A new dual-function device for optimal energy recovery and pumping for all capacities of RO systems

Abstract

The cost of energy consumption represents more than 50% of the total desalting water cost by reverse osmosis (RO) for conditions prevailing in Kuwait. Real prospects of decreasing this energy consumption exist by recovering the energy of the high pressure rejected brine. This rejected brine flowrate is about 70% of the feed flowrate and at pressure slightly below the feed pressure. In a single stage seawater RO desalting system, experience in Doha RO experimental station indicated that the energy consumed by the feed pump can be decreased by 27% when a reversed centrifugal pump type turbine is is used as an energy recovery device. A similar saving of 38% is expected when a Pelton wheel type turbine will be installed shortly in Doha RO station. Towards the maximum development in reducing energy consumption, a new rotor type pressure exchanger is now under development as an energy recovery and pumping device for RO seawater desalting system at Kuwait Institute for Scientific Research (KISR). Preliminary experiments proved the success of the device in recovering most of the energy from the rejected brine and decreasing the pumping energy of the feed to the membrane modules by 60%. This percentage represents the maximum saving of energy that can be sought in the RO seawater desalting technology. Through this development, the cost of desalting seawater can approach the cost of desalting brackish water, a significant advancement the desalting seawater by RO technology. This paper presents the technical characteristics of the pressure exchanger and its performance as an energy recovery device for RO system under real operating conditions in the Gulf area. A flow sheet that links the new device with the feed pump, rejected brine connections and booster pump is also presented.