Reverse Osmosis Design and Sizing

[aayub98]

thread164-414395


Hi all,

I am in my third year studying chemical engineering and my third year design project includes doing a detailed design of a reverse osmosis system and I am having much difficulty in being able to design the reverse osmosis by manual calculations. Most references just give typical heuristics on what can be expected from typical RO systems used commonly in industry today.

I have managed to calculate my osmotic pressure of the feed, permeate and reject stream, but I am also having difficulty with calculating the overall pressure drop from the feed to the permeate? Someone said that the permeate pressure would be at atmospheric pressure but another source disputed this so I am also not sure on what the expected value is.

I was wondering if anyone had any ideas on how to size my reactor using design method equations. Obviously as I am designing this from scratch then I have to optimise the process, which allows me the liberty of using sources to select values for my process, but of course everything has to be positively justified.

If anyone could help in assiting me with methods on how to size the membrane I would be most appreciative.

Thankyou.

note: I have also referenced a thread which was most useful to me in my research so it might give you an insight too on to what I am trying to achieve.

 

[ashtree]

Permeate is typically at atmospheric pressure but the actual pressure seen by the RO plant may be influenced by the relative altitude of the outlet. Most RO membrane manufacturers limit the backpressure to something like 30-50kpa. That does not limit the height that you can push to but if the outlet is higher than that you must do something to limit the backpressure on shutdown.

The other factor that may influence permeate pressure is if permeate throttling is included in the design. This is sometimes used on the first stage of a two stage machine to limit first stage recovery and eliminate the need for an interstage boost pump. In this configuration it is not unusual to lose several hundred kpa across the throttle valve.The downstream side of the throttle valve will be at or close to atmospheric pressure.


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

 

[bimr]

While it is admirable that you are trying to work through the RO design process, you would be better served if you talked to a RO application engineer. This calculation is not something that can be learned in a few months time. It probably takes someone 3-4 years working as an application engineer to learn how to do these system calculations properly.

Dow

It would be much easier to put together a few scenarios and call DOW and let them run through the calculations.