4 replies to this topic

[abhijit-tce]

Hi,
For two phase relief valve sizing, we have used HEM method and in datasheet we have reported properties at maximum mass flux. Now in aspen flarnet software, shall we give this properties or proerties at relieving condition for network analysis. Because based on this, psv outlet properties will change. Please suggest.

[PaoloPemi]

when a PSV discharges on a flare (network) normally

I run a software (to simulate the network, calculate

back pressures on each PSV  etc.etc.)

with flows and conditions at relieving condition

for a specific case

(i.e. fire, some accident etc.) , there could be

several cases to examine and, of course,

one selects as design case that  with maximum flows,

pressure drops etc. etc. on flare netwrok,

I have not experience with large networks

(I have PRODE PROPERTIES which

includes HEM model for PSV and piping

but not a solver fro networks,

so I have my own solver)

however I suppose the procedure is the same.

[abhijit-tce]

So wht shall I give?

[PaoloPemi]

does not Flarenet manual specify

which properties the software require ?

 

I have not  Flarenet,

if the above (consider flows and conditions

at relieving conditions for each specific case

i.e. fire, some accident etc.)

doesn't help I suppose you need

the details about how to enter

the values in the sofware,

usually these are discussed in the manual

and I would be surprised should it not clarify

this point,

 

Flarenuf or other experts here may adise.

Edited by PaoloPemi, 07 November 2013 - 08:41 AM.

[flarenuf]

abhijit

 

good question !

the problem here is that generally when people use flarenet they use the properties of the fluid in the pSV at design conditions. ie the values used to size the psv

this will usually be at accumulation pressure values.

in reality the flow, temp and pressure at relieving conditions with the actual selecetedlarger orifice size will be different and in most cases the relieving pressure will be less than the design  relieving pressure.

 

so which figs do you use ..

if this is the only PSV  relieving in a scenario then you should use the max mass flow to give you the better backpressure calc in fnt

if however this is only one of many PSV's releiving in a scenario then you could be using a mix of max mass flow for this pSV and design values for the other flows.

if it is 1 of many then look at the contribution of this PSV to the total scenario  load, is it 5% or 75%  what impact does it have on the backpressures in the network?

 

run fnt with your max mass flow and design flow and see if there is any noticeable difference in teh calculated results

if not then fine , if it does have an impact then  its down to engineeering judgement to determine the way forward.

 

probably not the " use this figure" answer you wanted but without the whole picture i cannot be more definitive

look at the impact of either way and decide ...

flarenuf