Comparison of the Availability of Trip Systems for Reactors with Exothermal Reactions (PSAM-0361)


The control of exothermal reactions is an important issue for chemical process safety. Such reactions may produce a runaway after stirrer or cooling failure. This is accompanied by a temperature and pressure increase either because gaseous reaction products are generated or the reactor contents starts to boil. The reactors used for these reactions are amongst others equipped with trip systems. These may, for example, be based on the fast injection of a reaction inhibitor or the fast dumping of the reactor contents into a knock-out tank. The measures mentioned are active, i.e. they require a number of components (e.g. sensors, pumps, valves etc.) to function in order to be successful. For reaching a high availability often redundant design is used. Additional gains in availability by further increasing the degree of redundancy are, however, limited by the possible occurrence of common cause failures. Nevertheless, the availability of the trip function may be improved if a passive trip system is used instead. The paper presents a comparison of the availabilities of typical trip systems of differing degrees of redundancy and human intervention with a patented passive trip system of own design. Weak areas of the designs of the different systems are identified and possible improvements are suggested. However, the passive trip system proves to be least dependent on inspections and tests and does not require a redundant design in order to achieve the highest availability of the investigated systems.

  • Abstract
  • Introduction
  • Investigated Trip Systems
  • Fault Tree Analysis
  • Reliability Data and Test Intervals
  • Results
  • Final Remarks and Conclusions
  • References

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