Design Energy Efficient Membrane Facilities: Optimization of Energy Consumption for Membrane Desalination Systems

摘要

An important consideration during membrane treatment plant design is the projected energyrnconsumption that will result from the selected process and system configuration. Minimizingrnenergy consumption can have a significant impact to the overall operations and maintenancern(O&M) costs of a new facility. Membrane desalination processes require high feed waterrnpressure to overcome osmotic pressure, induce meaningful permeate flow and accomplish saltrnwater separation. The energy requirement for a desalination facility is a composite value of rawrnwater pumping, pre-treatment losses, high pressure pumping, post-treatment losses, permeaternpumping and auxiliary needs. In each application category, the system configuration is different,rnand therefore, there is a somewhat different approach to optimization of power consumption.rnNanofiltration systems operate at higher recovery rates in the range of 80 – 90%, and therefore,rnare configured in either two or three stage units. Frequently an interstage booster pump is appliedrnto equilibrate flux rate at subsequent stages. Brackish units operate at recovery rate of 70 – 85%rnand are frequently arranged as two stage systems. Interstage boosters are used only for brackishrnapplications with very high feed salinity. Seawater systems typically operate at a recovery raternaround 50%, mostly in a single stage configuration. Feed pressure in nanofiltration systems is inrnthe range of 7 – 14 bar (100 – 200 psi). Brackish systems operate at higher feed pressures of 14 –rn28 bar (200 – 400 psi). Seawater RO process systems can require feed pressures of 45 – 70 barrn(650 – 1000 psi). In RO processes the permeate stream leaves the RO unit at close tornatmospheric pressure. The pressure of the concentrate stream is reduced from the feed pressurernvalue by pressure losses in the subsequent stages. Some of the energy of concentrate stream canrnbe recovered using energy recovery devices.rnFeasibility of energy recovery device applications depends on flow rate and pressure of thernconcentrate stream. This paper will describe common and more advanced solutions forrnoptimization of energy consumption in NF/RO systems, either through configuration of thernNF/RO systems or by incorporation of energy recovery devices. Features of various types ofrncommercial energy recovery equipment will be discussed. Energy saving examples will bernprovided utilizing actual installations for each type of application.