Good Intentions on Certain New Protection Systems Lead to Troubles

Good Intentions on Certain New Protection Systems Lead to Troubles 

Dowell, III, and Dennis Hendershot presented a technical paper entided, No Good Deed Goes Unpunished Case Studies of Incidents and Potential Incidents Caused by Protective Systems in March 1997. [9] All the material in that paper complements this chapter. 

Innovators designed this environmentally friendly system to eliminate the emissions from routine tank operations of emptying and filling, ambient temperature changes, etc., by routing such fumes to a flare system. [9] The low-pressure lifting lid was still available for emergencies such as fire exposure to the tank. 

However, the vent collection system that served the low-pressure feed tank also served a nearby distillation column that operated at nearly 15 psig and contained a toxic component. Physically the low-pressure tank was on the vent piping between the distillation column and the flare stack. During a distillation column upset, there was an increased flow to the flare. The vent header pressure increased. The vent piping diameter between the distillation column and the flare proved to be too small. Toxic fumes from the higher pressure system column were released from the low-pressure tank emergency tiffing lid. 

The authors discussed the inherently safer design changes of 1996, which included replacement of the atmospheric tank with a tank designed for 3.3 atm (50 psig). I quote the authors conclusions on what their case study teaches  

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