Double Pass RO

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Double Pass RO

What would be the concerns and considerations for direct connection of two passes of RO (i.e without intermediate tank, direct connecting of the first pass permeate lie to the suction line of second pass high-pressure pump)?

Please describe the required instrumentation and control philosophy. 

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14 Answers

  1. Dear Mr. Salman and all Contributors,

         Reverse Osmosis is not an appropriate process for desalination. A better process is Room Temperature Evaporation, which is the natural process used to avail potable water for mostly all human beings on this planet. Simply it consists of a tower water cooler and a condenser. Easy, simple, pure water generated, low maintenance and operation costs, if interested www.naturalseawaterdesalination.com. Thank you.

    1 Comment

    1. Can you treat the sea water in distillation process 

      However Re verse osmosis is treating sea water to make low cost portable drinking water how can you say reverse osmosis is not appropirate for desalination process  

      1 Comment reply

      1. Yes, reverse osmosis is an inappropriate desalination process even if it is accepted worldwide. RO refers to high pressure expensive pumps, expensive membranes, and when it comes to seawater desalination then it needs 2 consecutive stages, also expensive operational and maintenance costs. While Room Temperature Evaporation does not rely on any expensive equipment, and with low operational and maintenance costs. (www.naturalseawaterdesalination.com)

  2. start up the first stage RO pump.  The second stage RO pump should start automatically as the pressure reading reached 0.5 bar.  Both pass RO pump with inverter controlling is necessary for properly tuning.

     

  3. Our company has a patent on a 2 pass RO "WFIRO TM" that eliminates the inter-stage pump.  If anyone is interested we are willing to  license the technology.

    2 Comments

    1. I can remember Koch RO membrane program shows that since minimum 20 years no news about this. 

  4. As written by Davis bring back the 2nd pass RO concentrate  before RO 1 pump or in break tank before if applicable. Check with a RO Design program possibilities e.g. Lanxess 

  5. To make it clear the pressure sensor is to installate in the permeate line out of first RO before RO pump 2

  6. Install in outlet permeate a pressure sensor to make sure with VSD for the first RO pumpthat you always have 0,5 bar g  before the second RO pump also connected to the same sensor.Than you haven't a problem. BTW why not first pass RO with e.g. 30 bar and second pass without pump. 

  8. As per My experience inter-pass or Circulating Tank 100% required, to avoid any Operation breakdown startup shutdown or Flow variation, Even small Tank, We have same design dual site piping...................

  10. A buffer storage is always required for the flexibility of the plant ,during start up/shut down and regime changes.With out intermediate tank it is not possible.

  11. it is feasible in terms of process, but technically 1st pass system piping will need higher pressure rating which links to cost. In the end, you need to study the cost comparison. One thing good without intermediate tank is no contamination. Intermediate tank may contaminated by air if the tank is not sealed.

  12. The mass important for the system, the feed pump for the second RO must synchronize with the permeate 1st RO, Otherwise the feed pump for 2nd RO will make vacuum if rate 2nd pump RO  > rate permeate 1st RO. Vacuum will make failures the membranes in 1st RO. So you you must control the flow rate for rate permeate and flow rate 2nd feed pump and or recirculated small part to the pipe feed line after the install checked valve. 

  13. Not required the tank two pass system use two pump for more than 15000 ppm tds sf pump you can use  I will detail you how will connect provide the tds . 

  14. Hello Ali,

    You need to size the first pass High-Pressure pump to account for the back pressure of the second pass.  A back pressure allowance of 2 bar should be fine.  

    On start up you need to start the first pass before the second pass. 

    Put the second pass concentrate after the first pass cartridge filtration but before the high pressure pump.