Abstract

The Fire and Gas detection systems in many of the existing facilities were designed in a conventional method without software modeled design and therefore their performance are questionable. This is due to the fact that at the time when designed, the dispersion and fire were not yet widely implemented.

Since the major accidents are unlikely to occur and it is therefore uncommon to revisit and verify the adequacy of the design of these systems.

This paper discusses the importance of revisiting the design of the existing fire and gas detection systems and its rule in saving our facilities from major losses.

Introduction:

ZADCO top priority goal is to achieve the required production target within 25 years plan, while maintaining their successful record of safety of personnel and assets.

ZADCO Central Complex, presently is handling process streams having very low H2S content. In near future, gas breakthrough in the field will result in H2S contamination of the process streams at Central Complex. The H2S concentration is predicted to reach 1.0 mol% in process streams by year 2020.

The existing facilities of Upper Zakum were designed for sweet crude/gas, however new installation of sour gas injection and gas lift facilities together with the likelyhood of gas breakthrough thus a possibility of sour gas emission. For mitigation, a Quantative Risk Assessment Study was carried out resulting in identifying the necessity for a new toxic gas detection system.

Therefore a complete F&G study was conducted to identify the requirements of the toxic gas detection system plus assess the performance of the existing gas and flame detection system on Central Complex.

A detailed performance target criteria for each processing area was developed to define specific performance requirements for the fire and gas detection (both flammable and toxic) systems in different processing areas of the Central Complex.

The performance-based selection criteria for the overall Fire and Gas detection system take the following into consideration:

  • Type of detection

  • Response time

  • Coverage area

  • Maintenance requirements

  • Environmental conditions

  • Performance of the complete loop

The dispersion results identified the requirements of the new toxic gas detection system, and highlighted that the existing flammable gas detectors are inadequate and recommended additional flammable gas detectors to the existing gas detection zones.

The study also identified that in some areas of the plant, despite not containing major hazard source but is considered a critical location since major gas releases from adjacent decks can subject those zones to flammable gases.

Furthermore, fire events modeling was performed for representative fire events on the platform to define the basis for fire detector locations in the various areas of the plant.

The fire events identified that the existing frangible bulbs are very slow and insensitive to most fire events, this cannot therefore be relied upon to detect small-medium fires before they escalate and the present arrangement is unable to meet the performance target criteria.

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