SCRUBBER FOR A BOMB FACTORY

SCRUBBER FOR A BOMB FACTORY

Blue Star Ltd. yes, of Air conditioners fame, of all blessed companies bagged a technically complex project of designing, fabricating, installing and commissioning a scrubber unit to neutralize Hydrofluoric acid ( HF) gas.  The Client ? The Bomb Factory of The Indian Rare Earths Limited, under the Dept,.of Atomic Energy( DAE) Govt. of India.  Quite a scary customer ?

The only connection I could see that Blue Star had with water, wastewater, or any sort of waste emissions, was that they also made some water coolers.  I have absolutely no idea on what basis they bagged the Contract for such a complicated project in Feb. of 1990, when they engaged me to do the basic design and engineering of the scrubber system only in April of 1990.

The “Bomb Factory” is the nickname given by the local citizenry at Yelawal, some 40 Km from Mysore, on the Hunsur Road, to this establishment under the DAE.   The official designation on record of this plant is the “Rare Materials Processing ( RMP) unit.  The IREL website innocently claims that their products find use in such mundane industrial activities as manufacture of white pigments, welding electrodes, foundries, ceramics, refractories, abrasives for polishing glass/ TV tubes, and in sand blasting etc.  Whoever said they were processing materials for making atomic bombs ?

Now, all these hush-hush, high tech establishments of the Govt. of India operate at rarefied levels of technical excellence and integrity. Nuts and Bolts, Nitty Gritty of each piece of design and  engineering  is stripped bare and diligently scrutinized by battle hardened professionals from diverse fields of engineering and pure sciences. Indeed the civilians working in these companies carry ranks equivalent to those in the Indian Army such as Colonel, Brigadier etc., even as their designations will simply show :  Engineer- Grade E or some such monicker.  In this particular instance, the Director of the unit who had a PhD Degree in Chemical Engineering ( like yours truly) took a personal interest in the project, and toil I did  for my design to pass muster.

In a Scrubber, the target gas in vapour form (  HF in this case)  is absorbed in a liquid, in which the solute HF is soluble.   HF is present at 5 % concentration in a mixture with air, which is evacuated by means of two powerful air blowers in case of an emergency in the HF Storage Hall of the factory.  Design of a scrubber for such a System calls for several sets of Physical and chemical data : Chief among them are the Physical and chemical properties of the gas and liquid,  Solubility Curves of HF in Water / other scrubbing liquids,  Gas- Liquid Equilibrium Data, reactions of gas with the scrubbing liquid if any, Flooding velocities in the scrubber tower, Empirical equations for the kinetics of mass transfer from the gas to the liquid phase etc.  Precise data for several of these parameters not being readily available, one has to make judicious approximations using Raoult’s Law and Henry’s Law, and other applicable laws.

I made several trips to the Library of the Indian Institute of Science in those few days, ferreting out the requisite data from obscure technical Journals.  The IISc in those days allowed free and unfettered use of their Library to the general public :  A request to the Librarian, stating your purpose for use of their facility was all that was required.

The design, the calculations, and the technical report on the scrubber system were well received by the folks in the Bomb Factory.  Indeed during the mock trials and simulation of the emergency episode ( Accidental bursting of all HF cylinders in Building 17 of the RMP ), the system performed in an exemplary manner, with little or no adverse impact on the environment and surrounding habitations.

Dr. Ananth S Kodavasal                                                                          July 05, 2011

Footnote :

The Boffins in the Bomb Factory had overlooked a crucial factor in their initial design and tender specifications of the scrubber : they had proposed Potassium Hydroxide Solution ( KOH) as the scrubbing medium for capturing the Hydrofluoric acid.  In my report, I had pointed out that the reaction of HF with KOH would produce Potassuim Fluoride ( KF) , a sparingly soluble material, which would then precipitate out and clog up the scrubber tower, packed with Polypropylene fill media.  We then changed the scrubbing medium to water in the scrubber, and transferred the precipitation stage to outside the scrubber, using lime to produce CaF2, an easily disposable, harmless material, if handled properly.