Effectiveness of Water Sprays in Mitigating Toxic Releases

摘要

Water spray curtains are often advertised as means to mitigate the consequences of released chemicals from high pressure tanks. Spray curtain effectiveness claims by certain vendors are misleading-a curtain placed at the periphery of a tank will only scrub a puff of a release. A spray curtain that can effectively contain a consequential release will look very different and cost much more. Studies that demonstrate spray curtains to be effective assume low gas velocities. However, calculations show that pressurized liquid NH_3 or HF when released from an orifice to the atmosphere comes out at a high velocity and momentum in the form of a two-phase jet. The jet must travel quite a distance before the velocity drops enough to be effectively scrubbed by a water curtain. The water curtain therefore needs to be at this large distance and consequently the diameter of the water curtain manifold ring needs to be quite large to be effective. This paper presents engineering calculations to estimate jet velocity, diameter & concentration, calculations to evaluate the efficiency of water sprays and discussion of ivater spray curtain designs that are more effective.