failure of pump in phosphoric acid plant
failure of pump in phosphoric acid plant
(OP)
in our plants we have 10 centrifugal low pressure pumps, their impeller which is made by cast 20 alloy is corroded extremely, the plant is phosphoric acid and total analysed F is measured 14.5% and SiO2 15% and Cl 65 ppm, P2O5 is also 21.1%, now I want to know that with this kind of components: is it possible to have extreme corrosion which can cause failure of pump after only 1 month, if yes which material is better for this equipment.
I'll be happy to recieve your comments.
I'll be happy to recieve your comments.





RE: failure of pump in phosphoric acid plant
RE: failure of pump in phosphoric acid plant
BobPE
RE: failure of pump in phosphoric acid plant
Alloy 20 is no longer proprietary and there are at least 5-6 variations. Easy to get nailed.
Depending on your temperature 65 ppm chlorides will eat Alloy 20 like candy...although the cast Alloy 20 is better than some of the forged grades. Pumps,valves,pipe, generally are vulnerable...lined pumps are an option so are some of the proprietary grades (Hast. C (actually C276), Carp. 20, etc.). Hopefully you have enough silicate to control the florides.
RE: failure of pump in phosphoric acid plant
I've never heard of Fluoride numbers that high in filter acid. Where is your ore coming from? Even the worst Morrocan rock is only 4% F. Is it raw rock which has not been through a flotation process to beneficiate the phosphate up and drop the other impurities down? Having 21% P2O5 in the filter acid is also quite low; we usually get 26-27% in our dihydrate process. What is your free sulfate amount in the reactor? Yes, Alloy 20 might only last a month in your service.
Hacksaw - good point on the F/Si ratio.
To keep the hydrofluoric acid from chewing up your pumps you need at least 4 atoms of silica for each fluorine atom. A more typical fluoride amount in the filter acid is 1 - 2%. You are lucky if only the pumps are getting chewed up - what is the rest of your plant made of?
As far as metallurgy for your pumps, if you truely have those F and SiO2 numbers, you are going make some pump vendor rich. You need lots of chrome and moly. High cost choices would be Inconel 625, Alloy 59, or Hastelloy G-30. Medium cost - Ferralium 255 (UR52N+), 904L, or Cd4MCu would do better than Alloy 20 (we use Cd4MCu). There might be a non-metallic or lined pump out there, but in a phos acid plant the acid is never clean enough to prevent erosion. A pump manufacturer that might be able to help is Wilfley http://www.wilfley.com/
RE: failure of pump in phosphoric acid plant
Greg
ghopkins@rl-industries.com
RE: failure of pump in phosphoric acid plant
Regards,
SASC