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[cat]

Hi,

 

We have a HP condensate flash drum at the plant and the PSV keeps on popping. The initial suspect was that the HP steam trap/s is/are passing causing blowby conditions into the drum; however, upon steam trap survey with vendor, it was noted that the steam traps are in good conditions.

 

The condensate drum is designed at ~8.2 barg and so is the PSV.

HPS condensate is at 8.2 barg by paper, but in actual, we are getting 10-12 barg. (for info, HP steam is 42barg)

The vapor line is connected to the LP steam header which is 6.5-7 barg. Line size is 2" connecting the vapor line to the LP steam header with pipe length of <20m, Elevation + 4m

 

It was noted that no level indication in the drum. Transmitters were tested to be ok, and providing good readings.

 

The actual flowrate based on HP steam consumption is 5t/hr. Flash drum by design was based on 2TPH. We had a previous expansion, that increased the flow to ~3TPH, but the drum was deemed to be sufficient theoretically. We are still in the process of how to verify the actual flowrate of the condensate

 

My hypotheses for the frequent PSV popping are:

(1) The drum is undersized, and hence the fluid may not have a "sufficient" disengagement/high velocity, leading to liquid entrainment into the vapor line. Aside from this, the line connection at 2" is hydraulically limited to a certain flowrate

(2) The fluid itself is 2-phase, but relatively still "high in vapor" (though I am unsure how is this formed in consideration that the steam traps are "healthy)

(3) The level control valve is passing

 

Would like to know your thoughts on this matter. Thanks in advance.