8 replies to this topic

[h_eghbaly]

In boiler acid cleaning by citric acid.
without addition of ammonia, citric acid will dissolve Fe II and Fe III oxide. why we must add Ammonia to the boiler?
when we must add ammonia in this stage?
In last stage we must H2O2 to the boiler.
what is the goal of this stage?
what is the reation between H2O2 and Iron in this stage?

thanks.

[Atttyub194]

Dear All,

Good day!

Acid washing of Boiler should be considered as Last resort and is very risky operation. In my experience i have never seen acid cleaning successful and is only required if the water chemistry has not been controlled. However, caustic wash or boil out to be done to remove dirt , oil , greese in the boiler

[markymaark]

Without knowing what you're talking about.. perhaps the citric acid is for passivation. Then ammonia, a base, is added afterwards for neutralization even though ammonia is not the norm.

[isbarqi]

as far as I know, in boiler acid cleaning/pickling, we don't have to add ammonia. acid cleaning is definitely for scale and rust removal, so, all we need to do just dissolve that scale stuff with proper material. citric acid is one of them. besides, many acid can do that. HCl, H2SO4 is stronger, but more corrosive, usually need more corrosion inhibitor in order to prevent that cleaning agent for attacking the metal equipment it self instead of just dissolving the scale.

 

at last, we need to make a coating on the metal in order to prevent it from corrosion by making a metal oxide layer. it called passivation. H2O2 is one of passivating agent. also, there are many other passivating agent you can find, such as hydrazine, sodium nitrite, and DEHA.

[kkala]

Thanks to above members for supplying useful info. Alumina plants (Bayer process) use caustic cleaning systematically and  acid cleaning (say once per year) to clean equipment and piping from scales.  Acid cleaning was with diluted H2SO4 plus corrosion inhibitor, but details of cleaning procedure are not known to me. Some scale cleaning info (not dedicated to boiler) can be seen at < http://www.cheresour...scaling-problem>.

Can you clarify what form of ammonia is used? An aqueous solution (content?) or a salt?

[isbarqi]

Ammonia? in the common industrial cleaning equipment, as far as I concern, ammonia can be used for alkaline cleaning. it can replace caustic as degreasing agent because its ability to dissolve oil, grease, or fats. You might find it on some household cleaner as well. ammonia is not for descaling, but degreasing indeed.

another use of ammonia on cleaning industry is for passivation of steel combined with citric acid and oxidizing agent. more reference on : www.vecom.nl/english/documentation/tb/TB-2005-17-eng.pdf

 

aqueous solution usually been used

Edited by isbarqi, 27 February 2013 - 07:05 AM.

[kkala]

Thanks, reference indicates that ammonia + oxidant are introduced to the boiler water for passivation, (say) 1.5 h after introduction of citric acid. It should be NH3 aqueous, neutralizing citric acid (pH goes from about 1.5 to 9.5).

[isbarqi]

Thanks for the information. I even don't know that detail yet before.

I'm working on chemical cleaning specialist contractor, but I'm still rookie, fresh graduate. need more experience.

[kkala]

Interesting job, <http://www.cheresour...bitor-lab-test/> might be also useful.