Joule-Thomson vs LTS complexity and operating costs.

[cesarcf1977]

Good morning folks,

Consider a very small natural gas processing plant, roughly 10-15 MMscfd. Is there any significant difference in terms of operating complexity (i.e. number of people required to operate the facility) and the associated running costs (opex), between choosing a Joule-Thomson or a propane cooling plant?

We've been challenged on that, but having a look at the equipment, even if assigning a full time person to the propane unit, we see no other differences in terms of its daily operation or costs...at least not to make a difference to the project evaluation.

Thanks and regards.

 

[danschwind]

Cesar,

As no one has commented here yet, I will try to give you an overview (but no concrete answer, sorry).

If this is, as I assume, a new plant, it is imperative that the decision for either a J-T process or direct refrigeration process is based upon a thorough engineering analysis.

A J-T plant will, obviously, need more compression downstream to supply the pipeline. A direct refrigeration plant has much lower pressure drop altogether, but the added complexity may increase its cost compared to a J-T.

All in all, the feed and the HC's you wish to recover are of great importance to define the process. Usually, direct refrigeration is used on leaner feeds with lower expected recoveries, and J-T or even refrigerated J-T used for higher recovery rates.

If you are not separating propane, you will also need to consider buying it if you plan to use direct refrigeration.

There are some literature that may assist you overall, I would recommend the GPSA databook for a start.

Also, other guys way more knowledgeable than me here in the forums may assist you better.

Daniel
Rio de Janeiro - Brazil

 

[rotw]

In regard to compressing propane, keep in mind that typically these compressors (when it is centrifugal type) tend to have a relatively heavy/big frame when compared to natural gas applications. That is essentially because the Mach number at first stages inlet is high (the relative Mach no. can be generally supersonic or close) and that is due to Propane gas properties.
This has quite some implications as impellers have to be made much bigger so that the peripheral speed is decreased - at constant compression ratio - just to have benefit on lowering the Mach. no. (as a general trend). It is a marginal benefit, yet highly desired.

All in all, this was to say that the costs will go up when frame size is bigger (exp. forged construction may not be possible and casting would be required, bigger rotor and shaft ends, bigger oil consumption, increased utilities, etc.). Weight goes up and footprint too.

PS(edit): This is definitely not aimed as a decisive factor for your final technology selection.
It just highlights implications on compressor equipment which just a part of the overall picture that you have to figure out.

 

[georgeverghese]

Do we have an apple to apple comparison here in the fist place: Is the minimum operating pressure for the feedgas that the propane chiller option is capable of handling the same as that for the LTS option?
If they are, then it would be obvious that the LTS unit is inherently more reliable, requires less maintenance and would require less manning than that which relies on a C3 compression chiller unit. Going up the scale on compression reliability: recips; screw compressors, centrifugals.

 

[georgeverghese]

Oops,got my terms all mixed up:- I meant JT cooling option, not LTS option.