Corrosion of carbon steel by gaseous acetic acid at high temperatures 1

[mills82]

I am hoping that someone can provide knowledge in regards to a potential corrosion issue.

We are designing a wood torrefaction in which the wood gas produced is reheated and recirculated to provide energy into the processor. This wood gas contains a significant amount of acetic acid.

The processor is to be made of carbon steel, which is extremely vulnerable to acetic acid is liquid phase, but is this true for gaseous acetic acid?

Reading a few papers, they seem to suggest it is, however much depends on the relative humidity. The composition of the gas includes 45 wt% moisture and 15 wt% acetic acid, and will be no less than 250oC. How is relative humidity determined when there is no presence of air in the operating atmosphere?

I think that the high temperature will have a positive effect on the humidity. I imagine the corrosion is a problem when the atmosphere is 'wet', and am hoping that the high temperature will mean that this is avoided.

I understand that cold spots are inevitable and the design can incorporate local sections that will be corrosion proof for any condensate produce. However, the reactor itself is quite large (3.5m diameter, 18m long) and to replace carbon steel with stainless steel is unfeasible.

Any advice will be greatly appreciated!

Andy

 

[EdStainless]

I have seen Acetic acid equipment that is SS lined.

You humidity is simply the amount of water in the gas, and relative humidity would be compared to the saturation level.

Yes you will see attack in the gas phase, but estimating how much is another issue. The levels of O, CO2 and other gases will also have an impact.
I have seen papers about acetic acid attack in wood drying equipment.
I suggest that you keep hunting for info.
If you go into service with a steel vessel I would also suggest a very aggressive inspection routine for the first few months. With lots of UT thickness readings.


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Plymouth Tube

 

[Ron]

Acetic acid in gaseous or liquid state will corrode carbon steel. When the temperature is elevated, it is even worse.

Line it or coat it.