Building Heated 45% KOH Tank

[jw1591]

My company has charged me with preparing a proposal for a new process tank that will heat 45% KOH to 300 deg F. I believe a nickel based alloy would be the best fit for this process, but I have found several contradicting sites on the Web. The basic design of the tank is as follows.

- Roughly 55" X 63" and 79" tall, 1/4" thick wall
- Roughly 800 gallons of 45% KOH
- External 480V electric strip heaters
- mixer capable of turning liquid over 3 times a minute

This is an open top tank with a removable lid. I need use a material that has good heat transfer due to the external strip heaters, but still strong enough and weldable. Any help would be greatly appreciated.

 

[kenvlach]

Hi jw1591,
This is similar to a hot black oxide tank. See Figure 10 (page 69 of the pdf) in MIL-HDBK-205A PHOSPHATIZING AND BLACK OXIDE COATING OF FERROUS METALS. Note the gas burners beneath the tank, and the double wall construction for the combustion gases to surround the tank & exit near the top, and the external insulation.

http://assist.daps.dla.mil/quicksearch/basic_profile.cfm?ident_number=53933

Then get equipment quotes from the hot black oxide chemical & equipment suppliers: Electrochemical Products, Inc., Heatbath, & Luster-On.

http://www.epi.com

http://www.heatbath.com

http://www.luster-on.com

As the KOH concentration & temperature are within the range of alkaline fuel cells (AFC), take a look at the Fuel Cell Handbook, 7th Edn.

http://www.netl.doe.gov/technologies/coalpower/fuelcells/seca/pubs/FCHandbook7.pdf

 

[EdStainless]

Using external heaters raises your material requirements. The local high temp under the heaters will drive your material selection for the entire tank.
Do you run a tank like this now?

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http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[jw1591]

EdStainless,
We currently have a prototype system made of some old 304L stainless tanks we had in a warehouse. 304L and 316L stainless steel have known problems with stress corrosion cracking with 45% KOH above 200F, even though our current prototype has been in use for over a year. I am trying to build a system that will last 20 years. From what I have read my best bet is the high nickel alloys, Alloy 600, 400 or 200. My main problem is I have very limited experience with these metals and not sure which one is the best fit from a cost, heat transfer and fabrication standpoint.