Diluted Sulfuric Acid- Corrosion problem
Diluted Sulfuric Acid- Corrosion problem
(OP)
Dear All,
In our geothermal power plant we used a diluted sulfuric acid in the geothermal water pH modification system.
We "manufacture" the diluted sulfuric acid (about 0.8 -0.9 % w) by means of the dilution of the 98% sulfuric acid with the slip stream of the untreated geothermal water.
The dilution ratio is about 1: 100. The concentrated acid flow is 92 kg/hr and water flow is 10,000 kg/hr. The dilution water temperature is about 170 deg. C.
We are experiencing quite a few problems with the dilution system when the biggest problem is that we are getting extremely high corrosion rates (about 0.1" in two weeks) in the Hastelloy C276 piping, especially around the 98% acid injection point in the water slip stream and through the 2" Static Mixer (Hastelloy C276) which located 2 meter downstream of the concentrated acid injection "T".
Do you have an idea how I could find the cause of this problem?
Thanks in advance,
Mike
In our geothermal power plant we used a diluted sulfuric acid in the geothermal water pH modification system.
We "manufacture" the diluted sulfuric acid (about 0.8 -0.9 % w) by means of the dilution of the 98% sulfuric acid with the slip stream of the untreated geothermal water.
The dilution ratio is about 1: 100. The concentrated acid flow is 92 kg/hr and water flow is 10,000 kg/hr. The dilution water temperature is about 170 deg. C.
We are experiencing quite a few problems with the dilution system when the biggest problem is that we are getting extremely high corrosion rates (about 0.1" in two weeks) in the Hastelloy C276 piping, especially around the 98% acid injection point in the water slip stream and through the 2" Static Mixer (Hastelloy C276) which located 2 meter downstream of the concentrated acid injection "T".
Do you have an idea how I could find the cause of this problem?
Thanks in advance,
Mike





RE: Diluted Sulfuric Acid- Corrosion problem
Turbulence is another point of concern. Check if this mixing system is designed properly.
http://antwrp.gsfc.nasa.gov/apod/astropix.html
RE: Diluted Sulfuric Acid- Corrosion problem
RE: Diluted Sulfuric Acid- Corrosion problem
RE: Diluted Sulfuric Acid- Corrosion problem
RE: Diluted Sulfuric Acid- Corrosion problem
RE: Diluted Sulfuric Acid- Corrosion problem
RE: Diluted Sulfuric Acid- Corrosion problem
ash 9144,
I can't sure if teflon will survive at 170 degC.
RE: Diluted Sulfuric Acid- Corrosion problem
There is glass impregnated teflon which holds up at higher temps but I don't know if it can handle that environment.
RE: Diluted Sulfuric Acid- Corrosion problem
RE: Diluted Sulfuric Acid- Corrosion problem
RE: Diluted Sulfuric Acid- Corrosion problem
http://w
That link is to a company that produces superalloys and it outlines the corrosion resistance of tantalum.
RE: Diluted Sulfuric Acid- Corrosion problem
Thank you very much for your responses.
I would like to ask you a generally question, if the Hastelloy C276 could be considered for use (piping,static mixer) in a diluted sulfuric acid (particulary in the 20% - 80% range)at 95-100 deg. C ?
Thanks in advance,
Mike
RE: Diluted Sulfuric Acid- Corrosion problem
RE: Diluted Sulfuric Acid- Corrosion problem
Acid and water do not mix readily so you are probably getting a wide variation of acid concentrations at high temperatures (170 deg C) in the line before it reaches the static mixer. Only PTFE is resistant to the wide range of acid concentrations that are possible after the inject point.
RE: Diluted Sulfuric Acid- Corrosion problem
RE: Diluted Sulfuric Acid- Corrosion problem
RE: Diluted Sulfuric Acid- Corrosion problem
Thanks, I think the tantalum in spite of an high cost will be optimal solution for the static mixer.
What do you think?
RE: Diluted Sulfuric Acid- Corrosion problem
If you've got pressure loss (ie. pump head) available, there are plenty of ways to introduce turbulence to induce mixing without resorting to tantalum. If the pump itself is PFA lined, the pump can be used for mixing. Downstream of the pump, an option worth considering is a couple inexpensive PFA-lined ductile iron plug valves (Xomox, Durco etc.) in series. Fit them with gearwheel operators so they can be used to throttle flow, and have their ports arranged at alternating angles- that will generate plenty of turbulence to induce mixing.
You could also fabricate a simplified static mixer design from Hastelloy or even stainless steel and have it PFA spray/powder coated. All components would need to be generously radiused and free of porosity/pinholes/crevices etc. to make sure the coating was durable. Someone like ITT or Resistoflex probably sell such a beastie already.
RE: Diluted Sulfuric Acid- Corrosion problem
In each case we used a teflon lined tee and then a teflon heat exchanger to remove the heat of mixing.
ash9144 said it on Dec 10.
RE: Diluted Sulfuric Acid- Corrosion problem
I have known massive corrosion rate increase when ppm concentration of sulphides are present.
RE: Diluted Sulfuric Acid- Corrosion problem
RE: Diluted Sulfuric Acid- Corrosion problem
We have had so many instances of concentrations droppingonly very slightly and eating metal pumps all too quickly. ETFE or PFA lined systems have many years experience of safely handling varying degrees of Sulphuric.
Have you looked at PTFE/Teflon surface treatment such as Belzona coating, Edlon etc etc. I know they do them successfully to tanks, pump components ertc, and may well be worth investigating this further to cover your quill ?
Ash Fenn
www.cdrpumps.co.uk
RE: Diluted Sulfuric Acid- Corrosion problem
In-line mixing of acid into water has zones of strong acid gradually becoming weak acid. That transition develops high localized heat and the injection quill corrodes rapidly at the tip. As the quill tip is destroyed, additional corrosion moves gradually to the source of the strong acid. The quill is destroyed rapidly.
As an alternate mixing method, consider adding acid into vapor space above the aqueous solution. A spray nozzle is used to control droplet size and improves distribution. Small droplets are good. Large droplets might not mix and reach bottom of the tank causing problems there. Given some agitation in the tank, the small droplets will be dispersed and absorbed by the moving liquid.
Material selection for strong acid is simplified - it is strong acid. Material selection for dilute acid is simplified - it is weak acid. Reagents can be fed to the mix tank using flow controllers to obtain desired ratio.
RE: Diluted Sulfuric Acid- Corrosion problem
We used a molten salt applied Ta coating for a heated SS boss used in our process to resist 120C 65% HNO3 + organics that worked extremely well. A 304L SS boss would last at best 6 months as some of Ta ones were over 7 yrs old when the MOC was changed to all Ti. In fact none of the Ta coated components failed.
http://www.tantalum-coating.com/index.htm
http://www.tantalum-coating.com/Prodcoat.htm
htt
Once you resolve the quill problem, just remember that you may not have to have all the mixing elements coated. You can make your mixer in segments.
RE: Diluted Sulfuric Acid- Corrosion problem