High Pressure steam vent SILENCER

[coolcando]

We have a vendor's proposal for a new HP steam vent silencer .
The technical specs for which are,
1) massflow -- 50000kg/hr,
2)Steam condition at diffuser(silencer entrance):31 bar
3)There is a control valve u/s of this proposed silencer .Steam conditions u/s of this control valve is 41.1 bar and 400c.

I am asked to validate an existing silencer for abovementioned load so we don't have to buy a new one.Technical specs for existing silencer,

1) capacit :34000 acfm(actual cub feet per minute) .

I dont have any other data for this existing silencer.

My question is ,

1) How can I convert 50000 kg/hr rate to a volumetric rate?
2) At what point this capacity 34000 acfm is measured? At the diffuser or at the exhaust condition(atmospheric condition)

3) What does ACFM means? does it mean steam volume corrected considering adiabatic expansion?

4) Is this a case of adiabatic expansion?


Thanks for help

 

[hacksaw]

Without design drawings, a manufacturer, or name plate data on the silencer, you cannot assume anything.

There are low pressure vent silencers, that work at near ambient pressure. This should not be confused with a high pressure diffuser. These can withstand a much higher pressures and pressure drop.

The valve/diffuser expansion is not actually adiabatic, but you can assume that it is to get the approximate discharge conditions. Once you have the exit temperature at ambient pressure, you can check the ACFM of the vent silencer. Some silencers also have a inlet velocity limitation that must be observed.

 

[sshep]

Cool,

I would suggest getting a quote on a new unit anyway as these silencers didn't seem to be excessively expensive (last time we bought one), and the information will be valuable for decision making. Surely you know the manufacturer of the old unit (Pulsco, etc)- it would also be worth a call to verify the convention used for the flow, and maybe you can get them to check the new conditions as a bonus.

As to the rating check for the existing unit, you can estimate the pressure drop for the new conditions based on design flow once you have clarified the 34000acfm. Adiabatic pressure drop assumption is appropriate for the steam conditions but you must consider the control valve as well and calculate the distribution of the 41.1 bar dP across both the vent silencer and the control valve. The control valve will generate excessive noise if the dP is too high (generally noisy at dP/P1>0.5), in which case the silencer is too big. The other check to make is the exit velocity of the silencer, if excessively high then the existing silencer is too small. If both of these checks seem reasonable, then you may have a good shot at reusing the existing silencer.

This is my opinion, others may see it different.

best wishes,
sshep

 

[JimCasey]

Conditions upstream of the control valve:

P = 41.1 bar absolute pressure/input
T = 400 C temperature/input
x = 1.00 dryness fraction/output
h = 1381.69 Btu/lbm specific enthalpy/output
s = 1.61 Btu/lbm,F specific entropy/output
v = 0.071 m3/kg specific volume/output
--------------------------------

Assuming adiabatic/Isenthalpic expansion, the condition between the valve and the silencer inlet will be:
P = 31 bar absolute pressure/input
T = 392.52 C temperature/output
x = 1.00 dryness fraction/output
h = 1381.69 Btu/lbm specific enthalpy/output
s = 1.64 Btu/lbm,F specific entropy/output
v = 0.095 m3/kg specific volume/output

Assuming the silencer discharges to standard atmospheric pressure:

P = 1.013 bar absolute pressure/input
T = 368.71 C temperature/output
x = 1.00 dryness fraction/output
h = 1381.69 Btu/lbm specific enthalpy/output
s = 2.02 Btu/lbm,F specific entropy/output
v = 2.92 m3/kg specific volume/output
--------------------------------

Mass is conserved.
50,000 kg/hr x 2.92 m3/kg x 1 hr/60 min=2,433 acM/m. =85932.34 actual cubic feet per minute expanded to atmospheric.

Actual cubic feet depends on the pressure. STANDARD cubic feet always represent a fixed mass. There is no change in SCFM with pressure or temp.