Safety Health and Environment

Chemical plants are generally prone to hazards. Hazards are chemical or physical conditions that have the potential to cause damage to people, property and the environment. The prevention of accidents through the use of appropriate technologies to identify the hazards of a chemical plant and eliminate them before an accident occurs is what safety is all about.

In the plant for manufacturing ethylene carbonate, the ethylene oxide storage tank and external loop reactor are associated with lot of hazards. Identification of hazards and eliminating them using proper safety measures is mandatory.

14.1 Ethylene Oxide Storage Tank

Hazard Identifications and Safety Measures

14.1.1 Pressure build up in the tank leading to vapor leak

 If the inner walls of the tank surface are not clean, it may lead to polymerisation reaction. These reactions get initiated at ambient temperature by trace amount of iron dust. At high temperature, the reaction gets thermally initiated. Since polymerisation reaction is highly exothermic, it is self accelerating and can result in dangerous rise in pressure which leads to vaporization. High pressure build up eventually leads to explosive decomposition.  The storage tank is provided with a relief system. Relief system consists of a network of components like pipe to relief, the relief device, discharge pipelines, scrubber and flare. Pressure relief devices are installed at points where upset conditions create pressures that may exceed the Maximum Allowable Working Pressure (MAWP). Rupture discs are provided with embedded wires that are cut when the disc ruptures that can activate an alarm in the control room to alert the operator. Ethylene oxide vapours are completely soluble in water. A packed scrubber column follows the rupture disc. EO gets scrubbed with circulating water in the column. The residual EO vapours proceed to a flaring system. The objective of a flare system is to burn the toxic gas to produce combustion products that are neither toxic nor combustible. Thus enough safety measures have been taken to eliminate hazards due to pressure build up leading to vapour leak in storage tank.