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Chemical Process Technology

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Sunday, June 1, 2008

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Chemical Engineering share a new FAYF in May 2008. This FAYF is related to some tips and requirements of Acid Solution Storage especially in Material of Construction (MOC).

The acid solution discussed in this FAYF includes :
  • Sulfuric acid (H2SO4)
  • Phosphoric acid (H3PO4)
  • Hydrochloric acid (HCl)
  • Nitric acid (HNO3)
  • Hydrofluoric acid (HF)
Some simple tips in this FAYF as follow :

Sulfuric acid (H2SO4)
  • Reaction in H2SO4 potentially generate hydrogen (H2), ensure proper venting and dispersion
  • Carbon steel (CS) good for concentrated H2SO4 at normal ambient temperature.
  • Diluted H2SO4 is severely corrodes CS. Shall keep away moisture from CS tank e.g. Nitrogen blanketting
  • Polyvinyl chloride (PVC) pipe may be used
Phosphoric acid (H3PO4)
  • Rolled upward 3 m from tank bottom to allows free weld expansion and contraction (reduced stress)
  • Avoid corner weld which normally undue stresses occur (corrosion)
  • Heating required to avoid freezing in storage.
  • Use SS316 or rubber lined CS or Fiberglass Reinforced plastic. Avoid CS.
Hydrochloric acid (HCl)
  • HCl (fume) vent send to scrubber or flare for proper disposal
  • Use Rubber lined CS or Glass lined CS or FRP.
Nitric acid (HNO3)
  • Similar to HCl, Nitrogen Oxides (NOx) vent to scrubber
  • Upto 95 wt% @ ambient, use SS 304L
  • More than 95 wt%, use Aluminium Alloy
Hydrofluoric acid (HF)
  • Anhydrous HF has high vapor pressure. Tank should design for 60 psig (as minimum)
  • All welds shall be X-rayed and Stress-Relieved.
  • HF fume shall be vented to scrubber or flare
  • May use CS upto 66 degC and 70wt% HF
  • Potential Hydrogen Blistering (Read more how H2 blistering form ?). Periodic tank inspection for blistering.





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References
1. Grossel, S., Safe Efficient Handling of Acids, Chem. Eng. December 1998, pp. 104–112.
2. Anon., Phosphoric Acid, Rhone-Poulene Basic Chemicals Co., Shelton, Conn. (1992).



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