Abstract

As part of the continuous effort to reduce/minimize flaring, an optimization project was undertaken to reduce flaring during the normal operation phase by minimizing the purge gas flow rates to the minimum acceptable limit.

The previous purge gas flow overseen by the EPC Contractor was revised using the latest API standards (API 521). As a result, the study identified a major opportunity to optimize the off-shore flaring as summarized in table-1 below:

Table 1

minimum purge gas requirements to offshore HP flares

Minimum Purge Gas (Kg/hr)Actual designRevised Criteria from API (521)Revised design
EPCFlare vendorAir Ingress criteria for headerAir Ingress criteria for stackBack burning criteriaFlare vendor + Process margin
Plat-1 HP flare 787 72 48 17 54 79 
Plat-2 HP flare 787 72 48 17 54 79 
Minimum Purge Gas (Kg/hr)Actual designRevised Criteria from API (521)Revised design
EPCFlare vendorAir Ingress criteria for headerAir Ingress criteria for stackBack burning criteriaFlare vendor + Process margin
Plat-1 HP flare 787 72 48 17 54 79 
Plat-2 HP flare 787 72 48 17 54 79 

Revised criteria from latest API standards applied to the offshore HP flare showed that the minimum purge gas requirement should be lower than flare vendor recommendation (from the vendor datasheet).

A process margin is added to the recommended purge gas flowrate to cover for fuel gas composition and flow meter accuracy.

The new minimum purge gas requirement defined as a revised design was confirmed by company's technical team. The flare vendor also confirmed that the revised design was above the recommended minimum purge rates for the HP flare tip and committed to reduce air ingress and oxygen levels inside the flare tip and stack to acceptable points during normal purge scenarios. This would also ensure safety, reliability, and integrity.

Implementation of the purge gas reduction in the offshore HP flares was achieved by carrying out a step-by step reduction of the purge gas flow down to the flame visibility. A detailed Method of Statement was prepared to ensure a smooth purge gas reduction activity.

As the purge gas flow was reduced, the HP flare tip inspection frequency increased. At the initial stage, flare tip inspection frequency of 2 years was suggested in line with the platform shutdown schedule.

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