Citation

Endo Y, Yamaguma M. J. Japan Soc. Safety Eng. 2017; 56(5): 362-373.

Copyright

(Copyright © 2017, Japan Society for Safety Engineering)

DOI

10.18943/safety.56.5_362

PMID

unavailable

Abstract

A lot of fires and explosions due to electrostatic discharges in chemical plants have been reported, while a flammable volatile organic solvent is being dispensed into a container through a hose with a valve system. In our study, based on past accident cases, an experimental apparatus consisting of a stainless steel hose and a ball-valve system was developed, and a series of experiment was carried out to investigate static charge generation characteristics of liquids, including ethyl acetate, acetone, methanol, toluene, etc. In addition, countermeasures to mitigate static charge were suggested. Static charges of the liquid samples were found to be produced dominantly by electrification mechanism by spraying at the valve system, and it was recognized that there was a clear correlation between static charge and the conductivity of liquid, with the peak at around 10-8 S/m. In the case of ethyl acetate, with the conductivity of 1.8 × 10-8 S/m, extremely high static charges were observed that reached a level causing ignition of the vapor of ethyl acetate very shortly（within one second）or with a small amount （lessthan100g). Finally, it is found that, by attaching a hose joint with small bore to the outlet of the ball-valve system and the valve element being completely soaked in the liquid, the static charge can be reduced to safe level.

化学プラント等においては，ホースを使って有機溶剤を小分けする際に，静電気放電で着火したと推定される火災・爆発事故事例が多い．本研究では，過去の災害事例を参考に，ホースとボールバルブからなる液体流動・噴出実験装置を構築し，酢酸エチルを含む数種類の有機溶剤について静電気帯電量の測定を行うとともに，根本的な静電気対策を検討した．その結果，バルブでの液滴生成時の噴出帯電が支配的であり，溶剤の導電率10-8 S/m 付近で電荷発生がピークを示す傾向が得られた．例えば，酢酸エチル（1.8 × 10-8 S/m）の電荷は他の溶剤よりも顕著に大きな値を示し，ごくわずかな放出量（100 g 程度）でも着火を引き起こす静電エネルギーレベルに達することが判明した．また，ノズルの先端を小口径にしてバルブを液中に完全に浸すことによって放出時の液滴発生を抑制することにより，電荷をほぼ安全なレベルにまで低減できることを明らかとした

Language: ja

Keywords

Ball valve; Ethyl acetate; Liquid dispensing; Organic solvent; Spraying electrification; ボールバルブ; 噴出帯電; 小分け作業; 有機溶剤; 酢酸エチル