Designing a RO system

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I want to design a reverse osmosis system with 500 LPH capacity.

What are the criteria and stages for designing it? Specifically, I would like to know how to select the following systems for the said capacity:  

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7 Answers

  1. I'm retired after 49 years in the RO business and I didn't learn everything.  Why Parmar, would you expect to be taught "how to design an RO system"?   When you want a TV, would you expect someone to teach you how to build your own?  I assure you the specifications regarding a TV receiver are small compared with that of an RO system.  

    That, Parmar, is why the world has professionals who have studied, pursued an avocation and earned their living providing expert advice to people like you.   Just like any professional, be it the law, engineering or health for example, there are good ones and there are duds.  Seek the advice of an engineer who can tell you exactly what you need based on your specific requirements and the most important factor--the feedwater analysis.

    I am surprised that the responses so far are so condescending.   Are you all being kind?   Do you typically give your talent away? 

  2. I have designed a number of RO plants over the years and they are very tricky if done incorrectly.   The membrane size question is easy...basically the contact an RO supplier (I can supply some if you wish) and they give them your criteria and they will size the RO system needed to output your flow rate.   At a minimum ROs come in 2-stage units where the initial water flow passes through stage 1 and the permeate heads off to the clear while the concentrate from stage 1 will then pass through stage 2 to further to try to recover as much water as it can and then the permeate from stage 2 enters the clear well.  the reject water is then directed to a storage pit where it is either treated prior to discharge or sometime directly released to a lagoon.  There are 3-stage RO units but honestly, your pay back is quite low as the potable water produced from stage 3 (where the feed water is the concentrate is from stage 2) is very very low and is generally not worth.   I have not found a water that I would benefit from a stage 3 unit as the pressures are very high in stage 3 and cleaning them is a real pain.  

    The high pressure pump (or step-up pump) is always, well at least 98% of the time, attached to the RO skid and is determined by the manufacture.  RO units run at pressure between 100 psi and 150 psi typically.  The feed pump on the other is generally a lot lower and is simply used to transfer water from the storage reservoir to the step-up pumps.  Feed pumps generally run around 40-60 psi...their goal is also to force the water through the 5-micron pre-filters....the pre-filters are located between the feed pump and the step-up pumps.  

    Not sure what you mean by dosing rate as you do not add any chemicals to the water prior to the water entering the RO UNLESS you are referring to de-scaling chems and ORP chems.  PLEASE make sure that you have an automatic ORP sensor in front of the RO pumps with an automated shut-off valve.  RO membranes are EXTREMELY sensitive and after working with them for 10 years you must be careful...any precipitated material will damage your membranes.  ROs are meant for the removal of dissolved particles only.  Precipiated material or chlorine will absolutely reduce the life of your membranes.   I also highly recommend that at least once a month you have your operations staff probe each RO unit for conductivity in the permeate stream (and this is taught to you by the RO supplier) and if you find high conductivity then you know that one of the membranes have been ruptured and require replacement.  It also wouldn't hurt to send off at least one or two RO units for an autopsy as they will be able to determine what caused the failure.

    Sorry...for the long winded response...I could write several pages more and if need more info it might be easier to call me...just let me know.  Last thing...there are "loose" and "tight" membranes and yes they do make a difference and I HIGHLY HIGHLY recommend some kind of pre-treatment process...it will save the life of the membranes and make the operator's lives much easier and the water you produce will be that much better.   it is possible to go straight to RO but I am of the school of thinking of pre-treatment....always.

     

    Sincerely,

    Kurt

    2 Comments

  6. Without feed water analysis report, we can just give you a basic idea / layout - Make & model of components depends upon your water chemistry.

    1) Membrane 4040 - 2# 

    2) Feed water pump - 1hp

    3) HP pump - 10-12kg @ ??? flow rate

    4) Dozing pump 4/7 lph - dozing qnty depends upon feed water chemistry.

    5) FRP vessel - 1248 - 2#

    6) MPV filtration 20NB - 2#

     

  7. Parmar, There are a lot of parameters you have not mentioned, such as Water Chemistry, Permeate Goals, Percentage of Recirculated Concentrate, etc. But loosely put; Pre Filtration to protect Membranes from Abrasion Damage, a Pressure Pump producing 150 psi., your Membranes need to be at Least Twice of your required water production (due to waste), Storage for Product Water, a Delivery Pump from Storage to Point Of Use, and if water is for Consumption a way to Sanitize that water (Chlorination or UV).