Acid injection system for RO pretreatment
Acid injection system for RO pretreatment
(OP)
We have concentrated bulk HCl storage on site. We also have a supply and return HCl header that is always pressurized. What is the best way to setup acid injection on the RO feedwater line?
I thought about using a daytank that operators could fill once per week and would draw down and get injected into the 16" feedwater line using a chemical pump. However, the thought of an acid 'daytank' was not well received.
I'm hesitant to just run a line from the acid header to the 16" feedwater line for fear that the regulating valve could fail, causing large amounts of acid to get dumped into the line.
Looking for alternative ideas. Thanks!
ProjectEng





RE: Acid injection system for RO pretreatment
Regards,
Believe it or not : Eratosthenes, a 3rd century BC true philologist, calculated circumference of earth with the help of a stick and it's shadow. The error was just 4% to the present day calcuated value.
RE: Acid injection system for RO pretreatment
You should install a 3 valve block and bleed to prevent the water pressure from backing into you acid system in the event of failure of the acid pump.
If you are that concerned with control valve failure, you could add a second pH instrument to shut off the acid in the event of a failure.
RE: Acid injection system for RO pretreatment
The acid injection system this is typically configured with a bulk tank, day tank, metering pump, pressure relief loop back to the day tank, pressure sustaining valve at the injection point, an injection quill, a static mixer, a pH sensor, and a control loop that controls the dosing rate of the acid for the specified pH valve.
Acid injection and scale inhibitor injection are two of the most important systems to be engineered in a RO process, along with pre-filtration (typically 5 micron) of the raw water stream.
Good luck...
RE: Acid injection system for RO pretreatment
We have a dedicated pump supplying our acid which cuts out in event of a plant trip. Perhaps you should have a supply valve at the point you connect to the pressurised acid line that cuts the supply in event of a plant trip. This would negate the possibility of continuing to feed acid in case of a plant trip, and also give you an isolation point if you need to do maintenance downstream.
Edd
RE: Acid injection system for RO pretreatment
The pumping scheme that you are describing appears to be unsafe. You should also consider installing a 3 valve block and bleed to prevent the water pressure from backing into your acid system in the event of failure of the acid pump, valve, check valve or power. A 3 valve block and bleed is a commonly used technique to be ensure that an water into an acid tank accident will never happen.
A 3 valve block and bleed uses two normally closed valves and one normally open. In the event of a process failure, excess pressure is relieved to drain rather than to an upstream acid tank.
pipeline<---------X---------X-------<acid pump & tank
|
|
X (normally open)
to
drain
RE: Acid injection system for RO pretreatment
www.consulthai.com/2002/news/papers/On-site_versus%20.p...
RE: Acid injection system for RO pretreatment
Off the pressurized header, I already have a manual valve. I plan to add a strainer right after the manual, then the control valve. At the point of injection, I plan to add a ball check valve, then a manual valve, then an injection quill with its own little "cheapo" built-in ball check.
Wanted to bounce this off you guys to make sure I wasn't overlooking anything. Your thoughts and suggestions?
Thanks,
ProjectEng
RE: Acid injection system for RO pretreatment
RE: Acid injection system for RO pretreatment
RE: Acid injection system for RO pretreatment
I highly recommend that you hire a consultant with experience in RO plant design & construction to design the pump and injection system for you, otherwise OSHA may be writing about your proposed system in the near future!
RE: Acid injection system for RO pretreatment
RE: Acid injection system for RO pretreatment
pH = - log {H+}
reference: Chemistry for Environmental Engineers
RE: Acid injection system for RO pretreatment
Corning and Orion have pH meters capable of measurement range -1.99 to 19.99. Electrode probes are usually rated for pH 0-12 or 0-14 since materials of construction usually deteriorate at the limits. It is more accurate to titrate for concentrations of strong acids, anyway.