3 replies to this topic

[Leotop]

Hello,

 

At my plant, I am having issues with a molten liquid (Polyethylene Glycol [PEG], 500-8000 Molecular Weight) getting into vent lines and causing plugging on a particular reactor.

 

Downstream from the reactor where PEG is contained, is 2" and 4" vent piping, an overhead condenser, and a conservation vent which vents to a scrubber.  The PEG has been found in the piping between the conservation vent and the scrubber and has lead to plugging in this line and pressure accumulation in the reactor.

 

I am trying to do some root cause analysis and troubleshooting and I am quite baffled by this problem.  I am amazed that the PEG is able to transfer this far into the vent piping then freeze.

 

My top two theories are:

• The PEG has some vapor pressure at the 100-150°C temperature and 0.5 psig pressure we maintain on the reactor -- I'm looking into this one
• The PEG is being swept or entrained by nitrogen in the vessel and it is being carried downstream.  

The second theory is very baffling, but I'm trying to wrap my head around it using an equation.  I'm familiar with the Souders-Brown equation for maximum allowable vapor velocity in a liquid-vapor separator:

 

V = k * SQRT( (r_L - r_v) / r_v )         https://en.wikipedia...–Brown_equation

 

Will this equation work for my analysis?  If so, what do I use for the value "k"?  The given k value is for a mesh demister pad.

 

My intention is to determine the maximum allowable vapor velocity, then ensure I stay below that in the vapor head space to prevent entrainment of the PEG liquid.

 

If not, is there another equation I'm not familiar with (or forgetting)?  Any other theories or thoughts?

 

Thank you!

[latexman]

Has there been any overfills or foaming events that could explain the issue?

[Pilesar]

For Souders-Brown to help, you need to know the size of the droplets that you cannot see or sample. In my limited experience with other condensing polymers, solids find a way to coat cool vapor spaces. This is a serious problem for pressure relief devices. Keeping vent lines hot to remelt any condensation is necessary. If this is a 'the vent never did this before' situation, then latexman's questions are a good start. 

[breizh]

Hi,

Check for melting point of PEG, quite low!

When you sweep PEG with N2 you may have sublimation (?) of PEG or Crystallization(?) of PEG due to temperature drop. Again, check for N2 temperature in your process.

My 2 cents

Breizh