Glycol Regeneration Skid

[phuongnguyen]

My field is using plunger pump to circulate LEAN glycol from glycol surge drum to glycol contactor. Does anyone know why vacuum happens in the suction of plunger pump? And how to take a sample of glycol if it is vacuumed? (Sample point locates in a pipeline from glycol surge drum to plunger pump - as a file). Thanks in advance

 

[1503-44]

Most likely it is insufficient suction pressure, NPSH.
Hot glycol may also have high vapor pressure.
Both not good.
Is the pump being run at a high speed?
Also not good.

 

[phuongnguyen]

According to design, fuel gas purges into bottom of reboiler (connected with surge drum) and these drums vent to atmosphere so it’s hard to vacuum inside.
_ I think NPSH maybe due to scale precipitate in suction flowline.

 

[georgeverghese]

Vacuum in the suction line does not mean insufficient NPSH, since lean glycol vapor pressure is very low. On the other hand, lean glycol is often contaminated with gas condensate with high vapor pressure. Calculate the NPSHa at pump suction ( dont forget acceleration head loss component) with condensate vapor pressure to see if you are in the clear. Condensate vapor pressure is the same as surge drum pressure.
If you need to collect a sample, you can also get it from the surge drum.

 

[1503-44]

Plunger pumps can get difficult sometimes, as you must provide enough NPHS to overcome the plunger acceleration.

 

[phuongnguyen]

@gorgeverghese
We cannot take a sample from surge drum under vacuum condition unless we close the vent line and build up pressure in surge drum (0,02 -> 0,2)

 

[georgeverghese]

How is surge drum under vacuum pressure? Do you have a vacuum ( liquid ring pump or similar) on the vent condensor outlet(downstream of reboiler overhead)? The diagram you sent is not loaded properly; we cannot see anything.

 

[Compositepro]

Small vacuum pumps are readily available and can be used to get your sample. A syringe may even work.

 

[LittleInch]

Fluid temperatures are 90C?



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[phuongnguyen]

Sr for lately reply, We suspected that suction strainer was blocked so we opened for inspection.
Finally, we found that scale precipitated in strainer very hard

 

[1503-44]

Then it was insufficient suction pressure after all.

 

[phuongnguyen]

Unfortunately, there’s nothing changed. We keep investigating still shutdown job and internal inspection surge drum.
Appreciate any ideas .