9 replies to this topic

[Alaa55]

Hello fellow engineers/ chemists,

 

At our site we are going to commission a new ethylene refrigerant storage drum. Normal working temperature when filled and put in service would be around  -80°C.

 

Initial filling with ethylene liquid impose a risk of rapid cooldown from ambient temp to -80°C. What is the best approach to do initial filling safely. Initially the drum will be purged, dried and kept under positive nitrogen pressure of 0.1 barg. Our intention is to displace N2 with C2H4 vapors through piston purging several times. And then start transfer Ethylene liquid from a truck to the C2H4 storage drum using a pump with discharge pressure 10 barg. 

 

According to the PH diagram of Ethylene, if C2H4 is allowed to expand from 10 barg pressure to 0.1 barg pressure it will cool to very low temp about -100 °C and yields a mixture of saturated liquid and vapor.

 

A throttling valve on discharge of the pump can be utilized if this helps but again the final saturation temp at 0.1 barg will remain the same -100 °C. What am I missing here? 

Edited by Alaa55, 19 February 2023 - 07:18 PM.

[Pilesar]

First fill the drum with ethylene vapor, not liquid, to bring it to pressure. You may need an external heater for this.

[Bobby Strain]

Where is the supply of ethylene vapor for the initial purge from? What are the conditions in the  truck trailer?

 

Bobby

[Alaa55]

Pilesar. Unfortunately we don not have an Ethylene vaporizer/ heater. 

 

Bobby Strain. We have no source or method for generating Ethylene vapor. That is only our thinking about the problem. We need to get rid of N2 inside the vessel and then charge with Ethylene. 

[Pilesar]

You may need to contract with a third party to help with the initial pressurization of the vessel. Whatever steps you take should end up with ethylene vapor pressurizing the tank before adding ethylene liquid. Understand the minimum temperature for your vessel and do what it takes. If the system is not stainless steel, then you should not go from nitrogen to ethylene liquid. A three-step procedure may not be good enough, but check what would happen if you flushed the nitrogen out with propane, then slowly flushed the propane out with ethylene. There may not be a better way than using an external heater when filling with ethylene.

  Minimum design metal temperature (MDMT) for a pressure vessel is not the same as the minimum temperature of the contents under all conditions. MDMT is the minimum temperature of the metal at design pressure. ASME has a chart that indicates how far below MDMT should be safe when the pressure is reduced. In any case, your situation requires a full analysis by experts. Those who designed your plant should have suggestions.

[breizh]

Hi,

Did you contact your ethylene supplier to get support? What about SOP for start-up? This should be included in the process description.

What about renting/building a vaporizer for this particular step? 

https://www.armstron...vaporizers.html

My 2 cents

Breizh 

[Alaa55]

Pilesar, breizh, thanks for your advice. Well, the vendor argument is that no need for Ethylene vaporizer because all Ethylene liquid going to the drum will vaporize and no risk of rapid cooldown during initial filling. 

 

"Note: WHEN THE ETHYLENE FIRST ENTERS THE WARM DRUM AND PIPEWORK, MOST, IF

NOT ALL, WILL VAPORIZE. WHEN THE PIPEWORK BECOMES COOLER AND THE

PRESSURE BUILDS UP THE ETHYLENE WILL STOP FLASHING AND LIQUID WILL

FORM" 

 

However, the team is not fully convinced with his argument.

The Ethylene drum is double walled vacuum insulated, with the inner wall made from stainless steel.

[breizh]

Hi,

Consider reading this post :

https://www.cheresou...-tank-start-up/

 

note: you may want to contact companies like Linde/Chart and others.

 

https://files.charti...Jan2016_web.pdf

 

Stay safe.

 

Good luck,

Breizh 

[Pilesar]

The vendor argument makes sense to me. I think I could be convinced of that path with enough research and consideration.

[Bobby Strain]

If you have not selected an ethylene supplier yet, find one that is equipped with a vaporizer.

 

Bobby