8 replies to this topic

[engg]

calcium sulfate deposits arfe tough and hard and deposits in heating tubes of heat exchanger. Does any1 have any experience in removing it from tubes?

[S.AHMAD]

For hard scales in water cooler, hydro-jetting is good enough. Fo carbonate, chemical cleaning is also effective but I have no experience for sulphates.

[tarafdar]

Yes, calcium sulphate scale is hard to remove.If the scale thickness is small you can clean it chemically by using 0.1wt% NaOH(pH 12) at 35oC.
If the scale is thick you should go for mechanical cleaning.

[kkala]

There were CaSO4 deposits in the lower part of a phosphoric acid evaporation unit, we only introduced hot water and let the liquid circulate through the recirculation pum (http://www.cheresour...ch&fromsearch=1. Then mechanical cleaning was done.
EDTA may be useful nowadays for CaSO4 scales, see http://services.bepr... scale removal". Other useful info could be seen by googling "caso4 scale removal",

[engg]

For hard scales in water cooler, hydro-jetting is good enough. Fo carbonate, chemical cleaning is also effective but I have no experience for sulphates.

Yes, calcium sulphate scale is hard to remove.If the scale thickness is small you can clean it chemically by using 0.1wt% NaOH(pH 12) at 35oC.
If the scale is thick you should go for mechanical cleaning.

Thanks for you replies.
what do you mean by mechanical cleaning?
Which chemical can be used for carbonated though?

[breizh]

Mechanical cleaning means High pressure cleaning of the equipment I guess , up to 1000 bars

[kkala]

I should have been more precise in mentioned "mechanical cleaning" for the case of the phosphoric acid evaporation unit. At that time (late 1970s) high pressure cleaning was not yet applied in that fertilizer factory. Mechanical cleaning means that we used our hands and any necessary tools, mainly wired brushes. The relevant exchanger was dismantled, the deposits were tried to be removed by scrubbing or breaking, which needed caution.
In early 1980s pipe cleaning using pigs was known to be applied here, and so was high pressure cleaning in late 1980s. Both of them belong to mechanical cleaning. But hand tool cleaning, as before, also remained in the activities of mechanical cleaning. At least this was the concept used in a local alumina project.
Requirement for dismantling of equipment could be a good point to distinguish mechanical cleaning from other forms of cleaning (e.g. chemical cleaning). Following is pointed out on this.
- Pig cleaning does not need dismantling; but this concerns piping, not equipment.
- High pressure cleaning to remove equipment scales is assumed to need dismantling. Probably there are exceptions (?).
- Scale removal using hand tools (as in 1970s here) requires dismantling.
I have the impression that equipment mechanical cleaning still means dismantling and then assembly, any advice on it would be appreciated.

[pipef11]

For hard scales in water cooler, hydro-jetting is good enough. Fo carbonate, chemical cleaning is also effective but I have no experience for sulphates.

Yes, calcium sulphate scale is hard to remove.If the scale thickness is small you can clean it chemically by using 0.1wt% NaOH(pH 12) at 35oC.
If the scale is thick you should go for mechanical cleaning.

Thanks for you replies.
what do you mean by mechanical cleaning?
Which chemical can be used for carbonated though?

We have tried submersion on citric acid at 10%, after caustic soda at 5% for 5 hours each.

[bmb3a]

In Our sugar plant factory, we usually had the same problem in our evaporator. There were CaSo4 scale and CaSiO4 that even harder to descale.Now we used acid chemical for the 5th until 7th vessel, but after 4 or 5 cycle we use alkaline chemical (caustic soda is the best) to break the scale development circles. The step by step cleaning process are :

• Flush the vessel with clean water, we used to do it 2-3 times
• Fill the vessel with clean water, then fill in the chemical. Be Careful when you handling this kind of chemical because it's very harmful and corrosive.
• Boil it for 8-10 hours, if the water level decrease add with hot clean water
• After the boiling process is complete, let it soak the tube for 3-4 hours
• Drain the solution, flush with clean water. Beware the waste water is still harmful.
• Do the mechanical cleaning. We use the wired brush with man power to scrap the scale.You can use both man power or pneumatic / electric powered shaft.
• Flush with clean water again.
• Cleaning Process is done

I hope our experience is useful to you. Good luck