5 replies to this topic

[Mohammed Aljabobi]

Hi all,

 

I am currently sizing a PSV for a fuel gas filter for both fire and thermal relief cases.

Now, for the fire case I am using the liquid stream properties that is coming off of the bottom of filter. However, I am not really sure what stream I should be using for the thermal relief case. I believe that I should be using the vapor stream properties for my calcs, but I wanted to double check with some of the experts on this forum.

 

By the way, this forum rocks ... I learned a lot from it.

 

 

Thank you,

 

 

Mohammed

[ColinR33]

Mohammed,

 

Thermal relief more often refers to thermal expansion of a liquid in a liquid filled piece of equipment exposed to a heat input or a long piece of piping that can be blocked in and left to heat up in the sun.  This causes the fluid to expand and potentially overpressure the equipment or pipe.  Not something you would typically see in a fuel gas filter. 

 

You have anot attached any drawings of the system so I am shooting in the dark a bit here with my response.  The fire vapour generation case might be valid (but will there actually be liquid in your FG filter?  any scrubber/heater upstream?), but you should also check gas expansion as I would think the filter is normally dry.  Is there a source of HP fuel gas being let down in pressure to your filter?  If so you should look at instrumentation failure that could result in HP gas blowing through (but you should have a scrubber upstream with a PSV for this case if it is a credible scenario).

 

HTH

Colin

[Mohammed Aljabobi]

ColinR33,

 

Thanks for the quick response.

The fuel gas stream  shouldn't have any liquids actually now that I'm thinking about it and looking closely at the H&M table.

The filter doesn't have a HP gas being let down (you are exactly right there is scrubber upstream of the filter with a PSV for fire case). There is a pressure regulator right after the gas scrubber to reduce the pressure of the gas to 150# ANSI. 

 

So now I think the fire case scenario is highly unlikely as there shouldn't be liquid in the filter. 

Thermal expansion is also eliminated as well as there is no liquid. So, what would be a more reasonable scenario for this PSV? Blocked flow? Or should I do these three cases and then size the PSV for the most likely scenario?

 

Thank you,

 

Mohammed

[oscarsender]

There are two overpressure scenario for external fire case. One is liquid vaporization for those that contain liquids. The other one is overpressure due to gas expansion for those that contain gases. In this case, the second case may still be applicable.

[fallah]

Mohammed,

 

To submit a proper response it's needed having a simple sketch of the system you described...

[Mohammed Aljabobi]

Thank you guys for your help. 

I got a chance to discuss this with a colleague of mine and we came to the conclusion that a fire case is a reasonable basis for this filter. 

 

I do appreciate your input and sorry for not providing a sketch to help understand the problem.