High temperature Ammonia corrosion and MOC of AIG (Ammonia Injection Grid) 3

[YuJie_PV]

hi, all,
this is a question related to corrosion of SS under high temperature ammonia gas.
It's the AIG(Ammonia Injection Grid)in the Boiler system, which funcitons to control the NOx in flue gas by injecting gaseous ammonia of a high temperature around 400C.
the Ammonia distributing pipe are fabricated with 304, while i find the follow table in a corrosion handbook:

it implies that 304 is not compatible to the temperature higher than 90F（32C）, under which condition the corrosion rate is larger than 20 mpy， while in other sources, like NICKLE INSTITUTE states that "the stainless steels are used safely for high-temperature service in hot ammonia atmospheres". i believe both the sources, ther must be something wrong with my understanding, could you please shed some light on it? also, what is the corrosion mechanism of Ammonia in high temperature?

Thanks so much.

 

[hacksaw]

Your table appplies to a gas mixture without specifying the Molar content of the combined gases.
Yuo need a more reliable source.

 

[YuJie_PV]

thanks for response, hacksaw.
respectfully disagree.
below is the note to above table. it is pure chemical.

 

[hacksaw]

You may have several problems:
1. Hydrogen cracking inside your piping and injection grid when the ammonia breaks down
2. In your flue gas, you'll have H2O and various substances depending on what you are burning
3. Your process design will show the various gases and condensate in the stack gas present, SO2, CO2, H2S, H2O....
Most of that will be specific to your project

 

[YuJie_PV]

thanks hacksaw,
i am not quite concerned about the composition of the flue gas.
i currently just want to figure out why the corrosion handbook, which seems quite trustworthy, show data conflicting with NICKLE INSTITUE's statement, which largely undermine my trust to the entire book.

thanks

 

[hacksaw]

You hand bookseems to apply the NH4 refrigeration, not process plants that have much harsher environments especially when treating flue gases, of unidentified composition.

 

[YuJie_PV]

hacksaw, i don't think so. it's a handbook for general use.

 

[hacksaw]

General use, for the temperature range of NH4 cooling lines.

Your stated application is "AIG(Ammonia Injection Grid)in the Boiler system, which funcitons to control the NOx in flue gas by injecting gaseous ammonia of a high temperature around 400C" which is much harsher.

 

[EdStainless]

How hot is your Amm injection piping system?
Is the Amm actually pre-heated to 400C?
Or is it entering this line as liquid and then boiling before injection?
Your table does puzzle me.
My Compass guide shows pure dry Amm to 500F and wet to 600F with little to no corrosion, <0.05mm/yr.
This then gets more severe with increasing temperature and within another 100-150F they are both not recommended.
The worst thing for SS would be having any Cl contamination.
The exclusion of all oxygen lowers corrosion rates by 100x or more.


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P.E. Metallurgy, consulting work welcomed

 

[YuJie_PV]

@EdStainless,
"How hot is your Amm injection piping system?"
reply: i have no exact temperature number, but not very hot, i believe. the ammonia injecting piping starts from an ammonia evaporating vessels, which operates at around 40C。
“Is the Amm actually pre-heated to 400C?”
reply: No.
Or is it entering this line as liquid and then boiling before injection?
reply: No， the ammonia in the line is gaseous.
Thanks.

 

[YuJie_PV]

the handbook name is "Fundamentals of Metallic Corrosion: atmospheric and media corrosion of metals" authored by Philip A. Schweitzer.

 

[hacksaw]

YuJie_PV

First you claim is operation at 400DegC,
then a concern is expressed for operation at 400 Deg C, based on the data in one handbook. A hand book that is using data commonly associated with NH4 refrigeration services, but which you claim is valid data in your application.

No mention is made of the environment where your piping is located. For example, the injector matrix you've referred to is located in flue gas duct work, usually considered a corrosive environment.

Perhaps a bit of research on your part is needed. Good Luck!

 

[MJCronin]

I did some work on power plant Anhydrous Ammonia Injection systems and piping for a major Pollution Control OEM.

The systems took AA vapor from tanks, controlled flow via electric heaters, regulated the pressure for various grid-configured nozzles and then injected it into flue gas ductwork. The system was entirely 304/316 SS except ..

Except for the nozzles themselves and the short stub of piping that went through the flue gas duct wall

The material for the nozzles and short inlet stubs was HASTELLOY C-276 alloy (UNS N10276)

MJCronin
Sr. Process Engineer

 

[EdStainless]

That sounds right MJC.
Though 316 is rarely used in Amm service, 304 tends to preform better.
Definitely Ni alloy nozzles.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[YuJie_PV]

@EdStainless, what is name of your Compass guide? Would you please share it?
Thanks in advance

 

[EdStainless]

Chemical Resistance Guide for Metals and Alloys
Compass Publications

These guides are useful because they list so many different metals in hundreds of different environments.
I have many other sources as well, but most of them are very specific and this one is very general.

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P.E. Metallurgy, consulting work welcomed

 

[YuJie_PV]

THanks EdStainless