Methanol Fractionation Column Bottom trays Fallen

[MIANCH]

Hi All,
During turnaround of our methanol plant, we found 22 trays fallen and some of them bulged as well. corrosion is one of the problem but bulging the trays is not understandable, can any one explain what is the reason of trays fallen or bulging. our column have total 83 trays. plant is designed by UHDE in 1984.
Regards

 

[0707]

Water or steam blow up during start up or shut down.

 

[EmmanuelTop]

Look at DCS trends and find pressure spikes/surges during startup/shutdown. If you don't find anything, keep looking for similar profiles during normal operation, particularly for feed changes, start of standby pumps, etc.

There is no such thing as "common sense" - Apollo RCA

 

[georgeverghese]

Tray buckling is a sign of some transient vapor overload which has resulted in high tray dp. Excessively high tray dp can also occur if vapor flow is within normal range, but with many of the valves (variable valve or sieve or bubble cap type etc) on each tray blocked with dirt or corrosion debris. Also check DCS trends for high column dp.

 

[MIANCH]

0707, water agree, re-boiler tube leaks found.
EmmanuelTop, No DCS system existing, 50 year old plant by UHDE, Pneumatic control system, operation is not maintaining data very well.This methanol manufacturing facility is in Libya.
George; we have sieve trays, your though make sence, trays was full of rust and pressure difference is one of the cause, can you please let me know the step (procedure) to calculate delta pressure, normal operating pressure is 1.2 barg and column have 83 trays. operating temperature 120 [sup]0[/sup]C.
Column: Total trays 83
Tray 1-22: spacing 350 mm
Tray 23-39: spacing 520 mm
Tray 40-67: spacing 74 mm
Tray 68-83: spacing 11 mm
regards

 

[georgeverghese]

Design calculation for tray dp is rather complicated, and it is much less painful to search for this info in the process datasheet for the column. Alternatively, if you know max operating downcomer backup for a typical tray in each section of trays in height of liquid, you can convert this directly to tray dp. Otherwise, you may have to take a risk and guess that tray dp is approx 50-70% of tray spacing. (Tray dp = rho.g.h in kiloPascals , if you use rho in kg/m3, g= 9.81m2/sec, h= assumed downcomer height in m.)

Why is the tray spacing so small, <100mm in the upper sections?

 

[0707]

You are speaking about tray spacings
Tray 40-67: spacing 74 mm?
Tray 68-83: spacing 11 mm?

this is not normal from may point of view, your sieve trays are just holes or fix valves. You are talking about donut trays? The spacings you mention are too short in my opinion.

luis

 

[TiCl4]

Could it be that the column narrows down at the top due to a low flowrate that requires smaller diameter trays (and thus smaller tray spacing)? I know nothing about methanol fractionation, but I too find the tray spacing quite interesting

 

[MIANCH]

Luis,
Thank you for tray spacing point rising, I rechecked column drawing and found that 40-83 spacing is 400 mm.
TiCl4, Column is narrow from bottom side from tray 1-22, then expand it 2.5 m and then tray 23 start and dia is same until column top.
Note: all trays MOC is Carbon steel except top four trays (80-83).