HF process materials 3

[gafultz]

We have a client who would like to burn a material in one of our incinerators that will produce up to 5000 ppmv of HF gas at 1600-1800 deg F and near atmospheric pressure. The incinerator will be mild carbon steel probably lined with a high alumina (low silicon) refractory. The flue gas will be pulled by ID fan through a fire-tube boiler that will reduce the gas temperature to 375 deg F. It then enters a dry scrubbing system which will reduce the HF mass by 91% while the temperature falls only slightly before entering a 65 ft tall stack. The stack which is too small in diameter (16") to line with HF resistant refractory is partially exposed to low seasonable temperatures (New England winters) so it's possible that some HF will condense before leaving the stack. There will be some moisture from the combustion air and waste but not much. Does anybody have any experience with HF at these conditions who would like to recommend materials for refractory, boiler tubes, duct from boiler to scrubber and stack?

Thanks

 

[EdStainless]

And you have a permit for releasing this much HF?

You will see acid attack in other parts of your system. Think of hot HCl, only a lot worse.

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

 

[gafultz]

The owner has a temporary permit to construct only. The system is still in the design stages and other than the obvious concern for personnel we are concerned with the ability of the equipment to survive even though it will only be used a few days per year while producing HF gases.

 

[TomEun]

Basically you may have to consider the following three cases.

(1) HF gas corrosion at high temperature (@1800F, max. 5000ppmv, Velocity < 50ft/sec)
a. Recommended Inorganic Materials : Graphite CZR-1 (excellent), Graphite DFP-2 (excellent), Sapphire (good), Sintered silicon carbide (100% alpha grade- questionable @ 1800F), and Alumina (> 99.7% purity- questionable @ 1800F)
b. Recommended Metallic Materials : Not recommendable as a bare metal

(2) HF gas corrosion at Medium temperature (@375F, max. 5000ppmv, Velocity < 50ft/sec)
a. Recommended Inorganic Materials : Graphite CZR-1 (excellent), Graphite DFP-2 (excellent), Sapphire (good), Sintered silicon carbide (100% alpha grade- good), and Alumina (> 99.7% purity- good)
b. Recommended Metallic Materials : Monel 400 as a bare metal [cf, Nickel 200 is more preferable @ 1100F]

(3) HF acid corrosion under water condensation (400 ppmw < HF < 5wt%, Velocity < 10ft/sec, just below the boiling temperature of HF acid solution)
a. Recommended Inorganic Materials : Graphite CZR-1 (excellent), Graphite DFP-2 (excellent), Sapphire (good), Sintered silicon carbide (100% alpha grade- questionable @ 1800F), and Alumina (> 99.7% purity- questionable @ 1800F)
b. Recommended Organic Materials : PTFE, FEP, PFA, ECTFE, ETFE, PVDF, and CTFE
c. Recommended Metallic Materials : Monel 400 as a bare metal


Hope this helps,
Thomas Eun

 

[TomEun]

According to NACE Publication 5A171-2001 Revision, NIOSH (The National Institute of Occupational Safety and Health) recommended exposure limit of HF is 3 ppm time weighted average (8 hours) with a maximum of 6 ppm (15 minutes).