E. I. du Pont de Nemours & Co., Inc.
In basic conditions, hydrogen cyanide (HCN) can polymerize, potentially releasing HCN to the atmosphere. The HCN shipped in rail cars is stabilized with sulfuric acid and sulfur dioxide to prevent polymerization. Prior to the introduction of HCN, an incoming rail car is pickled with a dilute sulfuric acid solution to remove any residual HCN and to ensure acidic conditions in the rail car. This procedure consisted of a once through flush with the pickling water which was then pumped directly down the deep wells.
A project was approved to upgrade the capacity of the loading facilities. Along with this, an additional storage tank was installed along with controls and piping which would allow the pickling solution to be reused in the rail cars and then recycled back to the HCN process area. The facilities were designed so that after the HCN concentration in the pickling water reached 5%, the pickling water would be routed back to the HCN Absorber where it would be used as level make-up and the HCN removed and further refined in the train.
This recycle eliminates deep well disposal of the stream. Since installation of the project, the HCN concentration has not reached the 5% limit. It appears the HCN is flashing into the vapor space of the tank and being vented to the flare where it is burned. The pickling solution has only been sent back to the HCN refining train when the acid concentration of the solution dropped below the desired concentration.
Details of Reductions
Additional Information :
At design loading rates this equates to a reduction in waste water of 20 gpm and a 50% reduction in sulfuric acid, or an annualized savings of $42M.