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[Col_Kilgore]

Hello,

I have been asked to check some proposed vent and header sizes and would be very grateful for any comment on the method I will employ to do this (described below).

For info, the set-up is a reactor with vent leading to a CW condenser. There is a CV on the vent outlet, post condenser, and on the N2 line feeding the vessel and together these valves keep a nitrogen pad of 30mbar on the vessel. After the outlet CV, the vent joins a vent header (which other lines also join) and is then pulled though a scrubber by a vac pump for discharge. There is an N2 bleed to the header also, to give the pump something to chew on when nothing is coming from the vents. Fairly common set-up I guess.

The vessel is never under vacuum (barring disaster lol) its only pressure is 40mbarg.

The way I have considered approaching the matter is as follows:

Obviously there will be several scenarios for each vent to handle and the lines must be sized for the worst case of these.

I identified these scenarios as follows:

1) Outbreathing due to liquid inflow. Here the volumetric liquid flowrate in is equal to the volumetric flowrate out of 30mbarg nitrogen (in order not to exceed pad pressure). The starting pressure and flowrate of nitrogen can be used with the area of the vent, and pipe length/fittings etc to calculate a pressure drop along the vent and check for suitable velocity etc.

2) Nitrogen purging of vessel Here N2 conditions in = N2 conditions out (flow etc specified bu purge requirements). Thus we can get DP and velocity in the same way.

3) reflux (potentially?) Same idea using a chosen boil up rate for typical vessel contents.

The line will be sized to ensure suitable DP and velocity for whichever case is largest.

I will progress like this but would welcome any comment on how appropriate this method is and if there are any other considerations. Are there pressure accumulation/initial velocity considerations?

I am also a little unsure over:

1) ). Normally the scrubber will be running so there will be a vacuum on the header side of the vent CV, so the discharge will be pulled through. If I learn the set-point of vac the header pump will be controlling to (I think the header is maintain at a constant vac and flow, with the help of the N2 bleed as necessary - is there a typical header operating pressure?) and the header length etc, I can figure out the pressure on the vessel vent cv outlet. As long as the pressure arriving at the vent cv is greater than = pressure on other side then all is OK?

2) How should I check the size of the main header itself? Should I figure out the worst case outlet flowrates for every item leading to the header and then figure out this volume as the header vac pressure and check the vent size against that worst case cumulative flow?

Thanks a lot for reading and for any advice offered :-)