Concentration of Sulphuric Acid: Premature Failure of Bamag Pots.

摘要

In the Bamag process, dilute sulphuric acid (of about 70% strength) is reconcentrated to about 95% by boiling in a cast iron still pot. The acid for reconcentration flows down a packed column (dephlegmator), where its concentration during descent increases progressively, before the partially concentrated acid enters the pot via the base of the dephlegmator. In the pot it is further concentrated by boiling, and the concentrated acid overflows through a run-off pipe into an acid cooler and thence to storage at a rate determined by the input flow. Each pot contains about 10 tons of acid which is boiled and stirred. The operating life of a Bamag pot should exceed two years, but in recent times at Australian Explosives Factory 'A' several of its operating pots have had a life of less than 5% of this figure. This extremely short life is due to localized corrosion in the vicinity of the outlet at the liquid surface level. This paper examines the main factors that could contribute to this particular corrosion and to such a short life. Observed corrosion problems during operation of similar pots at other plants are also discussed. It is concluded that the short life of some pots at Factory 'A' is mainly due to weak acid reaching the cast iron walls of the pot, where it quickly cases the localized corrosion that leads to rapid failure. Simple procedures to prevent this are suggested.