3 replies to this topic

[Guito]

Hi everyone, 

 

I am currently studing ammonia transport and ammonia is transport by pipeline always in liquid state, however, I have found several papers which propose to use Natural gas pipelines to distribute ammonia.

 

So, my question is: Why ammonia is always transported in liquid form? for a matter of cost? smaller diameters, pumps vs compressors etc.

 

When you have a pressurize gas ammonia storage and you want to send that ammonia to another tank (semirefrigerated, refrigerated) not to long away 5 Km for example, would not be easier and maybe cheaper to send that ammonia via gas pipeline instead of using a liquid pipeline considering that you may only need a pump/compressor at the beggining of the line?

 

Thank you very much,

[Pilesar]

Review the pressure-temperature-phase data for ammonia. Why would you have a pressurized gas ammonia storage when it does not take a very high pressure to keep it a liquid? Your questions seem to relate to a real example somewhere that I am not familiar with, so I will provide some general answers about transport. 

  Pumping is often much cheaper than compressing. Pipeline transport should be reliably single phase. Liquids have smaller volume than vapor. Heat transfer in long pipelines affects temperature so that sending refrigerated fluid is likely not efficient.

  Whenever you have two choices in process design, the decision usually comes down to economics. Safety is a strong consideration but it still has an economic component.

  If you have a specific example you want to discuss, giving fuller details (volume, pressure, temperature, application, etc,) would probably get you more satisfactory responses.

  Welcome to this forum. I hope you will continue to contribute and offer your thoughts.

[Art Montemayor]

Guito:

 

I want to reinforce Pilesar’s comments and recommendations because I know them to be very important and constitute basic engineering thinking in solving problems – all of prime importance for young engineers or students to embrace and follow in their developing careers.

 

First – and foremost – study and thoroughly know the fluid you are dealing with, especially its phase equilibria and thermodynamic properties.  Note carefully the physical state of the ammonia fluid as a saturated liquid or as a gas.  The quickest and fastest way to do this is to look at a temperature-entropy or a Mollier diagram – or better yet, at the thermophysical properties database found at https://webbook.nist...hemistry/fluid/ which I have downloaded for you to inspect in the attached Excel workbook.  Note how easy and accurate you can access this type of important thermodynamic data.  The important point here is “know the nature of the beast” before embarking on your solution.

 

Secondly, note that at 30 ºC (86 ºF), ammonia saturated liquid is at 11.665 bara (169 psia).  This is a relatively benign pressure for a pipeline – especially for one of 5 km (3.1 miles) length.  Here is where common engineering sense (el ingenio) should kick in and indicate to you that it would be far simpler and more economical to employ a liquid centrifugal pump (like a regenerative turbine type) to pump the saturated liquid rather than using a compressor for such a relatively short distance.  This logic is not scientific, but rather ingenuity – “el ingenio”.  That’s what we engineers do: solve problems in the most simplest, safest, and economical manner.  And that, I believe, is what your instructor(s) desire from you.

 

As Pilesar indicates, you haven’t given us the “meat” of the proposed design: the Basic Data.  Basic Data is, for instance, the initial conditions of the ammonia, its flow rate, the size of the pipeline, the fluid conditions desired at the pipelines termination point, etc., etc.

Without Basic Data, we can’t offer you any more recommendations on how to approach and resolve this application.  If you furnish more information, we can offer more advice.

 

I highly recommend you learn more about the thermo data available free at the indicated U.S. government website.  You may have need of it in the future.  And don’t forget to spend more time in studying and learning more about phase equilibria and how fluids transform from one phase to another – and why.There is a document that deals on this subject on our website and is free for downloading.  The article’s title is “PNG 520 - Phase Equilibria in Crude Oil and Gas”.  Although the basic subject is hydrocarbons, the theory and thermophysical explanations apply to all chemical fluids.  You may find it very interesting and useful.

Saludos

 

   Propiedades de Amoniaco.xlsx   51.24KB   20 downloads  NH3 Mollier Diagram.jpg   157.62KB   3 downloads 

[Zauberberg]

Art, one can simply enjoy reading the simplicity and ingeniosity of your advices. Welcome back!