Methods of loading and unloading industrial NF membranes & RO membrane elements

2025-6-26 Jiangsu HID

Preface

Industrial reverse osmosis (RO) and nanofiltration (NF) technologies are widely used in seawater desalination, sewage treatment, chemical processes, food and beverage, etc. due to their excellent separation effects. As the core components of the system, the correct loading and unloading and installation of membrane elements are not only related to the separation effect, but also affect the membrane life and system operation economy.

1. Preparation for loading and unloading

- Prepare the following items before loading and unloading components:

Safety rubber boots, protective glasses, rubber gloves, silicone lubricant, pliers, clean cloth, glycerin.

- Inspection steps before loading and unloading components:

• Check the water pipes

Carefully inspect the upstream water inlet pipeline and thoroughly remove foreign matter such as dust, grease, metal debris, etc. If necessary, chemical cleaning procedures should be performed on the water inlet pipeline and reverse osmosis pressure vessel to ensure that all foreign matter is completely removed to ensure the normal operation of the system.

• Inlet water quality inspection

Strictly examine the quality of the incoming water. Before installing the elements in the membrane pressure vessel, ensure that the qualified water treated by the pretreatment system flows for at least 30 minutes, and test the quality of the incoming water of the reverse osmosis system to ensure that it meets the water inlet standards of the membrane elements. At the same time, check whether there is leakage in the piping system.

• Check the pressure vessel end plate structure

When disassembling the end plate and thrust ring of a pressure vessel, it should be noted that the end plate structures designed by different manufacturers may differ, so the corresponding structural schematics should be referred to during the operation.

• Thoroughly clean the pressure vessel

Rinse the opened pressure vessel thoroughly to remove dust and sediment. If further cleaning is required, make a mop large enough to fill the inner diameter of the pressure vessel, soak it up with a 50% glycerin solution, and drag it repeatedly inside the container several times until the inner wall is clean and lubricated.

• Check whether the system is running normally

Before installing the components, you must ensure that all parts and chemicals required to install and put the system into operation are complete and that the pretreatment system is operating normally.

• Confirm the replacement before unpacking

Only when you plan to start the system immediately, you can unpack and install the membrane element. Otherwise, the membrane element should be kept sealed in the original packaging.

2. Disassembly of components

When disassembling the membrane element in the system pressure vessel, two professionals must follow the following procedures:

• First, the external pipes at both ends of the pressure vessel need to be removed, and the end plates should be disassembled according to the instructions provided by the manufacturer. During the disassembly process, all parts should be numbered and placed in order.

• Next, remove the end plate assemblies from both ends of the pressure vessel.
  Finally, during the disassembly process, the membrane elements must be pushed out one by one starting from the water inlet end of the pressure vessel.

• Only one element is allowed to be pushed out at a time. When the element is pushed out of the pressure vessel, it should be caught immediately to avoid damage to the element or personal injury.

3. Install components

• Carefully remove the membrane element from the packaging box and check whether the position and direction of the brine sealing ring on the element are correct (the opening direction of the brine sealing ring must face the water inlet direction.

• Push the end of the membrane element without the brine sealing ring parallel to the water inlet end of the pressure vessel until the element is exposed about 10 cm outside the water inlet end of the pressure vessel. Note that the element must always be installed from the water inlet end of the pressure vessel.

• Insert the connecting inner joint between the components into the central water production tube of the component. Before installing the joint, apply a small amount of silicone-based "O" ring lubricant on the "O" ring of the joint. If not, directly moisten it with qualified pre-treated water.

• Carefully take out the second membrane element from the packaging box. Similarly, check whether the position and direction of the brine sealing ring on the element are correct. Carefully hold the element and insert the internal joint on the first element into the central water production pipe of the element. At this time, the connecting internal joint cannot bear the weight of the element. Push the element into the pressure vessel in parallel until the second element is exposed about 10 cm outside.

• Repeat steps (3) and (4) until all elements are installed in the pressure vessel. Transfer to the concentrate end and install the element internal joint on the water production center pipe of the first element. The length of the element and the pressure vessel determines the number of membrane elements that can be installed in a single pressure vessel.

4. Check items before starting the machine

• All equipment, including pipelines, containers, instruments and flow-through parts of water pumps, must be made of corrosion-resistant materials.

• All pipelines and equipment must meet the design pressure requirements.

• All pipelines and equipment should be able to meet the H range specified in the design (such as cleaning system)

• The multi-media filter is backwashed and cleaned, and the water quality is qualified.

• A clean new safety filter element has been installed upstream of the high-pressure pump.

• Before connecting the pressure vessel, the water inlet pipe and the high-pressure pipe have been cleaned and flushed.

• The location of chemical dosing point is accurate.

• Appropriate check valves and anti-siphon valves are installed on the drug delivery lines.

• Appropriate mixing measures are taken in the dosing water inlet pipeline.

• The drugs and their concentrations in the drug adding box are accurate.

• When the dosing metering pump stops, the reverse osmosis and nanofiltration devices can be shut down.

• When the reverse osmosis device and nanofiltration are shut down, the dosing metering pump can be shut down

• If oxidants such as chlorine are used, measures should be taken to ensure that the chlorine in the water entering the membrane system is completely removed.

• Measuring instruments that can effectively operate and monitor the pretreatment, reverse osmosis and nanofiltration systems are planned to be installed.

• The instruments listed in the plan are installed and functioning properly.

• Confirm that the instrument has been calibrated.

• A pressure safety relief valve is installed and set accurately.

5. Special matters and precautions

6. Special system start-up - thermal disinfection of RO membrane elements

For new thermal disinfection elements, their performance must be pre-adjusted before contact with hot water. The specific steps are as follows:

• Under the conditions of low pressure and low water output, use appropriate influent water (during the membrane pre-setting period, the qualified influent water must be free of residual gas, scale and fouling. It is best to use RO produced water, and pre-treated qualified produced water can also be used) to flush the thermal disinfection membrane element.

• In a low pressure environment where the transmembrane pressure difference between membrane inlet water and product water does not exceed 1.7 bar (25 psi) and the maximum inlet water pressure does not exceed 3 bar (43.5 psi), warm water with a temperature not higher than 45°C is used for circulation treatment.

• Continue to introduce hot water into the system until the temperature reaches 80°C.

• When the water temperature exceeds 45°C, the transmembrane pressure difference on both sides of the membrane should be maintained below 1.7 bar (25 psi).

• Under the above temperature conditions, the system is kept warm for 60 to 90 minutes.

• Allow the system to cool naturally to below 45°C.

• In a low-pressure environment where the transmembrane pressure difference between membrane inlet water and product water does not exceed 1.7 bar (25 psi) and the maximum inlet water pressure does not exceed 3 bar (43.5 psi), use qualified inlet water to flush the element.

• During the membrane pre-setting period, qualified feed water must be used that does not contain residual gas, scaling, or fouling. RO produced water is preferred, but pre-treated produced water that has passed the test can also be used.

Be sure to perform this step when the membrane element has cooled to below 45°C .