Dear Stephen, I am involved ...

Dear Stephen,

I am involved in this problem since decades, and I found as follows:

There are no safe techniques to prevent scaling by CaSO4 besides limiting the concentration of the brine below the saturation by CaSO4. The solubility is rather indipendent from pH but is heavily influenced by the temperature. The silubility is about 4200 ppm up to 45°C, then it sharply decreases to about 2500 ppm at 75°C, 1600 ppm at 100°C and below 1000 ppm at 150°C. The weight of Ca on CaSO4 is about 29%, hence the concentration of Ca in the brine should be less than 1200 ppm below 45°C, less than 725 ppm at 75 °C and lesst than 460 ppm at 100°C.

The oversaturation is always a very risky situation and the antiscalant for carbonates are ineffective for CaSO4. There is an antiscalant produced by Genesys effective for CaSO4 but the effectiveness is significant only up to 50°C and eventually zero above 60°C (Hence it is mostly used for ambient temperature processes like RO)

You may try to reduce the working temperature thus increasing the solubility and therefore to improve the Max brine concentration before scaling.

Alternatively you may try to install a ball cleaning system to keep the internal walls of the tubes bright through the continuous brushing of abrasive balls (details in the website of Taprogge and Others)

In any case my advice is not to work in risky conditions because the removal of scaling by CaSO4 cannot be made satisfactorily by acid cleaning and eventually requires for mechanical brushing. The adheramce of scaling on non-passivated tubes (like Titanium) is lower (easier brushing) than on passivated tubes.

Should you need any additional information, please contact me privately