Incinerator operation

[raingal79]

Hi,

Flue gas from incinerator goes through to a stack whereby the gas is 'sucked' through a venturi srucbber and scrubbed with low purity water to remove any dust particles in the gas. Recently we experienced the section just above the gas inlet nozzle to the stack thinning off and it was suspected that there's corrosion due to dissolved CO2 (produced from incineration). I wonder how soluble CO2 would be in water for that short period of time. This is further supported because pH of water in the stack was tested to be 8. Wonder if anyone has this similar experience?

Thanks.

 

[phex]

I would guess that substantial CO2 in water would bring pH down to below neutral to the acid side. pH 8 in my opinion would be an indication that CO2 is not the cause.

Is it possible that it is mechanical corrosion due to high velocities?

hth,
chris

 

[25362]

1. Phex may be absolutely right (probable erosion/corrosion effects). Anyway, you'd better indicate what refuse or waste is being incinerated, and the quality of "low purity water" being used.

2. SOx content could also be considered a factor especially if the flue gas is at a temperature below the dew point of sulfuric acid. A combination of HCl+water+CO+SOx has been identified as a corrodent in incinerators by helping in removing the iron oxide protective layer by causing its disruption and spalling, exposing new surface to corrosion, thus bringing about metal thinning.

3. A note on the pH subject at ambient temperatures. At pH~8, the approximate pH of seawater, of the three species H₂CO₃, CO⁼₃ and the ion HCO₃^-, the latter is the most prevalent. Their approximate mass fractions in water being 4%, 1%, and 95%, respectively.

 

[raingal79]

Thanks for replies.

The incinerator handles EG waste and so I can expect the flue gas to consist of CO2, H2O, N2 and O2 and small amount of NO, NOx (~20ppm), CO (~100ppm). Low purity water is just like demin water.

I am also thinking along the line that it could have been due to the flow profile of flue gas and low purity water used. Like to understand how gas escaping from water works and its impact of erosion/ corrosion.

Thickness check along the stack seems to suggest the thinning effect is not uniform and it's an indication of possible pitting corrosion.

raingal79

 

[jalvarez]

faingal79:
Temperature of the flue gas entering the scrubber? This sounds as a scrubber plus quenching.
Oxygen + water + high temperature... means corrosion for a CS, depending on concentrations.
I think that you may have good answers in the Corrosion Engineering forum. Suggest to repeat the question there.
Have a safe day
J.Alvarez

 

[siretb]

WAter in the stack at pH 8 seem to rule out coorosion due to HCl (hydrogen chloride), SO2 (sulfur dioxide) and CO2
However it is possible that the pH is not representative, either beacuse you have peaks of pollutants that escape the venturi (a Venturi is not that good a scrubber), or because fine ash entrained manage to neutralize the waters.
Have you tested for chlorides and sulfates in this water?

At any rate, I do not think that CO2 is your problem.

 

[steveen]

Low quality water? Is it deaerated? Pitting is indicative of o2 attack.
See jalvarez reply above.

Sounds like you are quenching a hot gas stream with a copious amount of water. Calculate your O2 balance