4 replies to this topic

[akashlovey]

here is a problem i'm facing.

 

1) heat exchanger is vertical cross flow combined type heat exchanger. 1-1 type exchanger . 

2) shell side : inlet from top and bottom  , outlet from mid section

    Tube side : inlet from bottom  outlet from top

3) shell side stream : Ethylene glycol water  inlet 40 deg C 10 barg ,  outlet 5 deg C  ,  Ethylene glycol is operating in closed circuit and it gains heat from other source after heat exchanger and comes back to heat exchanger again to inlet.

    Tube side stream : liquid ethane -170 deg C    P = 150 barg  , outlet gaseous ethane  0 deg C

 

Problem facing : Ethylene glycol circuit flow is around 4000 m3/hr and its flow fluctuates sometimes to 2000 m3/hr very often including its top and bottom flow , leading to triggering the low low flow alarm . we are having trip interlock for heat exchanger on low low flow alarm which leads to trip the heat exchanger very often. 

 

so after doing some troubleshooting we start venting in ehtylene glycol water line and results in some gas is coming from vent valve . after doing LEL test it show gas is having some hydrocarbon composition. but the pressure in Ethylene glycol water line remains same 10 barg.

[Saml]

Difficult to say with the information you provide.

 

Closed circuits normally have a null point or a pressure control point at pump suction where gas vents to a pot or vessel that is either to atmosphere or vented thru a pressure control system. ¿How is your system set up? May be it is designed to control the pressure at 10 bar.

 

Do you measure in this point? If it is a pressurized system ¿Do you see an increased pressure valve opening?

¿Is the pressure at the pump discharge constant or it fluctuates as if gas locked? LEL may be OK for a quick check, but you should search for ethane if you are suspecting a leakage. Also, the ethane inlet temperature is below the freezing point (or a point where viscosity is an issue) of the glycol water mix.  ¿Is there any possiblity of this being an issue?

[Bobby Strain]

That's a strange exchanger you describe. And the ethane temperature you show is even lower than you would expect for LNG. So, all your query is in doubt as to a real operation.

 

Bobby

[akashlovey]

Sorry guys consider liquid to be LNG and its temperature is -150 C

[akashlovey]

We have a suction expansion drum for glycol which is having a PCV discharge pressure fluctuates sometimes and PCV operates to maintain pressure due to which its level changes drastically and Glycol flow changes abruptly. We do venting from shell side and a lot of gas comes out from it. Usually in other exchangers only glycol comes out as it is filled completely in every case . we tried to fill the whole loop with glycol and start the exchanger but after 3-5 days same gas comesout from shell side.