liquid holdup in TEG absorber

[sani]

Hye Every one
can any one tell me rule to calculate the hold up of the liquid level in TEG dehydration absorber coloumn? also to calculate the different heights of liquid levels as HLL(High liquid level), NLL(Normal liquid level), LLL( low liquid level) for shutdown and control purposes."

[ibrahim]

What i can share is my experience regarding vertical vessel/column liquid volume holdup;

• LALL (low level trip) should be at least 100 mm above the level of the lower LG nozzle or according to NPSA requirement added to skirt height.
• LAL (low level alarm) should be either at least 100 mm above LALL or should be located so that there is sufficient liquid hold-up time between the two levels for operator intervention (typically 1 min to 2 min for action in the control room and 5 min for action by field operator).
• LAH (high level alarm). The minimum distance between LAH and LAL shall be 350 mm. The distance between LAL and LAH shall be such that there is sufficient liquid hold-up time between the two levels for control purposes. It should take 5 min to total product outflow for columns to furnaces or other columns.
• The Normal Level (NLL) should be positioned so that the control time is equally distributed between LAL and NLL and between NLL and LAH; this ensures optimum operation.
• LAHH (high level trip) is either at least 100 mm above LAH or located so that there is sufficient liquid hold-up time between the two levels for operator intervention. If the liquid has a foaming tendency, the distance between LAH and LAHH shall be increased by a further 250 mm.

Hope this helps

[tosif]

good thumb rules, ibrahim, nice sharing.
Special care should be taken for LALL and LAHH (both trip points), to avoid any damage to the process equipment. Do you have a check valve of U-seal type configuration of gas inlet pipe?

[sani]

thanks ibrahim for your reply. kindly can you tell me thumb rules to calculate the tower height for TEG Absorber? or is there any literature or equations regarding this calculation or its done on experience base in industry?

[ibrahim]

Absorber dimensions can only be evaluated using some simulator (like HYSYS, PROII) by doing heat and mass balance. Then you have to do hydraulic evaluation of HYSYS results using sizing software such as TRAY2000. I don't think there will be any direct rule to get that. Obviously it depends upon numerous factors including gas flows, composition, glycol flows (based on gas flows/comp) and temperatures pressures.
Can you specify you problem further?