Drying Tower Pump Tank Material

[doomster]

Good Day,

We have a project to replace the Drying Pump Tank of our Sulfuric Acid Plant. The management wants us to have an option analysis on the materials that will be used. The Drying Tower Pump Tank will operate at -2 kPa at 80 deg C and the service fluid is at 95-97% H[sub]2[/sub]SO[sub]4[/sub].
The existing material is Carbon Steel with Acid Bricks. Now, the management wants us to present an option analysis between Carbon Steel with Acid Bricks, SX material, and SUS 316L. I would like to know your thoughts about this matter.


Best Regards!

 

[EdStainless]

This is excerpted from the MTI Material Selector MS-1. This is the most authoritative guide to material selection in acid that I have ever seen.
In short, 316 will not work.
The caution in the last sentence has to do with impurities in the acid.
Another issue is concentration ranges. If your acid never drops below 93.5-94% then all metal will work. If you ever see 92.5% you may be in a world of trouble.

Drying Towers
The gas feed to the converter is dried with 98% acid, producing 93% sulfuric in the
process. Traditionally, the drying tower was brick-lined steel with a fluorocarbon or
other membrane behind the brick. The packing was ceramic saddles supported on
ceramic piers and beams or ceramic domes. The distributors were generally
Lewmet® 66 or similar alloy cast-iron troughs. Mist eliminators were, and still are,
made from stainless steel or more resistant alloy, PTFE, glass, or ceramic fiber
depending on the design and operating parameters of the tower.
This type of tower design is still common, but all-metal towers are also now being
constructed. These are typically made from one of the 5% silicon austenitic stainless
steels, which are also being used to make acid distributors, either trough or pipe
design. The packing is usually still ceramic saddles, although the packing supports
may be metallic.
All metal towers are sensitive to excursions from the normal operating acid concentrations
and temperatures. Localized hot spots, non-wetted areas, and weak-acid
formation have all resulted in tower failures. The gas inlet area is subject to weak-acid
formation due to the lack of acid flow and the wet gas entering the tower. Special
attention must also be paid to the area under the packing support to ensure that acid
flows evenly across the surface of the metal to avoid dry areas.
The high-silicon stainless steels (SX®, SARAMET®, and ZeCor®) are sensitive to
weak-acid formation and the resulting higher corrosion rates. Agrade of SARAMET®
has now been produced that is more tolerant of somewhat lower acid strengths (see
Figure 8.16). A nickel-based alloy such as alloy C-22 (N08022) is more forgiving if
weak acid forms inside the tower, but it is also more expensive. All-metal towers are
generally not recommended for metallurgical or acid-regeneration plants.10
10. Anon, “Drying Towers,” DKL Engineering (2002),

http://members.rogers.com/

acidmanual/materials_drytowers.htm.

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P.E. Metallurgy

 

[doomster]

Thank you EdStainless for a very informative response,

My concern for now is not with tower, our tower is doing fine. Our pump tank is our concern because it almost reach its end life.

Now, I need to evaluate the cost, sustainability, and maintainability of brick lined carbon steel, SX Material/ high silicon stainless steel.
I hope that you can help me what material will I use, given a lifetime of 10-15 years.


Regards,
Doomster

 

[EdStainless]

Ask a couple of question:
Is this a metallurgical or acid recovery plant?
Is there ever a risk of dropping below 94% acid?
If you answer yes to either of these then do not use metallic construction.

From MS-1 again:
Pump Tanks
Pump tanks for 98.5% product acid are typically brick-lined with a membrane of
high-silicon austenitic stainless steel.

If they really want a full metallic option then look at C22 (or 59 or 686) as it will be much more tolerant of process upsets and impurities.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

 

[doomster]

Thank you EdStainless

It is a metallurgical acid plant. Is it okay to stick with the traditional material selection (carbon steel with fully acid bricks)? Our Drying Tower Pump Tank has served for almost 35 years and it shows many signs that it can reach 2022 for the predicted replacement.

Anyhow, can I ask a copy of MS-1 if you don't mind? For reference only.

Great Thanks,
Doomster