RO Membrane Plant FLUSHING Recovery Rate

[connoriroc]

Hi all,

I finally have a worthy question for you all, I think....

I am investigating the membrane flushing recovery rate for a water plant in South Florida.

When a train is turned off, there is a post-run flush that occurs. I am wondering if there is a typical recovery rate and flow rate to shoot for during the train flush, or some literature I can reference. I know it is good to flush with low TDS water at a low recovery/high flow, but want to get a typical number.

Let me know if you need more info.

Thanks.
Connor.

 

[bimr]

This type of information would normally come from the equipment manufacturer / service representative. Have you contacted them?

 

[ashtree]

What you are refferring to is typically called a permeate flush, where you feed permeate into the RO plant at a high rate with the concentrate control valve open. Very little permeate is produced. Permeate flushing reduces salt and particulate accumulation and might result in slight pressure reductions. It may also help to reduce biofouling. A regular flushing program in some circumstances can reduce the frequency of CIPs.

Individual membrane manufacturers might have different flow rates and different vessel sizes require different rates, but for 8 inch vessels 5-10m3/hr per vessel is typically used. If you are trying to remove accumulated salts a low rate for a longer time is probably best, If you are trying to flush out accumulated particles go for the higher rate.

You should assume 0% recovery during a flush and some plant designs send any permeate produced to waste anyway. Most plants will actually produce some permeate but the amount is quite low. I have never measured it but i would thinjk 10-25% recovery at a guess.If you operate at a higher feed rate during the flush than you will get more than at the lowr rates due to the increase in operating pressures.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[connoriroc]

Bimr, we spoke with the membrane skid manufacturer and got a bit of info, but nothing definitive. As far as getting in touch with the membrane manufacturer, we are in talks with them.

Ashtree, that is a good number to get us in the ball park thank you! The plant does not flush with permeate (looking into this, $$$ restrictive) they currently flush the concentrate with raw water. We have done some mods (concentrate valve bypass, along with others) that have reduced flush recovery from about 74% to about 53%. Raw water quality is very good, low TDS, and the membranes easily produce permeate at even low pressures, so taking restriction off the concentrate line was critical for us even getting to 53%. One question, where is the 5-10 m3/hr figure coming from? Is it from experience or is there a document to be referenced?

Thank you both, this helps quite a lot.

 

[bimr]

Some product info:

Link

Link

 

[ashtree]

The Dow Filmtec RO membrane Technical Manual page 124 Table 6.2


Regards
Ashtree
"Any water can be made potable if you filter it through enough money"