How do I prevent CaSO4 Anhydrite Scale in a CaCl2 vaporization loop?
How do I prevent CaSO4 Anhydrite Scale in a CaCl2 vaporization loop?
(OP)
I have an industrial process with aqueous CaCl2. Water continuously flows in and is flashed out of the system but the CaCl2 inventory does not turn over. Trace sulfur accumulates and winds up as Calcium Sulfate Anhydrite in the 150'c HX. Supersaturation is enevitable and the resulting scale really messes up the Uo.
Does anyone have experience with a similar problem and was able to find a suitable solution, other than mechanical removal of the scale? I have several options I would like to explore and would love to hear ahead of time if some of them will lead me down a dead end path...
- Addition of MgCl2, or other (un)common ions.
- Electronic/magnetic fields. Do these things work? Would they be expected to work when the dissolved solids (as CaCl2) is already ~50%.
- Electrolytic technologies
- Phosphonates or other scale nucleation inhibitors.
Thanks for any help you can give...
PJHarder
Does anyone have experience with a similar problem and was able to find a suitable solution, other than mechanical removal of the scale? I have several options I would like to explore and would love to hear ahead of time if some of them will lead me down a dead end path...
- Addition of MgCl2, or other (un)common ions.
- Electronic/magnetic fields. Do these things work? Would they be expected to work when the dissolved solids (as CaCl2) is already ~50%.
- Electrolytic technologies
- Phosphonates or other scale nucleation inhibitors.
Thanks for any help you can give...
PJHarder





RE: How do I prevent CaSO4 Anhydrite Scale in a CaCl2 vaporization loop?
Re "Magic" water descalers?” Thread798-53236. Consenus is a waste of money.
Re common ion. Unless you can alter your process to use NaCl instead of CaCl2, not much chance. The Ca+2 has a stronger chemical attraction for the SO4-2 anion than other cations (except maybe barium, and possibly not at this T).
Electrolytic descaling should work (same as electrocleaning of metals) for occasional descaling, but long term use in concentrated chloride will lead to HXer dissolution, possibly with pitting. You could use your tank or a graphite electrode to complete the circuit. An earlier thread mentioned some success descaling carbonates from a pump shaft,
‘Removal of Carbonates Depsosition from Pumps by Electrolysis’
Thread124-47652
I am not familiar with scale inhibitors for these conditions. Give it a test.
Good luck,
Ken
RE: How do I prevent CaSO4 Anhydrite Scale in a CaCl2 vaporization loop?
I would reccommend an antiscalent of this type for your HX's and piping or vessel walls. We still do have scale build up on pump impellors and we are currently trying to determine why.
However a phosphonate based antiscalent should work well so give it a try.
Ronan
RE: How do I prevent CaSO4 Anhydrite Scale in a CaCl2 vaporization loop?
Chemical addition is probably our last choice alternative because of the adjoined processes. Phosphorous and other electronic impurities are important to us so unless we strike out completely, it is unlikely we will choose to go that route.
Wide open to other ideas, though.