QUANTITATIVE RISK ASSESSMENT: A CASE STUDY OF POLYMERIZATION REACTOR

Abstract

Chemicals have become a part of our life for sustaining many of our day-to-day activities. Polymers and plastics, especially polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polystyrene and polycarbonate comprise about 80% of the Chemical process industry's (CPI's) output worldwide. The magnitude and the diversification of the types of risk have increased concurrently with industrial development. At the same time, the threshold of risk acceptability of the population has decreased. In response to the above preoccupation, CPI and regulatory agencies have developed various methodologies and tools for risk analysis and assessment. In this report a comprehensive literature review along with a general risk assessment methodology is presented. As a case study a Vinyl chloride monomer (VCM) polymerization reactor which produces Poly-vinyl chloride (PVC) has been considered to assess the risks involved. The PVC plant is located on the western coast of India and uses BF Goodrich (Now Oxy Vinyl) technology. Qualitative as well as quantitative studies are carried out. Dow's Fire and Explosion Index has been calculated. A brief hazard and operability study (HAZOP) for the reactor along with a complete QRA for the worst case scenario as obtained from qualitative studies has been done. This includes a fault tree analysis (FTA) for finding minimal cut sets and the probability of the top event. Layer of protection analysis has been carried out for the reactor taking into account various categories of hazardous scenarios. The concept of independent protection layer (IPL) is explained and it is shown that a plant that may be safe but many a time it is only after a combination of independent and non independent protection layers. Individual risk contours have been plotted. The F-A curve is drawn and values like fatal accident rate and average death rate are calculated. For the case study it can be seen that risk targets are met overall but in some scenarios independent layer protection may alone not be enough. Finally a methodology which suggests simultaneous use of FTA and LOPA is suggested which may reduce resource usage and overcome drawbacks of traditional QRA in many cases.