(67f) Top 5 Contaminants from a Process Safety Perspective

Managing contaminants within olefins plants is necessary to ensure product integrity, long-term reliability, and process safety. This presentation will provide an overview on five contaminants that represent an elevated risk for process safety. These include nitrous oxide compounds (NOx), butadiene popcorn polymer (PCP), mercury, pyrophorics, and methyl acetylene and propadiene (MAPD).

1. NOx compounds can accumulate in cryogenic sections of ethylene plants during operation at temperatures below -100°C. Reactions with olefins/diolefins or impurities such as ammonia can result in the formation of NOx gums and salts, which can decompose explosively.
2. The formation of highly cross-linked polybutadiene, known as popcorn polymer (PCP), is a known risk in ethylene plants where butadiene streams can react with oxygen and/or peroxides. PCP grows and generates forces sufficient to deform and rupture process equipment.
3. Mercury accumulation can occur in cryogenic sections of ethylene plants, namely in aluminum plate-fin heat exchangers systems or “cold boxes.” It represents a personnel exposure safety risk during plant turnaround and maintenance activities. Also, mercury may cause corrosion in aluminum heat exchangers, leading to potential loss of containment.
4. Pyrophoric and self-heating safety risks are associated with materials that, when contacting air, are likely to heat over time. This may result in fire, equipment damage, and personnel exposure risks.
5. Methylene acetylene and propadiene are unstable at high concentrations and can decompose explosively. The risk is generated in certain areas of the C₃ and C₄ system.