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Flare purge after maintenance

Flare purge after maintenance

Flare purge after maintenance


Is there guidance of how long to purge a flare header prior to Return to service?


RE: Flare purge after maintenance

From the following document - see Fig 1 on page 10


I would suggest pressuring the header to 0.5barg with near pure N2, then blowdown, then repeat another cycle of pressuring to 0.5barg and blowdown again. That will prevent the subsequent methane fill of the header from combusting. The second cycle is to account for non ideal mixing of the header contents prior to blowdown.

RE: Flare purge after maintenance

Fig 1 on page 10 of that doc tells me methane at any concentration is not flammable in a N2 / O2 mix where O2 concentration is less than 13% v/v.

This document indicates a lower O2 concentration of 10-11% v/v for flammability of methane, close to the previous value cited. See page narrative and Fig 3 on page 4 of 7


The 2 cycles of pressurisation should get you down to < 10 % v/v O2.

RE: Flare purge after maintenance

AS flare knock out drum (KOD) is designed for low pressure so following procedure may be adopted for purging the flare system before taking it in line:
1. Close flare KOD outlet valve.
2. Open N2 from all sweep points in flare headers. (can remove RO for in N2 sweep points for purging purging purpose)
3. Take 0.5-0.7 bar pressure upto flare KOD
4. Open flare KOD outlet valve and depressurize upto 0.1-0.2 bar pressure.
5. Repeat this 4-5 times.
6. Take gas sample from flare KOD in bladder and analyse for oxygen percentage.
7. If oxygen in less than 1 %, can take flare in service.
8. install RO in N2 sweep points.

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