In 2007 we replaced all the mist eliminators elements (downstream the absorption tower) of our sulfuric acid plant. Two years later we found that the elements were very corroded and they should be replaced again as soon as posible. We analized the concentration of the sulfuric acid in the elements seal cups and we found that it is about 93%.
We looked for moisture in each section of the plant (downstream the drying tower, boilers and economizers) but not moisture was found.
Could someone explain me why the acid in the seal cups is diluted to 93%?

Thanks

It is difficult to find out from where the moisture entered to dilute the acid to 93%. My guess is the tower and pump tank must have operated at 93% H2SO4. It is possible that your concentration controller may be malfunctioning and does not cut off dilution water when the concentration reaches 98%.Do you check the concentration by taking sample of the acid and analysis in the lab? If there is shuffling of dilute acid from Drying tower and absorption tower, may be this shuffling needs adjustment.If moisture enters through boiler system leak, you would have noticed the bad stack.93% acid is definitely more corrosive and will attack the stainless steel mesh and cage part of the mist eliminatorAND THE ELEMENT gets crumbled.The glass fibre is not attacked by 93% H2SO4.
I hope you have now discovered the reasons for the failure of your mist eliminators. Do let us know.
V.V.Rao