Cool down of an ammonia export line using riser

[marcodlc]

Which criterias have to be followed for sizing the cool-down of an ammonia export line using risers?
How can i determine number and size of risers?
The fluid is anhydrous liquid ammonia at -33°C.

[Andy]

Which criterias have to be followed for sizing the cool-down of an ammonia export line using risers?
How can i determine number and size of risers?
The fluid is anhydrous liquid ammonia at -33°C.

Hello marcodlc

what is an export line

Kind Regards Andy

[Andy]

Which criterias have to be followed for sizing the cool-down of an ammonia export line using risers?
How can i determine number and size of risers?
The fluid is anhydrous liquid ammonia at -33°C.

Hello marcodlc

please introduce yourself and tell us a little about what you do.

Kind Regards

[marcodlc]

Hello marcodlc

what is an export line

Kind Regards Andy

Hi Andy.
I'm Marco and I'm a process engineer.

The export line i'm talking about is to transfer liquid Ammonia from a storage tank to a Ship Loading System.
The ammonia export line cooling-down is exceeded by feeding liquid ammonia on the export line and recovering the discharged vapour through the high point of line installed for the scope with a saw-tooth altimetric profile.
When the liquid ammonia is feed to the saw-tooth shaped line, the vapours are collected into the high points of line: the liquid level will control & open a valve located on top of riser and vapour will flow through the return line to the ammonia storage tank. When liquid will be present at the high points, the valve will automatically close. Attached you can find a very simplified sketch of the system.

[US Iceman]

Hi Marco.

Thanks for the information. This appears to be an atmospheric storage system for ammonia so, your original question now makes a lot of sense.

The risers you speak of are gas vent lines. And as you are using the LIC level controls for what we would call low-side float devices to vent the vapor created from flashing off.

My assumption for this is:

A) Calculate the heat load for a section of pipe (from ambient temperatures down to -33°C) for one of the inclined pipes (up) and one pitched down. These would be the total length per segment that would have to be cooled down. In your drawing this is the pipe segment between the risers.

B) The heat load divided by the latent heat of ammonia at -33°C will give you the total mass flow of ammonia that will flash off.

C) If you divide the mass flow by a time rate you allow for the cool down cycle you have the mass flow per riser. Now you can size your control valve.

D) Because the specific volume of the vapor at -33°C will be high you may have to calculate vapor velocity through the riser so that it does not go sonic. The control valve may have limits on vapor velocity into the valve itself.

Does that help?

[Segei]

Hi Andy.
I'm Marco and I'm a process engineer.

The export line i'm talking about is to transfer liquid Ammonia from a storage tank to a Ship Loading System.
The ammonia export line cooling-down is exceeded by feeding liquid ammonia on the export line and recovering the discharged vapour through the high point of line installed for the scope with a saw-tooth altimetric profile.
When the liquid ammonia is feed to the saw-tooth shaped line, the vapours are collected into the high points of line: the liquid level will control & open a valve located on top of riser and vapour will flow through the return line to the ammonia storage tank. When liquid will be present at the high points, the valve will automatically close. Attached you can find a very simplified sketch of the system.

Do you really need these risers? What for? What is the pressure in this export line?

[Andy]

Hi Andy.
I'm Marco and I'm a process engineer.

The export line i'm talking about is to transfer liquid Ammonia from a storage tank to a Ship Loading System.
The ammonia export line cooling-down is exceeded by feeding liquid ammonia on the export line and recovering the discharged vapour through the high point of line installed for the scope with a saw-tooth altimetric profile.
When the liquid ammonia is feed to the saw-tooth shaped line, the vapours are collected into the high points of line: the liquid level will control & open a valve located on top of riser and vapour will flow through the return line to the ammonia storage tank. When liquid will be present at the high points, the valve will automatically close. Attached you can find a very simplified sketch of the system.

Hello Marco

thank you for the diagram.

I'm still not sure what is going on.

What is the LIC.

Where are the Tanks

Do you employ any pumps or do you use a compressor

Kind Regards Andy

[US Iceman]

Andy,

The export line is a liquid ammonia transfer line from a storage sphere (or barge/tanker). The line is warm before the liquid ammonia is transferred. Prior to pumping liquid through the line it has to be cooled down. Otherwise the large volumes of vapor could prevent liquid flow.

This is not a normal refrigeration system, although one is involved on the storage sphere to maintain the sphere pressure at atmospheric pressure.

The LIC is a Level Indicating Controller for a control valve to vent the vapor from the export line risers.

[Segei]

Usually, it is pretty simple. Two lines are connected. Liquid line and vapour return line. Cooling down of liquid line should be done gradually by liquid ammonia. Evaporated ammonia will go to the vessel tank and will return back to the shore tank(sphere) through return line.

[Andy]

Andy,

The export line is a liquid ammonia transfer line from a storage sphere (or barge/tanker). The line is warm before the liquid ammonia is transferred. Prior to pumping liquid through the line it has to be cooled down. Otherwise the large volumes of vapor could prevent liquid flow.

This is not a normal refrigeration system, although one is involved on the storage sphere to maintain the sphere pressure at atmospheric pressure.

The LIC is a Level Indicating Controller for a control valve to vent the vapor from the export line risers.

Hello Iceman

thank you for the info. What way are the lines cooled, are they jacketed?

There was a large plant like this at Irish Fertilizers in Arklow, Sabroe SMC 180 (180mm pistons) compressors to keep the tanks down by sucking the vapour off the top. These plants tend to be the biggest ammonia plants around.

This system is also used to recover nh3 from fridge plants when they are decommissioned by using a liquid pump, transfer line and a vent line back to the fridge system, the bit I haven't seen before is the level control.

What way does the LIC work, is it an expansion valve with a heater, along the lines of a Sporlan level master.

Thanks again for thr info.

Kind Regards Andy

[US Iceman]

Hey Andy,

The LIC control is similar to a float switch controlling a solenoid valve. As the float in the LIC controller drops with the liquid level it sends a signal (typically pneumatic) to a control valve to open. In this case the arrangement would be used as a low-side float valve (except this one is in several components, instead of one). The LIC appears to be used to vent off the flash gas from the cooling process in the line.

Mu guess is the liquid ammonia is being pumped directly through the pipe being cooled.

...compressors to keep the tanks down by sucking the vapour off the top.

That is what I think this is also. In addition to the vapor off the top of the sphere, the flash gas in the export line is being compressed again also.

[Andy]

Hey Andy,

The LIC control is similar to a float switch controlling a solenoid valve. As the float in the LIC controller drops with the liquid level it sends a signal (typically pneumatic) to a control valve to open. In this case the arrangement would be used as a low-side float valve (except this one is in several components, instead of one). The LIC appears to be used to vent off the flash gas from the cooling process in the line.

Mu guess is the liquid ammonia is being pumped directly through the pipe being cooled.




That is what I think this is also. In addition to the vapor off the top of the sphere, the flash gas in the export line is being compressed again also.

Thanks Iceman

Interesting appliaction for Ammonia. Usually quite a large ammonia plant from my experience of such applications

Kind Regards Andy