Runaway reactions in aluminum, aluminum chloride, HCl, and steam: An investigation of the 1998 CONDEA Vista explosion in Maryland

Abstract

AbstractOn October 13, 1998, an explosion and fire occurred at a 3,000 gallon reactor in the linear alkyl benzene (LAB) process at the CONDEA Vista plant in Maryland. Process materials released from the various vessels and piping fueled a subsequent fire that took approximately two hours to extinguish. The accident investigation revealed that, prior to the explosion, the bottom of the reactor was plugged with approximately 180 gallons of a sludge‐like mixture of coarse aluminum powder, aluminum chloride, and various hydrocarbons. The explosion occurred approximately 10 minutes after steam was introduced at the bottom of the reactor in an effort to break up the sludge accumulation.A series of reduced‐scale chemical reactivity tests were completed to investigate the potential reactions between steam and manufactured sludge similar to what had accumulated inside the reactor. Rapid runaway chemical reactions were observed after steam was injected into this mixture, and pressures in excess of 45 barg (660 psig), and temperatures in excess of 700° F were recorded before the test vessels ruptured. A review of possible chemical reactions between steam, aluminum, and aluminum chloride confirms that the predominant reaction mechanism is the exothermic hydrolysis of aluminum chloride to produce HCl vapor. Significant amounts of hydrogen gas can also be generated as the aluminum reacts with the acid/steam mixture after it is stripped of its protective oxide coating. The investigators concluded that the root cause of this accident was direct and sustained contact between the steam and accumulated sludge at the bottom of the reactor.