The operation condition of seawater reverse osmosis systems will directly affect water production quality. There are many factors affecting the operation of seawater RO, of which main ones as follows:
Factors affecting the operation of seawater reverse osmosis systems.
Cellulose acetate membrane, polyamide membrane and composite membrane are subject to temperature. Membrane element (components) shows that the water is generally at 25 ?. It can make proper correction according to the manufacturer’s information at other temperature. Raising the water temperature properly, can reduce the viscosity of water and at the same time increase the membrane flux. Especially in the cold north areas, it is necessary to heat up the water. When running in the temperature above 20 ?, go up 1 ?, the flux increases about 3%.
Operating Pressure consists of osmotic pressure, net thrust and pressure drop of pipe. Osmotic pressure and the salt content in raw water are proportional to the water temperature, not to do with membrane performance. Net thrust is to make membrane element produce enough pressure for product water. Because permeable capacity is proportional to operating pressure, improving operating pressure will increase permeable capacity.
Membrane scaling is caused by sedimentation of non-soluble salt. Salt in the water is concentrated on the process of desalination of seawater reverse osmosis, when recovery rate is 50%, concentrated salt is 2 times. When recovery rate is 75%, concentrated salt is 4 times. This causes some salt ion concentration product over its solubility product. Concentration polarization and membrane module arranged in some parts of the uneven distribution will produce greater concentration. Concentrated water flow must be maintained in the undissolved salt precipitation condition, and kept suitable water recovery rate. The common scalings are CaCO3 and CaSO4. It can prevent CaCO3 and CaSO4 from forming by adding polyacrylic acid scale inhibitors.
4. Recovery Rate of Membrane Element
Generally it is expected that maximizing recovery rate of seawater reverse osmosis systems can get higher water production, however, because of excessive recovery rate, it will cause salt scaling in the system, thereby water production is subject to restriction. The typical recovery rate of sea water reverse osmosis technology, if it is common brackish pre-desalination, the recovery rate is 75?80%; If it is seawater ( 32500 ppm), max recovery rate is around 40%; If it is RO production in preceding stage.