Low flow rate measurement of H2O2
Low flow rate measurement of H2O2
(OP)
We are adding hydrogen peroxide ~35% concentration, and need to find an appropriate flowmeter and/or flow switch. The flow is 50-60 mL /min, and it will be coming directly from a positive diaphragm pump, pulsing once a second for less than half a second.
I think that we may want to use a differential pressure flowmeter. We have been looking at the coriolis, but the start-up costs are pretty high and we will need quite a few meters.
I think that we may want to use a differential pressure flowmeter. We have been looking at the coriolis, but the start-up costs are pretty high and we will need quite a few meters.





RE: Low flow rate measurement of H2O2
RE: Low flow rate measurement of H2O2
Sounds like you may already be using a metering pump. Just calibrate -- measure flows at different settings. Pump into a graduated container at different pump speeds (& strokes, if electric-powered), & prepare a chart or curve of the flow rate. If air-powered, measure flow as function of air pressure.
RE: Low flow rate measurement of H2O2
JMW
www.ViscoAnalyser.com
RE: Low flow rate measurement of H2O2
Regards
Stonecold
RE: Low flow rate measurement of H2O2
If you need a flow switch, look at the Efector thermal dispersion switches. They have adjustable switching points and if the lower housing is made with small enough flow passages, they work with flows this low.
Any flowmeter or transmitter you use will need to deal properly with the pulsile output of your pump, and most low-end flowmeter products produce significant errors due to their inability to generate an accurate mean flow out of all those pulses. Use a pulsation dampener to smooth things out so that whatever flowmeter you use will have a better chance of working.
You can forget about the calibration curve method- it won't work with peroxide. The oxygen you need to pump WITH the peroxide will cause you no end of trouble without a flow switch at minimum.
If it's basic indication with switching that you want, once you've got the flow properly pulse-dampened a rotameter will work fine. You can get an optical emitter/detector pair switch which will do a decent job of low flow sensing. But you need to make sure that you vent the oxygen produced by the slow decomposition of the peroxide or it will wreak havoc with your pump's ability to maintain prime- and with the flowmeter's readings. That can be done with a solenoid valve and timer interlocked to the flow switch, or by other means. Some of the pump vendors have their own little tricks to deal with peroxide.
If you actually need accurate flow measurement and transmission at these rates, you're pretty much stuck with either coriolis, thermal (Brooks, Porter, Horiba etc.)or positive displacement flowmeters. If you could find a magmeter with a tiny flowtube, that would work too- 35% is plenty conductive enough- but it's tough to get velocities high enough at these low flows to make the mag principle work properly. None of these options are what you'd call inexpensive, but coriolis is the most expensive by far- and although not totally insensitive to errors induced by any stray 2nd phase (oxygen) in there, it's the method of these which is least sensitive to this problem. Stay away from the laminar flow differential pressure units- they're junk even with water, and will be disastrous with peroxide.
RE: Low flow rate measurement of H2O2
If so, an ORP sensor & controller might be appropriate.
RE: Low flow rate measurement of H2O2
RE: Low flow rate measurement of H2O2
RE: Low flow rate measurement of H2O2
ranges of 6kg/hr. Its turndown ratio is high, a claimed 500:1, so your ~3.6kg/h should be within its range.
general description:
https://pia.khe.siemens.com/index.asp?Nr=13786
spec sheet:
https
Dan
RE: Low flow rate measurement of H2O2
RE: Low flow rate measurement of H2O2
see
http://www.alldos.com/pdf/209M-EN-15.820019.pdf
RE: Low flow rate measurement of H2O2
We were using diaphragm dosing pumps - the challenge we faced was a single source peroxide charging a steam line going to 14 different flowpaths at 2 second intervals. The steam backpressure varied as much as 5 psi from one path to the next, so that is what caused the problem with the dosing. The diaphragm was pneumatic, as well, so there were some paths that would get a double pulse with low backpressure, and other paths might not get a pulse at all.
The peroxide flow would not be turbulent, pulsing over a 20 m line would send a wave over, but I do hear the feedback about the pulsation dampener.
Also, the bigger issue became what is the actual flow through the line? We are using a dosing pump but did not have a representative continuous flow to be used for legal record. We were not catching each pulse of the pump on the data acquisition system - that may be a hardware problem.
Thanks for the feedback!
RE: Low flow rate measurement of H2O2