Advice on a peak blowdown rate required 1

[bouk]

Hi guys,

I need some advice.

I am doing some work with flarenet so I require some peak blowdown rates for my system. My blowdown valve is a globe valve (CV = 77). I am going to use hysys, but I am not sure about the vapour flow equation in Hysys, so I wonder if anyone knows a way to convert my CV into an equivalent area? Based on my values below, what are others getting as the peak blowdown rate?

These are my initial conditions:
100% vapour
system volume - 39.6 m3
pressure - 66.11 bara
temperature - 6.206 C
MW - 19.12
Z - 0.7764
Cp/CV - 1.184
viscosity - 0.01304
density - 70.12 kg/m3

 

[Latexman]

I recommend Crane Technical Paper No. 410 as a reference to allow you to check hysys calculations.

Good luck,
Latexman

Need help writing a question or understanding a reply? forum1529

 

[PaoloPemi]

if you do not include the heat exchanged (i.e. with vessel and other materials in contact with fluid) then you'll follow a isentropic path and you'll be able to determine (solving for P-S) the different temperatures at different pressures, from those you can calculate the max. flow solving the critical flow though your valve with the specific formulation from ISA (which is more accurate than convert to an area and solve as RO), you may calculate max flow starting from initial condition and then correct inlet density for reduced temperature and pressure.
If instead you wish (as I would recommend) to take in account the heat exchanged then you need to simulate the blowdown process,
generally the procedures available in simulators (I use Prode Properties but I guess your software applies a similar code) consider a RO (instead of a CV) to control the flow, then you need to convert your CV to an equivalent area, this is not simple as for a control valve there are different parameters to consider,
I would suggest to calculate the critical flow (through your CV) at initial condition and find the RO area which produces an equivalent result.

 

[SNORGY]

Find the closest sized Fisher globe valve to it, look up the Emerson catalogue data, use the Cg and Cv coefficients tabulated therein (the Cg might be tough to find), and apply the Universal Gas Sizing Equation. If you can't get the Cg directly you might need to follow the formulae and methodology that Fisher use in their Control Valve Handbook. The theory is treated quite nicely if you Google and obtain Fisher Catalog 21 Section 1 and Section 2. I just found both of those on line this afternoon.

 

[Latexman]

My Crane TP 410 is in English units. For control valve, equation 3-16:

K = 891d⁴/(C_V)²

On page A-20 for sharp edge orifice an approximation is:

K [≅] (1 - B²)/(C²B⁴)

d = ID, inches
C_V = gpm with 1 psi dP
B = orifice Beta
C = flow coefficient

These will get you started to "convert my CV into an equivalent area".

Good luck,
Latexman

Need help writing a question or understanding a reply? forum1529