As the start up and shut down operations may result in some problem when not performed properly, we would like to bring your attention to the recommended procedures as below.
Start-up procedure
Before starting up an RO system, it should be verified that all pretreatment systems ar eworking according to their specifications. It may be necessary to take water samples for analysis. In the case of polyamide (thin film composite) membranes free chlorine must be 0.0 ppm. The Silt Density Index (SDI) should be according to the RO design guidelines(typically < 5.0). On startup, the inlet valve should open prior to the initiation of the high-pressure pump, to completely fill the system with low pressure water (<100 psi [< 7 Bars]). This “soft start” will prevent hydraulic shock at startup. Pre-treatment chemical addition should begin at this time (making sure the chemicals are not over-injected). The high-pressure pump should then be started and the system slowly bought on-line, up to design permeate flow. If starting up after a period of shutdown, flush the permeate to drain for 30 minutes to remove residual preservation chemicals. Produced water permeate can be used when it meets the qualityrequirement of downstream processes.
• Check all valve settings are correct.
• Ensure that all air is flushed out at low feed pressure.
• Check pipe connections are tight.
• Close the feed pressure control valve.
• Reject valve is fully open.
• Start feed or HP pump.
• Slowly open feed control valve. Ensure that max feed flow per vessel is not exceeded.
• Slowly close reject valve.
• Check product flow.
• Fine tune the feed and reject control valves.
• Check the chemical addition, feed pH, LSI and the SDI.
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• Take the first reading of all operating parameters. This is important for future normalisation calculations.
• Measure conductivity of each vessel and identify out of spec performance and take necessary action.
• Take water samples and analyse.
• Compare performance with prediction.
• Check operation of safety devices.
• Lock the plant in automatic operation.
• It is recommended that all the operating parameters are measured several times in the first 48 hours.
Let the system stabilise for at least 1 hour. Shut down procedure
Permeate Flush
As salts in the feed water have concentrated up and exceeded their solubility during operation, they should be rinsed out prior to any shutdown (>15 minutes). Rinsing of the membranes with permeate water on shut will also aid the flushing of colloids and bacteria from the membrane surface.Flow rate during flushing should be based on the recommended cleaning instruction flowrates. This is normally 30 – 40 gpm [6.8 – 9.1 m3 /hr] per pressure vessel. Flushing time should be long enough for the conductivity out to equal the conductivity in. This is typically 15 – 20 minutes.If the permeate flush is unavailable, feed water can be used by allowing low-pressure water to replace the water within the system by delaying the inlet valve closing. Scale inhibitors hould be turned OFF during the permeate flush.If the water temperature in the membranes exceeds 115 oF, flush water should becontinuously passed through the system to prevent membrane degradation.
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• The feed pump and the inhibitor and acid dosing is shut down.( Keep the acid for CA)
• The feed valve is opened and the system is flushed with feed water for 10 minutes before the pretreatment train is shut down.
• The flushing tank should have been filled with permeate prior to shut down and the RO stack should be flushed with permeate water.
• The RO train can be stopped for up to 24 hours without preservation.
The start-up sequence is reversed by slowly opening the reject valve and closing the feed valve. In case of extended shutdown
In this case, preservation with sodium-bisulfite (1%).It is recommended to measure the pH regularly. A fresh solution is needed when the pH < 3.A fresh solution is also needed when the liquid becomes turbid or changes color. Regular inspections (weekly) are recommended.
Ensure that the elements do not dry out. RO Data Collection and Monitoring
Data collection is critical for monitoring the performance of the membrane system. Without it, there will bee no idea if the system is fouling, suffering from scale formation, or if themembranes are deteriorating.When operating data is recorded, it should be compared to previously established alert andalarm levels. These levels should be associated with well-defined response procedurescorresponding to the potential problem.The alert and alarm levels are set for a 15% change from normalized start up data.
Sayfa / Page 4/5 A good record keeping as mentioned on the table below will definitely help a lot along with chemical residual control. The data should then be normalized to extract the information.
Sayfa / Page 5/5 It should be noted that it is essential to clean membranes at an early stage of fouling. It is often difficult to clean excessively fouled membranes and irreversible damage may occur during the cleaning process.
Cleaning is recommended when on or more of the following parameters change by 10 – 15% after data normalization:
• An increase in product water conductivity or salt passage
• An increase in
• An increase in feed pressure
• A decrease in normalized permeate flow (NPF) output or flux.
If any of the above performance parameters deteriorates by more than 30%, it maybe impossible to recover plant performance by routine cleaning practices. Cleaning is not expensive and requires little amount of chemicals. As an example, a 1000m3/day plant would require a total cleaning solution of around 4000 liters. ΔP across the plant •
• The system is adequately protected or is flushed every 24 hours.
• The system is protected from extreme temperature conditions.
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