Warning! Explosion Danger: Spray-Drying of Nickel Nitrate-Starch Suspension
We wish to report an explosion and fire that occurred while spray-drymg a mixture-nickel nitrate, amine (to neutralize the acidity), starch, and inerts (alumina and zirconia&dissolved and suspended in a 50/50 isopropyl alcohollwater mixture. This suspension was being processed in a small benchtop spray drier, in which it was injected as an aerosol into a stream of hot air. The aerosol particles were then carried (and dried) by the hot air stream through a cyclone and collected in a receiver. The alcohoL'water vapor was vented to an exhaust duct. Thc process had operntcd uneventfully for about 90 min, and several 100 rrnlns ol'dw woduct had been collected in the receiver. ~ h & ,without: warning, a violent explosion occurred. The glass components of the drier were demolished and a 114-in.-thick aluminum clamp finger was broken by the explosion. Four persons in the room, including the operator of the drier, were injured by glass shrapnel. Fortunately, the injuries were minor, primarily cuts that required suturing.
620
Journal of Chemical Education
Examination of the drier and fragments of the glass components showed that the explosion originated a few inches below where the suspension and the hot air enter the drying chamber. It was found upon investigation that the drying air entered the system at 170 "C. It was also determined that when the dried product was heated above 134157 'C it self-ignited vigorously with incandescence and deflagration, and sometimes produced a flame. When the dried product was heated to the ignition temperature in a closed container, detonation occurred. We wish to alert all users of spray driers or similar operations to this accident. Any mixture of nitrate with easily oxidized material (e.g., starch) must be considered a probable hazard until tested and proven otherwise. We suggest that, before any operation or process of this type, a small quantity of the material to be dried should be heated to decomposition and its behavior carefully observed. C. A. Crutchfield Jim VanAckeren All eo-S gnal Aerospace Company
2525 West 190tn Street P.O. Box 2960 Torrance, CA 90509-2960
