Analysis Of Energy In RO/PRO Water Desalination Using Constrained Nonlinear Optimization

Today,the world is faced with water shortage and energy crisis,the popularization and application of membrane separation technology has made great contribution to mitigate this crisis,however,the process of membrane separation also goes with energy consumption,therefore,it is of great significance to seek an efficient and low energy consumption membrane water treatment technology for scientific and environmental protection.This paper presents a novel desalination process for coupled reverse osmosis and pressure retarded osmosis,which based on the technology of reverse osmosis.Contrasted with the classical reverse osmosis,the novel process can not only recycle the chemical potential energy from brine,but also dilute the brine before being discharge,in this way,the environment is protected simultaneously.In the first part of this paper,a constrained nonlinear optimization model for reverse osmosis and pressure retarded osmosis is formulated to minimize the normalized specific energy consumption and maximize the normalized specific energy production,respectively.In this optimization model,a set of dimensionless parameters in relation to membrane area,operating and design variables are used to build characteristic equations and simply the model formulation,the optimal solution of the model is obtained with Matlab’s optimization toolbox to realize process optimization.The underlying impacts of this dimensionless parameters and energy consumption are systematically explored.Next,analyzed the energy consumption of the novel hybrid system,the result shown that,the optimized γ should be 0.5～1.5 in reverse osmosis system,and the internal concentration polarization has significant impact on product of pressure retarded osmosis,for example,when the concentration polarization factor σ is 0.9,the maximized normalized specific energy production has decreased by 11%,and when σ is 0.8,it decreased by 28%.Moreover,the operating factors of reverse osmosis system play a decisive role in the overall energy consumption of the hybrid system.