Alkali chlorides can cause high temperature corrosion and it is known that alkali chlorides in gas phase is more crucial than that in solid phase (contained in fly ash)
Are there any papers or references comparing the phase of alkali chlorides when they pass through the boiler pass? That is, how much alkali chlorides does exist in gas phase and how much in solid phase?
My knowledge about this issue is somewhat limited, so any comment will be very helpful.
Thank you very much.
I disagree that the solid alkali chlorides from the fly ashes are less dangerous:
First, almost all of alkali chlorides outside the flame are solid (only in the combustion chamber is the temperature above 800°C, in all other parts of the boiler plant are significantly lower temperatures).
Secondly, corrosion on the surfaces of steel pipes is always at temperatures below 600°C (higher temperatures, the tube can not withstand anyway).
Thirdly, especially solid alkali chlorides in the form of sediments cause massive corrosion of the steel. This corrosion is running higher 160°C according to the following reaction (alkali chloride accelerate the oxidation of iron):
(6+2n)Fe + 3NaCl + (3+1,5n)O2 = 3NaFeO2 + FeCl3↑ + nFe2O3 , n >> 10
In this reaction arising gaseous iron chloride (> 156°C) is responsible for the rapid oxidation of iron, but alkali chlorides are solid (see attached).
Much information about corrosion in waste incineration plants you can see from the website of the company CheMin GmbH: http://www.chemin.de/Publikationen/Publikationen.php?L=2
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