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?/MULTI-FUNCTIONAL WATER PUMP CONTROL VALVE

Corrosion rates increase almost exponentially with temperature. Is there any way to decrease your dillution water temperature?

Turbulence is another point of concern. Check if this mixing system is designed properly.

98% sulfuric acid should not be corrosive to Hastelloy C. But as the concentration drops (particulary in the 30% - 80% range)and at your temperature it is corrosive. So I would have to agree with ash9144 that you should examine your choice of metallurgy in the mixing section.

Addition of concentrated sulphuric acid into water to form a weak acid solution should be done in PTFE lined pipe.  The high temperature and weak acid concentration is extremely corrosive to most metals.  The lined pipe should extend from the injection point through to the static mixer and another metre downstream of the static mixer.  The static mixer elements should also be PTFE.

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.

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