Dispersion Model and jet flame length

[loribadeaux]

I need some advice for the following proposed scenario:

HP fuel gas of 40-55bar is sent to a conditioning skid consisting of coalescer, heater and pressure reduction station.

There is a concern that in case of rupture/ puncture in the system (equipment or piping) the resulting released gas will ignite and the resulting flame can damage the piperack in the vicinity.

The first way against this kind of scenario would be fire protection measures for the piperack. The client do not want to do this.

So we've done a dispersion modelling and jet flame length calculation and the conclusion was that a max. 10m flame is acceptable; this flame length was to be achieve if the pressure is max.20bar and the flow rate about 5000kg/h of fuel gas.

In conclusion a flow orifice was proposed to be installed upstream the skid which will limit the flow rate to max. 5000Kg/h. But obvious the pressure loss through the orifice will not be enough to lower the pressure from 40-55 to 20bar so I believe that the proposed FO will not help too much with our possible safety problem.

I would like to hear some opinions regarding the proposed solution with the FO.

Thank you very much.

Lori

 

[ajs1972]

Is necessary to know the operating conditions for all the system. Maybe adjusting the FO to 20 bar, but this will impact in the flowrate and can cause a bottlenecking in the process.

By the other hand, what temperature is in the HP fuel gas? because depending of the temperature the threat zones can change.

Regards.

 

[nichs2]

You could also think about how long the jet flame would stay at the initial length for - as the system depressurises, then the flame will get smaller, and it may not impinge on your pipework long enough to give you a problem. If you could stick an ESDV somewhere, perhaps with remote actuation, and could limit the duration of the jet fire impinging on the rack to less than 10 minutes, then your piping might be ok.

Its important to properly assess any risk reduction options, taking into account how likely it actually is that the failure occurs so that the pipework is damaged (failure rate of pipework, size of hole, ignition probability, direction of flame). The FO might limit the length of any jet fire, but might adversely affect the rest of your system

I'm not sure the temperature of the fuel gas makes much difference. The temperature of the flame might, depending on the material of construction of your pipework (time to failure of different materials when exposed to high temperature).

No real answers in my post I realise, just more to think about...

 

[owg]

What is in the piperack?

HAZOP at

http://www.curryhydrocarbons.ca