Reverse osmosis flushing is the use of low-pressure and high flow water or inlet water to flush membrane components, removing pollutants or deposits attached to the membrane surface. Flushing flow rate: During device operation, particulate pollutants gradually accumulate on the surface of the membrane. If the flushing flow rate is equal to or slightly lower than the flow rate during water production, it will be difficult to flush pollutants out of the membrane element. Use a higher flow rate during flushing than during normal operation. Usually, the flushing flow rate in a single pressure vessel is: 8-inch membrane element: ≤ 10.9m3/h (28mil) or 12.1 m3/h (34mil) 4-inch membrane element: ≤ 2.7m3/h flushing pressure: During normal high-pressure operation, pollutants are pressed onto the membrane surface, causing contamination. So when rinsing, if the same high pressure is used, pollutants will still be pressed on the membrane surface, and the cleaning effect will not be ideal. Therefore, during flushing, it is advisable to increase the horizontal shear force by using low pressure and high flow rate as much as possible to flush pollutants out of the membrane element. The general inlet pressure should not exceed 0.4 MPa. Frequency of flushing: If conditions permit, it is recommended to frequently flush the system. Increasing the frequency of rinsing is more effective than performing a single chemical cleaning. The recommended frequency for flushing is once a day. Depending on the specific situation, the frequency of flushing can be controlled by oneself. matters needing attention:
① The inlet water pump needs to meet the inlet flow rate during normal operation (inlet flow rate=production water flow rate+concentrate water flow rate), and must also consider meeting the requirements of flushing flow rate.
② The selection of concentrated water pipelines and valves should also consider the high flow rate during flushing. When making water, due to the high recovery rate, the flow rate of concentrated water is relatively small. When performing flushing operations, low pressure and high flow are required, and almost all incoming water is discharged from the concentrated water pipeline. Therefore, when designing the concentrated water pipeline and valves, not only should the flow rate during water production be considered, but also the flow rate required for flushing should be taken into account. If only considering the flow rate during water production to design pipelines and valves, the pressure drop at the concentrated water pipeline and concentrated water valve during flushing may increase, which may not meet the required flow rate or exceed the flushing pressure requirement. Of course, it is also possible to consider setting up a dedicated flushing pipeline.
③ When selecting a flow meter, consideration should be given to the maximum flow that can be read during flushing. For multi-stage reverse osmosis systems, as shown in the figure below, in order to effectively flush the membrane components, it is necessary to design the system to be able to flush in sections. If a full section flushing is carried out, the flushing water and pollutants from the front section will flow into the rear section together, which can easily cause blockage in the rear section. The increase in the number of segments also means an increase in the number of membrane elements through which the flushing water flows. In order to meet the flow requirements, it is necessary to increase the inlet pressure. Due to the possibility of exceeding the allowable flushing pressure, the pressure on the membrane surface may increase, reducing the flushing effect. When performing the first stage flushing, fully open the valve of the first stage flushing concentrated water drainage pipeline, close the valve between the first stage concentrated water and the second stage inlet, and close the inlet flushing valves of the second and third stages. When performing the second stage flushing, fully open the valve of the second stage flushing concentrated water drainage pipeline, close the inlet flushing valves of the first and third stages, close the valve between the first stage concentrated water and the second stage inlet, and close the valve between the second stage concentrated water and the third stage inlet. When performing the third stage flushing, fully open the valve of the third stage flushing concentrated water drainage pipeline, close the inlet flushing valves of the first and third stages, and close the valves between the second stage concentrated water and the third stage inlet.
