System shutdown and precautions


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System shutdown and precautions

When the membrane system is shut down, it is necessary to flush the entire membrane system with pre treated qualified water supply or produced water, in order to replace the high salinity concentrated water from the pressure vessel and membrane components, until the conductivity of the concentrated water outlet is close to the conductivity of the inlet water, and proceed at a low pressure of about 3.0 bar (43.5 psi). High flow rate is beneficial for improving the flushing effect, but the pressure difference between the components or pressure vessels at both ends should not exceed the maximum specified value.

The low-pressure flushing inlet should not contain chemicals used for pre-treatment, nor should it contain scale inhibitors. After the flushing is completed, completely close the inlet valve. The reverse osmosis nanofiltration system should be completely filled with water. It is recommended to set the concentrated water discharge pipeline to an inverted U-shaped shape, with the top of the inverted U-shaped pipeline higher than the highest straight pressure vessel and a siphon breaking device installed.

If the water production pipeline is higher than the water level of the water tank, a device to prevent siphon damage should also be installed. When the system must be shut down for more than 48 hours, attention must be paid to preventing the membrane components from drying. After the components dry, there will be an irreversible decrease in water production. Adopt appropriate protective measures to prevent microbial growth or regularly rinse every 24 hours.

Shutdown protection of reverse osmosis membrane system

Short term shutdown preservation

The short-term preservation method is applicable to membrane systems that have been shut down for 5-30 days. At this point, the membrane element is still installed in the pressure vessel of the system.

The specific steps for saving operations are as follows:

a. Flush the membrane system with water, while paying attention to completely expelling gas from the system. Using a membrane system to flush the membrane system with produced water can help prevent pollution, and seawater desalination systems must flush the membrane system with produced water;

b. After filling the pressure vessel and related pipelines with water, close the relevant valves to prevent gas from entering the system;

c. Rinse every 5 days according to the above method.

Long term inactive storage

The long-term shutdown protection method is applicable when the membrane components are still installed in the pressure vessel of the system after being stopped for more than 30 days. The specific steps for saving are as follows:

1. Chemical cleaning of membrane components;

2. Use the membrane system to produce water and prepare suitable fungicides (for the types of fungicides, please refer to 8.3.2 in Chapter 8), and cycle and rinse the membrane device;

3. After the bactericidal agent fills the membrane system, close the valve and pump to keep the bactericidal agent in the membrane system. At this time, it should be confirmed that the system is fully filled;

4. If the temperature is below 27 ° C, 2-3 steps of operation should be carried out every 30 days with a new fungicide. If the temperature is above 27 ° C, the fungicide should be replaced every 15 days;

Before the membrane system is put back into use, rinse the system with low-pressure water for 1 hour, and then rinse the system with high-pressure water for 5-10 minutes. Both low-pressure flushing and high-pressure flushing should have all the produced water discharge valves of the system open. Before restoring the system to normal operation, it should be checked and confirmed that the product water does not contain any fungicides.

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