Reverse osmosis membrane pretreatment process design cleaning scheme

Cleaning scheme 1. Cleaning The pretreatment process design of the reverse osmosis system has been carried out to remove the pollutants from the raw water, but it cannot be completely removed. Therefore, the reverse osmosis system is very common. Fortunately, most pollutants can be removed by regular chemical cleaning. As long as the pretreatment works normally, there are no reasons that are difficult to control, such as changes in raw water quality or unavoidable microbial contamination, and the cleaning frequency can be as low as possible. Sometimes operation errors can cause membrane fouling, such as too high recovery rate or abnormal dosing system. The amount of contaminated water produced by the membrane will decrease, the salt rejection rate will decrease, and the pressure difference between the inlet and the concentrated water will increase. Membrane cleaning can make some acid-base agents (pH2-pH12), membrane cleaning liquid temperature up to 45 °C. Many pollutions, especially slime, increase with time and are compressed and thickened, which makes cleaning more difficult and the cleaning time is greatly extended. If the symptoms meet the following characteristics, immediately clean the membrane components: 10-15% reduction in water production after standardization, desalination rate decreased by 0.5%, differential pressure ΔP increased by 15% (compared with the initial 24-48 hour pressure difference)

2. Need to clean prescriptions and other equipment 1. Cleaning the medicine box: The chemical cleaning medicine box is usually made of PE or FRP and can withstand the PH range of 1-12.

3. Cleaning the heating device: The cleaning temperature should be as high as possible, such as 20-40 °C. Chemical cleaning should not be carried out below 10 °C because the cleaning efficiency is very low, so heating is required for cleaning. 3. Cleaning agents: cleaning uses strong acids and bases (such as hydrochloric acid, phosphoric acid, citric acid, sodium hydroxide, etc.). Therefore, it is very important to choose chemicals. Sometimes, the improper selection of chemicals may cause membrane damage or even damage. 4. Cleaning pump: The cleaning is an acid-resistant alkaline pump with a flow rate of 12-15m3/h and a head of 20-30 meters. 5. Install the corresponding pipes, valves and pressure gauges during cleaning. Connect the water outlet of the pump to the inlet of the membrane, connect the thick water pipe to the medicine box, and install a ball valve before connecting it to the original water tank to connect the medicine box and the pump.

4. Cleaning procedure 1. The cleaning procedure is a cycle cleaning, and the outlet pipe of the concentrated water is connected to the cleaning medicine box.

5. Inject pure water into the cleaning water tank, and the cleaning liquid should meet the needs of the pressure vessel and the pipeline volume. Add 1%-2% of the dosage to the cleaning water tank, the acidic pH value is greater than 1, and the alkaline pH value is not higher than 13. 4. It is best to heat the cleaning liquid to improve the cleaning efficiency.

6. The heated liquid is injected into the RO membrane through the pump, the flow rate is 10-15m3/h, and the lift is 20-30 meters. It must meet the requirements and should not be super high. Just after cleaning, a barrel of liquid medicine should not be recycled to the medicine box, and it should be directly discharged. It contains a lot of pollutants, which will directly affect the effect of the liquid medicine, resulting in poor cleaning. After there is no large amount of pollution, the liquid directly returns to the original medicine box for circulation cleaning. When cleaning, fully open the concentrated water discharge valve to reduce the pressure as much as possible, and close the water supply valve to prevent the liquid from flowing into the pure water tank. 6.1 cleaning procedures are generally first cycle cleaning for 1-2 hours, soaking for half an hour, sometimes soaking for 1 hour or longer will be very effective. Recycled for 1-2 hours. A total of 4 hours or more of this cleaning procedure was completed.

7. After the cleaning is completed, use reverse osmosis water or clean water (filtered and SDI<3, and free of residual chlorine and microorganisms, conductance value <10000μs/cm, rinse the membrane, rinse time is more than half an hour.

8. After the cleaning is finished, the system restarts, but the water may be discharged until the water conductivity and pH return to normal. Note that if the machine is shut down for more than 24 hours after washing, soak it with protective solution (1% sodium hydrogen sulfite solution) ).

9. When the system is running again, it is necessary to add a scale inhibitor. Since the conductivity of the pretreatment before the system is very high, exceeding 1000 μs/cm, the water quality is likely to cause fouling of the membrane and increase the conductivity. The amount of water produced is reduced, and the pressure is increased.

Therefore, when the system is running, it is necessary to add a scale inhibitor to the inside to reduce the degree of contamination of the membrane and reduce the number of cleanings. It can keep the equipment from being polluted for a long time. The amount of this scale inhibitor is 2-6 PPM. (Add 2-6 grams of scale inhibitor per ton of water) Cleaning formula Contaminant type Cleaning formula effect Inorganic salt (CaCO3, CaSO4, BaSO4) 1% hydrochloric acid 0.5% phosphoric acid 2.0% citric acid best general general metal oxide (iron) 0.5% phosphoric acid 1.0% sodium hydrogen sulfite good inorganic colloid (sand particles) 1% sodium hydroxide (NaOH), 30 ° C 0.025% sodium lauryl sulfate / 0.1% NaOH, 30 ° C good biofilm 2% oxidized Sodium, 30 ° C. 1.0% sodium edetate (EDTA sodium salt) and 0.1% NaOH, 30 ° C

Best and best (when the biofilm contains inorganic scale) organic matter 0.025% sodium lauryl sulfate / 0.1% NaOH, 30 ° C. 0.1% sodium tripolyphosphate / 1% EDTA sodium salt, good silicon 1% sodium hydroxide, 30 ° C. 1.0% sodium ethylenediaminetetraacetate (EDTA sodium salt) and 0.1% NaOH.