Reasons for the rupture of ultrafiltration membranes
Thread Content
Ultrafiltration is carried out using a horizontal setup with domestically produced internal-pressure membranes for dead-end filtration. During operation, it was found that one set had a higher flux; upon inspection, it was discovered that the shell of the ultrafiltration membrane was cracked. During normal operation and flushing, the pressure remained within the specified range; what caused the rupture?
It is very likely that it was caused by a sudden surge in pressure — since the ultrafiltration process is intermittent, flushing is required every 30–45 minutes, and this flushing is carried out by using PLC-controlled pneumatic valves； However, pneumatic valves have one drawback: they open or close quite quickly, usually within a few seconds. Therefore, after the flushing is complete, the sudden opening of the valve causes an instantaneous impact on the membrane – what is commonly known as water hammer effect. Although the pressure within the system is normal during operation, this sudden impact can be fatal to the membrane. If possible, it is recommended to replace it with an electric valve ； Another approach is to install a throttling device at the exhaust port of the pneumatic valve to control the exhaust speed, thereby controlling the speed at which the valve opens or closes. This post was last edited by tjsong on 2009-2-16 10:09.]
First of all, thank you for your reply. Our system uses electric valves; could it be that the high flow rate causes stress on the membrane?
A high flow rate during operation should not cause any impact. Generally, after backwashing is completed, due to the location of the backwash discharge valve, it is possible for the water-producing side of the membrane to be in a water-free state. If water is introduced suddenly after backwashing, a high flow rate at that time can easily cause damage to the ultrafiltration membrane. In such cases, two valves can be installed for water inlet – one with a normal diameter and another with a smaller diameter. After backwashing is complete, water is allowed to flow in through the valve with the smaller diameter; once operation is normal during that cycle, the valve with the normal diameter is used instead.