copes with the uncertainty of water consumption,and a one-off robust scheduling scheme is given by off-line calculation.The rescheduling is triggered when the RO unit fails,and the production plan is rearranged by the rescheduling.(3)Because of the uncertainty of the real water consumption and the forecasting data,a robust pre-scheduling model based on the chance-constrained programming is established.In order to minimize the operating cost,the system water storage and water supply conditions which contain uncertain variables are expressed in the form of chance constraints.The genetic algorithm,which improves the crossover,mutation and convergence criteria,is used to solve the model by random simulation.The simulation results show that: when the water consumption is uncertain,the static scheduling is not practical.The robust pre-scheduling proposed in this paper can deal with uncertain information effectively,and make the system run smoothly by sacrificing part of the economy.(4)The rescheduling is triggered by the failure of RO unit,the scheduling strategy is: when the fault occurs,the idle RO units will be used to instead of those broken ones,and work according to the pre-scheduling.If it cannot meet the need of freshwater demand,a rescheduling,which is a multi-objective function of the economy of operation and the degree of deviation,will be triggered to establish the new production plan.Considering the requirement of real-time,the rescheduling uses the idea of rolling horizon optimization.The global optimization problem is decomposed into multiple local optimization problems,therefore its solving speed speeds up.The simulation results show that the reactive rescheduling can quickly respond to the failure of the RO unit and reduce the operating cost of the system.Finally,the paper summarizes the full text,and points out the direction of the next research.